A production method for producing a halide includes a heat-treatment step of heat-treating, in an inert gas atmosphere, a mixed material in which LiX and YZ.sub.3 are mixed, where X is an element selected from the group consisting of Cl, Br, and I, and Z is an element selected from the group consisting of Cl, Br, and I. In the heat-treatment step, the mixed material is heat-treated at higher than or equal to 200° C. and lower than or equal to 650° C.

A method for producing a halide includes heat-treating a mixed material in an inert gas atmosphere, the mixed material being a mixture of (NH.sub.4).sub.aMX.sub.3+a and LiZ. The M includes at least one element selected from the group consisting of Y, a lanthanoid, and Sc. The X is at least one element selected from the group consisting of Cl, Br, I, and F. The Z is at least one element selected from the group consisting of Cl, Br, I, and F. Furthermore, 0<a≤3 is satisfied.

A method for producing a halide includes heat-treating a mixed material in an inert gas atmosphere, the mixed material being a mixture of (NH.sub.4).sub.aMX.sub.3+a and LiZ. The M includes at least one element selected from the group consisting of Y, a lanthanoid, and Sc. The X is at least one element selected from the group consisting of Cl, Br, I, and F. The Z is at least one element selected from the group consisting of Cl, Br, I, and F. Furthermore, 0<a≤3 is satisfied.

A method for the precipitation of rare earth sulphate, the method including subjecting a crude rare earth sulphate solution to precipitation in the presence of a water soluble, volatile, organic compound to produce a rare earth sulphate precipitate and an acidic supernatant. The organic compound is preferably selected from the group consisting of methanol, ethanol, iso-propanol, tert-butanol, acetone or mixtures thereof, and is preferably methanol. Preferably, the organic compound is used in the precipitation at a weight ratio of between 0.25:1 to 1.5:1, and preferably 0.5:to 1.25:1, with the crude sulphate solution.

A method for the precipitation of rare earth sulphate, the method including subjecting a crude rare earth sulphate solution to precipitation in the presence of a water soluble, volatile, organic compound to produce a rare earth sulphate precipitate and an acidic supernatant. The organic compound is preferably selected from the group consisting of methanol, ethanol, iso-propanol, tert-butanol, acetone or mixtures thereof, and is preferably methanol. Preferably, the organic compound is used in the precipitation at a weight ratio of between 0.25:1 to 1.5:1, and preferably 0.5:to 1.25:1, with the crude sulphate solution.

A method of processing a purified rare earth sulphate solution, the method including the steps of: contacting the purified rare earth sulphate solution with sodium hydroxide to precipitate rare earths as rare earth hydroxide, including the addition of an oxidant to oxidise cerium contained in the rare earth hydroxide precipitate; and selectively leaching the rare earth hydroxide precipitate with hydrochloric acid to form a rare earth chloride solution and a residue.

A method for the precipitation of rare earth sulphate, the method including subjecting a crude rare earth sulphate solution to precipitation in the presence of a water soluble, volatile, organic compound to produce a rare earth sulphate precipitate and an acidic supernatant. The organic compound is preferably selected from the group consisting of methanol, ethanol, iso-propanol, tert-butanol, acetone or mixtures thereof, and is preferably methanol. Preferably, the organic compound is used in the precipitation at a weight ratio of between 0.25:1 to 1.5:1, and preferably 0.5:to 1.25:1, with the crude sulphate solution.

A method for the precipitation of rare earth sulphate, the method including subjecting a crude rare earth sulphate solution to precipitation in the presence of a water soluble, volatile, organic compound to produce a rare earth sulphate precipitate and an acidic supernatant. The organic compound is preferably selected from the group consisting of methanol, ethanol, iso-propanol, tert-butanol, acetone or mixtures thereof, and is preferably methanol. Preferably, the organic compound is used in the precipitation at a weight ratio of between 0.25:1 to 1.5:1, and preferably 0.5:to 1.25:1, with the crude sulphate solution.

A process for the isolation and purification of substantially pure chemicals, including silica gel, sodium silicate, aluminum silicate, iron oxide, and rare earth elements (or rare earth metals, REEs), from massive industrial waste coal ash including a plurality of caustic extractions of coal ash at an elevated temperature, followed by an acidic treatment to dissolve aluminum silicate and REEs. Dissolved aluminum silicate is precipitated out by pH adjustment as a solid product while REEs remain in the solution. REEs are captured and enriched using an ion exchange column. Alternatively, the solution containing aluminum silicate and REEs is heated to produce silica gel, which is separated from the enriched REEs solution. REEs are then isolated and purified from the enriched solution to afford substantially pure individual REE by a ligand-assisted chromatography.

A process for the isolation and purification of substantially pure chemicals, including silica gel, sodium silicate, aluminum silicate, iron oxide, and rare earth elements (or rare earth metals, REEs), from massive industrial waste coal ash including a plurality of caustic extractions of coal ash at an elevated temperature, followed by an acidic treatment to dissolve aluminum silicate and REEs. Dissolved aluminum silicate is precipitated out by pH adjustment as a solid product while REEs remain in the solution. REEs are captured and enriched using an ion exchange column. Alternatively, the solution containing aluminum silicate and REEs is heated to produce silica gel, which is separated from the enriched REEs solution. REEs are then isolated and purified from the enriched solution to afford substantially pure individual REE by a ligand-assisted chromatography.