Emitted dust is the major contributor of heavy metal(loid)s in soils located near lead (Pb) smelters, but the mechanisms for transfer of the heavy metal(loid)s in dust are uncertain. The study systematically investigated the geochemical behaviors and liberation mechanisms of heavy metal(loid)s in this process. The results show that Pb, Zn, Cd, and As in two types of dust samples exceeded the allowable standards, and about 80% of Pb and Zn were present in mobile and bioavailable fractions. More than 70% of arsenic in bottom-blowing furnace dust existed in an acid-soluble fraction, while 60% of cadmium in reducing and fuming dust existed in the acid-soluble fraction. Pb isotope results showed that 97.12% of the Pb in the topsoil came from dust emitted during the smelting process. XRD and MLA results illustrated that PbSO4, ZnSO4, and CdSO4 were the major minerals in the dust, while the mineral phases of the topsoil were mainly quartz, calcite, dolomite, and muscovite. Based on a combination of mineralogical investigations and geochemical modelling, our findings suggest that liberation of the Pb, Zn, and Cd was primarily dependent on sulfate minerals under acidic conditions, whereas the liberation of As was related to adsorption by iron hydroxide.
The long-term operation of the lead smelter has brought serious heavy metal pollution to the surrounding soil. The microbial community structure and composition of heavy metal contaminated soil is important for the risk assessment and pollution remediation. In this study, a lead smelter operating for more than 60 years was used to investigate the effects of heavy metal pollution on soil microbial community structure and composition in vertical profile. The results showed that the heavy metal content decreases gradually with increasing vertical depth of the soil. The diversity of soil microbial community with moderate pollution was higher than that with low pollution. Regardless of the pollution level, the diversity of soil microbial community was higher in the surface layer than in the bottom layer. The dominant relative abundance genera include Perlucidibaca, Limnobacter, Delftia, Hydrogenophaga, Thiobacillus, Sulfurifustis and Sphingopyxis, showing a higher abundance of sulfur-oxidizing bacteria (SOB). XRD results showed the presence of PbSO4 in soil, may be due to the enrichment of SOB for the oxidation of sulfur. This sulfur cycle characteristic may be potential for the stabilization and remediation of lead (Pb) into PbSO4.
In this study, we evaluated effectiveness of three polysaccharide stabilizers (sodium carboxymethyl cellulose (CMC), sodium carboxymethyl starch (CMS), and a water-soluble starch) for stabilizing FeS nanoparticles, and tested the stabilized nanoparticles for immobilization of Cd2+ in water and soil. Fully stabilized FeS nanoparticles (100 mg/L FeS) were obtained using 0.010 wt% CMC, 0.025 wt% CMS, or 0.065 wt% starch. CMC-FeS showed a highly negative zeta potential, starch-FeS remained neutral, whereas CMS-FeS displayed a moderately negative potential. CMC-FeS showed the fastest sorption rate and highest sorption capacity for Cd2+. When a Cd-laden soil (58.3 mg/kg Cd) was amended with 100 mg/L CMC-FeS or CMS-FeS, the TCLP-leachable Cd was reduced by 88.4% and 68.0%, respectively. Both CMC-FeS and CMS-FeS were transportable through a model soil and showed high potential for in-situ immobilization of Cd2+ in soil. Nearly complete breakthrough occurred at 4.5 pore volumes (PVs) for CMC-FeS and about 25 PVs for CMS-FeS. When the Cd-laden soil was treated with 55 PVs of CMC-FeS and CMS-FeS suspensions (100 mg/L), the water-leachable soluble Cd was reduced by 98.2% and 98.0%, respectively. The three stabilizers may find their best uses in soil remediation according to the target contaminants, transport properties in soil, and material cost.
Soil particle size plays a crucial role in the distribution and occurrence of soil heavy metals (HMs). Comparative studies on the distribution of HMs across soil particle sizes of various areas affected by smelting are scarce. Three soil profiles, including smelting slag heap (SH), traffic area (TA), and adjacent farmland (FA), were sampled at an abandoned Pb smelting site, and the geochemical distribution and occurrence of HMs in different soil particle fractions (>150 µm, 45 −150 µm, and <45 µm) were comparatively investigated. Results showed different distribution of HMs across soil fractions between the smelting site and farmland. Average accumulation factors (F A) of HMs increased from 0.78 to 1.14 as the particle size increased in the SH related to the stockpiling and mechanical mixing of coarse slags, while decreased from 1.49 to 0.60 in the FA related to metal-enriched fine particles released from smelting. The coarser fraction had a higher mass loading of HMs (>50%) in the smelting site soils, where the contribution of waste residues was significant. Therefore, physical separation techniques are recommended in the remediation of soil contamination. The study connected smelting impacts and occurrence of HMs across particle sizes which has implications for remediation strategy.
