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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]

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]

[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]

Municipal solid waste incineration (MSWI) fly ash is a significant byproduct of waste-to-energy processes, and poses substantial environmental and health hazards if not treated properly. The process of Stabilization/Solidification (S/S) efficiently immobilizes hazardous elements present in the fly ash through a combination of physical and chemical mechanisms. The objective of this research is to thoroughly examine the feasibility of using chicken eggshell waste powder as a stabilizing agent for heavy metals, specifically targeting Pb, in MSWI fly ash. Experimental analysis involved varying eggshell waste to fly ash weight proportions, extending from 0.0 (control group), 7:3 up to 9.5:0.5 ratio, with designated curing durations of 2 and 72 hours, and maintaining a liquid-to-solid (L/S) ratio at 1.0 mL/g. In the two-hour curing period, the immobilization efficiency of Pb reached 100% with the addition of only 1.5% eggshell waste. Optimal ratios for Pb stabilization in MSWI fly ash were identified: maximum 2% eggshell waste for 2-hour curing and 1.5% for 72 hours due to elevated Pb and Cd levels of 7:3 ratio. Adding CaO mitigated these levels, enhancing stabilization and compliance with landfill criteria. The results demonstrated that the addition of CaO led to efficient immobilization of Pb, achieving approximately 99%. In addition, the observed enhancement in compressive strength resulting from the incorporation of CaO highlights its effectiveness in enhancing the stabilizing process of MSWI fly ash. By demonstrating the effectiveness of eggshell waste and CaO in stabilizing hazardous elements, this study advocates for scalable solutions and further research on long-term stability and environmental impacts. [Display omitted] • Chicken eggshell waste shows high potential as a stabilizing agent for Pb in MSWI fly ash. • A mere 1.5% addition of eggshell waste can achieve 100% immobilization of Pb, complying with landfill limit requirements. • The addition of CaO to the eggshell and fly ash mix achieves 99% immobilization of Pb with only 6.5% of CaO. • This innovative method also enhances compressive strength, presenting an eco-friendly solution for recycling eggshell waste. [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]

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 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]

Additives may be present in amounts higher than 50% within plastic objects. Additives in plastics can be gradually released from microplastics (MPs) into the aquatic environment during their aging and fragmentation because most of them do not chemically react with the polymers. Some are known to be hazardous substances, which can cause toxicity effects on organisms and pose ecological risks. In this paper, the application of functional additives in MPs and their leaching in the environment are first summarized followed by their release mechanisms including photooxidation, chemical oxidation, biochemical degradation, and physical abrasion. Important factors affecting the additive release from MPs are also reviewed. Generally, smaller particle size, light irradiation, high temperature, dissolved organic matter (DOM) existence and alkaline conditions can promote the release of chemicals from MPs. In addition, the release of additives is also influenced by the polymer's structure, electrolyte types, as well as salinity. These additives may transfer into the organisms after ingestion and disrupt various biological processes, leading to developmental malformations and toxicity in offspring. Nonetheless, challenges on the toxicity of chemicals in MPs remain hindering the risk assessment on human health from MPs in the environment. Future research is suggested to strengthen research on the leaching experiment in the actual environment, develop more techniques and analysis methods to identify leaching products, and evaluate the toxicity effects of additives from MPs based on more model organisms. The work gives a comprehensive overview of current process for MP additive release in natural waters, summarizes their toxicity effects on organisms, and provides recommendations for future research. [Display omitted] • Common additives released from MPs include heavy metals, PAEs, BPA, BFRs and PFAS. • Polymers, temperature, light and co-existed pollutants mainly affect additive release. • Chemicals in MPs bioaccumulate in organisms by ingestion and exert toxicity effects. • Some additives cause neurotoxicity, inflammation, metabolic disorders and cancer. [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]

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]

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]

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]

