摘要
Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD, DTA, dissolution analysis (DCB), IR, Mssbauer and X\|ray Electron Spin Resonance (ESR) spectroscopes. The purity of the samples and the degree of their 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 persist after chemical dissolution of free iron. The Mssbauer spectra of these clays show two doublets with isomer shift and quadrupole splitting typical of octahedrally coordinated Fe\+\{3+\}, in addition to third doublet with hyperfine parameter typical of Fe\+\{2+\} in the spectra of Abu\|Had kaolinite (H) sample. Six\|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 as well as non\|structural Fe.\; Little dispersion and low swelling indices as well as incomplete activation of the 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, the amount and site occupation of Fe associated with kaolinite samples show an inverse correlation with the parameters used to describe the degree of crystallinity 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, Mssbauer and X\|ray Electron Spin Resonance (ESR) spectroscopes. The purity of the samples and the degree of their 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 persist after chemical dissolution of free iron. The Mssbauer spectra of these clays show two doublets with isomer shift and quadrupole splitting typical of octahedrally coordinated Fe\+\{3+\}, in addition to third doublet with hyperfine parameter typical of Fe\+\{2+\} in the spectra of Abu\|Had kaolinite (H) sample. Six\|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 as well as non\|structural Fe.\; Little dispersion and low swelling indices as well as incomplete activation of the 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, the amount and site occupation of Fe associated with kaolinite samples show an inverse correlation with the parameters used to describe the degree of crystallinity perfection, color, brightness and vitrification range of these kaolinite samples.
关键词
白垩纪
粘土
铁相
矿物学
物理化学特征
光谱学
Cretaceous clay
iron phase
mineralogy
DCB treatment
spectroscopy
dispersion
crystallinity index
