SO2 is removed from mineral acids, e.g., HCl, in an exchange column consisting of an absorption section with 5-10 plates, a cooling section, and a stripping section with 10-15 plates at the bottom. The choice of stripping gas is detd. by the subsequent treatment of the SO2. Thus, when a 50:50 gaseous mixt. of HCl and SO2 is fed into the absorption section (70-85 Deg) at 120 L/h with air (stripping gas) fed at 40 L/h into the stripping section (15 Deg) and water at a rate to give a 30 or 20% concn. of HCl, the purified acid contains SO2 <2 and SO42- <1 ppm for both concns. The waste gas contains <1 ppm HCl. [on SciFinder (R)]