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Cyanide leaching technology was studied for low-grade oxidized gold ores in Guangxi Province. The gold grade of the raw ores was 1.32 g/t. The gold leaching rate was 90.91% under the optimal conditions for the following conventional leaching process: using steel forging as the grinding medium, a grinding fineness of −0.074 mm accounting for 92.53%, a stirring speed of 1500 r/min, a pulp leaching concentration of 28.57%, a pH value of 10.5, a temperature of 25 °C, a leaching time of 24 h, and a potassium cyanide consumption of 4 kg/t. A new type of mixed aid-leaching agent (0.6 kg/t) was used, with a dosage of potassium cyanide of 2 kg/t. All else being equal, the gold leaching rate increased by 2.17% to 93.20% after 18 h of aid leaching compared to that of conventional leaching for 28 h. Meanwhile, the amount of potassium cyanide used was reduced by 50%. The aid-leaching agents restored the surface activity of passivated gold particles and depressed the adsorption of gold and its complexes by gangue minerals. This approach could shorten the leaching time and increase the gold leaching rate. [ABSTRACT FROM AUTHOR]

Harsh environments such as saline and alkaline environments will affect solidification/stabilization quality, especially considering the long-term service cycle. To investigate the environmental influence on the leaching behavior of solidified/stabilized soils, the Pb2+ leaching behaviors of cement-stabilized contaminated clay (CSC) and ternary binder (CSG)-stabilized contaminated clay (CSGSC) under the endo/exogenous saline and alkaline attacking environment were discussed. Note that, the ternary CSG binder, consisting of cement, silica fume (SF), and desulfurization gypsum powder (DGP) in a ratio of 1:0.25:0.19, underwent pre-screening based on its unconfined compressive strength (UCS). Scanning electron microscopy was employed to reveal the environment-resisting mechanism. The leaching concentration of Pb2+ in the leachate from CSGSC was lower than that from CSC in both saline and alkaline environments with a same incorporation ratio (15%) to dry soils, indicating CSG’s efficiency. Under the exogenous environment, the Pb2+ cumulative leaching mass from the stabilized clays in saline environment was more than that in deionized water, while that under the endogenous environment was opposite. Microstructure analysis indicated that the SF and DGP in CSG facilitated the formation of calcium silicate hydrate and ettringite, resulting in a denser structure that greatly enhances the physical encapsulation and chemical fixation of Pb2+ cation. At the end, the different mechanism under endo/exogenous attacking environments was attributed to the cation influence on clay minerals and the formation of new substance. These findings provide a guidance for the remediation of contaminated soil in harsh environments. [ABSTRACT FROM AUTHOR]

In this study, the structure and phase transition of kaolin lithium clay at different calcination temperatures were studied and discussed; subsequently, the effects of Li leaching with sulfuric acid under various factors were investigated in detail. The experimental results indicated that an optimal Li leaching rate of 81.1% could be achieved when kaolin lithium clay was calcined at 600 °C for 1 h, followed by leaching with 15.0% sulfuric acid at 80 °C for 2 h. The TG-DSC, XRD, and SEM analyses showed that the layered structure of the clay was not destroyed during the leaching and calcination processes. During the process of calcination, kaolinite was converted to metakaolinite via dehydroxylation. During the process of leaching, the Al on the surface of the metakaolinite was dissolved by sulfuric acid, resulting in the destruction of the Al-O structure; then, Li+ was exchanged for H+ to the surface of the mineral and entered the solution under the action of diffusion. The leaching kinetics showed that the leaching process was controlled by a diffusion model, and the activation energy (Ea) was 41.3 kJ/mol. The rapid extraction of Li from calcined kaolin lithium clay with sulfuric acid leaching offers a high-efficiency, low-energy-consumption strategy for the utilization of new lithium resources. [ABSTRACT FROM AUTHOR]

Evaluating the corrosion behavior of borosilicate glass after irradiation holds vital importance for the safe geological disposal of high‐level radioactive waste. This study examined the leaching properties of three kinds of sodium‐borosilicate (RNa2O‒B2O3‒KSiO2, denoted as "NBS") glasses with the same R but varying K under 5 MeV Xe‐ion radiation to decipher the correlation between the corrosion mechanism and glass composition. After Xe‐ion radiation, an increase in [BO3] units was observed, indicative of the glass network depolymerization. Irradiated glasses exhibited a more significant change in [BO3] units over the leaching time compared to their pristine counterparts. There is a strong correlation between the initial dissolution rates of pristine glasses, the K value, and the proportion of Na. Additionally, the initial Si dissolution rate of the NBS glasses has been accelerated by heavy ion irradiation. For the same R value over the glass series, the initial Si dissolution rates in ternary borosilicate glasses change at similar rates after irradiation. This study concluded that the variation trend in the initial dissolution rate of Si and Na differs under ion radiation. [ABSTRACT FROM AUTHOR]

The MgO-based binder is a novel and effective material for solidifying municipal solid waste incineration fly ash (MSWI FA). In this study, the effect of MgO-based binders with different MgO contents on the solidification and stabilization of MSWI FA was investigated by adjusting the proportions of MgO, silica fume, and MSWI FA in the solidified system. The leaching behavior and immobilization mechanisms of Cd and Pb in the solidified bodies were focused on. The hydration products generated were characterized by XRD, FTIR, and TG analysis. The results demonstrated that the compressive strength of the solidified bodies and the immobilization efficiencies of heavy metals improved with the increase in MgO addition. The MSWI FA solidified by MgO-based binders could maintain low leaching toxicity over a wider pH range. The generated Mg-containing hydration products, including Mg(OH) 2 and M-C-S-H gels, were believed to contribute to the reduction of the leaching concentrations of heavy metals. The immobilization mechanisms of Pb and Cd were different: the immobilization of Pb came from chemical chelation, and Cd was stabilized from alkaline precipitation. In conclusion, this work provides new insights into applying MgO-based binders in MSWI FA solidification. [ABSTRACT FROM AUTHOR]

Coal mining produces a large amount of gangue that pollutes the environment, causing surface subsidence and damaging the groundwater systems. Backfill mining is an effective technology used to solve this problem, but there is a risk of polluting the groundwater due to the heavy metal ions present in the backfill material. Pb2+ has been determined to be a representative element because of its existence in coal gangue samples but not in fly ash. The risk of gangue-based cemented backfill causing groundwater pollution can be evaluated by studying the Pb2+ leaching from gangue under various conditions. When comparing the leaching amounts of Pb2+ from the coal gangue particles and the test blocks, it was found that cement filling has an obvious consolidation effect on the Pb2+ in coal gangue. The above process shows that cemented backfill has an obvious consolidation effect on the Pb2+ in gangue. The results of the theoretical analysis, X-ray, and SEM show that the consolidation mechanism can be divided into four modes: physical encapsulation, ion exchange, ion adsorption, and chemical reaction. The results are of great significance for revealing the leaching mechanism of the heavy metals in coal gangue, assessing the risk of heavy metal pollution in groundwater via gangue-cemented backfill, and improving the mining theory of the gangue-cemented filling and groundwater protection. [ABSTRACT FROM AUTHOR]

