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Industrialization has contributed significantly to the advancement and sustenance of human civilization. However, it has also posed serious challenges to environmental sustainability, notably through heavy metal pollution, which has severely impacted ecological systems. Recent studies have explored the use of biochar for the removal of heavy metals from aqueous solutions. This review underscores the diverse physicochemical and structural characteristics of biochar, derived from various biomass sources through different pyrolysis processes, and their varying adsorption efficiencies. The review aims to investigate current biochar production technologies, their unique properties, and their maximum removal efficiency and adsorption capacity for heavy metals. The primary adsorption mechanisms, adsorption isotherms, and kinetic models have been identified. Furthermore, the study confirms that optimal conditions—such as the choice of precursors, pyrolysis temperature, and an understanding of the advantages and limitations—are crucial for designing biochar with superior structural and physicochemical properties. This review provides an updated overview of biochar-based heavy metal treatment in aquatic systems, highlighting existing research gaps and suggesting future research directions. [Display omitted] • Efficiency of different biochars for water management was systematically reviewed. • Advantages and limitation of biochars production was discussed. • The engineered biochars has excellent structural and physiochemical properties. • The kinetics of the biochars-based system is well described by Pseudo second order. • More attention should be paid to biochar production and application at large scale. [ABSTRACT FROM AUTHOR]

The increased pollution of water resources by toxic heavy metals poses a huge threat to the aqueous ecosystem. Since the low concentrations of heavy metals are often highly toxic but difficult to remove, novel efficient adsorbents still need to be explored. Herein, the superparamagnetic thiol-functionalized oxygenous carbon nitride nanocomposite (CNO/Fe 3 O 4 -SH) with multifunctional groups such as –NH 2 , –OH, –SH, and –COOH was fabricated by a simple and eco-friendly method. The maximum adsorption capacities of Pb2+, As3+, and Cd2+ ions on CNO/Fe 3 O 4 -SH at pH = 6 were 80.79, 71.78 and 66.19 mg/g, respectively, when their equilibrium concentrations were 20 mg/L. Under the equilibrium concentration below 0.01 mg/L, the adsorption capacities of these heavy metals over CNO/Fe 3 O 4 -SH were much higher than those of other adsorbents. The competitive adsorption investigations showed that the adsorption order in polymetallic solutions was Pb2+ > As3+ > Cd2+. Adsorption kinetics and isotherms studies indicated that the adsorption of Pb2+, As3+ and Cd2+ by CNO/Fe 3 O 4 -SH was attributed to monolayer adsorption and the adsorption process was controlled by chemical adsorption. The thermodynamic experiments showed that the adsorption processes were spontaneous and endothermic. After six adsorption/desorption cycles, CNO/Fe 3 O 4 -SH maintained its original morphology and adsorption ability, indicating its excellent regeneration performance, which had significant potential application in the decontamination of trace heavy metal ions in water. [Display omitted] • Thiol-functionalized oxygenous carbon nitride was prepared for heavy metal removal. • CNO/Fe 3 O 4 -SH had high adsorption capacity at low concentrations of heavy metals. • Separation and regeneration of CNO/Fe 3 O 4 -SH was very simple and efficient. [ABSTRACT FROM AUTHOR]

This study assists in developing the circular economy concept by using waste as a construction material. A series of laboratory experiments examined the feasibility of replacing sand-bentonite mixture as a common media with electric arc furnace dust (EAFD) as an industrial by-product for constructing landfill cover and liner layers. The impact of EAFD on the geo-environmental properties of pristine sand and sand-bentonite mixtures was assessed. The results indicate that there was a significant decrease in the permeability coefficient and an increase in the splitting tensile strength, unconfined compressive strength, pH, electro conductivity, and water holding capacity of the sand-EAFD mixture compared to sand-bentonite specimens. Microstructural and mineralogical phase analyses were conducted using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared analysis to identify physical and chemical interactions. In addition, the toxic heavy metals leaching risk, such as lead, zinc, and cadmium to the groundwater was also investigated. Results show that as an innovative waste management technique, EAFD can be utilized to construct landfill cover and liner layers. This approach serves two important purposes: firstly, it helps conserve valuable materials like bentonite and sand, and secondly, it provides novel waste management for EAFD as an industrial waste based on the circular economy approach. • Electric Arc Furnace Dust (EAFD) can be safely used in cover and liner layers, significantly reducing soil permeability. • EAFD enhances soil's splitting tensile and unconfined compressive strength by forming new minerals. • Including EAFD increases soil pH, electrical conductivity (EC), and water holding capacity (WHC). • Using EAFD in landfill layers offers a novel waste management strategy and conserves natural resources. [ABSTRACT FROM AUTHOR]

Cleaner production (CP) can mitigate environmental harm caused by human activities and increase efficiency through whole-process control, promoting sustainable industrial development and reducing heavy metal pollutants. Heavy metal pollutants from zinc electrowinning have become pressing global concern. This review aims to introduce advanced methods and innovative technologies from 212 sources to enhance zinc electrowinning sustainability. Herein, the focus is on investigations of how to achieve sustainable emission reduction of heavy metal pollution in cathode wastewater and anode slime through CP perspectives and philosophy, including key processes, pollution causes, CP solutions, and implementation effects. Taking the heavy metal pollution at the anode and cathode as the starting point of technical methods, which methodology and details of each typical method were discussed. There were 4 promising technologies were found and highlighted: in situ brushing, efficient needle spray cleaning, pre-coated anode, and precise anode slime removal. The implementation of a complete CP technology set reduced plate cleaning wastewater by more than 80%, and plate anode slime by more than 85%. Additionally, by comparing reported outcomes in studies, big gaps in technology transformation from the existing research to the actual industrial application were found, and practical recommendations for further improving CP aspects of zinc electrowinning were provided. This review should prompt researchers to actively consider how to optimally apply the CP concept to the sustainable development of industry and society. [Display omitted] • Origins and pivotal mechanisms of heavy metal pollutants are examined. • Reduction scheme of heavy metal pollution is revealed from CP perspective. • Principal methodologies and attributes of 4 reduction strategies are delineated. • Future research direction of reducing heavy metal pollution is prospected. [ABSTRACT FROM AUTHOR]

Busia Gold mines in eastern Uganda generate significant wastes that contribute to environmental and health challenges in the region. This study assessed the extent of 9 potentially toxic metals (PTMs) present in Busia gold mine tailings. The study also evaluated environmental risks for each of the PTMs, using contamination indices. The indices were: index of geo accumulation (Igeo); potential ecological risk index (RI); contamination factor (CF); pollution load index (PLI) and ecological risk factor (ERI). Tailing samples were collected at two distinct depths; surface (0–30 cm) and deep (30–60 cm) from four sites. The samples were analyzed using an Atomic Absorption Spectrometry (AAS). The Igeo results showed that As and Hg recorded extreme pollution levels (Igeo >5) in all 4 sites. The other seven PTMs in all the sites were classified between heavily polluted to unpolluted categories. CF results revealed extreme contamination for Hg at site-A and As at site-M with moderate contamination of Ni, Zn, and Co at sites-C and B. RI findings showed that all the sites recorded RI > 600, with the highest (RI = 80, 407) at site-A, followed by site-C (RI = 74, 536). All the sites had a high level of ecological impact with greater potential for environmental risks in the area. In the case of PLI, all the sites were classified as polluted sites (PLI > 1). Sites-M and C recorded the highest (PLI = 12), followed by sites-B and A, with PLIs of 11 and 9, respectively. ERI findings for all the sites showed significant Hg, As, and Cd contamination, (ERI >320). Site-A recorded the highest Hg contamination (ERI = 78, 825). Site-M recorded elevated levels of As and Cd, with ERI of 1, 323, and 399, respectively. Pb at site-M posed considerable potential ecological risk with an ERI of 108, while Zn, Cu, Co, Ni, and Cr presented low ecological risk across all sites with ERI˂ 40. There is, therefore, need to properly manage tailings in Busia gold fields to minimize ecological contamination to avoid impacts on human, animal, and plant health. • Arsenic (As) levels were exponentially higher than other potentially toxic metals. • Five contamination indices show that all sites were classified as polluted-sites. • The indices revealed that As and Hg had extreme pollution levels across all sites. • At two sites, Hg concentration decreased with sampling depth. [ABSTRACT FROM AUTHOR]

Mapping the spatiotemporal distribution of soil heavy metals is a prerequisite for soil pollution prevention and control. However, current mapping methods make it difficult to balance robustness and interpretability. In this study, we proposed a spatiotemporal interpretable mapping framework for soil heavy metals and conducted a case study of soil cadmium (Cd) in cropland of the Poyang Lake region in China. The results showed that the average soil Cd concentration increased significantly (p < 0.01) from 0.13 mg/kg in 1983 to 0.19 mg/kg in 2010. Soil Cd in 1983 was mainly controlled by human activities and topography, whereas it was jointly driven by human activities, topography, and climate in 2010. In addition, the framework revealed the spatial distribution of soil Cd and their uncertainties at a 12.5-m resolution in 1983 (R 2 = 0.94) and 2010 (R 2 = 0.97). The top three covariates in 1983 were nighttime-light, PM 10 , and land surface temperature (day), whereas those in 2010 were mean annual minimum temperature, gross domestic product, and industrial enterprises, with Shapley additive explanation (SHAP) values of 0.44, 0.42, and 0.27, and 0.31, 0.11, and 0.09 mg/kg, respectively. By integrating machine learning, variable and model selection, and the SHAP module, the proposed framework achieves a balance between the robustness and interpretability in mapping the spatiotemporal distribution of soil Cd, going beyond the limitations of the classical statistical "smoothing effect" and the artificial intelligence "black box." Our study emphasizes the importance of considering time, space, models, variables, and mechanisms in digital soil mapping, which will enable more accurate and scientific predictions of soil contaminants across time and space. [Display omitted] • Developed a spatiotemporal interpretable mapping framework of soil heavy metal at a 12.5-m resolution. • Quantified the driving mechanism and spatiotemporal clustering pattern of soil Cd. • Integrated advanced digital soil mapping technologies and the explainable SHAP module. • Achieved a balance between robustness and interpretability. [ABSTRACT FROM AUTHOR]

