Improved bioleaching efficiency of metals from waste printed circuit boards by mechanical activation

The low bioleaching efficiency of Acidithiobacillus ferrooxidans results in its sparse industrial application for metal extraction from waste printed circuit boards (WPCBs). To improve the bioleaching efficiency of Acidithiobacillus ferrooxidans, we propose the use of mechanical activation to dispose WPCBs prior to performing bioleaching. Response surface methodology (RSM), scanning electron microscope- energy dispersive spectrometer (SEM-EDS), and laser particle size analyzer (LPSA) were used to optimize and analyze the mechanical activation process, respectively. The optimal conditions for mechanical activation was a milling time of 2 h, milling speed of 340 r min^-1, and ball material ratio (w/w) of 10/1; the bioleaching rates of Cu, Ni, and Zn were 94.33%, 90.69%, and 90.78%, respectively. The bioleaching rates of Cu, Ni, and Zn were 74.75%, 70.46%, and 71.05%, respectively, without mechanical activation pretreatment. SEM-EDS and LPSA analyses indicated that mechanical activation could lead to a smaller particle size and expose wrapped metals, thus improving the bioleaching efficiency oyf tyhe metals inside the WPCBs. The electrode potential of the metals was likely changed by the mechanical activation, resulting in an improvement of their bioleaching efficiency. Additionally, the bioleaching rates of Pb, Cr, and Cd after mechanical activation pretreatment were 10.29%, 74.89%, and 54.12%, respectively. Contrastingly, the bioleaching rates of Pb, Cr, and Cd without mechanical activation pretreatment were 5.18%, 59.97%, and 37.12%, respectively. Thereinto, the precipitation of PbSO₄ may result in a decrease of leached Pb. We propose a mechanical activation process for improving the bioleaching efficiency of metals from WPCBs.