Method For Recovering Rare Earths And Coproducts From Phosphogypsum And Phosphoric Acid Sludge

A method for treating phosphogypsum or phosphoric acid sludge allowing the recovery of rare earths, the method comprising the following successive steps:

• (a) treating the phosphogypsum or phosphoric acid sludge, respectively, according to the following steps (a1) or (a2):
• (a1) washing the phosphogypsum with a polar solvent and collecting the solid residue obtained;
• or
• (a2) separating the phosphoric acid sludge into a liquid phase and a solid residue and separately collecting the resulting solid residue and the resulting liquid phase;
• washing the solid residue obtained at the end of the treatment with a polar solvent at room temperature and separately collecting the solid residue obtained and the liquid phase obtained;
• and
• washing the solid residue obtained at the end of washing with a hot polar solvent and collecting the solid residue obtained and the liquid phase obtained;
• (b) drying, grinding and sieving the solid residue obtained at the end of step (a);
• (c) alkaline leaching the solid residue obtained at the end of step (b) with a strong mineral base, and collecting the solid residue obtained and the liquid phase obtained;
• (d) drying, grinding and sieving the solid residue obtained at the end of step (c);
• (e) acid leaching the solid residue obtained at the end of step (d) with nitric acid and collecting the solid residue obtained and the liquid phase obtained;
• (f) precipitating calcium nitrate crystals from the liquid phase obtained at the end of step (e) and collecting the solid residue and the liquid phase obtained;
• (g) adjusting the pH of the liquid phase obtained at the end of step (f) to a value of between 1 to 1.8 by adding a strong base and collecting the solid residue obtained and the liquid phase obtained;
• (h) drying the solid residue obtained at the end of step (g) to obtain a solid product containing rare earths.