Process for the thermochemical production of hydrogen. [sulfur-iodine cycle]

Hydrogen is thermochemically produced from water in a cycle wherein a first reaction produces hydrogen iodide and H/sub 2/SO/sub 4/ by the reaction of iodine, sulfur dioxide and water under conditions which cause two distinct aqueous phases to be formed, i.e., a lighter sulfuric acid-bearing phase and a heavier hydrogen iodide-bearing phase. After separation of the two phases, the heavier phase containing most of the hydrogen iodide is treated, e.g., at a high temperature, to decompose the hydrogen iodide and recover hydrogen and iodine. The H/sub 2/SO/sub 4/ is pyrolyzed to recover sulfur dioxide and produce oxygen.