Behavior of halloysite clay under formamide treatment

摘要: Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur a variety of particle shapes hydration states. When both halloysite kaolinite present given sample, differentiation between the two is problematic particularly when constituent dehydrated. Formamide intercalation test widely used to differentiate halloysite-(7 angstrom) from kaolinite. The soil this study was taken an Udalf B horizon. It sampled 1986, immediately studied, then stored. This selected due its high halloysite-(10 angstrom)content. formamide performed on 3 fractions (< 0.1, 0.1-1, 1-2 mu m) re-extracted stored soil. X-ray diffraction shows that hydrated halloysite, initially (in fresh sample), totally dehydrated after storage. Since interlayer water weakly held, can readily irreversibly dehydrate give corresponding form. Halloysite-rich samples should therefore be kept under controlled humidity conditions or water-saturated atmosphere if mineral remain fully hydrated. abundance tubes spheroids, estimated transmission electron microscopy (TEM) proportional amount derived sample. On other hand, storage natural dehydration, markedly underestimates concentration (30-40% halloysite-rich fractions). For reference halloysites, however, state does not affect intercalation. After progressive treatment, almost all intercalated whereas only 50% expanded Thus, actual by TEM, cannot reached even treatment with formamide. indicates behaviour physico-chemical properties modified dehydration. (c) 2006 Elsevier B.V. All rights reserved.