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Environmental Health - Toxic Substances

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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A

Table of Contents

A Flow-Through Cell for in situ, Real Time X-ray Absorption Spectroscopy Studies of Geochemical Reactions

By John E. Villinski, Peggy A. O'Day, Tim L. Corley and Martha H. Conklin

This report is available in pdf format: pdf Villinski.pdf 227KB

ABSTRACT

The contact of acid mine waste with mineral surfaces can result in a series of complex geochemical reactions, including mineral precipitation and dissolution, which are often kinetically controlled proceses. One problem in formulating rate expressions for dissolution/precipitation reactions is that intermediate species are often formed. Identification of these species can lead to more accurate models, and hence, better predictions of the fate of the various chemical species. The use of spectroscopic probes to directly identify chemical species often requires high vacuum, which can induce modifications in surfaces and surface species. Synchrotron X-ray absorption spectroscopy is an element-specific method which can be used to probe samples in an aqueous environment. We developed a flow-through reaction cell for use at the Stanford Synchrotron Radiation Laboratory (SSRL), Stanford CA, that allowed for spectroscopic probing of minerals undergoing precipitation or dissolution reactions. This cell, coupled with X-ray absorption near-edge structure (XANES) spectroscopy, allowed us to detect the changes in elemental speciation of manganese during the reductive dissolution of MnO2 by Fe(II). The use of this flow-through reaction cell will allow for the coupling of spectroscopic measurements of elemental oxidation states with conventional rate measurements.

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