Toxicity Characteristic Leaching Procedure Research Articles

Sustainable use of ferrochrome slag and quarry dust composites as cement-bound layers of flexible pavement

<p>In this study, an attempt was made to characterize ferrochrome slag as cement-bound layers of flexible pavement in view of its leaching behavior. Toxicity Characteristic Leaching Procedure (TCLP) test was conducted to assess the mobility of toxic elements in ferrochrome slag. Ferrochrome slag aggregate was classified as a non-hazardous material that has good physical and mechanical properties. The standards for cement stabilization set forth by the MoRTH can be met by two gradations, ferrochrome slag(F) and quarry dust(Q) in the ratios of 70/30 and 60/40(F/Q) respectively. Cylindrical specimens of cement contents (2%, 4%, and 6% dry weight, respectively) were cast at optimum moisture content and maximum dry density for 7 and 28 days of curing to perform unconfined compressive strength. The cylindrical specimens are subjected to a series of cycles consisting of alternative wetting and drying, and the corresponding weight loss for each cycle is recorded in order to evaluate the effect of subsequent cycles. The strength of cement-treated ferrochrome slag and quarry dust mixtures was measured before and after they were subjected to durability testing. The cement-treated F60Q40 mix showed better performance than the F70Q30 mix and it can be efficiently utilized as a replacement for granular sub-base and base courses of flexible pavement, thereby reducing leaching and environmental pollution.</p>

Utilization of phosphoric acid-modified biochar to reduce vanadium leaching potential and bioavailability in soil

Remediating vanadium (V) polluted soil has garnered widespread attention over the past decade. Yet, few research projects have investigated the stabilization of soil V using modified biochar, so the effects and interacting mechanisms between soil properties and modified biochar for V immobilization and stabilization remain unclear. Hence, this gap is addressed by determining the leaching behavior and mechanisms of soil V on different dosages of phosphoric acid (H3PO4) impregnated biochar (MLBC, 0.5%–4%). The applicability and durability in soil V immobilization was investigated under acid precipitation. The MLBC effect on V bioavailability and mobility was assessed first by CaCl2, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) extractions in different periods. The V concentrations significantly reduced in CaCl2, TCLP, and SPLP extract with MLBC at each dosage (30 d), while slight to significant increase in SPLP and TCLP extract V was recorded in a long-term incubation (90 d). Column leaching test further demonstrated the high durability of 4% MLBC in V stabilization under continuous acid exposure. Compared to the control (no-biochar), the accumulated V content in the leaching solution significantly decreased in MLBC-amended soil. Acid soluble fraction of V showed significant negative correlation with both soil organic matter (SOM) and available P, which was positively correlated with pH, suggested that pH, available P and SOM were key factors affecting the bioavailability of V in soil. Moreover, combining with the characterization results of MLBC and amended soil, the results revealed that H3PO4 modified biochar played a vital role on V immobilization and soil improvement by forming electrostatic adsorption, ion exchange, redox reaction or complexation with the increase of functional groups. These revealed an efficient and steady development of soil quality and treatment for soil V contamination, under MLBC operation to soil polluted with exogenous V.

Strength and leaching behavior of tailing-based paste backfill at high water content amended with lime activated ground granulated blast furnace slag and flocculant.

Flocculent is commonly used in mining activities to improve the concentration of tailing slurry by enhancing the sedimentation process of small tailings particles. The presence of flocculent in thickened tailings is unavoidable, and it affects the heavy metal leaching performances and mechanical and rheological characteristics of tailing-based cemented paste backfill (CPB). This study is carried out to investigate the physicochemical and leachability of CPB amended with flocculants and lime-activated ground granulated blast-furnace slag (GGBS). The stabilized samples were subjected to a series of model tests, including toxicity characteristics leaching procedure (TCLP) and pH, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction. Moreover, the CPB amended with anionic polyacrylamide (APAM) demonstrated better performance in terms of a decrease in heavy metal leachability besides higher mechanical strength than poly aluminum chloride (PAC) and poly ferric chloride (PFC) samples. Furthermore, the UCS results showed that increasing binder content up to 15% negatively influences strength improvement of all stabilized samples because of weak connections between soil particles and cementitious material, resulting in high leachability of heavy metals. The analysis of XRD and SEM showed that anionic polyacrylamide (APAM) cases exhibited more voluminous hydration products, resulting in a compact stabilized matrix and substantially reduced heavy metal leachability.