Pollucite has been proposed as an ideal candidate material for addressing the critical challenge of the safe trapping of the 137Cs radionuclide. However, its detailed corrosion mechanism remains elusive. In this work, we performed reactive and ab initio molecular simulations to explore the leaching behavior of Cs+ from pollucite glass–ceramics at the initial stage. The nonbridging oxygen ions on the surface are protonated at first, followed by the release of Cs+ associated with these oxygen ions. For the glass phase, the inner Cs+ could leach out due to the interaction with water molecules, whereas only the Cs+ present at the surface leach out for pollucite, confirming its remarkable chemical stability. The hydrolysis of Si/Al–O bonds in pollucite is thermodynamically unfavorable, and Al–O bonds are the weak spots. Moreover, the migration barriers of Cs+ in pollucite were calculated by the climbing image nudged elastic band method, and the high barriers reveal that pollucite immobilizes Cs+ stably. This study paves the way for predicting the long‐term safety of a nuclear waste immobilization repository. [ABSTRACT FROM AUTHOR]

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing CO 2 emissions. Mine tailings (MTs) rich in Si and Al can be served as a promising precursor for geompolymer preparation only when the severe defect in the low reactivity is overcame. Alkali-hydrothermal activation technology was used to enhance the reactivity of MTs, and then activated tailings (ATs) and slag served as the precursors for the one-part geopolymer (OPG) preparation. Activation mechanism of MTs, workability, compressive strength, and hydration reactions of OPG samples were studied. The crystalline mineral phases in the MTs reacted with NaOH to form the amorphous sodium aluminosilicate, thus increasing the amorphization degree. High NaOH content favored the MTs activation, and the ATs with high NaOH content tended to create a higher initial pH and release more active species (Si and Al) for the slag hydration. The increase of NaOH content shortened the setting time, decreased the fluidity, and increased the strength of OPG samples. This was because the duration of the induction period was shortened and the hydration rate in the acceleration period of OPG samples was improved with increasing NaOH content, which generated large amounts of calcium–sodium aluminosilicate hydrate (C(N)-A-S-H) gel and yield the compact microstructure. However, excessive NaOH content resulted in a poor microstructure, and it is likely responsible for the reduction in strength. [ABSTRACT FROM AUTHOR]

The mining industry produces a large amount of stone waste and tailings, which poses a threat to the environment. Dumping is the most common means of disposing of this industrial waste, contributing to soil degradation and water pollution with the acquisition of valuable land. Fortunately, it can be recycled in a variety of technologies, including the promising geopolymerization technology, which turns waste into value. This review paper presents recent advances in the production of mine tailings-based geopolymer composites from industrial waste as a potential sustainable building material. This article also provides in-depth studies on the behaviors and characteristics of mine tailings composites utilized in geopolymer production, such as physical properties, mechanical properties, durability properties, microstructural properties, thermal properties, leaching behavior, and potential applications. Besides, study developments are moving towards a comprehensive understanding of the environmental footprints and economic benefits of mine tailings-based geopolymer composites for building applications utilizing mine tailings as suitable concrete material. This review paper also highlights knowledge gaps that must be overcome to progress mine tailings composites for geopolymers, as well as future study opportunities based on prior research and existing challenges. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash (FA) is a typical hazardous waste due to its high contents of toxic heavy metals, and hence its disposal has attracted global concern. In this work, it was recycled into environmental-friendly CaO–Al 2 O 3 –SiO 2 system glass-ceramics via adding coal fly ash (CFA) and waste glass (WG). The effects of CaO/SiO 2 ratios and sintering temperatures on the crystalline phases, morphologies, mechanical and chemical properties, heavy metals leaching and potential ecological risks of glass-ceramics were investigated. The results showed that wollastonite (CaSiO 3), anorthite (CaAl 2 Si 2 O 8) and gehlenite (Ca 2 Al 2 SiO 7) were the dominant crystals in the glass-ceramics, which were not affected by CaO/SiO 2 ratio and sintering temperature. The compressive strength increased, while the Vickers hardness and microhardness decreased as increasing the sintering temperatures from 850 to 1050 °C, which reached their maximum values of 660.69 MPa, 6.14 GPa, and 7.43 GPa, respectively. However, the increase of CaO/SiO 2 ratio resulted into the reduction of the three mechanical parameters. As varying CaO/SiO 2 ratio from 0.48 to 0.86, the maximum compressive strength, Vickers hardness and microhardness were 611.80 MPa, 5.43 GPa, and 6.56 GPa, respectively. Besides, all the glass-ceramics exhibited high alkali resistance of >97%. The extremely low heavy metals leaching concentrations and low potential ecological risk of glass-ceramics further revealed its environmentally friendly property and potential application feasibility. [ABSTRACT FROM AUTHOR]

Neutralization enrichment residues containing As,Sb and Bi is an important intermediate product in the hydrometallurgy process of anode slime, which is rich in valuable metals such as Bi and Sb with a high recovery value. However, the efficient extraction of Bi and other valuable metals faces challenge due to existence of multiple metals and complex occurrence behaviors. In view of this, hydrochloric acid total leaching process was proposed to treat the enrichment residue. The effects of HCl concent ration, liquid-to-solid ratio, reaction temperature and reaction time on the leaching rate of Bi, Cu, Pb, As and Sb were investig ated. Moreover, the leaching kinetics of the Bi was also explored at the same time. The results show that the leaching rate of Bi, Cu, Pb, As and Sb are 97.4 %,96.1 %, 75.9 %, 93.6 %, and 96.0 % respectively under 6.0 mol/L HCl with liquid-to-solid ratio ( mL/ g) of 6 at 80 °C for 15 min. It is determined that the kinetic control conditions of Bi in the hydrochloric acid leaching process can be divided into two stages. The early stage of the leaching process is affected by interface mass transfer and diffusion. The leaching of Bi is controlled by the chemical reaction in the later stage. The activation energy of the reaction is 14. 50 kJ/ mol and 82. 80 kJ/ mol in these two stages, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analyzed physical and chemical properties and performed quantitative phase analysis of HAHCA at different coal combustion temperatures. • Clarified the relation between the leaching behavior of 28 valuable elements and coal combustion temperatures under acidic and alkaline conditions. • Most metals easily leached from HAHCA under acidic conditions when coal combustion at 600 °C–800 °C. • Only Mo achieved a high leaching rate under acidic and alkaline conditions. The evaluation of the application potential of high-alumina coal fly ash (HACFA) resources relies on the assessment of the phase composition and leaching behavior of valuable elements. Herein, we systematically investigated the particle size, specific surface area, and morphology of high-alumina high-temperature coal ash (HAHCA) produced under laboratory conditions at different temperatures and quantitatively analyzed phase transformations using the Rietveld method. The results revealed that the HAHCA particle size gradually increased, specific surface area gradually decreased, and pores became lesser with the increasing coal combustion temperature of high-alumina coal (HAC) from 400 °C to 1300 °C. Furthermore, HAHCA phases sequentially changed across various temperatures, its main phases at a coal combustion temperature of 400 °C included 29.8 % kaolinite, 6.9 % boehmite, and 5.4 % calcite, but the crystalline phases were the most abundant and turned into 41.2 % mullite, 13.7 % corundum, and 11.6 % plagioclase when the coal combustion temperature reached 1300 °C. Additionally, the leaching behavior of 28 major and trace valuable elements of HAHCA under acidic and alkaline conditions was investigated. Most metal elements easily leached from HAHCA under acidic conditions at coal combustion temperatures of 600 °C–800 °C: the optimal leaching efficiencies of Al, Li, K, Rb, Mg, Ca, Sr, and Ba were 67.64 %, 92.71 %, 76.67 %, 73.46 %, 86.74 %, 98.87 %, 98.42 %, and 61.19 %, respectively. Si, a nonmetallic element, achieved a high leaching efficiency of 48.27 % under alkaline conditions at a coal combustion temperature of 1300 °C. Interestingly, only Mo exhibited a high leaching efficiency of approximately 98 % under acidic and alkaline conditions. [ABSTRACT FROM AUTHOR]

