Faculty Publications

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Process engineering aspects in bioleaching of metals from electronic waste
(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Minimol, M.; Shetty K, V.; Saidutta, M.B.
Obsolete electronic devices and their components majorly contributed by the computer and mobile phone printed circuit boards (PCBs) constitute the electronic waste (e-waste). The e-wastes pose an environmental threat due to their eco-toxicological characteristics, thus making its management a mandate through an ecologically sustainable process. Further, the high concentration of metals in the e-waste makes it a secondary ore for metal recovery. Bioleaching is a bio-hydrometallurgical process, which is microbe-mediated dissolution of metals. Different nutritional classes of microorganisms like autotrophs and heterotrophs are active bioleaching agents of e-wastes. The mode of action of microbes for bioleaching of metals is obscure and is believed to ensue through redox reactions, protonic attack, or chelation. The process of bioleaching is influenced by biotic factors like the group and class of microorganism, growth rate, metabolic activity, etc. However, there are several abiotic factors that strongly affect the bioleaching efficiency. Development of a bioleaching process would need the study of various biological, nutritional, and engineering factors that influence the process. This chapter presents the critical analysis of various process engineering aspects in the bioleaching of metals from e-waste. To engineer a bioleaching process, (1) various biological, nutritional, and physicochemical factors, such as media composition, pH, e-waste loading, particle size, oxygen requirement, inoculum size, etc., should be optimized and (2) suitable bioreactor choice considering the microbial type, phases to be contacted, and the pattern of contacting followed by optimization of bioreactor operational parameters. This paper brings out a critical review of these bioprocess engineering aspects in bioleaching of metals from e-waste, directing the reader to the future scope of research on bioleaching, a bioremediation strategy to save and conserve environment for sustainable development. © 2020, Springer Nature Switzerland AG.
Biohydrometallurgical methods and the processes involved in the bioleaching of WEEE
(Elsevier, 2021) Minimol, M.; Shetty K, K.; Saidutta, M.B.
The obsession toward the latest electronics and electrical goods has led to the generation of undesirable quantities of Waste Electrical and Electronic Equipments termed as electronic wastes (e-wastes). E-wastes, especially the printed circuit boards, are rich in their metal concentration and are considered as secondary resources for urban mining. The management of the metallic portion of these wastes is achieved through established physical, chemical, and biological treatment technologies. Biohydrometallurgy is a significant technology to address the issue in an eco-friendly mode. The different processes of biohydrometallurgy include bioleaching, bioflocculation, bioprecipitation, biosorption, biooxidation, and bioreduction. Bioleaching plays a vital role in the dissolution of metals from the solid matrix into the leaching solution using microorganisms. The different methods of bioleaching to accomplish metal recovery from e-waste are one-step bioleaching, two-step bioleaching, and spent medium bioleaching. The method to be selected depends on several growth and process factors to be successfully implemented. This chapter focuses on the methods of bioleaching and the processes involved in each of these methods to opt the most appropriate one for efficient metal recovery. Studies on biohydrometallurgy would confront the glitches involved in e-waste disposal and recycling in a sustainable manner. © 2021 Elsevier Inc. All rights reserved.
Bioleaching of zinc from e-waste by A. aquatilis in fluidised bed bioreactor
(Taylor and Francis Ltd., 2023) Minimol, M.; Shetty K, V.; Saidutta, M.B.
Technological advancements with the use of new-generation electronic devices and accumulated electronic wastes (e-wastes) raise environmental concerns. E-waste, especially mobile phone Printed Circuit Boards (PCBs) is a rich source of metals. Bioleaching, a microbe-mediated metal dissolution process is employed for the recovery of metals. The operational parameters like particle size, inoculum percentage (v/v) and e-waste load (w/v) were optimised for Zn bioleaching by Alcaligenes aquatilis in shake flasks and fluidised bed bioreactor (FBR). The e-waste feed particle size of 0.175 mm and 5% inoculum was found to be the optimum for Zn bioleaching in both the shake flask and FBR. The optimum e-waste load was 5% in the shake flask and 2% in FBR. The maximum recovery of Zn was 0.6 mg/g (13.73%) in the shake flask and 0.57 mg/g (13%) in FBR, implying that FBR exhibits similar efficiency of Zn bioleaching as in the shake flask. Further three sequential batch runs increased the recovery to a maximum of 1.66 mg/g from 4.37 mg/g Zn present in the PCBs ie., 38% Zn recovery. This shows that efficient bioleaching of Zn on a larger scale can be achieved with sequential batches and applied for the simultaneous recovery of metals from PCBs. © 2023 Indian Institute of Chemical Engineers.

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