Leaching Behavior Research Articles

Assessment of the Long-Term Leaching Behavior of Incineration Bottom Ash: A Study of Two Waste Incinerators in Germany

The long-term leaching behavior of incineration bottom ash (IBA) was studied with large-scale samples from two German waste incinerators with grate technology. The observation period was up to 281 days. The aging processes proceeded faster in the outdoor storage of the samples. The dominant factor in the leaching behavior is the pH, which starts at values above 12 and decreases to values below 10 (outdoors, <11 indoors). Most heavy metals exhibit minimum solubility in this pH range. The solubility of Sb depends on the prevailing Ca concentration, due to the formation of low-soluble Ca antimonate. The very low sulfate concentrations observed in the leaching tests with fresh IBA could be explained by the presence of ettringite. In the course of the aging reaction, ettringite is transformed into gypsum. The results from batch tests were compared with those from column tests, showing reasonable agreement. Leaching dynamics can be better followed with column tests. All results confirm that the use of IBA is possible under German law.

Geopolymerization of MSWI fly ash and coal fly ash for efficient solidification of heavy metals: Insights into stabilization mechanisms and long-term leaching behavior

High levels of heavy metals (HMs) are present in municipal solid waste incineration fly ash (MSWI-FA), which requires proper management before landfilling. The aim of this study is to investigate the feasibility of co-disposal of MSWI-FA and coal fly ash (Coal-FA) using geopolymerization technology to solidify heavy metals and to analyze the long-term leaching behavior of heavy metals (HMs). The active silicon, aluminum, and calcium present in MSWI-FA and Coal-FA are essential for the synthesis of geopolymers. The geopolymer with 20 wt% MSWI-FA (M20) achieved the maximum compressive strength of 25.73 MPa, mainly due to the formation of C-A-S-H gels. Heavy metals were effectively immobilized and met the limits of GB18598–2019. The compressive strength of M20 was decreased by 1.6% in sulphuric acid-nitric acid leaching solution for 64 days, but decreased by 57.4% in the acetic acid leaching solution. The geopolymer was more stable in the acid rain environment, resulting in less leaching of heavy metals. The bulk diffusion model (BDM) and Finite Element Method (FEM) could satisfactorily describe the leaching behavior of HMs. The results provide valuable guidance for future waste management practices and the development of solidification processes for MSWI-FA.

Preparation and characterization of novel spontaneous foam ceramics based on all-solid waste

Foam ceramics were prepared through spontaneous foaming behavior using silicomanganese slag and desulfurization gypsum as raw materials. The effects of desulfurization gypsum content and firing temperature on foam ceramics' pore morphology and physical properties were investigated. The phases and microstructure of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and comprehensive thermal analysis (TG-DSC). The results showed that increasing the desulfurized gypsum content is beneficial for promoting the formation of a liquid phase and a uniform pore structure. The prepared ceramics exhibited low density (0.54 g/cm3), high porosity (80.56%), and compressive strength (5.85 MPa). Analyzing the toxic leaching behavior of heavy metal ions in the samples confirmed that all samples were safe and harmless. Furthermore, it was demonstrated through the self-foaming mechanism that desulfurization gypsum could be employed as a new type of spontaneous foam solid waste. This study provides an effective method for the synergistic preparation of foamed ceramics using silicomanganese slag and desulfurization gypsum. The utilization of solid waste in foamed ceramic production not only addresses the issue of significant waste accumulation but also offers economic benefits.

