INTERACTION OF VERMICULITE WITH ALIPHATIC AMIDES (FORMAMIDE, ACETAMIDE AND PROPIONAMIDE) - FORMATION AND STUDY OF INTERSTRATIFIED PHASES INTHE TRANSFORMATION OF MG-VERMICULITE TO NH4-VERMICULITE

The Mg-vermiculite from Santa Olalla has been treated with aliphatic a mides-formamide (FM), acetamide (AM) and propionamide (PM)-in aqueous solution. These treatments produce the transformation towards NH4-verm iculite and interstratified NH4-vermiculite-Mg-vermiculite phases. The NH4-vermiculite, Mg-vermiculite and interstratified (mixed-layer) pha ses have been identified from basal X-ray diffraction (XRD) interval p eaks between 10.3 Angstrom and 14.4 Angstrom, 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 (P -A/P-B), and P-AA, these interstratified phases can be divided into 3 categories: 1) If the P-A/P-B ratio is greater than or equal to 7/3 an d P-AA greater than or equal to 0.7, there are interstratified phases with a strong tendency toward segregation (case of FM, AM and PM). 2) If the P-A/P-B ratio is between 5/5 and 6/4, with P-AA in the range 0. 45-0.6, there are nearly regular alternating and random interstratifie d phases (case of AM and PM). 3) If the P-A/P-B ratio is less than or equal to 5/5 and P-AA less than or equal to 0.45, there are interstrat ified phases with a strong tendency toward alternation (case of PM). E xperimental evidence reported in the present work indicates that the m echanism of interaction of Mg-vermiculite with FM, AM and PM in an aqu eous medium takes place by ion exchange of NH4 between the layers. The hydrolysis of these aliphatic amides leads to the liberation of NH4into the medium. It has been found that the NH4+ sorption depends on t he physico-chemical characteristics of the particular aliphatic amide, and the transformation of Mg-vermiculite to interstratified and/or NH 4-vermiculite phases depends on the amide concentration. These treatme nts allow one to control the formation of interstratified and NH4-verm iculite phases.