Accumulation of sulfidic sediments in a channelised inland river system, southern Australia
- Authors: Wong, Vanessa , Cheetham, Michael , Bush, Richard , Sullivan, Leigh , Ward, Nicholas
- Date: 2016
- Type: Text , Journal article
- Relation: Marine and Freshwater Research Vol. 67, no. 11 (2016), p. 1655-1666
- Full Text: false
- Reviewed:
- Description: Accumulation of sulfidic sediments in freshwater environments is a relatively recent phenomenon and an emerging environmental issue. In the present study, benthic sediments along short (
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.
Anthropogenic forcing of estuarine hypoxic events in sub-tropical catchments : Landscape drivers and biogeochemical processes
- Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Bush, Richard , Sullivan, Leigh , Slavich, Peter
- Date: 2011
- Type: Text , Journal article
- Relation: Science of the Total Environment Vol. 409, no. 24 (2011), p. 5368-5375
- Full Text: false
- Reviewed:
- Description: Episodic hypoxic events can occur following summer floods in sub-tropical estuaries of eastern Australia. These events can cause deoxygenation of waterways and extensive fish mortality. Here, we present a conceptual model that links key landscape drivers and biogeochemical processes which contribute to post-flood hypoxic events. The model provides a framework for examining the nature of anthropogenic forcing. Modification of estuarine floodplain surface hydrology through the construction of extensive drainage networks emerges as a major contributing factor to increasing the frequency, magnitude and duration of hypoxic events. Forcing occurs in two main ways. Firstly, artificial drainage of backswamp wetlands initiates drier conditions which cause a shift in vegetation assemblages from wetland-dominant species to dryland-dominant species. These species, which currently dominate the floodplain, are largely intolerant of inundation and provide abundant labile substrate for decomposition following flood events. Decomposition of this labile carbon pool consumes oxygen in the overlying floodwaters, and results in anoxic conditions and waters with excess deoxygenation potential (DOP). Carbon metabolism can be strongly coupled with microbially-mediated reduction of accumulated Fe and Mn oxides, phases which are common on these coastal floodplain landscapes. Secondly, artificial drainage enhances discharge rates during the flood recession phase. Drains transport deoxygenated high DOP floodwaters rapidly from backswamp wetlands to the main river channel to further consume oxygen. This process effectively displaces the natural carbon metabolism processes from floodplain wetlands to the main channel. Management options to reduce the impacts of post-flood hypoxia include i) remodifying drainage on the floodplain to promote wetter conditions, thereby shifting vegetation assemblages towards inundation-tolerant species, and ii) strategic retention of floodwaters in the backswamp wetlands to reduce the volume and rate during the critical post-flood recession phase. © 2011 Elsevier B.V.
Arsenic effects and behavior in association with the fe(II)-catalyzed transformation of schwertmannite
- Authors: Burton, Edward , Johnston, Scott , Watling, Kym , Bush, Richard , Keene, Annabelle , Sullivan, Leigh
- Date: 2010
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 44, no. 6 (2010), p. 2016-2021
- Full Text: false
- Reviewed:
- Description: In acid-mine drainage and acid-sulfate soil environments, the cycling of Fe and As are often linked to the formation and fate of schwertmannite(Fe 8O8(OH)8-2x(SO4)x).When schwertmanniterich material is subjected to near-neutral Fe(III)-reducing conditions (e.g., in reflooded acid-sulfate soils or mining-lake sediments), the resulting Fe(II) can catalyze transformation of schwertmannite to goethite. This work examines the effects of arsenic(V) and arsenic(III) on the Fe(II)-catalyzed transformation of schwertmannite and investigates the associated consequences of this mineral transformation for arsenic mobilization. A series of 9-day anoxic transformation experiments were conducted with synthetic schwertmannite and various additions of Fe(II), As(III), and As(V). X-ray diffraction (XRD) and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy demonstrated that, in the absence of Fe(II), schwertmannite persisted as the dominant mineral phase. Under arsenic-free conditions, 10 mM Fe(II) catalyzed rapid and complete transformation of schwertmannite to goethite. However, the magnitude of Fe(II)-catalyzed transformation decreased to 72% in the presence of 1 mM As(III) and to only 6% in the presence of 1mM As(V). This partial Fe(II)-catalyzed transformation of As(III)-sorbed schwertmannite did not cause considerable As(III) desorption. In contrast, the formation of goethite via partial transformation of As(III)- and As(V)-sorbed schwertmannite significantly decreased arsenic mobilization under Fe(III)-reducing conditions. This implies that the Fe(II)-catalyzed transformation of schwertmannite to goethite may help to stabilize solid-phase arsenic and retard its subsequent release to groundwater. © 2010 American Chemical Society.
