The bauxite, a mineral rich ore, is an important source of metallic aluminum in industry. The Bayer process, developed in 1888, involves the extraction of alumina (Al2O3) from bauxite. One of the key stage of Bayer process is the crystallization of aluminum trihydroxide (Al(OH) 3), an intermediate product from which alumina is obtained by dehydration. Crystallization behavior and the morphology of aluminum trihydroxide depend strongly on the reactor temperature, the supersaturation defined by the concentration ratio of soluble [Al2O3]/[Na2O], noted as A/C ratio, and the presence of impurities. This crystallization behavior of aluminum trihydroxide was examined at various temperatures, initial concentration ratios of [Al2O3]/[Na2O] and concentrations of titanium oxide and ferric oxide as impurities. The X-ray diffraction analysis showed that only gibbsite, a polymorph of Al(OH)3, was produced at the end of all the experiments. An increase in the temperature, as well as an increase of the initial A/C ratio, resulted in an augmentation of the slurry density and the particle size distribution. The Scanning Electron Microscope (SEM) images of aluminum trhydroxide crystals revealed that the presence of titanium oxide favored the production of the small single crystals minimizing agglomeration. In the case of ferric oxide, the agglomerates were formed but showed a decrease of the average diameter as compared with the crystals formed without any impurities. Zeta-potential and settling velocity of aluminum trihydroxide in the presence and absence of impurities were also measured.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.31049 |
| Date | January 2000 |
| Creators | Dumortier, Remy. |
| 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 Chemical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001808171, proquestno: MQ70227, Theses scanned by UMI/ProQuest. |
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