Patent ID: 8501124

Claim:
A method of recovering salts of rare-earth elements from a solid mixture comprising at least one halophosphate and at least one compound of one or more rare-earth elements, wherein the method comprises the following steps: (a) carrying out acid attack on said mixture in a liquid medium; (b) adding a base to the medium obtained at the end of step (a) so as to raise the pH of said medium to a value of at least 1.5, whereby a first solid phase is obtained comprising one or more rare-earth elements at least partly in the form of phosphate and a first liquid phase comprising at least one alkaline-earth element of halophosphate and separating a first solid phase from the first liquid phase; (c) attacking the first solid phase resulting from step (b) with a strong base, whereby a second solid phase is obtained comprising one or more rare-earth elements at least in the form of hydroxide and a second liquid phase comprising a phosphate of a cation of the strong base and separating the second solid phase from a second liquid phase; (d) carrying out acid attack on the second solid phase resulting from step (c) under conditions such that the pH is below 3, whereby a third solid phase is obtained and a third liquid phase comprising at least one rare-earth salt and separating the third solid phase from the third liquid phase; (e) mixing the third solid phase resulting from step (d) with a solid alkaline compound and calcining the mixture thus obtained; (f) redispersing, in water, the calcined product resulting from the preceding step; (g) separating, from the dispersion obtained at the end of the preceding step, a fourth solid phase comprising one or more rare-earth elements at least in the form of hydroxide and a fourth liquid phase comprising at least one alkaline element; (h) preparing an aqueous dispersion of the fourth solid phase resulting from the preceding step and acidifying the dispersion thus obtained; and (i) separating, from the dispersion obtained at the end of the preceding step, a fifth solid phase and a fifth liquid phase comprising at least one rare-earth salt.