Risk Assessment And Study Of Control Methods For Metal Polluted Soils In A Lead-zinc Mine Of Dongjiang Lake

Heavy metal pollution of soil in the yard poses a serious threat to the ecological environment of Dongjiang Lake. In this study, there were 71 representative samplings had been collected in the Dongjiang Lake lead-zinc slag yard. The concentrations of Pb, Zn, Cu, Cd and As in soil were measured. The index of geo-accumulation, environmental capacity and the potential ecological risk had been used to assess the risk of heavy metals pollution. To determine the optimal eluent concentration, reaction time and ratio of liquid and solid, the oxalic acid, citric acid, EDTA and tea saponin had been used in leaching experiments. There were six kinds of different types of stabilizers( bone char,calcium oxide,sodium sulfide,calcium superphosphate, sodium diethyldithiocarbamate and ferrous sulfate) had been used in stability experiments to determin the optimal stabilizer and the dosage. In order to determine the best composite agents and the ratio of stabilizer compound stabilization experiment had been taken out. The main results are as follows:(1) The average concentration of Pb,Zn,Cu,Cd and As in the collected samples were 64,3.6,5.5,18.5 and 7.6 times as much as that of soil heavy metal background concentration in Hunan province. The sequence from high to low is Pb, Cd, As, Cu and Zn according to the exceeding. The sequence from high to low is Pb, Cd, As, Cu and Zn according to the index of geoaccumulation. The sequence from high to low is Pb, Cd, As, Cu and Zn according to the environmental capacity index. The sequence from high to low is Cd, Pb, As, Cu and Zn according to the potential ecological risk index.The most serious pollution area in this slag yard is the northeast, central and southwestern which used to storage the industrial solid wastes.(2) The results showed that utilization of oxalic acid is effective for removal of heavy metal from contaminated soil within 10 h,attaining 38.45% of Pb,39.33% of Zn,39.66% of Cu,34.61% of Cd,35.24% of As in the 0.2M, ratio of liquid and solid=25:1.(3)It found that add 3g/100 g of calcium oxide in soil could stabilize the Pb,Zn,Cu,Cd and As most efficiency. The stable rates were 73.82%, 38.11%, 75.00%, 42.94% and 57.69%.(4)The best composite agents for the group with ratio of 3:1 is stabilizer A(bone char, sodium sulfide).It could stabilize the Pb,Zn,Cu,Cd and As most efficiency. The stable rate were 99.05%、84.41%、64.29%、81.76% and 11.54%. The results of SEM showed that the soil surface is relatively rough, some crystals come out and the needle like or rod like crystal come out after use the treatment. So that the heavy metal had been stabilized and can’t be extraction.