Toxicity Characteristic Leaching Procedure Research Articles

Impact of hydrochar in stabilization/solidification of heavy metal-contaminated soil with Portland cement.

Stabilization/Solidification (S/S) using Portland cement is a common soil remediation technique for heavy metal-contaminated sites. However, due to the hindrance of cement hydration by heavy metals (HMs) and the high CO2 emissions from cement production, efforts have been made to reduce cement consumption. Supplementary cementitious materials (SCMs) present an efficient alternative for this purpose. This study investigates the impact of hydrochar and modified hydrochar as SCMs for remediating soils contaminated with Zn, Pb, and Cd. Forty treated soil samples were evaluated using unconfined compressive strength (UCS), pH, Toxicity characteristic leaching procedure (TCLP), and sequential extraction procedure (SEP) tests, and statistical analysis was conducted to assess the effects of binder content, hydrochar dosage, and hydrochar type. Results show that substituting cement with hydrochar or modified hydrochar reduces UCS by 10-40%, with hydrochar having a greater negative impact than modified hydrochar. pH values ranged from 6.98 to 12.64, facilitating HMs precipitation. In heavily contaminated samples, hydrochar or modified hydrochars significantly decreased the Zn, Pb, and Cd TCLP values by 55%, 63%, and 50%, respectively. In moderately contaminated samples, the reduction was slight for Zn and Pb, with no significant change for Cd. SEP test results indicated that hydrochar or modified hydrochar in cement improves the transformation of the acid-soluble fraction to the residual fraction of Zn and Pb, but not for Cd-contaminated soil samples. Overall, these findings suggest that incorporating hydrochar or modified hydrochar as SCMs in cement contributes to reducing cement usage and CO2 emissions while enhancing the stabilization efficiency of certain heavy metals in contaminated soils.

Utilization of coalmine overburden-furnace slag and fly ash mixed cement-treated subbase/base course material for sustainable flexible pavements: mechanical performance and environmental impact.

The scarcity of conventional aggregates with tremendous growth in highway construction and the indiscriminate dumping of industrial waste materials in precious landfills has become a huge global concern. This study is aimed at utilizing wastes from various industries, including coalmine overburden (OB) dump, basic oxygen furnace (BOF) slag, and fly ash to produce suitable and sustainable cement-treated subbase/base course layers (CBSB/CTB) for flexible pavement construction. Response surface methodology was used to optimize the composition of the blended material considering unconfined compressive strength (UCS) and Poisson's ratio. Results demonstrated that 50% OB dump, 40% slag, 5% fly ash, and 5% cement achieved a 7-day UCS of 4.84MPa and Poisson's ratio of 0.25, in line with IRC:37-2018 guidelines. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) analysis confirmed the presence of ettringite crystals, calcium-silicate-hydrate (C-S-H), and calcium-aluminosilicate-hydrate (C-A-S-H) gels which are the source of strength development in the blend. Further, a soaked California bearing ratio (CBR) of 136.08% and flexural strength of 2.06MPa after 7days and 28days of curing, respectively, demonstrates the overall strength of the stabilized waste. Approximately 4% weight loss was observed after wet-dry durability tests, indicating exceptional performance of the optimal blend in inclement weather conditions. Furthermore, the environmental impact of the blended material was studied through a leaching study. Fly ash had a high zinc (Zn) level, while BOF slag showed a rich concentrationof chromium (Cr), manganese (Mn), and iron (Fe) in the acid digestion test. In spite of this, the toxicity characteristics leaching procedure (TCLP) test indicated that the levels of heavy metals that leached from the stabilized material stayed considerably below the permissible limits set forth in Indian Standard, IS:10500 (2012). Finally, cost analysis showed a 51.6% reduction in construction cost with cement-treated industrial wastes instead of granular base/subbase made with conventional aggregates. The study recommends the suitability of the stabilized waste material as an alternate construction material for large-scale field applications, which could encourage the construction of flexible pavements that are environmentally benign, economical, and sustainable.