Arsenic mobilization in a seawater inundated acid sulfate soil
- Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh , McElnea, Angus , Ahern, Col , Smith, C. Douglas , Powell, Bernard , Hocking, Rosalie
- Date: 2010
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 44, no. 6 (2010), p. 1968-1973
- Full Text:
- Reviewed:
- Description: Tidal seawater inundation of coastal acid sulfate soils can generate Fe- and SO4-reducing conditions in previously oxicacidic sediments, This creates potential for mobilization of As during the redox transition. We explore the consequences for As by investigating the hydrology, porewater geochemistry, solid-phase speciation, and mineralogical partitioning of As across two tidal fringe toposequences. Seawater inundation induced a tidally controlled redox gradient. Maximum porewater As (∼400μg/L) occurred in the shallow (<1 m), intertidal, redox transition zone between Fe-oxidizing and SO 4-reducing conditions. Primary mechanisms of As mobilization include the reduction of solid-phase As(V) to As(III), reductive dissolution of As(V)-bearing secondary Fe(III) minerals and competitive anion desorption. Porewater As concentrations decreased in the zone of contemporary pyrite reformation, Oscillating hydraulic gradients caused by tidal pumping promote upward advection of As and Fe2+-enriched porewater in the intertidal zone, leading to accumulation of As(V)-enriched Fe(III) (hydr)oxides at the oxic sediment-water interface. While this provides a natural reactive-Fe barrier, it does not completely retard the flux of porewater As to overtopping surface waters. Furthermore, the accumulated Fe minerals may be prone to future reductive dissolution, A conceptual model describing As hydro-geochemical coupling across an intertidal fringe is presented. © 2010 American Chemical Society.
Decoupling between water column oxygenation and benthic phosphate dynamics in a shallow eutrophic estuary
- Authors: Kraal, Peter , Burton, Edward , Rose, Andrew , Cheetham, Michael , Bush, Richard , Sullivan, Leigh
- Date: 2013
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 47, no. 7 (2013), p. 3114-3121
- Full Text: false
- Reviewed:
- Description: Estuaries are crucial biogeochemical filters at the land-ocean interface that are strongly impacted by anthropogenic nutrient inputs. Here, we investigate benthic nitrogen (N) and phosphorus (P) dynamics in relation to physicochemical surface sediment properties and bottom water mixing in the shallow, eutrophic Peel-Harvey Estuary. Our results show the strong dependence of sedimentary P release on Fe and S redox cycling. The estuary contains surface sediments that are strongly reducing and act as net P source, despite physical sediment mixing under an oxygenated water column. This decoupling between water column oxygenation and benthic P dynamics is of great importance to understand the evolution of nutrient dynamics in marine systems in response to increasing nutrient loadings. In addition, the findings show that the relationship between P burial efficiency and bottom water oxygenation depends on local conditions; sediment properties rather than oxygen availability may control benthic P recycling. Overall, our results illustrate the complex response of an estuary to environmental change because of interacting physical and biogeochemical processes. © 2013 American Chemical Society.
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
Iron and arsenic cycling in intertidal surface sediments during wetland remediation
- Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh
- Date: 2011
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 45, no. 6 (2011), p. 2179-2185
- Full Text: false
- Reviewed:
- Description: The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe 2+ (32 mmol L -1) and As (1.81 μmol L -1) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe 2+ oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2-3), accompanied by oxidation of remaining Fe 2+. This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands. © 2011 American Chemical Society.
