Influence of Initial pH on Bioleaching of Selected Metals from e-Waste Using Aspergillus niger

Abstract

The information revolution has shown augmented growth in the production of information technology (IT) equipment like personal computers and mobile phones in addition to other electrical and electronic equipment (EEE) from the last two decades. Due to the higher obsolescence rate of EEE, waste EEE (WEEE) or electronic waste (e-waste) is presently growing at a faster rate than the municipal waste streams (Grossman, 2007). Baldé et al. (2017) estimated the global WEEE generation of about 44.7 million tonnes (Mt) in 2016 and expected to grow to 52.2 Mt by 2021. According to the recent joint study of the ASSOCHAM-NEC (2018), India generates a total of 2.0 Mt of e-waste. Each EEE contains a printed circuit board (PCB) as the main working component with heterogeneous elemental content, which includes base, toxic and precious metals. Studies have reported that obsolete computer PCB contains metal in the range of 20–24% Cu, 1–3% Ni, 0.6–6.3% of Pb, which are comparatively higher than the mineral ores. Because of their high content of base and heavy metals besides some amount of precious metals, make it valuable metal resource (Bandyopadhyay, 2008; Priya and Hait, 2018a). Recycling of metals from e-waste could save up to 90% of natural resources (Zhou et al., 2009). However, unscientifically PCB disposal in the environment creates environmental problems due to the presence of toxic metals (Sayilgan et al., 2009). Hence, metal recycling from waste PCB is the main obligation for economic development as well as for environmental protection (Deng et al., 2007). Metal recycling techniques like pyrolysis and hydrolysis are expensive, energy-intensive and generate secondary pollution (Ilyas et al., 2010; Pant et al., 2012; Priya and Hait, 2017). In the case of pyrometallurgy, heat treatment is given to wastes for metal recovery and the process is fast and efficient but emits toxic gases and requires high energy for operation. In hydrometallurgy, chemicals like mineral acids, ligand are used to recover metals efficiently from e-waste, however toxic nature of these chemicals is a major concern for their applicability (Priya and Hait, 2017). Effluent generated from these conventional metallurgical processes, which further needs treatment to dispose of into the environment safely (Priya and Hait, 2017). To overcome these aforementioned drawbacks, nowadays researchers are focusing on the metal recycling process, which is efficient as well as environmentally friendly.