The calcite/water interface. I. Surface charge in indifferent electrolyte media and the influence of low-molecular-weight polyelectrolyte

Suspensions of calcium carbonate in water with an indifferent background electrolyte (NaCl) have been investigated using several techniques. Particular attention was paid to the dissolution of calcite at equilibrium and as a function of sodium polyacrylate (NaPA) concentration. Also of interest was how this affects the magnitude of the surface charge and the zeta potential. The development of the interfacial charge is discussed with respect to the dissolved species and with regard to the kinetics of dissolution. The partial pressure of CO₂ in solution is believed to play a major role in determining the sign of the charge at equilibrium. In addition to effectively stabilizing calcite suspensions, NaPA was also found to act as a chelating agent at the calcite surface, enhancing the dissolution. The order of addition of NaPA to the suspensions was found to be important.