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| Bioleaching of heavy metals in sewage sludge using Acidithiobacillus ferrooxidans |
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Abstract To understand the bioleaching mechanism of heavy metals in sewage sludge by Acidithiobacillus ferrooxidans, batch experiments including blank, direct leaching (At. f), ferrous leaching (At. f+Fe2+), and ferrous and sulfuric acid leaching (At. f+Fe2++H2SO4) were conducted, and the composition and phase transformation of the sludge samples before and after bioleaching were investigated. Results showed that solubilization efficiency of Cu, Zn, Ni, Pb and Cr in ferrous and sulfuric acid leaching was 90.8%, 100%, 87.5%, 51.6% and 83.3%, which was higher than the other three systems. Moreover, quantitative calculation and kinetic study showed that the dissolved metals and rate constants (k) of the 5 heavy metals in direct-indirect (ferrous) leaching were higher than those in direct leaching. Furthermore, EDS and XRD analysis demonstrated that the sludge before and after leaching were mainly composed of carbon (26.2%~37.5%), oxygen (32.5%~45.7%) and aluminium salts and silica, but the loss of nutrient elements (such as P and Ca) was also observed. In addition, ICP-MS detection showed that other metals (such as Cd, Fe and Mn) were leached. The bioleaching process by addition of FeSO4?7H2O and H2SO4 was proposed, where the leaching of Cu, Pb, Cr and Ni in the sludge were controlled by indirect leaching, while the leaching of Zn resulted from both direct and indirect leaching.
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Received: 25 December 2013
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