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 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.

The present invention relates to a process for decomposing calcium sulfate (CaSO.sub.4) present in phosphogypsum (PG), comprising the following steps: a) providing a reactor containing phosphogypsum (PG) and a solid source of carbon (C), b) reacting a flow of dioxygen (Oz) with the source of carbon (C) so as to generate carbon oxide (CO), c) reacting carbon oxide (CO) obtained in step a) with calcium sulfate (CaSO.sub.4) of the phosphogypsum to produce calcium oxide (CaO) and sulfoxide (SO.sub.2) according to the following reaction: CaSO.sub.4+CO.fwdarw.CaO+SO.sub.2+CO.sub.2 wherein the mass ratio C/PG is between 0.2 and DA, and the mass ratio 15 O.sub.2/PG is between 0.5 and 1.5.

The present invention relates to a process for decomposing calcium sulfate (CaSO.sub.4) present in phosphogypsum (PG), comprising the following steps: a) providing a reactor containing phosphogypsum (PG) and a solid source of carbon (C), b) reacting a flow of dioxygen (Oz) with the source of carbon (C) so as to generate carbon oxide (CO), c) reacting carbon oxide (CO) obtained in step a) with calcium sulfate (CaSO.sub.4) of the phosphogypsum to produce calcium oxide (CaO) and sulfoxide (SO.sub.2) according to the following reaction: CaSO.sub.4+CO.fwdarw.CaO+SO.sub.2+CO.sub.2 wherein the mass ratio C/PG is between 0.2 and DA, and the mass ratio 15 O.sub.2/PG is between 0.5 and 1.5.

The present invention relates to a process for decomposing calcium sulfate (CaSO.sub.4) present in phosphogypsum (PG), comprising the following steps: a) providing a reactor containing phosphogypsum (PG) and a solid source of carbon (C), b) reacting a flow of dioxygen (Oz) with the source of carbon (C) so as to generate carbon oxide (CO), c) reacting carbon oxide (CO) obtained in step a) with calcium sulfate (CaSO.sub.4) of the phosphogypsum to produce calcium oxide (CaO) and sulfoxide (SO.sub.2) according to the following reaction: CaSO.sub.4+CO.fwdarw.CaO+SO.sub.2+CO.sub.2 wherein the mass ratio C/PG is between 0.2 and DA, and the mass ratio 15 O.sub.2/PG is between 0.5 and 1.5.

The present invention relates to a process for decomposing calcium sulfate (CaSO.sub.4) present in phosphogypsum (PG), comprising the following steps: a) providing a reactor containing phosphogypsum (PG) and a solid source of carbon (C), b) reacting a flow of dioxygen (Oz) with the source of carbon (C) so as to generate carbon oxide (CO), c) reacting carbon oxide (CO) obtained in step a) with calcium sulfate (CaSO.sub.4) of the phosphogypsum to produce calcium oxide (CaO) and sulfoxide (SO.sub.2) according to the following reaction: CaSO.sub.4+CO.fwdarw.CaO+SO.sub.2+CO.sub.2 wherein the mass ratio C/PG is between 0.2 and DA, and the mass ratio 15 O.sub.2/PG is between 0.5 and 1.5.

The present invention discloses a resource recovery method and a resource recovery system of desulfurized ash. The resource recovery method comprises: washing desulfurized ash with water, and performing solid-liquid separation to obtain solid residues rich in calcium sulfite and calcium sulfate and a solution rich in calcium hydroxide; preparing the solution into desulfurized slurry; and roasting the solid residues under the action of a reducing agent to obtain flue gas rich in sulfur dioxide and residues rich in calcium oxide. Therefore, the recovery of sulfur and calcium in the desulfurized ash is realized, and no solid waste, liquid waste, gas waste, etc. are produced in the process.

The present invention discloses a resource recovery method and a resource recovery system of desulfurized ash. The resource recovery method comprises: washing desulfurized ash with water, and performing solid-liquid separation to obtain solid residues rich in calcium sulfite and calcium sulfate and a solution rich in calcium hydroxide; preparing the solution into desulfurized slurry; and roasting the solid residues under the action of a reducing agent to obtain flue gas rich in sulfur dioxide and residues rich in calcium oxide. Therefore, the recovery of sulfur and calcium in the desulfurized ash is realized, and no solid waste, liquid waste, gas waste, etc. are produced in the process.

A method of producing a metal carbonate from an ultramafic rock material is provided. The method includes providing an ultramafic rock material comprising a metal silicate; reacting the ultramafic rock material with an acid to form a mixture comprising a salt of the metal; contacting the mixture comprising a salt of the metal with oxygen so as to aerate impurities in the mixture and/or to remove residual acid from the mixture; heating the resultant mixture to decompose the salt of the metal to form metal oxide; and reacting the metal oxide with aqueous ammonium carbonate to obtain the metal carbonate. A system for producing a metal carbonate from ultramafic rock material is also provided.