Achieving universal access to clean water, as mandated by SDG 6 – Clean Water and Sanitation, is crucial for supporting human health and environmental sustainability. Water treatment plants generate a by-product known as Water Treatment Plant Sludge (WTPS), comprising organic and inorganic substances. Traditionally, the disposal of WTPS poses environmental risks, including nutrient runoff and heavy metal contamination. This study investigates using centrifuged WTPS, without prior treatment, as an adsorbent to remove contaminants from treated wastewater, offering a sustainable waste management solution. Through comprehensive characterization using Scanning Electron Microscopy, Thermogravimetric Analysis, Fourier Transform Infrared Spectroscopy, and geo-environmental parameter assessment, the research evaluates the adsorption efficacy of WTPS. A factorial design methodology facilitated the systematic examination of adsorption tests. Findings indicate that WTPS exhibits adsorption capacities for phosphorus (q = 0.2 mg g-1), Chemical Oxygen Demand (q = 1.1 mg g-1), and metals under specific conditions. Maximum removal efficiencies for total coliforms and Escherichia coli were achieved with extended contact times, showcasing WTPS's potential as a robust adsorbent. The research demonstrates that centrifuged WTPS can significantly reduce concentrations of metals such as Pb, Co, and Ni (100%), Al (96%), Cu (95%), and Fe (93%) in treated wastewater, presenting a promising approach for enhancing wastewater quality. However, the interaction between WTPS and wastewater resulted in an increased concentration of Mn in the effluent, highlighting the complex dynamics of adsorption processes. In conclusion, centrifuged WTPS emerges as a viable, cost-effective adsorbent, aligning with sustainable waste management practices and circular economy principles. [ABSTRACT FROM AUTHOR]

The emergence of microplastics (MPs) and their coexistence with heavy metal contaminants pose potential risks to the safety of the subsurface environment and public health. Therefore, it is crucial to explore the co-transport of MPs (polypropylene (PP), polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE)) with the heavy metal Pb(II) under the surfactant (sodium dodecyl benzene sulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB)). In this study, column experiments were performed to investigate the co-transport of MPs and Pb(II) under surfactants. The co-transport mechanism of MPs with Pb(II) under surfactant was revealed by MPs stability and batch adsorption experiments. Experimental results showed that the presence of Pb(II) did not influence the mobility of MPs under CTAB and SDBS; however, MPs can affect the mobility of Pb(II). Specifically, under CTAB, the MPs increased the recovery rate of Pb(II) from 86% to 87.55%–97.55%. However, under SDBS, the high mobility of PS, PE, and PP inhibited the transport of Pb(II), and the recoveries of Pb(II) decreased from 79% to 57.53%–70.96%. The low mobility of PTFE and PMMA slightly promoted the transport of Pb(II). This could be attributed to two reasons. One aspect is the adsorption rate of Pb(II) by MPs, which plays a pivotal role in influencing the transport tendency of Pb(II) with MPs. Another aspect is the MPs stability, as greater stability enhances their dispersity and accelerates the adsorption rate of Pb(II), thereby facilitating the co-transport of Pb(II) with MPs. This study could provide valuable insights for assessing the transport and environmental impact of MPs and heavy metals in the presence of surfactants. [Display omitted] • Mobility of Pb in surfactant was affected by MPs stability and adsorption rate. • MPs stability followed the order of PP > PE > PS > PMMA > PTFE under CTAB or SDBS. • The different of MPs stability resulted in different transport of Pb(Ⅱ). • Mobile MPs under surfactant provided a unique transport pathway for adsorbed Pb(II). • An index δ was defined to describe the transport capacity of MPs carrying metal ions. [ABSTRACT FROM AUTHOR]

With the development of phytoremediation of heavy metals contaminated soils, the harmless disposal of hyperaccumulator plants has been imminent. In this study, the effects of typical aluminosilicates on the heavy metal migration during the combustion of ryegrass were compared. The addition of kaolin, montmorillonite, and γ-Al 2 O 3 were all effective in solidifying Pb and Zn. As the combustion temperature increased, the toxicity of remaining Pb and Zn decreased. Compared to montmorillonite, kaolin was more effective in capturing Pb and Zn at 600–825 °C, and the remaining Pb and Zn were mainly in acid-soluble form. The large amount of alkali/alkaline earth metals will react with the Si/Al components to form various potassium feldspars and calcium silicates, thus inhibiting the solidification of heavy/alkali metals. However, the Si in montmorillonite was more effective in converting Pb and Zn into residual form than kaolin when faced with the competition solidification of alkali/alkaline earth metals, at which time the percentage of Pb and Zn in the residual form increased from 13.27% and 6.00% to 39.21% and 9.84%, respectively. This work provided a research perspective based on the solidification of heavy metals by Si component, which enables a more comprehensive analysis of the differences in heavy metals solidification by Si/Al-based minerals. [Display omitted] • Cl prior to combine with K rather than heavy metals during combustion of ryegrass. • Kaolin captured more Pb and Zn than montmorillonite between 600–825 °C. • The Si in Montmorillonite converted more Pb/Zn into residual form than kaolin. [ABSTRACT FROM AUTHOR]

While traditional biochar demonstrates promising performance in diverse settings, its efficacy may be constrained under specific conditions of high acidity and heavy metal concentrations. In this study, researchers developed a new polysilicon-aluminum alkali mineral-enhanced biochar composite material, GBMSs (green biochar-metakaolin-sodium silicate), by pyrolyzing fibers from dragon fruit peels and blending them with metakaolin and sodium silicate. Using a response surface methodology, this environmentally friendly composite material was optimized for removing copper and zinc contaminants across a range of initial pH levels from 2 to 6. Experimental findings indicated that the adsorption capacity of GBMSs for copper and zinc was significantly enhanced, ranging from 1.5 to 4 times greater compared to pure biochar or biochar mixed solely with a silicon-aluminum mineral. Various analytical techniques including scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were utilized to examine the influence of poly-silica-aluminum alkali minerals (GBMSs) on biochar composites. The findings revealed an upsurge in surface binding locations and oxygen-related functional groups because of integrating GBMSs. This augmentation of electronegative features on the biochar surface was credited to the development of stabilizing silica-aluminum connections, ultimately boosting its adsorption effectiveness in acidic surroundings. By applying Langmuir and Freundlich models, it was deduced that the adsorption of GBMSs adheres to a multilayer uniform adsorption mechanism, with surface ion interchange and complexation restricting the adsorption capability. This research highlights the potential of clay mineral-altered biochar in efficiently dealing with intricate environmental contamination. [ABSTRACT FROM AUTHOR]

Heavy metals (HMs) in soil near metal smelting areas have attracted great interest due to their crucial threat to agricultural product safety and human health. We investigated HMs in agricultural soils and crops (wheat and maize) in a Pb/Zn smelting city, central China; analysed the exposure risk of HMs through multiple pathways in a soil-crop system through Monte Carlo simulations; and identified the key driving factors using random forest (RF) model. The results showed that most soil HMs exceeded their background level. Cd had the highest exceeding rate compared with the screening values and the highest exceeding rate (40%, in wheat) compared with the food safety limit. Additionally, Cd had the highest bioaccumulation capacity in both maize and wheat. In identifying the key driving factors of soil HMs, RF had a satisfactory prediction performance for As, Cd, and Pb, with corresponding R2 values of 0.47, 0.51, and 0.60, respectively, with the dominant factors being distance to the Pb/Zn smelter, coal washery, and road area, respectively. However, Cr and Hg exhibited lower R2 values which may be due to their limited influence from the selected anthropogenic, traffic, and industrial variables. Probabilistic health risk assessments through Monte Carlo simulations revealed that the non-carcinogenic risk was around the risk limit (HI = 1), while the carcinogenic risk for both children and adults exceeded the risk limit (TCR = 1E-04), and adults had higher carcinogenic risk than children, which was due to a longer duration of exposure and higher ingestion rate of crop grains in adults. Cd had the highest carcinogenic risk and the highest probability of exceeding the limiting risk. Briefly, levels of Cd in both soil and crops should be controlled, especially for the source of smelting emissions. The results of this study could be treated as valuable references for policymakers to formulate control strategies for soil HM pollution in agricultural areas near Pb/Zn smelting activities. [Display omitted] • Heavy metals (HMs) in soil-maize-wheat were analysed in a Pb/Zn smelting city. • Cd was most polluted and had the highest bioaccumulation in both maize and wheat. • Smelter, coal washery, and traffic were found to be key factors of soil HMs via RF. • Carcinogenic risk was unacceptable, with an over-threshold probability above 90%. • HM for Cd and the pathway of crop grain ingestion were the top risk contributors. [ABSTRACT FROM AUTHOR]

Cr(VI) is a major heavy metal contaminant that poses great threats to aquatic ecosystems and human health. To guarantee the safety of water quality, the development of in-situ and online sensors for monitoring Cr(VI) contamination events is crucial. In this work, sediment microbial fuel cell (SMFC) based sensors using floating cathode as sensing element were operated in outdoor environment for one year to monitor repeated Cr(VI) shocks in wetlands constructed with coastal alkaline soil (YC), paddy of acidic soil (YT), and paddy of neutral soil (NJ). K 2 CrO 4 solutions were added to the cathode four times in January, March, June, and September, respectively. Results showed that each Cr(VI) addition triggered a voltage peak and the voltage increments were linearly correlated with Cr(VI) concentrations within the range of 5–120 mg L−1 Cr(VI). The highest sensitivity was observed for YC (1.2 mV L mg−1) and YT (1.4 mV L mg−1) in June and for NJ (1.2 mV L mg−1) in September. XPS analysis demonstrated the reduction reaction of Cr(VI) to Cr(III) on the cathode might contribute to the generation of voltage peaks. Despite repeated shocks, Cr(VI) was immobilized in the soil and completely reduced to low-toxic Cr(III) with the consumption of soil organic matter, and the diversity and abundance of exoelectrogenic bacteria-associated genera were not inhibited. As a result, stable operation of the SMFC sensors was ensured. The SMFC sensors exhibited great potential for in-situ and online monitoring of Cr(VI) contamination events across various wetlands. [Display omitted] • SMFC sensors could monitor repeated Cr(VI) shocks in different types of wetlands. • The sensitivity of voltage response to Cr(VI) contaminations varied with seasons. • Cr(VI) was reduced and immobilized in soil, thus exoelectrogens were not inhibited. [ABSTRACT FROM AUTHOR]

The natural bioelectrochemical phenomenon termed as biogeobattery has exhibited a great ability to enlarge the effective remediation area even to meter-scale by the conductive electroactive bacteria (EAB) and native minerals matrix, which would be an evolution of heavy metal remediation by bioelectrochemistry in the future. In this review, starting from the introduction of elementary parts of the biogeobattery, the progresses of key conduits, cytochromes, and connectors for extracellular electron transfer (EET)-coupled heavy metal in the biogeobattery networks are discussed. Given that the shortage of enriched organics and conductive conditions in the natural biogeobattery has been identified as the main challenges for rapid metal reduction, the potential of native inorganic Fe/S/NH 4 as electron donors to drive the EET are discussed. Meanwhile, establishing conductive networks by minerals and carbon materials additives are evaluated to enhance the EET in the biogeobattery. Particularly, in order to manipulate the formation of the networks, an applicable high-resolution analytical method is firstly proposed here to further decipher the EET-coupled heavy metal reduction process. Overall, this review would contribute to the real application of bioelectrochemistry to reduce heavy metals from soils efficiently. [Display omitted] [ABSTRACT FROM AUTHOR]

