Stabilization Repair And Evaluation Research In Typical Copper And Cadmium Pollution Of Farmland Soil

Jiangxi Province owns a large number of nonferrous metals and rare earth mine,with the exploration of those mineral resources, environmental pollution of heavymetals has caused, besides, it can be harmful to the ecological environment especiallywhen partial heavy metal contaminations entered into farmland. In this paper, wefocused on the farmland around a smelter in Jiangxi which suffering the pollution ofcopper and cadmium, investigation and evaluation on the current pollution of heavymetals was mainly made. Based on the result of survey, indoor test and the pilot scaletest of stabilization remediation experiments in soil was done by using reagent Mfrom company A, the stabilization effects of reagent M was analyzed and evaluated.The results provide a basis in treating the heavy metal pollution of farmland and forthe acceptance of the effection.Based on the findings of this study, the following conclusions have been drawn:(1) Both Cu and Cd concentrations were exceeded China national standard,farmland environmental quality evaluation standards for edible agricultural products(HJ332-2006), in the study area. The results shown that the contents of Cu and Cdwere198.01mg/kg and1.31mg/kg respectively in the surface soil sample (0-20cm),which exceed bid3times and3.4times; while in the sample from20cm to40cm,they were48.97mg/kg and0.57mg/kg, respectively, Cu content not to exceed bid, butthe content of cadmium exceeded bid0.9times.(2) Bio-available heavy metal is the most important factors that affects thegrowth of plants. Bio-available Cu had significant linear correlation with the totalamount, while there was not relativity between bio-available Cd and the total amount.Besides, bio-available Cd at the same depth was more stable. The values ofbio-available Cu and Cd were respectively99.22mg/kg and0.37mg/kg which wereexceeded the standard of farmland environmental quality evaluation standards foredible agricultural products (HJ332-2006). According to the potential ecological riskindex, the evaluation results shown that the contaminated area was in a mediumecological risk with the high level pollution of Cd. While in the condition of pH3.2 leaching, the leaching concentrations of Cu and Cd were4.58mg/kg and0.04mg/kg,which both were low, thus the groundwater and surface runoff would notcontaminated by Cu and Cd on account of the low transfer characteristic. Thesecondary layer of soil with lower amount of Cu、Cd was less polluted comparingwith surface soil.(3) The chemical forms of Cu was as follows: weak acid soluble> reducible≈oxidizable> residual> water soluble, the mainly existing form of Cu in the studyarea is non-residual and the content of weak acid soluble Cu was about80mg/kg atmost in surface soil sample. Meanwhile, the chemical forms of Cu was in order ofweak acid soluble> reducible> oxidizable> residual> water soluble, the content ofweak acid soluble and reducible were0.78mg/kg and0.07mg/kg at most,respectively. The soil contaminating extent was evaluated by using RSP form theaspect of chemical forms, the surface soil was heavily polluted by Cu and Cd.(4) Remediating the heavy metal polluted agricultural land with reagent Mproduced by company A, which involves complexation/dissociation, absorption/desorption and oxidization/reduction, is a complicated physical and chemical reactionprocess. The indoor experiment found that though the dosage of reagent M had nosignificant effect on reducing the heavy metal in soil, it helped transfer the active Cuand Cd to stable. Under the optimal dosage at mass ratio of1‰, the weak acidsoluble and residual Cu reduced20.7%and14.3%, while the reducible, oxidizable Cuincreased19.0%and38.3%, respectively. In addition, the weak acid soluble andreducible Cd reduced25.3%and78.8%, while the oxidizable and residual Cdincreased10%and five times, respectively. Besides, the leaching concentration of Cu(2.08mg/kg) and Cd (0.01mg/kg) reduced56.1%and80%respectively comparingwith the soil without stabilizer. Under the dosage ratio of1‰-5‰, the value ofbio-available Cu and Cd reduced around28%and19%, respectively.(5) The variations of existing forms of Cu、Cd, leaching concentrations andbio-available forms in the pilot scale experiment were basically in accordance withthat in indoor experiment. The evaluation result of RSP shown that in the pilot scaleexperiment the pollution value of Cu was about4.2comparing with the control group;while the value of Cd was greatly reduced, when the dosage ratio of M comes to1‰, the value reduced17.54comparing with the control group, the extent ofcontamination declined from high to medium-high.