Influences of ferrous iron concentration and mixing speed on metal recovery from waste printed circuit boards using bio-Fenton process

Abstract

The feasibility of the bio-Fenton process using free glucose oxidase along with the influences of initial Fe2+ concentration (1–25 mM) and mixing speed (200–300 rpm) on the enzymatic metal bioleaching from waste printed circuit boards (WPCBs) of mobile phones were assessed. Results revealed an increasing metal bioleaching trend with a rise in Fe2+ concentration and mixing speed with 10 mM and 300 rpm, respectively being optimal. Maximum metal extraction efficiencies of around 96% Cu, 82% Ni, 53% Pb, and 100% Zn from the pulverized WPCB particles of 0.038–1 mm size with 1 g/L pulp density were achieved in 120 h. Degradation of polymeric matrix by hydroxyl radical (OH•) coupled with the oxidation of metals present in the WPCB matrix by Fe3+ ions generated from enzyme-catalyzed oxidation of Fe2+ ions contributed to the efficient and faster metal extraction during the bio-Fenton process. Further, the human toxicity and ecotoxicity impacts of the selected metals in WPCB as assessed by the USEtox® model were considerably reduced by the process. The bio-Fenton process followed by chemical precipitation with a yield of more than 99% can be regarded as an integrated beneficiation technique for metal recovery from WPCBs.