Developing alkali-activated controlled low-strength material (CLSM) using urban waste glass and red mud for sustainable construction

Using industrial waste in controlled low-strength material (CLSM) offers many benefits and addresses waste management issues. However, identifying optimal CLSM design while balancing environmental impacts and engineering properties poses a notable challenge. Herein, new alkali-activated CLSM formulations based on urban waste glass and red mud (RM) are proposed for the first time with systematic investigations into the material properties and sustainability. The formulations involve the ternary blends of slag, glass powder (GP) and RM as the binders and crushed glass as aggregate. Our observations show RM has a clay-like texture with complex crystalline phases rich in Al and Fe. Increasing the proportion of RM to GP notably decreases the flowability, extends the setting time and impairs the mechanical properties. Nevertheless, red mud demonstrates a crucial role of reducing bleeding level especially for the mixtures with high proportions of glass aggregate. The standard leachate tests as per toxicity characteristic leaching procedure (TCLP) show the heavy metals leached from the CLSM are below the concentration limits and exhibit low mobility. The microstructural and thermodynamic analyses reveal the precipitation of calcium-(sodium-)aluminosilicate hydrate (C-(N-)A-S-H) as the major binding material. The reactive Fe and Al in red mud most probably contribute to the formation of hydrogarnet phases. Moreover, the suggested CLSM formations typically exhibit reduced carbon emissions and lower costs compared to the traditional CLSM produced with cement and fly ash, underlining their environmental sustainability and cost-effectiveness. This study provides a potential guideline for the flowable fill construction in the regions with bauxite producers.

Assessing the mobility of Zn, Pb and Ni during the weathering of Nkana smelter copper slag, Zambia

Mine slag dumps could be point-sources of possible pollutants to the surrounding water and soils. The purpose of this study was to investigate the leaching behavior of zinc, lead and nickel from Nkana copper slag dump of Kitwe in Zambia. To assess the toxicity and hazardous nature of the slag, Bath Leaching EN 12,457–2:2002, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) were employed. The results from these techniques revealed that the copper slag was inert in the open or natural environment. Sequential extraction analysis was conducted to analyze the fractionation of the zinc, lead and nickel using a seven-step procedure. The sequential extraction analysis showed that the 3 metals were predominantly present in the residual fraction. The risk assessment code (RAC) showed that zinc and lead's mobility could pose an environmental risk categorized as low risk, with RAC values of 1.31 % and 1.50 %, respectively. Nickel's mobility fell within the no-risk category with a RAC of 0.32 %. Additionally, the effect of pH, particle size and contact time on the release of the 3 metals were investigated. The results showed that the highest concentrations of zinc and nickel were observed for longer period of exposure (>33 days), in acidic environments (pH 2.2 and pH 3.0), for particle size distribution (<75 μm). However, lead leaching was not affected by the variation of pH or particle size distribution but mostly by duration of exposure. X-ray diffraction (XRD) analysis revealed that diopside (CaMgSi2O6) and quartz (SiO2) constitute the primary phases within the sample. It is recommended to limit the exposure of slag material to acidic environments and minimize the fragmentation of the slag into finer particles as these conditions would promote increased release of zinc, lead and nickel to the surrounding environment.

Stabilization of clay soil using alkali-activated sewage sludge

This study investigates the innovative reuse of sewage sludge with eco-friendly alkaline solutes to improve clayey soil without conventional cementitious binders. The unconfined compressive strength (UCS) was the main criterion to assess the quality and effectiveness of the proposed solutions, as this test was performed to measure the strength of the stabilized clay by varying binders’ dosages and curing times. Moreover, the direct shear test (DST) was used to investigate the Mohr-Coulomb parameters of the treated soil. Microstructure observations of the natural and treated soil were conducted using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and FTIR. Furthermore, toxicity characteristic leaching procedure (TCLP) tests were performed on the treated soil to investigate the leachability of metals. According to the results, using 2.5% of sewage sludge activated by NaOH and Na2SiO3 increases the UCS values from 176 kPa to 1.46 MPa after 7 d and 56 d of curing, respectively. The results of the DST indicate that sewage sludge as a precursor increases cohesion and enhances frictional resistance, thereby improving the Mohr-Coulomb parameters of the stabilized soil. The SEM micrographs show that alkali-activated sewage sludge increases the integrity and reduces the cavity volumes in the stabilized soil. Moreover, TCLP tests revealed that the solubility of metals in the treated soil alkali-activated by sewage sludge significantly decreased. This study suggests that using sewage sludge can replace cement and lime in ground improvement, improve the circular economy, and reduce the carbon footprint of construction projects.

