Biological and chemical techniques for the extraction of valuable metals (especially Tantalum) from waste printed circuit boards and Tantalum capacitor scrap.

Metals are the heart of a country’s economy. A steady supply chain of metals independentfrom geopolitical instabilities is essential for the national and economic security of acountry. The move toward green technologies leads to an ever-growing demand for rareand critical metals. Hence, there is an urgent need to develop efficient recycling techniquesto recover these metals from suitable sources, for example from electronic waste.The impetus for conducting this research is to find the approaches and techniques to minevaluable metals from WEEE (waste electric and electronic equipment) to reduce thedependency on primary resources, grapple with electronic waste issues and contribute to asustainable society. In this context this thesis demonstrates the chemical and microbialleaching techniques for metal recovery from waste PCBs (printed circuit boards) andtantalum capacitors. Process fundamentals, perspectives and bottlenecks of both processesare discussed in detail. Tantalum recovery due to its criticality and very low recycling rate isaddressed.For microbial leaching acidophilic and heterotrophic microbial strains are employed.Comparative studies using organic and inorganic acids are also carried out. The studyinferred that microbial leaching as well as leaching with inorganic acids can be exploited forIBMs (industrial base metals) recovery. Tantalum was found to be mobilised by someunknown, self-growing species in a particular experiment, unfortunately attempts tocultivate, isolate and identify these species failed. It demonstrated the potential of microbialleaching of tantalum and opened a new research opportunity.A novel integrated model for the recovery of tantalum from tantalum rich waste bycombining hydrometallurgical and bio-metallurgical processes has been designed. Thesource material was first subjected to microbial leaching which solubilised most of themanganese and base metals, the residue was then subjected to chemical leaching whichsolubilised silver and remaining impurities leaving behind pure tantalum in concentratedform. The process proposed is also capable of recovering manganese and silver fromtantalum capacitor scrap. The study indicates that recycling of WEEE is feasible for recyclersand to benefit society if exploited efficiently and sensibly.