Selective removal of Fe impurities in the recovery of rare earth elements from carbonatite tailings using chemical routes

The increasing demand for rare earth elements (REEs) has led to the exploration of mining tailings as a potential secondary source. This study offers novel insights into the recovery of REEs from Fe-rich mine tailings sourced from a weathered carbonatite deposit. The REEs were recovered by selectively removing Fe impurities after acid-leaching. The paper details the comprehensive methodologies employed, including initial hydrochloric acid leaching and variable optimization such as acid concentration, liquid-to-solid ratio, temperature, and time. An alkali pre-treatment using NaOH was also investigated to assess its impact on the efficiency of REEs recovery. The study reveals that pH plays a significant role in the selective removal of Fe impurities and offers avenues for the production of high-purity, industry-grade REEs. The work is particularly ground-breaking in its exploration of selective Fe removal using a combination of dilute ammonium hydroxide and ammonium chloride. Through this method, a significant milestone was achieved: the precipitated solid primarily contained Fe (>96%), with minimal loss of REEs (only 0.22%) at a solution pH of 3.25 at 40 °C. This study is the first to demonstrate such high selectivity in the removal of Fe from acid leach liquors of this nature.