Iodine-sulfur (IS) thermo-chemical water-splitting process is a promising technology to produce hydrogen using solar or nuclear energy. To avoid the undesirable side reactions between HI and H2SO4 phases formed in Bunsen reaction of IS cycle, it is necessary to purify the two phases. The purification process could be achieved by reverse reaction of Bunsen reaction. In this paper, the purification process in continuous mode by reacting sulfuric acid and HI in a packed column was experimentally studied; the influences of operational parameters, including the reaction temperature, the flow rate of nitrogen gas, and the flow rate of the raw material solutions, on the purification efficiency, were investigated in detail. Based on the results, the suitable conditions for continuous purification process of two phases were proposed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.