Biotechnological recycling of hazardous waste PCBs using Sulfobacillus thermosulfidooxidans through pretreatment of toxicant metals: Process optimization and kinetic studies

• Published in: Chemosphere (Oxford) 2022-01, Vol.286, p.131978-131978, Article 131978
• Main Authors: Ilyas, Sadia, Srivastava, Rajiv Ranjan, Kim, Hyunjung, Ilyas, Nimra
• Format: Article
• Language: English
• Subjects: Bioleaching process; Dissolution mechanism; Electronic waste; Metals' recycling; Toxicant removal; Waste valorization
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.131978

The present study dealt with the restricted microbial tolerance for lead and tin during bioleaching of waste printed circuit boards (WPCBs) and lower extraction yields of valuable metals. Pretreatment of WPCBs in 4.0 mol/L HNO3 at 90 °C for 180 min duration prominently dissolved the toxicant metals before the microbial mobilization of valuable metals. Acid pretreatment followed the first-order kinetics that exhibiting an intermediate-controlled mechanism with the apparent activation energy determined to be Ea(Pb), 25.1 kJ/mol and Ea(Sn), 21.9 kJ/mol. Thereafter, the parametric optimization of aeration rate, O2-enrichment, external CO2 supply, temperature, and time for bioleaching of ground WPCBs was examined using Sulfobacillus thermosulfidooxidans (strain RDB). A favourable condition for Cu-bioleaching under higher oxidative environment in comparison to Ni and Zn exhibited the auto-catalytic behaviour of Cu2+ in the biological system. More than 92% of valuable metals were extracted under the optimal condition of aeration rate, 0.5 L/min; O2-enrichement dosage, 30%; external CO2 supply, 0.1%; temperature, 55 °C; and time, 18 days. The bioleaching kinetics followed shrinking core model that exhibiting the shifting of mass transfer from chemically-controlled to the diffusion-controlled mechanism. This process offers two-fold advantages that restoring the valuable metals with low-emission biotechnological route for waste valorization. [Display omitted] •Acid pretreatment of solder metals (Pb and Sn) from waste PCBs was studied.•First-order kinetics of pretreatment revealed its dependency on HNO3 concentration.•0.1% CO2 in O2-enriched air significantly improved the bioleaching efficiency.•Bioleaching performed at 10% pulp density yielded 93% Cu, 91% Ni, and 94% Zn.•Intermediate-controlled mechanism of metals' bioleaching was observed by Ea values.