Statistical Analysis of Acid Treatment of Different Types of Clay Minerals

Abstract

Bentonite, which is composed of montmorillonite, is modified with acid to change its properties for use in agricultural and environmental applications and color. Hydrochloric acid and sulfuric acid were used for acid activation. Acid activation has been widely studied, but this study aims to find the correlations between the studied physical, chemical, and mineralogical properties via regression analysis, which is used to describe the relations among different variables via analysis of variance. Based on different colors, six types of bentonite were analyzed for loss on ignition, specific weight, specific surface, water absorption, chemical and mineralogical composition, and were modified with different concentrations of hydrochloric and sulfuric acids. All the samples, regardless of their original color, changed to a greyish white, with the highest whiteness observed for the sample treated with 35% hydrochloric acid. The correlations among the loss on ignition, specific weight, and specific surface area are significant. The surface area of modified bentonite increases with increasing acid concentration, which may imply that the acid-treated bentonite becomes more porous. Hydrochloric acid has a more significant effect on the mineralogical content than sulfuric acid. As the acid concentration increases, the contents of montmorillonite, illite, and kaolinite decrease, whereas the content of quartz increases. Sulfuric acid changes the contents of montmorillonite, illite, and quartz less significantly. The changes in the Si4+, Fe2+, and Na+ contents are insignificant with increasing acid concentrations. The changes in Al3+ and Ca2+ contents are more significant with increasing hydrochloric acid concentration.