Mixed Amendments For Immobilization Of Cd,Pb,Cu And Zn In An Acidic Multi-Metal Contaminated Soil

At present, remediation methods for heavy metal contaminated soil include physical, chemical and biological treatments. Among them, chemical remediation typically employs soil amendments which could decrease the mobility and bioavailability of heavy metals by changing chemical forms of heavy metals in soils, through a variety of reactions of exchange/adsorption, dissolution/precipitation and organic complex between amendments and metals. Because of their low cost, and their simplicity but high effectiveness, in-situ immobilization is considered a suitable technology for treating the heavy metal contaminated soil in China, which is widely distributed, but at low or middle pollution level. The soils polluted by mine wastewater were always acid and contaminated with several metals. Because of different mechanism for immobilizating of different metals, one amendment may be effective for treating one or two kinds of heavy metals, but cannot be used for remediating multi-metal contaminated soils. The main objective of this paper was to find some mixtures of inorganic-organic amendments to increase soil p H and reduce the bioavailability of heavy metals in an acid multiple-metals-contaminated soil, which was contaminated by wastewater of mining. The results may provide suitable material and theory basis for treating and the remediating the acid multi-metal-contaminated soil in this area. The results were as follows:(1)Pot experiment show that mixed inorganic-organic amendments significantly increased soil p H and reduced the mobility of Cd, Pb, Cu and Zn. The inorganic-organic amendments could reduced exchangeable concentration and increased Fe-Mn oxide-bound significantly, resulting in the decrease in bioavailability of heavy metal and the accumulation of heavy metals by plant. Compare with phosphate rock, calcium-magnesium phosphate has higher effective-ness for remediating multi-metal contaminated soils.(2)The results of field experiment show that mixed inorganic-organic amendments significantly increased soil p H and reduced the mobility of Cd, Pb, Cu and Zn. The growth of the leave lettuce was improved in the remediated soil. The mixed inorganic-organic amendments are more effective than the mixed inorganic amendments. Posphate rock is lower cost and has longer effectiveness in practical application. Though all these mixed amendments significantly reduced the shoot Pb concentrations in in leave lettuce, it was still more than 0.3 mg? kg-1(limit in food hygiene standard). Therefore, the safety of the produced red leave lettuce in multi-metal contaminated soils, it needs to cooperate with planting low Pb-accumulation crops.(3)The analysis results by using high-throughput sequencing(HTS) technique show that the dominant microorganisms in multi-metal contaminated soils of the Dabaoshan area were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes and Nitrospirae etc.Mixed inorganic- organic amendments can improve soil microbial activity, microbial abundance and species diversity. The relative abundance of Proteobacteria decreased, while Acidobacteria increased in the remediated soil. There is a big difference in the effect of different amendments on soil microbial community structure and species diversity.