Thermal treatment of sepiolite— And palygorskite— Stearic acid associations

Abstract

The interactions between stearic acid and the clay minerals sepiolite and palygorskite and the thermal behaviour of the organo-clay associations were investigated by DTA, TGA and IR spectroscopy. The molten acid was adsorbed by the clay minerals, penetrating into the channels and exchanging zeolitic water. Inside the channels the acid was hydrated. When the organo-clay associations were ground, the acid dissociated to form stearate anions, due to interaction of the protons with newly exposed basic surface sites. Alkali halide disks of the organo-clay complexes were heated in stages up to 450°C and their IR spectra were recorded. Most of the adsorbed acid was liberated from the clay below 190°C. With NaCl disks, loss of organic material continued with a further rise in temperature, but with KCl and CsCl disks, increases in temperature led to decomposition of the acid, leaving a hydrocarbon residue. The thermal stability of the stearic acid—palygorskite association is lower than that of the sepiolite.