Optimization of Geopolymers for Sustainable Management of Mine Tailings: Impact on Mechanical, Microstructural, and Toxicological Properties

This study investigates the use of geopolymer technology as an alternative for the management of mine tailings, which is a serious environmental problem in mining areas, including the Arequipa region of Peru. In this study, the mixture of stabilized mine tailings with different percentages of binders (i.e., metakaolin and pumice) and their impact on the mechanical, microstructural, and toxicological properties of the synthesized geopolymers were analyzed. The ratios of mine tailings to binder material varied between 100/0 and 0/100. The activation was carried out with an alkaline solution of sodium hydroxide (10 M) and sodium silicate (modulus 2.5). Specimens were fabricated as 50 mm cubes, and the seven mix designs were evaluated in triplicate. The evaluations included compressive strength at 7, 14, 28, and 56 days of curing, chemical analysis by Fourier Transform Infrared Spectroscopy (FT-IR), microstructural characterization by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS), thermal behavior by thermogravimetry and differential thermal analysis (TGA/DTA) between 40 °C and 1000 °C, and toxicological tests by the Toxicity Characteristic Leaching Procedure (TCLP, EPA 1311) to determine the efficiency of immobilization of toxic metals. The results demonstrate significant improvements in compressive strength for the F50 specimens compared to A0, with increases of approximately 300%, 270%, and 461% observed at 7, 28, and 56 days of curing, respectively, with microstructural stability with an average pore size of 7.21 μm, and efficiency in the immobilization of heavy metals in geopolymers with 30% or 40% binder (60%–70% mine tailings). The leachate concentrations of As, Cd, Pb, and Hg were below the established thresholds, indicating that the stabilized mine tailings can be classified as “non-hazardous materials”. Geopolymers with 30% to 50% binder showed strength development with microstructural stability and efficiency in the immobilization of heavy metals, complying with current regulations. Therefore, these geopolymers are suitable for various applications and in different environmental conditions.

Investigating the Level of Metal’s Toxicity in Used Cell Phone Batteries by TCLP and WET Methods

Introduction: Batteries are widely used in all kinds of electrical and electronic equipment. These batteries contain several metals that lead to the leakage of metals into the soil and underground water in the burial places, which pose serious risks to human health and the environment. Materials and Methods: In this study, the concentration of 15 metals (Ag, Al, As, Ba, Cd, Co, Cs, Cu, Fe, Li, Mn, Pb, Sr, Zn, Ni) in different components of 7 used battery models was investigated using Waste Extraction Test (WET) and Toxicity Characteristic Leaching Procedure (TCLP) toxicity. The concentration of metals was measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Metal concentrations were compared with the United States Environmental Protection Agency (USEPA) and California Department of Toxic Substances Control (CDTSC) standards. Results: The results showed that the average concentration of metals in both WET and TCLP methods was high, but the concentration of most metals in WET method was relatively higher than in TCLP method. Conclusion: The results showed that the recovery of metals from batteries is necessary, moreover safe burial of batteries is essential to reduce environmental risks.

Technical and environmental assessment of sludge-derived slag generated from high temperature slagging co-gasification process as a sustainable construction material

Tremendous amount of sludge is generated annually from freshwater treatment or sewage. The high temperature slagging co-gasification converts the sludge to slag showing the potential application for construction material. In this study, the physico-chemical properties of 4 types of slags generated from the co-gasification of municipal solid waste (MSW) with sludge from freshwater treatment or sewage, and ashes from sludge incineration are comprehensively analyzed. Leaching performance of the sludge-derived slag and mortar (with slag as the fine aggregate), as determined based on Toxicity Characteristic Leaching Procedure (TCLP), batch leaching and column leaching tests, indicates the slag can be considered safe for reutilization. Compressive strength test demonstrates that the mortars perform excellently and have the potential to replace sand in concrete production. The consolidation coefficient of slag (1.6 – 39.1 m2/year) is lower than the sandy silt but higher than clay. Additionally, the coefficient of permeability (∼1.96 × 10-3 m/s), angle of shearing resistance (∼39°), and undrained shear strength (375.5 ± 54.8 kPa) of the slag are comparable to sand. The life cycle assessment (LCA) is also conducted to evaluate the environmental impacts and benefits of reutilizing sludge-derived slag as an alternative material for concrete production and land reclamation.

