Adsorption of cationic and anionic surfactants on natural and synthetic carbonate materials.

Adsorption of cationic and anionic surfactants on carbonate materials is investigated in this study. Cetylpyridinium chloride (CPC) and sodium dodecyl sulfate (SDS) are chosen as typical cationic and anionic surfactants, respectively. It is found that the cationic CPC exhibits negligible adsorption on synthetic calcite in deionized water compared with the adsorption of the anionic SDS. However, a substantial amount of adsorption of CPC is observed on natural carbonates, such as dolomite and limestone. X-ray photoelectron spectroscopy (XPS) reveals that that a substantial amount of silicon and aluminum exists in natural dolomite and limestone but not in synthetic calcite. The adsorption plateau of CPC on carbonates highly depends on the silicon composition in the carbonate samples due to the strong electrostatic interaction between CPC and negative binding sites in silica and/or clay. The adsorption of CPC on natural carbonates is reduced in the presence of 1atm CO2 compared with the case under 1atm air, while SDS precipitates out of the solution under 1atm CO2 due to its intolerance to divalent ions released from the carbonate surface as a result of CO2 acidification.