Hydrometallurgical recovery of manganese and nickel and isolation of tantalum from obsolete tantalum capacitor

Abstract

Tantalum capacitor demand is rapidly growing, primarily from the electronic and superalloy industries. Indeed, the global tantalum market is anticipated to boost at a compound annual growth rate of around 6% over the next decade. With increasing technological advancements, electronics' obsolescence rate has also increased. The obsolete capacitors from these electronics are a rich secondary resource for recycling strategically and economically significant metals. In this article, we have developed an environment-friendly hydrometallurgical route for recovery of manganese and nickel from the tantalum capacitors. Firstly, silica-free tantalum capacitor procured after pre-processing was leached using hydrochloric acid (1–3 M) for preferred dissolution of manganese and nickel, to facilitate a tantalum-rich residue. Manganese was then selectively separated from leach liquor using solvent extraction with D2EHPA and CYANEX272, with the extraction efficiency of each reagent compared. Quantitative dissolution of both manganese (99.9%) and nickel (98.9%), with no tantalum dissolution, was witnessed under the optimized leaching condition of 3 M HCl, 50 g/l pulp density, 60 °C, and 120 min. Kinetic data for manganese and nickel in the temperature range of 30–60 °C demonstrated the leaching reaction at the surface to be the rate controlling step. D2EHPA and CYANEX272 each showed excellent selectivity for manganese under the optimized conditions. However, CYANEX272 proved to be a better extractant in light of higher extraction efficiency in single-stage extraction (∼75%), than D2EHPA (∼40%), with less organic consumption. Above 99% manganese was selectively extracted with predicted 2-stages extraction by McCabe-Thiele plot using CYANEX272 under the optimized condition.