THE FEATURES OF IRON OCCURRENCE FORMS IN BENTONITE CLAY OF THE KAIBALSKOYE-2 DEPOSIT, REPUBLIC OF KHAKASSIA

The forms of iron occurrence in bentonite clay from the Kaibalskoye-2 deposit were determined using theoretical and experimental methods (elemental analysis, scanning electron microscopy and elemental mapping, powder X-ray diffraction with Rietveld refinement, Mössbauer spectroscopy, UV-vis diffuse reflectance spectroscopy, and quantum-chemical simulations). The total Fe2O3 content was found to be 8 wt%, while the montmorillonite content was 65 wt%. No minerals capable of containing significant amounts of iron were detected, however, iron can substitute aluminium isomorphously in the octahedral layers of montmorillonite. The results of scanning electron microscopy with elemental mapping show that a small amount of iron is concentrated as oxide and hydroxide inclusions in quartz and in aluminosilicates. Most of iron is uniformly distributed in the agglomerates of aluminosilicates, which means that iron is included into montmorillonite structure through isomorphous substitution. According to the data of Mössbauer spectroscopy, iron is represented by Fe3+ ions in octahedral positions. Absorption bands are observed to appear in the UV-vis diffuse reflectance spectra at longer wavelengths (at 420-600 nm) as a result of iron insertion into montmorillonite structure, which is confirmed by quantum-chemical simulation. Promising directions for the rational use of bentonite from the Kaibalskoye-2 deposit are proposed on the basis of the newly established data.