Rare earth elements extraction from Idaho-sourced surface soil by phytomining

Abstract

Environmentally-friendly and low emission extraction methods are needed to meet worldwide rare earth element (REE) demand. Within a greenhouse setting, we assessed the REE hyperaccumulation ability of four plant species (e.g., Phalaris arundinacea, Solanum nigrum, Phytolacca americana, and Brassica juncea) and the impact of amending REE-rich soil with biochar or fertilizer and watering with citric acid solution. Harvested samples were pyrolyzed, and the resulting bio-ores were acid-digested and underwent elemental analysis to determine REE content. Amending soil with fertilizer and biochar increased bio-ore production, while plant species explained most variation in bioaccumulation factor. Phalaris arundinacea achieved the highest average REE concentration of 27,940 ppm for targeted REEs (i.e., cerium, lanthanum, neodymium, praseodymium, and yttrium) and 37,844 ppm for total REEs. We successfully extracted REE-rich bio-ore from plant biomass and determined that soil amendment and plant species will be critical parameters in design and implementation of Idaho-based REE phytomining operations.