Acidity fractions in acid sulfate soils and sediments : Contributions of schwertmannite and jarosite
- Authors: Vithana, Chamindra , Sullivan, Leigh , Bush, Richard , Burton, Edward
- Date: 2013
- Type: Text , Journal article
- Relation: Soil Research Vol. 51, no. 3 (2013), p. 203-214
- Full Text: false
- Reviewed:
- Description: In Australia, the assessment of acidity hazard in acid sulfate soils requires the estimation of operationally defined acidity fractions such as actual acidity, potential sulfidic acidity, and retained acidity. Acid-base accounting approaches in Australia use these acidity fractions to estimate the net acidity of acid sulfate soils materials. Retained acidity is the acidity stored in the secondary Fe/Al hydroxy sulfate minerals, such as jarosite, natrojarosite, schwertmannite, and basaluminite. Retained acidity is usually measured as either net acid-soluble sulfur (SNAS) or residual acid soluble sulfur (SRAS). In the present study, contributions of schwertmannite and jarosite to the retained acidity, actual acidity, and potential sulfidic acidity fractions were systematically evaluated using S NAS and SRAS techniques. The data show that schwertmannite contributed considerably to the actual acidity fraction and that it does not contribute solely to the retained acidity fraction as has been previously conceptualised. As a consequence, SNAS values greatly underestimated the schwertmannite content. For soil samples in which jarosite is the only mineral present, a better estimate of the added jarosite content can be obtained by using a correction factor of 2 to SNAS values to account for the observed 50-60% recovery. Further work on a broader range of jarosite samples is needed to determine whether this correction factor has broad applicability. The SRAS was unable to reliably quantify either the schwertmannite or the jarosite content and, therefore, is not suitable for quantification of the retained acidity fraction. Potential sulfidic acidity in acid sulfate soils is conceptually derived from reduced inorganic sulfur minerals and has been estimated by the peroxide oxidation approach, which is used to derive the S RAS values. However, both schwertmannite and jarosite contributed to the peroxide-oxidisable sulfur fraction, implying a major potential interference by those two minerals to the determination of potential sulfidic acidity in acid sulfate soils through the peroxide oxidation approach. © 2013 CSIRO.
Schwertmannite in soil materials : Limits of detection of acidified ammonium oxalate method and differential X-ray diffraction
- Authors: Vithana, Chamindra , Sullivan, Leigh , Bush, Richard , Burton, Edward
- Date: 2015
- Type: Text , Journal article
- Relation: Geoderma Vol. 249-250, no. (2015), p. 51-60
- Full Text: false
- Reviewed:
- Description: Schwertmannite is a secondary iron mineral, found in acid mine drainage (AMD) and acid sulfate soils (ASS), that generates acidity when it transforms to stable mineral phases. Acidity liberated during schwertmannite transformation can seriously diminish water quality and soil health. Acidified ammonium oxalate (AAO) extraction in the dark coupled with differential X-ray diffraction (DXRD) analysis is routinely used to identify and to quantify poorly crystalline iron oxide phases such as schwertmannite in AMD environments. However, management of ASS environments is largely impacted due to lack of reliable methods to identify/quantify schwertmannite in soil materials. Our study aimed to evaluate the 15. min AAO extraction method to identify/quantify schwertmannite in soil materials. We extracted soil samples spiked with synthetic and natural schwertmannite (termed as natural organic rich schwertmannitic material) with acidified ammonium oxalate (AAO) for 15. min. We also examined soil samples spiked with schwertmannite through the DXRD analysis under ideal conditions assuming that only schwertmannite would dissolve during the extraction. Our data show that synthetic schwertmannite dissolved partially during the 15. min AAO extraction and as a result the recovered Fe content from schwertmannite-spiked soils was underestimated by ~. 20%. The data also show that soil materials could also influence the recovery of schwertmannite. Fe/S molar ratios of schwertmannite spiked at higher rates (2% and 5%) were closer to the expected ratios. In addition to schwertmannite, goethite and other unidentified minerals in natural organic rich schwertmannitic material also dissolved during the 15. min extraction time. The DXRD analysis data show that schwertmannite in soil materials at contents >. 5% may be identifiable through this approach. Our findings highlight that both the 15. min AAO extraction procedure and the DXRD analysis have limited applicability towards detecting schwertmannite accurately in soil materials. © 2015 Elsevier B.V.
