Abstract

Chrysotile from Thetford Mines in Quebec, Canada was treated first with mild formic or oxalic acid at concentrations of 0.5 to 2.0 N at 200°C in Teflon-lined 12.0 mL Parr bombs. The reaction products were identified by X-ray diffraction as a poorly crystalline Fe-bearing kerolite-like 2:1 layer silicate (which will be described as a kerolitic precipitate or a kerolitic mesophase in this report). Electron microscopic examination showed a thin foily morphology for this kerolitic mesophase that may have formed by the following reaction:

 
\begin{eqnarray*}&&{Mg_{6}Si_{4}O_{10}(OH)_{8(s)}_{chrysotile}^{}}\ +\ 6.02H^{+}_{(aq)}\ +\ 0.54Fe^{2+}_{(aq)}\\&&\ {\rightarrow}\ {(Mg_{2.46}Fe^{2+}_{0.54})Si_{4}O_{10}(OH)_{2}{\cdot}\mathit{n}H_{2}O_{(s)}_{kerolitic\ mesophase}^{}}\ +\ 3.55Mg^{2+}_{(aq)}\end{eqnarray*}
(1)

The magnetite impurity in the initial chrysotile asbestos served as the source of Fe in the above reactions. Subsequently, this kerolitic precipitate was reacted with 0.2 N NaOH for 48–96 h at 200°C and a highly crystalline smectite was formed with the same foily morphology as the kerolitic precipitate. X-ray spectral analyses of the kerolitic mesophase and smectite suggest the following reaction to have taken place:

 
\begin{eqnarray*}&&{(Mg_{2.46}Fe^{2+}_{0.54})Si_{4}O_{10}(OH)_{2}{\cdot}\mathit{n}H_{2}O(s)_{kerolitic\ mesophase}^{}}\ +\ 0.53Mg^{2+}_{(aq)}\\&&\ +\ 0.54NaOH_{(aq)}\ +\ 0.01Fe^{3+}_{(aq)}\ {\rightarrow}\\&&{Na_{0.54}(Mg_{2.99}Fe^{2+}_{0.01})(Si_{3.46}Fe^{3+}_{0.54})O_{10}(OH)_{2\ (s)}_{saponite}^{}}\ +\ 0.54Si^{4+}_{(aq)}\end{eqnarray*}
(2)

The reaction products, a kerolitic mesophase and smectite, possess a non-fibrous habit in contrast to the fibrous (asbestiform) morphology of chrysotile.

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