Coal combustion is the major contributor to global toxic selenium (Se) emissions. Inorganic elements in coals significantly affect Se partitioning during combustion. This work confirmed that the calcium (Ca) in ash had a stronger relationship with Se retention at 1300 °C than other major elements. Ca oxide chemically reacted with gaseous Se, and its sintering densification slightly affected Se adsorption capacities (44.45 −1840.71→35.17 −1540.15 mg/kg) at 300 − 1300 °C. Therefore, Ca in coals was identified as having potential for hindering gaseous Se emissions, and coals with increased Ca contents (2.74→5.19 wt%) were used in a 350 MW unit. The decreased Se mass distribution (3.54%→2.63%) in flue gas at air preheater inlet (320 −362 °C) confirmed the effectiveness of increased Ca content on gaseous Se emission reduction. More gaseous Se further condensed and was chemically adsorbed by fly ash when passed through an electrostatic precipitator, resulting in a significant increase in the Se content of fly ash. Additionally, the corresponding Se leaching ratio decreased from 4.88 − 35.74% to 1.87 − 26.31%, indicating enhanced stability of Se enriched in fly ash. This research confirmed the feasibility and environmental safety of sequestration of gaseous Se from flue gas to fly ash by increasing the Ca content in coals. [Display omitted] ● Se retention at 1300 °C is associated with Ca content in ash. ● Ca oxide removes more gaseous Se via chemical reaction during flue gas cooling. ● Coals with higher Ca contents will release less gaseous Se into flue gas. ● A higher Ca content in fly ash can enhance the stability of Se within. ● Electrostatic precipitator induces Se emission reduction with increased Ca content. [ABSTRACT FROM AUTHOR]

• M–S–H binder is a novel candidate used for MSWI fly ash immobilization. • Low alkalinity of M–S–H binder was beneficial for heavy metals encapsulation. • Immobilization mechanism of M–S–H solidified body was fully explored. Municipal solid waste incineration (MSWI) fly ash has become a challenge for waste management because it is rich in heavy metals and its output is increasing sharply year by year. A novel binder system for MSWI fly ash solidification/stabilization was produced by blending MgO and silica fume in this work. And several tests including compressive strength, toxicity leaching behavior, hydration products, pore structure and micromorphology of MgO-SiO 2 -H 2 O (M–S–H) binders without and with MSWI fly ash were conducted. Results showed that the compressive strength of MSWI fly ash-blended samples varied from 1.8 MPa to 29.3 MPa, and the maximum leaching concentration of Pb, Zn and Cd were 0.052 mg/L, 1.02 mg/L, 0.098 mg/L, which all met the national standard limitation on the landfill site. Besides, M–S–H binders could buffer against the harsh acid environment at a certain degree, which would provide a proper low alkalinity environment for immobilization of heavy metals such as Pb, Zn and Cd in MSWI fly ash. Meanwhile, the microstructure and morphology characteristics analysis results demonstrated that the favorable ion exchange and high specific surface area of hydration product contributed much to the excellent immobilization and adsorption characteristics on heavy metals, so it can be deduced that M–S–H binders mainly fixed the heavy metals by the physical encapsulation and chemical bonding. Overall, this work demonstrated that the application potential of M–S–H as immobilization binders in the field of sustainable construction materials and hazardous waste management, and providing a new way for the development and utilization of magnesium resources. [ABSTRACT FROM AUTHOR]

Solid waste, such as ferrochrome slag (FCS), has been extensively studied for its potential use as a construction material. This research focuses on utilizing FCS as the primary raw material to produce a high-strength ceramic aggregate, referred to as FCS-HSCA. The impact of calcination parameters on the performance of FCS-HSCA was investigated, while the underlying transformation mechanism was comprehensively explored. Subsequently, concrete with FCS-HSCA was prepared, and its influence on the performance of concrete was evaluated. The results reveal that the optimal performance of FCS-HSCA is achieved with a compressive strength of 310.3 MPa, a water absorption of 0.27%, and an apparent density of 2930 kg/m3. These characteristics are associated with specific parameters during the calcination stages, namely a preheating temperature of 1100 ℃, preheating time of 60 min, calcination temperature of 1500 ℃, and calcination time of 180 min. Moreover, the increased crystalline phases promote the solid dissolution of chromium into Mg(Al 1.5 Cr 0.5)O 4 , and the occurrence state of chromium is stable during the preparation of FCS-HSCA. This results in a decreased leaching value from 0.439 mg/L to 0.188 mg/L, reducing the impact on the environment and human health. Additionally, replacing FCS with FCS-HSCA in concrete enhances its compressive strength from 59.9 MPa to 66.1 MPa. This improvement is attributed to a notable reduction in the diameter of pores on the surface of FCS-HSCA, leading to a denser structure and improved bondability with cementitious composites. Finally, this novel approach maximizes the utilization of material characteristics while enhancing the stability of waste FCS. • A novel way to maximize the utilization of waste characteristics was proposed. • The optimal performance of FCS-HSCA was achieved through various analyses. • The surface roughness and performance variations were refined in preparing FCS-HSCA. • The improved bonding ability contributed to the increased performance of concrete. • The solidification of chromium was beneficial in reducing the environmental impact. [ABSTRACT FROM AUTHOR]

Metakaolin-based geopolymers are very promising materials for improving the safety of low and intermediate level radioactive waste disposal, with respect to ordinary Portland cement, due to their excellent immobilization performance for Cs+ and superior chemical stability. However, their application is limited by the fact that the leaching behavior of Cs+ is susceptible to the presence of other ions in the environment. Here, we propose a way to modify a geopolymer using perfluorodecyltriethoxysilane (PDFS), successfully reducing the leaching rate of Cs+ in the presence of multiple competitive cations due to blocking the diffusion of water. The leachability index of the modified samples in deionized water and highly concentrated saline water reached 11.0 and 8.0, respectively. The reaction mechanism between PDFS and geopolymers was systematically investigated by characterizing the microstructure and chemical bonding of the material. This work provides a facile and successful approach to improve the immobilization of Cs ions by geopolymers in real complex environments, and it could be extended to further improve the reliability of geopolymers used in a range of applications. [Display omitted] • A novel modification of geopolymer using perfluorodecyltriethoxysilane (PDFS) is proposed. • The diffusion of water in PDFS-modified geopolymer slows down significantly. • The Cs + leaching rate and the cumulative leaching fraction of PDFS-modified geopolymer reduce significantly in the leaching tests. • PDFS-modified geopolymer exhibits excellent reliability in complex environments with the presence of multiple competing ions. [ABSTRACT FROM AUTHOR]

Heap leaching uranium tailings (HLUTs) contain radionuclides and sulfuric acid, presenting some challenges for the disposal of cemented HLUTs backfill (CUTB), including low stability and potential environmental contamination. In light of these issues, using a blend of cement clinker (CL) and high content phosphorus slag (PS) as binders to replace traditional cement for the preparation of green and cost-effective CUTB were proposed. The fluidity, setting time (ST), mechanical properties, Radon (Rn) exhalation rate, uranium (U) occurrence form, U (Ⅵ) leaching behavior, and microstructure of CUTB with different PS contents were investigated. The results showed that the fluidity, bleeding rate and ST of slurry (PS content >40%) met the filling requirements. The strength of PS-based CUTB was initially low, but rapidly increased in subsequent periods, surpassing 2 MPa at 28 d and 4.5 MPa at 90 d (with 50–70% PS content). Moreover, the Rn exhalation rates and U (Ⅵ) leaching levels of CUTB were far lower than the stipulated limits. When PS content exceeded 50%, the migratory uranium content in CUTB was below 10% with low migration risks. With the addition of PS, the amount and degree of polymerization of C–S–H gels in the matrix increased, while gypsum and CH content decreased. The S/S of U (Ⅵ) and SO 4 2− was attributed to the combined effects of chemical immobilization of nascent minerals and physical adsorption/encapsulation of hydration products. Additionally, these hydrates effectively sealed micro-cracks on HLUTs particles surfaces and filled interlocking pores to decrease Rn exhalation. PS-based CUTB exhibited a high capacity increasing ratio and low cost. This research can promote the utilization of hazardous solid wastes such as HLUTs, reduce carbon dioxide emissions, and provide a theoretical basis for ensuring green and safe production in mining. [Display omitted] • PS-based CUTB has high strength and stability during mid-to-late periods. • The Rn exhalation rate of CUTB is significantly lower than that of HLUTs. • The migratory uranium content in CUTB is reduced after the addtion of PS. • U (Ⅵ) leaching levels of PS-based CUTB is far below that of cement-based ones. • C–S–H content is high, but gypsum and CH content is low in PS-based CUTB. [ABSTRACT FROM AUTHOR]

