Manufacture of calcium nitrite solutions with low nitrate content

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.

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