Iron-monosulfide oxidation in natural sediments : Resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions
- Authors: Burton, Edward , Bush, Richard , Sullivan, Leigh , Hocking, Rosalie , Mitchell, David , Johnston, Scott , Fitzpatrick, Rob W. , Raven, Mark , McClure, Stuart , Jang, Lingyun
- Date: 2009
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 43, no. 9 (2009), p. 3128-3134
- Full Text: false
- Reviewed:
- Description: Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 μ mol g-1), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an O 2 partial pressure of ∼0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 ± 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S0 8) was a key intermediate S oxidation product. Transmission electron microscopy showed the S0 8 to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S0 8 was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S0 8 particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S0 8 SO4 2- was madiated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here. © 2009 American Chemical Society.
Iron-sulfide and trace element behaviour in sediments of Coombabah Lake, southern Moreton Bay (Australia)
- Authors: Burton, Edward , Sullivan, Leigh , Bush, Richard , Powell, Bernard
- Date: 2008
- Type: Text , Journal article
- Relation: Marine Pollution Bulletin Vol. 56, no. 7 (2008), p. 1353-1358
- Full Text: false
- Reviewed:
- Description: Iron-sulfide minerals in benthic sediments may sequester potentially toxic trace elements that are introduced to estuaries from natural and anthropogenic sources (Chapman et al., 1998, Morse and Luther, 1999, Simpson et al., 2002 and Teasdale et al., 2003). Understanding iron-sulfide formation in benthic sediments is therefore central to assessing the risk posed by sedimentary trace elements (Machado et al., 2004, Burton et al., 2005a and Burton et al., 2006a). This report provides a baseline description of sedimentary iron-sulfide and trace element behaviour in Coombabah Lake – a sub-tropical estuarine lake in southern Moreton Bay, Australia (Fig. 1).
Mobilisation, alteration, and redistribution of monosulfidic sediments in inland river systems
- Authors: Cheetham, Michael , Wong, Vanessa , Bush, Richard , Sullivan, Leigh , Ward, Nicholas , Zawadzki, Atun
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Environmental Management Vol. 112, no. (2012), p. 330-339
- Full Text: false
- Reviewed:
- Description: The accumulation of monosulfidic sediments in inland waterways is emerging as a major environmental issue. Mobilisation and suspension of monosulfidic sediments can result in deoxygenation, acidification of the water column and mobilisation of trace metals. The controls on monosulfidic sediment mobilisation and the critical thresholds for its scour and entrainment have not been established. This study examines the effect of a minor flood event (average return interval of 5 years) on sulfidic sediment scour in the Wakool River in southern NSW, Australia. Five profiles were sampled within a small (~300 m) reach before and after a minor flood event to determine the degree of sediment scour and transport. The results indicate substantial scour of both monosulfidic sediments and underlying bed sediments (approximately 2100 m3). Changes in the sediment geochemistry suggest large concentrations of monosulfidic sediments had been suspended in the water column, partially-oxidised and redeposited. This is supported by 210Pb results from one of the profiles. These results suggest that these monosulfidic sediments can move as bed load during minor flood events. © 2012 Elsevier Ltd.
Monosulfidic black ooze accumulations in sediments of the Geographe Bay area, Western Australia
- Authors: Ward, Nicholas , Bush, Richard , Burton, Edward , Appleyard, Steve , Wong, Stephen , Sullivan, Leigh , Cheeseman, Paul
- Date: 2010
- Type: Text , Journal article
- Relation: Marine Pollution Bulletin Vol. 60, no. 11 (2010), p. 2130-2136
- Full Text: false
- Reviewed:
- Description: Mobilisation of sedimentary monosulfidic black ooze (MBO) may result in rapid deoxygenation and acidification of surface waters, and release of potentially toxic metals. This study examines the extent and nature of MBO accumulation in the Geographe Bay area, Western Australia. MBO accumulations were found to be widespread in benthic sediments of the Geographe Bay area with acid-volatile sulfide (AVS) contents as high as 320μmolg-1. The MBO materials often had unusually high dissolved sulfide (S-II) concentrations in their pore-waters (up to 610mgL-1) and elevated elemental sulfur (S0) contents (up to 51μmolg-1). Dissolved S-II is able to accumulate due to limited iron availability and S0 is largely its partial oxidation product. The availability of organic carbon and Fe limited MBO accumulation at many sites. A comparison of AVS and simultaneously extracted metal (SEM) concentrations has shown that metals are likely to be bound in sulfide complexes. © 2010 Elsevier Ltd.
