Separation of rare earth elements from contaminants and valuable components by in-situ precipitation during the hydrometallurgical processing of eudialyte concentrate

Abstract

Eudialyte – a sodium rich zirconosilicate – is often enriched in relevant amounts of Zr and Hf as well as other valuable metals such as rare earth elements (REEs), Mn and Nb. Due to its high solubility in mineral acids, all valuable components can be leached with high yields under mild conditions. The subsequent separation and purification of individual components from the resulting highly complex solutions can be challenging, especially due to the release of silica. This study deals with REE separation by in-situ precipitation during leaching of a thermally pre-treated H2SO4/eudialyte concentrate mixture. In contrast to common practice, the precipitation was undertaken before solid/liquid separation. Moreover, it was demonstrated that sulfuric acid plays a crucial role in the process, reducing REE and silica solubility and enhancing leaching yields of other valuable components (Zr, Hf, Mn and Nb). The best precipitation yield of 90% for REE was achieved by a solution phase comprising 117 g/L Na2SO4 and 477 g/L H2SO4 after 120 min at a temperature of 95 °C and a solid/liquid ratio of 150 kg/m3. After the precipitation step, REEs were transferred into the liquid phase by two different methods: direct water treatment and NaOH/HCl-route. Through direct water treatment, the separation efficiency decreased with an increasing solid/liquid ratio due to higher amounts of adsorbed mother liquor and a higher concentration of valuable components in it. The conversion of precipitated REEs into sparingly soluble hydroxides using NaOH and subsequent acid treatment using HCl significantly improved the purity of the REE solution. Compared with direct water treatment, the separation efficiency could be enhanced.