This chapter is based on: Işıldar, et al. Two-step bioleaching of copper and gold from

discarded printed circuit boards (PCB). Waste Management (2015),


108 | B i o l e a c h i n g o f c o p p e r a n d g o l d

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 (10

g/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 ± 2°C) in 7 days. A pure culture

of P. putida (strain WCS361) produced 21.5 ( ± 1.5) mg/L cyanide with 10 g/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 30°C in 2 days. This study provided a proof-

of-concept of a two-step approach in metal bioleaching from PCB, bacterially produced