Iron Adsorption by Montmorillonite Systems: II. Determination of Adsorbed Iron

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Abstract
Comparison of methods for determination of Fe adsorption capacity of montmorillonite and a qualitative method for differentiation of adsorbed and precipitated Fe are presented.Separate H‐montmorillonite samples (Wyoming Clay Spur, < 1µ diameter) were exchange‐saturated by washing with FeCl3, Fe2(SO4)3 and Fe(NO3)3 solutions. Excess ions were removed with either distilled H2O, absolute methanol, 95% ethanol, or 0.003M HCl. Fe retained by the systems after washing was removed with acidified 1N NH4OAc.Fe(III) removed after 0.003M HCl washing was essentially the same in all systems (between 1.17 and 1.25 me. per g.) but was much higher (up to 2.2 me. per g.) and quite variable from H2O or alcohol‐washed samples. The 0.003M HCl washing was found to remove negligible amounts of adsorbed iron. Base titration curves of all the samples were essentially the same, indicating that each system retained the same amounts of adsorbed Fe.The data indicate that excess Fe was precipitated in the systems where H2O and alcohols were employed for removal of the excess ions. Data are presented which show that adsorbed Fe may be qualitatively differentiated from precipitated Fe in the systems studied by using NH4F solution as an extracting reagent.

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