A novel approach for recovery of rare earths and niobium from Bayan Obo tailings

• A novel approach was employed for recovering RE and Nb from Bayan Obo tailings.
• Sulfating leaching and multiple hydrolysis were adoped in the process.
• Ti4+ and Fe3+ ions were reduced to Ti3+ and Fe2+ ions before hydrolysis.
• Impurities of Nb product were removed partly with NH3⋅H2O–H2C2O4 system.

It is difficult to economically recover rare earths (RE) and niobium (Nb) from Bayan Obo tailings by the existing metallurgical processes. In this study, a novel hydrometallurgy process was employed for separating and recovering RE and Nb from Bayan Obo tailings. Firstly, by sulfating roasting at 250 °C and subsequent leaching at 60 °C, the RE and Nb present in the polymetallic minerals can be efficiently extracted into the leach solution. Secondly, after the reduction of Ti4+ and Fe3+ ions (to Ti3+ and Fe2+ ions) with iron powders followed by hydrolysis at pH 2.01, the Nb can be efficiently precipitated from the leach solution. The impurities present in the precipitated product can then be removed by treating with NH3⋅H2O–H2C2O4 system at pH 4.50. Thirdly, the RE can be efficiently precipitated at pH 7.15 from the filtrate of above hydrolysis reaction mixture. Finally, the impurities present in the crude RE can be removed by oxalate co-precipitation method. The yield of RE and Nb in this novel process reaches up to 90% and 78%, respectively. Both the Nb (60.67 wt% Nb2O5) and RE products (>88.65 wt% RExOy) have high application value.