The topsoil of smelter sites is subjected to severe contamination by heavy metals (HMs). Existing numerical simulations typically treat soil and groundwater separately owing to data limitations and computational constraints, which does not reflect the actual situation. Herein, a three-dimensional coupled soil-groundwater reactive solute transport numerical model was developed using the Galerkin finite element method with the smelter as the research object. This model treats soil and groundwater as a whole system, providing a quantitative characterization of HMs migration patterns in soil and groundwater. The model used the reaction coefficient (λ) and retention coefficient (R) to describe the release and adsorption capacities of HMs. Results from the model were consistent with actual pollution distributions in the field, indicating the efficacy of the soil-groundwater remediation technology for severe soil and localized groundwater pollution. The constructed three-dimensional coupled soil-groundwater reactive solute transport model can describe and predict the distribution and transport diffusion behavior of HMs at the study site with good efficacy. The model was also used to simulate and predict the effects of remediation technologies during the treatment of smelting site contamination, providing guidance for optimizing the treatment plan.
Sediment is an important sink for metals within mining environments. This study employs a combination of positive matrix factorization (PMF), random forest (RF) and fuzzy analytic hierarchy process (FAHP) to investigate the source attribution and released effects of toxic elements in stream sediments originating from an abandoned lead/zinc mine. The results show that the integrated PMF-RF-FAHP approach allows for the quantitative identification of metal sources and the prioritization of control measures within the mine. The primary source of contamination in the mine stream sediments was identified as the toxic elements releasing from the ore sorting area, followed by contributions from the mining area. The transport of toxic elements from mine into stream sediments is influenced by surface water flows, of which the upstream ore sorting area is an important factor to the contamination of the tailings area, riparian zone and hazardous waste landfills. The levels of main toxic elements, such as As, Cd, Sb, and Tl in stream sediments significantly exceed the background values for stream sediments in China, respectively. The similarities in sources for As, Cd, Sb and Tl in both soils and sediments exceeded 60%. The ore sorting area accounted for 48% of As, 82% of Cd and 78% of Sb contamination, while the mining area accounted for 94% of Tl contamination. This study presents a valuable methodology for pinpointing pollutant sources in mines rich in toxic elements like As and Cd. It is valuable and helpful to provide insights into tracing metal contamination and facilitating regional environmental management, both during mine industrialization and after abandonment.
The release behavior of heavy metal(loid)s in Cu smelting flue dust, collected from a deserted Cu smelter, and its mineralogical control mechanism were studied using toxicity characteristic leaching procedure (TCLP) test and wide pH range (3–13) dependent leaching experiments. The concentrations of As, Cd, Cu, Pb and Zn in TCLP leachate were 704, 82.7, 2.08, 3.1 and 3.26 times threshold of corresponding elements listed in identification standards for hazardous wastes of China (GB 5085.3—2007), respectively. High release percentage of As ranged from 26.0% to 28.1% over the entire pH range. The leachability of Cd, Cu, and Zn was significantly high under acidic conditions, while that of Pb was highly released at pH 13.0. The geochemical analysis showed that As solubility was partly controlled by the new formation of Ca, Cu, Pb, and Zn arsenates under pH 5.5–11.5, and that of Cd, Cu, Pb, and Zn was mainly controlled by hydroxide precipitation under alkaline condition. BCR extraction and XRD analysis indicated that higher leachate Cd and Zn concentrations were consistent with their higher content of active forms in dust. The study provides scientific guidance for the treatment and disposal of the flue dust for heavy metal(loid)s pollution prevention.
