Quantitative Measurement of Paramagnetic Fe³⁺ in Kaolinite

Abstract

Abstract--A method is proposed to measure the absolute concentration of paramagnetic Fe 3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe 3+ signal is calibrated by calculating the powder EPR spectra of Fe 3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe 3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe 3+ ions and other iron species, such as Fe 3+ concentrated phases and Fe 2+ ions. The concentration of isolated structural Fe 3+ ranges between 200-3000 ppm and represents less than half of the total iron within kaolinite crystals.

Organic complexation and translocation of ferric iron in podzols of the Negro River watershed. Separation of secondary Fe species from Al species

“…We used a Fe-humic sample (T3: 2.85 g kg À1 diluted Fe III ; Weber et al, 2006) and a high defect kaolinite (FBT2: 1.25 g kg À1 diluted Fe III ; Balan et al, 2000), as standards to assess the concentration of diluted Fe III in organic and mineral phases, Fe III OM and Fe III K , respectively.…”

“…Distinct generations of kaolinites (Balan et al, 2007) and Fe-oxides (Fritsch et al, 2005) have been distinguished in lateritic profiles, underlying changes in weathering conditions. Molecular scale approaches also provide a direct assessment of diluted Fe III in kaolinites (Balan et al, 2000) or bound to organic complexes , and reveal the control of metallic ions on free radical concentration in humic acid-metal complexes (Jerzykiewicz et al, 2002).…”

Structural and Morphological Characterization of the PP-0559 Kaolinite from the Brazilian Amazon Region

“…17 The resonance line with g = 9.0 results from the so called 12Y, 1 ® 2 transition, between the energy levels 1 and 2, m s = -5/2 to m s = -3/2, in the y axis direction. The three lines with g-values of 5.0, 3.5 and 2.8 arise from the angular dependence of the spin transition inside the central doublet, m s = -1/2 (3) to m s = + ½ (4).…”

“…Those lines are due to absorptions of Fe 3+ in both Fe (I) and Fe (II) sites of kaolinites resulting from spin resonance arising from the three Kramer's doublets, whose energies are separated by crystal fields of rhombic symmetry. 17 Fe (I) and Fe (II) are two unequivalent crystal sites which Fe +3 can occupy in the octahedra in kaolinite.…”

Physical and chemical study of lattice kaolinites and their interaction with orthophosphate

“…Phosphate uptake was pH dependent with adsorption mechanisms on kaolinite and iron oxide surfaces dominant generally below pH 7 and precipitation by calcium ions dominant above pH 7. Maximum phosphate removal occurred at high pH values of 11.22 (97.1% Obviously, the presence of substituents alters the particle size and crystallinity and consequently the ionic adsorption capacity of the kaolinite (Balan et al 2000).…”