Milliampere-level direct current enhance cyanogenic capability of bacteria during the bioleaching of precious metals from waste printed circuit boards

Abstract

For the conservation and sustainable utilization of metallic resources, recovering precious metals from the vast quantity of waste printed circuit boards is an attractive avenue. Bioleaching has been proved as an environment-friendly and suitable recovery technology. However, the limited cyanogenic capability restricts the industrialization of this technology. To break this bottleneck, in this paper, an innovative bioleaching technology assisted by milliampere-level direct current was developed to enhance cyanogenic capability. Experimental results indicated 10 mA current was the most beneficial for cyanide production. At 10 mA, the cyanide concentration reached 5.05 mg/L, 1.48 times that of without electric current. With the assistance of milliampere-level direct current, the total energy required for the reaction from glycine anion to cyanide was decreased by 101.81 kcal/mol. Meanwhile, the added direct current reduced the relative abundance of Pseudomonadaceae but enriched Enterobacteriaceae. Clusters of orthologous groups function classification revealed that some functions involved in cyanide production such as secondary metabolites biosynthesis, transport and catabolism were more powerful. This work proposes a novel approach to break the bottleneck of low cyanogenic capability in bioleaching technology, providing crucial scientific information for the industrialization of bioleaching.