Stability of Silicate Coatings on Pyrite Surfaces in a Low pH Environment
Publication: Journal of Environmental Engineering
Volume 131, Issue 9
Abstract
The suppression of pyrite oxidation due to the formation of stable coatings of –silica and/or –hydroxy–silica complexes over pyrite surfaces in near-neutral and neutral solution pHs is well documented. On the contrary, there is currently no convincing experimental evidence that proves the existence of such a coating under low pH environments. Aqueous continuous flow kinetic experiments were conducted using coating solutions containing and at pH 6, 4, 3, and 2. Results showed that at pH 2, pyrite oxidation in the presence of silica is pseudofirst order and oxidation is not inhibited by silica. At pH 6, silica significantly reduced pyrite oxidation via a pseudofirst-order reaction that takes on several stages related to changes in the relative contributions of and . Iron speciation data suggests a surface adsorption mechanism at pH 6 and an electrochemical mechanism at pH 2 for pyrite oxidation. Scanning electron microscopy and energy dispersive x-ray spectroscopy also support the kinetic model and showed the absence of any significant silica coating at pH 2.
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Acknowledgments
This work is sponsored in part by a grant from the United States Environmental Protection Agency (USEPA). The writers wish to thank the many individuals who helped with the experimental setup, analysis of the data, and review of the manuscript. Dr. Daniel Strongin of the Chemistry Department provided very useful comments and made available to them his many laboratory resources, without which this paper may not have been possible. Also any mention of trade names is for identification purposes only and does not imply endorsement by the writers or the USEPA.
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© 2005 ASCE.
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Received: May 20, 2004
Accepted: Dec 22, 2004
Published online: Sep 1, 2005
Published in print: Sep 2005
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