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 t he formation of the hydration species >CO3H0 and >MeOH0 at the surface of a divalent metal carbonate MeCO3 (Me = Ca, Mn, Fe. etc.). The exis tence of these primary hydration species is supported by spectroscopic data. The following reactions are proposed to govern surface speciati on in the MeCO3(s)-H2O-CO2 system: >CO3H0 double-line arrow pointing l eft and right > CO3- + H+ (1) >CO3H0 + Me2+ double-line arrow pointing left and right >Co3Me+ + H+ (2) >MeOH2+ double-line arrow pointing le ft and right >MeOH0 + H+ (3) >MeOH0 double-line arrow pointing left an d right >MeO- + H+ (4) >MeOH0 + CO2 double-line arrow pointing left an d right > MeHCO30 (5) >MeOH0 + CO2 double-line arrow pointing left and right >MeCO3- + H+ (6). It is shown in this paper that the surface co mplexation model provides a systematic explanation of surface charge d evelopment and dissolution kinetics of carbonate minerals. The intrins ic stability constants of the surface complexation reactions agree wel l with the equilibrium constants of the corresponding complexation rea ctions in homogeneous solution.