Calcium carbonate precipitation method

A method for producing precipitated calcium carbonate by reacting an aqueous solution of calcium nitrate [ca(no3)2]with an aqueous solution of ammonium carbonate [(nh4)2c03]and allowing calcium carbonate to precipitate fron the resultant mixture containing nitrate [nh4no3]in the mother liquor, the process being characterised in that: (i)the calcium nitrate [ca(n03)2)] solution utilised in the processes is prepared by slaking lime [cao]in water in the presence of ammonium nitrate [nh4no3]to form calcium nitrate [ca(no3)2]and ammonium hydroxide [nh4oh]in solution, filtering the solution to render it solids free, and heating the filtrate to dissociate the ammonium hydroxide [nh4oh]and to drive ammonia gas [nh3]from the solution; (ii)the ammonium carbonate (nh4)2co3 solution utilised is prepared by absorbing ammonia gas [nh3]and carbon dioxide gas [c02]in water, the ammonia gas preferably being derived from the step in (i)above in which the ca(n03)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.