PROCESS TO PRODUCE HYDROGEN AND/OR HEMIHYDRATE CALCIUM SULPHATE FROM CALCIUM SULPHITE

摘要

2082957 9118131 PCTABS00008 A process for producing hydrogen and/or sulphur dioxide simultaneously with the production of calcium sulphate, either as calcium sulphate dihydrate or calcium sulphate hemihydrate from waste products containing calcium sulphite and other calcium salts. The waste solid containing calcium sulphite and other calcium salts is treated by the addition of aqueous sulphur dioxide solution or sulphuric acid solution to produce a liquid phase product. The liquid phase product may be separated from any remaining solid phase material and then subjected to the addition of sulphuric acid in the second step, wherein either calcium sulphate dihydrate salt or calcium sulphate hemihydrate is produced. The addition of sulphuric acid to the liquid phase results in the evolution of sulphur dioxide which may be used as such or in sulphur dioxide electrolysis cells in order to produce hydrogen and sulphuric acid. An especially unique feature of the process is that the sulphuric acid produced in generating hydrogen can be recycled to the step where the calcium sulphate crystals are produced.