Wettability Change Related to Adsorption of Organic Acids on Calcite: Experimental and Ab Initio Computational Studies

Abstract

Summary We have investigated the interactions between organic acids and a calcite powder by adsorption from an organic phase (benzoic acid and lauric acid in toluene) and from an aqueous phase (benzoic acid and lauric sodium salt). In addition to the experimental study, ab initio quantum chemistry calculations were performed for cluster models, simulating the interactions of molecules with calcite surface sites. At the toluene/calcite interface, acids chemisorb on surface calcium ions, replacing surface hydroxyls resulting from the previous surface hydration by water. This surface saponification phenomenon was predicted by ab initio calculations and confirmed by spectroscopic techniques. The adsorbed acids conferred a hydro-phobic character to calcite, with the higher contact angles in water for the longest alkyl chains in the organic acid. At the water/calcite interface, organic acids do not displace water. Our results support the possible existence of mixed wettability patterns, related to spatial distribution of pore sizes, in the specific case of organic acids with calcite.