Chemical and biological processes for multi-metal extraction from waste printed circuit boards of computers and mobile phones

Abstract

E-waste printed circuit boards (PCB) of computers, mobile-phones, televisions, LX (LongXiang) PCB in LED lights and bulbs, and tube-lights were crushed to ≥250 µm particle size and 16 different metals were analysed. A comparative study has been carried out to evaluate the extraction of Cu–Zn–Ni from computer printed circuit boards (c-PCB) and mobile-phone printed circuit boards (m-PCB) by chemical and biological methods. Chemical process showed the extraction of Cu–Zn–Ni by ferric sulphate was best among the studied chemical lixiviants. Bioleaching experiments were carried out with the iron oxidising consortium, which showed that when E-waste and inoculum were added simultaneously in the medium (one-step process); 60.33% and 87.50% Cu, 75.67% and 85.67% Zn and 71.09% and 81.87% Ni were extracted from 10 g L^-1 of c-PCB and m-PCB, respectively, within 10–15 days of reaction time. Whereas, E-waste added after the complete oxidation of Fe²⁺ to Fe³⁺ iron containing medium (two-step process) showed 85.26% and 99.99% Cu, 96.75% and 99.49% Zn and 93.23% and 84.21% Ni extraction from c-PCB and m-PCB, respectively, only in 6–8 days. Influence of varying biogenerated Fe³⁺ and c-PCB concentrations showed that 16.5 g L^-1 of Fe³⁺ iron was optimum up to 100 g L^-1 of c-PCB. Changes in pH, acid consumed and redox potential during the process were also studied. The present study shows the ability of an eco-friendly process for the recovery of multi-metals from E-waste even at 100 g L^-1 printed circuit boards concentration.