Immobilization Of Metals Research Articles

Evaluation of geotechnical, mineralogical and environmental properties of clayey soil stabilized with different industrial by-products: A comparative study

The utilisation of soil stabilization techniques employing binders like lime or cement enables the use of soils that are classified as disposable, thereby reducing the need for landfills and the consumption of natural resources. However, the production of lime and cement results in significant CO2 emissions. Therefore, the application of industrial by-products (IBP) for stabilizing expansive soils presents an opportunity to minimise the use of traditional binders. This study investigates the geotechnical, mechanical, mineralogical, and environmental properties of four IBP (biomass bottom ash, biomass fly ash, steel slag, and mixed recycled aggregate) combined with a silica-based nanomaterial for road layer applications. The technical feasibility of the use of IBP was demonstrated, especially in combination with nanomaterials, allowing a 66 % reduction in the percentage of added lime, obtaining significant improvements with minimal plasticity and swelling index and bearing capacity CBR values higher than 25 %, applying BBA, BFA and SS. An environmental assessment of leachate analysis was performance, showing an immobilization of heavy metals that makes the application of IBP feasible. In addition, a life cycle analysis study showed the environmental benefits of applying IBP, such as a 50 % reduction in CO2 emissions due to the reduction of lime, resulting from the use of these materials, thus promoting more sustainable economic models.

Endogenous silicon-activated rice husk biochar prepared for the remediation of cadmium-contaminated soils: Performance and mechanism

Biochar is widely used for the remediation of heavy metal-contaminated soils. However, pristine biochar generally has limited active functional groups and adsorption sites, thereby exhibiting low immobilization performance for heavy metals. In addition to carbon (C), silicon (Si) is another common macro-element present in rice husk biochar, but it often exists in the form of amorphous oxide and therefore contributes little to the adsorption performance for heavy metals. The transformation of amorphous Si oxide to dissolved silicate through a precipitation effect can significantly improve its heavy metal immobilization capability. Herein, the amorphous Si oxide in rice husk biochar was activated by sodium hydroxide and then the dissolved silicate was immobilized by calcium salt. The as-synthetized Si-activated biochar was used to remediate cadmium (Cd)-contaminated soils. The results indicated that Si-activated rice husk biochar could reduce Cd migration and environmental risks by the transformation from exchangeable Cd into carbonate-bound and residual Cd. With increasing Ca: Si molar ratio, the content of CaCl2 and H2O-extractable Cd exhibited a decreasing trend. Moreover, a higher addition amount of Si-activated biochar improved the Cd immobilization efficiency. The application of 1.0% Ca/Si molar ratio of 2: 2 Si-activated rice husk biochar decreased the CaCl2-Cd and H2O-Cd concentration by a maximum of 83.7% and 90.5% compared with pristine rice husk biochar, respectively. The present work proposes an approach for highly efficient remediation of Cd-polluted soils by biochar.

Structural Features, Chemical Diversity, and Physical Properties of Microporous Sodalite-Type Materials: A Review

This review contains data on a wide class of microporous materials with frameworks belonging to the sodalite topological type. Various methods for the synthesis of these materials, their structural and crystal chemical features, as well as physical and chemical properties are discussed. Specific properties of sodalite-related materials make it possible to consider they as thermally stable ionic conductors, catalysts and catalyst carriers, sorbents, ion exchangers for water purification, matrices for the immobilization of radionuclides and heavy metals, hydrogen and methane storage, and stabilization of chromophores and phosphors. It has been shown that the diversity of properties of sodalite-type materials is associated with the chemical diversity of their frameworks and extra-framework components, as well as with the high elasticity of the framework.

Fly ash admixture originating from lignite combustion in construction mortars – Time evolution of technical parameters and heavy metals leachability

The production of cement, the predominant construction binder, is associated with high energy consumption, enormous raw material depletion, and a large volume of CO2 emissions, making cement one of the most polluting materials. This study aims to contribute to the sustainability of the construction industry by significantly reducing the proportion of Portland cement (PC) in the composition of mortars. The binder content reduction was achieved by the addition of large amounts of fly ash admixture (FA) from lignite combustion while studying the effectiveness of the immobilization of heavy metals (HMs), which are present in FA, in the PC/FA matrix. Along with the analysis of the FA admixture amount on the properties of the prepared mortars, emphasis was put on the study of the influence of prolonged curing on the development of the physical parameters of the mortars and the immobilization efficiency of the HMs. It was revealed that FA can be added to PC by up to 20 wt%, enabling the production of construction mortars with high strength and low porosity, while confining hazardous substances such as HMs in the matrix. Prolonged curing at elevated relative humidity led to the continuous evolution and solidification of the mortar structure, improving its engineering properties and HMs immobilization efficiency.

