Indium, gallium and tin distributions between copper and slag in WEEE smelting conditions

M.Sc. Katri Avarmaa, M.Sc. Simon Yliaho, Prof. Pekka Taskinen

Some rare and valuable metals, such as indium and gallium, are essential in the modern electric and electronic applications. Significant growth in the production of e-devices has created a high pressure to supply these critical metals. At the same time, high volumes of waste electric and electronic equipment (WEEE) are produced. Thus, in order to meet the increasing demand and follow the sustainability targets, the recoveries of these valuable metals from WEEE need to be improved and maximized. This covers clarifying and investigating their behavior in existing WEEE process and recovery technologies. In general, copper scrap fraction of WEEE is processed through the pyrometallurgical metal-making circuits, where copper acts as the carrier metal. This study experimentally investigates the distribution behavior (LCu/s[Me] = [Me]Copper/[Me]Slag) of indium, gallium and tin between metallic copper and a FeOx-SiO2-Al2O3 slag. Aluminum is a general impurity metal in copper scrap and its presence will modify the slag properties, and thus affect the behavior of the minor elements in the process. To investigate the influence of aluminum in WEEE smelting, the experiments were executed in alumina crucibles. The experimental conditions were chosen to simulate both reducing and oxidizing process conditions of black copper smelting within the oxygen potential range of 10-5 – 10-10 atm at 1300 °C. The employed experimental technique was equilibration- quenching followed by Electron Probe Micro-Analysis (EPMA). Tin distribution coefficient between copper and slag increased from 0.1 to 100 as a function of decreasing oxygen partial pressure, and indium from 0.5 to 50. Gallium was mainly distributed into aluminous spinels with distribution coefficient (Lsp/s[Ga]) of 2 – 3. Gallium concentrations in copper were mainly below the detection limit of EPMA, and thus distribution coefficients between copper and slag were defined reliably only in the lower oxygen partial pressure range (10-9 – 10-10 atm) as 0.1 – 0.5.