Organic Acid‐Based Hydrothermal Leaching of LiFePO4 Cathode Materials

AbstractThis study conducts hydrothermal leaching of commercial LiFePO4 (LFPO) cathode materials with oxalic acid, citric acid, or glycine without any other oxidants or reductants. Of these acids, glycine exhibits the weakest leaching behavior, with the leaching efficiency of lithium (Li), iron (Fe), or phosphorus (P) less than 15% even at 200 °C and an acid concentration of 0.8 mol L−1 for 10 min. For oxalic acid, at 200 °C for 10 min, with a pulp density of 30 g L−1 and an acid concentration of 0.8 mol L−1, the leaching efficiencies for Li and P are 100% and 97%, respectively, and 98.5% of Fe precipitates as iron oxalate (FeC2O4) that can be used as a precursor for preparing LFPO cathode materials. Citric acid shows the highest leaching efficiency for Li, Fe, and P, reaching 96%, 100%, and 88%, respectively, at 90 °C for 10 min with a pulp density of 10 g L−1 and an acid concentration of 0.8 mol L−1. The continuous hydrothermal leaching of LFPO cathode materials with citric acid is first achieved. These results clarify the superiority of citric acid over oxalic acid and glycine with respect to the leaching efficiency for Li, Fe, and P from LFPO batteries under hydrothermal conditions.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

Investigation of leaching behaviors of carbonation-cured CSA cements using an electrically accelerated leaching test

The present study provides the investigation of leaching behaviors of carbonation-cured calcium sulfoaluminate (CSA) cements with varying initial sulfate contents using an electrically accelerated leaching test. The CSA cement samples were normally or carbonation-cured for 28 days before subjecting them to an electrically accelerated leaching condition for 14 days. The samples were characterized experimentally before and after accelerated leaching. In addition, the leaching behaviors of the CSA cement samples over a wide range of cumulative leached water were thermodynamically modeled to determine their likely performance in repository environments. The results indicate that the reaction of ye'elimite was significantly promoted by accelerated leaching, resulting in the formation of ettringite after leaching, regardless of the curing regime used. Calcium sulfates and C-(A)-S-H formed in the carbonation-cured samples were the first phases to decompose upon accelerated leaching, which is in good agreement with the thermodynamic modeling calculations. For the normally cured samples, the use of higher calcium sulfate in the mixture is preferred, considering the amount of leached ions, yet the opposite holds true for the carbonation-cured samples. In particular, the changes in the calculated volumes of the reaction products upon simulated leaching were smaller for the carbonation-cured samples than for the normally cured samples.

An Improved Understanding of Chalcopyrite Leaching Mechanisms: The Influence of Anisotropic Crystal Planes

Chalcopyrite (CuFeS2) particles, exposing anisotropic crystal planes during the grinding process, possess comprehensive surface properties that affect their leaching behaviors. In order to investigate the influence of anisotropic crystal planes on the leaching mechanisms, CuFeS2 particles with anisotropic crystal planes were produced by employing three-head laboratory grinder mill (TM), rod mill (RM), and ball mill (BM) and were then leached in a sulfuric acid solution at pH = 1. Based on the XRD, SEM, XPS, and simulation results, (112), (102), (312), (110), (116), (100), and (001) planes were mainly exposed on the CuFeS2 surface during the crushing and grinding process. In addition, fewer (112), (102), (312), and (110) planes but more (116), (100), and (001) planes were exposed on the CuFeS2 samples in the TM method than in the RM and BM methods. Since the leaching rates were in the order of (001) > (100) > (116) > (110) > (312) > (102) > (112) planes, the Cu extractions followed an order of TM > RM > BM. This study, therefore, provides an excellent theoretical basis for the effect of anisotropic crystal planes on CuFeS2 leaching, further improving the understanding of CuFeS2 leaching mechanisms.

Leaching Behavior of As and Pb in Lead-Zinc Mining Waste Rock under Mine Drainage and Rainwater.