Innovative technology and mechanism for comprehensive recovery of copper, nickel, zinc and iron in electroplating sludge

Electroplating sludge is a product of the purification of the electroplating wastewater by neutralization or flocculation precipitation, which belongs to dangerous solid waste. In the study, copper, nickel, zinc and iron from electroplating sludge were recovered by an innovative sulfidation roasting-flotation-magnetic separation technology. The effects of the crucial parameters on the sulfidation ratio of copper and nickel and the volatilization ratio of zinc during the sulfidation roasting were investigated. Under the optimal condition of the sulfidation roasting, the volatilization ratio of zinc reached 78.10 % and the sulfidation ratios of copper and nickel were 88.55 % and 97.86 %, respectively. The migration rule of valuable metals in the roasting process were illustrated by XRD and SEM-EDS. By the flotation treatment for the roasting products, copper-nickel mixed concentrates containing copper 2.377 % and nickel 10.28 % were obtained, and the recoveries of copper and nickel reached 83.73 % and 85.00 %, respectively. After treatment by the flotation, magnetic separation was carried out to obtain iron concentrate with iron grade and recovery of 73.77 % and 12.41 %. Finally, the toxicity characteristic leaching procedure was employed to prove the excellent stability of the heavy metals in the tailing. The study realized the efficient, comprehensive recovery of copper, nickel, zinc and iron from electroplating sludge, and provided a new idea for the harmless and resource utilization of electroplating sludge.

Soil residue ecotoxicology from biosurfactant extraction for oily soil decontamination process

Solvent extraction as part of oily soil decontamination process has been including rhamnolipid biosurfactant to be part for seeking its possibility for further implementation. Result of some researchers reported prospect of its implementation due to removal efficiency. This study reported post treatment process assessment to soil residue that remained after the completion of decontamination process. Soil toxicity examined involving Total Petroleum Hydrocarbon (TPH) concentration, Hydrocarbon Structure by using Gas Chromatography-Flame-Ionization Detection (GC-FID), Hydrocarbon bond identification by using Fourier Transform Infra-Red Spectroscopy (FTIR), Toxicity Characteristics Leaching Procedure (TCLP) analysis, Metal and Oxide Metal Content of the residual soil. Germination Index as biological indicator also involved as part of the study to give early indication of impact on residual treated soil. Germination index selected mung bean (Phaseolus radiatus) as object of study. Result showed that at residual soil TPH content could be reduced until 0.78%, there are simplification of hydrocarbon structure after treatment process included weakened of hydrocarbon bonding and concentration observed by FTIR. TCLP result showed residual soil was benign to the environment and Germination Index indicated improvement of mung beans germination after decontamination process.

A review of toxicity assessment procedures of solar photovoltaic modules

Environmental management of solar photovoltaic (PV) modules is attracting attention as a growing number of field-operated PV modules approach end of life (EoL). PV modules may contain small amounts of toxic metals, and the procedures for assessing and regulating the toxic metal content and release of such materials at EoL differ widely across nations. This paper provides an overview of the metal composition of PV modules and common procedures for toxicity assessment through extensive research and review of technical literature and legislative documents. This review focuses on three primary aspects: first, it explores the distribution of toxic elements within current and emerging PV module designs, with a specific focus on obtaining representative samples for proportional toxicity testing within different module laminate areas. Second, it examines a sampling standard and the diverse toxicity testing methods and regulations employed in various regions, encompassing standards like the Environmental Protection Agency (EPA) Test Method 1311 (Toxicity Characteristic Leaching Procedure, TCLP) in the U.S., Restriction of Hazardous Substances (RoHS) in Europe, and the Waste Extraction Test (WET) in California. Third, the review examines the sources of variability in toxicity testing outcomes, including techniques for securing homogeneous samples from non-uniform PV modules, selecting particle sizes representative of landfill conditions in extracted samples, determining appropriate leachate characteristics such as leaching agents and pH levels, and considering factors like test duration and temperatures. In summary, this review summarizes relevant regulations and offers a comprehensive overview of the strengths and limitations associated with several toxicity assessment procedures currently in practice.