The release of uranium from uranium tailings into the aqueous environment is a complex process controlled by a series of interacting geochemical reactions. In this paper, uranium tailings from a uranium tailings pond in southern China were collected at different depths by means of borehole sampling and mixed to analyze the fugacity state of U. Static leaching experiments of U at different pH, oxidant concentration and solid-to-liquid ratios and dynamic leaching experiments of U at different pH were carried out, and the adsorption and desorption behaviour of U in five representative stratigraphic media were investigated. The results show that U is mainly present in the residue state in uranium tailings, that U release is strong in the lower pH range, that the leached U is mainly in the form of U(VI), mainly from the water-soluble, Fe/Mn oxides and exchangeable fraction of uranium tailings, and that the reduction in U leaching at higher pH is mainly due to the combined effect of precipitation formation and larger particle size of platelets in uranium tailings. Experiments with different oxidant concentrations and solid-liquid ratios showed that the oxygen-enriched state and low solid-liquid ratios were favorable for the leaching of U from uranium tailings. Adsorption and desorption experiments show that U is weakly adsorbed in representative strata, reversibly adsorbed, and that U is highly migratory in groundwater. The present research results have important guiding significance for the management of existing uranium tailings ponds and the control of U migration in groundwater, which is conducive to ensuring the long-term safety, stability and sustainability of uranium mining sites. [Display omitted] • The leaching of U from uranium tailings was tested under different geochemical conditions. • Adsorption behaviour of U in representative geotechnical media in uranium tailings pond areas. • The release of U from uranium tailings is mainly from the water-soluble state. • Low pH, oxygen enrichment and low solid to liquid ratio conditions favour the release of U from uranium tailings. [ABSTRACT FROM AUTHOR]

The leaching of heavy metals from abandoned mine tailings can pose a severe threat to surrounding areas, especially in the regions influenced by acid rain with high frequency. In this study, the potential risks of heavy metals in the tailings collected from a small-scale abandoned multi-metal mine was assessed, and their leaching behavior and mechanism were investigated by batch, semi-dynamic and in situ leaching experiments under simulated and natural rainfall conditions. The results suggested that Zn, Cu, Pb, and Cd in the tailings could cause high/very high risks. Both batch and semi-dynamic leaching tests consistently confirmed that the leaching of heavy metals (particularly Cd) could lead to serious pollution of the surrounding environment. The leaching rates of heavy metals were pH-dependent and related to their chemical speciations in the mine tailings. The leaching behavior of Cu and Cd was dominated by surface wash-off, Zn was controlled by diffusion initially and then surface wash-off, and the leaching mechanisms of Pb and As varied with the pH conditions. It was estimated that acid rain could greatly elevate the release fluxes of Zn (20.8%), Cu (36.7%), Pb (49.9%) and Cd (35.3%) in the study area. These findings could improve the understanding of the leaching behavior of heavy metals from mine tailings and assist in developing appropriate management strategies. [Display omitted] • Cu, Zn, Pb and Cd in tailings posed high risks to surrounding areas. • Metal leaching under rainfall was correlated to the acid soluble form. • Leaching behavior and mechanism varied with elements and pH conditions. • Acid rain promoted the release fluxes of Cu, Zn, Pb, and Cd from tailings. • The predictions of release fluxes were verified by the in-situ experiments. [ABSTRACT FROM AUTHOR]

Casting is an important industrial process that used for metal processing and metal shaping. Materials produced by casting are used in several fields like jewelry, industrial benches, agricultural machines etc. Due to the large market share of the casting, the amount of waste from various production processes is quite high. Critical occupancy rate of landfill areas and the cost of disposal of hazardous wastes increase the need for industrial symbiosis. Accordingly, various studies are carried out to evaluate the wastes in concrete and mortar. This study aims to provide industrial symbiosis by recycling of waste in the construction sector and to investigate the environmental effects of waste. In this context, mortar mixtures were prepared in accordance with ASTM C109 standard by replacing the standard sand used in the cement mortar composition with 0% (reference), 10%, 20%, 30% and 40% by weight of waste casting sand (WCS). Environmental effects and leaching behaviors of the samples were investigated in three different curing environments. In addition to the environmental effects of mortar samples containing ADK, their mechanical properties were also investigated. As a result, it was concluded that ADK could be used 20% instead of fine aggregate in mortar production without causing a negative physical and environmental impact. The compressive strength values of the samples also satisfy the conditions stated in the standards. [ABSTRACT FROM AUTHOR]

• Leachate carbonation appears to be a major factor in lowering pH values. • Normal rain eluted more TOC and soluble ions from BA than heavy rain. • Heavy rain intensity did not affect cumulative TOC and soluble ion release. • Notable correlation exists between rainfall and leachate component concentrations. In Japan, approximately 64% of municipal solid waste incineration bottom ash (MSWI BA) is landfilled. Because landfills in Japan are operated without capping, the landfill body is directly exposed to climatic events. Increased frequency of heavy rain is predicted to affect the chemical stabilization of bottom ash (BA) landfill, as rainwater seeps into and interacts with landfill components. This study examined the effect of normal rainfall (15 mm/h) and heavy rainfall (25, 50, and 100 mm/h) events on the leaching behavior of ions (Cl−, Na+, K+, and Ca2+) and total organic carbon (TOC) in BA (<10 mm particle size) using a percolation column test. The results showed the decreased leaching of leachate components after heavy rainfall and increased leaching after normal rainfall. In addition, the pH fluctuated around 11–12 after heavy rainfall but decreased to 7–9 after normal rainfall. The carbonation of the leachate and BA layers appears to be the main factor in lowering the pH value. Changes in the TOC and ion concentrations can be explained by dissolution, dilution, and the contact time of water molecules and BA particles. The data showed that the cumulative TOC and ion release rates were not affected by heavy rain intensities. The release rate of leachate components during normal rainfall was higher than that in heavy rainfall in all the scenarios. Significant correlations were found between the leachate components (TOC, Cl−, Na+, K+, and Ca2+ concentrations) and rainfall variation. [ABSTRACT FROM AUTHOR]

To date, geopolymer has emerged as a promising and inexpensive precursor with potential application in trapping hazardous elements via physical encapsulation or chemical bonding. In this work, different high‐temperature products derived from Sr‐contained geopolymer precursors were prepared. Different to conventional hazardous elements that immobilized in the geopolymer precursor, which show decreasing leaching rates after high‐temperature treatments, leaching rates of Sr in the resulting high‐temperature products first increase and then decrease with the increasing heating temperature. Herein, we first shed light on the underlying reasons of such temperature‐dependent leaching behaviors by investigating effects of heating temperature on the phase composition, microstructure, and immobilization mechanism. Moreover, a novel immobilization strategy has been proposed based on the blocking effect of formed nepheline structures at 1200°C. Using this strategy, the leaching rate of Sr reduced to 5.82 × 10−7g cm−2 d−1 in the deionized water. [ABSTRACT FROM AUTHOR]

