Electronic Waste : Precious Metals Recovery
in this article, , Amir focuses on the bio-chemical recovery of precious metal from printed circuit boards.
Despite that printed circuit boards contains traces of gold estimated as 0.001 - 10 Kg gold per metric ton, the recovery from electronic waste is challenging and economically unfeasable in most cases. Presenlty, traces of gold can be recovered using existing methods of hydro-metallurgy and pyro-metallurgy.
On a typical printed circuit board there is basically 3 layers of metal plating. Therefore, using hydro-metallurgic method is based on treating wih acidic and basic solvents. Initially, printed circuit boards are crushed and soaked in copper chloride solution, then hydrochloric acid is added. The process is carried preferably inside bubbling reactor, in which oxygen is dissolved to oxidize copper and nickel. The suspension is filtered, the liquid phase contains dissolved copper and nickel. Only precious metal traces is now left in the solid phase for further treatment with leaching agents including cyanides, halides, thiourea and thiosulfates.
Furthermore, using pyro-metallurgic method is based on smelting furnaces, incinerations, and pyrolysis. Thus both hydro-metallurgic and pyro-metallurgic techniques demand substantial amount of energy and chemical reagents.
Recently, mint Innovation company , which is biometallurgy solutions provider with its headquarters and pilot plant in New Zealand, has taken an innovative approach based on bio-chemical hybrid technique that is similar to the hydro-metallurgic method. However, instead of treating the solid phase with leaching chemicals, microbial biomass is used for extraction. The process is called biosorption, in which bacterial strains adsorb gold from aqueous solutions.
Chemiprobe started “probing” on precious metal recovery from electronic waste since last week, and continuously networking with professionals. Therefore, the following research papers are recommended for technical details.