Transition Metals in Llano Vermiculite Samples: An EPR Study

Abstract

Abstract--Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(IV), Fe(llI), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 ~ The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 ~

Determination of chromium valence over the range Cr(0)–Cr(VI) by electron energy loss spectroscopy

“…In contrast, most water soluble Cr(III) electron spin resonance (ESR)). spectroscopy [42,53,54], highspecies do not occur naturally and are unstable in the field (HF)-EPR spectroscopy (for integer-spin "EPR-silent" environment [25]. Only under very acidic (pH < 5) or very transition metals) [55], Auger electron spectroscopy (AES) basic (14 <pH) conditions will Cr(III) exhibit solubility [56], and M6ssbauer spectroscopy [57].…”

The fate of structure-bound Mn2+during the decomposition of dolomite and in the resulting conversion products: An EPR study

“…This approach is based on the assumption that different chemical forms or different mineral phases of a multimineral system differ in their thermal and/or chemical stability. Schosseler and Gehring (1996) expanded this approach by using pulsed EPR techniques to support the assignment of paramagnetic species. The purpose of the present research is to analyze the fate of Mn 2+ in natural dolomite during thermal decomposition and in the resulting conversion products.…”

An EPR Study on the Chemical form of Mn2+in the Chinese Loess Samples

“…Electron paramagnetic resonance (EPR) spectroscopy is an analytical tool for identification and characterization of paramagnetic cations such as: Mnz+, Fe3+ and V4+ in natural systems, and is often used to investigate their behavior during the weathering and pedogenesis (10,13). In addition to its high sensitivity, needed for investigating elements which are highly diluted in natural systems, EPR gives a detailed description of the cation surroundings, including site geometry and ligandcation bond covalency.…”