;The reaction of HCl gas with hydrogrossular [Ca3Al2(SiO4)(0.8)(OH)(8.8)] was performed using a fixed-bed flow-type reactor above 400 degreesC. It was found that, upon heating, the hydrogrossular was dehydrated to mayenite phases [Ca12Al10Si4O32(OH)(6) and Ca12Al10Si4O35], which reacted with the HCl gas in the temperature range of 400-950 degreesC to finally produce wadalite (Ca12Al10Si4O32Cl6) and CaCl2. Thus, HCl gas could be efficiently removed from effluent gases above 400 degreesC. The amount of chlorine fixed per gram of wadalite and CaCl2 was 0.22 g. An apparent activation energy of 24.2 kJ/mol was obtained for the reaction between HCl and hydrogrossular, which was consistent with the values found in the literature for the reaction between HCl and CaO, i.e., 20.9, 22.8, or 28.1 kJ/mol.