Dissolution of Iron Minerals in a Sequential Extraction Optimised for use in Acid Sulfate Soils Sali

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Dissolution of Iron Minerals in a Sequential
Extraction Optimised for use in Acid Sulfate
SoilsSalirian Claff, Leigh Sullivan and Edward
Burton
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Acid Sulfate Soils - Features

• Acid Sulfate Soils contain pyrite
• Are stable under anoxic conditions
• They are often found in areas of
• agricultural or residential importance
• Oxidation leads to a number of negative
• environmental impacts

Pyrite framboids as seen under SEM
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Environmental Impacts

• Acidification of waterways
• Degradation of and terrestrial habitats
• Loss of agricultural productivity
• Corrosion of infrastructure
• Release of trace metals and other toxic elements
  into the environment

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Sequential Extractions
Total Metals a single extraction used.
Removes the metals bound to all geochemical
fractions Sequential Extraction a series of
reagents used to remove specific fractions
allowing a user to better understand mobility
and toxicity
total metals
organics
residual
oxides
adsorbed
carbonates
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Strengths and Limitations

• Strengths
• Ability to optimise method for specific soil type
  and particular mineral phases
• The sequential nature can improve the specificity
  of individual reagents
• Simple Risk Assessment tool
• Limitations
• Operationally defined
• Lack of specificity
• Metal readsorption and redistribution

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Extraction Overview

• Methodology
• 50ml reaction vessels
• 40ml reagent
• End over end shaking
• 10min centrifugation at 40000rpm
• Supernatant filtered and acidified

Sample following extraction and centrifugation
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Extraction Procedure
Extraction Steps
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Minerals

• 1. Akaganeite
• 2. Ferrihydrite
• 3. Goethite
• 4. Hematite
• 5. Jarosite
• 6. Magnetite
• 7. Pyrite
• 8. Schwertmannite

Mineral samples prepared for XRD analysis
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Results Magnesium Chloride
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Results Hydrochloric Acid
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Results Na-Pyrophosphate
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Results Citrate-Dithionite
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Results Nitric Acid
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Results Residuals
1. Akaganeite 2. Ferrihydrite 3. Goethite 4.
Hematite 5. Jarosite 6. Magnetite 7. Pyrite 8.
Schwertmannite
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Summary

• Aim
• To propose and optimise a sequential extraction
  scheme that is suitable for assessing metal
  mobility in acid sulfate soil bearing materials,
  in particular distinguishing between the organic
  and sulfidic phases
• Future Applications
• Assessment of metal fractionation under different
  management conditions (e.g. the CRC CARE National
  Acid Sulfate Soil Demonstration Site, East Trinity

Sample site at East Trinity, North Queensland.
Low pH and iron staining at the surface common in
actual acid sulfate soils