| On the basis of analyzing the soil pollution about one electroplating park in Zhejiang province, this paper has studied soil washing and solidification/stabilization to repair the contaminated soil. The soil washing is mainly to screen appropriate reagents and research their optimal operating conditions. The main content of solidification/stabilization is to determine the adding proportion of fixing agent and stabilizer. What’s more, the transformation of soil structure before and after remediation was also studied. Research results could provide theoretical foundation for practical application. The main conclusions are as follows:(1) Through analysis of the soil samples, the main heavy metal of exceed standard are Copper (Cu) and Nickel (Ni) with179.8mg/kg and99.6mg/kg respectively. In order to remediate more serious pollution sites, we made the soil over the standard of exhibition land (HJ350-2007) which Cu is600mg/kg and Ni is2400mg/kg. After preparation, the concentration of Cu and Ni is1070mg/kg and2708mg/kg respectively. The five forms of Cu are34.99%,13.46%,11.92%,6.71%, and32.91%respectively; the five forms of Ni are57.40%,2.44%,0.86%,0.70%and38.59%respectively. Then, the available form for Cu is67.09%and Ni is61.41%, existing high risk.(2) Through the removal effect of Cu and Ni by water, EDTA, acetic acid, oxalic acid, citric acid and humic acid, we found that the effect of EDTA and citric acid is the best. The optimal concentration of EDTA is0.05mol/L, and optimal washing time is10h, under this condition, the removal of Cu and Ni can reach70.60%and69.17%respectively. Then that for citric acid is0.2mol/L and8h, the removal rate of Cu and Ni is61.74%and57.96%. What’s more, we found that the removal of both Cu and Ni is better than other sequence using EDTA first and citric acid later, which is79.22%and73.07%respectively.(3) Through the results of solidification, the leaching concentration of Cu and Ni is0.09mg/L and0.03mg/L respectively under the rate of cement with soil is5:5, can satisfy the standards of both leaching toxicity identification and groundwater environmental quality. Then, the result also realize that the solidification of Ni is better than Cu. In addition, when the addition rate of stabilizer is30%for gypsum and15%for bamboo charcoal, the leaching concentration of Cu can satisfy the standards, which are0.68mg/L and0.90mg/L respectively. However, the stabilization of Ni is not good, possible reason is its high original concentration.(4) Though the analysis of Fe, Ca, K in the leachate, we found that although the washing effect of EDTA and citric acid are very outstanding, they also remove too many soil matrix elements. When washing in the first time, the removal amount of Fe, Ca, and K is2459mg/kg,304mg/kg and246mg/kg respectively by EDTA, is2041mg/kg,325mg/kg and312mg/kg respectively by citric acid. When washing in the second time, the removal amount of Fe, Ca, and K is653mg/kg,357mg/kg and115mg/kg respectively by EDTA, is1393mg/kg,84mg/kg and130mg/kg respectively by citric acid. Therefore, we suggest using citric acid when washing once, using EDTA first and citric acid later when washing twice, can reduce the removal amount of Fe, Ca, and K relatively.(5) The strength of5:5solidification is6.9MPa, which can satisfy the standard of basic level and bottom basic level (CJJ/T80-98). That is to say, this kind of solidification can be used to pave both two substratum and all kinds of roads in city. After stabilization by30%gypsum or15%bamboo charcoal, the five forms rates of both Cu and Ni have changed very much. The detailed cases are as follows:the exchangeable form has reduced; the carbonate form, iron-manganese form and organic form have all increased; the residual form of Cu has increased, but that of Ni has reduced. Overall, the effective form of Cu has reduced by66.41%and55.88%from67.09%; however, the effective form of Ni has increased by63.39%and63.90%from61.41%. So, we can consider both stabilizers can stabilize Cu well but Ni badly. |
PDF Full Text Request