Life Cycle Assessment of Tantalum and Niobium Recycling from Hard Metal Scrap

Abstract

Secondary hard metal contains valuable tantalum and niobium, which could be recovered after chemical recycling of the scrap; however, the environmental impacts of their recycling have not been earlier quantified. This study provides gate-to-gate life cycle inventory data on tantalum and niobium recovery from the Ta-Nb-rich residue after the leaching of cobalt in the chemical recycling of hard metal and first assessment of the environmental impacts of tantalum and niobium coproduction. The environmental impacts were quantified using life cycle assessment (LCA) based on data acquired by process simulation. Two processes were evaluated: one based on conventional HF leaching used in the primary production of tantalum and niobium and one prospective HF-free process using NaOH. The results show that environmental impacts of Ta-Nb recycling can outperform primary production environmentally if the Ta and Nb content in the raw material is high enough. At the process level, a benefit is gained even with a lower content, but at the product level, higher contents are required for tantalum recovery to be worthwhile. In HF-based recycling, increasing the Ta and Nb contents each from 2.5 to 5 wt % decreases the value of global warming potential (GWP) of Ta recycling from 1.24 times the GWP of primary tantalum production to 0.72 times the GWP of primary tantalum production. The environmental impacts of the recycling processes mostly originate from the background processes. The most burdening process hot spots of recycling included the leaching and effluent treatment stages for the HF-based process in which HF and lime were the largest contributors. For the HF-free process, the largest contributions were due to NaOH used in the caustic conversion as well as oxalic acid in the solvent extraction.