At present, the pollution of arsenic (As) and lead (Pb) is becoming increasingly serious. The pollution caused by the release of As and Pb from lead-zinc mines has seriously affected the water and soil environment and threatened human health. It is necessary to reveal the release characteristics of As and Pb. The actual scene of mine drainage (MD) and rainwater (RW) leaching waste rocks is the one of the main reasons for the release of As and Pb. However, the leaching behavior of As and Pb in these waste rocks under MD and RW suffered from a lack of in-depth research. In this study, we investigated the occurrence of As and Pb in waste rocks (S1-S6) by using X-ray diffraction (XRD) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), and then, the changes in As and Pb concentration and the hydrochemical parameter in leaching solution were systematically studied. Furthermore, the correlation between the release of As and Pb and mineral composition was also evaluated. Results showed that these waste rocks were mainly composed of carbonate and sulfide minerals. As and Pb were mainly bounded or associated with sulfide minerals such as arsenopyrite, pyrite, chalcopyrite, and galena in these waste rocks, and small parts of As and Pb were absorbed or encased by clay minerals such as kaolinite and chlorite. Under MD and RW leaching, the pH, redox potential (Eh), and electric conductivity (EC) of each waste rock tended to be consistent due to their buffering ability; the leachate pH of waste rocks with more carbonate minerals was higher than that of sulfide minerals. Both As and Pb were released most under MD leaching in comparison to RW, reaching 6.57 and 60.32 mg/kg, respectively, due to MD's low pH and high Eh value. However, As in waste rock released more under alkaline conditions because part of the arsenic was in the form of arsenate. As and Pb release were mainly positively correlated with the proportions of sulfide minerals in these waste rocks. MD leaching significantly promoted the release of As and Pb from waste rocks, which would cause a great threat to the surrounding environment, and control measures were imperative. This paper not only reveals the As and Pb pollution mechanism around the lead-zinc mining area but also provides a theoretical basis for the prevention and control of As and Pb pollution in the future.

An innovative dual-strengthening pretreatment to improve Li and Co leaching in spent lithium-ion batteries: Pyrolysis combined with mechanical grinding

The presence of PVDF prevents the contact of leaching solution and LiCoO2, which is the decisive factor leading to the low leaching efficiency of electrode materials. Therefore, a dual-strengthening pretreatment method is proposed to remove PVDF more efficiently and enhance the leaching of the LiCoO2. To determine the enhanced effect of the PVDF removal and the leaching of LiCoO2 treated by dual-strengthening pretreatment, the leaching behavior of the untreated, ground, pyrolyzed and dual-strengthening pretreated LiCoO2 were compared. XPS and SEM-EDS were used to evidence the removal of the PVDF, while the XRD was used to analyze the composition of the leaching slag to evidence the leaching behavior. The XPS results show that dual-strengthening pretreatment on PVDF removal is better than that of the single treatment. SEM confirms that the electrode material can achieve the double effect of pyrolysis residue removal and particle size reduction after dual-strengthening. The leaching enhancement of dual-strengthening is more significant than the single pretreatment, and the improvement of single pyrolysis is greater than that of grinding by detecting the leaching rate of Li and Co using ICP-MS. The leaching rate of Li and Co in the dual-strengthening LiCoO2 is 96.25 % and 95.21 %, it is 95.16 % and 94.50 % in the pyrolyzed LiCoO2, while it is 73.96 % and 66.78 % in the ground LiCoO2. The mechanism of the dual-strengthening treatment lies in the full removal of PVDF to expand the dispersion of LiCoO2 particles. The present study provides an innovative strengthening approach to LiCoO2 leaching.

Solidification of municipal solid waste incineration fly ash with alkali-activated technology

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.

Study on semi-dynamic leaching and microstructure characteristics of MSWI fly ash solidified sediment

