THERMAL INVESTIGATIONS ON ALUNITE AND ITS MIXTURES WITH QUARTZ AND DICKITE

Thermal decomposition of alunite and of mixtures of alunite with dickite or quartz or both has been studied, and x- ray determinations of the products at various stages of the decomposition have been made. Between 600 and 700 C the product from alunite is a mixture of anhydrous alum and amorphous alumina; between 700 and 770 C the anhydrous alum breaks down into aluminum sulfate and alkali sulfate; then in the prominent 850 C endothermic reaction three- quarters of the sulfate is lost, leaving a mixture of alkali sulfate and /U- alumina. The area of the 850 C endothermic peak may be used as a measure of the percentage of alunite in alunitized rocks.