Isomorphous Substitution of Iron for Aluminium in Some Soil Kaolinites

Abstract

Abstract--Clay ( < 2 ttm) and fine silt (~20/~m) fractions of twenty seven soil samples from eight tropical ferruginous profiles of the Mysore Plateau (India) were analysed for kaolinite by dehydroxylation and selective dissolution. The considerable amounts of iron extracted by the procedure and the closeness of the SiO2/R203 molar ratios (2.00-2.18) to the ideal value of 2.00 indicated that iron was a structural constituent of the kaolinites, The calculated unit cell cation composition of the kaolinites showed a substitution of 0.114).82 atoms of Fe(III) for A1 in every four octahedral sites. The kaolinites in these soils appear to be products of crystallization from weathering solutions.

Hydrothermal (200°C) synthesis and crystal chemistry of iron-rich kaolinites

“…This value is significantly smaller than that of Rengasamy et al (1975), and is closer to the 0.075 ~ value, measured by Russell & Clark (1978) for Fe 3+ in octahedral sites of nontronite, and to 0-087 ~ for Fe and Mg substitutions in smectites (Desprairies, 1983). IR spectroscopy confirms increasing Fe for AI substitution in kaolinite with increasing (a) of the starting glass.…”

“…Because of the low Fe content of natural and previously synthesized kaolinites, variations in b-parameter measurements were generally not significant and beyond the resolution of the method (Calvert, 1981). For natural kaolinites with expected higher Fe contents, Rengasamy et al (1975) observed an increase in the b-parameter of 0-312 • per substituted Fe 3+ atom but this value is questionable (Herbillon et al, 1976;Calvert, 1981). Because of the way cations are allocated to octahedral positions, Rengasamy et al (1975) have probably overestimated the structural Fe content.…”

“…In fact, detailed chemical analyses (Rengasamy et al, 1975;Li6tard, 1977), electron microprobe analyses (Jepsen & Rowse, 1975), M6ssbauer spectroscopy (Malden & Meads, 1967;Janot et al, 1973;Jefferson et al, 1975;Komusinski et al, 1981;Fysh et al, 1983), ESR spectroscopy (Angel & Hall, 1972;Meads & Malden, 1975;Herbillon et al, 1976;Mestdagh et al, 1980;Mestdagh et al, 1982;Brindley et al, 1986), infrared spectroscopy (Mendelovici et al, 1979), as well as EXAFS spectroscopy (Bonnin et al, 1982) and more recently, NMR spectroscopy (Stone & Torres-Sanchez, 1988), show that small variable amounts of iron (up to almost 3% Fe203) can be accommodated within the octahedral sheet of kaolinites. Moreover, the content of structural iron showed some relationship to kaolinite defects.…”

Mössbauer Effect Studies of Iron in Kaolin. I. Structural Iron

“…Copyright 9 1983, The Clay Minerals Society microprobe (e.g., Jepson and Rowse, 1975), chemical (e.g., Rengasamy et al, 1975), electron spin resonance (ESR) (e.g., Meads and Malden, 1975), and infrared (Mendelovici et al, 1979) studies. The considerable number of studies employing ESR techniques have recently been reviewed by Hall (1980).…”

Weathering of a Chromian Muscovite to Kaolinite

“…Clearly, kaolin group minerals are able to accommodate structural Cr so that retention of some Cr in kaolinite formed from muscovite could be anticipated. Similarly, kaolin group minerals may accommodate substantial amounts of structural Fe (Rengasamy et aL, 1975;Herbillon et al, 1976).…”