The causticizing reaction plays a crucial role in the chemical recovery cycle of the Kraft pulping process used by most of the paper industry. Kraft recovery operations include concentration of spent pulping liquor, burning to recover energy and chemicals, smelt formation, smelt dissolution, causticizing, white liquor clarification, calcium carbonate thickening, and mud washing. This proposal is part of the PI's work to improve the many aspects of the Kraft process in an attempt to make it more amenable to control. Improved process control should decrease capital and operating cost for the process and increase productivity. Causticizing converts an aqueous solution of sodium carbonate and sodium sulfide (green liquor) into caustic solution (white liquor) and lime mud (CaCO (s)). The product caustic solution is used in the digestion process to delignify wood and other vegetable matter. The objective of the proposed research is to obtain experimental data and estimate parameters required to verify a thermodynamic model of the causticizing reaction. The problem is to determine when equilibrium has been attained and to improve the approach to equilibrium. The causticizing efficiency is a maximum at equilibrium. Increases in productivity and decreased operating and captital costs would result if the causticizing efficiency can be improved. This proposal is aimed at defining an expression for the equilibrium conversion. The data will be directly applicable to processing wood and other vegetable matter into pulp by the Kraft and Soda processes. In addition, the data can be applied to chemical processes wherever causticizing reactions are used; for example, the production of caustic soda.