Study On The Remediation Of Arsenic Contaminated Soil By Arsenic Stabilization

Arsenic as a high toxic metalloid element is widely distributed in the environment,the abundance of which in the crust of the earth ranks the20th. During the development ofthe industries, the mining of the minerals and the application of chemicals containingarsenic, the problem of arsenic pollution arising has become more and more serious,especially for the soils around mining sites. Therefore, the remediation of arseniccontaminated soil has been received much attention. Stabilization technique is a promisingtechnology in soil remediation for its simple and cost-effective.The arsenic contaminated soil studied was collected from a chemical industrycorporation of Wu Han which produced sulfuric acid using pyrite as the raw material.Arsenic is a thiophil element. It will be released to the environment during the miningprocessed with high temperature. As the corporation has been relocated and the placewould be used as residents living place, it is necessary to evaluate the arseniccontamination and restore the highly arsenic contaminated place. Ferrous sulfateheptahydrate （FeSO₄·7H₂O） was used as the active iron source. The influence of the molarratios of iron to arsenic, water to soil ratios and pH were investigated. The stabilizationefficiency was evaluated by the Toxic Characteristics Leaching Procedure according to theMethod1311of the US EPA regulation. The main conclusions were as follows:（1） Mixed concentrated acid digestion was carried out to transport the iron andarsenic elements in soil sample into the aqueous sample. The concentration of arsenic andiron were analyzed by silver diethyldithiocarbamate spectrophotometry ando-phenanthroline spectrophotometry, respectively. The results indicated that the arsenicconcentration was799mg kg^-1and iron content was up to38%in the top soil; while forthe sub soil, arsenic concentration was1026mg kg^-1and iron content was18%.（2） The soluble arsenic was extracted by the TCLP extraction fluid and the valencestate of arsenic was analyzed. The TCLP concentration of arsenic in the top soil was far less than1mg L^-1without needing remediation. However, the TCLP concentration ofarsenic in sub soil sample was as high as3.5mg L^-1which was unfit for human living.Therefore it is necessary to remedy the subsoil.（3） FeSO₄·7H₂O was used as the active iron source for arsenic stabilization. Theresults showed that when the Fe/As（T CLP）was equal to100, the ratio of water to soil equalto1:4, the stabilization efficiency of arsenic was up to90%. The TCLP concentration ofarsenic was decreased from3.5mg L^-1to0.3mg L^-1after stabilization treatment whichcould satisfy the target of stabilization.（4） Sequential extractions according to Tessier method were conducted for thedetermination of arsenic and iron species before and after treatment. It showed that arsenicconcentration in the form of exchangeable and carbonate bound was decreasedsignificantly and the concentration of arsenic in residual form was increased after thestabilization with Fe2+. This implied the bioavailability and environmental toxic of arsenicwas decreased significantly.