Bioleaching of copper from large printed circuit boards for synthesis of organic-inorganic hybrid

Abstract

The present study described a process for copper (Cu) bioleaching from waste printed circuit boards (PCBs). The 45 (± 0.18) mg/g Cu was found in waste PCBs. Acidiphilium acidophilum (NCIM 5344) (A. acidophilum) and hydrogen peroxide (H₂O₂) were used for two-step Cu bioleaching. A. acidophilum showed growth in 9K medium containing glucose and sulfur. During the growth the bacteria decreased medium pH from 3.5 (± 0.01) to 1.0 (± 0.02) in 10 days. The results showed that it required 2.5 h to leach all of the Cu from single PCB piece using 60 mL culture supernatant + 15 mL H₂O₂ at 60 °C temperature and static condition. The leached Cu was further used to synthesize the organic-inorganic hybrid (OIH). For this study, egg white was used as a polyphenol oxidase (PPO) enzyme source. The morphological, elemental, and structural analysis was carried out using scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Further the PPO enzyme activity was tested in OIH and crude enzyme (egg white). The egg white showed 0.00014 (± 0.00001) U/mg/min PPO activity while OIH showed 0.005 (± 0.00016) U/mg/min PPO activity. The pH 7 and 30 °C temperature were found to be optimum for PPO enzyme activity. The OIH was applied for phenol degradation. It degraded 95 (± 0.49)% of phenol (5 mM). The efficiency of phenol degradation decreased with an increase in phenol concentration.

Keywords: Bioleaching; Organic-inorganic hybrid; Phenol degradation; Waste PCBs.