MINIMIZING SOLVENT EXTRACTION IN RARE EARTH SEPARATION THROUGH FRACTIONAL PREECIPITATION

Abstract

Rare earth elements play a crucial role in today’s high‐tech world, with applications ranging from electric‐vehicle motors and wind‐turbine generators to smartphones and computer hard drives, thanks to their unique and superior magnetic, optical, and catalytic properties. However, their end use requires high purity (>99%) rare earth elements. Traditionally, achieving such purity at an industrial scale involves solvent extraction, a process that relies on costly chemicals and typically requires hundreds of separation stages. To contribute to ongoing efforts to make REE separation more sustainable by reducing the number of processing steps and minimizing chemical consumption, this project investigates the effectiveness of fractional precipitation as an initial step to separate cerium (Ce) and lanthanum (La) from the REE concentrate before the solvent extraction process. This study uses synthetic samples consisting of cerium carbonate, neodymium nitrate and lanthanum oxalate to evaluate the approach. Ammonium hydroxide (NH₄OH) was used to adjust the pH of REE solutions during fractional precipitation. Mixtures of La and Ce (1:1 by mass, total REE concentration of 5 g L⁻¹) were prepared in 0.1–0.5 M nitric acid or citric‐acid solutions at 40 °C. A 25% NH4OH was then slowly added while monitoring pH, observing colour changes, and measuring the remaining concentration of La, Ce and Nd using Inductively Coupled Plasma Mass Spectrometry (ICP‐MS). At 0.5 M HNO₃ and around pH 4.5, more than 80% of Ce precipitated out as Ce‐hydroxide. In contrast, the citric‐acid system showed minimal Ce precipitation even at pH 7–8, due to strong citrate complex formation. For separating neodymium and lanthanum, oxalic acid performed poorly compared to NH4OH in the precipitation process. These results demonstrate that a single‐stage HNO₃–NH₄OH precipitation step can replace multiple solvent extraction stages, significantly reducing chemical use, simplifying the separation process, and lowering environmental impact. This paves the way for easier recovery of high‐purity Ce and La in downstream processing.