Partitioning of metals in a degraded acid sulfate soil landscape : Influence of tidal re-inundation
- Authors: Claff, Salirian , Sullivan, Leigh , Burton, Edward , Bush, Richard , Johnston, Scott
- Date: 2011
- Type: Text , Journal article
- Relation: Chemosphere Vol. 85, no. 8 (2011), p. 1220-1226
- Full Text: false
- Reviewed:
- Description: The oxidation and acidification of sulfidic soil materials results in the re-partitioning of metals, generally to more mobile forms. In this study, we examine the partitioning of Fe, Cr, Cu, Mn, Ni and Zn in the acidified surface soil (0-0.1. m) and the unoxidised sub-soil materials (1.3-1.5. m) of an acid sulfate soil landscape. Metal partitioning at this acidic site was then compared to an adjacent site that was previously acidified, but has since been remediated by tidal re-inundation. Differences in metal partitioning were determined using an optimised six-step sequential extraction procedure which targets the " labile" , " acid-soluble" , " organic" , " crystalline oxide" , " pyritic" and " residual" fractions. The surficial soil materials of the acidic site had experienced considerable losses of Cr, Cu, Mn and Ni compared to the underlying parent material due to oxidation and acidification, yet only minor losses of Fe and Zn. In general, the metals most depleted from the acidified surface soil materials exhibited the greatest sequestration in the surface soil materials of the tidally remediated site. An exception to this was iron, which accumulated to highly elevated concentrations in the surficial soil materials of the tidally remediated site. The " acid-soluble" , " organic" and " pyritic" fractions displayed the greatest increase in metals following tidal remediation. This study demonstrates that prolonged tidal re-inundation of severely acidified acid sulfate soil landscapes leads to the immobilisation of trace metals through the surficial accumulation of iron oxides, organic material and pyrite. © 2011 Elsevier Ltd.
Reactive trace element enrichment in a highly modified, tidally inundated acid sulfate soil wetland : East Trinity, Australia
- Authors: Keene, Annabelle , Johnston, Scott , Bush, Richard , Burton, Edward , Sullivan, Leigh
- Date: 2010
- Type: Text , Journal article
- Relation: Marine Pollution Bulletin Vol. 60, no. 4 (2010), p. 620-626
- Full Text: false
- Reviewed:
- Description: This study examines the abundance of trace elements in surface sediments of a former acid sulfate soil (ASS) wetland subjected to marine tidal inundation. Sediment properties of this highly modified study site are compared with those of an adjacent unmodified, intertidal mangrove forest. Whilst some trace elements (Al, Cd, Mn, Ni and Zn) were clearly depleted due to mobilisation and leaching in the previous oxic-acidic phase, other trace elements (As and Cr) displayed significant enrichment in the tidally inundated ASS. Many trace elements were strongly associated with the reactive Fe and acid volatile sulfide (AVS) fractions, suggesting that trace elements may be adsorbed to abundant reactive Fe phases or sequestered as sulfide minerals. These findings provide an important understanding of the fate and mobility of reactive iron, AVS and trace elements during tidal remediation of a formerly acidified Great Barrier Reef (GBR) catchment. © 2010 Elsevier Ltd.
