An object of the present invention is to provide a technique for obtaining a calcium carbonate particle group having a high ratio of cubic calcium carbonate particles. The present invention provides a calcium carbonate particle group including: 70.0% or more of cubic calcium carbonate particles relative to the number of particles in the entire calcium carbonate particle group. A length of each piece of the cubic calcium carbonate particles is 0.5 m or more and 15.0 m or less and difference in the length of the pieces of the same cubic calcium carbonate particles is 0.5 m or less. The calcium carbonate particle group includes 90.0% or more of light calcium carbonate particles relative to the number of particles in the entire calcium carbonate particle group.

The present invention provides a production method of calcium carbonate whereby carbon dioxide is fixed as calcium carbonate by a safe and simple method. The production method of calcium carbonate disclosed herein includes the following steps. Step (S1) of preparing a slurry including calcium hydroxide, and step (S2) of precipitating calcium carbonate by generating fine bubbles including carbon dioxide from a fine bubble generator that is provided with a porous section having micropores, and supplying the carbon dioxide into the slurry including the calcium hydroxide in a container configured to prevent carbon dioxide from being released into the atmosphere. Here, the fine bubble generator supplies carbon dioxide so that a flow rate of carbon dioxide is 40 to 2500 ml/min per 1 mol of the calcium hydroxide.

The present invention relates to the use of a depolymerized carboxylated cellulose solution for preparing an aqueous Precipitated Calcium Carbonate (PCC) slurry by slaking a material containing calcium oxide in water, followed by carbonation of the milk of lime thus obtained. The depolymerized carboxylated cellulose solution has a solid content of 25 wt. % to 40 wt. %, based on the total weight of the solution and a molecular weight of between 10 000 g/mol to 40 000 g/mol.

The present invention provides a process for preparing a precipitated calcium carbonate product. The process comprises the steps of preparing slaking quick lime to obtain slaked lime; and subjecting the slaked lime, without agitation, without prior cooling in a heat exchanger, and in the absence of any additives, to carbonation with carbon dioxide gas to produce PCC. The newly prepared product develops better performance thanks to improved resistance during processing.

Techniques for converting a portion of a carbonate to hydroxide include receiving an alkaline carbonate solution that includes between 0.1M (moles per liter of solution) to 4.0M hydroxide and between 0.1M to 4.1M carbonate; reacting, in a slaking process, quicklime (CaO) and a low carbonate content fluid to yield a slurry of primarily slaked lime (Ca(OH).sub.2); and reacting the Ca(OH).sub.2 slurry and the alkaline carbonate solution to grow calcium carbonate (CaCO.sub.3) crystal aggregates of 0.0005 mm.sup.3 to 5 mm.sup.3 in volume in a fluidized-bed reactive crystallizer.

The invention provides a method of producing a filler comprising calcium carbonate (PCC), preferably to be used in paper or paper board production or in fibre based composites. The method of the invention comprises the steps of; providing fly ash generated in paper or paper board production; fractionating said fly ash in at least one step, whereby a coarser fraction is separated from a finer fraction; forming a suspension of said coarser fraction; adding carbon dioxide to said suspension to form precipitated calcium carbonate. The method of the invention avoids problems with high amounts of arsenic and heavy metals in the production of filler comprising PCC, when using ash generated in paper or paper board production as a raw material. It has been shown that harmful elements, such as arsenic and heavy metals, are primarily accumulated in the finer fractions of the fly ash. Thus, by using the coarser fraction in the step of carbonation, the amount of arsenic and heavy metals in the final product is reduced.

The present invention relates to a process for the production of a precipitated divalent metal ion carbonate product from a divalent metal ion carbonate which was recovered from waste, the precipitated divalent metal ion carbonate product having an improved brightness, the process comprising the steps of: providing a low-purity divalent metal ion carbonate material, the divalent metal ion carbonate material being recovered from waste; calcining the divalent metal ion carbonate material in order to obtain a divalent metal ion oxide; slaking the divalent metal ion oxide in order to obtain an aqueous suspension of a divalent metal ion hydroxide; carbonating the aqueous suspension of the divalent metal ion hydroxide with a carbon dioxide containing compound in order to obtain fine precipitated divalent metal ion carbonate particles; post-treating the fine precipitated divalent metal ion carbonate particles to obtain fine discrete precipitated divalent metal ion carbonate particles; adding the fine discrete precipitated divalent metal ion carbonate particles to an aqueous suspension of divalent metal ion hydroxide that was obtained by slaking high-purity divalent metal ion hydroxide in order to obtain a resulting reaction mixture; and carbonating the resulting reaction mixture in order to obtain the precipitated divalent metal ion carbonate product having an improved brightness.

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.

Aspects of the invention include methods of removing carbon dioxide (CO.sub.2) from a CO.sub.2 containing gas. In some instances, the methods include contacting CO.sub.2 containing gas with a bicarbonate buffered aqueous medium under conditions sufficient to produce a bicarbonate rich product. Where desired, the resultant bicarbonate rich product or a component thereof may then be stored or further processed, e.g., combined with a divalent alkaline earth metal cation, under conditions sufficient to produce a solid carbonate composition. Aspects of the invention further include systems for practicing the methods, as well as products produced by the methods.

The present invention concerns a process for producing calcium carbonate from a calcium-containing alkaline slag material, the process containing the steps of extracting the alkaline slag material in a series of extraction steps, including at least 2 extraction steps, using extraction solvent(s) containing salt in an aqueous solution, whereby a calcium-containing filtrate and a residual slag is formed in each extraction step, separating the residual slag from the filtrate after each extraction step, carrying each residual slag to the following extraction in the series of extractions, to be used as raw material in said following extraction, and discarding the residual slag separated from the last extraction, carrying each filtrate to the previous extraction in the series of extractions, to be used as extraction solvent in said previous extraction, and carrying the first filtrate, separated from the first extraction step, to a carbonating step, carbonating calcium as calcium carbonate from the first filtrate, the first filtrate also used as the carbonation solvent, and using a carbonation gas, whereby calcium carbonate precipitates, separating and recovering the calcium carbonate from the remaining carbonation solvent, and recycling the remaining carbonation solvent to the last extraction step in the series of extraction steps, to be used as extraction solvent.