On Gold(I) Complexes and Anodic Gold Dissolution in Sulfite–Thiourea Solutions

Microfluidic Fabrication of Micropolymer Inclusion Beads for the Recovery of Gold from Electronic Scrap

A composite material, referred to as micropolymer inclusion beads (μPIBs), was fabricated for the first time using a microfluidic technique and applied successfully for the recovery of Au(III) from simulated digests of electronic scrap. Best results for the extraction of Au(III) were achieved with μPIBs consisting of 55% (m/m) poly(vinyl chloride) as the base polymer, 35% (m/m) Aliquat 336 as the extractant, and 10% (m/m) 1-tetradecanol as a modifier. The size and surface morphology of the μPIBs were examined using optical microscopy and scanning electron microscopy, respectively. A batch of 200 mg μPIBs allowed the complete and selective extraction of Au(III) (2.85 mg) from 50 mL of a simulated digest of electronic scrap containing other metal ions, including 1365 mg Cu(II). The extracted Au(III) was quantitatively stripped from the μPIBs into 50 mL of 0.1 mol L^-1 solution of thiourea. No Cu(II) and only sub-microgram levels of Cd(II) and Zn(II) were detected in this solution, thus confirming the suitability of the μPIBs for the efficient recovery of Au(III) from digests of electronic scrap. The microfluidic method used in this study is expected to be applicable for the fabrication of μPIBs for the selective separation of other chemical species by varying the composition of the beads.

Effect of Acid Leaching Pre-Treatment on Gold Extraction from Printed Circuit Boards of Spent Mobile Phones

The effect of a preliminary acid leaching for the recovery of gold by thiourea from printed circuit boards (PCBs) of spent mobile phones, was investigated. Preliminary leaching is aimed to recover copper in the leachate that would compete with gold in the successive leaching of the residue with thiourea, thus preventing the formation of the gold-thiourea complex. Two hydrometallurgical routes were tested for the recovery of copper first, and gold after. The first one was based on a two-step leaching that utilizes sulfuric acid and hydrogen peroxide in the preliminary leaching and then thiourea for the recovery of gold in the successive leaching: A copper and gold recovery of 81% and 79% were obtained, respectively. In the second route, nitric acid was used: 100% of copper was recovered in the leachate and 85% of gold in the thiourea successive leaching. The main operative parameters, namely thiourea and ferric sulphate concentrations, leach time, liquid-solid ratio, and temperature were studied according to a factorial plan strategy. A flowsheet of the processes was proposed, and a mass balance of both routes was obtained. Finally, qualitative considerations on the technical and economic feasibility of the different routes were made.