Adsorption of methanoic acid onto the low-index surfaces of calcite and aragonite

We have employed atomistic simulation techniques to investigate the effect of the adsorption of methanoic acid on the surfaces of calcite and aragonite. We have calculated surface energies and adsorption energies for all the surfaces considered, and compared the surface energies with those of the pure surfaces. Generally the methanoic acid molecules coordinate via their doubly bonded oxygen atom to surface calcium atoms, with the hydroxyl hydrogen atom directed towards oxygen atoms of surface carbonate groups. The hydrogen bonded to the carbon atom of the methanoic acid is usually pointing away from the surface, which is of considerable significance since we are using methanoic acid as a model adsorbate for long chain carboxylic acids, that are used extensively in the process of flotation. We suggest that the replacement of the hydrogen atom of the methanoic acid with a long chain hydrocarbon would not result in significantly different interactions and, thus, would give similar adsorption energies (-54 to -113 kJ mol(-1) on calcite, -40 to -83 kJ mol(-1) on aragonite).