Enhanced phosphorus adsorption using modified drinking water treatment residues: A comparative analysis of powder and alginate bead forms

This study provides an analysis of the phosphorus adsorption efficacy of three modified drinking water treatment residues (MDWTRs): MDWTR-P (powdered form), MDWTR-D2, and MDWTR-D5 (alginate bead-entrapped forms with bead diameters of 2 mm and 5 mm, respectively). The preparation process involved washing and drying the drinking water treatment residue, followed by grinding and sieving to achieve particle sizes below 90 μm. The residue was then incinerated at 600 °C in oxygen-limited conditions. Subsequently, the MDWTR was formulated into alginate beads by mixing with sodium alginate and FeCl3 solutions, resulting in spherical particles of specified diameters. The evaluation of surface area, pore volume, pore size, and CHN concentration revealed that MDWTR-D5 possesses the largest surface area (284.7 m2 g−1) and highest micropore volume (0.04 cm3 g−1), indicating a greater capacity for adsorption. SEM-EDS analysis demonstrated significant compositional changes post-treatment, particularly elevated phosphorus levels, confirming effective adsorption. Metal content analysis indicated high aluminum levels in MDWTR-P and increased iron content in MDWTR-D5. Toxicity Characteristic Leaching Procedure (TCLP) and in vitro bioaccessibility (IVBA) tests confirmed the non-hazardous nature of all MDWTRs, ensuring their safety for environmental applications. Kinetic analyses using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models highlighted the superior performance of MDWTR-D5, with the highest equilibrium adsorption capacity and initial adsorption rate across all tested concentrations, suggesting both high efficiency and rapid adsorption potential. Further validation using Langmuir and Freundlich isotherms revealed MDWTR-D5's highest monolayer adsorption capacity (22.88 mg g−1) and Freundlich adsorption capacity parameter (6.97 mg g−1). Statistical analysis via one-way ANOVA confirmed significant differences in phosphorus concentrations among the MDWTRs samples (p-value <0.001), consistently underscoring MDWTR-D5's superior adsorption performance. These findings highlight MDWTR-D5's potential as an effective adsorbent for phosphorus removal in wastewater treatment, emphasizing its applicability in environmental remediation strategies.

Fluoride removal using a rotating anode electro-coagulation reactor: Parametric optimization using response surface methodology, isotherms and kinetic studies, economic analysis and sludge characterization

The presence of fluoride in drinking water can cause various diseases, such as dental fluorosis and skeletal fluorosis. The present study aims to intensify the fluoride removal using a rotating anode electro-coagulation (EC) reactor with providing the proper hydrodynamics conditions. This fluoride removal is modeled and optimized using Response Surface Methodology (RSM) and central composite design (CCD) with varying operational parameters (rotation speed: 20–80 RPM, current: 0.2–1.0 A, initial fluoride concentration: 8–40 mg/L and time: 15–75 min). The maximum fluoride removal is obtained as 96.87% (predicted) and 95.40% (experimental) for the optimized process parameters, initial concentration of 32 mg/L, 0.8 A current, 60 min, and 60 RPM of rotating speed. Kinetic analysis reveals that the removal process adheres to a second-order kinetic model, suggesting that the rate of fluoride removal is dependent on the concentration of fluoride ions present. Isothermal studies indicate that the effective sorption of fluoride onto the generated flocs follows a sips isotherm. The optimal cost analysis is carried out to determine the operational cost as 0.256 USD/m3 for F removal of 93.49% at initial concentration 24 mg/L, time 50 min, current 0.7 A, and rotation 70 rpm and presenting a cost-effective solution for fluoride mitigation. Further, characterizations of the resultant sludge through X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and the Toxicity Characteristic Leaching Procedure (TCLP) confirmed the safe disposal potential of the sludge. The findings show a promising approach for fluoride removal, combining high efficiency, economic viability, and environmental safety.

