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Abstract

A method of producing relatively pure calcium carbonate from a relatively impure source of calcium oxide, characterized in that the method comprises the steps of slaking the calcium oxide source in water to produce an aqueous hydrated lime slurry; treating the slurry by the addition thereto of a water soluble source of anions which anions are capable of forming a salt with calcium ions which salt has a dissociation constant greater than the dissociation constant of calcium hydroxide; separating the solid content of the slurry from the liquid fraction content thereof to obtain a substantially solids-free solution of calcium ions and anions; intimately contacting the solids-free liquid fraction with carbon dioxide gas at a selected rate to maintain the temperature of the solution within a specific range and to lower the pH of the solution to a pre-set value conducive for the formation of a precipitate of calcium carbonate in which one of the crystalline forms, selected from the group consisting of calcite, vaterite and aragonite, predominates; and separating the precipitated calcium carbonate from the mother liquor.

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First Claim