Abstract: The Mg-vermiculite from Santa Olalla has been treated with aliphatic amides—formamide (FM), acetamide (AM) and propionamide (PM)—in aqueous solution. These treatments produce the transformation towards NH4-vermiculite and interstratified NH4-vermiculite-Mg-vermiculite phases. The NH4-vermiculite, Mg-vermiculite and interstratified (mixed-layer) phases have been identifed from basal X-ray diffraction (XRD) interval peaks between 10.3 Å and 14.4 Å, and confirmed by direct Fourier transform method, as well as by atomic absorption spectrometry (AAS), infrared (IR) spectroscopy and thermal analysis.
According to their NH4-vermiculite/Mg-vermiculite probability coefficients ratio (PA/PB), and PAA, these interstratified phases can be divided into 3 categories: 1) If the PA/PB ratio is ≥ 7/3 and PAA ≥ 0.7, there are interstratified phases with a strong tendency toward segregation (case of FM, AM and PM). 2) If the PA/PB ratio is between 5/5 and 6/4, with PAA in the range 0.45–0.6, there are nearly regular alternating and random interstratified phases (case of AM and PM). 3) If the PA/PB ratio is ≤ 5/5 and PAA ≤ 0.45, there are interstratified phases with a strong tendency toward alternation (case of PM).
Experimental evidence reported in the present work indicates that the mechanism of interaction of Mg-vermiculite with FM, AM and PM in an aqueous medium takes place by ion exchange of NH4 between the layers. The hydrolysis of these aliphatic amides leads to the liberation of NH4+ into the medium. It has been found that the NH4+ sorption depends on the physico-chemical characteristics of the particular aliphatic amide, and the transformation of Mg-vermiculite to interstratified and/or NH4-vermiculite phases depends on the amide concentration. These treatments allow one to control the formation of interstratified and NH4-vermiculite phases.