Production of sulfuric acid from the scrubbing solution obtained in the desulfurization of coke-oven gas

A process for the production of sulfur dioxide from a scrubbing solution obtained by desulfurization of coke-oven gas with ammonia, said scrubbing solution comprising ammonium thiocyanate, ammonium thiosulfate, sulfur, free ammonia and ammonium salts of weak acids having a dissociation constant at room temperature of less than about 1 - 5 .times. 10.sup.-.sup.2, which comprises:

• a. admixing said scrubbing solution with an amount of sulfuric acid sufficient to react with both said free ammonia and said ammonium salts of said weak acids to form ammonium sulfate under conditions such that said ammonium thiocyanate and ammonium thiosulfate remain in solution;
• b. concentrating the resultant scrubbing solution to a water content of about 40-78% by weight under conditions to substantially prevent undesired oxidation of ammonium thiocyanate according to the equation NH.sub.4 SCN + O.sub.2 .fwdarw. HCN + SO.sub.2 + NH.sub.3 and the subsequent entrance of HCN into the gaseous phase;
• and
• c. combusting the thus-concentrated solution to form sulfur dioxide according to the following reactions:
• NH.sub.4 SCN + 3 O.sub.2 = N.sub.2 + 2 H.sub.2 O + CO.sub.2 + SO.sub.2
• (nh.sub.4).sub.2 s.sub.2 o.sub.3 + 2.5 o.sub.2 = n.sub.2 + 4 h.sub.2 o + 2 so.sub.2
• (nh.sub.4).sub.2 so.sub.4 + o.sub.2 = n.sub.2 + 4 h.sub.2 o = so.sub.2
• s + o.sub.2 = so.sub.2.