Effects of accelerated carbonation on fine incineration bottom ash: CO2 uptake, strength improvement, densification, and heavy metal immobilization

Incinerating municipal solid waste (MSW) can effectively reduce its mass and volume while producing electricity. However, this process generates incineration bottom ash (IBA), which is an aggregate-like waste containing heavy metals. Due to the higher heavy metal contents, fine IBA can be removed from total IBA and treated separately to promote the use of IBA. Furthermore, MSW incineration generates carbon dioxide (CO2), which is another concern. In this context, it is beneficial to use accelerated carbonation to treat fine IBA, because it can not only contribute to carbon capture but also provide carbonated IBA that may be utilized as aggregates in civil engineering. The accelerated carbonation process of fine IBA is affected by many parameters. Therefore, this study investigated the effects of CO2 pressure (PCO2), initial water content (wi), and carbonation time on the properties of carbonated IBA, including CO2 uptake, unconfined compressive strength (UCS), density, and leaching of heavy metals. The evolution of mineralogy and microstructure of carbonated IBA was also analyzed. The results showed that IBA with wi of 15% and PCO2 of 200 kPa could achieve a CO2 uptake of 6% of IBA mass. The carbonation time significantly affected UCS and dry density of carbonated IBA. As the carbonation time increased from 0 h to 120 h, the UCS increased from 67 kPa to 691 kPa while the dry density increased from 1.38 g/cm3 to 1.51 g/cm3. Compared with untreated IBA, the leaching concentrations of Cu, Cr, Zn, and Pb from carbonated IBA were reduced significantly. As the carbonation time increased, the microstructure of carbonated IBA became denser. This densified structure was one of the reasons for the strength improvement and dry density increment of carbonated IBA.

Coupling of biochar and silicon for Phyto-management of Cd contaminated soil using Brachiariamutica

Contamination of soil with heavy metals is a threatening global environmental problem. With increasing urbanization, it is very important to design economical and environment-friendly mitigation measures to have pollutant free soil. Phytoremediation is an advancing technique to extract pollutants from soil to achieve eco-sustainability. This study aimed to investigate the combined impact of biochar and silicon on growth attributes of Brachiaria mutica grown in cadmium (Cd) contaminated soil. The biochar was prepared by co-pyrolysis of agricultural left-over biomass (rice husk, bamboo leaves and corn cob in a 1:1:1 ratio) and physio-chemical characters were studied by FTIR, SEM-EDX and proximate analysis. A pot study was conducted to evaluate the potency of biochar and silicon in lowering the Cd uptake by para grass grown under Cd spiked soil. Total 8 treatments were planned by taking 1 % and 2 % biochar with 0.01 % and 0.02 % silicon. The results have shown that treatment 8 (2 % biochar and 0.02 % silicon) exhibited maximum improvement in growth parameters such as shoot length by 2.64-fold and root length by 44.9 %, along with improving the antioxidant defense system of Para grass (CAT by 2-fold and POD by 56.4 %). Application of treatment 8 also decreased Cd concentration in the shoot and root by 48.8 % and 47.4 %, respectively. Treatment 8 was most effective in reducing CaCl2 extractable Cd in soil up to 56.1 %. Based on this data, treatment 8 was most effectual in suppressing Cd stress. Biochar produced from other agricultural waste material along with Si as inorganic amendment can be used to immobilize other toxic heavy metals at field level. Heavy metals immobilization potential of Si and biochar can be tested by harvesting other grasses and oil seed crop species.

The promoting effect of Fe on the immobilization of heavy metals in MSWI FA–lead–zinc tailings-based backfill materials under field application: Dynamic simulation leaching and immobilization mechanisms