The clean-up of acid mine drainage (AMD) is challenging, as classical treatment including a pH neutralization step produces large amounts of toxic sludge. Here we demonstrated that removal of heavy metals through adsorption at low pH was achievable with the use of ε-MnO 2 adsorbent, which could be produced in a simple one-step process. The material, which was negatively charged even at pH 2, exhibited outstanding potential for the removal of heavy metals at strongly acidic pH. At pH 2, adsorption capacities were achieved of 172.14 mg/g towards Pb2+ (at an initial concentration of 400 mg/L), 65.64 mg/g for Fe3+ (at 300 mg/L) and 8.5 mg/g for Cd2+ (at 10 mg/L). Mechanistic studies revealed that ion exchange was the main adsorption mechanism for removal of Pb2+, while electrostatic interaction was dominant for Fe3+ and Cd2+ removal. In the case of Pb2+ adsorption, double corner sharing (DCS) complexes were formed at the edges, which promoted the dissolution of structural Mn(III), thereby generating Mn2+ and vacancies which promoted Pb2+ adsorption via an ion exchange process. In the case of Fe3+ and Cd2+ adsorption, along with electrostatic adsorption, triangle corner sharing (TCS) dominated complex formation at the intermediate vacancies, and less Mn2+ was released. Note that the Mn2+ was in dynamic equilibrium with structural Mn(Ⅲ) and Mn(Ⅳ). The actual AMD was retreated in 5 cycles by ε-MnO 2 , the removal rates of 100% were achieved for Pb2+, Fe (total) and Mn2+, together with 98% for Cu2+ and 95.1% for Cd2+, all of which reached the national emission standards. This approach is a highly suitable option for AMD treatment that avoids toxic sludge formation. [Display omitted] • Direct adsorption of heavy metal ions by ε-MnO 2 at pH 2 from actual acid mine drainage. • The adsorption capacity was highly achieved of 172.14 mg/g towards Pb2+ at pH 2. • Metal adsorption mechanisms were explored by EXAFS spectroscopy and Mn2+ dissolution. • The form of DCS complexes was promoted ion exchange process between Pb2+ and Mn2+. • The common heavy metals in actual AMD reached the emission standards after treatment. [ABSTRACT FROM AUTHOR]

The safety and feasibility of directly treating hyperaccumulators with heat is constrained by the substantial presence of volatile heavy metals (HMs) within these plants. The combination of acid pretreatment and heat treatment holds potential for both energy recovery from hyperaccumulators and the transfer of their HMs to specific phases. This study aimed to reveal not only the pyrolysis and gasification kinetics and products of arsenic-hyperaccumulator (Pteris vittate L.) (PV) pretreated with HCl or H 3 PO 4 but also the migration, distribution, and leaching of HMs in products and interaction between HMs and minerals. The HCl-pretreated PV exhibited similar decomposition behaviors and mechanisms to the control PV, with a gradual decrease in overall activation energy (E m). In contrast, H 3 PO 4 changed the behaviors and increased E m. The relative yield of syngas and biochar rose with increased acid concentration. Given the pyrolysis and gasification-induced volatile products released at 550, 750, and 950 °C, HCl increased the relative yield of aromatic compounds and reduced the formation of ring-opening products compared with PV. Compared with HCl, H 3 PO 4 increased the emissions of aromatic compounds and ketone. HCl promoted the loss of HMs, including accelerating their volatilization from the solid phase and increasing their leaching concentration from the biochar. HMs were mostly retained in the H 3 PO 4 -pretreated PV biochar with a low leachable rate, gradually decreasing with the rising temperature. The maximum energetic performance and HM immobilizations were optimized using artificial neural networks. This study revealed plausible reaction pathways and immobilization mechanisms, involving the interactions between minerals and HMs due to Cl or P introduced by the acid pretreatment. Overall, our findings provide new insights into the pyrolysis and gasification behavior of acid-pretreated hyperaccumulator. In particular, the H 3 PO 4 pretreatment not only produced high-yield, high-quality bio-oil products with low HM content but also retained the HMs in the biochar. [Display omitted] • Composition, relative yields, and temperature dependency of volatiles were revealed. • HCl-pretreated PV promoted the HMs volatilization and leaching from solid phase. • H 3 PO 4 -pretreated PV retained most HMs in the biochar with a low leachable rate. • Interactions among HMs, minerals, and acid pretreatment were revealed. • Energetic performance and HM immobilizations were optimized via neural networks. [ABSTRACT FROM AUTHOR]

Upcycling the solid biomass waste into bio-oil and biochar are promising solutions to mitigate environmental pollution caused by solid waste and offer value-added products with tremendous applications, simultaneously. The bio-oil and biochar could be considered as excellent alternatives to the petroleum-based asphalt, however, the application potential of bio-oil and biochar could be compromised, due to the high oxygen content of the bio-oil and presence of heavy metals in the biochar. In this study, biochar modified asphalt (BMA) and biochar modified bio-asphalt (BMBA) were successfully developed using wood waste as feedstock. 16 polycyclic aromatic hydrocarbons (PAHs) and 6 heavy metals were mainly assessed by adsorption characteristics using prepared samples. The major results demonstrates that the concentrations of Cd2+, Cr3+, Cu2+, and Ni2+ elements leached from bio-asphalt was within the acceptable levels (2 mg/L) regarding environmental pollution. And adsorption ability of bio-asphalt was selective and that the ability of BMBA in reducing heavy metals concentration was better than BMA. Major parameters including rainfall time and solar irradiation time could slightly affect the toxicity of PAHs leached from bio-asphalt in the road runoff. Biochar and bio-oil were promising additives for petroleum-based asphalt given its environmental benefits and sustainable properties. [Display omitted] • 16 PAHs and 6 heavy metals leaching toxicity of bio-asphalt are investigated. • The heavy metal adsorption ability of bio-asphalt is selective. • Rainfall time and irradiation time increase PAHs leaching toxicity of bio-asphalt. • Biochar protects asphalt from heavy metal and PAHs pollution. • There are synergistic effects of rainfall and irradiation on heavy metals and PAHs in bio-asphalt leachate. [ABSTRACT FROM AUTHOR]

Biochar has exceeded expectations for immobilizing heavy metals (HMs), but the potential ecological risks of its long-term burial in soil limit its practical application on a large scale. To address this challenge, a novel separable water-hardened magnetic composite biochar sphere (WMBCS) was prepared and applied to remediate agricultural soils contaminated with Cd, Pb, and As. The first application of WMBCS is simultaneously effective in removing Cd (3.2–12.7%), Pb (3.3–13.1%), and As (5.0–25.6%) from soil, and the removal rates are enhanced with increasing soil moisture, application dose and incubation time. WMBCS is more efficient for removing Cd and Pb in mildly contaminated alkaline soils than in heavily contaminated acidic soils. Compared with other regeneration methods, shaking and ultrasound-assisted EDTA-2Na efficiently elutes HMs with a dissolution efficiency of over 75% within 4 h, accompanied by the lowest rate of mass loss (7.6%) and Fe leaching (475.1 mg kg−1). After 5 rounds of successive cyclic remediation, WMBCS exhibits high adsorption efficiency (26.5–30.6% for Cd, 25.4–30.2% for Pb, and 30.2–41.0% for As), magnetic separation efficiency (98.8–99.8%) and regeneration efficiency (92.3–95.4%). The main mechanisms involved in the adsorption and regeneration of WMBCS include ion exchange and chelation. WMBCS is an economical and eco-friendly material with vast unexplored potential for use in agriculture. [Display omitted] • Green adsorbents effectively remove Cd, Pb and As from contaminated soil. • EDTA-2Na is effective for heavy metal desorption and WMBCS regeneration. • Ultrasound assistance could accelerate the WMBCS regeneration. • Regenerated WMBCS exhibits excellent adsorption and magnetic separation capabilities. • WMBCS removes heavy metals and regenerates through physical and chemical effects. [ABSTRACT FROM AUTHOR]

Stainless-steel slag is a hazardous solid that has caused severe chromium contamination globally. This study proposes an environmentally benign vitrification process for efficient recycling and solidification of Cr from stainless-steel slag using waste copper slag and coal tar residue. The transformation behaviors of heavy metals (Cr, Cu, Pb, Zn) and the Cr toxic leaching mechanism are also determined in this work. The findings indicated that compared with Cu and Fe phases, the Mg(Al,Cr) 2 O 4 and chemically dissolved Cr phases were not easily reduced via coal tar residue, leading to the leaching of highly toxic Cr3+/Cr6+ during the toxicity characteristic leaching procedure (TCLP). Under optimal conditions, 95.56% Cr, 97.71% Fe, and 99.71% Cu could be recovered in the form of high value-added crude stainless-steel, and 99.62% Pb and 99.19% Zn could be enriched in the dust. The furnace slag TCLP result indicated that the leaching concentrations of Cr, Cu, Pb and Zn were 1.82 mg/L, 0.1 mg/L, 0.38 mg/L, and 2.58 mg/L, respectively. More importantly, the concentrations of residual Cr, Cu, Pb and Zn in the furnace slag were only 0.095 wt%, 0.028 wt%, 0.0192 wt%, and 0.011 wt%, respectively. These findings indicate that treated slag can be categorized as general solid waste, minimizing the environmental risks of heavy metals. The results of this study are significant for the sustainable development of the stainless-steel industry and copper metallurgy. [Display omitted] • A novel process for efficient recycling and solidification Cr is proposed. • The heavy metals (Cr, Cu, Pb, Zn) transformation behaviors were determined. • The Cr recovery ratio increases obviously by 16% compared with current research. • The leached contents of Cr, Cu, Pb, and Zn were 1.82, 0.10, 0.38, and 2.58 mg/L. [ABSTRACT FROM AUTHOR]

It is necessary to detoxify municipal solid waste incineration fly ash (MSWIFA) to facilitate resource utilization. The current research focused on the treatment of heavy metals in MSWIFA which is relatively well-developed, while dioxins (PCDD/Fs) need to be treated with more referable programs. Based on the excellent lipophilicities of dioxins, readily available, nontoxic, harmless, and easily treatable animal fats have been used to separate the dioxins from MSWIFA samples, thereby reducing the toxic equivalence of the MSWIFA. The experimental results indicated that animal fats significantly reduced the toxic equivalence of untreated, water-washed, and acid-washed MSWIFA samples, with reductions in the dioxin toxicity equivalence of up to 70%. Furthermore, in studies of heavy metal leaching, water washing followed by pig fat (FP) separation was identified as the optimal approach for the separation of dioxins from MSWIFA. Under the optimal conditions, the toxicity due to dioxins was reduced by over 70% after separation from MSWIFA with recycled animal fats. The environmental and economic benefits of this treatment option were analyzed on this basis. • The dioxins in MSWIFA can be separated by fat. • MSWIFA with low toxicity equivalent and low heavy metal leaching can be obtained. • The net dioxin content can be reduced to around 20 ng TEQ/kg after multiple cycles. • The separation of dioxins by FP can obtain significant economic benefits. [ABSTRACT FROM AUTHOR]

