Bioleaching of gallium from gallium arsenide by Cellulosimicrobium funkei and its application to semiconductor/electronic wastes

The aim of this work was to screen and characterize heterotrophic bacteria for gallium arsenide (GaAs) leaching. Ga in the form of GaAs has been extensively used as a semiconductor substrate material. The advantage of using microbes for gallium recovery is the fact that this method is a safer, environment-friendly and includes energy-saving processes, which can leach metals at relatively low concentrations. Eight bacterial isolates were isolated from cadmium-, and arsenic-contaminated soil in the presence of GaAs. Pad I and NKS III showed the highest efficiency in Ga leaching at approximately 63–81% after 15 and 30 days, respectively. The analysis of 16S rDNA sequences indicated that strain Pad I was close to strain NKS III; it was characterized and identified as Cellulosimicrobium funkei (C. funkei). Further investigation revealed that the ability of Ga leaching from GaAs by this bacterium involved amino acids. This process occurred in a weak base pH range. The results show a potential application of C. funkei to leach Ga from semiconductors or electronic wastes. The in-depth mechanism of bacterial leaching of Ga from GaAs was also investigated.