Surface Oxidation of Pyrite as a Function of pH

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• 作者：Pascale Bonnissel-Gissinger ; Marc Alnot ; Jean-Jacques Ehrhardt ; and Philippe Behra
• 刊名：Environmental Science & Technology
• 出版年：1998
• 出版时间：October 1, 1998
• 年：1998
• 卷：32
• 期：19
• 页码：2839 - 2845
• 全文大小：111K
• 年卷期：v.32,no.19(October 1, 1998)
• ISSN：1520-5851

文摘

Pyrite, the most abundant metal sulfide at the surface ofEarth, plays a key role in many processes such as acid minedrainage, redox cycling of metals at oxic-anoxic boundariesof lake bottom, and degradation of pollutants. Theoxidation of pyrite was studied in batch experiments overa large range of pH (2.5-12), with trace oxygen. Surfaceanalysis of the samples was performed using X-rayphotoelectron spectroscopy (XPS). Speciation of theaqueous species was investigated by inductively coupledplasma atomic emission spectrometry (ICP-AES), ionicchromatography, and UV-vis spectrophotometry. The pyritesurface can drastically change with the pH, which wasnever at steady state and tended to reach an acidic valuewhatever the initial pH. For pH <4, Fe(II) and SO₄^2-were released into solution; from XPS analyses, the pyritesurface presented O-H groups, an Fe-deficient compositionFe_1-xS₂, and iron(III) (hydr)oxide traces. Whatever the pH,the sulfur of the FeS₂ surface was mainly under the (-I)state oxidation. When the pH increased, Fe(II) disappearedand the surface was covered with iron(III) (hydr)oxides.This overlayer did not passivate the sample against furtheroxidation, and a decrease in pH was still observed.