Rapid industrialization and urbanization have resulted in the widespread contamination of soil by potentially toxic metal(loid)s (PTMs). Among these, arsenic (As), cadmium (Cd), chromium (Cr) lead (Pb) and nickel (Ni) are particularly concerning, affecting millions of hectares of arable land globally and posing significant threats to food security and human health. Biochar (BC) has emerged as a promising soil amendment due to its ability to mitigate soil pollution by immobilizing contaminants. But how biochar-linked free radicals affect this process in plants and soil remains murky. Additionally, the mechanism of the geochemical transformation of PTMs in soil-plant systems influenced by biochar-based free radicals is unclear. Here, the influence of free radicals on immobilization, and transformation of PTMs in the soil-plant system under various BC and Comp treatment was investigated. Six treatment groups (1% and 2% biochar, compost, combined application, and control) were randomly assigned to pots in a randomized complete block design (RCBD) to test their effects on maize growth. Results revealed that there was a noticeable rise in the concentration of free radicals in both the BC and Comp treatments compared to the control and the combined application of BC and Comp treatments. The biochar treatment showed a slight reduction in these functional groups, suggesting possible adsorption or sequestration onto the BC surface while the Comp treatment led to an increase in functional groups associated with carbohydrates, proteins, and lipids, indicating enhanced organic matter content. The combined treatment exhibited intermediate effects, suggesting a synergistic interaction between Comp and biochar. X-ray diffraction analysis indicated that the BC did not demonstrate significant alterations in soil mineralogy, suggesting minimal direct effects on mineral dissolution or transformation. Conclusively, biochar-generated free radicals, especially hydroxyl radicals (•OH), play a crucial role in PTMs (i.e., Cd, Cr, Ni, As and Pb) immobilization in soil-plant systems. This study provides novel insights into biochar's mechanisms for mitigating PTMs pollution, paving the way for optimized soil amendment strategies. • BC and Comp influence free radicals generation in the soil-plant system. • BC & Comp treatments affect maize growth influence PTMs availability. • BC-based free radicals play a pivotal role in the geochemical transformation of PTMs. • Reveals distinct effects of BC and Comp amendments on soil functional groups. • BC and Comp demonstrate synergistic effects on FR generation and PTM transformation. [ABSTRACT FROM AUTHOR]

The microbial induced carbonate precipitation (MICP) technique has been shown to immobilize a wide range of heavy metals. However, the MICP process for removing uranium-dominated composite heavy metals ignores the formation of substances such as uranyl carbonate, which can easily lead to uranium migration. Furthermore, the by-product ammonia is one of the bottlenecks limiting the application of MICP. In this work, the microbially induced struvite precipitation (MISP) method was used to enhance U immobilization while reducing by-product contamination. The results showed that the optimal uranium removal rate of the MISP process was increased by 82.98% compared to the MICP. Characterization results confirmed the co-precipitation of U with NH 4 + in the form of uramphite and struvite, while the participation of U changed the mineral crystal shape. Stability experiments showed that the maximum release of U from struvite was only 1.27%, which is much lower than the minimum release of U from CaCO 3. As a result, the MISP process both enhanced uranium immobilization efficiency, decreased the risk of uranium migration-release, and reduced the environmental impact of the by-product ammonia. These results provided a new perspective for studying U contamination remediation and its co-precipitation behavior in microbial mineralization. [ABSTRACT FROM AUTHOR]

Environment-friendly and cost-effective disposal and reutilization of sludge wastes are essential during the wastewater treatment process. Converting sludge wastes into ceramsite by sintering treatment is a promising strategy for sludge treatment. This paper summarizes existing processes and technologies for regenerating ceramsite from sludge wastes. The synthesis process including raw material pretreatment, sludge characteristics analysis, batching, mixing and molding, drying and preheating, sintering and cooling is discussed. Then, the effects of additives, sintering temperature and time, and sludge content on the preparation and properties of sludge-based ceramsite are summarized. Integrating mechanistic insights and different physicochemical properties highlighted the understanding of the different applications (environmental remediation and architecture ingredients) of sludge-based ceramsite. High-temperature sintering sludge-based ceramsite exhibited excellent performance for the removal of contaminants due to the high porosity, large surface area, and good biocompatibility. Besides, the sludge-based ceramsite could also be used as concrete aggregate and asphalt mixtures due to its high strength, thermal insulation, and seismic resistance. Finally, the challenges and proposals for sludge-based ceramsite are proposed. This paper can provide a theoretical basis and guidance for the preparation and application of sludge-based ceramsite. [Display omitted] • Sludge-derived ceramsite can be used as support material for biofilters. • Sludge-derived ceramsite can be applied as medium filler for constructed wetland. • Sludge-derived ceramsite as adsorbents can effectively remove heavy metals. • Sludge-derived ceramsite has three main roles as a bulking agent in composting. • Sludge-derived ceramsite can also be utilized in concrete and asphalt mixtures. [ABSTRACT FROM AUTHOR]

Sodium dimethyl dithiocarbamate (SDD) is commonly applied to mitigate the release of heavy metals (HMs) into the environment from municipal solid waste incineration fly ash (IFA). Despite this common application, limited research has been conducted on the impact of environmental conditions on chelate destabilization during long-term landfilling. In this study, a batch leaching test was performed on chelated IFA buried for 10 years, revealing that the leaching concentrations of Pb and Cd exceeded landfill standards by 51.7% and 26.0%, respectively, indicating the chelate destabilization occurrence. To elucidate this phenomenon, various physicochemical experiments were conducted to unveil the underlying mechanisms emphasizing changes in HMs fractions (Pb, Cd, Cr, Ni, Zn, Cu) under acidic corrosion, and exploring the microscopic perspective of the chelate destabilization process. The key findings were summarized as follows: (I) The immobilization effect of SDD on Zn and Cd was not highly effective, with most of these metals being fixed on IFA through inorganic complexes. Theses HMs destabilization showed a negative correlation with the pH levels, indicating that higher acidity facilitated the release of HMs (59.0 mg/kg for Zn and 5.8 mg/kg for Cd). (II) After exposure to acid corrosion, the stable fraction of HMs decreased, because HM-SDD complexes decomposed into inorganic salts and carbon disulfide. This process further exacerbates the transporting effect of HMs on chelated IFA, thereby increasing the long-term leaching risk. (Ⅲ) A leaching equilibrium of HMs existed at the IFA surface, primarily influenced by the types and concentrations of anions in the leachate. This study contributes to a deeper understanding of the factors influencing the stability of chelated IFA and provides valuable insights into the long-term environmental implications of such materials in landfill settings. • Acid corrosion led to an increase in leaching risk through changes in heavy metals fractions. • Dissolved SDD had a transporting effect on heavy metals. • A leaching equilibrium of heavy metals was observed at the surface of fly ash. • Chelate destabilization mechanisms were discussed based on microscopic insights. [ABSTRACT FROM AUTHOR]

The Mekong River holds significant importance as a transnational water system within the Asian region. This study investigated the pollution characteristics, origins, and health risks associated with eighteen toxic metal (loid)s (TMs) across various depths in five cascade reservoirs located in the upper Mekong. The findings revealed that naturally sourced TMs (As, Cd, Li, Mo, Sb, and Sr) exhibited elevated levels in upstream reservoirs due to the interception effects of cascade dams. Anthropogenically sourced TMs (Co, Cu, Ni, Pb, and Zn) showed heightened concentrations in downstream reservoirs, linked to increased human activities in the downstream region. In deep-water reservoirs, the vertical distribution of redox-sensitive elements was influenced by thermal stratification, with concentrations of As, Cs, Li, Mo, Rb, Sr, and U notably higher in the hypolimnion than the epilimnion. Importantly, the concentrations of all elements in these cascade reservoirs meet Chinese and WHO drinking water standards. Water quality index (WQI: 9.2–19.1), heavy metal evaluation index (HEI: 0.96–1.37), and Nemerow index (NI: 0.35–0.56) confirmed the commendable quality of the cascade reservoir waters. The health risk assessment identified As, Sb, U, and Tl as primary contributors to non-carcinogenic risks in the cascade reservoirs. In the context of a series of cascade dams along this substantial river, this research establishes a solid foundation for preventing TM pollution and ensuring the long-term sustainability of water resources. [Display omitted] • 18 metal (loid)s were examined across various depths in five cascade reservoirs. • Thermal stratification in deep reservoirs can affect the distribution of elements. • Waters in these cascade reservoirs exhibited exceptional quality. • As, Sb, U, and Tl posed greater non-carcinogenic risks in the cascade reservoirs. [ABSTRACT FROM AUTHOR]