municipal solid waste incineration (MSWI) fly ash partially replaces cement to solidify sediment, and then can be used as intermediate cover materials in landfill as one of the resources utilization ways of MSWI fly ash and sediment. The strength and the semi-dynamic leaching characteristics of MSWI fly ash solidified sediment under hydrochloric acid attack at different pH were studied by means of unconfined compressive strength (UCS), semi-dynamic leaching, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). Results revealed that the UCS strength increased as the curing age and cement content increased. When the curing content is 50% and the replacement ratio of MSWI fly ash is 75% and 80%, the UCS of 7 d can be greater than 50 kPa. The primary contribution to the strength development was from silicic acid gels such as calcium silicate hydrate (C–S–H) and carbonates. Notably, the leaching behavior of Zn and Cu within the solidified sediment underwent substantial alterations. The leaching amount of heavy metals in a strong acidic environment (pH = 2) is significantly greater than that in a weak acidic (pH = 4) and neutral (pH = 7) environment. Conversely, minimal disparities were observed in the leaching characteristics of Zn and Cu between the weakly acidic and neutral environments. Ca(OH)2, C–S–H and carbonate exhibits a remarkable acid-resistant buffering capacity in the solidified sediment. The obvious diffusion coefficient (Dobs) was less than 10−9 m2/s in semi-dynamic leaching tests. Moreover, the mobility of Zn and Cu surpassing 12.5, coupled with a leaching index exceeding 8, further attests to the favorable S/S outcome achieved. Based on these findings, the solidified material is confidently recommended to be used as suitable landfill middle soil cover material.

Composition‐dependent leaching behavior in ion‐irradiated borosilicate glasses: A corrosion mechanism study

AbstractEvaluating 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.

Investigating the impact of inoculation on bioleaching of copper flotation concentrate using a continuous reactor at pilot scale - study case: Tizert deposit

The world is witnessing a major challenge of energy transition which involves the decline of fossil fuels specifically, but which increasingly calls on metallic resources, base metals, mainly copper. The main methods of processing copper minerals are pyrometallurgical and hydrometallurgical processes. Biohydrometallurgy appeared as a very interesting and promising alternative way. In this context, the bioleaching process was studied for the treatment and upgrading of the Tizert concentrate from the Tizert deposit, located 160 km southeast of Agadir, Morocco. Chemical, mineralogical and metagenomic characterizations were carried out on samples from the Tizert deposit. Metagenomic analysis of deposit samples revealed the abundance of genera Paenibacillus (11.38 %), followed by Phynylobacterium (7.54 %) when DSM 670 medium was used while Acidithiobacillus (41.48 %) and Pseudomonas (35.01 %) were abundant when DSM 71 medium was used, indicating the need to use selected consortium species for copper bioleaching experiments. Inoculation with the three species Acidithiobacillus ferrooxidans DSM 583, Leptospirillum ferriphilum DSM 14647 and Acidithiobacillus thiooxidans DSM 14887 was carried out. Laboratory scale leaching experiments with and without inoculation with the bacterial consortium were carried out on the copper concentrate obtained by flotation pretreatment, to compare the copper leaching behavior and yield. Inoculation with exogenous bioleaching bacteria improved the copper yield to 91 % compared to the leaching process without inoculation. These results were confirmed by a pilot-scale study with a copper yield of 95 %.

Accelerated Osteogenic Response of Electrodynamically Stimulated Mg1-xCaxSi1-xZrxO3 (x = 0-0.4) Bioelectrets.

MgSiO3-based biodegradable ceramics demonstrated remarkable potential for treating small-scale bone defects and temporary bone replacement. In addition, the dissolution behavior of MgSiO3 bioceramics can be tuned by doping of Ca and Zr elements at Mg and Si sites, respectively. The present study reported the influence of formation of Ca- and Zr-codoped Mg1-xCaxSi1-xZrxO3 (x = 0, 0.1, 0.2, 0.3, and 0.4) bioelectrets and electrodynamic stimulation toward improving their osteogenic response. Mg1-xCaxSi1-xZrxO3 electrets were successfully synthesized by a solid-state route. A detailed X-ray photoelectron spectroscopy (XPS) analyses revealed that the electrets produced oxygen-deficient active sites. The formation of Mg1-xCaxSi1-xZrxO3 electrets significantly increased the surface hydrophilicity. Inductively coupled plasma (ICP) analyses were used to examine the leaching behavior of Ca/Zr-codoped MgSiO3 bioceramics. In vitro cell culture analyses indicated that the osteogenesis of MG-63 cells was remarkably enhanced on the electrodynamic field-treated Mg1-xCaxSi1-xZrxO3 bioelectrets as compared to hydroxyapatite (HA). Moreover, a better osteogenic response was observed for higher concentrations of Ca (0.3 and 0.4) and Zr (0.3 and 0.4) doping in the MgSiO3 bioelectrets. Further, the mechanism of enhanced cellular functionality was revealed by the measurement of intracellular Ca2+.

