Leaching isomorphism rare earths from phosphorite ore by sulfuric acid and phosphoric acid

Most of the phosphorite deposits in the world contain isomorphism rare earths (RE) which are considerably difficult to be leached into solution in the wet phosphoric acid process. In this work, a systematic study of leaching RE using sulfuric acid, phosphoric acid, mixed acid and two-step leaching of phosphoric acid and sulfuric acid was performed. The aims are to illuminate the main factors that inhibit RE leaching and to provide insights into the further enrichment of RE in the wet phosphoric acid solution. The results indicate that H₂SO₄ is not an effective acid for leaching isomorphism RE from phosphorite ore. The low RE leaching efficiency attributes to the RE co-crystallized and encapsulated by phosphogypsum (PG) as well as the precipitation of RE by RE sulfates or phosphates. High concentration of H₃PO₄ can enhance the dissolution and diffusion of RE ions. Hence, the optimized leaching mode of improving RE leaching efficiency is to adequately dissolve phosphorite ores in high concentration of H₃PO₄ solution and then add H₂SO₄ to crystallize PG. The effect of co-crystallization or encapsulation of PG on RE can be decreased due to the crystallizing mode of PG in the bulk solution instead of on the interface of solid reactants. RE leaching efficiency can be high up to 65% by the optimized leaching mode.