Coastal areas are facing increasing heavy metal contamination from various human activities, posing a severe threat to aquatic and coastal biodiversity. Mangroves, abundant in coastal and marine ecosystems, are particularly vulnerable to the accumulation of toxic inorganic pollutants and heavy metals (HMs). Mangroves have proved to be effective in mitigating heavy metal pollution through a range of mechanisms, including avoidance, chelation, sequestration, tolerance, excretion, and filtration. Studies highlighted a higher metal bioconcentration of metals in mangrove roots compared to leaves, indicating their remarkable endurance capability towards high levels of HMs. The uptake of HMs by mangrove roots occurs through passive diffusion across cell plasma membranes or active transport, regulated by metal ion transporters and influenced by electrochemical and/or concentration potential gradients. In phytoremediation strategies, mangrove plants employ several physiochemical mechanisms to avoid HMs uptake, such as cell wall immobilization, complexation with biomolecules like phytochelatins (PCs), and extracellular barriers at the root endodermis. Moreover, mangroves can develop iron-plaques on their root surface, acting as reservoirs for immobilized HMs and significantly influencing their sequestration, particularly in wastewater containing Cr, Pb, and Ni ions. Mangroves would also trigger antioxidant defenses to cope with the absorbed HMs and normalize the excessive production of reactive oxygen species (ROS)-mediated oxidative stress. However, the antioxidant response in mangroves varies depending on the concentration and type of toxic HMs, plant species, and exposure duration. Additionally, mangroves excrete excessive amounts of HMs through salt glands via adaxial trichomes, allowing them to mitigate phytotoxicity. Although mangroves demonstrate a high tolerance capacity towards HMs, hydrological alteration, deforestation, marine construction, and marine anthropogenic activities pose significant threats to several global mangrove species. In conclusion, conducting multiple toxicity tests using early mangrove seedlings are imperative that threshold effect concentrations of various HMs be determined under natural environmental conditions encompassing nutrients, salinity, temperature, and the presence of several contaminants. Besides, long-term, large-scale mesocosm experiments in real-field settings should be conducted in future to obtain more realistic and reliable insights into the uptake and tolerance of HMs in mangroves. [Display omitted] • Coastal ecosystem is endangered due to heavy metal contamination due to anthropogenic activities. • Mangroves ecosystem faced adverse effects of HMs toxicities. • Mangroves species mitigate HMs toxicities dependent on HMs type and concentration. • Mangroves tolerate HMs toxicity through cell wall immobilization, complexation with biomolecules and extracellular barriers. • Mangroves Phytoremediate HMs phytotoxicity through salt glands via adaxial trichomes. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag negatively impacts ordinary Portland cement performance when replacement levels exceed 5%. This necessitates the exploration of alternative applications for the slag. Simultaneously, a high-volume slag utilization is desired to benefit slag recycling as supplementary cementitious materials. Therefore, this study aims to optimize the air granulated BOF slag substitution potential in belite calcium sulfoaluminate cement by investigating the hydration products in standard mortar. The reactivity of the novel binder is correlated with workability, and mechanical performance by thermal, mineralogical, and microstructure analysis. Consequently, the 10–30% replacement delays the final setting time by inhibiting the ettringite formation leading to a decrease in mechanical performance till 28 days. At later ages (28–180 days), the 30–50% substitution exhibited the synergy in mechanical performance, which is attributed to the hydrogarnet, calcium silicate hydrate, and strätlingite formation. Moreover, all the mortar samples exhibited heavy metals' leaching and drying shrinkage below the permissible limit. [Display omitted] • Early age reactivity of BCSA-slag composite is dominated by ettringite formation. • Strätlingite, C–S–H, and katoite enhance the binding capacity of the composite. • 30% BOF slag replacement is recommended for best performance. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitation (MICP) is an effective and eco-friendly technology for remediating heavy metal-contaminated sites. In this study, we investigated the response discrepancies and proposed the dominant removal mechanism of the ureolytic bacteria Brucella intermedia TSBOI for different heavy metal species (Cu, Pb and Zn) under concentration gradients (0.1, 0.2, 0.4, 0.8, and 1.6 mmol/L), and explored the remediation of soil heavy metal pollution by B. intermedia TSBOI under laboratory conditions. The results showed that the heavy metal concentration significantly affected the bacterial cell concentration, urease activity, cell morphology, surface functional groups, and removal efficiency of B. intermedia TSBOI. The presence of Ca2+ negatively affected the biomass and urease activity to some extent but had a non-negligible positive effect of removing heavy metals and was more conducive to the formation and precipitation of biomineralization products. The ability of B. intermedia TSBOI to produce urease intracellularly and secrete it in large quantities to act extracellularly is key to the sustained immobilization of heavy metals and the outstanding performance of B. intermedia TSBOI bacterial solution. The results of heavy metal-contaminated soil remediation showed that B. intermedia TSBOI effectively increased the proportion of carbonate-bound states of Cu, Pb and Zn in the soil and reduced the bioavailability of heavy metals within 30 days. B. intermedia TSBOI could adapt fully to the soil environment and became a dominant genus. [Display omitted] • Formation of stable biomineralized precipitation of heavy metals facilitated by Ca2+. • The crystal structure of CaCO 3 induced by B. intermedia TSBOI is vaterite. • Biomineralization dominates B. intermedia TSBOI removal of Cu, Pb, Zn. • Effective enhancement of the carbonate bound state of soil heavy metals using B. intermedia TSBOI. • B. Intermedia TSBOI is suitable for Cu, Pb, Zn pollution remediation of acidic soil. [ABSTRACT FROM AUTHOR]

Biosensors play a very important role in pollutant monitoring, but there are still some problems such as stability, repeatability and low detection limits. Therefore, it is necessary to explore ways to increase the performance of biosensors. In this study, biochar-MFC sensors were constructed for heavy metals monitoring in constructed wetlands (CWs), and the correlation, repeatability and anti-interference were studied. At 1.0 M/L concentrations of heavy metals (Ni, Cu, Zn and Cr), CW with biochar as filler (B-CW) had an output voltage of 0.69 V, extending the detection limit of the sensor. B-CW had advantages in anti-interference and reproducibility. The results showed that B-CW had higher abundance of electrogenic bacteria than CW. Shewanella and Proteobacteria , main electricity-producing bacteria, increased 3-fold. The electrochemically active microorganism Shewanellaceae made up 6.2% of the B-CW microbial population, but was not detected in CW. The abundance of key genes AarC increased by 1295.8% in B-CW. More importantly, the abundance of extracellular electron transport chain related genes (MtrA , OmcA) increased significantly (p < 0.01). Biochar can promote oxidative phosphorylation, thus increasing the sensor's output voltage and detection range. This study is expected to provide support for the engineering application of MFC sensor in CWs. [Display omitted] • MFC-sensors can effectively detect heavy metals in constructed wetlands. • Extracellular electron transfer significantly increased in biochar system. • Biochar increased genes associated with oxidative phosphorylation by about 27%. • Biochar significantly enhanced the repeatability and anti-interference of the sensor. [ABSTRACT FROM AUTHOR]

Mercury ions (Hg2+) are one of the most physiologically toxic heavy metal ions in water. Developing adsorbents for separating and removing mercury ions from aquatic systems has important environmental and social significance. Owing to the hard-soft-acid-base interaction between mercury and sulfur (S) atoms, two-dimensional layered MoS 2 holds great promise in capture physiologically toxic Hg2+ from water, but most S atoms are located inside the bulk MoS 2 , hindering the effective contact with mercury. Defects engineering is considered as an effective way to adjust the structure and achieve superior performance of MoS 2. However, reasonable and fine defect modulation to enhance the mercury adsorption performance remains a challenging task. Herein, we reported that molybdenum sulfide with Mo-vacancy structure (MV-MoS x) was fabricated via hydrothermal method and employed to uptake Hg2+. The results showed that this defect type significantly increased the concentration of Mo stripping defects, exposed more active S atoms, and provided MoS x with excellent adsorption performance in adsorption capacity, adsorption kinetics, distribution coefficient, selectivity and so on. In particular, MV-MoS x demonstrates a substantial actual adsorption capacity for mercury, reaching as high as 3723.3 mg/g, which is in close proximity to its theoretical adsorption capacity of 3945.95 mg/g. More importantly, a functionalized composite aerogel system based on MV-MoS x was constructed, which successfully reduced the concentration of Hg2+ solution below the concentration permitted by drinking water standards. Our study not only provide a theoretical basis for the design of novel defect engineering, but also expand the application of transition metal sulfides in the enrichment and separation of heavy metal ions. [Display omitted] • Defect engineering was proposed to improve the adsorption performance of MoS 2 in the field of environmental remediation. • The MV-MoS x with abundant Mo atomic vacancies and accessible binding sites was synthesized. • MV-MoS x could capture 3723.3 mg/g Hg2+ from aqueous solution. • The removal mechanism was illustrated in detail. • MV-MoS x /VFs was fabricated and employed to filter wastewater. [ABSTRACT FROM AUTHOR]

Co-combustion of municipal sludge (SS) and coal slime (CS) is an effective route to achieve the co-disposal of solid wastes. This work addresses the problem of heavy metal pollution in co-combustion ash, aiming to reveal the effect of interactions in SS-CS co-combustion on the behavior of heavy metals and the control mechanism of minerals using the inductively coupled plasma mass spectrometry (ICP-MS) technique and the Community Bureau of Reference (BCR) method. The residual rate of heavy metals in CS ash monotonically decreased with increasing combustion temperature, while the residual rate of heavy metals in SS tended to increase when it was burned at high temperatures. Increased temperature enhanced the effect of SS-CS interaction on heavy metals. The interaction significantly inhibited the volatilization of As, and the As residue of the blend containing 50% CS (5SS5CS) at 1000 °C was 14.9% higher than the theoretical value. Typical minerals in SS had significant effects on heavy metal migration in CS, and the effects of CaO and Fe 2 O 3 on heavy metals were mainly due to chemical interactions, in which CaO fixed As in the form of Ca 3 (AsO 4). Density functional theory calculations show that the optimal adsorption sites for both As and As 2 O 3 on the CaO(001) surface were O-top sites, and the presence of O defect on the surface led to enhanced interaction of As 2 O 3 with the surface. Co-combustion led to an increase in the residual fractions of heavy metals, but the exchangeable and acid soluble fraction of As in 5SS5CS was still as high as 19.3%, so the ecological impact of As should be considered in further utilization of the co-combustion ash. [Display omitted] • The residual rate of Cr in SS and CS remains above 80%. • Synergy exists between SS and CS in the fixation of heavy metals. • The effects of minerals in SS contribute to synergy. • Co-combustion increased the RES fraction in ash. [ABSTRACT FROM AUTHOR]

During urbanization, excessive development and utilization pose varying risks and challenges to the ecosystems of many urban lakes. Sediments are invaluable archives of past ecosystem changes. By analyzing variations in 210Pb and other geochemical indicators in sediment cores, it is possible to assess how susceptible lakes are to the impacts of climate change and human-induced pollution, which is crucial for urban planning and the management of lake environments. This study investigated the status of heavy metal pollution in Lake Longquan, Chengdu City, and reconstructed the historical evolution of its ecological environment using 210Pb dating. Three main conclusions are drawn. (1) Currently, Cd, Cu, Pb, Zn, Cr, and organic matter in the surface sediments of Lake Longquan are highly enriched in the southeastern, central, and northeastern regions. Cd levels even reach 1.54 mg/kg in the southeastern part of the lake near the town. The high overlap of heavy metal distribution with historical aquaculture areas and some tourist areas indicates that aquaculture and tourism are important sources of heavy metals that increase their bioavailability. (2) Lake Longquan is currently at a high potential ecological risk level, and the high potential risk level of Cd may cause ecological safety problems. The biological toxicity of As should be considered, too. (3) The risk evolution in Lake Longquan can be divided into six stages: (i) Before 1977, the ancient river. With the destruction of forest vegetation and the intensification of rock weathering, ecological risks increased. (ii) 1977–1989, construction and development. Due to human factors and the joint influence of heavy precipitation events, ecological risks increased; and (iii) 1989–2010, development prioritized protection. Due to the ineffective implementation of protection policies, aquaculture increases risks. (iv) 2010–2017, development. As a provincial resort and tourism area, the significant increase in human activities has led to constantly rising sedimentation rates and heavy metal concentrations, resulting in an ecological risk peak. (v) 2017–2020, protection. The efficient implementation of lake protection and restoration policies proved to be effective, and the ecological risk started to decrease. (vi) After 2020, protective development. The government's plan to reduce fertilizer usage and increase forest cover will help control ecological risks. It is necessary to continue controlling tourism and aquaculture activities, and transitional areas should be established around lakes for city residents to engage in lakeside sightseeing and recreational sports. This study provides valuable references for controlling and preventing heavy metal pollution in urban lakes. [Display omitted] • Reconstructed the environmental quality evolution process of typical urban lakes at various development stages. • Cd is the primary risk element in Lake Longquan. • The proportion of anthropogenic sources of heavy metals in sediment is as high as 68.17%. • Aquaculture and tourism are the main sources of heavy metals. • Short-term heavy precipitation can amplify the impact of human activities, thereby accelerating the sedimentation rate. [ABSTRACT FROM AUTHOR]

