Method for selective separation of thorium and cerium from a solid concentrate comprising same and one or more further rare earth metals and acidic rare earth solution thereof

A method for separating thorium and cerium from a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals, comprising the steps of increasing to pH 1.8 the pH of an aqueous composition comprising from 6 to 21 weight % nitric acid, from 25 to 33 weight % phosphoric acid, from 3.5 to 5 weight % calcium, and amounts of compounds of thorium, cerium and one or more further rare earth metals, the weight % being relative to the total weight of the aqueous composition, and subsequently precipitating and separating the solid concentrate comprising the compounds of thorium and cerium, further comprising the steps of:

• a) contacting the solid concentrate with an acid to achieve an acid composition comprising cerium ions with a pH of less than 0.5;
• b) reacting the acid composition obtained in step a) with ozone or heating the acid composition obtained in step a) at a temperature ranging from 110° C. to 130° C. for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition to an oxidation state of +IV;
• c) increasing, to at most 2, the pH of the composition obtained in step b), resulting in the precipitation of thorium and cerium compounds;
• and
• d) separating the precipitated thorium and cerium compounds from the composition obtained in step c) to obtain an aqueous acidic rare earth solution depleted in thorium and cerium.