Method of treating calcium nitrate contained in denitration waste liquid

摘要

The present invention provides a method of converting NO3- ions which are contained in denitration waste liquids to nonpoisonous N2 gas or to valuable by-products. In the method of the invention, concentrated sulfuric acid is added to the waste liquid which results from denitration of exhaust gases which contains calcium nitrate and calcium chloride to obtain a mixed solution of nitric acid, hydrochloric acid, sulfuric acid and calcium sulfate. The ratio of the chloride ions to nitrate ions in the mixed solution is adjusted within the range of Cl-/NO3- = 2-3; the mixed solution is heated to 110 DEG to 150 DEG C after adjusting the concentration of sulfuric acid in the solution to 10 to 70% by weight to thereby convert the mixed solution to a mixed gas essentially including NOCl, Cl2 and nitrogen oxides. The mixed gas is then passed through concentrated sulfuric acid having a concentration higher than 80% which is maintained at a temperature of 80 DEG to 150 DEG C to obtain a nitrosylsulfuric acid solution. A mixed gas containing SO2 and H2O is passed into the thusly formed nitrosylsulfuric acid solution to obtain a mixed gas containing NO, NO2 and SO2 which is then introduced into a reducing solution to convert the nitrogen oxides to N2 gas.