Calcium carbonate precipitation from aqueous solutions containing Aerosol OT

In supersaturated solutions containing Ca2+, HCO3-, CO32- and Aerosol OT(AOT) at 45 degrees C, AOT shows an inhibitory effect in the nucleation of vaterite under certain concentrations (i.e < 160 ppm AOT when [Ca](T) = Sigma C = 0.01M) and blocks its solvent-mediated transformation to calcite at relatively high concentrations, i.e. 200 ppm when [Ca](T) = Sigma C = 0.01M or 800 ppm when [Ca](T) = Sigma C = 0.1M. This last phenomenon is explained by the total coverage of the vaterite surface. Most probably, the formation of a double AOT layer has taken place, in a way similar to that observed in the aqueous system AOT-calcite. When supersaturated solutions are seeded with calcite, perhaps a change in the growth mechanism from normal growth (for 0 and 13 ppm AOT) to 2D-nucleation mediated growth (at 25 and 50 ppm AOT) takes place. For supersaturation ratios S < 3.5, growth rates usually decrease when the concentration of AOT rises, while for S > 3.5 the effect is the opposite, AOT acting as a surface catalyst.