Efficient separation of Al and Fe impurities from La-Ce chloride solution by pH adjustments with ammonium bicarbonate in the presence of triammonium citrate

The separation of aluminum from rare earths (REs) by precipitation using pH adjustments with ammonium bicarbonate (ABC) is not satisfactory because of their co-precipitation, which affects the crystallization and the purity of rare earth carbonate. Therefore, it is extremely challenging to obtain high recovery of REs with high purity due to loss of REs during precipitation. This paper proposes a precipitation method using ABC in the presence of triammonium citrate (TAC) to separate aluminum from lanthanum and cerium. The results show that the removal efficiency of iron and aluminum and the loss of REs due to coprecipitation (%) depend on the dosage of TAC and ABC and the solution pH. A complementary relationship exists between the removal efficiency of aluminum and the loss of REs during precipitation. The optimal dosage of TAC is linear with the concentration of aluminum or the molar ratio of aluminum to iron. It was found that the removal efficiency of iron, aluminum and the loss of REs during precipitation are 100 %, 93 % and 5.6 %, respectively, for an iron‑aluminum ratio of 0.05, and the optimal dosage of TAC is 4–5 % of the aluminum content. After removing the aluminum and iron, the calcined RE₂O₃ product with purity of 99.6 % and aluminum content of 0.31 % was obtained. Compared with the products without purification or purification without the addition of TAC, the purity of RE₂O₃ product increased by 9.31 % and 1.39 %, and the aluminum content decreased by 1.99 % and 0.78 % respectively. The addition of TAC can promote the precipitation of aluminum at lower pH through its coordination with iron and aluminum, while reducing the loss of REs during precipitation and decreasing the effect of iron on the removal efficiency aluminum.