摘要 |
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)2CO3! and allowing calcium carbonate to precipitate from the resultant mixture containing nitrate ¢NH4NO3! in the mother liquor, the process being characterised in that: (i) the calcium nitrate ¢Ca(NO3)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 ¢CO2! in water, the ammonia gas preferably being derived from the step in (i) above in which the Ca(NO3)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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