A method for releasing impurities from a calcium-based mineral is described. The method comprises reacting a calcium-based mineral containing impurities with an aqueous solution of one or more ionic salts at a temperature of approximately 85 C. or above, wherein at least one of the calcium-based mineral and the one or more ionic salts comprises sulphate and at least one of the calcium-based mineral and the one or more ionic salts comprises ammonium, and wherein the concentration of the solution is approximately 25% or higher mass fraction, such that double salt crystals are formed and impurities are released. The method further comprises separating the double salt crystals from the impurities. Various products of the process are also described.

The present application pertains to methods for making metal oxides and/or citric acid. In one embodiment, the application pertains to a process for producing calcium oxide, magnesium oxide, or both from a material comprising calcium and magnesium. The process may include reacting a material comprising calcium carbonate and magnesium carbonate. Separating, concentrating, and calcining may lead to the production of oxides such as calcium oxide or magnesium oxide. In other embodiments the application pertains to methods for producing an alkaline-earth oxide and a carboxylic acid from an alkaline earth cation-carboxylic acid anion salt. Such processes may include, for example, reacting an alkaline-earth cation-carboxylic acid anion salt with aqueous sulfur dioxide to produce aqueous alkaline-earth-bisulfite and aqueous carboxylic acid solution. Other useful steps may include desorbing, separating, and/or calcining.

The present application pertains to processes producing oxides using a weak acid intermediate. In one embodiment a material comprising calcium carbonate is reacted with a solution comprising aqueous carboxylic acid to form a gas comprising carbon dioxide and a solution comprising aqueous calcium carboxylate. The solution comprising aqueous calcium carboxylate is reacted with sodium sulfate to form a solution comprising aqueous sodium carboxylate and a solid comprising calcium sulfate. The solution comprising aqueous sodium carboxylate is reacted with sulfur dioxide to form sodium sulfite and an aqueous carboxylic acid. The sodium sulfite is separated from said aqueous carboxylic acid and reacted to form a solid comprising calcium sulfite which is decomposed to form calcium oxide and sulfur dioxide.

The present application pertains to processes producing oxides using a weak acid intermediate. In one embodiment a material comprising calcium carbonate is reacted with a solution comprising aqueous carboxylic acid to form a gas comprising carbon dioxide and a solution comprising aqueous calcium carboxylate. The solution comprising aqueous calcium carboxylate is reacted with sodium sulfate to form a solution comprising aqueous sodium carboxylate and a solid comprising calcium sulfate. The solution comprising aqueous sodium carboxylate is reacted with sulfur dioxide to form sodium sulfite and an aqueous carboxylic acid. The sodium sulfite is separated from said aqueous carboxylic acid and reacted to form a solid comprising calcium sulfite which is decomposed to form calcium oxide and sulfur dioxide.

Systems and methods for the use of highly reactive hydrated lime (HRH) in circulating dry scrubbers (CDS) to remove sulfur dioxide (SO.sub.2) from the flue gas.

The present application pertains to processes producing oxides using a weak acid intermediate. In one embodiment a material comprising calcium carbonate is reacted with a solution comprising aqueous carboxylic acid to form a gas comprising carbon dioxide and a solution comprising aqueous calcium carboxylate. The solution comprising aqueous calcium carboxylate is reacted with sodium sulfate to form a solution comprising aqueous sodium carboxylate and a solid comprising calcium sulfate. The solution comprising aqueous sodium carboxylate is reacted with sulfur dioxide to form sodium sulfite and an aqueous carboxylic acid. The sodium sulfite is separated from said aqueous carboxylic acid and reacted to form a solid comprising calcium sulfite which is decomposed to form calcium oxide and sulfur dioxide.

Systems and methods for the use of highly reactive hydrated lime (HRH) in circulating dry scrubbers (CDS) to remove sulfur dioxide (SO.sub.2) from the flue gas.

There are provided processes for removing H.sub.2S from a gas. The processes comprise contacting the gas with an aqueous composition comprising at least one calcium compound, thereby obtaining CaS and a H.sub.2S lean treated gas stream, while maintaining the pH at about 9.5 to about 13.0; and contacting the CaS with an aqueous oxidant solution, converting the CaS into at least one of CaSO.sub.3 and CaSO.sub.4, while maintaining the pH at about 9.5 to about 13.0.

There are provided processes for removing H.sub.2S from a gas. The processes comprise contacting the gas with an aqueous composition comprising at least one calcium compound, thereby obtaining CaS and a H.sub.2S lean treated gas stream, while maintaining the pH at about 9.5 to about 13.0; and contacting the CaS with an aqueous oxidant solution, converting the CaS into at least one of CaSO.sub.3 and CaSO.sub.4, while maintaining the pH at about 9.5 to about 13.0.

There are provided processes for removing H.sub.2S from a gas. The processes comprise contacting the gas with an aqueous composition comprising at least one calcium compound, thereby obtaining CaS and a H.sub.2S lean treated gas stream, while maintaining the pH at about 9.5 to about 13.0; and contacting the CaS with an aqueous oxidant solution, converting the CaS into at least one of CaSO.sub.3 and CaSO.sub.4, while maintaining the pH at about 9.5 to about 13.0.