Physicochemical properties of clayey deposits slurry treated by lime-activated ISSA and GGBS considering seawater salinity effect

This study sheds light on the engineering and environmental performance of lime-activated incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) treated Hong Kong marine deposits (HKMD) slurry by stabilisation/solidification (S/S) technology, which is proposed using as fill materials in reclamation projects. The S/S performance of the treated HKMD with distilled water and seawater under different salinities was investigated. The results show that seawater could help S/S treated HKMD gain strength by using activated industrial wastes (ISSA and GGBS). The hydration and pozzolanic reactions between ISSA, GGBS, CaO and clayey compositions in HKMD make contributions to the strength development, porosity decrease and heavy metals stabilisation, which is supported by the characterization analysis including thermo-gravimetric (TG) analysis, mercury intrusion porosimetry (MIP) tests, nitrogen adsorption/desorption isotherms (NAI), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and the leaching test of toxicity characteristic leaching procedure (TCLP). Seawater of 1.8% salinity (18 g/kg) is better than the distilled water and seawater of 3.6% salinity as a substrate solution in the S/S treated HKMD, because of the highest unconfined compressive strength and lowest porosity in the treated samples. The highest pH may account for its highest strength under the 1.8% salinity conditions. The S/S process could effectively stabilize the contaminants regardless of the curing time and the salinity of the mixing solution, and the leachates from the stabilized HKMD are environmentally safe and meet the requirement of standard in Hong Kong on the recycling treated soil. Therefore, recycling wastes—ISSA and GGBS with lime can be used as an appealing binder to stabilize/solidify marine deposits as environmental-friendly reusable materials in reclamation projects.

Reusing ceramic waste in fired brick and as cement additive

AbstractBACKGROUNDAlthough there has been considerable research on the utilization of ceramic and tile waste (CTW) in concrete production, there has been a noticeable lack of studies examining its application in fired brick manufacturing and the use of ceramic glaze powder as an additive in cement. The aim of this study is to assess the potential of reusing CTW as concrete aggregate and as part of fired brick composition. Furthermore, this research investigates the potential application of glaze powder as a novel cement additive, which has not been previously explored.RESULTSThe results indicate that bricks made from waste materials had a moisture absorption of 12.2% and flexural strengths ranging from 15.39 to 24.2 MPa. X‐ray diffraction analysis showed that quartz and kaolinite were the dominant crystalline phases in bricks made from raw glazed ceramic. The concentration of heavy metals in the toxicity characteristic leaching procedure leachate of the waste materials decreased after the firing process during the manufacturing of bricks due to oxidation, immobilization and encapsulation processes, with levels below standard limits. In concrete, the use of 20% ceramic glaze powder as a partial cement replacement resulted in a 55% increase in compressive strength. Additionally, the leaching of barium decreased by 70% and that of strontium decreased by 17%.CONCLUSIONThis study highlights the promising utilization of CTW in fired brick production and the effective incorporation of ceramic glaze powder as a cement additive. The findings suggest enhanced mechanical properties and decreased heavy metal leaching, indicating the viability of CTW reuse in sustainable construction practices. © 2023 Society of Chemical Industry (SCI).

Stabilization/solidification of heavy metal-contaminated marl soil using a binary system of cement and fuel fly ash.

The stabilization/solidification (S/S) method is one of the most effective remediation techniques for treating contaminated soils. Several stabilizers, mostly the cementitious materials, have been used for the S/S treatment. In this paper, the feasibility of utilizing fuel fly ash (FFA) as a partial replacement of ordinary Portland cement (OPC) for the S/S treatment of marl soil contaminated with heavy metals was investigated. Two industrial waste materials, namely steel and electroplating wastes, were used to synthetically contaminate the marl soil. The stabilizers comprising of OPC and FFA were mixed with the contaminated soil at different dosages ranging from 10 to 40%, by mass, and a total of 48 S/S-treated soil mixtures were prepared. A series of experiments, including density, porosity, permeability, unconfined compressive strength (UCS), and toxicity characteristics leaching procedure (TCLP), were carried out on the soil mixtures to evaluate the efficiency of the proposed S/S treatment. Test results showed that the incorporation of FFA at higher volumes reduced the density and increased the porosity and permeability of the treated mixtures. Although FFA addition resulted in reducing the UCS values by an average of 46%, and this reduction was more significant at higher FFA percentages, the UCS values of all mixtures were more than 0.35 MPa (350 kPa), which passed the minimum requirements set by USEPA. In addition, the metal immobilization ability of the proposed treatment was confirmed by the TCLP analysis. As compared to the negative effect of the contamination of the soil by the electroplating waste, the contamination of the soil by steel waste had a higher negative effect. The results of this study would contribute in selecting an environment-friendly treatment of the contaminated soils using industrial waste materials, such as FFA, as a partial replacement of OPC. Nevertheless, the present study is an initial attempt to explore the possibility of utilizing FFA as a partial replacement of OPC in S/S treatment of marl soil contaminated with heavy metals. It is recommended to conduct another study in future including analysis of the treated soil mixtures using XRD, SEM, and FTIR techniques to better understand the stabilization/solidification mechanism and its implications on the test results.

