Gallium and rare-earth elements: a critical review of their roles, recovery, and sustainability challenges

Abstract

Gallium (Ga) and the rare-earth elements neodymium (Nd) and dysprosium (Dy) are important materials for many of today’s electronic products, renewable energy systems, and advanced materials. However, processes for separating these elements from ores and reprocessing them often involve a lot of energy and corrosive chemicals with significant environmental impacts. Therefore, in the current review, we will focus on the geological occurrence of Ga and REEs, the extraction process, and sustainability issues, including the chemistry of the lixiviants used in hydrometallurgical operations. Gallium is usually extracted as a by-product to the mining of aluminum and zinc, while Nd and Dy are extracted directly from the minerals bastnasite and monazite, often using acidic or alkaline leaching. Recently, new low impact techniques such as deep eutectic solvents, ionic-liquids, organic acids and biological lixiviants, for safer and more selective recovery have been introduced, mostly from waste materials such as red mud, fly ash and electronic scrap. Overall the development of closed-loop recovery systems and environmentally-friendly lixiviants are crucial to limit the environmental impact and ensure the long-term availability. The new extraction technologies involving both chemical and biological processes will play a critical role in ensuring the global supply of Ga, Nd and Dy in a growing low-carbon economy.