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A computer modelling study of the interaction of organic adsorbates with fluorapatite surfaces

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Abstract

Computer modelling techniques were employed to investigate the adsorption of a selection of organic surfactant molecules to a range of fluorapatite surfaces, and new interatomic potential models for the apatite/adsorbate interactions are presented. The adsorbates coordinate mainly to the surfaces through interaction between their oxygen (or nitrogen) atoms to surface calcium ions, followed by hydrogen-bonded interactions to surface oxygen ions and, to a much lesser extent, surface fluorides. Bridging between two surface calcium ions is the preferred mode of adsorption, when the geometry of the adsorbates allows it, and multiple interactions between surfaces and adsorbate molecules lead to the largest adsorption energies. All adsorbates containing carbonyl and hydroxy groups interact strongly with the surfaces, releasing energies between approximately 100 and 215 kJ mol−1, but methylamine containing only the –NH2 functional group adsorbs to the surfaces to a much lesser extent (25–95 kJ mol−1). Both hydroxy methanamide and hydroxy ethanal prefer to adsorb to some surfaces in an eclipsed conformation, which is a requisite for these functional groups. Sorption of the organic material by replacement of pre-adsorbed water at different surface features is calculated to be mainly exothermic for methanoic acid, hydroxy methanamide and hydroxy ethanal molecules, whereas methyl amine would not replace pre-adsorbed water at the fluorapatite surfaces. The efficacy of the surfactant molecules is calculated to be hydroxy aldehydes > alkyl hydroxamates > carboxylic acids ≫ alkyl amines. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic surfactants for use in mineral separation by flotation.

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Acknowledgements

NHdL thanks the Engineering and Physical Sciences Research Council UK for an Advanced Research Fellowship and grant no. GR/S67142/01. PEN and DM thank the National Research Foundation and the Council for Scientific and Industrial Research, South Africa, and the Royal Society, UK, for financial support.

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  1. Timothy G. Cooper

    Present address: The Pfizer Institute for Pharmaceutical Materials Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK

Authors and Affiliations

  1. Materials Modeling Center, University of Limpopo (formerly University of the North), Private Bag X1106, Sovenga, 0727, South Africa

    Donald Mkhonto & Phuti E. Ngoepe

  2. School of Crystallography, Birkbeck College, University of London, Malet Street, London, WC1E 7HX, UK

    Donald Mkhonto, Timothy G. Cooper & Nora H. de Leeuw

  3. Department of Chemistry, University of College London, University of London, 20 Gordon Street, London, WC1H 0AJ, UK

    Nora H. de Leeuw

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  1. Donald Mkhonto
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Correspondence to Nora H. de Leeuw.

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Mkhonto, D., Ngoepe, P.E., Cooper, T.G. et al. A computer modelling study of the interaction of organic adsorbates with fluorapatite surfaces. Phys Chem Minerals 33, 314–331 (2006). https://doi.org/10.1007/s00269-006-0080-3

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  • DOI: https://doi.org/10.1007/s00269-006-0080-3

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