CO2 emissions could be reduced with capture and storage (CCS) methods. CCS causes costs for the industry, creating an extra barrier for implementation of these techniques. A recently developed mineral carbonation process producing a valuable product covering process implementation costs is advanced towards commercial scale. In this two-step process, calcium-rich steel converter slag is treated with an aqueous ammonium salt solution to selectively extract the calcium. Then the dissolved calcium is removed from the process liquid as pure precipitated calcium carbonate (PCC) by introducing gaseous CO2 to the system. This concept would utilise waste material from steel industry, and spare the natural resources used for conventional PCC production. Experimental results have shown that papermaking grade PCC can be produced with ammonium nitrate, chloride or acetate solvents. The used solvent has also been regenerated and recycled between the process stages, which reduces the need for fresh solvent and lowers the process costs. To maximise the PCC production in a continuous process, a thermodynamic process model in Aspen Plus is now constructed. The modelling results are validated with a series of semi-continuous experiments. It is found that by using staged carbonate precipitation the yield of pure product is increased. Ammonium nitrate is observed to enable the highest conversion of calcium from steel slag to calcium carbonate also in continuous operation. At ambient conditions the process steps generate heat but this low temperature heat cannot be utilised. The mixing and pumping energies for process operation are small in comparison to the heat duties in chemical reactors. Preliminary results on solid-liquid separation studies, on washing of the solid outlet streams, as well as on recovery and make-up needs of process chemicals are discussed. The work is a continuation of work presented by Said et al. at 22nd ECOS in Brazil 2009.