Stable Remediation Of As And Cd In Soil By Surfactant Modified Zeolite And Biochar

In recent years,with the continuous and complex changes in my country’s industrial and agricultural production,and the rapid acceleration of urbanization,environmental pollution has become increasingly prominent.The characteristics of environmental problems are concomitant and comprehensive.The common pollution of arsenic（As）and cadmium（Cd）has always been a typical problem in Chinese farmland and historical metal mining and smelting activities.The immobilization of As and Cd in soil has faced many difficulties because of the unique properties of the two metals.At present,common heavy metal contaminated soils were repaired by physical,chemical,and biological methods,among which stable fixation is a more effective and generally applicable method.Zeolite and biochar are common and cost-effective adsorbents.Due to their negative surface charge,zeolite and biochar only have many capacities for adsorption for cationic pollutants.Many recent studies have used surfactants to modify zeolite.Therefore,in this study,the researcher choose Hexadecyl trimethyl ammonium Bromide（HDTMA）to modified zeolite and biochar,applied them to the remediation of As and Cd contaminated soil,and evaluated the remediation effect.In this study,the researcher have prepared HDTMA modified materials（including modified zeolite and modified biochar）that can simultaneously adsorb heavy metal anions and cations,then the modified zeolite was combined with As and Cd contaminated farmland soil.The modified biochar was interacted with the heavily As and Cd contaminated soil in the mining area to determine and evaluate the physical and chemical properties of the soil and the pollution of heavy metals.The increase in surface zeta potential indicated that HDTMA modification gives the material the ability to adsorb As.The sequential extraction results showed that compared with the other two treatment groups,the percentage of residual As in the HDTMA modified zeolite treatment group increased（2.7～5.9%）,and the HDTMA modified zeolite reduced the potential toxicity of soil As.In addition,Cd in the soil can be effectively stabilization by zeolite and modified zeolite.Modified zeolite can effectively improve the soil microbial environment.Besides,the bioavailability of As and Cd in the soil has reduced after adding modified zeolite.Therefore,HDTMA modified zeolite is a potentially beneficial stabilizer for repairing As and Cd contaminated soil.In the study on the stability of soil As and Cd using modified biochar,continuous extraction experiments of contaminated soil showed that As and Cd in the soil mainly exists in the form of residues.With the addition of biochar and modified biochar,the fluidity of As and Cd in the soil has enhanced.In addition,the potential toxicity of As and Cd increases.The extraction results of Na H₂PO₄ showed that biochar increased the utilization rate of As by 3.23～22.76%,while the HDTMA modified biochar reduced the utilization rate of As by 4.80～13.41%.Potted cabbage experiments showed that biochar and modified biochar increased the biomass of cabbage.Compared with biochar,modified biochar（HB5）reduced the absorption of As and Cd by plants.Therefore,two types of biochar have promoted the transformation of As and Cd in the soil from a stable state to a mobile state.However,HDTMA modified biochar has the effect of reducing the bioavailability and toxicity of As and Cd.