Research On Bioleaching And Stabilization/Solidiifcation Of Heavy Metal Contaminated Sediment

For the past few years, the xiangjiang river has become one of the most seriousrivers with heavy metal pollution, Due to the development of various mining andmineral processing related enterprise in Hunan province which was the home ofnon-ferrous metals. Xiawan Stream flows in zhuzhou is the main channel ofwastewater from zhuzhou QingShuiTang industrial zone, heavy metals wasaccumulated in the sediments after decades, the content exceeds the control standards.The heavy metal in Sediment may cause secondary pollution by releasing to theoverlying water because of changes in the external environment, So it is verynecessary to treatment and dispose the sediment contaminated with heavy metals inXiawan Stream of xiang jiang. Bioleaching is gaining increasing attention ofresearchers because of the characteristics of short period, high efficiency, low cost.The cement system solidification and stabilization （S/S） is the best technology fortreating poisonous and harmful waste,it could reduce cost and capacity expansionratio by adding fly ash and other heavy metals chelating agent. So we chose thebioleaching to treat contaminated sediment of the Xiangjiang River in Changshasection and the cement-fly ash-dithiocarbamate（DTCR）system to solidify andstabilize （S/S） river bottom sediments of Xiawan Stream in view of the characteristicsof contaminated sediment, respectively.Substrate dosage and Solid concentration are the most important factors affectingthe treatment effect and cost in bioleaching. In this study, ferrous sulfate was selectedas energy substrate to cultivate the bioleaching dominated bacterium of Thiobacillusferrooxidans. The results demonstrated that the removal ratios of Cd, Zn and Cu insediment were83.1%,75.3%and61.2%respectively after6days, when the solidconcentration was13%, the substrate dosage was19.5g/L. The heavy metals mainlyexisted as residual state after bioleaching, and the concentration of them were lowerthan the control standards for pollutants in sludge from agricultural use. The leachingof organic matter/sulfide-bound Cu needed lower pH compared to Zn and Cd, and theindirect leaching was its main mechanism. In the bioleaching system with Fe²⁺assubstrate, the adsorption and coprecipitation of ihleite was one of the importantreasons for the decrease of soluble metals in later period.A cement-fly ash-dithiocarbamate（DTCR）system was used to solidify and stabilize （S/S） river bottom sediments containing heavy metals, the optimumconditions were selected by testing of compressive strength and leaching toxicity. Theresults demonstrated that with the dosage of cement increased, compressive strengthof the solidified products was also enhanced but the concentration of heavy metals inleachate was decreased. When the ratio of cement to dried sediment reached to0.6,the compressive strength of the cement solidified products （after7days） was higherthan the standard value of0.98MPa. Further studies showed that the compressivestrengths of solidified products from7days and28days were1.2MPa and2.7MPa,respectively, when the mass ratio of cement: flyash: sediment was0.54:0.06:1.0,however the leaching concentration of heavy metal was increased. Whencement:flyash:DTCR:sediment was0.54:0.06:0.012:1.0, the compressive strengths ofsolidified products from7days and28days could reach to1.1MPa and2.1MParespectively. And after handled with the acetic acid buffer solution method theleaching concentration of Cd, Pb,Zn and Cu were0.102mg·L^-1,0.189mg·L^-1,0.180mg·L^-1and0.032mg·L^-1, respectively.