Today, heavy metals remain crucial pollutants in municipal waste due to their danger and leaching behavior. The purpose of this study is to analyze the sources of heavy metals in mixed municipal waste, including from recently introduced products, and to identify their composition and leaching properties in various fractions. The author has measured the concentration of four heavy metals (lead, cadmium, nickel, and chromium) in various fractions sampled from an operational municipal waste facility in the town of Pirna (Saxony, Germany). Batteries and waste electrical and electronic equipment (WEEE) were found to be the main sources of heavy metals in municipal waste, while a relatively high metals' content was also detected in the rubber fraction. To assess leaching behavior, landfill simulation reactors were used to simulate conditions over several decades. The metals' weight in the input and output waste was compared. The lowest leaching rate was found for lead, while the highest was found for cadmium and chromium. In addition, it was confirmed that the degree of leaching depended on the humidity and organic matter in the landfill: the higher the moisture and organic matter, the more heavy metals are leached from the waste. [ABSTRACT FROM AUTHOR]

Alkali-activation is effective municipal solid waste incineration fly ash (MSWIFA) solidification/stabilization (S/S) technology. Percolation and migration of heavy metals in MSWIFA S/S matrix is a complicated and slow process. Here, several alkali-activated MSWIFA samples are selected to comparatively investigate the long-term leaching behavior and environmental availability of Pb, Zn and Cd when exposed in different erosion environment. Acid environment posed the more serious destroy to MSWIFA S/S matrices. RAC demonstrated that potential risk level of heavy metals is higher in acid rain environment, and Cd, Zn showed the prominent risk. When soaked in acid rain solution, the surface of alkali-activated MSWIFA S/S matrices was cracked seriously and a large number of hardened slurry peeled off. However, more stable structural properties and lower heavy metal leachability can be found in alkali-activated MSWIFA/aluminosilicate. The immobilization efficiency of Pb, Zn and Cd were all above 99.0%. Microstructure and morphology results indicated that there is new phase Friedel's salts generated and much more amorphous substance such as C-(A)-S-H gel with incorporation of aluminosilicate, which all contributed much to the formation of compact and stable microstructure, then significantly facilitated the encapsulation of heavy metal. These findings will provide theoretical basis and new insight for resource utilization and security landfill of MSWIFA. • Leaching behavior of heavy metals affected dramatically by pH of erosion environment. • Environmental availability of Pb, Zn and Cd was assessed by Tessier extraction tests. • Acid rain erosion scenario tend to increase potential environmental risk. • Aluminosilicates facilitated the structural stability and immobilization properties. • Friedel's salts are newly generated in MSWIFA S/S matrices with aluminosilicates. [ABSTRACT FROM AUTHOR]

Herein, we prepare Cr-containing glass ceramics from argon-oxygen-decarburization stainless steel slag and characterize their physicochemical properties (e.g., Cr stability), revealing the occurrence of a diopside solid solution → akermanite-gehlenite solid solution phase transition with increasing slag content. The properties of all ceramics (slag content = 40–80 wt%) met the requirements of the construction industry for building materials, with the highest flexural strength (137.83 MPa) as well as good acid and alkali resistance achieved at a slag content of 50 wt%. Moreover, the prepared ceramics were subjected to Cr leaching tests, which revealed that (i) Cr leached into aqueous solution was mainly present in the form of Cr3+ and largely precipitated as Cr(OH) 3 and (ii) the layered structure of akermanite-gehlenite glass ceramics can partially bind Cr and thus facilitate its effective immobilization. • Glass ceramics were prepared from argon-oxygen-decarburization stainless steel slag. • The physicochemical properties and environmental safety of these ceramics were probed. • All ceramics met the requirements of the construction industry for building materials. • A Cr leaching mechanism was established. [ABSTRACT FROM AUTHOR]

Refuse derived fuel (RDF) is produced in large amounts but its heterogeneous nature and low calorific value reduce the potential for energetic valorization of this material. In this work, the torrefaction and carbonization of RDF was studied in a temperature range of 200–400 °C and residence times from 15 to 60 min, yielding chars with increased density, high heating value (HHV), carbon content, ash content and fixed carbon. Leaching experiments showed that some inorganic components like calcium or chlorine could be removed from the RDF char, upgrading its fuel quality. For temperatures in the torrefaction range (200 °C and 250 °C), energy yields were higher than 96.3% and process energy efficiencies were higher than 85%, but the HHV of the RDF chars were lower than 19.4 MJ kg−1. In the carbonization range (300 °C to 400 °C) it was possible to obtain RDF chars with HHV in the range of 20.1–26.2 MJ kg−1, with energy yields from 84.5 to 91.7% and process energy efficiencies from 70.8 to 79.2%. The obtained results showed that thermochemical processing can be used to upgrade RDF thus promoting sustainable solutions for its management and valorization. • Torrefaction and carbonization of industrial RDF was studied at different conditions. • Carbonization yielded the RDF chars with higher carbon content and heating value. • Chlorine and ash contents of the RDF chars could be reduced by water leaching. • Carbonization presented energy efficiencies compatible with autothermal operation. [ABSTRACT FROM AUTHOR]

Chemical additives leaching from microplastics and their effects on physiology of microalgae are of environmental significance. So far, these issues remain unclear. Here, the leaching behavior of fluorescent additives from polyurethane sponge microplastics in simulated (acidic, saline, and basic water) and natural waters (river, lake, wetland, and sea water) was investigated. Release amount of additives increased with increasing solution pH and leaching time. The maximum release amount was reached at the leaching time of 12–24 h and the 3,3′-diaminobenzidine-like substances were identified in the leachate. The leached concentrations of fluorescent additives in simulated and natural waters followed the order of basic water > saline water > seawater > West Lake > River > Wetland. Effects of leachate and microplastics on growth and photosynthesis of Chlorella vulgaris were further evaluated. The maximum quantum efficiency of photosystem II (F v /F m) decreased with increasing leachate concentrations. Only high content (1.6 g L−1) of microplastics exerted significant inhibitory influence on cell photosynthesis when microalgae were exposed to microplastics alone. Retention of algal cells inside the porous sponge microplastics did not change their photosynthetic efficiency. These findings indicate that leaching process of additives from microplastics depends mainly on water environments and the leached chemicals may pose ecological risks to aquatic organisms. Unlabelled Image • Release amount of additives increased with increasing solution pH and leaching time. • Different leaching patterns of additives in simulated and natural waters were observed. • The photosynthetic efficiency decreased with increasing leachate concentrations. • Retention of algal cells in microplastics did not change their photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

