Calcite is calcium carbonate (CaCO3). You would therefore see the protonation of carbonate to bicarbonate to carbonic acid and its dissociation into CO2 and water. These pH-dependent processes play an important role both in the formation and the dissolution of calcite.

Dear Sir. Concerning your issue about the variation of surface charge of calcite with pH changes. The electrical state at the calcite aqueous solution interface has been investigated using a streaming potential method applied to systems containing no gas phase. Experimental results have allowed a clear and unambiguous identification of the major surface ions as Ca2+ and CO32− species and have also shown that other solution species, including H+ and OH−, have no significant direct influence on the surface charge of calcite over the range pH 7–12. Induced changes in the pH of aqueous calcite dispersions in the directions of increasing and of decreasing calcite solubility have been shown to result in the formation of a new solid phase at the calcite crystal surface. Formation of this surface material leads to more positive values of the calcite ζ-potential and it is suggested that this surface precipitation phenomenon could be at least partly responsible for the diversity of experimental results which have been obtained from electrokinetic studies of aqueous calcite dispersions. I think the following below links and the attached files may help you in your analysis:

http://www.ugr.es/~grupo179/pdf/GCA%202011.pdf

http://www.ux.uis.no/~ah/hiorth_tipm.pdf

Thanks