Recoveries of rare elements Ga, Ge, In and Sn from waste electric and electronic equipment through secondary copper smelting

Abstract

The recycling and recovery of valuable metals from waste materials is one of the key issues in maintaining the sustainability of base and rare metals. Especially WEEE (Waste Electric and Electronic Equipment) can be considered as a high potential resource for a number of valuable and critical metals like gallium, germanium and indium. During the mechanical processing of WEEE, these metals are primary separated into the non-ferrous scrap fractions, including copper fraction. As a consequence, the behavior of these valuable metals and the possibility of their recycling in secondary copper smelting are of great interest. This study experimentally investigates the distribution behavior of indium, gallium, germanium and tin between metallic copper and lime-free / lime-containing alumina iron silicate slags (L^Cu/s[Me] = [Me]_Copper/(Me)_Slag), as well as between solid Al-Fe spinel and slags (L^sp/s[Me] = {Me}_spinel/(Me)_slag). Moreover, the copper-slag-spinel equilibrium systems are examined. The experiments were executed simulating high alumina-bearing copper scrap smelting in typical black copper smelting conditions of pO₂ = 10^-10-10^-5 atm (1 atm = 1.01325 × 10⁵ Pa) and T = 1300 °C. The experimental technique employed utilized a highly advanced equilibration-rapid quenching method followed by Electron Probe Micro-Analysis (EPMA). The results show that tin and indium can be efficiently recovered into the copper phase in reducing process conditions (pO₂ below 10^-7 atm), whereas gallium dissolved preferentially into the solid spinel phase in all conditions examined. Gallium dissolution into slag and spinel was found to occur as GaO_1.5, whereas indium in spinel was determined to be as InO_1.5. In addition, germanium was seen to distribute preferentially into the copper phase with L^Cu/s[Ge] = 2-4, although its concentrations in all phases present were relatively low. Thus, the main route for germanium can be considered to be vaporization.

Keywords: Black copper; Critical elements; E-waste; Equilibria; Recycling.