Long-term metal smelting activities can lead to enrichment and dispersion of heavy metals in the site soil and groundwater. The migration and prediction of heavy metals from soil to groundwater in an abandoned lead/zinc smelting site were studied using machine learning model. The results showed that heavy metals in site soil mainly accumulated in the fill layer, and vertically migrated to groundwater significantly. The mean of Pb, As, and Cd in site soils significantly exceeded the screening value of risk control standard for soil contamination of development land. The mean of Zn, Cd, Pb and As in groundwater exceeded the corresponding groundwater Class VI limit of standard for groundwater quality of China. Soil contamination of heavy metals was serious in the pyrometallurgical area, hydrometallurgical area and raw material storage area, and Cd and Pb in the upper soil layer had a strong migration potential downward with active and reducible state. The synergistic remediation for site soil and groundwater in smelting site was suggested when groundwater level was below 5 m and soil Cd concentration exceeded 344 mg/kg, or when the soil active Pb concentration exceeded 5425 mg/kg.
Due to high reactivity and relatively low cost, nano zero-valent iron (nZVI) has become an alternative material for in-situ remediation of contaminated sites. However, factors such as short transport distance and easy deposition in porous media also seriously restrict its injection remediation effect. The optimum ratio of bentonite and kaolin supported nano zero-valent iron (K-nZVI) in the remediation agent was determined by sedimentation and rheological tests. The transport characteristics of deionized water and bentonite suspensions carrying K-nZVI in porous media under different injection pressures were investigated using simulating column tests. The results show that bentonite suspensions could significantly improve the stability and dispersibility of K-nZVI. The proportion of bentonite and K-nZVI are 5% and 0.4%, respectively, which is the best ratio of the remediation agent. The transport capability of K-nZVI carried by deionized water increases with the increase of injection pressure, while there is a critical injection pressure for bentonite suspensions carrying K-nZVI remediation agent. The numerical simulation results show that the diffusion radius of K-nZVI is positively correlated with the injection pressure and negatively correlated with the viscosity of the remediation agent. The results provide theoretical guidance for the remediation project of heavy metal pollution in non-ferrous smelting sites.
To improve the remediation and antioxygenic properties of ferrous sulfide (FeS) nanomaterials toward heavy metals is the focus of current research. This study employed a combination of sodium carboxymethylcellulose (CMC) and sodium dodecyl benzene sulfonate (SDBS) for the modification of FeS nanomaterials supported by porous silicon (SiO2/FeS) to serves as an efficient amendment for cadmium pollution. The optimized slurry with the mass ratio of CMC/SDBS to be 1:3 showed enhanced dispersion and antioxidant effects on SiO2/FeS (the mass ratio of surfactant to FeS was 1:1). This formulation exhibited the smallest particle size (D 50 = 0.66 µm) and the highest absolute Zeta potential values exceeding 30 mV. Also, the obtained products demonstrated effective remediation of cadmium-contaminated solutions, with Cd(II) primarily forming stable CdS and CdSO4 products through ion exchange and chemical precipitation. The adsorption capacity of SiO2/FeS-CMC/SDBS 1:3 for cadmium in air and nitrogen was remained during 30 d, reaching about 158 mg/g. Notably, under low concentration Cd contamination, the adsorption capacity of SiO2/FeS-CMC/SDBS 1:3 exceeded that of SiO2/FeS-CMC and SiO2/FeS-SDBS without acidification risk. In summary, this research highlights the improved remediation and antioxygenic properties achieved through CMC and SDBS co-modification of SiO2/FeS, providing a new amendment for Cd remediation.
As an industrial byproduct of smelter operations, smelting slag has brought certain environmental issues including without taking safety precautions or using appropriate management. Through a thorough analysis of the literature published in the last years, the latest research progress on the characteristics, resource utilization pathways, and safety utilization evaluation of non-ferrous metal smelting slag was introduced in this work. Key findings indicate that different ore concentrate materials, smelting conditions and types determine chemical and mineralogical characteristics of smelting slag. Moreover, smelting slag exhibits extremely high flexibility in various applications, not only as metal recovery and construction materials, but also as agricultural fertilizers and remediation agents. At the same time, the importance of conducting strict safety assessments under various utilization scenarios to mitigate its potential environmental risks is emphasized. In addition, this article also emphasizes the direction of future research, including creating a comprehensive and quantized environmental risk assessment method of heavy metals in soil-slag mixtures, as well as exploring more innovative utilization methods of smelting slag. Overall, this review is significant for promoting research on the use of smelting slag in environmental protection and sustainable resource utilization.
