Microbiological recovering of metals from printed circuit boards by Acidithiobacillus ferrooxidans

Microbiological processes were applied to mobilize metals from printed wire boards. Acidithiobacillus ferrooxidans isolated from a acidic mine drainage was grown and acclimated in the presence of printed wire boards and then used as bioleaching bacteria to solubilize metals from scraps of printed wire boards. Two Face Copper Clad Laminate (TFCCL), TFCCL with green non-conductive coating and actual printed wire boards are chosen as experimental samples of the representative forms of the printed wire boards. Variation of percentages of metal solubilization, pH, and redox potential with time are recorded in the course of leaching experiment. It was shown that A. ferrooxidans could not only efficiently bioleach the main metal copper but also bioleach other minor metals such as zinc, lead, nickel as well. All the percentages of copper, zinc, lead, nickel solubilized into the leaching solution from actual printed wire boards basically increased with decrease of sieve fraction of sample. A. ferrooxidans was able to mobilize Cu into the leaching solution from the actual printed wire boards by 99.0% at 9 days of bioleaching time and 0.5~1.0 mm of sieve fraction, and leach 92.5, 97.1, 74.5, 63.2% of the available copper, zinc, lead, nickel from the actual printed wire boards at 5 days of bioleaching time and 0.35~0.5 mm of sieve fraction, respectively. Experimental results of variation of pH and redox potential of leaching solution with time implied that Fe³⁺ oxidized from Fe²⁺ in the culture medium in presence of A. ferrooxidans caused the mobilization of metals.