Experimental Study On Washing Of Heavy Metal Contaminated Soil In A Nonferrous Metal Smelter In Yunnan

With the development of mining,smelting and processing industries of non-ferrous metals in China,heavy metal pollution in soil has become serious.The washing remediation method because of its advantages of good repair effect,low cost,strong adaptability and repair short cycle has the good application prospect.However,there are few studies on undisturbed heavy metal contaminated soils in non-ferrous metals smelting sites,and most of the research on chemical washing remediation technology focuses on the choice of a single washing agent and the exploration of its washing conditions,while few reports on the study of the combination of washing agents.Therefore,this paper chooses the heavy metal contaminated soil in a waste non-ferrous metal smelter in Yunnan as the research object,carries out single and compound washing experiments respectively,and explores the optimum combination of washing agents and the optimum washing conditions.Furthermore,the morphological changes and washing mechanism of heavy metals in contaminated soils before and after washing were discussed.The results can be found as follows:Different types of single eluents have different removal effects on heavy metals in soil.The removal effects of eluents on Cd,Pb,As and Zn in soil are as follows:FeCl3>HCl>EDTA>oxalic acid>rhamnolipid>deionized water.For HCl,FeCl3,oxalic acid and rhamnolipid,the concentration of eluent is the key to determine the the washing effect.HCl and FeCl₃ can effectively remove heavy metals in soil,the optimum washing concentration were 1mol·L^-1 and 0.5mol·L^-1,the optimum liquid-solid ratio was 8:1,and washing time of 8h.Oxalic acid has poor washing effect on Cd,Pb and Zn,while rhamnolipid needs to be mixed with acid eluent to give full play to its role.For two kinds of compound eluents,the optimum elution conditions are as follows:The optimum compound ratio of FeCl₃(0.5mol·L^-1)&rhamnolipid?1%?is1:1,the optimum liquid-solid ratio is 10:1,and the washing time is 12 h.The optimum compound ratio of HCl(0.5mol·L^-1)&rhamnolipid?1%?is 2:1,the optimum liquid-solid ratio is 10:1,and the optimum elution time is 24h.Both of them can remediate Cd and As in the soil of the non-ferrous metal smelting site to meet"Soil Environmental Quality Risk Control Standard for soil contamination of development land"?GB36600-2018?.From the morphological analysis of heavy metals,the main morphology of Cd,As and Zn in the contaminated soil of the non-ferrous metals smelting site are acid extractable,while Pb is the largest residual.Active heavy metals in soil can be effectively removed by combined washing,and some active heavy metals can be converted into bio-unusable residues,which can greatly reduce soil biological toxicity.