Little was known about the leaching behavior of potentially toxic elements (PTEs) from soils under the interaction between freeze-thaw (F-T) cycle and the solutions of varying pH values. In this study, PTEs leachability from soils before and after F-T tests was evaluated using toxicity characteristics leaching procedure (TCLP) test. The microstructure and mineralogical evolution of soil mineral particles were conducted using pores (particles) and cracks analysis system (PCAS) and PHREEQC. The results indicated that during 30 F-T cycles, the maximum leaching concentrations of PTEs were 0.22 mg/L for As, 0.61 mg/L for Cd, 2.46 mg/L for Cu, 3.08 mg/L for Mn, 29.36 mg/L for Pb and 8.07 mg/L for Zn, respectively. Under the coupled effects of F-T cycle and acidification, the porosity of soil particles increased by 4.79%, as confirmed by the microstructure damage caused by the evolution of pores and cracks. The anisotropy of soil particles increased under F-T effects, whereas that decreased under the coupled effects of F-T cycle and acidification. The results from SEM-EDS, PCAS quantification and PHREEQC modeling indicated that the release mechanism of PTEs was not only associated with the microstructure change in mineral particles, but also affected by protonation, as well as the dissolution and precipitation of minerals. Overall, these results would provide an important reference for soil remediation assessments in seasonal frozen areas.
Potential toxic elements (PTEs) generally co-existing in soils make a great challenge to the sustainable development and utilization of smelter contaminated sites. This study delved into the pollution characteristics of PTEs and conducted the field-scale remediation of PTEs stabilization. The results indicated that Cd, Pb, Zn, and As were identified as the main PTEs pollutants in soils with exceedance rates of 75.80% for Cd, 76.43% for Pb and 88.54% for As, respectively. The distribution patterns of PTEs were closely associated with soil physicochemical properties, pollutant transport routes, hydrogeological conditions, formation lithology, smelting process and smelting workshop distribution. Soil PTEs mainly originated from smelting activities, such as the emissions of smelting wastewater, flue gas and slags. In addition, a combination of mixture agents and chelating agent (TJ400) showed excellent performance for the synchronous stabilization of Cd, Pb and As within 7 d, and the mixing degree between stabilization agents and contaminated soils was over 90%. The present results would offer practical guidance in developing a suitable remediation scheme based on a comprehensive investigation of the pollution characteristics of PTEs in soils.
Chromium (Cr) contamination in soil is one of the most severe environmental issues, which poses significant health hazards to humans. In this study, the stabilization mechanism of Cr-contaminated soil by polysulfide-supported nZVI@biochar (PS-nZVI@BC) and the resultant bioavailability of Cr was studied. The addition of PS-nZVI@BC is capable of decreasing 92.0% of leachable Cr(VI) in the soil after 30 days of treatment. According to sequential extraction analysis, the exchangeable Cr in soil decreased drastically from 20.8% to 4.0% after PS-nZVI@BC addition, which was mostly converted to Fe-Mn oxided and organic matter-bound forms. The stabilization mechanisms include electrostatic adsorption, redox reaction, surface complexation, and precipitation. The soil fertility of Cr-contaminated soil was effectively improved by PS-nZVI@BC, and the toxicity of Cr in soil to maize seedlings was reduced. These results demonstrated the great potential of utilizing PS-nZVI@BC for the remediation of Cr-contaminated soils.
Uranium tailings discharged into uranium tailings ponds could generate environmental pollution issues. Microbial-induced phosphate mineralization could reduce the release of uranium, in turn effectively managing pollution. However, it is unclear that how the phosphorus additives affect the microbial structure of uranium tailings under biomineralization. Herein, we evaluate the microbial community succession during Bacillus spp. remediation of uranium tailings, when adding hydroxyapatite (HS) and β-glycerol phosphate pentahydrate (GP). The results show that phosphorus additives effectively changed pH and uranium leaching concentration, significantly increased bacterial richness, and promoted microbial community succession, whilst promoting actinobacteria to Firmicutes and Proteobacteria populations. The two additives influenced the bacterial community succession patterns differently, with GP eliciting the greater enhancement. Additionally, GP enhanced the growth of core species and recognized the phylum firmicutes as a crucial taxon. The abundance of Bacillus, Pseudomonas, Desulfotomaculum, and Clostridium_sensu_stricto_12 was higher in GP treatments, indicating the substantial roles played by these genera in the microbial community. The results provide evidence of the involvement of the two phosphorus additives in bioremediation and bacterial community perturbations and thus provide new insights into the biomineralization technologies for uranium tailings.
