摘要
Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD, DTA, dissolution analysis (DCB), IR, M*issbauer 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 M*issbauer spectra of these clays show 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 octahedral symmetry and as non-structural Fe. Little dispersion and low swelling indices as well as incomplete activation of investigated montmorillonite samples by NaCO\-3 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.
Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD, DTA, dissolution analysis (DCB), IR, M*issbauer 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 M*issbauer spectra of these clays show 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 octahedral symmetry and as non-structural Fe. Little dispersion and low swelling indices as well as incomplete activation of investigated montmorillonite samples by NaCO\-3 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.
关键词
白垩纪
铁相
矿物学
物理化学性质
光谱学
结晶度
页硅酸盐矿物
Cretaceous clay
iron phase
mineralogy
DCB treatment
spectroscopy
dispersation
crystallinity index