Revolutionizing Waste Management: Solidification of Landfill Leachates Using Alkali-Activated Slag

AbstractLandfill leachate is a highly hazardous effluent characterized by a high concentration of recalcitrant pollutants, presenting a significant environmental challenge. This study investigated the solidification of landfill leachate contaminants using sodium hydroxide-activated Granulated Blast Furnace Slag (GBFS). The stability of the resulting geopolymer was evaluated through unconfined compressive strength and leaching tests. Optimal curing conditions were identified as 7 days at a sodium hydroxide concentration of 12 M, achieving an unconfined compressive strength of 45.738 MPa at a liquid-to-solid ratio of 15%. A linear relationship was observed between the liquid-to-solid ratio and flow workability, with maximum flow workability evidenced by an average diameter of 242 mm at a liquid-to-solid ratio of 0.25. However, a minimum liquid-to-solid ratio of 0.15 was necessary to obtain a workable mortar. The produced geopolymers were characterized using X-ray Fluorescence (XRF) for mineralogical analysis, Scanning Electron Microscopy (SEM) for morphological examination, and the Toxicity Characteristic Leaching Procedure (TCLP) for leaching tests. The findings demonstrated the successful solidification of landfill leachate using GBFS geopolymer. The leachability tests revealed that the geopolymer did not release metals in concentrations exceeding the allowable limits set by the United States Environmental Protection Agency (USEPA), indicating effective encapsulation of the pollutants within the geopolymer matrix. Furthermore, the resultant geopolymer brick is eco-sustainable and can be classified as a green construction material.

Strength, durability, and toxicity characteristics of water treatment sludge based geopolymers for subgrade application

This study examined the strength, durability and toxicity characteristics of geopolymer made from water treatment sludge (WTS) using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binding materials for the subgrade application. The mechanical properties of WTS-FA-GGBS geopolymers were assessed considering various parameters such as binder proportions, curing period, curing condition, Sodium silicate (SS) to Sodium hydroxide (SH) ratio (i.e. SS/SH), and Sodium hydroxide (NaOH) concentration. The results showed that increasing binder proportions, NaOH concentration, and curing period positively impacted the strength of the WTS-FA-GGBS geopolymer. The unconfined compressive strength (UCS) of the geopolymer samples with an SS/SH ratio of 2.5 showed higher compressive strength than those at an SS/SH ratio of 1. WTS-FA-GGBS geopolymers cured at 100°C showed increased UCS values after 1 to 3 days, but strength decreased after 7 days due to a faster geopolymerisation reaction, resulting in excessive moisture loss and microcracks in the geopolymerized samples. The study also found that all the geopolymer samples met the minimum strength criteria for cement-stabilized mix with a maximum mass loss of 8.17 % are well within the specified limits (<14 %) as per IRC:37–2018. The California Bearing Ratio (CBR) values of WTS-FA-GGBS geopolymers, which range from 41.11 % to 260.32 %, surpass the minimum criteria for cement stabilized subgrade or subbase material, as specified by IRC: SP:89–2010. Additionally, the changes during geopolymerization were confirmed by FESEM, EDS, and XRD analysis. The toxicity characteristic leaching procedure (TCLP) test results showed that the amounts of heavy metals in the geopolymer leachate were within the USEPA-mandated limits.

