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.

Aspects of the invention include a method of producing a cement material comprising step of: first reacting a calcium-bearing starting material with a first acid to produce an aqueous first calcium salt; second reacting the aqueous first calcium salt with a second acid to produce a solid second calcium salt; wherein the second acid is different from the first acid and the second calcium salt is different from the first calcium salt; and thermally treating the second calcium salt to produce a first cement material. Preferably, but not necessarily, during the second reacting step, reaction between the first calcium salt and the second acid regenerates the first acid.

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.

A clinker that has a total content of C.sub.3A and C.sub.4AF of 22 to 40 mass %, calculated according to Bogue's formulas, and an iron modulus of 0.8 to 1.3 is pulverized with gypsum. Alternatively, the clinker after pulverization is mixed with gypsum powder. A pulverization agent comprising N-methyl-di-ethanol-amine and/or di-ethanol-isopropanol-amine is used in the pulverization.

The disclosure discloses a production method for producing cement and co-producing sulfuric acid from phosphogypsum. The method includes: pretreating and purifying the phosphogypsum to reduce insoluble phosphorus, water-soluble phosphorus impurities, and most free water in the phosphogypsum, directly feeding the materials kneaded and granulated with a reducing agent into a reduction and decomposition integrated rotary kiln with a fluidized preheating function, and controlling to carry out step-by-step heating, drying, dehydration, reduction and decomposition in a gas phase atmosphere under pulverized coal combustion; using sulfur dioxide gas generated after reduction and decomposition to produce the sulfuric acid after dust removal and purification; making the materials after reduction and decomposition enter an oxidation calcining kiln for sintering a cement clinker, and controlling to heat, mineralize and sinter the cement clinker in the gas phase atmosphere under the pulverized coal combustion.

Aspects of the invention include a method of producing a cement material comprising step of: first reacting a calcium-bearing starting material with a first acid to produce an aqueous first calcium salt; second reacting the aqueous first calcium salt with a second acid to produce a solid second calcium salt; wherein the second acid is different from the first acid and the second calcium salt is different from the first calcium salt; and thermally treating the second calcium salt to produce a first cement material. Preferably, but not necessarily, during the second reacting step, reaction between the first calcium salt and the second acid regenerates the first acid.

Aspects of the invention include a method of producing a cement material comprising step of: first reacting a calcium-bearing starting material with a first acid to produce an aqueous first calcium salt; second reacting the aqueous first calcium salt with a second acid to produce a solid second calcium salt; wherein the second acid is different from the first acid and the second calcium salt is different from the first calcium salt; and thermally treating the second calcium salt to produce a first cement material. Preferably, but not necessarily, during the second reacting step, reaction between the first calcium salt and the second acid regenerates the first acid.

Cement compositions including ordinary Portland cement, a secondary cementitious material (SCM) including one or more of pozzolan, metakaolin, limestone, or gypsum in an amount of up to approximately 70% of a replacement level of ordinary Portland cement, and between approximately 0.05% by weight of cement (bwoc) and 2% bwoc of aggregates of mesoporous carbon nanoparticles (3DG) carbons. The cement compositions regulate nucleation and time-lapsed growth of calcium silica hydrates during initial hydration. The 3DG carbons include aggregates of mesoporous carbon nanoparticles, which include one or more interconnected bundles of electrically conductive graphene layers. The 3DG carbons include oxygen containing functional groups disposed on one or more of the surfaces of the 3DG carbons or within the 3DG carbons.

Cement compositions including ordinary Portland cement, a secondary cementitious material (SCM) including one or more of pozzolan, metakaolin, limestone, or gypsum in an amount of up to approximately 70% of a replacement level of ordinary Portland cement, and between approximately 0.05% by weight of cement (bwoc) and 2% bwoc of aggregates of mesoporous carbon nanoparticles (3DG) carbons. The cement compositions regulate nucleation and time-lapsed growth of calcium silica hydrates during initial hydration. The 3DG carbons include aggregates of mesoporous carbon nanoparticles, which include one or more interconnected bundles of electrically conductive graphene layers. The 3DG carbons include oxygen containing functional groups disposed on one or more of the surfaces of the 3DG carbons or within the 3DG carbons.