The formation of bentonite: mass balance effects

Abstract

The alteration of volcanic material into bentonite produces an important loss of mass originated by the hydrolytic action of a large amount of hydrothermal solutions. The latter solutions also provide essential elements for the formation of these materials. Mass balance gains and losses in 52 samples from several bentonite deposits show that the greatest element losses correspond to Si, and to a lesser extent to Na and K. There are some gains in Fe, Ca, Mg and H2O. On the other hand, there is a good correlation (r=0.87) between the amount of matter lost and the amount of smectite formed. In addition, the relationship between matter loss and the chemical composition of the neoformed smectite has been studied, and it has been observed that the chemical composition of smectite varies with increasing matter loss. The initial smectite contains less A1, and more Fe and Mg in comparison to the final smectite.