HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Dermatas, D. Articles by Grubb, D. G. Search for Related Content PubMed PubMed Citation Articles by Dermatas, D. Articles by Grubb, D. G. GeoRef GeoRef Citation Agricola Articles by Dermatas, D. Articles by Grubb, D. G. Related Collections Heavy Metals Experiment Design Soil Analysis

TECHNICAL REPORTS

Heavy Metals in the Environment

Influence of X-Ray Diffraction Sample Preparation on Quantitative Mineralogy

Implications for Chromate Waste Treatment

W.M. Keck Geoenvironmental Lab., Castle Point on Hudson, Stevens Inst. of Technology, Hoboken, NJ 07030, USA

^* Corresponding author (mchrysoc{at}stevens.edu)

Received for publication June 1, 2006. Powders of chromite ore processing residue (COPR) were mineralogically evaluated using quantitative X-ray powder diffraction (XRPD) to illustrate the impacts of sample preparation procedures. Chromite ore processing residue is strongly alkaline, reactive, contains minerals of varying hardness and absorption coefficients, and exhibits significant amorphicity. This poses a challenge to produce powders for XRPD analysis that are sufficiently fine and of uniform particle size while avoiding mineral reactions and overgrinding effects. Dry, hand pulverization to different grain sizes, and wet, mechanical pulverization (micromilling) using four milling liquids (cyclohexane, isopropanol, ethanol, and water), and variable milling durations (up to 15 min) were evaluated. Micromilling with a light, nonpolar, highly evaporative liquid such as cyclohexane with a milling time of 5 min mitigated systematic errors such as microabsorption and preferred orientation as it produced finer and more uniform particle size distributions than the hand-pulverized powders, while simultaneously affording the least time for sample preparation. Conversely, the use of water as milling liquid resulted in extensive hydration reactions during sample preparation, causing mischaracterization and significant underestimation of its reactive brownmillerite content, which can complicate the remediation design process for COPR. Hand pulverization emerged as a necessary complement to quantify Cr(VI)-containing, softer minerals destroyed during mechanical milling, the quantification of which has also important implications for COPR treatment design. The findings of this study may be applicable in a variety of geochemically complicated and reactive environmental media (metal-contaminated soils, stabilized/solidified media, inorganic waste), and points to the importance of the sample preparation method to obtain reliable quantitative XRPD results.

Abbreviations: COPR, chromite ore processing residue • XRPD, X-ray powder diffraction • RQA, Rietveld quantification analysis • MA, microabsorption • PO, preferred orientation • SEM, scanning electron microscopy