Considering the environmental pollution caused by the direct stacking or landfilling of various sludge, the combustion characteristics of bituminous coal, Fe-rich industrious sludge, and their blend were studied using thermogravimetric analysis at non-isothermal and isothermal conditions. It was found that the volatile matter in sludge with low C/H ratios will be released and burned in the low-temperature stage, then the generated heat will promote extra heat for the combustion of fixed carbon in coal when the addition of sludge was greater than 60%. The used Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods were more accurate for coal, sludge, and their blend with low sludge addition. After comparing the activation energy, a suitable addition of sludge was found to improve the combustion and kinetic characteristics of fixed carbon but do less help to volatile matter in coal. As to the heavy metals emission, the synthetic effect of the blend combustion enhanced the Pb emission when sludge addition was more than 60% but almost did not affect Cr, Ni, Zn, and Cu. By sampling dynamically during the co-combustion, it was found that the leaching toxicity of heavy metals was greatly related to the combustion degree. The stabilization of Al, Ca, Cr, and Zn was finished as their leaching toxicity decreased to a constant value before the burnout of fixed carbon (100∼120s) while that of Ni was slightly delayed, especially when the coal was added. Besides, the leaching concentration of Cu gradually increased with combustion time and its stabilization cost more time. Such a time-controlled combustion strategy may also be worthy of further research to help dispose of other solid wastes with similar composition. [Display omitted] • The FWO and KAS methods were more accurate for co-combustion with low sludge addition. • Combustion of volatile matter in sludge helped the combustion of fixed carbon in coal. • The volatilization of Pb was promoted with the sludge addition in blend combustion. • Leaching concentrations of metals were greatly related to the combustion degree. [ABSTRACT FROM AUTHOR]

Hazardous wastes containing non-ferrous metals have significant value in recycling. However, the recycling process generates leaching residues (HWLR) with high levels of heavy metals, posing a risk to the environment. Based on the component characteristics of HWLR, silica residue (SR), and silicon tetrachloride cracking slag (STCS), the feasibility of co-thermal treatment for the efficient disposal of HWLR, SR and STCS was verified in this study. According to the SiO 2 –Na 2 O–CaO ternary system diagram, the melting point of the system decreases gradually with the appropriate increase in SiO 2 content when the CaO/Na 2 O ratio in the system was determined to be about 2.33. When the theoretical liquid phase content of the mixed system of 100%, the thermal treatment temperature could be lowered to 1100 °C, which is significantly below the melting points of HWLR, SR, and STCS individually. The experimental results confirmed that thermal treatment at temperatures above 1000 °C effectively eliminated the leaching toxicity of Cu, Ni, Zn, Cr, Cd, and Pb in the mixed samples of HWLR, SR, and STCS, which can mainly be attributed to the formation of a glass network structure during the thermal treatment process. This study demonstrated that low-temperature melting treatments could efficiently and thoroughly solidify heavy metals in HWLR, SR, and STCS. [ABSTRACT FROM AUTHOR]

Phosphorus-containing materials are effective in remediating heavy metal-contaminated soil. However, the excessive release of phosphorus could become a new environmental risk. On the basis of the concept of developing slow-release soil passivators from phosphorus-containing solid wastes, three materials—phosphoric acid-phosphate tailings (PPT), heat-treated PPT (H-PPT), and chitosan-coated PPT (C-PPT)—were successfully prepared from phosphate tailings (PT). The phosphorus in both H-PPT and C-PPT showed slow-release properties in aqueous solutions, and their release behaviors could be well fitted by the Korsmeyer-Peppas model. The stabilization efficiency of the slow-release materials for lead increased with the gradual release of phosphorus, with a maximum increase from 56.09% to 91.41%. In experiments simulating phosphorus loss, the slow-release materials H-PPT and C-PPT showed decreased phosphorus leaching concentrations (from 72.33 to 12.70 and 0.73 mg/L) and rates (from 10.01% to 1.69% and 0.43%) compared with those of PPT, significantly reducing the environmental risk. Meanwhile, the remediation process has to some extent improved the structure and function of the soil microbial community, which in turn has contributed to the stabilization of lead. Overall results suggest that PT-based slow-release materials may be an excellent strategy and technology for solving phosphorus loss because it achieves resource utilization of PT and solves the secondary pollution caused by the application of phosphorus-containing materials, thereby avoiding phosphorus pollution and improving the utilization of phosphorus resources. [Display omitted] • PPT, H-PPT, and C-PPT were obtained by phosphoric acid activation, heat polymerization, and chitosan coating. • Weakly acidic environments were more conducive to the formation of stable precipitates from phosphate and Pb. • H-PPT and C-PPT had slow-release properties for stable release of phosphorus to passivate Pb. • H-PPT and C-PPT significantly reduced the risk of P loss and improved the microbial community structure. [ABSTRACT FROM AUTHOR]

The emission of heavy metal elements (especially the most toxic Hg) from coal-fired power plants has always been a hot issue in the environmental field. Nickel selenide was first applied to flue gas mercury removal in this work, and a new adsorbent of Nickel selenide (Ni 0.85 Se) loaded with graphite carbon nitride (g-C 3 N 4) was developed to effectively remove elemental mercury. When the loading mass of g-C 3 N 4 is 20%, NS/20CN has 100% mercury removal efficiency. Meanwhile, it will not be poisoned by NO and SO 2 in the flue gas. At the same time, NS/20CN also has strong magnetism that is not permanently magnetized, and can be separated from the downstream magnetic field of WESP for heat treatment to recover ultra-low concentrations of Hg0 and reused. Therefore, this work demonstrates that NS/20CN adsorbent has excellent performance and economy in efficiently removing elemental mercury and has also broadened the application of Nickel selenide in the environmental field, providing an efficient guidance method for the treatment of other environmental pollutants. [Display omitted] • Nickel selenide was first used in coal flue gas mercury removal. • We have adopted advanced experimental and simulation research methods. • The material can cope with various situations in practical applications. • Strong magnetic materials can be recycled and treated after mercury removal. • We have provided the best usage strategy for the practical application. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration fly ash (FA) is a pressing issue in urban development. In FA treatment, washing is a common dechlorination pre-treatment. During washing, considerable heavy metal would leach due to the abundant alkaline substances, posing challenges to the heavy metal stabilization. Also, with high alkalinity, FA has potential to co-dispose of waste sulfuric acid (hazardous waste). Addressing these, our study presented a novel pH-controlled sulfuric acid washing for FA dechlorination during the sintering preparation of lightweight aggregate (LWA). It was aimed at enhancing heavy metals stabilization and enabling the co-recycling of FA and waste sulfuric acid. By controlling a pH of 10.50 during sulfuric acid washing, the leaching rate of Pb, Cd, Zn, Cu, Ba, and Cr was below 2%, which was a marked improvement over conventional water washing. Sulfuric acid washed FA (SFA) can be used to produce standard-compliant LWA by sintering with bentonite and SiC. The SFA-based LWA stabilized heavy metals more effectively than LWA using FA and water-washed FA. At a 30 wt% addition rate, the stabilized rate of Pb and Cd increased from 11.7% (using FA) to 72.4% (using SFA), and from 6.3% (using FA) to 49.0% (using SFA), respectively. During washing and sintering, XPS analysis further investigated the transformation of Pb, Cu, and Zn into stable states (Pb-glass, Cu 2 O/CuO, and ZnAl 2 O 4), enhancing their stabilization. Our study introduces a novel method for co-recycling FA and waste sulfuric acid, offering enhanced environmental sustainability and deeper insights into the mechanism of heavy metal stabilization. [Display omitted] • pH-controlled sulfuric acid washing notably reduced the heavy metal leaching rate. • LWA conforming to standards can be produced from sulfuric acid washed MSWI fly ash. • Heavy metal stabilized rates in LWA were increased by the sulfuric acid washing. • Stabilization mechanism of Pb, Cu and Zn were studied through chemical form changes. • Validated feasibility of co-recycling waste sulfuric acid and MSWI fly ash in LWA. [ABSTRACT FROM AUTHOR]

In acidic mine wastewater, Mn and Fe are among the prime heavy metals and pose a great threat to the ecological environment and human health. Combining biological and physical methods to treat heavy metal contaminated water bodies is a promising remediation technique. In this study, grapefruit peel biochar immobilized Acinetobacter sp. AL-6 (co-system) was applied to treat the contaminated water with co-existing Mn2+, Fe2+ and NH 4 +-N. The results showed that almost 100% of Mn2+, Fe2+, Zn2+ and Cu2+ were removed in bioreactor, and was transferred to Mn2+, Fe3+, Zn2+ and Cu2+ precipitates on the surface of co-system without N 2 O accumulation. Especially, Mn2+ and Fe2+ were adsorbed in extracellular polymers (EPS) of strain AL-6. The present study mainly confirmed that the combined system of biochar and bacteria had great potential in the complex water removal of multiple heavy metals and NH 4 +-N, and also revealed the regulation of heavy metals by the EPS of strain. [Display omitted] • Biochar-immobilized Acinetobacter can be applied for Fe and Mn bioremediation. • EPS production was promoted by higher Fe for resisting unscrupulous stress. • Fe and Mn can be adsorbed by the surface of EPS. • CO 2 could suppressed by the increasing Fe concentration. [ABSTRACT FROM AUTHOR]

