Browsing by Author "Loan, MJ"

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    An investigation of goethite-seeded Al(OH)(3) precipitation using in situ x-ray diffraction and rietveld-based quantitative phase analysis
    (Wiley-Blackwell, 2010-06) Webster, NAS; Madsen, IC; Loan, MJ; Knott, RB; Naim, F; Wallwork, KS; Kimpton, JA
    An in situ X-ray diffraction investigation of goethite-seeded Al(OH)3 precipitation from synthetic Bayer liquor at 343 K has been performed. The presence of iron oxides and oxyhydroxides in the Bayer process has implications for alumina reversion, which causes significant process losses through unwanted gibbsite precipitation, and is also relevant for the nucleation and growth of scale on mild steel process equipment. The gibbsite, bayerite and nordstrandite polymorphs of Al(OH)3 precipitated from the liquor; gibbsite appeared to precipitate first, with subsequent formation of bayerite and nordstrandite. A Rietveld-based approach to quantitative phase analysis was implemented for the determination of absolute phase abundances as a function of time, from which kinetic information for the formation of the Al(OH)3 phases was determined. © 2010, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    An investigation of the mechanisms of goethite, hematite and magnetite-seeded Al(OH)(3) precipitation from synthetic Bayer liquor
    (Elsevier, 2011-09-01) Webster, NAS; Loan, MJ; Madsen, IC; Knott, RB; Kimpton, JA
    The precipitation of Al(OH)3 from synthetic Bayer liquor at 70 degrees C seeded with goethite, hematite and magnetite particles was investigated in order to gain insight into the nucleation and growth mechanisms in the presence of these materials. A combination of characterisation techniques was employed including conductivity analysis, particle size analysis, electron microscopy and in situ synchrotron X-ray diffraction. The magnetite seed was less active for promoting Al(OH)(3) precipitation than the goethite and hematite, based on a comparison of the induction time before the onset of measurable precipitation. For each seed material, the early stages of precipitation were characterised by relatively slow deposition of gibbsite on the seed particles. Precipitation then proceeded via a two-stage mechanism, where gibbsite and small amounts of bayerite and nordstrandite precipitated concurrently. The outcomes of this investigation have implications for the nucleation and growth of scale on mild steel process equipment, and are also relevant for alumina reversion which causes significant process losses through uncontrolled precipitation. (C) 2011 Elsevier B.V.