1. Department of Chemical Engineering, University of Leuven, W. de Croylaan 46, B-3001 Heverlee, Belgium, Fysico-Chemische Geologie, University of Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium, and SIDMAR N.V., J. Kennedylaan 51, B-9042 Gent, Belgium