Highlights • Two-stage leaching is a highly efficient method to recover valuable metals. • Leaching time, temperature, [H 2 SO 4 ] and oxidant addition during leaching were significant. • Ferric ion improved the leaching of Cu and Zn except of As. • Metals' phases and surface morphology of the raw materials were changed during the leaching. Abstract In order to efficiently recover zinc and copper from arsenic-rich copper smelting hazardous dusts after alkali leaching of arsenic, an optimum two-stage leaching process by using sulfuric acid media was developed in this study. The leaching behaviors of zinc, copper, arsenic and iron under different experimental conditions (such as: leaching time, temperature, sulfuric acid concentration and oxidant addition), were studied systematically. The results indicated that 98.4% zinc and 96.01% copper were leached using the first-stage of neutral leaching under conditions including final pH 5.0 ± 0.1, time 1 h, temperature 90 °C and the second-stage of sulfuric acid leaching under conditions including initial sulfuric acid concentration 190 g/L, leaching time 2 h, temperature 90 °C and 1.4 times oxidant addition. Meanwhile, 99.58% lead and 98.93% bismuth were remained in the sulfuric acid leaching residues which can be recovered by pyrometallurgical processes. The leaching behavior relationships among copper, zinc, arsenic and iron were also modeled. Results indicated that the ferric ion improved copper and zinc leaching. SEM study demonstrated that the leached surface was corroded, and EDS and XRD results indicated that zinc and copper oxides were disappeared during leaching while lead oxide was transformed into anglesite, and tin oxide was remained in the residues. [ABSTRACT FROM AUTHOR]

• Cu can be transformed to ferrite spinel with tailings brick raw materials. • The phase structure of Zn is affected by the sintering temperature. • The leaching rate of Pb is high due to the formation of PbSO 4 by sintering. • Sintering of the tailings brick raw material effectively fixes heavy metals. In this study, the mixing mechanism and phase transition process of different metals during the sintering of tailings bricks with four different metal oxides (CuO, PbO, ZnO, and CdO) at temperatures ranging from 700 to 1100 °C for 2 h were investigated. The properties of the sintered product was characterized and analyzed, and the results showed that the main crystalline phases are quartz, cristobalite, hematite, and mullite while the metal oxides are ascribed to copper ferrite spinel (CuFe 2 O 4), gahnite (ZnAl 2 O 4), zinc ferrite spinel (ZnFe 2 O 4), lead feldspar (PbAl 2 Si 2 O 8), and cadmium feldspar (CdAl 2 Si 2 O 8). Further analysis indicates that the heavy metals were transited into spinel or silicate structures with favorable efficiency. This indicates a good heavy-metal fixation effect from the structural change after the sintering process. Finally, the leaching experiments of the sintered samples suggest that the metal leaching decreased to a low and stable value when the sintering temperature was higher than 950 °C, which meets the China standard (GB 5085.3-2007). The above results indicate that the sintering process facilitates the combination of Cu, Zn, Pb and Cd offering an effective and safe method for the application of materials that contain tailings. [ABSTRACT FROM AUTHOR]

• A germanium bearing secondary zinc oxide was evaluated mineralogically. • Germanium exists in zinc and lead bearing minerals dispersedly. • Leaching behavior of Ge was revealed by leaching tests and residue characterization. • The limiting reasons of Ge and Zn leaching rates were found out. • 99.7% of Ge and 99.4% of Zn could be leached in oxygen pressure leaching. To improve the sulfuric-acid leaching of germanium-bearing secondary zinc oxide, the occurrence states and sulfuric-acid leaching behavior of germanium in secondary zinc oxide were investigated experimentally via inductively coupled plasma optical emission spectrometry (ICP–OES), X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS), electron probe microanalysis (EPMA), and chemical phase analysis combined with leaching tests. The germanium-bearing secondary zinc oxide was produced via a fuming process of lead smelting slag and zinc leaching residue in a lead and zinc smelter. The results show that zincite, wurtzite, galena, and anglesite are the major minerals containing zinc and lead in the secondary zinc oxide. Further, these zinc- and lead-bearing materials contain germanium (without independent minerals). In the sulfuric-acid leaching process without oxidant, wurtzite and galena cannot be leached, which results in a loss of germanium. Anglesite, which exists originally in the secondary zinc oxide or was formed in the leaching process, contains a low amount of germanium and exhibits a loss of germanium in the residue. Moreover, the leaching efficiencies of germanium and zinc increased to 99.7% and 99.4% in the leaching process under oxygen pressure, respectively. [ABSTRACT FROM AUTHOR]

Abstract Incineration is widely adopted in modern waste management because it provides an effective way to minimize municipal solid waste that needs to be disposed of in landfills. The ash residue is often disposed by landfilling. Alternatively, the incineration ash may be recycled and reused for various applications. The crucial issues, however, are the leaching of harmful elements during the use and the end-of-life phases. This review summarizes extensive studies on leaching behavior of municipal solid waste incineration ash. Specifically, pollutants generated through leaching, factors governing leaching, methodologies to study leaching, leaching mechanisms, and treatments to reduce leaching. Many types of pollutants are generated through leaching from municipal solid waste incineration ash, in which heavy metals and organic contaminants are the most toxic and concerned. Ash properties, pH and liquid to solid ratio are the main factors governing municipal solid waste incineration ash leaching. Leaching behavior of municipal solid waste incineration ash is complicated and existing methods to evaluate leaching may not be able to represent the field conditions. Solubility and sorption are the two major leaching mechanisms. Many treatment methods have been proposed. However, not all methods are effective and some approaches are associated with high energy and high cost, which makes them less economically feasible and attractive. Graphical abstract Unlabelled Image Highlights • Hundreds of pollutants are generated through leaching from MSWI ash. • Ash properties, pH and L/S ratio are the main factors governing MSWI ash leaching. • Existing methods to evaluate leaching may not be able to represent the field conditions. • Solubility and sorption are the two major leaching mechanisms. • Not all treatment methods are effective and some approaches are associated with high energy and high cost. [ABSTRACT FROM AUTHOR]

Abstract The batch experiments were conducted to understand sorption process of bithionol (BIT) in yellow soil (YS) and red soil (RS), while column leaching experiments were performed to evaluate the leaching behavior of BIT and levamisole (LEV) in the tested soils. The adsorption and desorption data fitted well with the Freundlich isotherms (R2 ≥ 0.94). The distribution coefficient of BIT in the YS and RS were 104 and 98.3 L/kg, respectively. Hysteresis was observed for bithionol desorption in the YS and RS, with hysteresis coefficient of 0.917 and 0.928, respectively. Dissolved organic matter (DOM) addition and acid condition enhanced the adsorption of BIT in the soil. Both BIT and LEV showed poor leaching potential in the tested soils. More than 80% of BIT and LEV remained in the surface soil layer and the amount of the two target compounds in the leachates accounted for less than 1% of overall recovery. DOM showed little influence on the concentration of BIT and LEV in the leachates collected at different time. The results could fill the gap on the behavior of BIT and LEV in soil under laboratory conditions. Highlights • Dissolved organic matter (DOM) content and pH can affect the adsorption of bithionol. • Hysteresis was observed for bithionol desorption in the tested soils. • Higher DOM content decreased the mobility of bithionol and levamisole in the column. • Bithionol and levamisole showed poor leaching potential in the tested soils. [ABSTRACT FROM AUTHOR]

• Na 2 S∙xH 2 O was used to stabilize stainless steel pickling sludge. • Speciation and leaching behavior of heavy metals were examined. • The optimal pH range for stabilizing is 5.5-10. • With 7 days stabilization the products can be safely reused as roadbed materials and aggregates. This article presents an original study on stabilization of heavy metals in SSPS using sodium sulfide hydrate. The speciation and pH dependent leaching of the target heavy metals (Cr, Cu, Ni and Zn) based on GB 5085.3 and GB 16889 in both raw SSPS and stabilized products were examined. Results indicated that Cr and Ni are the two main toxic elements in SSPS. The BCR sequential extraction indicated that 55.2% of Cr in raw SSPS exist as Fe-Mn oxides, while water soluble Cr which is mainly consists of Cr(VI) accounts for 3.50%. After stabilization, the residual fraction Cr reached to more than 60% and Cr(VI) was not detected. The leaching concentration of Ni meets the limit of reuse SSPS, meanwhile, the sum proportion of sulfides and residual Ni increased from 8.68% to a maximum value of 31.82%. pH dependent leaching tests expound that the leaching concentrations of Cr, Ni, Cu and Zn are significantly high at pH = 2. The leaching concentrations of Cu, Ni and Zn are extremely low when pH varied from 7 to 13. The best stabilization pH span is from 5.5 to 10 for SSPS. The XRD and SEM-EDS analysis showed that the major compounds in treated SSPS were bassanite and plaster of Paris (POP). Since the extreme conditions such as pH = 2 or pH = 13 are infrequently, the stabilized SSPS can be safely reused in roadbed materials, bricks and concrete aggregates based on China HJ/T 301. [ABSTRACT FROM AUTHOR]

