Silver, gold and palladium leaching from pre-prepared electronic scrap using bromine-bromide solution

Abstract

The leaching of silver, gold, and palladium from printed circuit boards in the bromine - bromide system after preliminary removal of the associated metals and copper has been investigated. It was established experimentally that the dissolution of gold with a turnover of leaching solution from a previously prepared PCB concentrate in comparison with the leaching of the original electronic scrap proceeds at a higher rate and much more completely, so the average degree of gold extraction rose from 87.2 to 89.39%. The consumption of bromine decreased from 20-32 to 12 kg Br₂ per ton of scrap. So by seven leaching stages, it was possible to obtain a productive solution with the content, g · dm^-3: 0.0652 Au, 0.015 Pb, 0.00052 Cu. Pretreatment PCB concentrate also increases the rate and completeness of silver and palladium leaching. At the same time, preliminary removal of the main part of copper allows reducing its content in the productive solution by almost 10 times. Under the conditions of collective leaching of silver, gold and palladium with a slightly acidic (pH = 1.98) bromine-bromide solution, with a content of 100.8 g · dm^-3 of bromide ions, it is possible to convert 98.64% Au, 97.23% Ag and 98.33% Pd to the solution. The kinetics of precipitation of gold, silver and palladium from productive solutions using zinc dust, copper powder and hydrazine solution has been studied. As a results it was to precipitate gold on zinc dust in the form of cement powder with a purity of 99.4% and collective (Ag-Pd) and (Au-Ag-Pd) products using a 10% solution of hydrazine with content, mass. % : 1.18 Cu, 90.6 Ag, 7.2Pd and 1.2 Cu, 83.31Ag, 7.15 Pd, 7.95 Au, respectively.