Iron‐Bearing Kaolinite in Venezuelan Laterites. II. DTA and Thermal Weight Losses of KCl and CsCl Mixtures of Laterites

Abstract

AbstractKCl and CsCl mixtures of Venezuelan laterite samples were examined by DTA. These laterites contain iron‐bearing kaolinite. The first endothermic peak at ∼300°C is characteristic of goethite and gibbsite. A second endothermic peak at 470–512°C characterizes kaolinite. In KCl mixtures, the maximum of this peak decreases with increasing iron content of the kaolinite crystal. In CsCl mixtures, such a relationship is obtained only after the removal of the gibbsite from the lateritic sample. A third endothermic peak at 650–760°C is characteristic of the melting of the salt. The intensity of this peak may be used as a reference. KCl may thus serve as an internal standard for the determination of kaolinite in a series of laterite samples. CsCl, which forms a complex with kaolinite, cannot be used as an internal standard. The fourth endothermic peak results largely from the evaporation of the salt. The location of this peak in the CsCl mixtures depends on the iron content of the kaolinite. The laterite—alkali halide mixtures were subjected to weight losses at temperatures between 105 and 1000°C. In addition to the dehydroxylation processes, hydrolysis of the salts on the surfaces of kaolinite, and the evaporation of HCl take place in the CsCl mixtures and to a lesser extent in the KCl mixtures. In the CsCl mixtures, when the dehydroxylation stage of the kaolinite was studied in stages, it was found that kaolinites with a high iron content tend to lose weight mainly at a high temperature (550°C) whereas those with a low iron content tend to lose weight even at 450°C.