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.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.100226 |
| Date | January 2007 |
| Creators | Gella, Vera. |
| 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 | Master of Engineering (Department of Mining, Metals and Materials Engineering.) |
| Rights | © Vera Gella, 2007 |
| Relation | alephsysno: 002668679, proquestno: AAIMR38483, Theses scanned by UMI/ProQuest. |
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