Urban mining of precious metals via oxidizing copper smelting

Abstract

Recycling of precious metals from end-of-life electronics is a key factor for sustainable and efficient raw material usage. Simultaneously with the depletion of natural ore resources, the urban mines are storing increasing amounts of valuable and, more importantly, rare metals. To fulfill the targets of sustainability and move towards circular economy, the liberation of these valuables from wastes back to production and use needs to be improved. This study investigates the recoveries and behavior of gold, silver, palladium and platinum in copper smelting conditions at 1300 °C and pO2 = 10−5–10−7 atm. The investigated system includes a copper alloy with three different type of slags in silica saturation: pure iron silicate, iron silicate with 10 wt% alumina and iron silicate with 10 wt% alumina and 5 wt% lime, providing information on the influence of alumina and lime on precious metal recovery possibilities. A highly advanced equilibration-quenching technique, followed by EPMA and sensitive LA-ICP-MS analyses, has been adopted to execute the experiments. Results show that gold, platinum and palladium are recovered very efficiently in copper, as their distribution coefficients between copper and slag, LCu/s, were greater than 104 under every experimental condition studied and with all slag compositions. Silver distributed 30–60 times more in copper phase than was lost to slag. The addition of alumina into the slag somewhat decreased the distribution coefficient of silver, whereas gold and palladium distribution coefficients were increased. Lime addition improved the recovery of every precious metal (Pt unclear) into the copper phase. The concentrations of platinum in the slags were mainly below the detection limit of the used LA-ICP-MS, providing a minimum distribution coefficient of 106.