Effects of EDTA on the leaching behaviors of Cs(I) and Co(II) from cement waste forms

Cementation is extensively employed for immobilizing radionuclides in low- and intermediate-level radioactive wastes generated during the decommissioning of nuclear power plants. Ethylenediaminetetraacetic acid (EDTA), used as a decontamination agent during the decommissioning process, can be introduced into the cement waste form containing radionuclides. This study investigated the effects of the EDTA present in simulated radioactive decommissioning wastes on the leaching behaviors of Co and Cs immobilized in the cement waste form. Co leaching was facilitated by the formation of highly mobile Co–EDTA complexes. However, Cs leaching was impeded by the competition for leaching with other metal–EDTA complexes. Moreover, the EDTA-induced carbonated layer with a dense pore structure played a crucial role as a retardation barrier for the Cs leaching. The calcite contents of the samples with 8 wt% EDTA were approximately three times higher than those of the samples without EDTA. The introduced EDTA affected the leaching behaviors of both Co and Cs, as well as the microstructure evolution of the cement waste form. Nevertheless, the addition of EDTA had a relatively low positive effect on the efficiency of Cs immobilization, but also an obvious negative effect on the efficiency of Co immobilization, regardless of the concentration of EDTA. Finally, an EDTA dosage of 1 wt% in the cement waste forms containing Co or Cs is suggested as a potential waste acceptance criterion for solidified low- and intermediate-level radioactive waste.

Mixing uniformity effect on leaching behaviour of cement-based solidified contaminated clay

Mixing uniformity is essential for the quality control of the contaminated clay's solidification. To investigate the effect of the mixing uniformity on the leaching behaviour of the cement-based solidified contaminated clay, this study proposed a quantitative method to characterize the mixing uniformity and investigated the leaching behaviour by the leaching toxicity tests and semi-dynamic leaching tests. X-ray computed tomography (X-CT) was employed to reveal the internal mesoscopic structure. In this case, Pb2+ was selected as a tagged pollutant because of the widespread attention at heavy metal-contaminated sites. The leaching toxicity indicates the significant Pb2+ concentration deviation among the parallel specimens and non-association with the mixing uniformity. However, the Pb2+ cumulative leaching mass and observed diffusion coefficient by the semi-dynamic leaching tests both decrease with the mixing uniformity. X-CT image analysis reveals that the high cement zones wrap the low cement zones with different dimensions in the heterogeneous solidified matrix. Moreover, the specimen pretreatment method in the existing leaching toxicity standards may be inadequate because of the overall encapsulation destruction by the crushing process and representativeness uncertainty when sampling. However, for semi-dynamic leaching, the Pb2+ migration depends on the uniformity, reflecting the continuous distribution of high cement zones.

Study on Synergistic Effect of Xanthan Gum and Sodium Methylsiliconate on Mechanical Strength and Water Stability of Phosphogypsum Road-Based Materials.

To address the issues of low strength, poor water stability, and hazardous substance leaching associated with using phosphogypsum (PG) as a direct road-based material, the traditional approach involves employing inorganic cementing materials to stabilize PG, effectively addressing the problems. This study innovatively utilizes the xanthan gum (XG) and sodium methylsiliconate (SM) as curing agents for PG to solve the above problems. An organic curing agent stabilized PG was prepared by dry mixing XG and PG. The unconfined compressive strength, water stability, and leaching behavior of stabilized PG were investigated, the leaching behavior was characterized by ion leaching concentration, and the mechanisms behind the strength development of stabilized PG were explored by SEM and FTIR. The experimental results indicate that the single incorporation of XG reduced the strength and water stability of stabilized PG, while the single incorporation of SM had a limited effect on strength and water stability. In addition, the dual incorporation of XG and SM significantly improved the strength and water stability of stabilized PG. At the same time, the dual incorporation of XG and SM greatly reduced the leaching of hazardous substances from stabilized PG. These results demonstrate the feasibility of using stabilized PG for road base materials.

