| While the fast growth of industries brings economic take-off,it also brings various environmental problems,which cause significant damage to human health and sustainable development of ecological environment.Among them,heavy metal pollution in water and soil is an environmental problem that needs to be solved.Heavy metals are not only difficult to degrade,but also accumulate in living organisms,so effective measures must be taken to treat them.Adsorption is considered as one of the promising technologies to treat heavy metal pollution in water because of its high efficiency and low cost.In-situ immobilization technology in heavy metal contaminated soil is of wide interest because of its fast results and easy operation.The key to the widespread application of these two technologies is the synthesis of efficient and environmentally benign heavy metal adsorbing/solidifying agents.As a naturally occurring mineral clay,layered double hydroxide(LDH)is homologous to environmental soils,and therefore is cost-effective and environmentally friendly for remediation of heavy metal contamination in the environment.However,natural LDH is scarce in nature and its purity is not high enough to meet the demand of practical use.However,the synthetic LDH process is prone to structural stacking,which reduces its heavy metal adsorption and immobilization properties.Moreover,LDH is alkaline in nature,and its application in soil may have certain effects on soil microorganisms.The above problems limit the applications of LDH in the environmental heavy metal contaminant treatment.In this study,the introduction of bentonite with a layered structure as a support material for the synthesis of LDH can effectively reduce the stacking generated during the synthesis of LDH,and the adsorption performance of the synthesized LDH-bentonite modified material for heavy metals Pb and Cd is significantly improved.Compost,as an effective soil conditioner and with the presence of functional groups on its surface that can adsorb heavy metal pollutants,can effectively reduce the bioavailability of heavy metals in soil by applying it in synergistic LDHbentonite modified material to the soil contaminated with heavy metals Pb and Cd.Moreover,the synergistic effect of LDH-bentonite modified materials and compost can effectively reduce the effect of the materials on soil microorganisms.This study lays the theoretical research foundation for the simple and efficient preparation of LDH-modified materials and their practical application in environmental heavy metal pollution remediation.The main elements and key findings of this study are as follows:1.To improve the issue of stacking that often occurs during the synthesis of LDH,and to increase the specific surface area and adsorption capacity of the material,bentonite was used as a supporting material to synthesize bentonite-supported LDH modification material through a simple coprecipitation method.Adsorption experiments were carried out on the synthesized modified materials,and the LDH-bentonite modification material with the best adsorption effect was selected based on the adsorption capacity.Experimental results showed that the iron and magnesium ions loaded on bentonite through adjusting p H with alkali solution formed the best modified material,FeMg-LDH@Bentonite,for the adsorption of heavy metals such as lead and cadmium.Characterization of FeMg-LDH@Bentonite showed that the FeMg-LDH was uniformly loaded on the bentonite,forming a threedimensional layered petal structure.Compared with FeMg-LDH,the modified material FeMg-LDH@Bentonite has higher thermal stability and a larger specific surface area,making it more adaptable to the environment,with more adsorption sites,and therefore enhancing the overall adsorption performance of the modified material.2.In this study,the adsorption performance and mechanism of FeMgLDH@Bentonite were investigated.Pb(Ⅱ)and Cd(Ⅱ)were chosen as representatives of heavy metals to study the adsorption capacity of the modified materials.Batch adsorption experiments revealed that various parameters,such as contact time,p H,initial concentration,cation content,and temperature,had a clear influence on the adsorption performance.The maximal adsorption capacities of FeMg-LDH@Bentonite for Cd(Ⅱ)and Pb(Ⅱ)were found to be 510.2 mg/g and 1397.62 mg/g,respectively,exceeding those of traditional adsorbents.The adsorption kinetics study showed that the adsorption of heavy metals on the modified material can be simulated by the pseudo-second-order kinetic model and the Langmuir model,suggesting that the adsorption was mainly a uniform chemical adsorption on the surface of the modified material.The adsorption mechanism of the modified material was investigated using various characterization methods,such as XRD,SEM,TEM,FTIR,and XPS.The results indicated that surface complexation,ion exchange,and chemical precipitation mechanisms might exist.In addition,the modified material shows great potential in treating natural water contaminated with heavy metals,demonstrating its feasibility for environmental applications.3.The performance and mechanism of FeMg-LDH@Bentonite combined with compost for the remediation of cadmium and lead-contaminated soil were investigated.FeMg-LDH@Bentonite was mixed with compost at different ratios and applied to potted rice plants contaminated with cadmium and lead.The application of the modified material with compost affected the soil p H,water-soluble organic carbon(WSOC),and soil organic matter(OM)content.The bioavailability of cadmium and lead in the soil was reduced,resulting in a decrease in the concentration of cadmium and lead in different parts of the rice plant.The application of FeMg-LDH@Bentonite to small-scale paddy fields for cadmium pollution treatment was effective in reducing the bioavailability of cadmium in paddy soil.An economic evaluation of the modified material showed that it had good practical application prospects with low cost and simple preparation compared to existing methods.FeMgLDH@Bentonite has a good effect on passivating heavy metals in soil,and compost can provide necessary nutrients to the soil,changing soil characteristics.The synergistic effect of the two can decrease the bioavailability of the soil heavy metals and improve the soil quality.4.This study investigated the effects of FeMg-LDH@Bentonite and compost used as a remediation agent on microorganisms in cadmium and lead contaminated soil.The results showed that the application of FeMgLDH@Bentonite and compost in different ratios had no significant effect on the activity of soil peroxidase,but had different effects on the activity of soil urease.The mixture also had a significant impact on the bacterial diversity and community structure,as well as the abundance of specific bacterial groups in the soil.The compost in the remediation agent is rich in organic matter,which can effectively improve soil nutrient status and microbial composition,while the modified material can fix heavy metal ions in the soil.Therefore,the synergistic effect of the two can reduce the bioavailability of heavy metals in contaminated soil and improve soil environment. |
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