Seawater-induced mobilization of trace metals from mackinawite-rich estuarine sediments
- Authors: Wong, Vanessa , Johnston, Scott , Burton, Edward , Bush, Richard , Sullivan, Leigh , Slavich, Peter
- Date: 2013
- Type: Text , Journal article
- Relation: Water Research Vol. 47, no. 2 (2013), p. 821-832
- Full Text: false
- Reviewed:
- Description: Benthic sediments in coastal acid sulfate soil (CASS) drains can contain high concentrations (~1-5%) of acid volatile sulfide (AVS) as nano-particulate mackinawite. These sediments can sequester substantial quantities of trace metals. Because of their low elevation and the connectivity of drains to estuarine channels, these benthic sediments are vulnerable to rapid increases in ionic strength from seawater incursion by floodgate opening, floodgate failure, storm surge and seasonal migration of the estuarine salt wedge. This study examines the effect of increasing seawater concentration on trace metal mobilization from mackinawite-rich drain sediments (210-550
Selective oxidation of arsenite by peroxymonosulfate with high utilization efficiency of oxidant
- Authors: Wang, Zhaohui , Bush, Richard , Sullivan, Leigh , Chen, Chuncheng , Liu, Jianshe
- Date: 2014
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 48, no. 7 (2014), p. 3978-3985
- Full Text: false
- Reviewed:
- Description: Oxidation of arsenite (As(III)) is a critical yet often weak link in many current technologies for remediating contaminated groundwater. We report a novel, efficient oxidation reaction for As(III) conversion to As(V) using commercial available peroxymonosulfate (PMS). As(III) is rapidly oxidized by PMS with a utilization efficiency larger than 90%. Increasing PMS concentrations and pH accelerate oxidation of As(III), independent to the availability of dissolved oxygen the addition of PMS enables As(III) to oxidize completely to As(V) within 24 h, even in the presence of high concentrations of radical scavengers. On the basis of these observations and theoretical calculations, a two-electron transfer (i.e., oxygen atom transfer) reaction pathway is proposed. Direct oxidation of As(III) by PMS avoids the formation of nonselective reactive radicals, thus minimizing the adverse impact of coexisting organic matter and maximizing the utilization efficiency of PMS therefore, this simple approach is considered a cost-effective water treatment method for the oxidation of As(III) to As(V). © 2014 American Chemical Society.
Simultaneous redox conversion of chromium(VI) and arsenic(III) under acidic conditions
- Authors: Wang, Zhaohui , Bush, Richard , Sullivan, Leigh , Liu, Jianshe
- Date: 2013
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 47, no. 12 (2013), p. 6486-6492
- Full Text: false
- Reviewed:
- Description: Arsenic and chromium are often abundant constituents of acid mine drainage (AMD) and are most harmful as arsenite (As(III)) and hexavalent (Cr(VI)). To simultaneously change their oxidation state from As(III) to As(V), and Cr(VI) to Cr(III), is a potentially effective and attractive strategy for environmental remediation. The coabundance of As(III) and Cr(VI) in natural environments indicates their negligible direct interaction. The addition of H 2O2 enables and greatly accelerates the simultaneous oxidation of As(III) and reduction of Cr(VI). These reactions are further enhanced at acidic pH and higher concentrations of Cr(VI). However, the presence of ligands (i.e., oxalate, citrate, pyrophosphate) greatly retards the oxidation of As(III), even though it enhances the reduction of Cr(VI). To explain these results we propose a reaction mechanism where Cr(VI) is primarily reduced to Cr(III) by H2O2, via the intermediate tetraperoxochromate Cr(V). Cr(V) is then involved in the formation of •OH radicals. In the presence of ligands, the capacity of Cr(V) to form •OH radicals, which are primarily responsible for As(III) oxidation, is practically inhibited. Our findings demonstrate the feasibility for the coconversion of As(III) and Cr(VI) in AMD and real-world constraints to this strategy for environmental remediation. © 2013 American Chemical Society.