Opal (amorphous silica, SiO2·nH2O), a solid waste byproduct of the alkaline extracting alumina from coal fly ash, exhibits strong adsorption properties and is a secondary/clay mineral in the soil. Combining opal with sand to construct opal/sand aggregates for desertification soil remediation holds the potential for large-scale ecological disposal. Unfortunately, the aggregate structure still gaps from natural soil aggregates resulting from inorganic mineral deficiencies. Herein, the effects of five inorganic mineral amendments, limestone (CaCO3), desulphurization gypsum (CaSO4·2H2O), hematite (Fe2O3), tricalcium phosphate (Ca3(PO4)2) and gibbsites (Al(OH)3), on aggregate formation, stabilization, and pore characteristics without the organic matters were investigated in short-term cultivation experiments. Meanwhile, associated adsorption mechanisms were elucidated. Results indicated only gypsum effectively reduced the aggregate’s pH, most enhanced water-holding capacity, albeit increased electrical conductivity. All amendments facilitated aggregate formation and mechanical-stability, with gypsum, CaCO3, and Fe2O3 improving water stability. Various analysis techniques, including XRD, SEM, nano-CT, FT-IR, and XPS, provided insights into the physisorption and chemisorption of minerals onto sand/opal, generating interfaces conducive to aggregation. Compared to CK (control check, without amendment addition), amended macroaggregates demonstrated increased porosity, reduced pore quantity and mean pore diameter (MPD), denser pore structure, improved interpore connectivity, and more complex pore networks, dominated by <80 µm diameters and boundary pores. Notably, desulphurization gypsum elicited the most significant variations, increasing MPD of microaggregates and 2–5 nm mesopores, and decreasing total pore volume and 0–2 nm micropores, while Ca3(PO4)2 and Al(OH)3 improved >15 nm mesopores. Overall, inorganic minerals, the “skeleton” of soil, effectively upgraded opal/sand aggregates’ physical structure and accelerated aggregate formation quickly. Therein, desulphurization gypsum optimized macroaggregate formation and stability. Desulphurization gypsumamended aggregates serve as soil-like substrates to accelerate the ecological reconstruction of desertification areas.
Cadmium (Cd) is a biologically non-essential and toxic heavy metal that enters the environment through natural emissions or anthropogenic activities, posing threats to human health. The efficient expression of metal-chelating proteins (MCP) in microorganisms can enhance microbial remediation of Cd. In this study, a heterologous expression system (GEM01) of MCP encoded by the mcp gene in E. coli was constructed, and the adsorption effect and potential mechanism on Cd were explored. The results indicated that Cd2+ significantly enhanced the abundance of mcp gene in GEM01, thus increasing the Cd2+ biosorption capacity (8.09 mg/g, 2.32 times higher than the control). The retention of Cd2+ during the autolysis of GEM01 was 87.87%. Fluorescence spectroscopy and molecular dynamics simulations demonstrated that there was a strong interaction between Cd2+ and MCP. FT-IR demonstrated that some functional groups (e.g., carboxyl group and methyl group) in MCP were involved in the interaction between MCP and Cd2+. Molecular docking further demonstrated that polar and hydrophilic residues (e.g., aspartic acid, glutamic acid, serine, and histidine) on the surface of MCP bound to Cd2+ via electrostatic attraction. These findings offer new insights into Cd2+ bioremediation by MCP and genetic resources for microbial remediation of heavy metal pollution.
