Abstract: Soluble thiosulphates present in aqueous redox systems comprising at least one salt of an anthraquinone di-sulphonic acid and at least one water soluble compound of metal having at least two stable oxidation states, for example a vanadate, are converted to sulphates by introducing oleum or sulphuric acid into the lower half of a vessel containing said thiosulphate containing redox solution, wherein the sulphuric acid has a concentration of from 10-98% w/w H.sub.2 SO.sub.4 and the amount of said sulphuric acid is such that the gram molecular weight ratio of sulphuric acid to thiosulphate is from 1:2 to 1:3, and thereafter separating the sulphate formed for example by using a solubility lowering technique. The process is carried out at ambient temperature and at a temperature of from 70.degree. C. up to the boiling temperature of the acidic mixture.

Abstract: Thiosulphate ions present in gas purification liquors, particularly those employed for removing H.sub.2 S by washing with aqueous alkaline solutions of vanadium compounds and anthraquinone disulphonic acids, are decomposed to sulphide and hydroxyl ions by exposing the liquor to a hydrogen rich gas at elevated temperature e.g., 650.degree. C. The liquor may be evaporated and the solid residue subjected to decomposition. Any thiocyanate ions are hydrolyzed; it being necessary to mix steam with the hydrogen rich gas if a solid residue is being decomposed.