Selenium and concomitant anions removal in a fixed bed bioreactor to satisfy drinking water regulations and subsequent stability check of selenium-laden biosludge

This is the first successful report on selenium bio-attenuation to satisfy drinking water regulations as per Indian Standards (10 μg/L) in the presence of concomitant nitrate and sulfate from water sources utilizing a fixed bed bioreactor. The bioreactor was immunized with blended microbial culture and worked in downflow mode under anoxic conditions at 30 ± 2 °C for around 190 days under varying influent selenate (100–500 μg/L as selenium), nitrate (50 mg/L), sulfate concentrations (as per selenium removal) and necessary dose of acetic acid (as COD, a carbon source) in synthetic groundwater, operated at an empty bed contact time (EBCT) of 45–120 min. After supplying an adequate dosage of sulfate and alteration of EBCT, selenium was found to comply with drinking water regulations and nitrate was completely removed. X-ray diffraction and transmission electron microscopy analyses depicted nanocrystalline selenium sulfides (SeS and SeS2) formation as the possible mechanisms of selenium removal. Extended toxicity characteristic leaching procedure (TCLP) extractions confirmed a maximum selenium leaching of 52 and 282 μg/L during anoxic and oxic extractions, respectively. Long-term column leaching (>3-month equilibration) under aerobic conditions at pH 7 confirmed the produced precipitate to be essentially stable (∼0.14% Se leaching). This work exhibits the synchronous bioremoval of selenium and its co-anions from contaminated water complying with drinking water standards, and leaving a stable and non-hazardous selenium-laden biosludge.

In-situ halloysite coupled with ex-situ nano-aluminosilicate on heavy metals fate during pyrolysis of solid wastes in a rotary kiln and potential application of pyrolysis residue

During the pyrolysis of heavy metal-containing solid waste, the immobilization and stabilization of heavy metals (HM) is of great significance for its safe disposal and resource utilization of pyrolysis products. This study aims to enhance the enrichment and stability of HMs in pyrolysis residues from HM-containing solid waste in a rotary kiln by combining in-situ halloysite (Hal) with ex-situ nano-aluminosilicate (NC2.6). With 13 % Hal and 10 % NC2.6, the relative retention rate of Cd, Pb, Zn, Cu, and Cr increased by 4.82 %, 29.45 %, 20.98 %, 1.71 %, and 2.61 %, respectively, at 700 ℃. Bureau Communautaire de Référence (F4 > 85 %) and Toxicity Characteristic Leaching Procedure (7.536 mg/L at 10 % addition ratio) extraction results showed that NC2.6 adsorption products exhibit low toxicity, suitable for landfill disposal. The mobility of HMs in pyrolysis residues significantly decreased with increasing temperature and Hal addition. At 13 % Hal addition, low-risk pyrolysis residue (RI = 22.23) was obtained at 700 ℃. Dynamic adsorption experiments evaluated the feasibility of using this pyrolysis residue for methylene blue (MB) adsorption. Under the conditions of a 6 cm adsorption column height and a solution flow rate of 2.5 mL/min, the HM concentration in the effluent met relevant standards, and the adsorption capacity reached 22.733 mg/g. Furthermore, DFT simulations explored the effect of HMs in biochar on MB adsorption, revealing that the adsorption energy between Zn and N reached −281.03 kJ/mol, significantly lower than that of common oxygen-containing functional groups (COC, CO, HOCO, and OH), indicating more stable adsorption. The findings of this research offer novel insights into the immobilization of HMs during the pyrolysis of HM-containing solid waste and resource utilization of HM-containing pyrolysis residue.

Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Objectives : This study aims to evaluate the feasibility of converting waste chitosan adsorbents, laden with microalgae, into biochar for application as a stabilizing agent to remediate heavy metal-contaminated soil and improve soil quality.Methods : Waste chitosan adsorbents were converted into biochar through two processes: dry thermal carbonization at 400°C to produce pyrochar and hydrothermal carbonization at 200°C to produce hydrochar. The elemental compositions, surface functional groups, morphologies of the biochars were evaluated by elemental analyzer, FT-IR spectrometer, and SEM analysis. The arsenic and heavy metal adsorption characteristics of the produced biochars were assessed. Additionally, the produced biochars were applied as stabilizing agents to arsenic and heavy metal-contaminated soil with varying mixing ratios of 2, 5 and 10 wt%. After a one-week soil stabilization experiment, soil properties and TCLP(Toxicity Characteristic Leaching Procedure) leaching tests were conducted.Results and Discussion : The pyrochar produced from waste chitosan exhibited a porous structure with high pH (pH 10) and minimal surface functional groups. The hydrochar consisted of spherical particles with functional groups such as hydroxyl and amine groups on the surface, exhibiting a slightly acidic pH of 5.8. Pyrochar has a higher adsorption capacity for cationic heavy metals compared to hydrochar due to its porous structure and high pH. On the other hand, when applied to soil, hydrochar demonstrated superior stabilization efficiency for arsenic and heavy metals. This is attributed to the diverse surface functional groups containing oxygen on the hydrochar. The stabilization efficiency was influenced by the biochar mixing ratio, with a 5% hydrochar application resulting in 10-64% stabilization efficiency for all elements.Conclusion : This study confirmed that biochar produced from waste chitosan effectively stabilizes arsenic and heavy metals in soils. Additionally, the quantity of biochar used can impact its effectiveness in stabilization.