The application of coal gangue as a soil amendment shows promise in increasing silicon availability, potentially serving as a silicon fertilizer in agriculture. However, the rapid release of silicon from coal gangue compared to the slow absorption by plants hinders its effective use. This study explored the formation of iron-containing secondary minerals on coal gangue surfaces using pyrite and citric acid to stabilize arsenic in contaminated soils and slow down silicon leaching. After co-ball milling, the silicon leaching rates for coal gangue and the composite C@PC-10 were 0.44% and 0.22% at 60 min, and 1.11% and 1.38% at 120 min, respectively. Stabilization tests showed that C@PC-10 achieved removal efficiencies of 71.3% for water-extractable arsenic and 55.9% for NaHCO3-extractable arsenic over 30 d. Acid-soluble arsenic decreased from 32.8% to 24.1%, while residual arsenic increased from 26.5% to 36.9%. Acid rain simulations demonstrated that C@PC-10 limited leachate arsenic concentration to 28.9 mg/L over 120 d, compared to untreated soil with 59.8 mg/L. Analytical techniques like XRD, XPS, and FT-IR confirmed that pyrite oxidation during ball milling led to the formation of jarosite and FeOOH, enhancing arsenic adsorption capacity. Overall, the C@PC-10 composite shows promise as a remediation material for controlled silicate release and arsenic mitigation in soil environments.
Heavy metal composite pollution is becoming increasingly serious. In this study, CaAl-layered double hydroxide (CaAl-LDH) was prepared using the facile co-precipitating method, and was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Lead(II), Cd(II), and As(V) were selected as the representative heavy metals to evaluate the adsorption capability of the synthesized CaAl-LDH by the batch experiments. The maximal adsorption capability of CaAl-LDH for Pb(II), Cd(II), and As(V) was 786.6, 437.2 and 72.9 mg/g, respectively. The adsorption mechanism of Pb, Cd and As may be surface precipitation, isomorphic substitution and ion exchange within the interlayer spaces of LDH, respectively. In conclusion, this experiment provides a LDH material with fast and efficient adsorption performance for both anionic and cationic metals, indicating its potential for practical application in the remediation of heavy metal composite pollution.
Adsorption is considered an effective strategy for removing Cr(VI) from wastewater, but disposal of spent adsorbents is still a thorny problem. This work aims to develop an efficient adsorbent for Cr(VI) removal and recycling spent adsorbent as catalyst for the removal of organic dyes. In this study, MgAl-mixed oxides adsorbents (MgAlO) were synthesized via hydrothermal and calcination steps to effectively adsorb Cr(VI) from wastewater. The influence of initial pH and temperature on the adsorption performance of MgAlO was investigated. The maximum adsorption capacity for Cr(VI) was 95.2 mg/g at a MgAlO dosage of 1.0 g/L and a pH value of 5.5. The combination of XRD, FT-IR, and UV-vis DRS analyses revealed that CrO4 2− anions were intercalated into the interlayer spaces of layered double hydroxides, and high temperatures can accelerate the reconstruction of MgAlO. The adsorption of Cr(VI) by MgAlO followed the pseudo-second-order kinetic model, which included intra-particle diffusion, film diffusion, and chemical reaction. Furthermore, the resulting spent adsorbent (Cr-MgAlO) after adsorption was reused as a catalyst for methyl orange (MO) removal after adsorption (75.6% removal rate) and showed no significant decrease in removal rate after 5 cycles. The results of this study provide insights into the reuse of spent Cr(VI) adsorbent for environmental catalytic applications, which are of great importance for the disposal of waste adsorbent.
Hazardous arsenic antimony dust (HAAD), a perilous by-product with significant antimony and arsenic concentrations generated in lead smelters, poses a substantial environmental threat. The imperative of resource recycling and the innocuous processing of HAAD stand as prevalent challenges and pressing priorities. This study introduces an innovative vacuum vaporization-condensation technique to synthesize Sb2O3. ICP analysis evidenced an enhancement in the purity of the Sb2O3 product from an initial 73.96% to 91.35%, with a concomitant reduction in As impurities from 18.10% to 6.20%, and residual contaminants approximating 0.17% following a dual-phase vacuum process. XRD assessments affirmed the feasibility of direct Sb2O3 synthesis via vapor-phase migration and condensate amalgamation, achieving substantial As2O3 impurity diminution. SEM and EPMA observations underscored a homogenous particulate morphology in the refined Sb2O3. This methodology underscores its environmental compatibility, characterized by zero gaseous effluent, absence of wastewater expulsion, and elimination of reagent usage, thereby mitigating environmental detriments.
