The recycling of pure metallic indium from waste LCD screens by a combined hydro-electrometallurgical method

Highlights

• Selective leaching of In was achieved with dilute H₂SO₄.

• Indium was concentrated by cross-current leachate recirculation.

• Indium can be selectively extracted by cementation.

• Low cementing agent consumption and high sponge purity can be assured.

• Electrorefining the melted sponge can produce 99.999% cathode.

Abstract

The Liquid Crystal Display (LCD) panels were removed and crushed to be leached. Sulphuric acid of 0.25 M H₂SO₄ was found best for relatively fast reactions and selectivity, recovering >99% of the indium from the indium‑tin oxide (ITO) layers, while >95% of the tin content was left in the solid residue. As potential impurities, Sn, Fe, Mn, Ni, Zn, Bi, Pb, Al and Cu were analysed in the solutions and in the final product. Synthetic solutions of larger volumes corresponding to the obtained leachate were used for developing the purification and metal recovery steps. Metallic indium was extracted selectively from the solution by cementation on Al plates. The purity of the primary indium deposit was controlled by increasing the temperature to 50–60 °C and keeping the pH in the 0.25–0.5 range, while the aluminium consumption was close to the stoichiometric value. The cemented sponge was vacuum-melted to produce an indium anode block of >99.9% purity for electrorefining. According to the galvanostatic and potentiodynamic results, the optimal electrolyte conditions were found as 50 g/dm³ In, 1 M free Cl⁻ ions, pH 1. The cathodic deposition of Zn, Mn, and Fe was negligible; however, the prior removal of Cu and Sn from the solution is required for producing high-purity indium. Generally, increasing the cathodic current density in the range of 150–600 A/m² enhanced the purity of the cathodes, while a maximum pH 2 value should be assured. Chloride ion concentration strongly influences the deposit morphology.