Microwave precipitation of CaCO3 from homogeneous solutions

The precipitation of calcium carbonate, calcite, from homogeneous complexed solutions formed by Ca-citrate and HCO3-/CO32- has been carried out in batch and MSMPR reactors activated by microwave radiation. In the batch experiments, monodisperse calcite crystals with ellipsoidal or peanut-like shapes have been obtained under certain experimental conditions, while in the continuous precipitation experiments the calcite crystals present ellipsoidal shapes. These morphologies are unusual for the phase calcite. In the continuous precipitation experiments, the rate of nucleation observed is higher than the one measured in a conventional MSMPR reactor in equivalent conditions. A possible explanation to this fact lies in the specific effect of microwaves in weakening the Ca-H2O bonding of the inner hydration sphere of calcium, thus favoring its dehydration, which is the rate controlling factor in the precipitation of calcium carbonate.