List of Titles

Isolation and characterisation of recalcitrant organic components from an estuarine sediment core

- Mylotte, Rosaleen, Verheyen, Vincent, Reynolds, Alicia, Dalton, Catherine, Patti, Antonio, Chang, Rung, Burdon, James, Hayes, Michael

Authors: Mylotte, Rosaleen , Verheyen, Vincent , Reynolds, Alicia , Dalton, Catherine , Patti, Antonio , Chang, Rung , Burdon, James , Hayes, Michael
Date: 2015
Type: Text , Journal article
Relation: Journal of Soils and Sediments Vol. 15, no. 1 (2015), p. 211-224
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Description: Purpose The purpose of this research was to isolate humic substances and humin from an estuarine sediment core using a novel sequential extraction procedure to characterise the isolates, to determine their compositions and to understand how the organic matter (OM) changes with time. Materials and methods The sediments were exhaustively extracted using the following media: 0.1 M NaOH; 0.1 M NaOH + 6 M urea; and dimethylsulphoxide (DMSO) + H2SO4 (94:6 v/v). Pyrolysis gas chromatography mass spectroscopy (pyGC/MS), and nuclear magnetic resonance (NMR) spectroscopy were the analytical tools that gave the most significant data for the characterisation of the organic isolates. Results and discussion The results indicate subtle molecular compositional differences in relation to the alkaline and alkaline-urea isolates. The humic acids (HAs) and fulvic acids (FAs) are readily solvated in aqueous alkaline media compared to the aqueous insoluble hydrophobic humin (HU) components. In addition to aliphatic hydrocarbons, peptide materials make considerable contributions to the component structures of the isolates. Aryl and O-aryl C units characteristic of lignin, and of cutan structures from plants, indicate contributions from terrestrial OM to the organic components in the HU, especially from the base of the core. The evidence suggests that components of terrestrial plant materials and of microbial biomass are preferentially preserved with time and make the major contributions to the OM retained over long time scales. The data acquired provide detailed information about the origins, compositions, nature and the associations of the OM in the estuarine sediment core. Such information provides a greater understanding of the role of these organic components in the carbon (C) sink. Conclusions Humic acids and FAs are mineralised with time whereas HU is highly recalcitrant and represents a long-term sink for organic C. Humin is a separate organic entity and does not conform to the definitions of a humic substance. Terrestrial OM is preserved over long time scales in the environment. Protein makes significant contributions to all the organic isolates and its preservation suggests encapsulation in hydrophobic domains, or interactions with clay minerals.

Liberation of acidity and arsenic from schwertmannite : Effect of fulvic acid

- Vithana, Chamindra, Sullivan, Leigh, Burton, Edward, Bush, Richard

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
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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.

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