Integrated method for the commercial and industrial utilisation of calcium sulphate whilst obtaining rare earth elements from the production of phosphoric acid

An integrated process for producing sulfuric acid and cement clinker and for obtaining rare earths, the process comprising performing the following steps in an integrated plant complex:

• (a) treating calcium sulfate separated from phosphoric acid in step (f) with an acid to obtain a suspension comprising purified calcium sulfate;
• (b) separating the purified calcium sulfate in solid form from a liquid phase of the suspension, wherein the purified calcium sulfate that is separated off contains at least 50% by weight of anhydrite based on dry calcium sulfate,
• (b1) treating the purified calcium sulfate that is separated in step (b) with water or with a salt- and/or chelate ligand-containing aqueous solution to leach rare earths out of the calcium sulfate, wherein a weight ratio of solids to liquid for the leaching of the rare earths is 1:1 to 1:10, wherein a dwell time for the leaching of the rare earths is 5 h to 68 h,
• (b2) separating the further-purified calcium sulfate from step (b1) in solid form from a liquid phase of a suspension obtained in step (b1) with one or more rare earths present in the liquid phase;
• (c) mixing the further-purified calcium sulfate that is separated off in step (b1) with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production;
• (d) burning the raw meal mixture to obtain the cement clinker, forming sulfur dioxide as offgas;
• (e) feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid;
• and
• (f) forming the calcium sulfate and separating the calcium sulfate off as a solid by-product during production of the phosphoric acid in a reaction of raw phosphate with the sulfuric acid to form the phosphoric acid.