Review on Cyanogenic Bacteria for Gold Recovery from E-Waste

Abstract

Electronic waste (E-waste) is recognized as a new emerging and fast-growing waste stream, and may be considered as a secondary ore for the recovery of some precious metals (such as gold). A number of control technologies have been conducted for gold recovery, and in which, cyanidation is widely used. In recent years, an alternate approach to the gold cyanidation process is being considered, in which the aim is to replace with the microorganism, specifically cyanogenic bacteria such asChromobacterium violaceum,Pseudomonas fluorescens,Pseudomonas aeruginosaandEscherichia coli.All these species can produce cyanide ions and dissolve gold in their metabolic processes. The mechanism is a combination of chemical knowledge (interaction of metals and cyanide) with microbiological principles (biological cyanide formation) regarding metal solubilization from waste printed circuit boards and the formation of water-soluble cyanide complexes. And the activity of cyanogenic bacteria is affected by many factors, such as pH, dissolved oxygen pulp density and nutriment, especially several metal ions, which can serve as the catalyst in the metabolism. Now researchers are devoting themselves to looking for the proper conditions, not only from the bacteria themselves, but also the combination of many methods, which can reinforce the cyanide generation and improve gold leaching efficiency. At present the reported leaching efficiency of gold with cyanogenic is approximately 70%. As the continuous optimization of conditions, the industrial application can be expected soon.