Distribution and Influence of Iron Phases on the Physico—Chemical Properties of Phyllosilicates

Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD,DTA,dissolution analysis(DCB),IR,Moessbauer and X-band Electron Spin Resonance(ESR) spectroscopies.The purity of the samples and the degree of structural order were determined by XRD.The location of Fe in the octahedral sheet is characterized by absorption bands at-875cm^-1 assigned as Al-OH-Fe which is present after chemical dissolution of free iron.The Moessbauer spectra of these clays sow two doublets with isomer shift and quadrupole splitting typical of octahedral coordinated Fe^3 ,in addition to third doubler with hyperfine parameter typical of Fe^2 in the spectra of Abu-Had kaolinite (H)sample.6-lines magnetic hyperfine components which are consistent with those of hematite are confirmed in the spectra of both Isel and Rish kaolinite samples.Goethite was confirmed by both IR and DTA.Multiple nature of ESR of these clays suggested structural Fe in distorted octaedral symmetry and as non-structural Fe.Little dispersion and low swelling indices as well as incomplete activaiton of investigated montmorillonite samples by NaCO3 appear to be due to incomplete disaggregation of montmorillonite particles.This can be explained by the ability of Fe-gel to aggregate the montmorillonite into pseudo-particles and retard the rigid-gel structure.However,extraction of this ferric amorphous compound by dithonite treatment recovers the surface properties of the montmorillonite samples.On the other hand,amounts and site occupation of Fe associated with kaolinite samples show a negative correlation with the parameters used to describe the degree of crystalline perfection,color,brightness and vitrification range of these kaolinite samples.

Distribution and influence of iron phases on the physico-chemical properties of phyllosilicates

Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD, DTA, dissolution analysis (DCB), IR, Mössbauer and X-band Electron Spin Resonance (ESR) spectroscopies. The purity of the samples and the degree of structural order were determined by XRD. The location of Fe in the octahedral sheet is characterized by absorption bands at ～875 cm^?1 assigned as Al-OH-Fe which is present after chemical dissolution of free iron. The Mössbauer spectra of these clays show two doublets with isomer shift and quadrupole splitting typical of octahedral coordinated Fe³⁺, in addition to third doubler with hyperfine parameter typical of Fe²⁺ in the spectra of Abu-Had kaolinite (H) sample. 6-lines magnetic hyperfine components which are consistent with those of hematite are confirmed in the spectra of both Isel and Rish kaolinite samples. Goethite was confirmed by both IR and DTA. Multiple nature of ESR of these clays suggested structural Fe in distorted octahedral symmetry and as non-structural Fe. Little dispersion and low swelling indices as well as incomplete activation of investigated montmorillonite samples by NaCO₃ appear to be due to incomplete disaggregation of montmorillonite particles. This can be explained by the ability of Fe-gel to aggregate the montmorillonite into pseudo-particles and retard the rigid-gel structure. However, extraction of this ferric amorphous compound by dithonite treatment recovers the surface properties of the montmorillonite samples. On the other hand, amounts and site occupation of Fe associated with kaolinite samples show a negative correlation with the parameters used to describe the degree of crystalline perfection, color, brightness and vitrification range of these kaolinite samples.