Method for producing phosphoric acid and calcium sulphate quality suitable for a clinker process for the commercial and industrial utilization of calcium sulphate

A process for producing sulfuric acid and cement clinker, the process comprising:

• a) digesting raw phosphate in a first step with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in a form of dihydrate, hemihydrate, or a combination of hemihydrate and dihydrate, and phosphoric acid;
• b) separating off the calcium sulfate as a solid from a liquid phase of a suspension that is obtained;
• c) treating the calcium sulfate from step (b), separated off from the phosphoric acid, and/or calcium sulfate/phosphogypsum from a stockpile with an acid to give a suspension with purified calcium sulfate and a P2O5-containing acid solution;
• d) determining a tMIN, wherein tMIN is a time at which an acid concentration during the treatment in step (c) is a minimum, and separating off the purified calcium sulfate after step (c) as a solid from a liquid phase of the suspension that is obtained, wherein the separation of the purified calcium sulfate from the suspension is started at a time in a range from tMIN+30 minutes to tMIN−30 minutes;
• and
• e) mixing the purified calcium sulfate that is separated off and obtained in step (d) with admixtures and reducing agent to give a raw meal mixture for cement clinker production;
• f) burning the raw meal mixture to give the cement clinker, with sulfur dioxide being formed as an offgas;
• and
• g) supplying the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.