APPLICATION OF CLAY MINERALS FROM CAYO GUAN, CUBA, AS SORBENTS OF HEAVY METALS AND CERAMIC RAW MATERIALS

The behaviour of kaolinitic clays from a reservoir in Cayo Guan was studied by hot stage microscopy. The clays, which are rich in iron oxides and which have low silica content, proved to be refractory in nature, with softening appearing > 1500 C. The workability of the clays was assessed by determining their plasticity by the Casagrande method; only one sample was found to be suitable for extrusion. Vitrification diagrams show that the water absorption capacity is < 0.6% at 1400 C. A program was designed to calculate porcelain stoneware compositions prepared from modified clays and adding low-cost raw materials to facilitate glassy phase (K feldspar and glass cullet) formation and/or increase the SiO2 content (sand and diatomaceous earth). A composition consisting of 60% clay, 30% feldspar and 10% diatomaceous earth, calcined at 1250 C at a heating rate of 15 C/min, had a water absorption of 0.8% and linear shrinkage of 21%, with no observable deformation. The clays were also treated with acid to eliminate the high iron content and study their use as sorbents of heavy metals such as Cd2+ or Cr3+.