Biogenic sulfuric acid-driven leaching coupled with ionic liquid-modified solvent extraction for enhanced copper recovery from waste telecommunications printed circuit boards

Growing volumes of electronic waste (e-waste) highlight the need for improved approaches to recovering valuable metals, particularly copper, from waste telecommunications printed circuit boards (WTPCBs). Although bioleaching has been investigated for copper recovery from e-waste, the downstream separation of copper from the metal-rich leachate generated by bioleaching has received comparatively limited attention. To our knowledge, this study is the first to investigate a hybrid approach for copper recovery from WTPCBs that combines spent-medium bioleaching with ionic-liquid (IL)-assisted solvent extraction (SX). The composition of the WTPCB was determined by ICP-OES elemental analysis, which revealed copper as the predominant metal (2.7 × 10⁵ mg/kg). FTIR analysis identified carbonyl, silicate, and hydroxyl functional groups and confirmed the presence of clear structural changes after bioleaching. Acidithiobacillus thiooxidans cultures reached peak biogenic sulfuric acid production after 17 days, and these metabolites were then used for bioleaching to solubilize a significant amount of the metals. The use of cell-free metabolites eliminates microbial toxicity and removes pulp-density limitations. Using the optimized conditions of 30 °C, 50.0 g/l pulp density, and 140 rpm resulted in substantial copper dissolution (7241.0 mg/l) after 7 days. Subsequently, copper recovery from the bioleachate done through SX. While di-(2-ethylhexyl) phosphoric acid (D2EHPA) alone extracted 1050.0 mg/l Cu, incorporating 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) significantly improved performance, reaching 2715.2 mg/l at an optimal D2EHPA/[BMIM][Cl] ratio (D/I) of 1/2. Further optimization by adjusting the aqueous phase pH to 4.3 and adding sodium acetate increased extraction to 3199.7 mg/l. Five stages of extraction achieved an overall copper recovery of 80.0%, while subsequent stripping with 2 M H₂SO₄ recovered 60.0% of the loaded copper. By integrating bioleaching with IL-assisted SX, the study supports the development of an efficient route for high copper recovery at ambient temperature with lower energy and reagent demand, offering a potential bench-scale framework for sustainable WTPCB recycling.