Two-Step Leaching of Valuable Metals from Discarded Printed Circuit Boards, and Process Optimization Using Response Surface Methodology

Abstract

Waste electrical and electronic equipment (WEEE) is an important secondary source of valuable metals. Particularly discarded printed circuit boards (PCB) contain high concentrations of valuable metals, varying greatly among the type of board, the manufacture year, source device, and utilized PCB production technology. Chemical hydrometallurgical processing is an efficient method to selectively extract and subsequently recover metals from discarded polymetallic PCB. In this work, we propose a two-step process to extract copper (Cu) and gold (Au) from a discarded high-grade telecom server PCB. The boards contained 262.4 and 0.320 mg/g Cu and Au, respectively, which constituted the 98.1% of the total value of metals. The metal extraction process was optimized using Response Surface Methodology (RSM) by central composite design (CCD). The optimized process parameters showed that 3.92 M sulphuric acid, 3.93 M Hydrogen peroxide, 6.98% (w/v) pulp density and 3.7 hours contact time, and 0.038 M Copper sulphate, 0.3 M í µ 2 í µ 3 2 − 0.38 M Ammonium Hydroxide, 10.76% pulp density (w/v) 6.73 hours were optimal for the maximal extraction of Cu and Au, respectively. At optimal conditions, 99.2% and 92.2% of Cu and Au, respectively, were extracted from the discarded PCB.