Leaching and recovery of rare earth elements, copper, nickel, silver and gold from used smartphone circuit boards

Abstract

Printed circuit board (PCB) assemblies constitute a concentrated source of valuable metals. This study evaluates the performance of a complete hydrometallurgical process for extracting and recovering rare earth elements (REE), Cu, Ni, Ag and Au from leachates produced from PCB found in smartphones via four selective leaching steps. In a REE leachate ([Dy] = 43 mg/L, [Gd] = 5 mg/L, [Nd] = 266 mg/L, [Sm] = 35 mg/L, [Tb] = 8 mg/L, [Ho] = 2 mg/L), 92 % of REE was precipitated at room temperature with H₂C₂O₄/REE molar ratio of 2/1. Calcination of the REE-oxalate precipitates at 800 °C resulted in a mixture of rare earth oxides (REO) with a 91 % purity. From the base metal leachate ([Cu] = 19,376 mg/L and [Ni] = 1,264 mg/L), Cu was electrodeposited during 120 min (pH = 3, current 270 A/m²) while Ni was precipitated by addition of oxalic acid (H₂C₂O₄/Ni molar ratio of 2/1, pH 4.4, T = 60 °C, t = 60 min), followed by calcination at 600 °C for 4 h to form NiO (93 % purity). Three oxidative leaching steps (10 % w/v solids, T = 80 °C, t = 180 min, 1.0 M H₂SO₄, 67 g H₂O₂/L, T = 80 °C, t = 180 min) solubilized 97 % of Ag. Subsequently, with the addition of Cu (Cu/Ag mass ratio of 2), at room temperature and 120 min, Ag was precipitated 99.4 % in the first leachate ([Ag] = 488 mg/L). A Zn/Au mass ratio of 30 precipitated 99.1 % of gold at the room-temperature from the gold leachate ([Au] = 107 mg/L).