PURPOSE: To obtain high purity sodium sulfate by mixing Cr-contg. salts into a V- contg. aq. sodium sulfate soln. recovered from an exhaust gas desulfurizer; acidifying the soln.; adding a reducing agent to it alkaline to remove chromium hydroxide- base precipitates formed; and concentrating the remaining soln.

CONSTITUTION: Chromium-contg. salts are mixed into a vanadium-contg. aq. sodium sulfate soln. in a Cr to V ratio of 1W30 by wt., and the soln. is adjusted to pH≤4 with mineral acid. After adding a reducing agent such as sodium sulfite or ferrous sulfate the soln. is adjusted to pH≥8 with caustic alkali to form a chromium hydoxide-base insol. substance, which is separation-removed. The remaining soln. is concentrated to obtain sodium sulfate crystals. Thus, high purity sodium sulfate is produced from the vanadium-contg. aq. sodium sulfate soln. recovered from an exhauat gas desulfurizer.