Physicochemical characteristics of bottom ash from waste-to-energy incineration pilot plant in Indonesia

Municipal solid waste (MSW) disposal has emerged as a major concern in large cities across Indonesia. Waste-to-energy (WtE) incineration is an attractive method that can significantly reduce volume of waste; however it generates residues, namely bottom ash and fly ash. This study presents the characteristics of bottom ash from the MSW WtE incineration pilot plant in Indonesia. The physicochemical characterization of bottom ash was determined X-ray fluorescence (XRF) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). The results showed that CaO (46.80%) was the major component, followed by SiO2 (12.30%), Al2O3 (8.80%), and Fe2O3 (8.20%). SEM images showed that the surface morphology of bottom ash appeared flaky, rod-like, and irregular shape. Inert materials, like iron scrap, glass, ceramic, and stone, accounted for 16.7% of the total dry weight of bottom ash. Toxicity characteristic leaching procedure (TCLP) test of 11 heavy metals in bottom ash was carried out, and all of them were detected at very low concentration, indicating that bottom ash possessed a low risk level to human health and environment. This study provides important information on the characteristics of bottom ash from MSW WtE incineration in Indonesia that would be useful in facilitating management and disposal of bottom ash.

Turning fly ash and waste gypsum into a resource for backfilling applications

Flue Gas Desulfurization Gypsum (FGDG), an industrial by-product generated by power plants, was thermally treated and incorporated in cement-free fly ash bricks. This study aimed to determine the effects of using a thermally treated FGDG as an additive to improve the mechanical and structural properties of cement-free fly ash bricks. FGDG was thermally treated for 2 h at different temperatures. The influence of varying amounts (10–50%) of thermally treated FGDG on the performance of cement-free bricks was analyzed through mechanical properties, micrography, durability, the evolution of particle size distribution and environmental characteristics experiments. The effect of curing temperatures and curing age on the strength development and microstructural properties was also investigated. A Toxicity Characteristic Leaching Procedure (TCLP) was carried out to determine the leachability of metals from the synthesized FA cement-free brick. The results showed that the FGDG had a high calcium oxide content. In contrast, FA is mainly composed of silica, and both materials carry cementitious properties making both good raw materials for this study. The FA cement-free bricks containing 30% of thermally treated FGDG, oven-cured at 60 ℃, yielded the highest unconfined compressive strength (UCS) of 7.14 MPa. However, curing at ambient temperature for 28 days yielded a better UCS of 7.37 MPa. The particle size distribution showed that particles transformed from fine particles at 7 days to larger particles at 28 days due to particle growth. Durability tests showed that the developed bricks could withstand 7 wet/dry cycles. The TCLP showed that the leachability concentrations of all metals are within the limit and, therefore, can be potentially used as a building material in backfilling. The synthesis of FA/FGDG composite will aid in reducing the generated waste gypsum in landfills consequently eradicating human health challenges and loss of biodiversity. This paper showed that developing FA/FGDG composites will reduce their environmental impact and make them a resource for other valuable products such as backfilling applications and green building bricks.

The beneficial reuse of contaminated sediment: Long-term assessment of fly ash and lime-based mixtures

