Hydrous carbonate sequestration of carbon dioxide using steelmaking slag was studied using a METSIM process model to analyze experimental data and estimate the reactor operating results. Several scenarios of a two-stage system with water/slag contact in reactor 1 and leachate/carbon dioxide contact in reactor 2 were investigated. These scenarios included batch vs continuous processing and fresh water input vs water recirculation. The METSIM leaching and carbonation models were verified with results obtained from previous slag sequestration experiments. Fresh water additions to reactor 1 allowed the highest leaching efficiency and resulted in excellent carbonation in reactor 2, but a continuous system has a high water demand. Recirculation of the spent leachate minimizes the fresh water addition required, but inhibits the leaching process by producing a calcium carbonate product layer on the slag particles in reactor 1. Increasing the slag surface area, slag/solution ratio, or reactor residence time partially overcomes product layer "blinding." Optimal residence times were defined for different process parameters and slag particle sizes.