| Based on the analysis of soil physicochemical properties, soil quality of waste dump ofYongping copper mine, Jiangxi province, was evaluated. Desorption efficiencies of differentextractants were assessed in laboratory scale and the potential environmental risks of soil heavymetals were analyzed. A feasible technology using heavy metal stabilizers associated with phytoremediation was proposed on basis of field experiments. The main conclusions were as follows:(1)The physicochemical properties of soil in the waste dump of Yongping copper mine weredetermined through collecting five representative soil samples from the waste dump in the eastand west, respectively. The pH of soil samples from the west dump was lower than the east dump.The soil texture was mainly loamy and sandy. The CEC of most soil samples was less than10cmol/kg. On basis of the soil characteristic survey, this study assessed the soil nutrition and heavymetals contamination of the west and east waste dump in the Yongping copper mine, through afuzzy comprehensive evaluation method. The results indicated that the main pollution factors ofwaste dump are Cu, Cd, Zn and the sequencing for the pollution degree of heavy metals is Cu> Cd>Zn>Pb. The comprehensive evaluation of heavy metal contamination showed that all the areas ofthe waste dump were heavily polluted. The contents of total K and N were very low and soilnutrients of all the soils were deficient. Two main factors limiting the natural re-vegetation includeare high contents of heavy metal and low contents of soil nutrient.(2)The desorption behaviors of copper and zinc from contaminated soils of Yongpingcopper mine were investigated using citric acid, oxalic acid, EDTA and NTA, Chemical fractionsof copper and zinc were examined by the modified BCR sequential extraction method. Theextraction efficiency of different extractants was less than60%for Cu,35%for Zn, however, theextraction efficiency was higher than35%. EDTA was most effective when the concentration wasless than0.02M, but oxalic acid showed excellent capacity of extracting Cu when theconcentration was more than0.02M. Zn had the similar desorption behavior. For Cd, thesequencing of extracted Cd for DE1and DE3was EDTA>CA> NTA>>OA, for DE2, DE4andDW1was EDTA>CA≈NTA>>OA. The distribution of chemical fractions of Cu varied in different soil samples, and the dominant speciation was residual and reducible species. For Zn, theresidual fraction dominated the speciation in selected soils. For Cd, the acid-soluble fraction madeup the highest percentage. After extracting with citric acid, oxalic acid, EDTA and NTA, theacid-soluble fraction and reducible fraction of Cu and Zn were reduced. The potential environmentrisk was reduced after extraction, however, the risk would increase if ambient environmentchanged.(3)Stabilizers associated phytoremediation technologies were evaluated in terms of plantgrowth index and heavy metal accumulation index. The selected plants were tolerant to heavymetals and spatial layout of vegetation was reasonable. Six proposed solutions were able toenhance phytoremediation using soil amendments, in which chicken manure compost was superiorto wormcastand combined use of plant ash and manure had the best efficiency. The optimumcondition for soil remediation was:20cm new soil covered the contaminated soils with amountsof lime neutralizer, using plant ash and chicken manure compost as stabilizers. This strategy wasfound to enable rapid vegetation and then stabilize the soil heavy metals. |
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