Research Of Heavy Metals Pollution Soil Risk Evaluation And Chemical Leaching

This paper carried out a detailed survey on Long shui plating garden in dazu county,Chongqing, collected different levels and sample blocks of soil. The paper analyzed thedistribution of site heavy metals, evaluated the environmental risks of the site heavymetal contaminated soil, and made a chemical leaching repair experimental study oncontaminated soil, the conclusions are as follows:The content of four kinds of heavy metals of seven soil samples in the0~20cm and20~60cm sampling layer are examined, the results show that: In all soil sampling layers,the topsoil is high in Cu and Zn, but the subsoil is high in Ni and Cr. The averagecontent of four heavy metals, comparing with state soil environment quality secondarystandard, Cu is not exceeded, but other three metals Zn, Ni, Cr exceeded1.44,6.24,2.72times respectively. The average content of heavy metals are higher than the localsoil background value, Cr is highest, other three heavy metals are Cu, Zn, Ni are3.2,4.17,9.57times.According to the examined results in the content of seven kinds of heavy metals ofseven soil samples in the0~20cm and20~60cm sampling layer, the contaminated soil isassessed with ecological risk and health risk. The ecological risk assessment result ofcontaminated soil is shown:The comprehensive pollution degree and ecological risk ofthe1#and3#sample plots are most serious, they need to be governed, Cr and Ni aretwo heavy metals, which are most polluted and highest ecological risk in the wholeplated garden.The health risk assessment result of contaminated soil is shown:7sampleplots have potential non-carcinogenic health hazard on children and adults, but1#,3#,and6#are most serious, which are focused repair objects. In four heavy metals, Cr ishighest in non-carcinogenic risk, the contribution rate on non-carcinogenic risk hazardreaches82.55%~96.42%, followed by Ni, Cu and Zn has no non-carcinogenic riskhazard human body, Cr should be removed in priority in repair governance. Cr hashigher carcinogenic effect on adults than on children, and has carcinogenic risk in the20cm~60cm level of1#and3#plots.The research result of mixed eluent technological parameters is shown: Comparingthree sets of combination eluent with single eluent, the removal rate of mixed eluent2(0.2mol·L-1oxalic acid+0.2mol·L-1EDTA) is higher than mixed eluent1(0.1mol·L-1oxalic acid+0.2mol L-1EDTA), mixed eluent3(0.5mol·L-1oxalic acid+0.2 mol·L-1EDTA), single EDTA and oxalic acid: Liquid-solid ratio changes of eluent andsoil result in removal rate difference, liquid-solid ratio of5:1is best to remove fourheavy metals: The leaching time of Heavy metal ions in the soil to reach adsorptiondesorption equilibrium is4h, the removal rate of Cu, Zn, Ni, Cr are50.47%,86.67%,61.53%,72.68%respectively: Mixed eluent has good removal effect on heavy metals ina wide pH range, after taking various factors into account, pH6is more appropriate:The first two leaching has removed most heavy metals, the removal rates of Cu, Zn, Ni,Cr are72.22%,82.25%,64.70%,75.13%, the third removal has no significantcontribution to the total removal efficiency of heavy metals comparing with the first twoleaching.After processed with mixed eluent, exchangeable state, carbonate binding state andFe, Mn oxidation state content of Cu, Zn, Ni, and Cr are largely improved than beforeprocessing, which means mixed cream lotion can change distribution pattern of heavymetals in the soil, and convert them to unstable and biological high effectiveness state,so as to achieve effective repair effect.