Sorption of Arsenic(V) and Arsenic(III) to schwertmannite
- Authors: Burton, Edward , Bush, Richard , Johnston, Scott , Watling, Kym , Hocking, Rosalie , Sullivan, Leigh , Parker, Gretel
- Date: 2009
- Type: Text , Journal article
- Relation: Environmental Science and Technology Vol. 43, no. 24 (2009), p. 9202-9207
- Full Text: false
- Reviewed:
- Description: This study describes the sorption of As(V) and As(III) to schwertmannite as a function of pH and arsenic loading. In general, sorption of As(V) was greatest at low pH, whereas high pH favored the sorption of As(III). The actual pH of equivalent As(V) and As(III) sorption was strongly loading dependent, decreasing from pH ∼ 8.0 at loadings <120 mmolAs mol Fe -1 to pH ∼ 4.6 at a loading of 380 mmolAs molFe -1. Sorption isotherms for As(V) were characterized by strong partitioning to the schwertmannite solid-phase at low loadings and sorption capacities of 225-330 mmolAs(V) molFe -1 at high loadings. In contrast, the As(III) isotherms revealed a weak affinity for sorption of As(III) versus As(V) at low loadings yet a greater affinity for As(III) sorption compared with As(V) at high loadings (when pH > 4.6). Sorption of As(V) and As(III) caused significant release of SO 4 2- from within the schwertmannite solid-phase, without major degradation of the schwertmannite structure (as evident by X-ray diffraction and Raman spectroscopy). This can be interpreted as arsenic sorption via incorporation into the schwertmannite structure, rather than merely surface complexation at the mineral-water interface. The results of this study have important implications for arsenic mobility in the presence of schwertmannite, such as in areas affected by acidmine drainage and acid-sulfate soils. In particular, arsenic speciation, arsenic loading, and pH should be considered when predicting and managing arsenic mobility in schwertmanniterich systems. © 2009 American Chemical Society.
Tidally driven water column hydro-geochemistry in a remediating acidic wetland
- Authors: Johnston, Scott , Keene, Annabelle , Bush, Richard , Sullivan, Leigh , Wong, Vanessa
- Date: 2011
- Type: Text , Journal article
- Relation: Journal of Hydrology Vol. 409, no. 1-2 (2011), p. 128-139
- Full Text: false
- Reviewed:
- Description: Managed tidal inundation is a newly evolved technique for remediating coastal acid sulphate soil (CASS) wetlands. However, there remains considerable uncertainty regarding the hydro-geochemical pathways and spatiotemporal dynamics of residual H+ and metal(loid) mobilisation into the tidal fringe surface waters of these uniquely iron-rich landscapes. Here, we examine the hydrology and water column chemistry across the intertidal slope of a remediating CASS wetland during several tide cycles. There was extreme spatial and temporal dynamism in water column chemistry, with pH fluctuating by ∼3 units (∼3.5-6.5) during a single tide cycle. Acute acidity was spatially confined to the upper intertidal slope, reflecting surface sediment properties, and tidal overtopping is an important pathway for mobilisation of residual H+ and Al3+ to the water column. Marine derived HCO3- was depleted from surface waters migrating across the intertidal slope and a strong gradient in HCO3- was observed from the tidal fringe to the adjacent tributary channel and nearby estuary. Tidal forcing generated oscillating hydraulic gradients in the shallow fringing aquifer, favouring ebb-tide seepage and driving rapid, heterogeneous advection of groundwater on the lower intertidal slope via surface connected macropores. A combination of diffusive and advective flux across the sediment-water interface led to persistent, elevated surface water Fe2+ (∼10-1000μM). The geochemical processes associated with Fe2+ mobilisation displayed distinct spatial zonation, with low pH, proton-promoted desorption occurring on the upper intertidal slope, whilst circum-neutral pH, Fe(III)-reducing processes dominated the lower intertidal slope. Arsenic was also mobilised into surface waters on the lower intertidal slope under moderate pH (∼6.0) conditions and was strongly positively correlated with Fe2+. Saturation index values for aragonite were substantially depressed (-1 to -5) and significantly negatively correlated with elevation, thereby presenting a barrier to re-colonisation of the upper intertidal slope by calcifying benthic organisms. These findings highlight the spatially complex hydrological and geochemical controls on surface water quality that can occur in tidally inundated acid sulphate soil environments. © 2011 Elsevier B.V.