Currently, research on solid waste-based backfill materials containing municipal solid waste incineration fly ash (MSWI FA) was primarily concentrated at the laboratory stage, with insufficient studies on their leaching safety and heavy metal immobilization mechanisms under field application. This study demonstrated that MLBM (Binder weight ratio: MSWI FA: steel slag (SS): blast furnace slag (BFS): flue gas desulfurized gypsum (FGDG): coal fly ash (CFA) = 10 %:33.6 %:33.6 %:12.8 %:20 %; binder-to-lead–zinc tailings (LZT) ratio was 1:8; mass concentration was 60 %) exhibited excellent leaching safety in actual backfilling. The study found that MLBM posed no risk of heavy metal and anion leaching under various leaching standards. Furthermore, MLBM showed no risk of harmful element leaching within a simulated percolation period of 100 years. The release mechanisms of Pb, As, Zn, and Cr in MLBM were diffusion, diffusion, flushing, and dissolution, respectively. The immobilization efficiency of Pb, Zn, Cr, As, Cl−, and SO42− positively correlated with the pH value (pH>7.5). The immobilization mechanism included: 1) Formation of insoluble heavy metal compounds. In the MLBM system (The pH ranged from 7.89 to 8.87), Fe(III) (Fe(OH)3(aq) and Fe(OH)4−) contributed to the immobilization of Pb2+ and SO42− and oxidized As(III) (H2AsO3−) and Cr(III) (Cr(OH)3(aq)), forming As(V) (HAsO42−) and Cr(VI) (CrO42−), respectively. 2) Adsorption. The negatively charged surface of C–(A)–S–H gel could immobilize Zn2+ and Pb2+ through adsorption, and the ionic forms of Pb(II) and Zn(II) were PbOH+ and ZnOH+, respectively. This study provided theoretical support for the leaching safety and immobilization mechanisms of solid waste-based backfill materials containing MSWI FA in field applications.

Improving the growth of pea plant by biochar–polyacrylamide association to cope with heavy metal stress under sewage water application in a greenhouse

Sewage water is extensively used for irrigation, serving as a valuable resource for plant growth to enhance agricultural productivity. However, this practice also results in a significant accumulation of heavy metals in the soil, posing potential environmental and health risks. A study was designed to evaluate the combined effect of amendments on heavy metal immobilization in soil and improved growth and yield in pea plants. For this, the soil for each treatment was mixed with biochar (BC) (1% w/w), polyacrylamide (PAM) (0.5% w/w), and also applied in combination. Pea plants were irrigated with tap water (TW), sewage water (SW), and tap + sewage water (TW + SW). A factorial design was applied to analyze data statistically. The combined application of the biochar and polymer showed a positive response by significantly enhancing the plant growth parameters (39%–84%), physiological attributes (67%–69%), and reducing Cd (56%) and Cr (65%) concentration in soil applied with SW and TW + SW. Moreover, treatment with a combined application of BC and PAM significantly reduced Cd concentrations by 43% in roots, 50% in shoots, and 91% in grains. Similarly, Cr concentrations were reduced by 51% in roots, 51% in shoots, and 94% in grains compared to the control. Overall, the study results indicate reduced bioaccumulation and health risks associated with potentially toxic elements (PTEs), supporting the application of the polymer and biochar for irrigating pea plants with TW + SW. Leveraging the combined benefits of polymer and biochar amendments appears to be an effective strategy to remediate PTE-contaminated soil, thereby increasing plant growth and yield.

Tetrasodium iminodisuccinate modified montmorillonite for Pb and Cd adsorption from water: Characterization and mechanism

Heavy metal pollution is a huge hazard to the water environment and modified clay adsorbents have been widely used to remove heavy metals from water. Degradable anionic chelating agents have a greater potential for the immobilization of heavy metals, so tetrasodium iminodisuccinate (IDS) was introduced to modify montmorillonite (Mt) for Pb(II) and Cd(II) adsorption from water in this study. IDS was bound with Mt by sonication, heating, and acidity to form IDS-Mt, and characterized by XRD, FT-IR, SEM, and zeta potential analyzer. The batch adsorption experiments revealed that IDS-Mt5 had excellent adsorption capacity of Pb(II) and Cd(II) up to 214.73 mg/L and 104.07 mg/L, respectively. The adsorption process of IDS-Mt on Pb(II) and Cd(II) was consistent with the Sips model and PSO model, indicating that the adsorption was heterogeneous and chemical. The adsorption capacities of IDS-Mt in the second cycle remained above 76 % for Pb(II) and 69 % for Cd(II) of the initial ones, respectively. IDS was immobilized on the interlayer and edge surfaces of Mt through interactions or forming hydrogen bonds facilitated by ultrasonic under acidic heating conditions. Pb(II) and Cd(II) were immobilized by IDS-Mt through cation exchange, negative charge attraction at the edge surface, and IDS chelation. IDS-Mt was an excellent adsorbent with strong dispersibility and swelling properties for Pb(II) and Cd(II) removal from contaminated water. This study provides a new solution for the anionic modification of Mt and a new material for the treatment of heavy metal wastewater.

