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Precipitation of aluminum (oxy)hydroxides from concentrated chloride solutions by neutralization

The precipitation and crystallization of aluminum (oxy)hydroxides from chloride solutions by neutralization appears to be quite complex and depends on several parameters, namely, temperature, the OH/Al molar ratio, aging and solution composition. The precipitation of aluminum from AlC13 solutions was found to be complete at substoichiometric OH/Al ratios (typically ~ 2.7), and resulted in the production of an amorphous material that transformed to crystalline phases upon aging at OH/Al ≥3. The predominant phases precipitated from 0.5M AlCl3 solutions at 22, 60 and 95° C at an OH/Al ratio of 3 after 24 hours of aging were pseudoboehmite, bayerite and boehmite, respectively. Increasing the OH/Al ratio and aging time at both 22°C and 60°C promoted crystallization of bayerite over poorly crystalline boehmite. At 95°C, regardless of aging time or degree of neutralization, boehmite was consistently obtained. Increasing the AlCl3 concentration to 2.0M proved to suppress the crystallization of bayerite at 22°C and 60°C, and favoured the crystallization of pseudoboehmite instead. Between the bayerite and pseudoboehmite products, the former exhibited the best settling behaviour (30% settled slurry density after 1 week), while settling did not occur at all for the latter. / Precipitates produced from mixed AlCl3-NaCl solutions exhibited an increasing tendency to form pseudoboehmite over bayerite with increasing sodium chloride concentration. Upon neutralizing mixed AlCl3-MgCl 2 systems, the final solution pH decreased significantly with increasing magnesium chloride concentration. Furthermore, increasing concentrations of MgCl2 promoted the precipitation of poorly crystalline mixed magnesium-aluminum-hydroxide hydrates, identified as Mg6Al2(OH)18·4.5H 2O by XRD. Increases in temperature (up to 125°C), aging time (48 hours) and OH/Al ratio (3.45) were unsuccessful in improving the crystallinity or transformation of these precipitates.

Identiferoai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.100226
Date January 2007
CreatorsGella, Vera.
PublisherMcGill University
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
LanguageEnglish
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Formatapplication/pdf
CoverageMaster of Engineering (Department of Mining, Metals and Materials Engineering.)
Rights© Vera Gella, 2007
Relationalephsysno: 002668679, proquestno: AAIMR38483, Theses scanned by UMI/ProQuest.

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