Patent ID: 6036933
Filing Date: 2000-03-14
Classification: C01F,C01P

Abstract:
A method for producing precipitated calcium carbonate comprising the following steps:(i) preparing an aqueous solution of calcium nitrate and ammonium hydroxide by slaking lime in water, in the presence of an aqueous ammonium nitrate solution;(ii) rendering the solution of calcium nitrate and ammonium hydroxide solids-free;(iii) heating the solids-free solution of calcium nitrate and ammonium hydroxide to dissociate the ammonium hydroxide and to drive ammonia gas from the solution, thereby producing an aqueous solution of calcium nitrate;(iv) preparing an ammonium carbonate solution by absorbing ammonia gas and carbon dioxide gas in water;(v) mixing the aqueous solution of calcium nitrate produced in step (iii) with the aqueous solution of ammonium carbonate produced in step (iv);(vi) allowing calcium carbonate to precipitate from the mixture produced by the mixing of calcium nitrate with ammonium carbonate, as described in step (v), and thereby separating it from a resulting ammonium nitrate-rich mother liquor; and(vii) recycling the ammonium nitrate-rich mother liquor to step (i).