Precipitating Rare Earth by NH4HCO3 from a Concentrated Rare Earth and Magnesium Sulfate Solution

Abstract

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.