Phytoremediation, as a green, sustainable, and cost-effective plant-based remediation technology has garnered great attention for remediating heavy metals (HMs) from polluted soil and water resources. However, HM type and concentration, phytoremediation method, climatic conditions, type of plant species, potential of biomass production, level of plant sensitivity, and signaling pathways efficiency are all crucial factors affecting plant's phytoremediation performance. Ornamental, medicinal, and aromatic plants with medicinal, pharmaceutical, cosmetics, and decorative uses are promising species for the phytoremediation of HMs from soil and water due to their fast growth and high biomass production. Furthermore, new genetic technologies such as, the clustered regularly interspaced short palindromic repeats – CRISPR associated protein 9 (CRISPR/Cas9) gene/genome editing system, may become a tool that provides sustainable phytoremediation by targeted editing of genes of interest to improve the phytoremediation capacity of the selected ornamental plants (OPs) without raising genetically modified organisms (GMO) concerns. This review summarizes the current state of knowledge associated with protection mechanisms and molecular aspects of plant tolerance to HMs by ornamental, medicinal and aromatic plants. The review also focuses on the use of genetically engineered ornamental and medicinal aromatic plants applying recent advances in CRISPR/Cas9 genome editing to enhance phytoremediation properties. Risk assessments and regulatory approaches associated with environmental protection, livestock, and human health for transgenic plants released into the environment are also discussed. This work elicits interdisciplinary aspects and an understanding of the long-term management of HMs using ornamental, medicinal, and aromatic plants in an innovative way that no prior study has considered. [Display omitted] • Phytoremediation technology removes heavy metals from soil with low drawbacks. • Ornamentals with high growth rates are appropriate candidates for phytoremediation. • CRISPR technology is used to modify genes involving phytoremediation efficiency. • Gene/genome editing of ornamentals develops a sustainable and clean environment. [ABSTRACT FROM AUTHOR]

Large quantities of acid mine drainage (AMD) generated through the oxidation of sulfide-bearing minerals, particularly pyrite, pose a significant global environmental challenge. The implementation of efficient and fundamental governance methods is crucial as current conventional approaches fail to address the root cause of this problem. To investigate the technique of controlling AMD at its source, a 10-day static experiment was conducted in order to examine the inhibitory effect of Sporosarcina pasteurii (S. pasteurii) on oxidative acid production from pyrite under varying redox potentials (Eh) and Ca2+ concentrations. Additionally, a 180-day dynamic column experiment was carried out to assess the long-term stability of its inhibition and heavy metal fixation. The results of both short-term and long-term analysis indicate that the metabolic activity of S. pasteurii has beneficial effects on the control of AMD through sulfur oxidation, even in the presence of strong oxidants such as H 2 O 2 and FeCl 3. 1. It stabilizes pH within the neutral to alkaline range; 2. It maintains Eh at a low potential reducing environment; 3. It promotes an increase in SO 4 2− concentration, followed by a decline and stabilization at lower concentrations; 4. It supplies carbonate for pyrite oxidation, maintaining a balance between acid production and consumption. Additionally, SEM, XRD, and XPS results demonstrated that the mineral surface appeared flat without prominent characteristic peaks of oxidation products, indicating effective inhibition of pyrite oxidation by S. pasteurii. The immobilization experiments for heavy metals showed that Cd exhibited the highest fixation effect with a rate of 94%; Mn, Cu, Zn, and Co had the second best fixation effect with ion concentrations decreasing by 82%, 83%, 87%, and 88% respectively; Ni and U(VI) decreased by rates of 75% and 69% respectively. These experimental findings suggest that S.pasteurii can effectively inhibit pyrite oxidation as well as sulfur-containing uranium waste rock oxidation while providing long-term stabilization for heavy metal immobilization. [Display omitted] • S. pasteurii. can keep solution pH in a neutral to alkaline environment. • S. pasteurii. can maintain solution Eh at a low REDOX potential and reduce SO 4 2− to H 2 S. • S. pasteurii has long-term stability in inhibiting sulfur oxidation and fixing heavy metals. • Source control on AMD of sulfur-containing uranium tailings based on MICP can be realized. [ABSTRACT FROM AUTHOR]

Coal-fired winter heating (CWH) results in serious air pollution, but limited studies have investigated its threats to health and ecosystem. The environmental impact and social cost of CWH in China at the province level was quantified via a "bottom-up" life cycle assessment approach. The ecosystem damage and social cost of CWH maintained high values over the last decade, although exhibited a downward trend. Approximately 688 Mt CO 2 eq of greenhouse gas emitted from CWH activity in 2019, accounting for 4.9% of China's total emission. Shandong and Liaoning Provinces dominated the nationwide environmental and economic burdens of CWH. Heavy metals atmospherically emitted from CWH exerted significant carcinogenic impacts and showed a correlation with regional cancer incidence (e.g., respiratory, reproductive, urinary, neurological, and blood-lymphatic systems), indicating the potential multi-system damage of CWH. Energy-saving buildings, geothermal utilization, efficient heavy metal end-point control technology, and improving emission factors quality are highly recommended. [Display omitted] [ABSTRACT FROM AUTHOR]

The rationalized recycling of waste dry batteries is of great significance to the circular development of resources. In this research, the feasibility of using waste dry batteries in asphalt modification was discussed. Waste dry battery powder (WDBP) was extracted from discarded zinc-manganese dry batteries, and its composition, micromorphology and heavy metal emissions were characterized. Further, the modified asphalts with different WDBP contents were also prepared, and the enhancement effect of WDBP on the physicochemical properties of the binder was evaluated. The results indicate that WDBP mainly contains inorganic carbon and metal oxides. Under acid rain and neutral environment, the heavy metals from WDBP are mainly Zn, Mn and Cd, and their concentrations exceed the concentration limits of Class I surface water in China. The heavy metals in WDBP can be physically solidified for the use of WDBP in asphalt modification. Meanwhile, WDBP can enhance the flow deformation resistance of the binder at the medium-high temperatures, further improve its rutting resistance. However, the WDBP may be have adverse impact on the low-temperature cracking resistance of asphalt, and the WDBP modified asphalt (WDBP-MA) is more suitable for the application in the areas with heavy traffic and hot climate. In addition, the WDBP can enhance the aging resistance of asphalt. Overall, the conclusions confirm the feasibility of applying WDBP to asphalt modification, which can provide a new approach for rational recycling of waste batteries and development of modified asphalt. • The characteristics of waste dry battery powder (WDBP) were analyzed. • The WDBP modified asphalt (WDBP-MA) were successfully prepared. • The physicochemical properties and aging resistance of WDBP-MA were comprehensively investigated. [ABSTRACT FROM AUTHOR]

Zinc leaching residue is a hazardous solid waste with difficult treatment, high hazard and high yield, and it is a great challenge to treat it efficiently, harmlessly and economically among the various methods available. This paper introduced a micro-crystallization method to process zinc leaching residue into glass-ceramics with excellent performance and high value. The heavy metals in the raw material were well solidified in the glass-ceramics, eliminating the high hazard of heavy metals and other components. The bending strength, compressive strength, and Vickers hardness of the glass-ceramics prepared at the sintering temperature of 950 °C were 69.2 MPa, 434.3 MPa, and 6.66 GPa, respectively, while the water absorption, density, and acid and alkali corrosion resistance were excellent. The relationship between the microstructure and properties of glass-ceramics was investigated using traditional analytical techniques such as XRD, Raman, and SEM, and the mechanism of solidification of heavy metals Pb, Zn and Mn in glass ceramics were innovatively researched by the modified BCR sequential leaching test and XPS analysis. Anorthite and diopside ferrian were the two main crystalline phases in glass-ceramics. The sintering temperature affected the formation and growth of crystals, and determined the crystal size and crystallization rate, thus affecting the properties of glass-ceramics. Part of the heavy metal was solidified in the amorphous phase in the glass-ceramic, and the other major part entered the crystal as an impurity substitution to form a solid solution at a specific location. The zinc leaching residue based glass-ceramic had been studied, which was pioneering and with excellent performance and environmental safety. Thus, the safe and economical treatment of these hazardous wastes promotes the clean, green and efficient development of related industries. [Display omitted] [ABSTRACT FROM AUTHOR]

Trace elements contamination in estuarine and bay ecosystems has become a serious problem, especially in bays with frequent aquaculture activities. To explore the pollution risk, sources and trends of pollution trace elements in Dongshan Bay, a typical aquaculture bay in China, the concentration and spatial distribution of seven trace elements in surface sediments were investigated. In this study, Zn was the element with the highest content in surface sediments, followed by Pb and Cr, while Cd was the lowest, but the average concentrations of Cd and Hg exceeded the regional background values. High levels of trace elements were distributed in estuaries and aquaculture areas, which were illustrated also by the SOM model. An evaluation of the pollution load index (PLI), geo-accumulation index (I geo) and potential ecological risk index (PERI) demonstrated that Cd and Hg were the principal pollution elements and ecological risk factors in the surface sediments of the Bay. A positive matrix factorization model (PMF) revealed that the main sources of trace elements were natural sources, petrochemical industry and fossil fuel combination emissions, use of agricultural fertilizer, and industrial and agricultural sewage discharge. Comparative analysis found that since 2008, the mean content of Cu, Pb, Zn, and As have decreased significantly, while the content of Cd, Hg, and Cr have increased significantly. This information will help marine management efforts in taking effective measures to prevent environmental risks caused by trace elements pollution, especially related to aquaculture. [ABSTRACT FROM AUTHOR]

Black soldier fly larvae (BSFL) are used to digest municipal sludge, and its excretion and the sludge residue (BSFL sand) have attracted much attention. However, little research has been conducted on the quality of the BSFL sand produced with high concentrations of copper (Cu) and cadmium (Cd) and its effect on plant growth. We collected BSFL sand from previous studies to assess its feasibility as an organic fertiliser. The results showed that with the increase in Cu and Cd concentrations, pH (5.84–6.73), electrical conductivity (2.38–3.37), and organic matter (82–96%) increased continuously, moisture (20–25%), and total nutrients (4.19–5.26%, TN + P 2 O 5 +K 2 O) content decreased. Cu and Cd stress significantly (P < 0.05) reduced the content of free amino acids and fatty acids in the BSFL sand, and the germination index of cucumber seed also decreased continuously (30–73%), especially the mildew phenomenon that occurred in the Cu-1500 (mg/kg) group. In conclusion, BSFL sand can be considered a fertiliser when Cu and Cd concentrations in the initial sludge are lower than 900 and 120 mg/kg, respectively. However, considering the problems of Cu and Cd enrichment, their concentrations should be lower than 222 and 2.54 mg/kg, respectively. This study provides a theoretical basis for applying BSFL sands in agricultural production. Studies on the effects of Cu and Cd on the quality of insect and sludge co-composting products. [Display omitted] • Municipal sludge can be used as a raw material for BSFL composting. • A high concentration of Cu and Cd stress will reduce the quality of composting. • In the control group, BSFL sand meets the quality standard for fertilizer. • High EC (2.4–3.4) is the biggest problem in the final composting product. • In the initial MS, we recommend Cu and Cd below 222 and 2.54 mg/kg, respectively. [ABSTRACT FROM AUTHOR]

