Study On New Technology Of Cd Containing Slag Treatment With Indigenous Microorganism

By adsorption and precipitation 70%-90% of the heavy metals were transferred to the sediment in the sewage treatment process. If this sewage were not effectively treated, heavy metals will easily cause serious harm to environment. In this paper, the preliminary analysis on characteristics and environmental activity of heavy metals in sediment was conducted. To expand of cultivated microorganisms, Cd leaching effect was studied by adding 9k medium. The orthogonal and single factor experiments were conducted to determine the optimum which used indigenous microbial to leach Cd. The environment activity and toxicity were discussed for the leaching residue; the main conclusions are as follows:(1) The results show that the valuable metals in the slag mainly are Zn,Pb,Fe,Cu,Mn and Cd. The high content of toxic elements in the slag mainly are Zn,Pb,Mn,Cd and Cu, the harmful heavy metals in sediment exist in the form of non-crystalline. The percentage of acid-extractable Zn and Cd were larger, 37.72% and 34.44% respectively; the percentage of Mn relatively high, reaching 49.67%;The percentage of Oxidizable Zn and Pb were higher, respectively, the amount of 34.16%, 34.68%; The percentage of residual Pb and Cu were high, respectively, the amount accounted for 39.72% and 61.69% of total.(2) It was found that sediment has indigenous microbial with the leaching of Cd .By 16S rDNA sequence of PCR-RFLP analysis showed that: the indigenous microorganisms came from Bacillus (Bacillus spp.).(3)The results from the Orthogonal experiments show that the bioleaching rates of Cd were mainly affected by the temperature, leaching medium pH, pulp density in bioleaching system.The degree were pulp concentration> leaching time> leaching medium pH values> leaching temperature; by the single factor experiment shows that Optimum conditions were , leaching time 96h, pulp concentration 7%, the best medium pH 3.0, optimum temperature is 30℃. Under the optimal conditions in the sediment Cd leaching was 89%; the slag gradually in color from light gray to red and eventually become brick red.(4) The concentration for leaching toxity of Cd, Mn, Cu, Pb, Zn was significantly decreased, by the leaching before 4530mg/kg, 7650mg/kg, 830mg/kg, 29530mg/kg and 62350mg/kg decreased to 730mg/kg, 1280mg/kg, 390mg/kg, 13810mg/kg and 15650mg/kg, Leaching efficiency were 84%, 83%, 52%, 53% and 75%. (5) The concentration for leaching toxity of Cd, Cu, Pb, Zn in the bioleached residues are always less than the the Standards for "hazardous waste identification standard" (GB 5085.3-2007) after the bioleaching process. The residue can be used as general solid waste treatment and disposal.