A process for converting gypsum into precipitated calcium carbonate including reacting a mixture comprising gypsum and a seed, a mineral acid, or both with at least one carbonate source, whereby precipitated calcium carbonate is produced in the form of calcite and/or aragonite directly without conversion from a vaterite polymorph. Also, a process for converting gypsum into precipitated calcium carbonate including providing a mixture comprising i) gypsum ii) a seed, a mineral acid, or both iii) at least one additive selected from the group consisting of ammonium sulfate, an organic acid, or an iron material, and reacting the mixture with at least one carbonate source to produce precipitated calcium carbonate in the form of vaterite.

The present invention relates to a process for producing an aqueous suspension of precipitated calcium carbonate, an aqueous suspension of precipitated calcium carbonate and a precipitated calcium carbonate obtained by the process, a process comprising the precipitated calcium carbonate and its use.

Provided herein are methods and systems to form calcium carbonate comprising vaterite, comprising dissolving lime in an aqueous base solution under one or more precipitation conditions to produce a precipitation material comprising calcium carbonate and a supernatant solution, wherein the calcium carbonate comprises vaterite.

Techniques for growing crystalline calcium carbonate solids such that the crystalline calcium carbonate solids include a volume of 0.0005 mm.sup.3 to 5 mm.sup.3, include a slaker to react quicklime (CaO) and a low carbonate content fluid to yield a slurry of primarily slaked lime (Ca(OH).sub.2); a fluidized-bed reactive crystallizer that encloses a solid bed mass and includes an input for a slurry of primarily slaked lime, an input for an alkaline solution and carbonate, and an output for crystalline calcium carbonate solids that include particles and an alkaline carbonate solution; a dewatering apparatus that includes an input coupled to the crystallizer and an output to discharge a plurality of separate streams that each include a portion of the crystalline calcium carbonate solids and alkaline carbonate solution; and a seed transfer apparatus to deliver seed material into the crystallizer to maintain a consistent mass of seed material.

A recycling and waste management process receives municipal solid waste (MSW) with substantial organic content to form a self-sustaining Hydrothermal Mineralization (HTM) process based on Supercritical Water Oxidation (SCWO) to receive supercritical steam and carbon dioxide with potential for electrical generation before forming calcium carbonate suitable for concrete production. Hydrothermal mineralization (HTM) provides a rapid elimination of organic wastes while simultaneously producing a non-emissive and thermally stable cement additive to act as a carbon sink. Hydrothermal mineralization (HTM) provides a rapid disposal pathway for organic wastes, a green source of electricity and a final product that can be coupled with traditional and alternative cement productions to reduce carbon footprints of cement production.

Methods of precipitating carbon dioxide stripped from natural gas or a post-combustion source are disclosed herein. The methods include provision of an aqueous spent caustic solution comprising carbon dioxide and adding a source of calcium ions to precipitate calcium carbonate and form a brine solution. The source of calcium ions is primarily calcium chloride and has calcium hydroxide as less than 1% wt/wt of the source of calcium ions. The method can include collecting the calcium carbonate precipitate, washing the calcium carbonate precipitate, and drying the calcium carbonate precipitate.

Particles of a carbonate compound, such as calcium carbonate, in an amorphous form may be precipitated from solution, freeze dried and compressed to form transparent or translucent objects. The objects may, for example comprise blocks, bricks or other shapes that may be used in construction of buildings. Advantageously the carbonate compound may incorporate carbonate ions obtained by capture of carbon dioxide from an atmosphere of air, flue gas, exhaust gas or the like. Captured carbon may be sequestered in the objects indefinitely.

Organic-inorganic composite particles that can be dispersed in a solvent and/or a resin as primary particles having an organic group on the surface of inorganic particles, the organic-inorganic composite particles having negative birefringence.

Techniques for growing crystalline calcium carbonate solids such that the crystalline calcium carbonate solids include a volume of 0.0005 mm.sup.3 to 5 mm.sup.3, include a slaker to react quicklime (CaO) and a low carbonate content fluid to yield a slurry of primarily slaked lime (Ca(OH).sub.2); a fluidized-bed reactive crystallizer that encloses a solid bed mass and includes an input for a slurry of primarily slaked lime, an input for an alkaline solution and carbonate, and an output for crystalline calcium carbonate solids that include particles and an alkaline carbonate solution; a dewatering apparatus that includes an input coupled to the crystallizer and an output to discharge a plurality of separate streams that each include a portion of the crystalline calcium carbonate solids and alkaline carbonate solution; and a seed transfer apparatus to deliver seed material into the crystallizer to maintain a consistent mass of seed material.

Provided is a method for preparing a stable amorphous calcium carbonate (ACC), which can be obtained either in suspension or as a powder. The method comprises stepwise combination of a soluble calcium salt, a soluble carbonate, a first and second stabilizer, and a water miscible organic solvent as described herein. The present invention further relates to stable ACC suspensions and dry powders produced by the method of the present invention.