Dehydration–rehydration in magnesium vermiculite: conversion from two–one and one–two water layer hydration states through the formation of interstratified phases

Abstract

The dehydration-rehydration of Mg-vermiculite, as large flakes (7 x 5 x 0.1 mm3) and powder (< 80 pm), has been studied. Samples were treated in a sealed bomb at 140 and 100 "C for several days. After dehydration, they were rehydrated at room temperature. The samples were examined by X-ray diffraction, and the results are analysed here for the first time by the direct Fourier transform method. The resu!ts indicated the formation of two-water layer hydration states (14.4, 14.2, and 13.8 A phases), and one-layer Mgvermiculite ( 11.5 A phase) segregated phases, besides binary interstratified one-two water layer hydration states of Mg-vermiculite phases. The existence of interstratified phases was confirmed in Mg-vermiculite flakes in the conversion from two-one and one-two water layer hydration states in Mg-vermiculite flakes by dehydrati0n;rehydration treatments. The dehydration takes place through interstratified phases consisting of alternations of 13.8 and 11.5 A components (25.3 A, regular interstratified phase). The transformation towards the 11.5 A phase at 140 "C is more rapid than at 100 "C. The rehydration produces mixed layers consisting of alternating 11.5 and 14.2 A components (random interstratified phases). Using powdered Mg-vermiculite, the changes occur faster than in the flakes, and are produced only at 140 "C. Under these conditions, no interstratification can be detected, and the dehydration-rehydration takes place spontaneously.The presence of the interstratified phase in the conversion of two-one and one-two water layer hydration states arises from the mobility of the water molecules in the crystals. The results suggest that the large particles permit a low mobility of water molecules and the thermodynamic equilibrium between the original and final segregated phases gives rise to a regular phase, characterized by the loss of an equal number of water molecules in the interlayer space. In the case of rehydration, the process is reversed. The transformation from two-to one-water layer Mg-vermiculite throughout interstratified phases depends on the temperature, time of treatment and particle size.

Study of the dehydration process of vermiculites by applying a vacuum pressure: formation of interstratified phases

“…At higher temperatures, only the phase with an interlayer distance of d = 11.5 A Ê persists. These results are in accordance with those of Reichenbach ad Beyer (1994) and Ruiz-Conde et al (1996).…”

“…In this study, three vermiculites from different geological settings, thus with different chemical compositions, have been analysed. Furthermore, the evolution of the hydration states with time and temperature, at these low pressures, have also been studied and compared with those at atmospheric pressure, reported previously (Collins et al, 1992;Reichenbach and Beyer, 1994;Ruiz-Conde et al, 1996). The interstrati ed states formed during the dehydration process, at these conditions, were analysed by the direct Fourier-transform method using the INTER program (McEwan et al, 1961;Ruṍz Amil et al, 1967;Vila and Ruṍz Amil, 1988).…”

Unusual X-Ray Characteristics of Vermiculite from Wiry, Lower Silesia, Poland

“…Similar heating procedures at 250~ produced an irrational series of basal maxima (Figure 2). These results generally agreed with Mg-exchanged vermiculite behavior under heating (cf Collins et al 1992;Reichenbach and Beyer, 1994;Ruiz-Conde et al, 1996). Figure 3 shows X-ray patterns of different size-fractions of the studied sample.…”

Interstratified vermiculite–mica in the gneiss–metapelite–serpentinite rocks at Hafafit area, Southern Eastern Desert, Egypt: From metasomatism to weathering

“…Peaks at 12.63 and 7.28 Å probably represent hydrophlogopite-like layers interstratification (Moore and Reynolds, 1989). The 12.63 Å phase is probably originated from twoand one-sheet hydrates (Collins et al, 1992;Ruiz-Conde et al, 1996;Marcos et al, 2003). Walker (1961) concluded that the 12.63 Å reflection is attributed to interstratifications between contracting and non-contracting phases.…”