Abstract: Calcium nitrate with low nitrate content is prepared by reacting in a series of absorption reactors lime slurry and nitrogen oxide gases. The lime slurry flows serially through the series of absorption reactors with a major portion being recycled to the inlet of a Venturi absorber in each reactor. Nitrogen oxide gases flow cocurrently with the slurry from each reactor to the following Venturi inlet and are contacted by recycle slurry in each Venturi with a molar ratio of calcium hydroxide to nitrogen oxides of at least about 20. Slurry from the last reactor with a calcium nitrite content of below about 22 weight percent and a calcium hydroxide content of at least about 2 weight percent may be freed of unreacted calcium hydroxide, for example by treatment with NO.sub.x gases, and then concentrated to the desired product concentration. The exit gases may be scrubbed with incoming lime slurry after passing through a holdup vessel which increases the ratio of NO.sub.2 to NO.

Abstract: A process for the production of high purity calcium thiosulfate by a metathesis reaction of ammonium thiosulfate and calcium hydroxide or calcium oxide is disclosed. Aqueous solutions of high purity calcium thiosulfate, in concentrations up to about 30% by weight, are prepared by removing substantially all of the co-product ammonia under conditions which minimize the decomposition of the thiosulfate ion. Heating the reaction mixture to a temperature of about the boiling point at atmospheric pressure is used to prepare aqueous solution of about 10% by weight calcium thiosulfate, and lower reaction temperatures are employed to prepare more concentrated aqueous solutions of calcium thiosulfate up to about 30% by weight, which is the saturation point.