Speciation and measurement of aluminium in environmental systems.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Aluminium speciation is of importance, as certain Al species are toxic to algae, fish and plants. The work within this thesis is directed towards the development and application of analytical methods to determine aluminium speciation in environmental systems. Significant changes to soil properties in New Zealand have occurred as a result of land management practices. This work contributes to the knowledge of soil aluminium chemistry by developing and applying techniques which enable changes to the concentrations of toxic Al species in soil solution to be quantified. An established technique for Al fractionation, using oxine-derivatised Fractogel, was applied to environmental situations in which Al is of importance. Detailed investigations of the aluminium speciation in soil solutions from a range of sites were performed. A pAl – pH curve was constructed from measurements of 'free AI' concentrations in soil solutions. The possible mechanisms controlling Al3+ concentrations in soil solution, including an Al – fulvic acid binding curve are discussed. The impact of land use change from grassland to conifer forest on the Al concentrations in soils and soil solutions was examined, and the effects of afforestation on soil chemistry quantified. The Al speciation in a sequence of high country pastoral soils was also studied. Complementary experiments such as root elongation bio-toxicity studies and aluminium complexation-capacity determinations were performed to provide information on the impacts of soil acidification. In a study of relevance to the water treatment industry, a series of Al complexation capacity titrations were carried out to compare the Al-binding interactions between a commercially-available synthetic flocculant (polyacrylamide) and those of a natural polymeric flocculant (sodium alginate). Fundamental method development studies were performed. The application of oxinederivatised Fractogel to the fractionation of FeII and FeIII was examined. The ability of the resin to sequester FeII and/or FeIII from organic complexes was investigated. The developed protocol allowed quantification of FeII by using a simple flow injection analysis (FIA) manifold. The addition of a line containing a reducing agent to the manifold allowed an online reduction of Fe III and hence total Fe (FeII + FeIII) to be determined. The development of a new Al3+ fractionation protocol is also described. The method involves a short reaction (ca. 1.1 s) between a sample and an iminodiacetate controlled-pore glass resin in an FIA manifold. The performance of the resin was tested to determine whether Al was sequestered from organic complexes, from samples of high ionic strength or from Al-hydroxy polymer solutions. Samples of humic waters and soil extracts were analysed, and the results compared with those obtained by established methods. The equilibrium reactions between aluminium (III) and two known plant exudates, caffeic and chlorogenic acids, have been studied by potentiometric and spectrophotometric titrations in aqueous solution (I = 0.10 M Kel, 25.0°C), and the stability constants determined.