Selective Biosorption Behavior Of Precious Metal Ions On Magnetotactic Bacteria And Gold Recovery From Gold(III) Contained Solution

With the rapid development of novel technologies in industries,the demand of precious metal in the world is increasing. However, due to the limited reserves of precious metal, the recovery technology from precious metal contained wastes has drawn more attention recently. Therefore, the aim in the present study is to investigate the feasibility of applying the coupling technology, selective biosorption and HGMS (high gradient magnetic separation), into the gold recovery from industrial wastewater.A magnetotactic bacterial isolate (MTB-3) with a high biosorption capacity to metal ions was isolated and purified from the Jizhuangzi sewage treatment plant. By means of series of the physiological biochemical experiments and the 16S rDNA sequence analysis, this strain was identified as Stenotrophomonas sp.The optimal biosorption conditions of Stenotrophomonas sp. MTB-3 to Au(III), Cu(II) and Ni(II) in single, binary and ternary systems were investigated, and the results of kinetic and equilibrium studies indicated that MTB-3 showed a high selectivity to Au(III) in multi-systems. The results of the desorption experiments suggested that 91.3% Au adsorbed on the biomass could be recovered when the thiourea concentration was 0.8 M, and the biomass could be used more than three times with an essential prerequisite that the re-biosorption ratio was more than 80%.The biosorption mechanisms of MTB-3 in the removal of Au(III), Cu(II) and Ni(II) were investigated using theory models, combined with the chemical analysis, such as Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and chemical modification experiments. The results indicated that the static attraction and surface complexation reactions were the main mechanisms as for the biosorption of Cu(II) and Ni(II), while adsorption together with bioreduction were the dominant mechanisms as for Au(III). The preliminary microcosmic model of biosorption of metal ions by MTB-3 was then developed on the basis of biosorption mechanisms.After analyzing the force and their moment acting on the metal loaded MTB-3 in the magnetic field, the axial saturation build-up model was established to describe the performance of the MTB-3 cells in the HGMS process. Combined with the phenomenology model, kinetic characteristic of the movement of the metal loaded cells in the whole magnetic separator was described and predicted.Based on the high magnetotaxis and the high selective biosorption capacity of Stenotrophomonas sp. biomass, a coupling technology"selective biosorption and HGMS"was put forward in this study to recover gold from wastewater. The results showed that the recovery ratio for gold and copper were 90.2% and 81.0%, respectively, and the discharged water could meet the national drainage standard for gold(III) and copper(II).