Releasing impurities from a calcium-based mineral

A method for releasing impurities from a calcium-based mineral to produce gypsum, the method comprising:

• reacting a calcium-based mineral containing impurities with an aqueous solution of one or more ionic salts at a temperature of approximately 85° C. or above, wherein at least one of the calcium-based mineral and the one or more ionic salts comprises sulphate and at least one of the calcium-based mineral and the one or more ionic salts comprises ammonium, and wherein the concentration of the solution is approximately 25% or higher mass fraction such that double salt crystals are formed and impurities are released separating the double salt crystals from the impurities;
• reacting the double salt crystals with an aqueous solution to precipitate gypsum;
• and
• separating the gypsum from the aqueous solution.

A method for releasing impurities from a calcium-based mineral to produce a mixture of rare earth elements or precious metals, the method comprising:

• reacting a calcium-based mineral containing a mixture of rare earth elements or precious metals with an aqueous solution of one or more ionic salts at a temperature of approximately 85° C. or above, wherein at least one of the calcium-based mineral and the one or more ionic salts comprises sulphate and at least one of the calcium-based mineral and the one or more ionic salts comprises ammonium, and wherein the concentration of the solution is approximately 25% or higher mass fraction such that double salt crystals are formed and impurities are released;
• separating the double salt crystals from the mixture of rare earth elements or precious metals;
• and
• collecting the mixture of rare earth elements or precious metals.