Rob
Ansys Employee

OK. Assuming the calcium is a "fluid" rather than a disolving solid make a multibody part (DesignModeler) or use ShareTopology (SpaceClaim) to get a conformal mesh. Label the volumes to suit. Then in Fluent you patch in the materials. Note, a granular phase has a packing limit, so always patch those at 0.01 below the limit to avoid interesting consequences. 

If the calcium is disolving you have a different problem, and you may need to read up on moving mesh, surface reactions and UDFs.