Here, a novel approach to the detoxification and reuse of waste activated carbon (WAC) through co-gasification with coal-water slurry (CWS) is proposed. To evaluate the harmlessness to the environment of this method, the mineralogical composition, leaching characteristics, and geochemical distribution of heavy metals were investigated, enabling the leaching behavior of heavy metals in gasification residues to be explained. The results showed that the gasification residue of coal-waste activated carbon-slurry (CWACS) contained higher concentrations of Cr, Cu, and Zn, while those of Cd, Pb, As, Hg, and Se were well below 100 μg/g. Further, the spatial distributions of Cr, Cu, and Zn in the mineral phases of the gasification residue of CWACS were relatively uniform overall, and no obvious regional enrichment was observed. The leaching concentrations of various heavy metals in the gasification residues of the two CWACS samples were all lower than the standard limit. Following the co-gasification of WAC with CWS, the stability of the heavy metals in the environment was enhanced. Meanwhile, the gasification residues of the two CWACS samples showed no environmental risk for Cr, low environmental risk for Pb and Hg, and only a moderate environmental risk for Cd, As, and Se. [Display omitted] • Detoxify and reuse the waste activated carbon through co-gasification with CWS. • The leaching behavior of heavy metals in gasification residues was explained. • The residue after co-gasification of WAC and CWS is non-hazardous. • Modified BCR method was used to study the geochemical distributions. • The environmental risk of the CWACS gasification residues was evaluated. [ABSTRACT FROM AUTHOR]

The indirect steel slag (SS)-based carbon capture, utilization, and storage (SS-based CCUS) process is recognized as a promising way for simultaneous mitigation of CO 2 emissions and valorization of wastes. Even so, much still needs to be done for sizeable and economic implementations of the SS-based CCUS process, such as enhancement of the selective extraction efficiency of Ca from SS, and a prior prediction of the Ca extraction potential of SS. It is necessary to simultaneously study mineralogy, morphology, solution chemistry, and passivation layer during the dissolution process of SS to improve the overall understanding of the Ca extraction behavior and dissolution mechanism. Therefore, in this work, three kinds of SS were investigated, such as basic oxygen steel slag (BOFS), electric arc furnace slag (EAFS), and ladle furnace slag (LFS). First, the mineral phase composition, and Ca distribution of various SS were identified and compared. In addition, the Ca extraction behavior and passivation mechanism of various SS were investigated by carrying out a series of leaching and corrosion tests in NH 4 Cl and CH 3 COOH solution. Results showed that whilst the Ca contents of the three SS samples were similar, the leaching behavior and the Ca extraction yield were significantly different. In addition, various passivation layers were observed, which was formed closely related to the dissolution manner of mineral phases in various solution environments, which was further assessed at atomic level. [Display omitted] • The mineralogical composition partly determined the distinct leaching behaviors of SS. • Various passivation layers were observed after leaching SSs in the different solvents. • The passivation layer formed may be related to the distinct dissolution manner of phases. • Roles of mineralogy and solvent on the dissolution of SS were assessed at the atom level. [ABSTRACT FROM AUTHOR]

• Contact with CaCl 2 solution greatly reduces the adsorption capacity of CSH for Pb. • For MgCl 2 solution, most portlandite in mortars was decomposed to form brucite. • The lower the adsorbability of Pb on CSH, the larger the Pb leaching amounts. • The amount of Pb leaching in CaCl 2 solution is three times larger than that in other solutions. • Large leachate quantity for CaCl 2 solution was not caused by pore structure alterations. This study investigates how chloride-based salts affect the immobilization and leaching of Cu, Zn, and Pb from cement hydrates and analyzes the associated internal changes in crystalline phase. Results showed that the amount of Pb leached is highest in mortar when it contacts with CaCl 2 solution. A key reason for this outcome is that calcium silicate hydrate (CSH) has the lowest Pb adsorption in CaCl 2 solution. Exposure to MgCl 2 solution resulted in the decomposition of most portlandite to form brucite in mortars, lowering the pH to ∼9. This caused the lowest leaching rate of Cu, Zn, and Pb in MgCl 2 solution. [ABSTRACT FROM AUTHOR]

