Showing items 1 - 4 of 4

Arsenic effects and behavior in association with the fe(II)-catalyzed transformation of schwertmannite

- Burton, Edward, Johnston, Scott, Watling, Kym, Bush, Richard, Keene, Annabelle, Sullivan, Leigh

  • 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.

Electrochemical analysis of highly reactive pyrite

- Watling, Kym, Burton, Edward, Johnston, Max, Bush, Richard, Sullivan, Leigh

  • Authors: Watling, Kym , Burton, Edward , Johnston, Max , Bush, Richard , Sullivan, Leigh
  • Date: 2010
  • Type: Text , Conference proceedings
  • Full Text: false
  • Description: Highly reactive pyritic material, exposed during the construction of the Pennsylvania Interstate Highway 99 (I-99), has been characterized by X-ray diffraction, Raman microprobe spectroscopy, electron microscopy and electrochemical methods. Mineral standards of marcasite, arsenopyrite and pyrite were compared in order to determine the cause of the rapid acidification and liberation of dissolved metals observed in the exposed Pennsylvanian pyritic material. Linear sweep voltammetry found no significant differences in the electrochemical activity, however, a significantly lower open circuit potential was found in the reactive pyrite material than in the pyrite or marcasite standards. In addition to sulfur and iron, high concentrations of zinc and aluminium impurities were observed in Energy Dispersive X-ray analysis of the finest crystals of the Pennsylvanian pyritic material. © The Electrochemical Society.

Raman, infrared and XPS study of bamboo phytoliths after chemical digestion

- Watling, Kym, Parr, Jeffrey, Rintoul, Llew, Brown, Christopher, Sullivan, Leigh

  • Authors: Watling, Kym , Parr, Jeffrey , Rintoul, Llew , Brown, Christopher , Sullivan, Leigh
  • Date: 2011
  • Type: Text , Journal article
  • Relation: Spectrochimica Acta - Part A : Molecular and Biomolecular Spectroscopy Vol. 80, no. 1 (2011), p. 106-111
  • Full Text: false
  • Reviewed:
  • Description: Raman, infrared and X-ray photoelectron spectroscopies have been used to examine the effect of various chemical digestion methods on the composition of bamboo phytoliths. Intact bilobate phytoliths, suitable for interrogation by Raman microprobe analysis, were isolated by a microwave wet ashing technique using hydrogen peroxide with nitric and hydrochloric acids. The occluded phytolith carbon presented evidence of cellulose, lignin and carboxylic acids. Nitrate from the nitric acid used in the digestion was observed in homogenized samples of the isolated phytoliths; in addition to nitrogen of plant origin occluded within the phytolith, which was observed as amine nitrogen and ammonia. Intact bilobate phytoliths were not observed following an exothermic hydrogen peroxide/sulfuric acid digest, suggesting that these structures ruptured during this digestion procedure. The silicate network was significantly altered during isolation using the exothermic hydrogen peroxide/sulfuric digest, with surface hydroxyls undergoing condensation to form a SiO 3 ring structure. © 2011 Elsevier B.V. All rights reserved.

Sorption of Arsenic(V) and Arsenic(III) to schwertmannite

- Burton, Edward, Bush, Richard, Johnston, Scott, Watling, Kym, Hocking, Rosalie, Sullivan, Leigh, Parker, Gretel

  • 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.
  • 1