Iron precipitate accumulations associated with waterways in drained coastal acid sulfate landscapes of eastern Australia

Iron precipitate accumulations from surface environments surrounding waterways (such as the side of drains and soil surface horizons) in acid sulfate soil landscapes were analysed for their mineralogy, micromorphology and chemical properties. Schwertmannite (Fe8(OH)5.5(SO4)1.25) was the dominant mineral in these accumulations. Goethite (α-FeOOH) was the other iron precipitate mineral identified in these accumulations and the data indicate that this iron mineral was formed from schwertmannite, often as pseudomorphs after schwertmannite. The schwertmannite in these accumulations had similar morphology and chemical properties to schwertmannite reported for environments affected by acid mine drainage. The activity of Fe3+ in the drainage waters in these landscapes appears to be controlled by schwertmannite during both low flow (dry season) and flood conditions. Iron precipitate accumulations contained appreciable amounts of stored acidity (i.e. titratable actual acidity of between 164 and 443 mol (H+) t–1, and 1900 to 2580 mol (H+) t–1 of schwertmannite upon complete conversion to goethite) that tends to buffer these waters to very acidic conditions (i.e. pHs ~3.0–3.5). The relationship between water quality (i.e. pH and sulfate concentration) and type of iron precipitate mineral formed should enable the mineralogy of the iron precipitates in these surface environments to be used to help identify the degree of severity of degradation in these acid sulfate soil landscapes and to monitor the effectiveness of remediation programmes.

[1]  N. Breemen.  Soil forming processes in acid sulphate soils , 1973 .

[2]  N. Breemen.  Genesis and solution chemistry of acid sulfate soils in Thailand , 1976 .

[3]  N. Breemen.  Genesis, Morphology, and Classification of Acid Sulfate Soils in Coastal Plains , 1982 .

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

[5]  R. Naidu,et al.  Iron deposits and microorganisms in saline sulfidic soils with altered soil water regimes in South Australia. , 1992 .

[6]  M. Melville,et al.  Control of soil acidification by fluvial sedimentation in an estuarine floodplain, eastern Australia , 1993 .

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

[8]  Melville,et al.  Acidification of an estuarine tributary in eastern Australia due to drainage of acid sulfate soils , 1996 .

[9]  Jerry M. Bigham,et al.  SCHWERTMANNITE AND THE CHEMICAL MODELING OF IRON IN ACID SULFATE WATERS , 1996 .

[10]  C. W. Childs,et al.  Natural and anthropogenic schwertmannites from Towada-Hachimantai National Park, Honshu, Japan , 1998 .

[11]  D. L. Parkhurst,et al.  User's guide to PHREEQC (Version 2)-a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations , 1999 .

[12]  B. Eyre,et al.  Behaviour of aluminium and iron in acid runoff from acid sulphate soils in the lower Richmond River catchment , 1999 .

[13]  U. Schwertmann,et al.  Color Identification of Iron Oxides and Hydroxysulfates , 1999 .

[14]  S. Peiffer,et al.  Electron flow in an iron‐rich acidic sediment—evidence for an acidity‐driven iron cycle , 2000 .

[15]  L. Fontboté,et al.  Element cycling and secondary mineralogy in porphyry copper tailings as a function of climate, primary mineralogy, and mineral processing , 2001 .

[16]  Jerry M. Bigham,et al.  Assessing mine drainage pH from the color and spectral reflectance of chemical precipitates , 2002 .

[17]  U. Schwertmann,et al.  Scavenging of As from acid mine drainage by schwertmannite and ferrihydrite: a comparison with synthetic analogues. , 2002, Environmental science & technology.

[18]  P. Rojík,et al.  Iron-rich precipitates in a mine drainage environment: Influence of pH on mineralogy , 2003 .

[19]  A. Brand,et al.  Formation and stability of schwertmannite in acidic mining lakes , 2004 .