Mineralogy, chemistry and potential applications of a white bentonite in San Juan province, Argentina

A white bentonite deposit of Pleistocene age located in San Juan Province, Argentina, has very promising commercial applications because of its mineralogy and physical and chemical properties. The bentonite occurs in the Lower Member of the Las Trancas Formation which is a hydrothermally altered rhyolitic to rhyodacitic pumice and breccia. Analysis shows the major minerals present are smectite and opal-CT along with minor amounts of quartz, clinoptilolite, feldspar and biotite. The majority of the quartz, clinoptilolite, and biotite occurs in the >325 mesh fraction. The smectite is mainly a sodium montmorillonite along with some calcium and magnesium in the exchange positions. The <2 mum fraction consists of almost pure smectite and opal CT. Scanning electron micrographs show a typical corn flakes texture, which is characteristic of sodium montmorillonite. The physical and chemical properties including particle size, surface area, water and oil absorption, swelling index, cation exchange capacity, viscosity, and brightness indicate after wet beneficiation, that the processed white bentonite could be used in many industrial applications. These include paper coating and filling, paint, pharmaceuticals, cosmetics and filtering agents. Also the fine particle size fraction of <2 mum could be used to make an excellent quality organoclay. (C) 2004 Elsevier B.V. All rights reserved.