Microscopic Study On Remediation Of Cadmium And Arsenite Co-contamination By Fe-Mn Co-doped Titanosilicate In The Environment

Heavy metal pollution is becoming increasingly serious.Heavy metal complex pollution has become the focus and difficulty of environmental pollution improvement.In particular,the co-contamination of cadmium and arsenic in the environment has attracted widespread attention.Therefore,the topic of remediation of co-contamination of cadmium and arsenic has also become a research hotspot.In this study,iron(Fe)and manganese(Mn)elements with strong affinity for arsenic(As)were selected to prepare Fe-Mn co-doped titanosilicate(ETFMS-10)with both adsorption and oxidation capacity by hydrothermal method.It was used to deal with Cd and As co-contamination aqueous solution and soil for adsorption experiment and soil culture experiment,and its adsorption/immobilization effect was explored.The material was characterized by a series of methods including SEM-EDS,BET,XRD and XPS.The the maximum adsorption capacity of Cd and As in the singlepollutant system and the effect of initial p H,adsorption time and initial pollutant concentration on the co-adsorption in the dual-pollutant system were investigated.The characterization results confirmed that Fe and Mn were successfully doped in the ETS-10 structure.The modified material showed larger pore volume and specific surface area,which was more conducive to the adsorption of heavy metals.In a single pollutant system,the maximum adsorption capacity of ETFMS-10 for Cd(101.86 mg/g)and As(3.18 mg/g)was much higher than that of ETS-10 for Cd(42.18 mg/g)and As(0.51mg/g).In a dual pollutant system,the experimental results showed that the removal efficiencies of Cd and As by ETFMS-10 were more than 98% and 70% across p H 4 ～8,respectively,and the capture of Cd and As on ETFMS-10 was mainly controlled by chemical adsorption.In adition,XPS analysis showed that Fe mainly served as adsorption sites on the ETFMS-10,while Mn was chiefly employed as an oxidant.The main mechanisms for Cd(II)and As(III)removal on ETFMS-10 included electrostatic attraction,ion exchange,and an inner-sphere M-O-As complex formation.These results indicated that the prepared ETFMS-10 had a broad application potential in the treatment of Cd and As co-contamination.Based on the aqueous solution adsorption experiments,ETFMS-10 was used to remediate Cd and As co-contaminated soil,and the effects of ETFMS-10 on soil physicochemical properties,enzyme activities and the stabilization effects on Cd and As were investigated.The results showed that soil p H and EC were significantly increased with the addition of ETFMS-10.The p H was increased by 1.00 and 1.89 in the 1% and 3% treatment groups,and the EC was increased by 330.50 and 902.50 μs/cm,respectively.ETFMS-10 significantly decreased the leaching toxicity of Cd in soil and promoted the conversion of exchangeable Cd and residual Cd to reducible Cd.Meanwhile,the addition of ETFMS-10 reduced Ca-As fraction and increased the O-As fraction.In addition,ETFMS-10 did not significantly change soil acid phosphatase,and it inhibited soil invertase activity and enhanced soil dehydrogenase activity.To sum up,the material showed the immobilization effect of As in soil in a short period of time(30 days),and although it did not show good stabilization effect on soil Cd,it could reduce the leaching toxicity of soil Cd.The material needs to be further studied and optimized to become a good soil stabilizer in the remediation of Cd and As cocontaminated soil.