The influence of oxalate-promoted growth of saponite and talc crystals

Dirk Schumann; Hyman Hartman; Dennis D. Eberl; S. Kelly Sears; Reinhard Hesse; Hojatollah Vali

doi:10.1346/ccmn.2013.0610413

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The influence of oxalate-promoted growth of saponite and talc crystals

Dirk Schumann·Hyman Hartman·Dennis D. Eberl·S. Kelly Sears·Reinhard Hesse·Hojatollah Vali

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Abstract

The intercalating growth of new silicate layers or metal hydroxide layers in the interlayer space of other clay minerals is known from various mixed-layer clay minerals such as illite-smectite (I-S), chlorite-vermiculite, and mica-vermiculite. In a recent study, the present authors proposed that smectite-group minerals can be synthesized from solution as new 2:1 silicate layers within the low-charge interlayers of rectorite. That study showed how oxalate catalyzes the crystallization of saponite from a silicate gel at low temperatures (60ºC) and ambient pressure. As an extension of this work the aim of the present study was to test the claim that new 2:1 silicate layers can be synthesized as new intercalating layers in the low-charge interlayers of rectorite and whether oxalate could promote such an intercalation synthesis. Two experiments were conducted at 60ºC and atmospheric pressure. First, disodium oxalate solution was added to a suspension of rectorite in order to investigate the effects that oxalate anions have on the structure of rectorite. In a second experiment, silicate gel of saponitic composition (calculated interlayer charge −0.33 eq/O 10 (OH) 2 ) was mixed with a suspension of rectorite and incubated in disodium oxalate solution. The synthesis products were extracted after 3 months and analyzed by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The treatment of ultrathin sections with octadecylammonium (n C = 18) cations revealed the presence of 2:1 layer silicates with different interlayer charges that grew from the silicate gel. The oxalate-promoted nucleation of saponite and talc crystallites on the rectorite led to the alteration and ultimately to the destruction of the rectorite structure. The change was documented in HRTEM lattice-fringe images. The crystallization of new 2:1 layer silicates also occurred within the expandable interlayers of rectorite but not as new 2:1 silicate layers parallel to the previous 2:1 silicate layers. Instead, they grew independently of any orientation predetermined by the rectorite crystal substrate and their crystallization was responsible for the destruction of the rectorite structure.

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Dirk Schumann, Hyman Hartman, Dennis D. Eberl, S. Kelly Sears, Reinhard Hesse, Hojatollah Vali. 2024-01-01. The influence of oxalate-promoted growth of saponite and talc crystals. https://doi.org/10.1346/ccmn.2013.0610413

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