In recent decades, sediment has been recognised as a problematic resource due to its potentially harmful effects and the large quantities present in water bodies. There is a need to properly manage large quantities of dredged sediments so that they can be used as a resource and not necessarily treated as a waste product. This research investigates the effects of ageing and maturation of solidified/stabilized mixtures of contaminated sediment with fly ash and lime. The effects of ageing on the microstructural properties and chemical integrity of mixtures were studied for 7 days, 28 days, and 7 years using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), X-ray diffraction analysis (XRD), and DIN (German Standard Procedure for Water, Wastewater and Sediment Testing (Group S)) and TCLP (Toxicity Characteristic Leaching Procedure) leaching tests. The results of the microstructure and strength analysis showed that the use of fly ash and lime as binders promoted the permanent structural integrity of the sediment. The treated sediment with 20 wt% fly ash and 10 wt% lime (F20L10) achieved higher overall strength compared to the mixture containing only 30 wt% fly ash (F30). The speciation and redistribution of metals and As in the treated sediment mixtures during the long-term evaluation indicate a strong reduction in their mobility. This material can be considered environmentally friendly and can be used as a fill material in road construction. The investment and operating costs are justified in this solution for sediment management. However, it is important to monitor the produced material over time to ensure that it remains effective and sustainable in the long term.

Mechanical and environmental performances of an epoxy-resin-based recycled artificial stone containing hazardous sediment

Solidifying and stabilizing hazardous sediment from petrochemical activities are not only expensive but make also high-volume waste to landfills. Parallel, finding alternative aggregates with lower costs can reduce the capital cost of artificial stone. For the first time, a combination of hazardous sediments and stone waste was used as aggregates to produce the recycled artificial stones. Furthermore, the target of this study is to evaluate the behavior of these recycled artificial stones under external forces and weathering, as well as in the acid environment. In order to evaluate the properties of the stones containing hazardous sediment, the compressive strength, the brightness variation, and water absorption under UV radiation, 60 cycles of salt attack, 60 cycles of freezing and thawing, and 60 cycles of thermal shock cycles were evaluated. In order to assess the leaching of heavy metals, according to the US toxicity characteristic leaching procedure (TCLP) and DIN38414-S4, two leaching tests were used to evaluate the leaching of the heavy metals under rainfall and acid environment, like soil. In order to conduct leaching tests, three spices from the crushed zone of the stone under compressive test were used. The results show that the stones have suitable performance in comparison to the performance of the artificial stone containing nonhazardous sand, travertine stone, and treated travertine stone using epoxy resin and nanocomposite. Based on the results, P90HSa10Eb25T25, with 39.3 MPa compressive strength, 3.02 color variation under 60 cycles of salt attack, and 1.59 color variation under UV radiation, has the best performance among the recycled artificial stones.

Mechanical activation for sulfidic tailings treatment by tailings: Environmental aspects and cement consumption reduction

Sulfidic mine tailings are one of the massive hazardous solid wastes, containing large amounts of toxic heavy metals. Poor management of tailings can lead to the production of acid mine drainage and the heavy metal transfer emissions into the environment. Thus, in this study, mechanical activation was used to reuse a combination of carbonate tailings (TC) and sulfidic tailings (TS) for concrete construction purposes and to effectively immobilize heavy metals. The results showed that after tailings treatment, the heavy metal leaching rate was significantly below the allowed criteria based on the toxicity characteristic leaching procedure (TCLP). The mercury intrusion porosimetry (MIP) test results on the specific surface area and porosity after the activation pointed out increase and reduction, respectively. In the concrete sample containing 20 % cement-replacing activated tailings, the critical pore diameter after 28 curing days was 60 nm, which was less than that of the control sample with a critical pore diameter of 150 nm. According to X-ray diffraction (XRD) and scanning electron microscopy (SEM), ettringite and calcium silicate hydrate gel acted as hosts for heavy metals ions and played an inevitable role in stabilizing metal pollutants. Results revealed that the compressive strength of the sample containing 20 % of the activated tailings after 28 curing days was 31.2 MPa, which was higher than the strength of the control sample (26.99 MPa). Overall, it was concluded that the combined mechanically activated mine tailings can be a viable substitute for cement (up to 40 %) for constructing concrete samples. The utilized combined approach led to diminish adverse effect of sulfide content in concrete samples besides the cement consumption reduction.