Jarosite quantification in soils : An enhanced sequential extraction procedure
- Authors: Vithana, Chamindra , Sullivan, Leigh , Bush, Richard , Burton, Edward
- Date: 2014
- Type: Text , Journal article
- Relation: Applied Geochemistry Vol. 51, no. (2014), p. 130-138
- Full Text: false
- Reviewed:
- Description: A two-step sequential extraction procedure established for the quantification of acidity producing ferric and ferrous sulfate minerals such as melanterite and jarosite in acid mine wastes was evaluated for quantification of jarosite spiked in soils. The procedure involves in sequence anoxic water extraction, roasting the solid residue after anoxic water extraction at 550. °C for 1. h, and 4. M HCl extraction of the roasted solid. Soil and quartz samples were spiked with known amounts of synthetic and natural jarosite and their recovery was measured using the suggested two-step sequential extraction procedure. The recoveries of synthetic and natural jarosite were calculated on the basis of the S contents of the initially spiked jarosite in soil and quartz samples. Less than 50% of the spiked jarosite was recovered. The missing S is partially attributable to the retention of jarosite by the Teflon filter membrane used during the filtration of the anoxic water extract. Further investigations also demonstrated a lower 4. M HCl-S extractability from jarosite samples roasted at 550. °C than those roasted at 450. °C. S recovery from jarosite-spiked quartz samples increased to 45-70% by replacing the Teflon filter membrane with the Cellulose Acetate filter membrane and including this filter paper in the second step roasting. This modified method is a step forward in the development of methods to accurately and reliably quantify jarosite in soil materials. © 2014 Elsevier Ltd.
Stability of schwertmannite and jarosite in an acidic landscape : Prolonged field incubation
- Authors: Vithana, Chamindra , Sullivan, Leigh , Burton, Edward , Bush, Richard
- Date: 2015
- Type: Text , Journal article
- Relation: Geoderma Vol. 239, no. (2015), p. 47-57
- Full Text: false
- Reviewed:
- Description: Schwertmannite and jarosite are two of the main secondary iron(III) minerals commonly found in acidic, iron and sulfate-rich environments such as acid mine drainage and coastal acid sulfate soils (CASS). Both minerals exert major influence on the water and soil quality in these environments. While there are many studies conducted on the stability of these two minerals under controlled laboratory conditions, the behaviour of schwertmannite and jarosite under field conditions and the factors influencing their behaviour have not been investigated directly. In the present study, we examined the net transformation of introduced schwertmannite and jarosite samples incubated in a typical acidic CASS environment. Pure (synthetic) schwertmannite and jarosite samples were exposed to two main chemical regimes: 1) aerobic-acidic water column and 2) anaerobic-neutral sediment in a CASS environment. Changes in mineralogy, micromorphology, and composition of schwertmannite and jarosite samples were monitored over a period of 12months. Schwertmannite suspended in the water column and buried in sediments transformed to goethite by the end of 12months but more quickly in anoxic, reducing sediments. However, schwertmannite incubated in the acidic water column transformed at a much faster rate than those reported for acidic and aerobic conditions in the laboratory. Jarosite incubated in both the water column and sediments was also transformed to goethite but at a much slower rate than schwertmannite. Dissimilatory microbial reduction and Fe2+-catalysed transformation likely played a major role in accelerating the transformation of both minerals to goethite in sediments. The transformation of both minerals in the water column was sensitive to the hydrological conditions and fluctuations in the water column in relation to antecedent rainfall. In comparison, the sediment's geochemistry was relatively stable and consequently the rate of transformation and dissolution of both schwertmannite and jarosite in this environment was not appreciably affected by variable hydrology. © 2014 Elsevier B.V.
