SCHWERTMANNITE AND THE CHEMICAL MODELING OF IRON IN ACID SULFATE WATERS

Abstract Analyses of ochreous sediments and associated solutions from twenty-eight mine drainage sites showed that precipitates formed at pH 6.5 or higher were composed of ferrihydrite (nominally Fe5HO8 · 4H2O) or a mixture of ferrihydrite and goethite (α-FeOOH), whereas those precipitated from waters having pH values in the range of 2.8 to 4.5 were predominantly schwertmannite (ideally Fe8O8(OH)6SO4) with trace to minor amounts of goethite. Solutions of intermediate pH values produced mixtures of ferrihydrite and schwertmannite. Only one sample, formed at pH 2.6, contained a significant amount of jarosite (H, K, Na)Fe3(OH)6(SO4)2. A solubility window of log IAPSh = 18.0 ± 2.5 was calculated for schwertmannite from selected mine drainage solutions with pH values in the range of 2.8 to 3.2. The relationship between pH and log αFe3 over the full range of drainage waters was consistent with published results from other sources, and the combined mineralogy-chemistry data were used to compute a new pe-pH diagram for the system FeSKOH that included a field of metastability for schwertmannite. The metastable nature of schwertmannite was confirmed in a long-term (1739 d) aqueous equilibrium study wherein a pure, synthetic specimen was completely transformed to goethite over a period of 543 days. The pH and computed activity of Fe 3+ in the final equilibrium solutions yielded a log KGT = 1.40 ± 0.01 for goethite. Additional field data supporting a paragenetic relationship between jarosite, schwertmannite, ferrihydrite, and goethite were obtained from a naturally acid alpine stream. Similar results were predicted from the water chemistry using a nonequilibrium reaction path model that included appropriate solubility data for the mineral phases of interest.

[1]  N. Breemen,et al.  Translocation of Iron In Acid Sulfate Soils: I. Soil Morphology, and the Chemistry and Mineralogy of Iron in a Chronosequence of Acid Sulfate Soils1 , 1975 .

[2]  J. Dixon,et al.  Minerals in soil environments , 1990 .

[3]  M. Fishman,et al.  Methods for determination of inorganic substances in water and fluvial sediments , 1989 .

[4]  A. E. Greenberg,et al.  Standard methods for the examination of water and wastewater : supplement to the sixteenth edition , 1988 .

[5]  E. Murad,et al.  Schwertmannite, a new iron oxyhydroxysulphate from Pyhäsalmi, Finland, and other localities , 1994, Mineralogical Magazine.

[6]  W. Lindsay.  Chemical equilibria in soils , 1979 .

[7]  William L. Bourcier,et al.  Current status of the EQ3/ 6 software package for geochemical modeling , 1990 .

[8]  Udo Schwertmann,et al.  A poorly crystallized oxyhydroxysulfate of iron formed by bacterial oxidation of Fe(II) in acid mine waters , 1990 .

[9]  K. Bencala,et al.  Reactive iron transport in an acidic mountain stream in Summit County, Colorado: A hydrologic perspective , 1989 .

[10]  U. Schwertmann,et al.  Mineralogy of precipitates formed by the biogeochemical oxidation of Fe(II) in mine drainage , 1992 .

[11]  D. Nahon,et al.  Geochemistry of laterites, stability of Al-goethite, Al-hematite, and Fe (super 3+) -kaolinite in bauxites and ferricretes; an approach to the mechanism of concretion formation , 1985 .

[12]  Jerry M. Bigham,et al.  Influence of pH on mineral speciation in a bioreactor simulating acid mine drainage , 1996 .

[13]  J. W. Ball,et al.  Final revised analyses of major and trace elements from acid mine waters in the Leviathan Mine drainage basin, California and Nevada; October 1981 to October 1982 , 1989 .

[14]  P. K. Theobald,et al.  The precipitation of aluminum, iron and manganese at the junction of Deer Creek with the Snake River in Summit County, Colorado , 1963 .

[15]  J. Brown.  Jarosite-geoethite stabilities at 25 °C, 1 ATM , 1971 .

[16]  J. Jambor.  Mineralogy of sulfide-rich tailings and their oxidation products , 1994 .

[17]  W. Feitknecht,et al.  Die Ermittlung der Löslichkeit von Eisen(III)‐hydroxiden mit 59Fe I Fällungs‐ und Auflösungsversuche , 1961 .

[18]  E. Teller,et al.  ADSORPTION OF GASES IN MULTIMOLECULAR LAYERS , 1938 .

[19]  Charles N. Alpers,et al.  Solubility of jarosite solid solutions precipitated from acid mine waters, Iron Mountain, California, U.S.A. Solubilité des solutions solides de jarosite précipitées à partir des eaux minières acides, Iron Mountain, Californie, U. S. A , 1989 .

[20]  U. Schwertmann,et al.  The first occurrence of schwertmannite in a natural stream environment , 1995 .

[21]  D. Jones,et al.  Processes controlling metal ion attenuation in acid mine drainage streams , 1983 .

[22]  L. E. Fox,et al.  The solubility of colloidal ferric hydroxide and its relevance to iron concentrations in river water , 1988 .

[23]  David L. Parkhurst,et al.  Revised chemical equilibrium data for major water-mineral reactions and their limitations , 1990 .

[24]  Jerry M. Bigham,et al.  CHEMICAL COMPOSITION OF OCHREOUS PRECIPITATES FROM OHIO COAL MINE DRAINAGE , 1991 .