| In recent years,the problem of heavy metal pollution in farmland soil has been intensifying in China,bringing serious harm to soil environmental quality and human health.To manage this problem,in situ passivation repair is considered one of the most effective methods.Based on the control of cadmium pollution in alkaline soil in northern China,this study used high-speed shear gel method to modify the sulfhydryl group of palygorskite（PAL）,prepared sulfhydryl modified palygorskite（MPAL）,and characterized its physicochemical properties by XRD,FT-IR,SEM,BET pore structure analysis and simultaneous thermal analysis TG-DSC.Through a series of solution adsorption tests,the adsorption effect of MPAL with different mass ratios on Cd2+was explored,the best modified materials were screened,and the effects of different Cd2+concentration,adsorption time and pH value on the adsorption performance of MPAL were explored.Combined with XRD,FT-IR and XPS,the adsorption mechanism of cadmium by MPAL was explored.Finally,the effects of PAL and MPAL on Cd content,soil pH and cabbage in soil DTPA extraction were investigated by soil passivation test and indoor cabbage potting test,so as to evaluate the remediation effect of MPAL in cadmium-polluted alkaline soil.The main research results are as follows:（1）Through a series of physicochemical characterizations,such as XRD,FT-IR,SEM,ET pore structure analysis,it is confirmed that when the mass ratio of（3Mercaptopropyl）trimethoxysilane to palygorskite is 1:1,the sulfhydryl-modified palygorskite has the best adsorption effect.At the same time,sulfhydryl modification did not destroy the crystal structure of natural wisp stone,with BET surface areas of 111.84 and 88.70 m2/g,and average pore sizes of 7.98 and 11.32 nm,respectively.（2）The results showed that both PAL and MPAL could effectively adsorb Cd2+in aqueous solution,and the adsorption effect of MPAL was better than PAL.The pseudo second order kinetics model is more suitable to describe the dynamic change process of Cd2+adsorption on PAL and MPAL.MPAL reaches the adsorption equilibrium in about 90 minutes,which is faster than PAL.Freundlich isotherm absorption can describe the adsorption data better.Under the experimental conditions,the saturated adsorption capacity of MPAL is 44.41 mg/g,which is significantly higher than that of PAL（33.65 mg/g）.（3）PAL and MPAL could significantly reduce the Cd content in the ground parts of cabbage under different treatments.The effect of MPAL on the absorption of Cd by cabbage was better than PAL,and the maximum Cd content in the ground parts of cabbage could be reduced by 39.14%and 79.61%,respectively.In addition,different treatments could significantly increase the biomass of brassica oleracea L.,and the biomass of brassica oleracea L.was increased by 1 and 4.65 times when the amount of two passivating materials was 0.3%,respectively.The content of Cd extracted from DTPA in soil was decreased by 28.15%and 53.60%when the content of Cd was 0.3%.The soil pH value was increased by 0.24 and 0.07 units,respectively.（4）X-ray diffraction peak analysis,FTIR functional group vibration mode analysis and binding energy analysis of key elements of XPS showed that PAL adsorbed Cd through the formation of surface complexation between the surface hydroxyl group and Cd2+,while MPAL also provided a large number of sulfhydryl functional groups as adsorption sites,and formed complexation precipitation through the complexation reaction between the surface hydroxyl group and the sulfhydryl group and Cd2+. |
