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Abstract

A method for producing precipitated calcium carbonate by reacting an aqueous solution of calcium nitrate [Ca(NO.sub.3).sub.2 ] with an aqueous solution of ammonium carbonate [(NH.sub.4).sub.2 CO.sub.3 ] and allowing calcium carbonate to precipitate from the resultant mixture containing nitrate [NH.sub.4 NO.sub.3 ] in the mother liquor, the process being characterized in that: (i) the calcium nitrate [Ca(NO.sub.3).sub.2)] solution utilized in the processes is prepared by slaking lime [CaO] in water in the presence of ammonium nitrate [NH.sub.4 NO.sub.3 ] to form calcium nitrate [Ca(NO.sub.3).sub.2 ] and ammonium hydroxide [NH.sub.4 OH] in solution, filtering the solution to render it solids free, and heating the filtrate to dissociate the ammonium hydroxide [NH.sub.4 OH] and to drive ammonia gas [NH.sub.3 ] from the solution; (ii) the ammonium carbonate (NH.sub.4).sub.2 CO.sub.3 solution utilized is prepared by absorbing ammonia gas [NH.sub.3 ] and carbon dioxide gas [CO.sub.2 ] in water, the ammonia gas preferably being derived from the step in (i) above in which the Ca(NO.sub.3).sub.2 solution is heated; and (iii) the ammonium nitrate used is derived from the precipitation phase during which calcium carbonate is precipitated from the mother liquor containing ammonium nitrate.

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