A process may involve treating calcium sulfate separated from phosphoric acid with acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from a liquid phase of the suspension, treating the purified calcium sulfate with water or with a salt- and/or chelate ligand-containing aqueous solution to leach rare earths out of the calcium sulfate, separating the further-purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate that is separated off with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker and thereby forming sulfur dioxide as offgas, and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.

A process may involve treating calcium sulfate separated from phosphoric acid with acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from a liquid phase of the suspension, treating the purified calcium sulfate with water or with a salt- and/or chelate ligand-containing aqueous solution to leach rare earths out of the calcium sulfate, separating the further-purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate that is separated off with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker and thereby forming sulfur dioxide as offgas, and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.

A method of treating a sulphate-bearing stream which includes the steps of hydrolysing aluminium sulphate to produce a chemically-reactive aluminium trihydroxide and sulphuric acid, adding lime to immobilize the sulphuric acid as gypsum and using the aluminium trihydroxide to remove sulphate from the sulphate-bearing stream without interference of sulphate derived from the aluminium sulphate used as an aluminium source in the hydrolysis step.

A process for producing sulfuric acid and cement clinker may use calcium sulfate that is formed as a solid by-product and separated off in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid. The process comprises treating calcium sulfate separated from the phosphoric acid with an acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker, with formation of sulfur dioxide as offgas, and subjecting the sulfur dioxide formed to offgas purification and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid. The sulfuric acid produced may be used as starting material in phosphoric acid production.

In an aspect, provided herein are methods for producing sulfuric acid and hydrogen gas, the methods comprising steps of: providing sulfur dioxide formed by thermal conversion of a sulfur-containing species; electrochemically oxidizing said sulfur dioxide to sulfuric acid in the presence of water; and electrochemically forming hydrogen gas via a reduction reaction. In some embodiments, the methods comprise a step of thermally converting said sulfur-containing species to said sulfur dioxide. Systems configured to perform these methods are also disclosed herein. Also provided herein are methods and systems for producing sulfuric acid and hydrogen gas by electrochemically forming the sulfuric acid and the hydrogen gas in a mixture comprising a sulfur material, a supporting acid, and water. Also provided herein are methods and systems for producing a cement material.

A new integrated method to capture polluted CO.sub.2 using CaO produced from phosphogypsum calcination using sulfur as non-CO.sub.2 fuel where (1) both pollutants of phosphogypsum and CO.sub.2 are transformed into environmentally neutral or useful products such as limestone or clinker and sulfuric acid; (2) low-CO.sub.2 CaO produced from calcination of phosphogypsum with sulfur as fuel can be used to produce low-CO.sub.2 clinker that replaces the use of high-CO.sub.2 limestone as raw material; (3) the use of sulfur as fuel to calcine phosphogypsum allows the production of low-cost sulfuric acid.

A new integrated method to capture polluted CO.sub.2 using CaO produced from phosphogypsum calcination using sulfur as non-CO.sub.2 fuel where (1) both pollutants of phosphogypsum and CO.sub.2 are transformed into environmentally neutral or useful products such as limestone or clinker and sulfuric acid; (2) low-CO.sub.2 CaO produced from calcination of phosphogypsum with sulfur as fuel can be used to produce low-CO.sub.2 clinker that replaces the use of high-CO.sub.2 limestone as raw material; (3) the use of sulfur as fuel to calcine phosphogypsum allows the production of low-cost sulfuric acid.

Fire resistant gypsum panels are provided herein, with assemblies including the same, and methods for making the same. A gypsum panel includes a set gypsum core and a mat facing material. The set gypsum core includes a fire resistant additive. The fire resistant additive consists essentially of clay, or a non-intumescent fire resistant additive. The panel displays an acceptable fire rating without requiring the use of vermiculite or intumescent materials.

A new integrated method to capture polluted CO.sub.2 using CaO produced from phosphogypsum calcination using sulfur as non-CO.sub.2 fuel where (1) both pollutants of phosphogypsum and CO.sub.2 are transformed into environmentally neutral or useful products such as limestone or clinker and sulfuric acid; (2) low-CO.sub.2 CaO produced from calcination of phosphogypsum with sulfur as fuel can be used to produce low-CO.sub.2 clinker that replaces the use of high-CO.sub.2 limestone as raw material; (3) the use of sulfur as fuel to calcine phosphogypsum allows the production of low-cost sulfuric acid.

A new integrated method to capture polluted CO.sub.2 using CaO produced from phosphogypsum calcination using sulfur as non-CO.sub.2 fuel where (1) both pollutants of phosphogypsum and CO.sub.2 are transformed into environmentally neutral or useful products such as limestone or clinker and sulfuric acid; (2) low-CO.sub.2 CaO produced from calcination of phosphogypsum with sulfur as fuel can be used to produce low-CO.sub.2 clinker that replaces the use of high-CO.sub.2 limestone as raw material; (3) the use of sulfur as fuel to calcine phosphogypsum allows the production of low-cost sulfuric acid.