Coal gasification slag (CGS) and Fe-modified CGS (FGS) were employed to remediate cadmium (Cd) and arsenic (As) in co-contaminated agricultural soils. Adsorption experiments in aqueous systems and stabilization experiments in soil were conducted to evaluate the passivation potential of the CGS and FGS. The maximum adsorption capacities of FGS for Cd and As were 5.82 and 9.69 mg/g, while those of CGS were only 0.99 and 0.92, respectively. X-ray diffraction patterns showed that iron oxide was successfully loaded onto FGS. And the complexation of Cd and As with Fe2O3 and FeOOH significantly improved the adsorption capacity of FGS. The concentration of soil extractable Cd (DTPA) was reduced from 0.70 to 0.58 mg/kg with FGS application, which was likely facilitated by the pH increased from 6.46 to 7.03 and the complexation of Cd with oxygen-containing functional groups or FeOOH. The concentration of dissolved As in soil decreased from 15.33 to 13.72 mg/kg owing to the complexation of As with FeOOH. By demonstrating the application potential of FGS as soil remediation agents and revealing the stabilization mechanism of Cd and As, this study is expected to facilitate the recycling of CGS as an adsorbent for soil remediation.
This study aimed to synthesize porous geopolymers from tailing slurry, a byproduct of bauxite mining, for use as potential materials for groundwater remediation. The effects of various factors, such as foaming agents, liquid-solid (L/S) ratio, and foam stabilizers, on the geopolymers’ pore structure and adsorption properties were investigated. Batch experiments and characterization methods were conducted to evaluate the adsorption capacity and mechanism of the geopolymers on binary heavy metals (Pb2+ and Cu2+). The results showed that adjusting the foaming behavior resulted in a porous geopolymer with porosity of 81.4%, connectivity of 17.2%, and water absorption rate of 122.9%. The presence of closed pores and capillaries hindered the removal performance of heavy metals. In contrast, optimizing foaming behavior could increase the adsorption capacity of Pb2+ from 7.49 mg/g to 24.95 mg/g by improving pore connectivity. The main removal mechanisms include physical sealing, chemical precipitation of heavy metal ions with —OH, and the formation of chemical bonds T (Si, Al)—O—M (Pb, Cu). Tailing slurry-based porous geopolymers (TPGs) demonstrated excellent heavy metal removal performance and exhibited great potential in remediating mine-polluted groundwater.
Biochar has been considered as a promising material for soil remediation, particularly for its ability to reduce the bioavailability of cadmium (Cd) in soil through sorption. However, long-term remediation may cause Cd to be released from a fixed state, making the recovery of biochar as an adsorbent for Cd removal an area of increasing interest. The study aims to synthesize biochar with magnetic properties using petroleum sludge containing iron in one-step, and investigate their adsorption efficiency and passivation mechanism for Cd in liquid-solid phase, as well as ecological risks. The results indicate that the petrochemical sludge waste can be directly resourced into magnetic biochar (PSMBCs) using hypoxic pyrolysis, and that it exhibits good recycling performance in water/soil. Specifically, the obtained biochar showed strong sorption capacity for Cd (18.4 to 29.8 mg/g) due to surface mineralization and cation-π coordination, which played a critical role. After applying 1.5% of PSMBCs for 30 d in paddy soil, the bioavailable content of Cd was decreased by 85.0%. Importantly, the biochar leachates did not have any toxic effects on wheat root elongation. Therefore, this study presents a promising strategy for the benign disposal of petrochemical sludge and their utilization for the remediation of Cd-contaminated soil.
This study analyzed the pollution level, distribution, sources, and ecological impact of six heavy metals (As, Cd, Cr, Cu, Zn and Pb) in soil from Linli County, China. The concentration analysis showed that the concentration of Cd in all samples exceeded the background value, and the exceeding rate reached 100%, while the average concentrations of other elements were similar to the background value, and the exceeding rate was under 15%. The pollution level of Cd was the most severe according to geo-accumulation index and enrichment factor, while other elements were under mild pollution level. The results of self-organizing map (SOM) and positive matrix factorization (PMF) analysis showed that agricultural activities were one of the main sources of heavy metal elements in soil, and natural weathering and industrial pollution could also lead to soil pollution. Cd appeared to be the most significant pollutant element in the soil of Linli County, and it had the largest impact on the ecological environment. Overall, this study provides guidance for soil pollution control and related policies, aiming to reduce the pollution of heavy metal elements in soil and the hazards to the ecological system caused by agricultural production and industrial activities.