A critical updated review of all stages of the tantalum recycling chain from waste of tantalum capacitors

Tantalum (Ta) is classified by the European Union as a critical metal. Up to date, Ta is irreplaceable in many technological areas but the Ta recycling rate from current end-of-life products is less than 1%. Capacitor's productions represent around 34% of the total Ta applications and recycling the high content of Ta contained in the waste tantalum capacitors (WTCs) present in the waste printed circuit boards (WPCBs) of electric and electronic equipment is crucial and urgent and will definitively contribute to the long-term sustainability of Ta demand. This paper reviews critically all processes of the Ta recycling chain of WTCs starting in the selection and disassembly of WTCs from the WPCBs, pre-treatment stage and, finally, the refinery process to recover the Ta sintered body. Regarding the identification, selection and disassembly process, several methods are discussed and compared, such as manual versus automatic and robotic identification and disassembling. Concerning the pretreatment stage, the main advantages and disadvantages of the crushing of the WTCs, which aims to remove or detach the epoxy resin that surrounds the WTCs, are analysed and discussed. Subsequently, the various thermal (pyrolysis, roasting, combustion, solvolysis, steam gasification and hydrogenation) and physical-mechanical (sieving, magnetic separation, eddy-current separation, corona electrostatic separation, and density separation) treatments for recovering Ta are reviewed. Lastly, refinery processes, such as, as hydrometallurgy, chloride metallurgy, thermal purification, and magnesium thermal reduction process and ionic liquids extraction, are assessed. At the end, future insights, perspective and conclusions are pointed out.