The agricultural soil contaminated with vanadium (V) has been attracting attention due to its adverse effect on human health and ecosystems. In this study, the leaching risk and transformation characteristics of V in contaminated paddy soils collected from the vicinity of stone coal smelting area were evaluated by a column leaching experiment with simulated acid rain (SAR). The results showed that the amount of soluble V leached was slight and only accounted for 0.04-0.06% of the total V, however, the concentrations of V in leachates after leaching with 10 years of rainfall precipitation using SAR at pH 4.5, pH 5.6 and neutral pH 7.0 were found to to be 49.0, 71.3 and 61.1 µg/l, respectively, which were higher than or near to the V threshold limit of Chinese Environmental Quality Standards for Surface Water (50 µg/l) (GB 3838-2002). The percentages of V in both the reducible and oxidizable fractions of the soils increased by 2.10-3.50%, whilst that in residual fraction decreased by 4.52-6.07% after leaching. The results suggest that the mobility of V in polluted paddy soil is increased by long-term rainfall leaching and poses a potential risk of V pollution in surrounding water. [ABSTRACT FROM AUTHOR]

This work reports the first results of an on-going activity aimed at the scale up of the wet-route carbonation of steel slag for storing CO 2 and generating a product with valorization potential. Two batches of Basic Oxygen Furnace slag (BOF1 and BOF2) collected at different times from a steelmaking plant downstream iron recovery were used to perform the tests in a pilot-scale rotary kiln unit part of ENEA's research infrastructure. The tests were carried out at ambient (25 °C- 37 °C) and enhanced temperature (45 °C-53 °C), under a 40-47% CO 2 flow, at atmospheric pressure for a reaction time of 30 min. In each experiment around 1000-1500 g of BOF slag was employed. The residues were humidified in order to achieve a liquid to solid ratio of 0.17 l/kg. This value was selected on the basis of the results of preliminary lab-scale static and dynamic experiments that are also presented in this paper. The product collected at the end of each test was cured at controlled conditions (T=25 °C e RH=100%) for 28 days and then characterized in terms of particle size, CO 2 uptake and environmental behavior. The mean diameter (D 50 ) of the obtained product was around 1 mm for the tests performed at room temperature and slightly lower for the test performed at 50 °C, i.e. around twice the size of the starting material. The CO 2 uptake measured for samples collected immediately after the tests was quite similar (4-6% wt.), whereas after curing a 50% increase was observed for all BOF1 slag samples, while only a slight increase was observed for BOF2 slag. These results are significantly higher than the ones of the lab-scale tests. The leaching behavior of the product appeared also to be significantly affected by the treatment performed in the pilot plant. [ABSTRACT FROM AUTHOR]

Coal gangue is one of the largest industrial solid waste all over the world, and many methods have been proposed for the recycling of coal gangue. In the present study, the feasibility of using coal gangue as landfill liner material is studied through a series of laboratory tests in terms of hydraulic conductivity, sorption characteristics and leaching behavior. The results indicated that the hydraulic conductivity of coal gangue could be smaller than the regulatory requirement 1 × 10 −7 cm/s with a void ratio less than 0.60. The batch sorption experiments performed on Pb 2+ and Zn 2+ illustrated that the coal gangue showed remarkable sorption capacity for the two heavy metals, and the sorption capacity for Pb 2+ was larger than that for Zn 2+ . Both the pseudo first-order and pseudo second-order models fitted well with the sorption kinetics data of the Pb 2+ and Zn 2+ on the coal gangue, and the Langmuir model was found to best-fit the sorption isotherms. The sorption capacity decreased in presence of multiple heavy metals, both for Pb 2+ and Zn 2+ . Concentrations of heavy metals leached from the coal gangue were all below the regulatory limits from China MEP and U.S. EPA. These desirable characteristics indicated that the coal gangue has potential to be used as landfill liner materials. [ABSTRACT FROM AUTHOR]