Mechanical, freeze-thaw resistance and heavy metals leaching properties of alkali-activated recycled concrete powder solidified sludge

Solidified sludge was an efficient method to consume the large amount of sludge, which can be used as the subgrade filler in road engineering. However, the traditional solidified materials, such as cement and lime, consumed a large amount of natural resources and increased carbon emissions. This study used the alkali-activated recycled concrete powder (ARCP) to solidify sludge, which could be used as a potential subgrade stabilization filler. The optimal factors of ARCP were firstly determined by orthogonal test according to the compressive strength. Then the influences of different ARCP dosage, sludge moisture content and curing method on the mechanical properties, freeze-thaw resistance and heavy metals immobilization of the ARCP solidified sludge (ARCPS) were investigated. At last, microstructures of ARCPS were analyzed by SEM, XRD and TG-DTG tests. The experimental results demonstrated that the optimal mixture for ARCP: the silicate modulus of 1, liquid-solid ratio of 0.48 and calcium hydroxide content of 3 %. The solidified process by ARCP improved the mechanical properties and freeze-thaw resistance of ARCPS greatly. The 7 d unconfined compressive strength of ARCPS could reach 1305–2033 kPa when the sludge moisture content was 15 %, which meet the requirement of 500 kPa from the Chinese standard. The frost heaving rates of ARCPS were between non-frost heaving and mild frost heaving. The sludge moisture content was the most important factor affecting the freeze-thaw resistance of ARCPS. The properties of ARCPS were further improved after carbonation curing. The leaching mass concentration of heavy metals decreased significantly after the solidification of sludge. After 5 freeze-thaw cycles, the heavy metal leaching concentration increased but was still met the requirement of standards. SEM results showed that the surface of carbonated ARCPS was covered by dense scale-like carbonation products, which further enhanced the strength and freeze-thaw resistance of ARCPS. The results can be used to guide the application of sludge and ARCP in construction.

Immobilization of heavy metals with chlorine and liquid phase formation during thermal treatment of MSWI fly ash

Due to effective detoxification, thermal treatment is a preferred treatment technology of municipal solid waste incineration (MSWI) fly ash. However, immobilization behavior of heavy metals during thermal treatment is unclear. In this work, a circulated fluidized bed fly ash with SiO2 addition and a grate furnace fly ash with high silica-aluminum coal ash addition were used to investigate combined effect of active chlorine content, liquid polymerization degree, temperature of initial liquid phase formation and liquid phase formation rate on the immobilization ratios of Zn, Pb and Cd by principle component analysis (PCA). The results show that the decrease in active chlorine content favors the immobilization of Zn, Pb and Cd because chlorination volatilization is reduced. Both the increase in liquid polymerization degree and the formation of initial liquid phase at low temperature promote the immobilization of Zn, Pb and Cd for physical encapsulation. However, a rapid formation of liquid phase is not favorable for the immobilization of Zn, Pb and Cd, because transfer of heavy metals between crystals and liquid phase is impeded by high viscosity of liquid phase during fusion. The results can provide a reference for how to achieve the immobilization of heavy metals by adjusting the chemical composition of MSWI fly ash during thermal treatment.

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.

Anionic surfactant-activated remediation of Pb, Cd, As contaminated soil by electrochemical technology

Lead (Pb), cadmium (Cd) and arsenic (As) contamination in soils show a growing environmental concern. However, owing to the significant differences in chemical characteristics, remediating heavy metal(loid)s of Pb, Cd and As is challenging. Herein, anionic surfactant-activated electrochemical approach was proposed to realize efficient immobilization of As, Cd and Pb heavy metal(loid)s from contaminated soils. In this innovative method, calcium lignosulfonate (CL) as anionic surfactant was used to activate Cd and Pb from contaminated soils into solution, afterwards anodically generated Fe (II) ions by the electrochemical process react with Pb and Cd to form precipitates. Meanwhile, owing to the strong binding capacities of Fe (II) ions, As contaminations were remediated. Moreover, via various characterizations and cyclic voltammetric method, the reaction kinetics and phase transformation process during the electrochemical process were analyzed in detail. These findings show great potential in optimizing the design of electrochemical treatment, which will be applied in remediating multi-component heavy metal(loid) polluted soils.

