| Cadmium（Cd）and arsenic（As）are internationally recognized as potentially car-cinogenic and toxic elements that are easily enriched in crops after migration and trans-formation in soil,and in organisms through the food chain,posing a serious threat to human health.Due to the opposite chemical properties of Cd and As,the availability of the two contaminants cannot be reduced simultaneously in the soil,and soil amendments on the market are expensive.Therefore,it is urgent to develop efficient and inexpensive soil amendments to reduce the enrichment of Cd and As in crops.Coal gangue,as a coal-based solid waste,contains a large amount of silicate and silica-aluminate.It has a great potential for Cd adsorption,but has poor adsorption performance for As.To solve the above technical problems,this study（1）analyzes the properties,total amount and frac-tions of potentially toxic elements of coal gangue and its effects on soil microbial diver-sity for comprehensively evaluating the potential and feasibility of developing soil amendments based on coal gangue;（2）prepares magnetic porous materials（MPCG）by modifying coal gangue,then analyses its adsorption performance and mechanisms on Cd（Ⅱ）and As（Ⅴ）;（3）studies the effects of MPCG on soil physicochemical properties and the stabilization efficiency for Cd and As in contaminated soil,and use characterization techniques（SEM-EDS,XRD and XPS）to explore the potential stabilization mechanisms of MPCG for Cd and As;（4）investigates the effects of MPCG on soil physicochemical properties,nutrients,available Cd and As,Cd and As accumulation in crops and rhizo-sphere soil microorganisms to explore the mechanisms of MPCG for regulating Cd and As accumulation in crops.The main conclusions are as follows:（1）Properties and environmental risk of coal gangue.The concentrations of poten-tially toxic elements in coal gangue were lower than the risk screening values of the Soil Environmental Quality-Agricultural Land Soil Pollution Risk Control Standard（GB15618-2018）（p H>7.5）.According to the comprehensive index of ecological risk and potential ecological risk,the potential ecological risk of coal gangue was low.The results of the risk assessment index showed that there is no risk of As and Cr in the coal gangue samples,and Cd,Cu,Ni,Pb and Zn in the gangue samples of Zhujidong mine and Xinzhuangzi mine were medium risk,while Cd,Cu,Ni,Pb and Zn in others samples both were low risk.In addition,coal gangue had little effect on soil microbial diversity and community structure.Considering the potential ecological risk index,risk evaluation index of coal gangue and its influence on soil microbial diversity,the environmental risk and ecological risk of tested coal gangue samples were low.（2）Preparation of gangue-based magnetic porous material and its adsorption mech-anism for cadmium and arsenic.Coal gangue was thoroughly mixed with 0.10 mol/L Fe SO4·7H2O solution,filtered and dried,then 5%Ca O was added and pyrolyzed at 800°C for 2 hours to prepare the coal gangue-based magnetic porous materials（MPCG）.The MPCG that was prepared under this condition had the best removal effect for Cd（Ⅱ）and As（Ⅴ）.MPCG showed an irregular reticular porous structure with a smooth surface,and its surface elements mainly were O,Al,Si,S,Ca and Fe.Fe mainly existed in the form of magnetite,hematite and pyrite in MPCG.The adsorption processes of Cd（Ⅱ）and As（Ⅴ）by MPCG are mainly chemical adsorption,which can adsorb Cd（Ⅱ）from water by ion exchange,electrostatic attraction,surface complexation and precipitation/co-precipita-tion,and adsorb As（Ⅴ）from water by electrostatic attraction,surface complexation and precipitation.Compared with other adsorbents,MPCG showed higher adsorption capac-ity for Cd（Ⅱ）and As（Ⅴ）,which were 103.79 and 579.43 mg/g,respectively.（3）Mechanisms of coal gangue-based magnetic porous materials reducing the bioa-vailability of cadmium and arsenic in soil.The stabilization effect of MPCG on Cd and As was significantly higher than that of coal gangue,which reduced the available Cd and available As by 14.22～30.41%and 17.94～29.81%,respectively,and promoted the trans-formation from unstable Cd/As to stable Cd/As.The stabilization mechanisms of MPCG for Cd included adsorption,ion exchange,complexation and precipitation.MPCG rapidly enriched Cd to the surface through adsorption and ion exchange.At the same time,Cd complexed with Si-OH and-OH on the surface of MPCG,and further formed a more stable insoluble precipitate with Ca（OH）2 on the surface and inside of MPCG.The stabi-lization mechanisms of MPCG on As included adsorption,oxidation,complexation and precipitation/co-precipitation.MPCG adsorbs As（III）/As（V）to the surface by electro-static attraction,and As（III）/As（V）can combine with iron oxides and hydroxides in MPCG to form stable complexes and precipitates/coprecipitates.Meanwhile,part of As（III）was oxidized by Fe（III）and·OH to form As（V）with low mobility and toxicity.In addition,MPCG can promote sulfate reduction by increasing the abundance of sulfate-reducing bacteria（dsr A）in soil.The sulfide can precipitate with As and Cd to reduce the bioavailability of Cd and As in soil.（5）Effects of coal gangue-based magnetic porous materials on cadmium and arsenic accumulation in soil crops.MPCG can promote the growth of Brassica chinensis L by improving the acidic environment,increasing nutrients and reducing the availability of Cd and As in soil.When adding 3%MPCG in soil,the available Cd and available As in soil decreased by 15.98%and 58.98%,respectively,and the biomass of Brassica chinen-sis L increased by 48.97%.In addition,MPCG significantly increased the relative abun-dance of aio A and dsr A,but decreased the relative abundance of Geobacyeraceae in rhi-zosphere soil.Under the synergism of microorganisms,MPCG can significantly reduce the uptake of Cd and As by crops,and can promote the uptake of Si by crops by increasing the content of available Si in soil,which inhibited the transport of Cd from crop roots to shoot,and thus reduce the accumulation of Cd in the shoot of crops.Figure 66 Table 18 Reference 268... |