This article presents an original study on stabilization of heavy metals in SSPS using sodium sulfide hydrate. The speciation and pH dependent leaching of the target heavy metals (Cr, Cu, Ni and Zn) based on GB 5085.3 and GB 16889 in both raw SSPS and stabilized products were examined. Results indicated that Cr and Ni are the two main toxic elements in SSPS. The BCR sequential extraction indicated that 55.2% of Cr in raw SSPS exist as Fe-Mn oxides, while water soluble Cr which is mainly consists of Cr(VI) accounts for 3.50%. After stabilization, the residual fraction Cr reached to more than 60% and Cr(VI) was not detected. The leaching concentration of Ni meets the limit of reuse SSPS, meanwhile, the sum proportion of sulfides and residual Ni increased from 8.68% to a maximum value of 31.82%. pH dependent leaching tests expound that the leaching concentrations of Cr, Ni, Cu and Zn are significantly high at pH = 2. The leaching concentrations of Cu, Ni and Zn are extremely low when pH varied from 7 to 13. The best stabilization pH span is from 5.5 to 10 for SSPS. The XRD and SEM-EDS analysis showed that the major compounds in treated SSPS were bassanite and plaster of Paris (POP). Since the extreme conditions such as pH = 2 or pH = 13 are infrequently, the stabilized SSPS can be safely reused in roadbed materials, bricks and concrete aggregates based on China HJ/T 301. [ABSTRACT FROM AUTHOR]

Abstract The Great East Japan Earthquake and subsequent tsunami in 2011 generated massive amounts of disaster waste and tsunami deposits, one-third of which comprised soil and sediment, which are expected to be re-used; however, there has been no previous experience or knowledge of recovered soil. In this study, up-flow column leaching tests were conducted to investigate the elemental leaching behavior in this soil and sediment following its separation and treatment (hereafter termed "recovered soil") to assess whether it can be safely re-used without posing any environmental risk. The pH of the leaching water was slightly alkaline throughout the test period, regardless of the source of the recovered soil. Concentrations of calcium and sulfate ions in the leaching water varied in a similar way to the electrical conductivity (EC), with a stable state being observed initially followed by a rapid decrease until typical concentrations were reached, whereas sodium and chloride ions derived from seawater made a relatively small contribution to the EC. In terms of toxic elements, zinc and copper concentrations decreased as the volume of leaching water increased, whereas lead, fluoride, and arsenic concentrations increased as the concentration of calcium and sulfate ions decreased, indicating that the dissolution of large quantities of compounds such as calcium sulfate controlled the toxic element behavior in the recovered soils. Consequently, there is a need for continuous and careful monitoring of areas where recovered soil is re-used or treatment of the recovered soil prior to its re-use. Highlights • Recovered soil (RS) is soils separated from disaster waste and tsunami deposits. • Column tests were conducted to elucidate the elemental leaching behavior in RS. • Ca2+ and SO 4 2− ions were dominant in the leaching water, not Na+ and Cl−. • Such ions control toxic element behavior in RS. • Pb, F, and As concentrations increased with decrease in Ca2+ and SO 4 2−. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Heavy metal amounts and leaching in China were compared to those on a global scale. • The RAC index corresponding to heavy metal leaching concerned with FA compositions. • Alkalinity and S-Cl contributed to the heavy metal leaching potential in statistics. • A new leaching index (Φ) was defined according to the compositional variety in FA. • The quick prediction of Pb and Cd stability from FA was achieved via the index Φ. Abstract In the current work, a quick prediction of the heavy metal (HM) leaching potential in municipal solid waste incineration fly ash (MSWI FA) was developed based on the statistical data between the HM leaching behaviors and the compositional variety in FA from China. In the comparison of the surveyed (508 data points) leaching concentrations, Pb and Cd leaching amounts in FA exceeded the Toxicity Characteristic Leaching Procedure (TCLP) limits most frequently. Moreover, the chemical compositions (pH and soluble chlorine (S-Cl)) of FA were proposed to have significant linear correlations with the Pb and Cd leaching. This corresponded to the chemical fraction change of the HM (risk assessment code (RAC)), which was relative to the pH of FA and chloride. This suggests that the HM stability can be evaluated by these factors. To verify this hypothesis, principal component analysis (PCA) and multiple linear regressions were used to evaluate the relationship between 5 indices and the leaching concentrations of Pb and Cd in 160 MSWI FA samples after stabilization/solidification from eastern China. It is indicated that pH, S-Cl and free CaO were the critical variables in Pb and Cd leaching. Accordingly, a new index, Φ, combined with the logistic model was proposed to predict the leaching potential. It is revealed that the high risk of the exceeding the limits for HM leaching occurred when Φ was below 12.5. Our results assess the HM stability in MSWI FA with its compositional variety in a statistical way, which gives an approach for the quick prediction of HM leaching potential. [ABSTRACT FROM AUTHOR]

• The stress-induced damage of cemented paste backfill (CPB) is defined. • The influence of damage and initial pH on the metal leaching behavior is presented. • The pH and conductivity of the leachate increase with the increasing damage of CPB. • The release process of metallic elements in CPB is divided into three stages. • The release rate of metallic elements is described by Kinetic equations. Cemented paste backfill (CPB) is generally considered environmentally friendly when used in mining operations. However, the combination of geological stresses and groundwater seepage in an underground environment may cause the metallic elements contained in CPB to escape confined areas and potentially pollute the external environment. In this paper, geological stress-induced damage to CPB and the initial pH levels of the surrounding environment are assessed to determine their influences on the metal leaching behavior of CPB. Research methods used in the analysis include component characterization, static leaching tests, and kinetic theory analysis. The research results show that: as damage to CPB increased, both the pH and conductivity of the leachate increased, while the concentration of metallic elements in the leachate also increased except for aluminum (Al). Different metallic elements showed various leaching behaviors as the initial pH of the leaching solution increased. The release process of metallic elements from CPB can be segmented into three separate stages: the surface release stage, the internal release stage, and the adsorption and precipitation stage. Kinetic equations are obtained to describe the release rate of metallic elements. The leaching process is a dynamic equilibrium system formed by the release, absorption, and precipitation of metallic elements in the leachate. This research provides data for the evaluation of environmental effects on CPB. [ABSTRACT FROM AUTHOR]

