Gold Extraction from Electronic Waste

A gold-bearing cable was obtained from the local electronic junk shop. The yellow cable (15 mg) was first leached with a mixture of HBr and H₂O₂ overnight. Subsequently, the acid concentration in the HAuBr₄-containing leaching solution was adjusted to 1 M with ultra-pure H₂O, and the insoluble impurities were removed by filtration. A saturated aqueous solution of β-CD containing ∼1 M HBr was added to the leaching solution, forming the HAuBr₄⊂β-CD complex. Upon adding 0.1% (v/v) of DBC, the solution became gradually cloudy. After stirring for 5 min, the co-precipitate of HAuBr₄·DBC⊂2β-CD was separated from other metals by filtration and washed with ultra-pure H₂O. The metals trapped in the co-precipitates were analyzed by ICP-MS by comparing them with the metal concentrations of the solution before and after adding DBC. In order to convert the [AuBr₄]⁻ anions trapped in the co-precipitate to gold metal, the HAuBr₄·DBC⊂2β-CD co-precipitates were dispersed in an aqueous solution and reduced with N₂H₄·H₂O. After centrifugation and washing with H₂O to dissolve the residual β-CD, gold metal was obtained. β-CD, which dissolves in the aqueous solution, can be recycled by precipitating with acetone and followed by recrystallization.