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.

Abstract: A dry alkaline earth metal silicate or an alkali metal silicate is reacted with a concentrated mineral acid to form silico-formic acid and hydrogen salt. The acid and hydrogen salt is reacted with a dry alkali metal carbonate or hydroxide to produce monosilanal. Monosilanol is reacted with water to produce monosilandiol.

Abstract: A process for the production of chlorine dioxide and a sulfate salt comprising mixing an aqueous solution of a chlorate, sulfuric acid and sulfur dioxide, reacting said mixture under reduced pressure near the boiling point of said solution at a temperature of 50.degree. to about 95.degree. centigrade to generate chlorine dioxide, removing water from the chlorate solution as water vapor with the generated chlorine dioxide, feeding replenishing amounts of aqueous chlorate to said reaction mixture to increase the concentration of the cation of said chlorate so as to have it exceed the saturation point of the sulfate of said cation under said reaction conditions, crystallizing a sulfate salt of said cation from said reaction mixture and recovering said sulfate salt.

Abstract: Hydrogen sulfide-containing waste gases whose complete treatment is indispensable from the viewpoint of environmental pollution problem, are purified in two steps consisting of a first step in which the gases are absorbed in an aqueous solution of sodium hydroxide or/and sodium sulfide, and a second step in which sulfuric acid and sulfur dioxide gas are simultaneously introduced into the resulting solution after absorption to deposit sulfur. Further, for recovery of the resulting sulfur, a particular apparatus is provided.