The application of algae-based technology for wastewater treatment and metabolites extraction relies on algal biomass yield. This study investigated the effect of steel slag supplement as a Ca2+ source on growth of green algae Chlorella sp. The improvement was dose-dependent. Small dose improved microalgae growth, while high dose exhibited negative effect on growth, chlorophyll a and oxygen evolution. The optimal dose of 0.75 g/L steel slag with leaching Ca2+ of 25 mg/L achieved maximum dry weight of microalgae, which was 1.4 times higher than the control. Dissolved oxygen was proposed to monitor growth, as it changed prior to Chl-a/Chl-b and Caro/Chl. Correlation analysis revealed that growth enhancement was due to combined effect of Ca2+, pH and HCO 3 -. Furthermore, microalgae accelerated Ca2+ leaching from steel slag. Heavy metals were below the limit of wastewater treatment effluent criteria. Nutrients removal ability of microalgae harvested from steel slag was improved. The investigation verified that CaO in steel slag was feasible to trigger microalgae growth, which attained recycling economy and environmental sustainability. [Display omitted] • Ca2+ leaching from steel slag served as a stimulator for Chlorella growth. • Microalgae biomass with 25 mgCa2+/L was 1.4 times higher than the control. • The improvement was dose-dependent and due to Ca2+, pH, HCO 3 -. • Heavy metals lower than WWTP effluent permit. • Nutrients removal ability of microalgae was superior. [ABSTRACT FROM AUTHOR]

Nearly 1.3 billion tons of food are discarded annually in the production process. In this study, a novel slow-release nitrogen fertilizer with water absorbency was developed using leftover rice and crosslinking methods. Urea was incorporated as the nitrogen source in a leftover rice-g-poly(acrylic acid)/montmorillonite (LR-g-PAA/MMT) network, and then the leftover rice-g-poly(acrylic acid)/montmorillonite/Urea (LR-g-PAA/MMT/Urea) retained in the soil, and used as the loss control agent for water and nutrients. Variables including concentrations of acrylic acid, montmorillonite, N,N´-methylenebis acrylamide (MBA), and potassium persulfate (KPS) were investigated. Samples were with a water absorbency of 102.6 g/g in distilled water and 25.1 g/g in 1.0 wt% NaCl solution under optimized conditions. Swelling measurements and water-retention indicated that higher-covalent cations would aggregate the hydrogels and decrease swelling. Investigating leaching behavior showed that these samples have the potential to carry the necessary nitrogen (N). The results demonstrated that the LR-g-PAA/MMT/Urea had a low leaching losses of N (19.7%) compared with pure urea (52.3%). Therefore, the developed fertilizer may be widely applicable in agriculture and horticulture, and could provide a new platform for reusing leftover rice. [ABSTRACT FROM AUTHOR]

The leaching behavior of six typical toxic metals (Pb, Zn, Cr, Cd, Cu and Ni) from raw and chemically stabilized (phosphate and chelating agent) municipal solid waste incineration (MSWI) fly ash were investigated using citric acid. Leaching tests indicated that phosphate stabilization can effectively decrease the leaching of Zn, Cd and Cr; whereas chelating agent stabilization shows a strong ability to lower the release of Pb, Cd and Cu, but instead increases the solubility of Zn and Cr at low pH conditions. Sequential extraction results suggested that the leaching of Pb, Zn and Cd in both the stabilized MSWI fly ash samples led to the decrease in Fe/Mn oxide fraction and the increase in exchangeable and carbonate fractions. The leaching of Cr was due to the decrease in exchangeable, carbonate and Fe/Mn oxide fractions in phosphate-stabilized and chelating agent-stabilized MSWI fly ash. The leaching of Cu in both stabilized MSWI fly ash was greatly ascribed to the decrease in Fe/Mn oxide and oxidisable fractions. Moreover, predicted curves by geochemical model indicated that both stabilized MSWI fly ash have the risk of releasing toxic metals under strong acid environment. [ABSTRACT FROM AUTHOR]

Cathode ray tubes (CRTs) waste generation has become a great environmental challenge worldwide. CRT glass possesses reasonable intrinsic strength, low water absorption and rich in silica, which makes the glass suitable for use as sand or pozzolan in construction materials. This work presents a comprehensive overview of literature reporting on the reuse of CRT glass to prepare glass-ceramics; cement mortar, paste, and concrete; and bricks. The effects of various critical factors on the resulting products’ performance, preparation mechanisms, leaching behavior, lead fate, and environmental and human safety were investigated. The comparison of these recycling methods, and directions for future research were discussed and reported as well. Preparing cement mortar, paste, and concrete from CRT glass offer added advantages in terms of quantity of recyclable cathode ray tube glass at a given time, with minimal environmental and economic implications and thus could be an a promising value-added uses for CRT glass. The geographical distance between waste CRT glass sources and processing facilities, public policies should be taken into account in its recycling. [ABSTRACT FROM AUTHOR]

Large volumes of decontamination wastes (DW) generated by off-site decontamination activities in Fukushima Prefecture have been incinerated since 2015. The behavior of radioactive cesium during incineration of DW was investigated at a working incineration plant. The incineration discharged bottom ash (BA) and fly ash (FA) with similar levels of radiocesium, and the leachability of the radiocesium from both types of ash was very low (<1%). These results are significantly different from those obtained for the incineration of contaminated municipal solid waste (CMSW) reported in earlier studies. The source of radiocesium in DW-FA is chiefly small particles derived from DW and DW-BA blown into the flue gas, not the deposition of gaseous synthesized radiocesium compounds on the surfaces of ash particles in the flue gas as observed in CMSW incineration. This source difference causes the behavior of radiocesium during waste incineration to differ between DW and CMSW. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modified magnesium slag is used to prepare the filling material (MFPB). • MFPB has excellent early and long-term mechanical properties. • The leaching behavior of MFPB raw materials were investigated. • Three different methods were used to assess the leaching risk of MFPB. • MFPB is a non-polluting, sustainable and environment-friendly filling material. Magnesium slag is a by-product of magnesium smelting industry, and its massive discharge has seriously threatened human health and ecological environment. In order to solve the environmental problems caused by magnesium slag, a mine backfill material (MFPB) was prepared with modified magnesium slag-fly ash cemented aeolian sand in this paper, and the long-term mechanical properties and leaching behavior of MFPB were investigated. The strength of the MFPB increased with increasing curing time, and the strength reached 4.984–17.140 MPa at 300 d, with FA20 having the highest strength. In terms of environment: (1) Except that FA has certain risks, the leaching levels of other raw materials meet the class III groundwater standard (III-GQSL) in GB/T 14848–2017. (2) The leaching level of MFPB based on the SPLP procedure meets the III-GQSL, and has a significant stabilization/solidification effect on hazardous elements; (3) The results of the LEAF test showed that pH and liquid–solid ratio were important factors affecting the leaching of harmful elements in MFPB. MFPB has good mechanical properties and environmental friendliness, and has the potential for large-scale safe application in mine backfilling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of heavy metal on properties and hydration process is discussed in LW/B-CC. • Precipitation containing Pb and Cr(Ⅵ) inhibits cement early hydration, reducing the complexity of C-S-H. • Generation of combined water declines free water content and compressive strength. • Mn2+ is suitable to be solidified in LW/B-CC, but C r O 4 2 - is difficult metal for immobilization. Solid wastes have been consumed to prepare cement-based materials, and the heavy metals are also solidified in matrix. However, the influence of soluble heavy metal on properties and hydration process is unclear in low water/binder cement-based composite (LW/B-CC). Fresh and hardened properties of UHPC (a typical LW/B-CC) are investigated after introduction of Mn2+, Pb2+, and C r O 4 2 - . Because of the declination of free water, addition of Mn and Pb leads to reduction of compressive strength in a low water/binder ratio, with the latter declining by 15.1 MPa and 10.3 MPa, respectively, after curing 80 d. Pb and Cr doped UHPC reduce the hydration degree by 6.6% and 3.6%, respectively, and the silicon tetrahedral chain complexity of C-S-H also decreases. Overall, this research clarifies the impact of three heavy metals on properties and hydration in LW/B-CC, which provides insights into recycling solid wastes, and solidifying heavy metals. [ABSTRACT FROM AUTHOR]