Sustainable reuse of modified incineration sewage sludge ash (M-ISSA) for stabilization of highly As-contaminated soil

Arsenic (As) is an environmental hazardous contaminant, seriously threatening human health. Chemical activation can effectively enhance As adsorption performance of incinerated sewage sludge ash (ISSA). Through modification, the iron (mainly present as hematite) in the ISSA was rearranged to KFeO2. Based on the results of the present study, addition of modified ISSA (M-ISSA) in contaminated soil had a positive effect on As immobilization. A set of laboratory batch experiments including toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), and sequential extraction procedure (SEP) were carried out to investigate effects of M-ISSA dosages and curing time on immobilization of As contaminated soil (100, 500, 1000 mg As/kg soil). Results indicated that a higher addition amount of M-ISSA enhanced the effectiveness of stabilization and significantly reduced the As leachability after a stabilization period of 28 d. Particularly, in 1000 mg As/kg soil, M-ISSA reduced the labile As concentration in the TCLP test from 21.45 to 0.73 mg/L and in the SPLP test from 27.75 mg/L to 7.83 mg/L. M-ISSA transformed As in soil to more stable forms that were bounded to amorphous iron hydrous oxides. The number of stable fractions saw a sharp rise from 31% to 60%, when the M-ISSA addition was 5%. Different characterizations were conducted including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), in order to demonstrate the stabilization behavior and mechanism of As and M-ISSA. The main stabilization mechanism was associated with adsorption and coprecipitation processes. Overall, this study proposed a novel recycling method for ISSA that could be chemically modified into a reliable and efficient additive for the immobilization of As contaminated soil.

Sustainable Stabilization of Cadmium (Cd)-Contaminated Soil with Biochar-Cement: Evaluation of Strength, Leachability, Microstructural Characteristics, and Stabilization Mechanism

ABSTRACT To facilitate the solid waste reuse of cadmium (Cd)-contaminated soil and biochar and reduce the high emission of cement materials, we employed biochar-cement composite stabilizer to remedy Cd-contaminated soil. We assessed the effects of the biochar-cement composite stabilizer dosage and curing time on stabilized soil strength by using unconfined compressive strength (UCS) tests, leaching concentration and stabilization rate in Cd-contaminated soil stabilized by biochar-cement by using toxicity characteristic leaching procedure, and mechanism of change in strength and leaching characteristics by using scanning electron microscopy and X-ray diffraction. The research results demonstrate that biochar addition to cement-stabilized soil promoted cement hydration reaction and increased particle agglomeration. A low dosage of biochar improved stabilization effects. The optimal biochar dosage was 5%, which enhanced the early growth speed of the UCS. More cement improved the stabilized soil’s UCS. At a 5% cement dosage, adding biochar significantly reduced Cd leaching concentration, and improved the stabilization rate. At a 10% cement dosage, the biochar-cement composite stabilized soil’s stabilization rate was >99.8%. Calcium silicate hydrate, calcium aluminate hydrate, and ettringite were the main products of biochar-cement stabilized soil that filled soil and biochar pores; these substances encapsulated, adsorbed, or exchanged ions of Cd2+, achieving stabilization effects.

