A Combination Of Bioleaching And Coprecipitation For Deep Removal Of Contaminating Metals From Dredged Sediment By Acidophilus Thiobacillus

Abstract:With the development of modern industry, heavy metal pollution is more and more serious. In this paper, the bioleaching of compound heavy metal polluted sediment and coprecipitation effect of heavy metals were studied.The bioleaching experiment was conducted based on the compound heavy metals polluted sediment in Xiawan port of Zhuzhou city, Hunan provin. Several factors including the changes of leaching microorganism surface properties, the relationship between biological leaching efficiency and the microorganism which affect the bioleaching process were investigated. The results show that bioleaching can achieve an ideal effect with the lower pH and the increase of ORP, especially for Mn, Cu, Zn, the leaching efficiency can be higher than85%. But only a fraction of Pb, Hg and As can be dissolved out. At the same time, the surface of bacteria will change a lot, including changes in cell buffer power, ionic functional groups on the surface of the bacteria and etc.Although the coprecipitation of heavy metals has the opposite effect on the efficiency of bioleaching, coprecipitation mechanism of heavy metal is of great importance. In this paper, coprecipitation was studied by amplification experiment. The coprecipitation mediated by Acidithiobacillus ferrooxidans of chromium and the compound heavy metals of copper, cadmium and lead were investigated. Results showed that the formation of precipitation can be mediated by A. ferrooxidans, with lower pH and the increase of ORP. The precipitation efficiencies of chromium were enhanced uniformly by Acidithiobacillus ferrooxidans. Especially in the30mg/L and60mg/L chromium groups, the maximum precipitation efficiency of chromium was improved from56.22%,55.01%to75.72%and74.37%on the fourth day. But chromium coprecipitation efficiency reduced as the initial chromium concentration increasing at the early stage. Combination contamination of heavy metals, the coprecipitation efficiency and heavy metal species have a close relationship, the efficiency of coprecipitation was Pb>Cu>Cd. Coprecipitation characterization results show that the main composition was jarosite, a class of secondary minerals. The precipitation mediated by A.ferrooxidans had a better crystalline form and more uniform dispersion.