TWO-STEP LEACHING OF METAL VALUES FROM DISCARDED MOBILE PHONE PRINTED CIRCUIT BOARD USING BIOGENIC FERRIC ION WITH COPPER LEACHING KINETICS

Abstract

Discarded mobile phone printed circuit boards (mobile phone PCBs), a prominent component of electronic waste, represent a significant secondary resource for metal recovery. Mobile phone PCBs contain significant amounts of copper and other critical metals, making them a good option for bioleaching, which is a sustainable and environmentally friendly alternative to conventional metal extraction methods. However, slow reaction kinetics often hinder bioleaching, limiting its industrial-scale applicability. This study utilized mixed culture consortia of iron oxidizing microorganisms dominated by Leptospirillum ferriphilum, which were chemolithotrophic microbes thriving in highly acidic conditions and high ferric iron concentrations responsible for enhanced copper recovery through a two-step bioleaching process. All the bioleaching experiments were conducted at a controlled temperature of 35±5 ℃ and pH controlled to 1.5 with a Pulp Density (P.D.) of 10% while varying biogenic ferric iron concentrations from 9–18 g/L, which served as the main lixiviant for metal extraction. The results demonstrated that increasing biogenic ferric iron concentration significantly improved copper recovery and reduced leaching time. In the first leaching step, 50-83% copper extraction efficiencies were achieved at biogenic ferric iron concentrations of 9-18 g/L. During the second leaching step, copper extraction exceeded 99% within 5.5-3.5 days for the corresponding ferric concentrations. The elevated biogenic ferric iron levels facilitated this rapid and efficient copper extraction, accelerating the leaching kinetics. Post-leaching analyses, including XRF, SEM-EDS, and XRD, confirmed >95% copper recovery following solid-liquid separation. The study highlights the effectiveness of the two-step bioleaching process and underscores the potential of biogenic ferric iron in overcoming the limitations of traditional bioleaching methods. This research demonstrates a fast, simple, and sustainable bioleaching method for the efficient recovery of copper from mobile phone PCBs, offering a promising pathway for industrial applications in e-waste management and contributing to the circular economy.