Metal encapsulation of waste foundry sand stabilized with alkali-activated binder: Batch and column leaching tests

Waste stabilization processes are important to add value and reduce environmental risks related to metal contamination of soils and groundwater. This study evaluated the metal encapsulation of: (i) waste foundry sand (WFS) stabilized with an alkali-activated binder (AAB), compared to (ii) WFS-Portland cement (PC) mixture. The AAB was composed by sugar cane bagasse ash (SCBA), hydrated eggshell lime, and sodium hydroxide solution. The metal leaching behavior from WFS-AAB and WFS-PC was investigated through batch and column tests according to NBR 10005 and ASTM D4874 methods, respectively. All WFS-AAB and WFS-PC mixtures showed no metal toxicity. WFS-AAB matrices encapsulated the heavy metals Cd, Cr, and Pb from WFS and SCBA. Leaching results from NBR 10005 method were more favorable than ASTM D4874 for water quality limits (CONAMA 460, Dutch List, and EPA). Binder type, metals leaching patterns, and leaching test procedures were key factors in understanding the environmental performance of cemented WFS.

Experimental assessment of utilizing copper tailings as alkali-activated materials and fine aggregates to prepare geopolymer composite

Globally, there is an increasing attention drawn by copper tailings (CT) due to the environmental problems caused by its tremendous storage volume and low recycling rate. With the purpose of promoting the sustainability and value-added utilization of CT, this study used CT powder with particle size ≤ 0.075 mm, granulated blast furnace slag (GBFS), and fly ash (FA) to prepare CT/FA-GBFS geopolymer paste composites. Also, 0.075–0.6 mm CT sand was also used as a replacement of natural fine aggregates. The effect of CT powders on the mechanical strength of the geopolymer paste was assessed, as well as the influence of CT sand on the mechanical strength and the heavy metal leaching behavior of CT-GBFS geopolymer mortar. The obtained results from the study demonstrate that CT powder exhibits partial participation in the geopolymerization reaction within an alkaline environment. Additionally, it manifests a filling effect when incorporated as micro powders. It is noteworthy that the compressive strength of the geopolymer paste improved by 18% and the flexural strength by 74% when the CT content reached 45%. Furthermore, in the context of CT-GBFS geopolymer mortar, the 20% replacement ratio of CT sand yields a more favorable interfacial transition zone (ITZ) between the geopolymer paste and the mixed sand. This improved ITZ improves the mechanical properties of the mortar by about 10% compared to other experimental groups. Finally, when CT were immobilized in the CT-GBFS geopolymer mortar, the leaching of heavy metals from copper tailings was significantly reduced, eliminating the impact of CT utilization on the environment.

Immobilization enhancement of heavy metals in lightweight aggregate by component regulation of multi-source solid waste

Integrated recycling of solid waste containing heavy metals is a critical environmental challenge. In this study, a green solution to reduce heavy metal leaching from solid waste is demonstrated by combining contaminated soil, industrial sludge and lithium slag in pairs to produce lightweight aggregates (LWAs). The physical properties and heavy metal leaching behavior of LWA samples were systematically investigated and characterized. The results showed that industrial sludge reduced the density and water absorption of LWA, while the high content of lithium slag was detrimental to the physical properties. LWA containing 80% contaminated soil and 20% lithium slag had the lowest particle density of 1.47 g/cm3 due to the hollow structure caused by the low viscosity and violent generation of SO2. LWAs with lithium slag leached excessive Cu and Cr relatively, while heavy metals were immobilized well in LWAs with contaminated soil and industrial sludge as the main components. Because the flux components of industrial sludge could enhance the encapsulation of heavy metals by glass phase. In addition, the co-immobilization of multiple heavy metals was observed in the spinel phase. This study provides an efficient and safe method for the synergistic recycling of solid waste.