Impact assessment of Zeolite, Ca-bentonite and Biochar amendments on Cd bioavailability and fractions in polluted calcareous soils

The refining of polluted soils by heavy elements is one of the most important environmental policies in industrialized and developing countries. Using adsorbents is a suitable procedure for the immobilization of heavy metals in polluted soils. This study aimed to assess the immobilization of Cadmium (Cd) in polluted calcareous soil affected by the application of organic and inorganic amendments including Biochar (from grape pruning residues) and natural Zeolite and their interaction under wheat cultivation. The treatments used in this study were two amendments of Zeolite and Biochar (from grape pruning wastes) at three levels (0, 1, and 4%) and three levels of Cd contamination (0, 75, and 150 mg/kg soil). A 16-week incubation period was considered for the homogenization of the amendments in soil and wheat was grown according to the standards procedure. At the end of incubation, different fractions of Cd including residual, exchangeable, bonded to organic matter, bonded to carbonate and bonded to iron and manganese. Also available Cd by DTPA and EDTA methods and 1000-grain weight of wheat were measured. The results showed that the highest amount of Cd bound to organic matter was obtained in 4% Biochar treatment to 15 mg/kg. The highest and lowest amounts of Cd extracted with DTPA were obtained in the control one (92 mg/kg) and the level of 4% Biochar (67 mg/kg), respectively. The results showed that increasing the amount of Biochar and Zeolite amendments increased the weight of 1000 grains of wheat in all treatments. According to the results of the study, the use of Biochar and Zeolite reduced the amount of Cd extracted by DTPA ( 82.436 mg/kg) and EDTA (115.605 mg/kg). Finally, the results showed that the use of Biochar and Zeolite has reduced active Cd and its mobility in the soil due to increasing organic and carbonate fractions. Combining biochar and zeolite in soil remediation efforts can enhance their effectiveness in reducing the concentration and mobility of active Cd. The biochar provides a stable carbon matrix for long-term immobilization of Cd, while the zeolite offers additional adsorption capacity and ion-exchange capabilities. This synergistic effect can lead to improved soil quality and reduced environmental risks associated with Cd contamination.

Pyrite functionalized Black Soldier Fly feces biochar for mine soil quality improvement and heavy metals immobilization

Frequent mining activities have led to an increasing transfer of heavy metals to the soil. Pyrite functionalized Black Soldier Fly feces biochar composite material (BFFS) was synthesized to immobilize Cu and Pb in contaminated mine soil and improve soil quality in our study. Incubation experiments showed that BFFS significantly reduced the leaching rates by 96 % and 90 % for Cu and Pb, respectively, when compared to the control after 220 days. Speciation transformation analysis further revealed that BFFS could significantly reduce easily labile fractions of Cu and Pb, and transformed to recalcitrant fractions. Moreover, BFFS significantly improved the quality of mine soil combined with soil quality index analysis. The potential toxicity and bioavailability of Cu and Pb can still be effectively reduced by BFFS, even during a 90-day field experiment. In addition, the mine soil improved by BFFS further promoted the survival and growth of ramie. Multiple characterization analyses and related experiments indicated that ion exchange, adsorption, complexation, and coprecipitation mainly contribute to the high efficiency immobilization of Cu and Pb by BFFS. These findings could bring some fresh perspectives on the development of immobilization materials and related technologies for the economical, green and sustainable remediation of heavy metals contaminated mine soil.

Simultaneous Immobilization of Heavy Metals from Multi-metal Contaminated Soil Amended with Chrysopogon Zizanioides Root Micro Powder

Simultaneous Immobilization of Heavy Metals from Multi-metal Contaminated Soil Amended with Chrysopogon Zizanioides Root Micro Powder

Discarded substrates from soilless hydroponic horticulture as potential amendments for metal-contaminated soils

Soil contamination with metals is a major threat for the environment and public health since most metals are toxic to humans and to non-human biota, even at low concentrations. Thus, new sustainable remediation approaches are currently needed to immobilize metals in soils to decrease their mobility and bioavailability. In this work, we explore the application of discarded substrates from hydroponic cultivation, namely coconut shell and a mixture of coconut shell and pine bark, for immobilization of metals (Cd, Cr, Ni, Cu, Pb, Hg, Sb and As) in a naturally contaminated soil from a mining region in Portugal. The immobilization capacity of substrates (added to the soil at 5% mass ratio) was assessed both individually and also combined with other traditional agriculture soil additives (limestone and gypsum, at 2% mass ratio) and nanoparticles of zero-valent iron (nZVI) at 1–3% mass ratio. The overall results obtained after a 30-d incubation showed that the discarded substrates are a viable, economic, and environmental-friendly solution for metal remediation in soils, with the capacity of immobilization ranging from 20 to 91% for the metals and metalloids studied. Furthermore, they showed the capacity to reduce the soil toxicity (EC50 ∼ 6000 mg/L) to non-toxic levels (EC50 > 10000 mg/L) to the bacteria Aliivrio fischeri.

