A SURFACE COMPLEXATION MODEL OF THE CARBONATE MINERAL-AQUEOUS SOLUTION INTERFACE

A surface complexation model for the chemical structure and reactivity of the carbonate-water interface is presented. The model postulates the formation of the hydration species >CO3H0 and >MeOH0 at the surface of a divalent metal carbonate MeCO3 (Me = Ca, Mn, Fe. etc.). The existence of these primary hydration species is supported by spectroscopic data. The following reactions are proposed to govern surface speciation in the MeCO3(s)-H2O-CO2 system: >CO3H0 double-line arrow pointing left and right > CO3- + H+ (1) >CO3H0 + Me2+ double-line arrow pointing left and right >Co3Me+ + H+ (2) >MeOH2+ double-line arrow pointing left and right >MeOH0 + H+ (3) >MeOH0 double-line arrow pointing left and right >MeO- + H+ (4) >MeOH0 + CO2 double-line arrow pointing left and right > MeHCO30 (5) >MeOH0 + CO2 double-line arrow pointing left and right >MeCO3- + H+ (6). It is shown in this paper that the surface complexation model provides a systematic explanation of surface charge development and dissolution kinetics of carbonate minerals. The intrinsic stability constants of the surface complexation reactions agree well with the equilibrium constants of the corresponding complexation reactions in homogeneous solution.