Abstract: A process for treating a hydrogen sulfide-containing gas in a closed loop system wherein said gas is passed through and absorbed by an alkaline aqueous absorbent containing an alkali carbonate and an oxidation catalyst. The solution containing the dissolved hydrogen sulfide is oxidized with an oxygen-containing gas to convert the absorbed hydrogen sulfide into elementary sulfur and sulfur salt compounds. After separation of the elementary sulfur from the solution, the solution is re-circulated for use as alkaline absorbent. A part of the re-circulated solution is diverted and subjected to mixed-combustion with an auxiliary fuel in a combustion furnace at an air ratio lower than 0.9 and at a temperature of 700.degree.C to 1100.degree.C to thermally decompose the sulfur compounds into hydrogen sulfide and an alkali carbonate.