Microbial-mediated metal(loid) immobilization in mulch-covered tailings

Mulch coverage of mining tailings can create anaerobic conditions and consequently establish an anoxic environment that promotes the metabolic processes of anaerobic microorganisms. This anoxic environment has the potential to decrease heavy metal mobility and bioavailability. While tailings exposed to sunlight have been extensively studied, research on the effects of microbial-mediated geochemical cycling of heavy metals in mulch-covered tailings is scarce. This study aimed to examine the effects of mulch coverage-induced alterations in the structures of tailing microbial communities on the biogeochemical processes associated with heavy metals. Mulch coverage significantly reduced the pH of the tailings and the tailings exhibited heavy metal bioavailability. Random forest analysis demonstrated that mulch coverage-induced changes in the As/Cd-contaminated fractions and nutrients (total organic carbon and total nitrogen) were the most crucial predictors of microbial diversity and ecological clusters in the tailings. Notably, different from direct metal(loid) immobilization, mulch coverage can facilitate heavy metal immobilization in tailings by promoting microbial-mediated Fe, S, and As reduction. Overall, this study demonstrated that mulch coverage of tailings contributed to a reduction in heavy metal mobilization, which can be attributed to shifts in microbial-mediated Fe, S, and As reduction processes.The study provides valuable insights into the potential of mulch coverage as a remediation strategy and underscores the importance of microbial-mediated processes in managing heavy metal pollution in tailing systems.

The influence mechanism of fulvic acid on Fe(II)-catalyzed transformation of Cr(III)-bearing schwertmannite: pH effect and nanoscale redistribution of Cr and C

The interactions between schwertmannite (Sch), chromium (Cr), and dissolved organic matter play a significant role in the cycling of Cr and carbon (C) in acid mine drainage (AMD) contaminated soils. However, mechanism insights into the immobilization of Cr and C during the Fe(II)-catalyzed, fulvic acid (FA)-mediated reductive transformation of Cr(III)-bearing Sch (Cr-Sch) remain unclear. In this study, we investigated the mechanisms underlying sequestration of Cr and C during the Cr-Sch transformation under various FA concentrations and pH conditions. Solid-phase transformation analysis revealed that the pH increasing from 3.5 to 7.0 favored the transformation of Cr-Sch to lepidocrocite (Lep) and/or goethite (Goe), while the transformation rate and degree decreased with increasing FA concentration from 10 to 100 mg/L. By means of the distribution of elements observed in spherical aberration corrected scanning transmission electron microscopy, Cr was predominantly adsorbed on the Lep and Goe surfaces, and Cr may be partially sequestered by Goe. Meanwhile, FA was adsorbed onto the surfaces of Goe and Lep, and the incomplete defect structure of Lep provided space for C immobilization. This study provides a basis for an in-depth understanding of the nanoscale mechanisms of Cr and FA redistribution during Cr-Sch transformation and can be used for developing strategies for the immobilization of heavy metals and C in AMD-polluted environments.

Selective lead capture using amide-containing COFs: A novel strategy for efficient soil remediation

A critical consideration in the application of phytoremediation to remediate sludge soil contaminated with heavy metals is the potential for leaching risks that prevail prior to the efficient uptake of these metals by plants. The most cost-effective method is to use heavy metal stabilizers with selective adsorption. A novel amide-based COF material (COF-TH) has been synthesized as a heavy metal stabilizer for Pb. COF-TH exhibits significant selectivity for Pb in five-metal-mixed solutions, with a distribution coefficient KD as high as 3279 mL·g–1, which was more than 7.3 times that of other heavy metals. The maximum adsorption capacity of COF-TH for Pb was 189 mg·g–1. The adsorption fitted Langmuir model and intra-particle diffusion model, and satisfied pseudo-second-order kinetic model. The excellent selectivity and adsorption performance originate from the complexation between abundant amide groups and Pb ions. Pot experiments and leaching assays confirm that COF-TH decreased Pb leachate concentrations by 77.8 % without significantly decreasing total phytoextracted amounts of other heavy metals, due to the high selectivity of COF-TH to Pb. Additionally, its positive impact on plant growth and microbial diversity makes it a promising soil remediation agent. This investigation offers a novel approach to mitigate the leaching risk of a specific heavy metal Pb during sludge land application by integrating soil phytoremediation with stabilization techniques.