[Effect of total solids concentration on heavy metals bioleaching from contaminated sediment].

The effect of total solids concentration on heavy metals bioleaching from contaminated sediment was investigated in shake flasks. The results demonstrated that an increase in total solids concentration reduced the rates of sediment pH reduction, ORP increase and metal removal. During this bioleaching process, the removal of Zn, Cu, and Cr rapidly enhanced and then gradually approached the maximum removal efficiency when sediment pH decreased from 5.0 to 2.0 and the ORP increased from 200 mV to 520 mV. After 12 days of bioleaching, about 60%-85% of Zn, 65%-100% of Cu, and 17%-35% of Cr could be removed from various sediments of 3%-13% solids content, respectively. It was found that the variation of sediment pH in this bioleaching process could be estimated by a modified Boltzmann model. The analysis of speciation distribution of metals indicated that the unremoved Cu, Zn, and Cr in the bioleached sediment mainly existed in residual fraction, and that the percentpages of Cu, Zn, and Cr bound to this fraction were 76.2%, 81.2%, and 82.7%, respectively. From economical consideration, the recommended total solids concentration for the bioleaching of metals from the sediment is 10%.