Epoxy resin for solidification/stabilization of soil contaminated with copper (II): Leaching, mechanical, and microstructural characterization

Among different types of heavy metal-contaminated soil, copper (Cu)-contaminated soil is very serious, and the Cu concentration in it is usually very high. It is common to solidify/stabilize Cu-contaminated soil using alkaline cementitious material. However, the remediated Cu-contaminated soil fails to meet the requirements of environmental safety and load-bearing capacity. This dilemma in the remediation of Cu-contaminated soil hinders the effective utilization of land resources. In this study, epoxy resin (EP) was utilized to solidify/stabilize Cu-contaminated soil due to its stable and rapid curing performance and excellent resistance to acid, alkali, and salt erosion. The mechanical properties, environmental effects, and curing mechanism of EP-cured Cu-contaminated soil were investigated. The results showed that the application of EP significantly enhanced the unconfined compressive strength (UCS), cohesion and internal friction angle of Cu-contaminated soil. All specimens met the UCS criterion specified by the United States Environmental Protection Agency (USPEA), namely no less than 0.35 MPa, which indicated that those EP-cured Cu-contaminated soil were qualified for practical engineering applications. According to the toxicity characteristic leaching procedure (TCLP), the application of EP enhanced the stability of Cu in Cu-contaminated soil. The leaching index of Cu ranged from 11 to 14. A high leaching index showed that the S/S treatment was safe and effective and the remediated Cu-contaminated soil satisfied the environmental requirement for heavy metals. This study confirmed the feasibility of utilizing EP in the solidification/stabilization (S/S) technology to convert high-concentration Cu-contaminated soil into secure and stable engineering materials. The remediation of Cu-contaminated soil by EP lays a solid foundation for the safe treatment and reuse of heavy metal-contaminated land resources.

Towards circular and sustainable restoration of a deeply polluted river basin: The Odiel River catchment (SW Spain)

The Ría de Huelva estuary located in SW Spain is heavily polluted by acid mine drainage leachates and phosphate fertilizer industry effluents. This study assesses the effectiveness of a solid waste rich in calcite originated during the remediation of industrial effluents using the passive dispersed alkaline substrate (DAS) technology, for the treatment of highly acid and polluted mine drainages. The research consists of flowing the mine leachates through a column loaded with a combination of an alkaline reagent (i.e., calcite-rich waste resulting from the treatment of industrial leachates) scattered in a non-reactive matrix (i.e., wood chips) to increase the pH of acidic water while decreasing the solubility of dissolved pollutants. The alkaline treatment achieved average removal percentages of 100 % for Al and Fe, and close to 90 % for Cu. However, the treatment was not effective for other metals present in mine drainages such as Co and Ni. These results are comparable to those achieved in the DAS treatment with commercial limestone. The precipitation of oxyhydroxysulfates (i.e., schwertmannite and basaluminite) and carbonates (i.e., malachite and hydrozincite) minerals could be controlling the solubility of pollutants during the treatment. The solid wastes from the DAS treatment were subjected to two standardized leaching tests (EN 12457-2 from the European Union and toxicity characteristic leaching procedure (TCLP) from the United States) in order to ensure suitable management and avoid potential environmental impacts. According to European Union legislation, the high mobility of Cu, Zn and SO4 confers some solid wastes from the DAS treatment the hazardous waste classification. However, according to United States regulation, these same solids are considered non-hazardous wastes. This research could help to improve the environmental sustainability of acid mine drainage treatment with DAS technology by replacing marketable limestone with a low-cost alkaline waste.

Immobilization of cadmium in river sediments by different modified nanoscale zero-valent iron: performance, mechanisms, and Fe dissolution.

Modified nanoscale zero-valent iron (NZVI) exhibited great potential for the remediation of heavy metal contaminated river sediments, but its mechanisms and environmental risks are still unclear. This study systematically discussed the performance and the mechanisms of modified NZVI materials, i.e., sodium alginate-coated NZVI (SNZVI), rhamnolipid-coated NZVI (RNZVI), and graphene oxide-loaded NZVI (GNZVI), for the stabilization of Cd in sediment, with the exploration of their stability to Cd at various pH values and Fe dissolution rate. Compared with the control, the toxicity characteristic leaching procedure (TCLP) leachable Cd decreased by 52.66-96.28%, and the physiologically based extraction test (PBET) extractable Cd decreased by 44.68-70.21% after 56 days of incubation with the immobilization efficiency varying according to GNZVI > RNZVI > SNZVI > NZVI. Besides, the adsorption behavior of Cd on materials was fitted with the Freundlich model and classified as an endothermic, spontaneous, and chemical adsorption process. SEM-EDX, XRD, and FTIR results verified that the stabilization mechanisms of Cd were principally based on the adsorption, complexation of Cd2+ with secondary Fe minerals (including Fe2O3, γ-Fe2O3, and γ-FeOOH) and precipitation (Cd(OH)2). From the risk assessment results, it was observed that the materials were favorable for Cd stabilization at a pH range from 7 to 11, meanwhile, the leaching concentration of Fe in the overlying water was detected below the limit value. These findings pave the way to developing an effective strategy to remediate Cd contaminated river sediments.

