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This article in JEQ

  1. Vol. 32 No. 4, p. 1299-1305
     
    Received: Mar 11, 2002


    * Corresponding author(s): dhphillips2003@yahoo.com
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doi:10.2134/jeq2003.1299

Impact of Sample Preparation on Mineralogical Analysis of Zero-Valent Iron Reactive Barrier Materials

  1. D. H. Phillips *,
  2. B. Gu,
  3. D. B. Watson and
  4. Y. Roh
  1. Environmental Sciences Division, Oak Ridge National Lab., P.O. Box 2008, Oak Ridge, TN 37831

Abstract

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.

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Copyright © 2003. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.32:1299–1305.