Effect of schwertmannite and jarosite on the formation of hypoxic blackwater during inundation of grass material
- Authors: Vithana, Chamindra , Sullivan, Leigh , Shepherd, Troy
- Date: 2017
- Type: Text , Journal article
- Relation: Water Research Vol. 124, no. (2017), p. 1-10
- Full Text: false
- Reviewed:
- Description: This study focused on understanding the effect of schwertmannite and jarosite, commonly found in floodplains containing acid sulfate soil materials, on the characteristics of the hypoxic blackwaters that can form when floodplain vegetation experiences prolonged inundation. The formation of these ‘blackwaters’ was simulated in the laboratory by inundating flood-intolerant pasture grass leaf material in both the presence of schwertmannite/jarosite (schwertmannite and jarosite treatments) minerals and their absence (control treatment) at 27.5 °C for 32 days. The presence of either schwertmannite or jarosite was able to decrease the concentrations of DOC, nutrients (e.g. NH3 and PO4 3−) and the biological oxygen demand (BOD) in the incubating water compared to the control treatment. Being fresh and labile, the pasture grass material liberated DOC immediately following inundation with a concomitant decrease in dissolved O2 thereby resulting in anoxic and reducing conditions in the incubating water. With the onset of anoxic and reducing conditions, the biogeochemical cycling of DOC in schwertmannite and jarosite treatments might have proceeded via microbially mediated iron(III) and sulfate reduction and electron shuttling processes. Under anoxic, slightly acidic conditions, microbially mediated iron(III) reduction and subsequent dissolution of schwertmannite and jarosite were triggered by liberating Fe2+, SO4 2− and alkalinity to the incubating water. The resultant increase in pH led to SO4 2− reduction in schwertmannite, and the Fe2+ catalysed transformation of both schwertmannite and jarosite to goethite. Schwertmannite almost completely transformed to goethite within two weeks of incubation. Iron(III) in goethite (formed from schwertmannie transformation) was also reduced and likely proceeded via direct microbial reduction or via electron shuttling using the humic acids in the incubating water derived from pasture grass. These findings are highly useful in managing the coastal low lying acid sulfate soils landscapes which are subject to frequent flooding during wet seasons. © 2017 Elsevier Ltd
Liberation of acidity and arsenic from schwertmannite : Effect of fulvic acid
- Authors: Vithana, Chamindra , Sullivan, Leigh , Burton, Edward , Bush, Richard
- Date: 2014
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 372, no. (2014), p. 1-11
- Full Text: false
- Reviewed:
- Description: Schwertmannite is one of the major components that produces acidity in acid mine drainage (AMD) and acid sulfate soils (ASS) and is also known to be an effective scavenger of Arsenic (As) in such environments. Fulvic acid (FA) is an active component of natural organic matter (NOM) and is known to interact strongly with both schwertmannite and As. Two main environmental hazards related to schwertmannite are acidity liberation and potential re-mobilization of adsorbed or co-precipitated As upon hydrolysis. This study focused on understanding the behaviour of As-substituted schwertmannite with regard to the potential of acidity liberation, the effect of FA on acidity liberation from both pure and As-substituted synthetic schwertmannites, and the effect of FA on arsenic mobilization from As-substituted synthetic schwertmannite. This was investigated by means of short-term (48. h) titrations. The liberation of acidity from As-substituted schwertmannite and the effect of FA were examined at two pH values (i.e. 4.5 and 6.5) typical for ASS environments.As-substituted schwertmannite liberated a greater amount of acidity in comparison to pure schwertmannite at both pHs. Concentration of FA and pH each showed a strong influence on the liberation of acidity from both pure and As-schwertmannite. At the acidic pH (4.5), FA inhibited acidity liberation from schwertmannite. At the near neutral pH of 6.5, the concentration of FA played a critical role in affecting the liberation of acidity from schwertmannite. The initial liberation of acidity was enhanced from pure schwertmannite at pH6.5 by low FA concentration (1mgL-1) and from As-schwertmannite by both low (1mgL-1) and moderate (10mgL-1) FA concentrations. Interestingly, higher FA concentrations (25mgL-1) inhibited acidity liberation from both types of schwertmannite in comparison to the control (pure/As-schwertmannite titrated without added FA). FA enhanced the liberation of As from the As-schwertmannite at both pHs under oxidising conditions and the rate of As liberation was greater at the near neutral pH. The present study provides new insights on the effect of As-substitution on acidity liberation from schwertmannite and the role of FA on: a) liberation of acidity, and b) As mobilization, from schwertmannite. © 2014.