Leaching Performance of Nanotechnology-Induced High-Arsenic-Bearing Tooeleite-like Mineral Nanowaste

For arsenic decontamination from groundwater, arsenic crystallization is becoming adopted due to its sustainability and economic benefits. However, arsenic crystallization technology is a two-step process, which makes it complex and generates hazardous waste. Successful efforts toward making it a single-step process are presented here. The addition of nanorods and ball-milled zinc sulfide nanoparticles to arsenic-contaminated water result in highly monodispersed and high-arsenic-containing mineralized nanowaste with a crystalline structure similar to the mineral Tooeleite ((Fe3+6(As3+O3)4SO4(OH)4·4H2O)). This study reports the results of a short-term stability test based on a toxicity characteristic leaching procedure and a long-term stability test of the mineralized synthetic nanowaste produced from water treatment. The Tooeleite-like mineralized nanowaste passed short-term stability tests. Arsenic in the leachate were found to be 1.1 ± 0.2 mg L−1 and 4.8 ± 0.3 mg L−1 from waste generated by the nanorod and ball-milled nanoparticles, respectively. The crystallinity was well preserved, as observed from the post-stability-test diffraction patterns, consequently proving that the waste product can be non-hazardous and therefore would not require any secondary treatment before final disposal.

Coupling electrokinetic remediation with flushing using green tea synthesized nano zero-valent iron/nickel to remediate Cr (VI).

This study focuses on a flushing-electrokinetic remediation technology of hexavalent chromium from the chromium slag dump site. A suspension of nanoscale zero-valent iron/nickel fabricated from green tea (GT-nZVI/Ni), was employed as an eluent to degrade Cr (VI) and enhance the remediation effectiveness of a single EK. The removal efficiency of Cr (VI) was compared under different voltages, electrode spacings and pH values of the anolyte. The results demonstrated that the combined flushing and EK achieved a removal rate of Cr (VI) in the soil throughout all the experiments ranging from 83.08 to 96.97% after 120h. The optimal result was obtained when the voltage was 28V, the pH value of anolyte was 3 and the electrode spacing was 15cm. The removal of Cr (VI) reached 91.49% and the energy consumption was 0.32606kW·h·g-1. The underlying mechanisms responsible for the removal of Cr (VI) by GT-nZVI/Ni flushing-EK primarily involved electromigration, reduction and adsorption co-precipitation processes. The fractionation analysis of Cr (VI) concentration in the soil after remediation showed that the presence of GT-nZVI/Ni facilitated the conversion of Cr (VI) into oxidizable and residual states with low mobility and toxicity. The results of toxicity characteristic leaching procedure (TCLP) indicated that the leaching concentration of Cr (VI) was below 1mg·L-1, complying with the standards set by the Environmental Protection Agency. Additionally, the phytotoxicity testing revealed that the germination index (GI) of the remediated soil reached 54.75%, indicating no potential harm to plants.

Understanding the release, migration, and risk of heavy metals in coal gangue: An approach by combining experimental and computational investigations

The lack of understanding on the environmental fate and implications of heavy metals in coal gangue (CG) has restrained its utilization. Conventional extraction methods provide empirical measures of heavy metal speciation, lacking a detailed description of bound strength, which limits long-term risk assessment. In this study, the releasing and migrating behavior of six heavy metals (Cd, As, Pb, Ni, Cu, and Cr) were investigated through an approach by combining experimental and computational investigations. The corresponding mechanisms and risks were understood and discussed on a molecular level. The results suggested that CG is primarily a natural kaolinite α-quartz and anatase mineral. The sequence extraction results showed that heavy metals in CG are mainly distributed in stable silicate and iron manganese oxide-bound states. The toxicity characteristic leaching procedure test advised Cu, Cr, Ni, and Pb had a high toxic level and thus required long-term monitoring and controlling. A quantum chemical calculation demonstrated that the heavy metals were more likely to be embedded in silicate minerals with high binding energy than those binding on the anatase surface. The findings of this research provide a promising approach to comprehensively evaluate the stability mechanism and potential long-term risks of heavy metals in solid waste.