The utilization of rich-reserve Zhundong coal is limited due to the high sodium content, which can cause severe fouling and slagging troubles in a traditional boiler. The collected drill data of sodium, chlorine and ash in Zhundong coal, as well as the vertical samples including roof, up seam (US) coal, parting, low seam (LS) coal and floor were characterized and investigated. It is found that the sodium content in Zhundong coal is a magnitude higher than chlorine content and decreased with the increasing depth to roof of the coal seam, which agrees well with the changing trend in vertical samples: roof > US coal > LS coal > parting > floor. The determined Na 2 O content in ash was lower than the converted content indicated part of sodium volatilized during ashing process. Water soluble sodium (H 2 O-Na) predominated and accounted for 65.50, 82.49 and 64.35 wt% in US coal, parting and LS coal, respectively. H 2 O-Na content is affected by migration and evaporating of coalbed water. SEM-EDX and XRD results indicated that Na, S, O and Ca are the main elements in sodium-rich minerals of roof. With higher H 2 O-Na and less specific surface area and microporous volumes, parting has an obviously higher initial leaching rate and leachability. The shrinking core model shows that the diffusion rate constant ( K p ) is 0.002 and 0.005 h −1 for LS coal and parting, respectively. 88.63 wt% of H 2 O-Na in LS coal was leached out, and final Na 2 O content is markedly lower than the threshold value of coal-fired boiler. [ABSTRACT FROM AUTHOR]

• Green LWAs were successfully via cement-alkali-autoclaved composite process. • Security and feasibility of green and non-sintered LWAs prepared by MSWI were verified. • Particle integrity and inclement environments were systemically explored. • The excellent structure had a good role in sealing the heavy metals in the inclement environment. With the rapid development of urbanization and the economy, the amount of municipal solid waste incineration fly ash (MSWI fly ash) dramatically increases and stacks up. Declining the leaching concentration of hazardous heavy metals in municipal solid waste incineration fly ash and enlarging the application range in wastewater and biosorption of non-sintered LWAs have always got more attention from more and more researchers. Green and non-sintered LWAs were prepared by using the waste solids (MSWI fly ash and coal fly ash) as raw materials through autoclave technology. In the meantime, the effect of severe leaching environment (pH = 1, 3, 5 and 7) on the stabilization of heavy metals in the LWAs with MSWI fly ash and extra heavy metals were systematically investigated by means of Inductively Coupled Plasma Optical Emission Spectrometer, X-ray diffraction, Fourier Transform Infrared Spectrometer, X-ray photoelectron spectra and Scanning electron microscope. The results revealed that the heavy metals are well immobilized in the LWA matrix through physical encapsulation and adsorption by hydration products (C-S-H). The leaching rate (LR) and cumulative leaching rate (CLR) of heavy metals, phase compositions and chemical structures in LWAs with heavy metals at pH of 1 are significantly changed, but the cumulative leaching rate of Pb2+ is lower than that of Zn2+ and Cu2+. The structure of hydration products in the matrix will be broken and reformed to gypsum under an acid environment (pH = 1). The leaching rate and cumulative leaching rate of heavy metals in LWAs with heavy metals under various leaching environments are much lower when the pH is above 1, which could meet the leaching requirement. This research could provide theoretical support for the application of non-sintered and municipal solid waste incineration fly ash based LWAs in concrete. [ABSTRACT FROM AUTHOR]

• Leaching behavior of ultra-high performance concrete was investigated. • Flow environment and steel fiber content had a significant effect on leaching behavior. • Compressive strength loss at the same degraded ratio of ordinary concrete and UHPC were compared. • A cubic compressive strength predictive model was established. Ultra-high performance concrete (UHPC) is a cementitious material with exceptional durability. Uncertain is, however, the leaching behavior of UHPC in a flow environment. To investigate the leaching behavior of UHPC under the influence of moving water, accelerated tests simulating various naturally flowing solution conditions were conducted. The effect of flow environment, steel fiber content, and superplasticizer content on the degradation of UHPC was investigated. There are three flow velocities: static (0 m/s), low (0.3 m/s), and high (2 m/s), as well as three leaching solutions: 6 mol/L ammonium chloride, 3 mol/L ammonium chloride, and natural groundwater. Mass loss, porosity, degradation depth, flexural strength, and compressive strength were measured. The result showed that the maximum degradation of UHPC was observed in a high-velocity flow environment containing 6 mol/L ammonium chloride. Porosity, mass loss, degradation depth, and compressive strength loss following deterioration declined as the steel fiber content rose, reaching a minimum at 2% steel fiber in the same flow environment. The loss of flexural strength decreases and subsequently increases as the steel fiber content increases. The largest reduction in compressive strength was 16.4%, and the maximum reduction in flexural strength was 48.2%. At the same degraded ratio, the compressive strength loss of UHPC is significantly less than that of ordinary concrete. A predicted model for the loss of UHPC's cubic compressive strength is established. [ABSTRACT FROM AUTHOR]

