PURPOSE: In the preparation of calcium nitrite by blowing an NO-NO2 mixed gas into slurry of calcium hydroxide, to obtain the titled aqueous solution having a high concentration in high selectivity, by regulating the blowing speed depending upon reaction stages.
CONSTITUTION: An NO-NO2 mixed gas having 1.5W20 NO/NO2 molar ratio and 1W14vol% NO2 concentration is blown into slurry of calcium hydroxide having 30W50wt% concentration and 10W75°C solution temperature, the reaction and adsorption are carried out, to prepare an aqueous solution of calcium nitrite (concentration; 40W60wt%). In the method, the blowing speed of the mixed gas is (i) 10W2,000mole (NO2)/hr.m3 (slurry) at the early stage of the reaction, (ii) 10W 800mole (NO2)/hr.m3 (slurry) after the formation of basic calcium nitrite, and (iii) the blowing of the mixed gas is stopped in a state of ≥8pH during the decomposition period of basic calcium nitrite, and it is filtered.
IKEDA OSAMU
ISHITSUKASA EIJI