Mechanical properties and stability of zinc-contaminated red clay cured by MICP synergistically activated MgO

Microbially Induced Carbonate Precipitation (MICP) technology offers an innovative approach for the solidification and stabilization of heavy metal-contaminated soils; However, the mechanical strength and long-term stability of this remediation method have not been thoroughly investigated. This study introduces an innovative curing and stabilization technique using MICP-activated MgO to address the geotechnical challenges posed by zinc ion-contaminated soils. To investigate the effect of zinc ions on soil and the optimal efficacy of MICP-activated MgO in curing zinc contamination, experiments were conducted on zinc-contaminated soils with varying zinc ion concentrations (0.05%, 0.1%, 0.5%, 1.0%), dry densities (1.35, 1.4, 1.45, 1.5g/cm³), and activated MgO admixtures (1%, 2%, 5%, 10%). The effectiveness of MICP-activated MgO was evaluated through macroscopic analysis and stability tests, including unconfined compressive strength tests, direct shear tests, and the Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that zinc ions disrupted soil particle cementation, enlarged inter-particle pores, and significantly reduced both unconfined compressive strength and shear strength. The optimal dosage of MICP-activated MgO for curing zinc-contaminated soil was determined to be 10%, resulting in an unconfined compressive strength of 1.196MPa and a Zn2+ leaching concentration of 0.1414mg/L. The combined actions of MICP-activated MgO facilitated the formation of alkaline magnesium carbonate, calcium carbonate, and magnesium hydroxide. These compounds filled the inter-particle pores of zinc-contaminated soil, encapsulating and co-precipitating zinc ions, thereby enhancing the soil's strength and stability. These findings establish a theoretical foundation for the engineering application of MICP-activated MgO in the remediation of zinc-contaminated soils.

Impact of biochar produced at different pyrolysis conditions on heavy metal contaminated soil.

This study aimed to assess the effectiveness of urban derived biochars such as Sugarcane bagasse (SB), Brinjal Stem (BS), and Citrus Peel (CP) produced at two different pyrolysis conditions (450 and 600°C for 60min) for soil heavy metal bioremediation potential. An ex-situ study was conducted to remediate single heavy metal-contaminated SoilRite with lead (Pb), copper (Cu), chromium (Cr) and cadmium (Cd), with biochars applied at different rates. Heavy metal status in soilrite was evaluated using various extraction methods (water-soluble, exchangeable, TCLP (Toxicity Characteristic Leaching Procedure), and PBET (Physiologically Based Extraction Tests)) to determine the biochar treatments' efficacy. The findings show that SB biochar at 450-60 are more effective in immobilizing heavy metals in water-soluble (Cd-100% Pb and Cu-70%), exchangeable (Pb:91%, Cd and Cu by 70-80%) and PBET-extracted forms (Cd-91%, Pb-80%, and Cu-75%), whereas biochar derived from BS (84%) and CP (90%) at 600-60 are more effective in immobilizing TCLP-extracted form of Pb and Cu. Urban derived biochars significantly reduced the toxicity of Pb, Cu, and Cd in various extractable forms and can stabilize and convert them into less accessible forms except for Cr. These extraction methods aid in evaluating environmental risks and influencing remediation strategies for soil heavy metal pollution. Urban biochar, as a cost-effective and eco-friendly solution, significantly solves this issue, facilitating sustainable waste management.

Study on heavy metal leaching from steel slag in coastal soft soil and its environmental impact

ABSTRACT To explore the environmental impact of steel slag deposited within a coastal soft soil foundation, the steel slag produced by a steel plant in Fangchenggang city was chosen as a case study. Seawater was collected from the coastal foundation, and water with different levels of salinity was obtained by low-temperature evaporation, filtration, sterilisation, and dilution. Leaching tests of steel slag in artificial seawater with different levels of salinity were carried out according to the Toxicity Characteristic Leaching Procedure (TCLP). The results showed that with the increase in the leaching time and salinity of the solution, the concentration of heavy metals in solution displayed an upward trend; however, the rate of increase decreased once the concentration reached a certain level. From an environmental perspective, it is not advisable to use steel slag as a filler near drinking water, and steel slag should not be used as a foundation material in the high-salinity coastal soft soil layer.