[Display omitted] • Foam glass–ceramic with good performance was developed by multiple solid wastes. • Desulphurisation gypsum was used as foaming agent in this study. • The results show that the use of material prepared in this study is safe for the environment. Direct materialisation is a large-scale solid waste utilisation approach with economic and environmental benefits. This study explored a novel process for the utilisation of multiple solid wastes, including fly ash, blast furnace slag and desulphurisation gypsum, for foam glass–ceramic preparation. The high-temperature decomposition reactions of desulphurisation gypsum were analysed to investigate its suitability as a foaming agent. The effects of the sintering temperature during the preparation process and the raw material composition on the properties of the prepared foam glass–ceramic were investigated. The optimum parameters were a desulphurisation gypsum addition amount of 7 wt% and a sintering temperature of 1,200 °C, while the corresponding bulk density, thermal conductivity and compressive strength were 1.21 g/cm3, 0.153 W/m K and 11.23 MPa, respectively. Finally, the migration and transformation of heavy metals during the preparation process and the leaching behaviour of heavy metals from the final material were analysed. The recycling of multiple solid wastes for foam glass–ceramic production has significant economic and environmental benefits. The excellent thermal insulation and strength properties of foam glass–ceramic make them suitable for manufacturing wall insulation materials. [ABSTRACT FROM AUTHOR]

• The leaching properties of borosilicate glasses irradiated with heavy ions were investigated using the MCC-1 static leaching method. • The structure of irradiated glass was more easily altered than pristine glass under leaching condition. • The influence of irradiation on leaching rate of borosilicate glass was evaluated by the measurement of the initial dissolution rate. Irradiation of ions could increase the leaching rate of borosilicate glass obviously. Borosilicate glass is a promising material for immobilization of high-level radioactive waste (HLW). The leaching behavior of borosilicate glass is crucial for the safety of HLW deep geological disposal. Borosilicate glasses were irradiated with 5 MeV Xe ions. After irradiation, the leaching behaviors of borosilicate glasses were investigated using the MCC-1 static leaching method at 90 °C. The solutions were analyzed by inductively coupled plasma optical emission spectrometry. The structure of the glasses was characterized with Fourier transform infrared spectroscopy, Raman spectroscopy and grazing incident X-ray diffraction. With radiation of ions, [BO 4 ] units were transformed into [BO 3 ] units, which decreased the polymerization of glass network. The [BO 3 ] units of glasses with and without irradiation both decreased gradually as the leaching time increased. After irradiation, the leaching rates of glasses increased obviously. The strength of the glass network deteriorated after irradiation and the structure of irradiated glass was more easily altered than pristine glass under leaching condition. [ABSTRACT FROM AUTHOR]

The valorization of bauxite residue faces severe challenges arising from its unreactive chemistry and ecotoxicity. The construction sector is widely considered the most viable option for the large-scale consumption of bauxite residue to mitiate its continued global accumulation. However, the use of bauxite residue as a supplemetary cementitious material in concrete is limited by its chemical composition and the degradation it causes in the structural properties. Alkali activation of bauxite residue is an alternative technique to produce construction materials, but conventional methods require either high-temperature calcination of the bauxite residue or the use of large proportions of other precursors to form strong alkali activated materials, adding significant cost. This has stymied commercial efforts to valorize bauxite residue. In this study, an alternative methodology is showcased to alkali activate bauxite residue in its filter-pressed form, eliminating the need for drying and calcination. This is the first alkali activation process to utilize high content of bauxite residue (>70%) without drying and milling, offering a substantial reduction in valorization costs and complexity. Alkali activated materials composed of 80% bauxite residue were produced that exceed 11 MPa in strength, meeting the ASTM requirements for interior bricks. The microstructure was characterized by mercury intrusion porosimetry and isothermal nitrogen adsorption. The alkali activation pacified the trace metallic pollutants in the bauxite residue and the leachate meets surface water standards. This methodology presents a unique avenue to valorize bauxite residue at a large scale as a construction material without cost-prohibiting pretreatment steps. [ABSTRACT FROM AUTHOR]