Resumen de Las bentonitas de Benavila (Portugal): Caracterización mineralógica y propiedades
Maria Isabel Dias, Silvério Prates, María Mercedes Suárez Barrios
The igneous massif of Benavila (Portugal) is constituted by rocks of granitoid nature, especially granodiorites associated to quartzdiorites, partially covered with palaeogenic sediments. A chemical, mineralogical and textural characterisation of clay materials deriving from weathering of those rocks has been done.
Clays resulting of the weathered granodiorites of Benavila, are very rich in smectites. The X-ray diffraction (XRD) results of the bulk sample enhance the clayey characteristics of those materials, mainly associated to calcite, and traces of quartz and feldspars. A monomineralic clay sample has been chosen for a more detailed study. The clay fraction XRD results enhance the presence of only smectite, that is well crystallized and dioctahedral. A structural formula for this smectite of Benavila is proposed. The chemical analysis points to a Tatatila smectite type, relatively enriched in iron.
The exchange cation capacity has been calculated in the bulk sample and in the < 2 f-lm fraction. The Specific Surface area has been evaluated in the 77°K nitrogen adsorption-desorption isotherms, applying the BET method. A porosity study has also been made through the t-curves. The results obtained with all those analyses are lower than the usually presented in literature.
