Extraction of copper and the co-leaching behaviour of other metals from waste printed circuit boards using alkaline glycine solutions

Waste printed circuit boards (WPCBs) are a complicated and valuable fraction of electric and electronic waste. The recycling of them is critical to avoid environmental pollutions and to reuse resources. In particular, the ewaste import bans have been implemented in many traditional waste-importing countries in recent years, which is making the sustainable recycling essential and crucial for the advanced economies. In this study, a sustainable approach using alkaline glycine solution for the extraction of copper (Cu) from WPCBs, and the leaching behaviour of other metals (Ni, Al, Fe, Pb, Sn, Co, Zn, Au, Ag and Pd) is presented. Various leaching parameters, including initial pH, glycine concentration, solid content, oxidant, particle size, temperature and time were investigated. A maximum Cu extraction of 96.5 % was achieved, with high co-extraction of base metals (BMs). The extraction of BMs was dependent on the pH of leaching solution, which was highly correlated with other variables. BMs extraction was largely influenced by glycine concentration and solid content, while the sensitivity to H2O2, temperature, and particle size was insignificant. SEM-EDS analysis of leaching residue indicated that the unleached Cu may be locked in inert layers, e.g. Sn/solder materials. The kinetic analysis showed that the extraction of Cu from WPCBs (100 %<2mm) at room temperature with ambient O2 in air as an oxidant was mainly controlled by internal diffusion. 1. Introduction In the past two decades, the number of waste electric and electronic equipment (WEEE or e-waste) has been increasing at an alarming rate (Ogunseitan et al., 2009; Wang et al., 2016). According to the recent statistics, the number of WEEE produced around the global has been 44.7 Mt/y (6.1 Kg/inhabitant, Kg/inh) in 2016, and the amount is forecasted to increase to 52.2 Mt/y (6.8 Kg/inh) by 2021 (Baldé et al., 2017). Today, the developed and rapidly developing countries generate majority of WEEE while most of them finally ends up in developing economies (Lee et al., 2018; Li et al., 2018). However, with the restrictions and bans on WEEE import by the traditional developing economies (Janjevic, 2018; Kannan et al., 2016; Lee et al., 2018), WEEE will be increasingly problematic for developed countries due to the hazardous impact to human, animals and the environment. In Australia, only about 10 % of WEEE is now treated with recycling, and more than 50 % was landfilled, stored or incinerated in 2010 (Khaliq et al., 2014). Considering environmental protection, e-waste should better be disposed of in countries where they are generated, which is also what Basel Convention