Production of rare earth enrichment from the in situ leaching solution of ion-adsorbed rare earth ores greatly decreases the treatment scale and significantly reduces production energy consumption and cost. However, the generated rare earth enrichment has a high content of impurities. Further purification of rare earth is necessary. Therefore, a process comprised of sulfuric acid leaching and removing aluminum by the neutralization precipitation method to obtain the purified rare earth solution was proposed. The results of acid leaching revealed that at a sulfuric acid concentration of 1.75 mol/L, a temperature of 60 °C, a liquid–solid ratio of 5:1 mL/g, a leaching time of 0.5 h, and a stirring rate of 300 r/min, leaching efficiency of rare earth and magnesium reached 99.11% and 97.39%, respectively, while the leaching efficiencies of aluminum and silicon reached 72.91% and 55.26%, respectively. The comparison of different precipitants during the neutralization precipitation process showed that MgO was the best precipitant for the efficient removal of aluminum and low loss of rare earth. The results of removing aluminum revealed that when the final pH of the rare earth leaching solution was controlled to be 4.7, the reaction temperature was 25 °C, the slurry concentration of MgO was 0.3 mol/L, and the feeding rate of the MgO slurry was 0.5 mL/min, the removal rate of aluminum was 99.49%, and the loss rate of rare earth was 13.93%. The obtained purified rare earth solution contained 19 g/L of rare earth and less than 0.01 g/L of aluminum. Kinetic studies showed that the apparent activation energy of the aluminum removal process was 6.8 kJ/mol, indicating that the precipitation process was controlled by a mass transfer diffusion reaction.

The ammonium bicarbonate precipitation method has become one of the main ways to extract rare earths from rare earth leaching solutions due to its advantages of simple operation, mature technology, and low cost. Therefore, the objective of this study was to explore the precipitation of rare earth carbonate (REC) from a concentrated rare earth and magnesium sulfate solution by ammonium bicarbonate. The terminal pH to precipitate rare earth was determined. The effects of factors including the feeding rate, temperature, ammonium bicarbonate concentration, seed dosage, and stirring rate on the rare earth precipitation efficiency, the Mg and SO₄²⁻ amounts in the obtained REC, and the median particle sizes of the REC were investigated. The effects of these factors on the Mg and SO₄²⁻ amounts in the REC and the median particle sizes of the REC were compared by one-way analysis of variance (ANOVA). The results showed that at a terminal pH of 6.8, a feeding rate of 0.5 mL/min, a temperature of 25 °C, an ammonium bicarbonate concentration of 0.6 mol/L, a crystal seed dosage of 7.5%, and a stirring speed of 300 r/min, without aging, the contents of rare earth oxide (REO), MgO, and SO₄²⁻ in the REC were 57.69%, 0.23%, and 1.68%, respectively, superior to the requirements of the current Chinese national standard (GB/T 16479-2020) for REC. The rare earth precipitation efficiency was 99.78%. Among the investigated factors, the pH was the main factor affecting the rare earth precipitation efficiency. The seed dosage significantly changed the median particle sizes of the REC and the Mg content of the REC. For SO₄²⁻, its content was fluctuant and could be controlled at a relatively low value by the seed dosage and specific stirring rate.