Computer simulation of calcite growth inhibition: A study of monophosphonate interaction with calcite

Abstract

We have performed atomistic surface simulations of the interaction of monophosphonate growth inhibitor ions with the planar and obtuse stepped { 10 1 ¥ 4 } surfaces of calcium carbonate. We show that phosphonate inhibitor ions have a smaller adsorption energy on the planar { 10 1 ¥ 4 } surface compared to the obtuse stepped { 10 1 ¥ 4 } surface in accordance with experiment; and that the binding energy of the inhibitor with the surface is dominated by electrostatic forces. We find that replacement processes which simulate the irreversible incorporation of monophosphonate ions at terrace and step sites are energetically more favourable than those calculated for the diphosphonate ion. The inhibition mechanism proposed to operate for the deprotonated monophosphonate/calcite system is via the binding or incorporation of monophosphonate ions to the calcite obtuse step sites and kink sites thus slowing step flow and thereby destroying and/or delaying the formation of potential kink sites and step assembly.