The production of high-purity gallium from waste LEDs by combining sulfuric acid digestion, cation-exchange and electrowinning

Abstract

White light beads containing light emitting diodes (LED) were removed from the commercial light bulbs and treated with a complex, but easily implementable hydro-electrometallurgical method to recover pure Ga. Using concentrated H2SO4 as the digesting agent at 180 °C for 60 min resulted in > 90% efficiencies of gallium and indium solubilization by the subsequent water leaching. All metals - except for Ag – could be fixed in a strongly acidic cation-exchange resin by loading the solution into a chromatographic column. Indium, Cd, Pb and Sn are selectively eluted with 1 M HCl, while Al can be transferred into the aqueous phase using a 0.25 M NaF solution. Gallium is recovered in a pure eluate from the resin with 3 M NaOH, and finally, Y is eluted with 0.5 M Na2CO3. The cathodic deposition of Ga from the alkaline eluate was studied by potentiodynamic and galvanostatic methods. As high current efficiencies as 99% could be reached in solutions of 50 g/dm3 Ga and 6 M free NaOH at 300 A/m2 cathodic current density. Decreasing the NaOH concentration to 1.5 M resulted in a 10 ∼ 15% decrease in the current efficiency. Lower Ga concentrations also reduced the current efficiency significantly. The cell voltages were in the range of 2.1–2.4 V, yielding a relatively low (2 kWh/kg) specific energy consumption. The obtained cathodes were immersed into 2 M HCl at 55 °C, resulting in 99.999% Ga metal melted from Ti mother plates.