RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

A surface complexation model for the chemical structure and reactivity of the carbonatewater 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: CO₃H⁰a2>CO₃⁻ + H⁺(1) CO₃H⁰ + Me²⁺a2>CO₃Me⁺ + H⁺(2) MeOH₂⁺a2 >MeOH⁰ + H⁺(3) MeOH⁰a2 >MeO⁻ + H⁺(4) MeOH⁰ + CO₂a2 >MeHCO₃^o (5) MeOH⁰ + CO₂a2 >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.