Recovery of rare earth from the ion-adsorption type rare earths ore: II. Compound leaching

• Compound leaching with magnesium salt was proposed to realize ecological leaching.
• The contents of ion-exchangeable Mg2 +/Ca2 + can be adjusted by compound leaching.
• Mg2 +/Ca2 +/NH4+ compound leaching leads to 94% RE efficiency and 49% Al efficiency.
• The optimal content of ion-exchangeable Mg2 +/Ca2 + was 628.57 mg/kg and 77.77 mg/kg.
• The soybeans could grow normally and its average plant height was up to 25.5 cm.

In order to coordinate the content and ratio of ion-exchangeable calcium and ion-exchangeable magnesium in the soil and reduce ammonia nitrogen pollution, recovery of rare earth from the ion-adsorption type rare earths ore with magnesium–ammonium, magnesium–calcium and magnesium–ammonium–calcium compound leaching agent was studied in this paper. Results showed that the leaching ability was in the order of (NH4)2SO4 > NH4Cl > MgSO4 > MgCl2 ≈ CaCl2 under the same total cationic charge. The content of ion-exchangeable magnesium and ion-exchangeable calcium in water washing tailings could be adjusted to be suitable for the plant growth by changing the composition of leaching agent. In the magnesium–ammonium–calcium compound leaching system, when the mole ratio of magnesium–ammonium–calcium was 15:25:60, 628.57 mg·kg− 1 ion-exchangeable magnesium and 77.77 mg·kg− 1 ion-exchangeable calcium in water washing tailings were achieved, while the ratio of ion-exchangeable calcium and magnesium was 8.08. Moreover, the aluminum leaching efficiency was only 49.2% and the rare earth leaching efficiency could be above 94%. Furthermore, the soybeans could grow normally with water washing tailings in magnesium–ammonium–calcium compound leaching system with an average plant height of 25.5 cm. The application of magnesium–ammonium–calcium compound leaching agent could significantly reduce the ammonia nitrogen pollution, maintain the soil nutrient so as to reduce the dosage of calcium–magnesium fertilizer, and may realize the ecological friendly leaching of the ion-adsorption type rare earths ore.