Research On The Changes Of Heavy Metals Morphology And The Removal Mechanism By Bio-leaching

In this paper, the heavy metals content in the sludge was determined, and its morphology was analyzed. Bio-leaching method was used effectively remove heavy metals in the sludge. By optimization the parameters of bio-leaching, the optimum leaching conditions was determined, the mechanism of bio-leaching was discussed. Eventually, the determination of heavy metals content reached the sludge agricultural acid and alkaline standard, a reasonable, economic and efficient way of removing heavy metals in the sludge.The content and results of the experimental research:(1)Taiyuan Hexi central sewage treatment plant concentrated sludge was used as the research object, the heavy metals content and its existing morphology was determined. The heavy metals content in the initial sludge was determined by atomic absorption spectrophotometry. The results showed that, all the determined heavy metals did not beyond the sludge agricultural alkaline standard, but Zn element has exceeded the sludge agricultural acid standard by comparing with our country agricultural sludge standard; the morphology of the heavy metals was determined by continuous measurement, Cu and Cd is mainly existed in the steady state, the difference of Zn and Pb content between unstable state and stable state is not too large.(2)The concentration of substrate and inoculums is tested in this experiment and optimized. The results showed that adding mixture sulfur bacteria inoculation could promote the leaching efficiency of Cu, Zn, Cd and Pb in sludge and reduce leaching cycle; the more inoculums leaching the sooner leaching started. With the higher sulfur concentration, the removal rate of heavy metals in sludge was higher, and, the pH value of sludge declined faster. According to various factors such as cost and bioleaching efficiency, the inoculums of 2% and sulfur concentration of 3g/L were selected as the optimal parameters.(3)The transformation among different heavy metals form during bioleaching could be described by continuous measurement, and the bioleaching mechanism could be indirectly presumed with variation of heavy metals forms. The results showed that, Cu at initial sludge mainly existed as sulfide precipitate form, most of which turned to exchangeable form, and was changed by direct mechanism. The original forms Zn were mainly carbonate precipitate and organically bound by indirect mechanisms; Cd was leached by indirect mechanisms; Pb was leached by the cooperation of both direct and indirect mechanisms. The toxicity and bioavailability is different because of the existing form of the heavy metals, so the research on the transformation of the heavy metal profiles is very important.