Layer Charge Properties of Smectites and Vermiculites: Tetrahedral vs. Octahedral

Abstract

AbstractTotal layer charge and charge of octahedral sheets of 2:1 soil clays were estimated by combining alkylammonium ion exchange technique and the Hofmann and Klemen effect. The estimation of charge before and after Hofmann and Klemen effect (Li‐saturation and heat treatment) gave the total layer and tetrahedral charge, respectively. The difference of total and tetrahedral charge provided the charge contribution of octahedral sheets, assuming that a complete neutralization of octahedral charge was achieved by Li+ migration during the heat treatment. As much as 50% of the charge was found to be located in the octahedral sheets in soil smectites and soil vermiculites. Clays with total layer charge in the vermiculitic range that accommodated both double (1.8 nm) and single (1.4 nm) interlayers of glycerol in the interlayer spaces formed only double‐layer complexes after Li+ treatment, indicating a reduction in total layer charge, plus a random distribution of charge in both octahedral and tetrahedral sheets of each 2:1 layer. Trioctahedral vermiculites with a total layer charge comparable to the total layer charge of dioctahedral soil vermiculites gave only single layer complexes with glycerol after Mg‐saturation. These sorption characteristics can be explained in terms of Coulomb's law and the higher concentration of negative charge of trioctahedral vermiculites in the tetrahedral sheet compared with dioctahedral soil vermiculites.