GB515429A - Improved treatment of waste acids containing nitric acid - Google Patents

Abstract

515,429. Nitric and sulphuric acids. PAULING, H. May 31, 1938, No. 16257. Drawings to Specification. [Class 1 (ii)] In treating waste acids containing nitric acid and organic matter with steam in countercurrent, only that quantity of steam is employed which is necessary for heating the acid to the point of decomposition of the organic constituents and for expelling the nitrous gases, the nitric acid being left in the waste acid. Further nitric-acid may be added to the waste acid, if necessary for the complete decomposition of the organic constituents. The mixed acid thus freed from organic constituents and nitrous gases and consisting for example of nitric acid; sulphuric acid and water 'may be treated if desired under partial vacuum in a second stage with steam in counter-current in order to distill off and condense the nitric acid. Alternatively, the purified mixed acid, before the expulsion of the nitric acid, may'be subjected to evaporation and the vapour subjected to a rectifying concentration to recover a mixed acid containing say 65 per cent. of nitric acid and 10-12 per cent. sulphuric acid. By treating this acid with steam, 99 per cent. nitric acid may be recovered. If the concentration of nitric acid in the purified mixed acid is not sufficiently high to produce a concentrated nitric acid vapour on treatment with steam, the dilute nitric acid vapour evolved may be rectified in a separate countercurrent apparatus. This is effected by admitting to the counter-current apparatus into which the nitric acid and water vapour mixture enters at the bottom, a return of water from a condenser connected in sequence to the countercurrent device, the quantity of water corresponding to the quantity of concentrated nitric acid condensed in the counter-current device. The surplus water separated in the condenser is preferably employed in the absorption of the nitrogen oxides from the first stage.