Single pretreatment of discarded printed circuit boards for enhanced gold dissolution by bio-lixiviant through an...

The selective leaching of precious metals from discarded printed circuit boards (DPCBs) is challenging due to their complex multi-metallic composition. In particular, the high copper content increases cyanide consumption during cyanidation, thereby reducing gold extraction efficiency. To address this, an alkaline sequential strategy, combining glycine-assisted alkaline pretreatment with a bio-lixiviant, is applied for the first time. As an eco-friendly chelating agent, glycine facilitated the removal of 100 % the copper under optimized conditions. The optimal conditions were a glycine/DPCB powder ratio of 2:1, 1 % H₂O₂, pH 11, 36 h. The experiments were conducted at a pulp density of 10 g/L with DPCB particles smaller than 75 μm. This single pretreatment almost selectively leached copper, while Al, Fe, Si, Sn, and Ni remained in the residue. This can also enhance the purity of copper during its subsequent recovery from the obtained copper-rich solution in the future. In the subsequent stage, bio-cyanide, used as a bio-lixiviant, achieved high dissolution efficiencies for gold (51.6 %) and silver (68.2 %) from DPCBs. This was achieved using only 35 ppm of bio-cyanide produced by Bacillus megaterium. This work outlines an environmentally friendly process and an effective alternative for the leaching of gold from DPCBs.