Amorphous iron-aluminium oxides are ubiquitous in the environment and control the availability of heavy metals (Pb, Cu). Oxide physicochemical properties are affected by the proportion of Fe and Al, the Fe/Al ratio. Five amorphous oxides containing Fe and/or Al were synthesised: "Fe" (only Fe); "3FeAl" (3 moles Fe per mole Al, Fe/Al = 3); "FeAl" (Fe/Al = 1); "Fe3Al" (Fe/Al = 0.3); "Al" (only Al). Kaolinite clay was also investigated along with kaolinite to which Fe-Al oxides had been added. / The effect of Fe/Al ratio on these physicochemical properties was studied: (1) Specific surface area---EGME retention; (2) pH-dependent cation and anion exchange capacity---Ca(NO3)2 saturation; (3) Particle size density---sieving, pipette methods; (4) Surface charge density---potentiometric titrations. / The Fe/Al ratio influenced the specific surface area: Fe and 3FeAl had significantly greater surface areas than Fe3Al and Al; FeAl exhibited the maximum surface area. The cation exchange capacity increased rapidly above pH 5, with Fe > 3FeAl > Al > Fe3Al > FeAl at pH 6 to 7. Surface charge density of low Fe/Al oxides was more sensitive to pH changes implying ≡AlOH surface hydroxyl groups are more easily protonated and de-protonated than ≡FeOH species. An open (porous) structure of loosely linked small particles was proposed with SO42- anions forming bridges between Al3+ and Fe3+ ions during oxide precipitation while inhibiting extensive crystal growth. / Pb and Cu retention was measured using 24 hour batch suspension tests with varying pH and contaminant concentrations (0.5 to 25 mmol/L). Higher Fe/Al ratio oxides retained more Cu and Pb at all pH values. Cu retention (0.5 to 5 mmol/L) and Pb retention (all concentrations) followed Fe > 3FeA > FeAl > Fe3Al > Al but at 25 mmol Cu/L, only Fe accumulated more Cu. However, low Fe/Al ratio oxides preferentially sorbed Cu over Pb from multi-contaminant solutions. Adsorption rather than bulk precipitation was the dominant accumulation mechanism. Geochemical modelling suggested surface precipitation occurred at higher contaminant concentrations. / Adding oxides to kaolinite significantly increased the clay's specific surface area, surface charge density and contaminant retention capacity; higher Fe/Al ratio oxide-amended clays retained more Pb and Cu. / Amorphous Fe-Al oxides substantially enhance heavy metal accumulation by soils with higher Fe/Al ratio oxides being particularly effective.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36683 |
| Date | January 1999 |
| Creators | Potter, Hugh, 1967- |
| Contributors | Yong, Raymond N. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Civil Engineering and Applied Mechanics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001740220, proquestno: NQ64646, Theses scanned by UMI/ProQuest. |
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