Inhibition of adhesion and precipitation of CaCO3 by aminopolyphosphonate

The effect of a phosphonate inhibitor [ethylenediamine-N,N,N',N', tetrakis (methylenephosphonic acid)] (EDTMP) on the formation and transformation of CaCO3 on solid surface and in bulk solution was investigated by using quartz crystal microbalance technique and ion concentration measurements in bulk solution. The amount of CaCO3 adhered on a gold surface of QCM sensor and ion activity product of the suspension were measured simultaneously as a function of time in the presence of various concentrations of EDTMP ranging from 10(-6) to 10(-4) M. An amorphous CaCO3 (ACC) immediately precipitates from highly supersaturated solution and transforms to crystalline polymorphs (calcite and vaterite) in bulk solution. On the other hand, calcite exclusively grows on the surface in the absence and presence of the inhibitor. Even at very low concentrations of EDTMP (10-6 M), the amount and rate of adhesion are suppressed down to 30%, whereas the precipitation process is not essentially altered. The inhibitor, up to 10(-5) M, hardly affects the transformation of ACC to crystalline CaCO3 in solution, whereas the transformation of vaterite to calcite in solution and the growth of calcite directly adhered on the surface are completely suppressed during this stage. The transformation processes in the solution and the adhesion on the surface are completely stopped by the presence of 10(-4) M EDTMP. The inhibition of the adhesion process is attributed to the adsorption. of the inhibitor on the growing calcite adhered on the solid (gold) surface. The effect of the inhibitor on the growth of calcite on the surface is similar to that of the transformation to calcite in the solution. The presence of the inhibitor causes deformation of the crystal morphology. of both the adhered and precipitated crystals. The strong depression of adhesion of crystals (calcite) is caused by the adsorption of inhibitor on the solid surface. The increase in the ratio of initial concentrations of calcium to carbonate causes a decrease in the rate of adhesion on the surface and transformation of the precipitate in solution, whereas it hardly affects the amount of adhesion. (C) 2003 Elsevier B.V. All rights reserved.