This study evaluates the effectiveness of dispersed alkaline substrate (DAS) technology to treat highly acidic and contaminated leachates from the oxidation of sulfide-rich mining wastes under wet temperate oceanic climate conditions. To address this issue, leachates from the abandoned mine at Parys Mountain (NW Wales) were passed through two sets of multistep columns filled with a mixture of a fine-grained alkaline reagent (i.e., limestone, MgO, or BaCO 3) scattered in an inert matrix. The set of columns with the limestone-DAS plus MgO-DAS combination achieved a near total removal of Fe, Al, Zn, Cu, Mn, As, Co, Cd, and Ni. However, the elimination of SO 4 was not significant (around 7%). The limestone-DAS plus BaCO 3 -DAS combination also achieved a high effectiveness for base metal/loids, allowing the removal of Fe, Al, Zn, Cu, As, and Cd with rates of nearly 100%. In addition, the system with the BaCO 3 -step had a higher effectiveness in eliminating SO 4 (around 53%) than the combined treatment with the MgO-step. According to PHREEQC code calculations, the precipitation of oxy-hydroxy-sulfates (i.e., schwertmannite and basaluminite) and carbonate (i.e., malachite, hydrozincite and calcite) phases may have controlled the solubility of pollutants during the passive treatment. The chemical compositions of the treated waters complied with the threshold values defined by irrigation standards, except for Mn in the BaCO 3 -DAS output. [Display omitted] • Multistep DAS treatment systems improved notably the chemical water quality. • Total metal removal was achieved with the limestone-DAS plus MgO-DAS combination. • MgO is more effective than BaCO 3 for the removal of divalent metals contained in AMD. • Metal concentrations in the MgO-DAS output are below the limits for irrigation water. • Solids from DAS systems could be considered a secondary source of base metals. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) contains plenty of PO 4 3− and F− and some heavy metals. Phosphorus ore flotation tailing (POFT) mainly consists of dolomite (CaMg(CO 3) 2) and calcium fluophosphate (Ca 5 (PO 4) 3 F). Traditional methods of POFT and PG storage could seriously damage the ecological environment. In this study, an innovative method for simultaneous stabilization/solidification (S/S) of PG and POFT was studied. The effects of PG and POFT mass ratio, S/S pH, solid-liquid ratio and temperature on the concentrations of PO 4 3− and F− in the leaching solution as well as the characteristics of POFT and PG were studied. Meanwhile, the simultaneous S/S mechanisms of PG and POFT and leaching test were investigated. The results showed that the concentrations of F− and PO 4 3− in the leaching solution were 6.0 mg/L and 4.0 mg/L, respectively, when the mass ratio of PG and POFT was 1:1 and the initial pH was 8.0 after being solidified for 30 days. F− and PO 4 3− were mainly stabilized as (Ca, Mg, Zn)F 2 and (Ca, Mg, Zn) 3 (PO 4) 2 , respectively. Leaching test results showed that PO 4 3− was reduced from 508.0 mg/L to 4.0 mg/L, and the concentrations of all the measured heavy metals and F− were within the permitted level for the GB8978-1996 after 30 days S/S. Image 1 • Simultaneous S/S of PG and POFT is an economically feasible method. • F− and PO 4 3− were mainly stabilized in the form of chemical precipitates in PGP. • Heavy metals concentrations were within the permitted level after 30 days S/S. [ABSTRACT FROM AUTHOR]

Sustainable management of contaminated biomass derived from phytoremediation of metal(loid) polluted soil and water is of great importance to avoid environmental risks from secondary pollution of the contaminants. In this regard, pyrolysis technology may reduce the environmental risk of the contaminants and produce different bio-products from contaminated biomass. In this work, slow pyrolysis of Avicennia marina biomass was conducted to compare the pyrolysis properties of heavy-metal-contaminated and uncontaminated biomass and its potential to generate pyrolytic products, such as biochar, bio-oil and pyrolytic gas at a varying temperature range from 300 to 800 °C. The results indicated that the properties of biomass and derivatives were affected significantly by both pyrolysis temperature and the presence of heavy metal(loid)s. The heavy metal(loid)s in biomass contributed to higher biochar and pyrolytic gas yields at the expense of bio-oil. Increasing pyrolysis temperature induced the volatilisation of heavy metal(loid)s in biochar samples. At the same pyrolysis temperature, the contaminants significantly increased the ash content whilst decreased the fixed carbon content in biochars (p < 0.05). Furthermore, it was noticed that the quality of bio-oils was improved by the presence of metal(loid)s, as the pyrolysis of contaminated biomass produced 8–11% hydrocarbons in the bio-oil samples with less oxygenated compounds as compared to uncontaminated biomass that produced only 4–5.8% hydrocarbons in the bio-oil. Moreover, biomass abound with trace metal(loid)s produced more H 2 and CO 2 during pyrolysis compared to uncontaminated biomass. Overall, this study demonstrated that pyrolysis is an efficient way for converting heavy metal contaminated biomass obtained from phytoremediation into valuable products, contributing to the sustainability of phytoremediation. Image 1062189 • Contaminated and uncontaminated biomass and pyrolytic products were studied. • Temperature and contaminants affected biomass and pyrolysis products properties. • The biochar yield was significantly increased with presence of heavy metal(loid)s. • Heavy metal(loid)s were enriched in biochars by pyrolysis at lower temperatures. • Hydrocarbons in bio-oils increased greatly with presence of heavy metal(loid)s. [ABSTRACT FROM AUTHOR]

The integrated utilization of wastes in a cement kiln has become an international megatrend. Various hazardous compounds containing in wastes might be enriched in the particulate matter (PM) emitted during the waste disposal and cause adverse environmental consequences. In order to evaluate the potential environmental issues caused by the PM emission from the cement kiln for co-processing wastes, the chemical characteristics and formation mechanism of the PM was investigated for the first time by using a laboratory-scale tube furnace to simulate this process. PM was collected to analyze the major components (heavy metals, inorganic and organic components) and morphologies. The results reveal that volatile heavy metals in municipal sewage sludge (MSS) can be enriched in PM. The process can elevate the levels of sulfate and the organic contents in PM, and the existence of organic moieties such as CN+ and CHN+ suggest that the co-processing of MSS can affect the PM organic compositions. Single particle imaging analyses indicate that PM can be classified into nine types based on their elemental compositions. Further analysis reveals that most particles usually mix with other types of particles and those mixed particles may cause a more serious impact on the environment. Based on the TEM observation, a two-step formation mechanism of PM is proposed. Our findings point out the potential environmental adverse effects and call attentions to a full environment assessment of this new type of cement production process, and also indicates stringent measures should be taken to reduce PM emissions during this process. Image 1 • Volatile elements are found to be enriched in the particulate matter. • Municipal sewage sludge can elevate the contents of organic and sulfate in particulate matter. • Most particles are usually mixtures of two or more types of aerosols. [ABSTRACT FROM AUTHOR]

This article presents an original study on the feasibility of reuse fly ash (FA) solidified/stabilized stainless steel pickling residue (SSPR). SSPR was characterized using different leaching procedure and solidified/stabilized using aluminum potassium sulfate dodecahydrate (KAl(SO 4) 2 .12H 2 O) amended fly ash. A modified four-step Community Bureau of Reference (BCR) sequential leaching test and risk assessment code (RAC) was employed to evaluate the potential hazards of metals in SSPR. Results show that SSPR mainly consists of sulfates and heavy metals. The major elements are Ca and Fe, with the total amount of 191,600 and 122,400 mg/kg. Cr is the most notable metal with a total amount of 22,500 mg/kg. Its concentrations in HJ/T 299 and HJ/T 300 extracts are 28.6 and 285 mg/L respectively. Another metal that is of some concern is Ni, its concentration in HJ/T 300 extract is 229 mg/L and total content in the residues is 10,690 mg/kg. The RAC of four list heavy metals are: Ni (61.36%) > Zn (43.48%) > Cr (20.64%) > Cu (19.83%). Therefore, SSPR has a higher potential to be hazardous to the environment. After treatment by 10% of KAl(SO 4) 2 .12H 2 O with 40% of FA 2 (10KA40FA 2), the concentration of Cr is 7.9 mg/L in HJ/T 299 extract and 12.68 mg/L in HJ/T 300 extract. While these two values for Ni is 0 and 14.34 mg/L. The RAC of the metals after treatment by 10KA40FA 2 followed the order of Ni (20.38%) > Zn (10.59%) > Cu (8.54%) > Cr (7.71%). The unconfined compression strength (UCS) tests showed that the 7-d UCS of the 10KA40FA 2 remolded sample achieved 3556.2 kPa which was much higher than that of raw SSPR remolded sample of 1746.7 kPa. Image 1 • Stainless steel pickling residue (SSPR) was characterized using different extraction methods. • Results indicate that Cr and Ni are the most toxic heavy metals in SSPR. • KAl(SO 4) 2 .12H 2 O amended fly ash can stabilize the heavy metals in SSPR effectively. • The stabilized SSPR has the highest 7-d UCS of 3556.2 kPa. • The SSPR treated by 10% of KAl(SO 4) 2 .12H 2 O with 40% of FA 2 can be safely used as roadbed materials. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash contains significant amounts of heavy metals (e.g., Cd, Cu, Pb and Zn) and is therefore considered to be a hazardous waste requiring proper treatment prior to its disposal. In this work, an integrated hydrometallurgical process for treatment of MSWI fly ash was evaluated. Valuable metals, e.g. Cu and Zn, were first recovered by combining leaching and extraction sequentially. In the next step, the t removal of Cd and Pb from the remaining leachate using four types of iron-based adsorbents was evaluated. The leaching was optimized with respect to pH, leaching time and liquid to solid ratio. A test done under optimal conditions gave metal releases of 100% and 80% for Cu and Zn as well as 100% and 85% for Cd and Pb, respectively. The resulting leachate was contacted with organic phases based on kerosene containing the extractants LIX860N–I for Cu extraction and Cyanex 572 for Zn extraction in two consecutive steps. Efficient extractions were achieved, thus demonstrating that the combination of leaching and extraction can be successfully used for the recovery of Cu and Zn. Adsorption of heavy metal ions on various iron based sorbents to detoxify the aqueous effluent from the extraction showed good removal efficiency (more than 95%) for both Cd and Pb. The results of this study show that the proposed integrated process is a promising tool that can be used in the strategy for metal recovery and detoxification of MSWI fly ash. Image 1 • A integrated method for recovery and clean up of metals from fly ash was developed. • Enhanced leaching gave a high yields of Cu (100%) and Zn (>80%) with HCl. • Removal of Cd and Pb in wastewater was proposed by adsorption. • A removal efficiency of >95% for both Cd and Pb was achieved. • The adsorption kinetics well followed the pseudo-second-order model. [ABSTRACT FROM AUTHOR]