A thermodynamic and experimental investigation to develop a new process for converting sulfur dioxide to elemental sulfur by a two-step process involving barium sulfide and barium sulfate has been carried out. In this process, the starting raw material barium sulfate is reduced by a suitable reducing agent to produce barium sulfide, which is used to reduce sulfur dioxide to elemental sulfur vapor and regenerate barium sulfate. The results indicate that the BaS-SO2 reaction produces mainly sulfur vapor and solid barium sulfate and that the products from the BaSO4-H-2 reaction are mainly water vapor and barium sulfide. In this Part 1, results on the kinetics of the BaS-SO2 reaction are presented. The experiments were carried out at temperatures between 850 and 1000 degrees C and sulfur dioxide partial pressures between 4 and 43 kPa by the use of a thermogravimetric analysis technique. The rate of this reaction was demonstrated by the conversion of 40% freshly produced barium sulfide in 10 min at 1000 degrees C under a sulfur dioxide partial pressure of 8.7 kPa. The reactivity increased somewhat during the first three cycles, but remained largely unchanged thereafter. This characteristic is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants. A pore-blocking model was found to fit the reaction rate. The reaction was essentially independent of sulfur dioxide partial pressure between 4.3 and 43 kPa and has an activation energy value of 170 kJ/mol (40.8 kcal/mol). The reduction kinetics of barium sulfate with hydrogen gas is reported in Part II. (c) 2006 Elsevier Ltd. All rights reserved.