Two-Step Bio-Dissolution of Metals from Printed Circuit Boards Using Acidophilic Iron- and Sulfur-Oxidizing Mesophiles

To date, electronic waste (e-waste) is the fastest-growing waste stream worldwide due to technological advancement and the advent of the Fourth Industrial Revolution. Although e-waste is an environmental hazard, these materials are considered good secondary sources of metals. This study examined the bioleaching of metals from printed circuit boards, where a two-step bioleaching approach was used with iron–sulfur-oxidizing microorganisms at different e-waste particle sizes. The metal analysis from the different particle sizes (PSs) showed that copper (Cu), tin (Sn), and lead (Pb) were predominantly deposited in the coarser fraction, ranging from 500 to 710 µm at 28.7, 20.5, and 11.1 wt.%, respectively. On the other hand, metals such as iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), and aluminum (Al) were mostly deposited in the finer fraction, which ranged from 38 to 150 µm at 37.3, 5.9, 8.8, 1.3, and 4.2 wt.%, respectively. After the bioleaching process, it was observed that higher metal extraction occurred at a PS ranging from 38 to 150 µm, which achieved recovery efficiency rates of 62.9%, 68.2%, 95.3%, 86.1%, 61.9%, 47.2%, 21.2%, and 63.6% for Al, Cu, Fe, Mn, Ni, Pb, Sn, and Zn, respectively, over 10 days.