Two step bioleaching of copper and gold from discarded printed circuit boards (PCB)
An effective strategy for environmentally sound biological recovery of copper and gold from discarded printed circuit boards (PCB) in a two step bioleaching process was experimented. In the first step, chemolithotrophic acidophilic Acidithiobacillus ferrivorans and Acidithiobacillus thiooxidans were used. In the second step, cyanide producing heterotrophic Pseudomonas fluorescens and Pseudomonas putida were used. Results showed that at a 1% pulp density (10g/L PCB concentration) 98.4% of the copper was bioleached by a mixture of A. ferrivorans and A. thiooxidans at pH 1.0 1.6 and ambient temperature (23+ 2degC) in 7days. A pure culture of P. putida (strain WCS361) produced 21.5 1.5)mg/L cyanide with 10g/L glycine as the substrate. This gold complexing agent was used in the subsequent bioleaching step using the Cu leached (by A. ferrivorans and A. thiooxidans) PCB material, 44.0% of the gold was mobilized in alkaline conditions at pH 7.3 8.6, and 30degC in 2days. This study provided a proof of concept of a two step approach in metal bioleaching from PCB, by bacterially produced lixiviants.
Waste management