The recovery of precious and base metals of a metal concentrate from ground waste printed circuit boards (PCBs) is described in detail. Samples were treated with NaOHaq. to remove the soldering mask. Experiments were performed in acidic medium (HF, H2SO4, CH3COOH or H3PO4) using H2O2 as oxidant. Base metals were leached in high yields (>99 wt.%) at ~40 ºC after ~1 h (HF), ~2 h (H2SO4), ~4 h (H3PO4) and ~5 h (CH3COOH). Lead precipitated in the presence of H2SO4 and HF. Precious metals were not oxidized. Ceramic/fiberglass components were dissolved in the presence of HF. Silver, palladium and gold were recovered from the insoluble solid, in this order, by a sequential oxidative treatment in aqueous medium. Recovery of leached elements was possible by a combination of solvent extraction and precipitation. The choice of the extractant and the precipitant were essential to recover them with high yields. The leachates from H3PO4 + H2O2 experiments could not be processed above pH 2.5. Leaching of waste PCBs in the presence of a weak organic acid is possible but a multistage separation scheme for elements recovery is unavoidable as PCBs is a complex material in terms of composition.

This work examines the leaching of printed circuit boards (PCBs) from cell phones in aqueous solutions containing HF + H2O2 or HF + NaClO under mild experimental conditions. The PCBs were not ground but were previously treated with 6 mol L-1 NaOH at 50 ºC for 1 h to remove their soldering mask. The HF + H2O2 mixtures leached copper and base metals (except lead) at 35-40 ºC, leaving a solid residue containing lead and noble metals. Leaching was fastest (1 h) when HF and H2O2 concentrations were at least 5 mol L-1 and 3 mol L-1, respectively. The processing of the solid residue is also described in detail. It was leached with water at ~90 ºC followed by HNO3aq. at 25 ºC. Lead, palladium and silver were recovered in this order, leaving gold as final solid. After 1 h at 35-40 ºC, 5 mol L-1 HF + 0.3 mol L-1 NaClO mixtures leached the base metals, copper, gold and palladium. Gold was recovered by liquid-liquid extraction with methyl isobutyl ketone. Silver precipitated as chloride. This salt was isolated by leaching with NH3aq. Loss of fluoride ions (as HF) was below 0.5 wt.% after leaching and handling the solid residue.