PRODUCTION OF CHLORINE DIOXIDE

A mixture containing chlorine dioxide, chlorine and alkali metal salt is continuously generated; in the process an alkali metal chlorate, an alkali metal chloride and a strong mineral acid comprising sulfuric acid are continuously reacted in a single vessel generator-evaporator-crystallizer in proportions to generated chlorine dioxide and chlorine, in the absence of a catalyst; the acidity of the reaction solution is maintained within the range of from above 4 to about 11; and the reaction solution is subjected to a vacuum to effect evaporation of water vapor; chlorine dioxide and chlorine are withdrawn in admixture with the water vapor and alkali metal salt of the mineral acid is crystallized within the generator-evaporator-crystallizer and continuously withdrawn therefrom; in the improvement of the invention alkali metal salt crystals produced in the generator-evaporator-crystallizer are continuously passed in the form of a slurry into the top of a separatory column, in a downward flow while countercurrently a stream of hot water is passed continuously upwardly through the column at a rate sufficient to effect washing of the downwardly flowing crystals, whereby chlorate, chloride and acid values recovered therefrom are continuously and substantially completely returned to the generator-evaporator-separator, and acid salt crystals are converted to neutral acid salt crystals; the substantially pure neutral alkali metal salt crystal slurry is removed from the bottom of the separatory column; the process has particular utility in treating sulfurcontaining effluent emanating from chlorine dioxide generators.