Highly-efficient process for recovering gold from discarded mobile phones using pretreatment and mild extraction

Abstract

Existing methods for recovering gold from electronic waste are based on mechanical and hydrometallurgy approaches. However, these methods usually use toxic chemicals and demonstrate low gold extraction efficiency (Ge) due to the negative influence of organic materials and other industrial metals also present in the waste. In this work, a more efficient and more environmentally friendly process is proposed that can achieve a high Ge from electronic waste by pre-treatment and pre-extraction before gold extraction. The powdered waste was first pre-treated by a supercritical water oxidation (SWO) process to remove organic materials and then pre-extracted using a mixture of FeCl3 and HCl to remove industrial metals. The solid powder thus produced was then re-extracted by a DMF-CuCl2-NaCl mild extraction system to complete the recovery of the gold content. Experimental results indicated that pre-treatment temperature, pre-treatment time, and the concentration of the FeCl3 and HCl solutions all significantly influenced the amount of gold extracted. The optimal parameters for achieving the highest Ge extraction (99.6%) using the DMF-CuCl2-NaCl extraction system were determined as follows: an extraction temperature of 65 °C, an extraction time of 70 min, a stirring speed of 420 rpm, a sample size of ≤ 850 µm, a solid/liquid (S/L) ratio of 1:12 g·mL−1, a CuCl2 concentration of 0.8 mol·L−1, and a NaCl concentration of 1.6 mol·L−1. After gold extraction, water was then used to precipitate the gold in the form of nanoparticles. Under optimal conditions (70%v/v water, 80 min), over 98.4% of the gold could be recovered in this way.