Bioleaching of gold from waste printed circuit boards by alkali-tolerant Pseudomonas fluorescens

This paper evaluated the ability of Pseudomonas fluorescens to leach gold from waste printed circuit boards (WPCBs). Gold was recovered as gold-cyanide complex and cyanide was produced by Pseudomonas fluorescens. In this paper, the effect of pH on gold leaching efficiency was studied, the P. fluorescens was domesticated to grow at higher pH (pH 8 and 9), and the concentration of cyanide ions (CN-) available for bioleaching was increased in alkaline pH. The results showed that at 0.67% w/v pulp density of pretreated waste printed circuit boards powder, mutated bacteria attained gold biorecovery of 27% at pH 9, while the unadapted bacteria only 23% of bioleaching efficiency was achieved. Results revealed that bioleaching efficiency of gold from waste printed circuit boards decreased with the increase of pulp density, and 0.33% w/v pulp density had the maxnium influence to bioleaching efficiency of gold, which could reach 42%. In the two-step bioleaching process, the initial amounts of bacteria had a certain impact on the leaching efficiency, and 3.33% v/v of the initial bacterial liquid was a suitable addition. The type of substrate also affected the leaching bioleaching efficiency. The leaching efficiency in the later stage of gold leaching will be greatly improved to 54%, when glycine and methionine were added to the medium for cyanide production. This may be due to positive effect by the methionine, which could regulate the glycine pool of the cells.