Impact of sample preparation on mineralogical analysis of iron reactive barrier materials

Permeable reactive barriers (PRBs) of zero-valent iron (Fe0) are increasingly being used to remediate contaminated ground water. Corrosion of Fe0 filings and the formation of precipitates can occur when the PRB material comes in contact with ground water and may reduce the lifespan and effectiveness of the barrier. At present, there are no routine procedures for preparing and analyzing the mineral precipitates from Fe0 PRB material. These procedures are needed because mineralogical composition of corrosion products used to interpret the barrier processes can change with iron oxidation and sample preparation. The objectives of this study were (i) to investigate a method of preparing Fe0 reactive barrier material for mineralogical analysis by X-ray diffraction (XRD), and (ii) to identify Fe mineral phases and rates of transformations induced by different mineralogical preparation techniques. Materials from an in situ Fe0 PRB were collected by undisturbed coring and processed for XRD analysis after different times since sampling for three size fractions and by various drying treatments. We found that whole-sample preparation for analysis was necessary because mineral precipitates occurred within the PRB material in different size fractions of the samples. Green rusts quickly disappeared from acetone-dried samples and were not present in air-dried and oven-dried samples. Maghemite/magnetite content increased over time and in oven-dried samples, especially after heating to 105°C. We conclude that care must be taken during sample preparation of Fe0 PRB material, especially for detection of green rusts, to ensure accurate identification of minerals present within the barrier system.

Impact of sample preparation on mineralogical analysis of zero-valent iron reactive barrier materials

Permeable reactive barriers (PRBs) of zero-valent iron (Fe⁰) are increasingly being used to remediate contaminated ground water. Corrosion of Fe⁰ filings and tbe formation of precipitates can occur when the PRB material comes in contact with ground water and may reduce the lifespan and effectiveness of the barrier. At present, there are no routine procedures for preparing and analyzing the mineral precipitates from Fe⁰ PRB material. These procedures are needed because mineralogical composition of corrosion products used to interpret the barrier processes can change with iron oxidation and sample preparation. The objectives of this study were (i) to investigate a method of preparing Fe⁰ reactive barrier material for mineralogical analysis by X-ray diffraction (XRD), and (ii) to identify Fe mineral phases and rates of transformations induced by different mineralogical preparation techniques. Materials from an in situ Fe⁰ PRB were collected by undisturbed coring and processed for XRD analysis after different times since sampling for three size fractions and by various drying treatments. We found that whole-sample preparation for analysis was necessary because mineral precipitates occurred within the PRB material in different size fractions of the samples. Green rusts quickly disappeared from acetone-dried samples and were not present in air-dried and oven-dried samples Maghemite/magnetite content increased over time and in oven-dried samples, especially after heating to 105°C. We conclude that care must be taken during sample preparation of Fe⁰ PRB material, especially for detection of green rusts, to ensure accurate identification of minerals present within the barrier system.

An assessment of the earth pressure coefficient in overconsolidated clays

The determination of the earth pressure coefficient K 0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering. While the methods for evaluation of K 0 are reliable for normally consolidated soils, significant difficulties still exist in evaluating K 0 in overconsolidated clays, given that it is influenced by the stress history of the material, together with the age, structure, mineralogical composition and depositional environment. Indeed, some of these factors are responsible for the soil becoming anisotropic. The existing framework for prediction of K 0 in overconsolidated soils does not account for any influences caused by anisotropy. The work reported in this paper evaluates the validity of a revised relationship between K 0oc and OCR (overconsolidation ratio) using data obtained from laboratory investigations. The tests were performed on reconstituted and undisturbed samples of Belfast Upper Boulder Clay, London Clay and Gault Clay. Tests were also performed on reconstituted samples of kaolin. The values of K 0oc were determined using various approaches, including on-sample measurements. The results have confirmed that reliable predictions of K 0oc can be made using the proposed relationship.

Mineralogical and chemical characterization of some vermiculites from the mozambique belt of tanzania for agricultural use

Vermiculite minerals are locally available in the Mozambique Belt of Tanzania but are not currently commercially exploited. In part this may be due to lack of any precise characterization. This study was carried out as a first step to assess the suitability of these vermiculites for crop production by characterization of their mineralogical and chemical compositions. X-ray diffraction and scanning electron microscopy combined with an energydispersive X-ray system were used to establish the mineralogy. Electron microprobe analysis and inductively coupled plasma-mass spectrometry were used to study the chemical compositions and to identify any possible issues related to chemical composition that might affect their use if applied as soil conditioners. The samples were characterized as vermiculites and hydrobiotites with a wide variety of accessory minerals. Accessory minerals that might be of some concern are galena, fibrous amphiboles and sepiolite. The total levels of Ni in all vermiculites, and Cr in some, were also found to be high relative to common European standards and this might limit their potential as soil conditioners. It is clear that a field assessment of the bioavailability of various elements would be necessary before decisions relating to potential agricultural use could be made. © 2009 The Mineralogical Society.

Physico-geochemical and mineral composition of neem tree soils and relation to organic properties

The Neem tree, the oil of which has a long history of pesticide, fertilizer and medicinal use in India, has been studied extensively for its organic compounds. Here we present a physical, mineralogical and geochemical database resulting from the analyses of two Neem soil profiles (epipedons) in India. Neem tree derivatives are used in the manufacture of a variety of products, from anti-bacterial drugs and insecticides to fertilizers and animal feeds. A preliminary geochemical and mineralogical analysis of Neem soils is made to explore the potential for chemical links between Neem tree derivatives and soils. Physical soil characteristics, including colour, texture and clay mineralogy, suggest the two pedons formed under different hydrological regimes, and hence, are products of different leaching environments, one well-drained site, the other poorly drained. Geochemically, the two Neem soils exhibit similarities, with elevated concentrations of Th and rare earth elements. These elements are of interest because of their association with phosphates, especially monazite and apatite, and the potential link to fertilizer derivatives. Higher concentrations of trace elements in the soils may be linked to nutritional derivatives and to cell growth in the Neem tree.