The Mechanism of Dehydration of Mg-Vermiculite

G. F. Walker
Division of Industrial Chemistry, C. S. I. R. O., Melbourne, Australia

Abstract: The hydrated Mg-vermiculite lattice contains double sheets of water molecules interleaved wittl silicate layers. In the fully hydrated condition, each water sheet is arranged in a regular hexagonal pattern and the interlayer cations are located midway between water sheets in octahedral coordination.

Release of water molecules from interlayer positions leads at first to a gradual contraction of the basal spacing from 14.81 A, during which the water network becomes increasingly distorted. The contraction ceases temporarily at 14.36 A while further water is withdrawn. When the probability that a cation has a complete octahedral “shell” of water molecules at a given instant falls below a certain value, an abrupt contraction to 13.82 A takes place during which the cations are displaced to sites near the silicate layer surfaces.

Release of further water causes a contraction to a lattice (11.59 A) in which single sheets of water molecules are interleaved with the silicate layers. The 11.59 A phase is stable until only a small proportion of the interlayer water remains, when an approximately regular interstratification of 11.59 A and 9.02 A (dehydrated) layers develops. The final traces of interlayer water are retained in the interior of the crystal with great tenacity owing to the sealing of the crystal near the edges.

Clays and Clay Minerals; 1955 v. 4; no. 1; p. 101-115; DOI: 10.1346/CCMN.1955.0040115
© 1955, The Clay Minerals Society
Clay Minerals Society (www.clays.org)