Implication of calcium hydroxide in the seawater neutralisation of bauxite refinery liquors

Palmer, Sara J., Smith, Matthew, & Frost, Ray L. (2012) Implication of calcium hydroxide in the seawater neutralisation of bauxite refinery liquors. In 9th International Alumina Quality Workshop, 18-22 March, 2012, Perth, WA.


Tricalcium aluminate, hydrocalumite and residual lime have been identified as reversion contributing compounds after the seawater neutralisation of bauxite refinery residues. The formation of these compounds during the neutralisation process is dependent on the concentration of residual lime, pH and aluminate concentrations in the residue slurry. Therefore, the effect of calcium hydroxide (CaOH2) in bauxite refinery liquors was analysed and the degree of reversion monitored. This investigation found that the dissolution of tricalcium aluminate, hydrocalumite and CaOH2 caused reversion and continued to increase the pH of the neutralised residue until a state of equilibrium was reached at a solution pH of 10.5. The dissolution mechanism for each compound has been described and used to demonstrate the implications that this has on reversion in seawater neutralised Bayer liquor. This investigation describes the limiting factors for the dissolution and formation of these trigger compounds as well as confirming the formation of Bayer hydrotalcite (mixture of Mg6Al2(OH)16(CO32-,SO42-)•xH2O and Mg8Al2(OH)12(CO32-,SO42-)•xH2O) as the primary mechanism for reducing reversion during the neutralisation process. This knowledge then allowed for a simple but effective method (addition of magnesium chloride or increased seawater to Bayer liquor ratio) to be devised to reduce reversion occurring after the neutralisation of Bayer liquors. Both methods utilise the formation of Bayer hydrotalcite to permanently (stable in neutralised residue) remove hydroxyl (OH-) and aluminate (Al(OH)4-) ions from solution.

Impact and interest:

Citation counts are sourced monthly from Scopus and Web of Science® citation databases.

These databases contain citations from different subsets of available publications and different time periods and thus the citation count from each is usually different. Some works are not in either database and no count is displayed. Scopus includes citations from articles published in 1996 onwards, and Web of Science® generally from 1980 onwards.

Citations counts from the Google Scholar™ indexing service can be viewed at the linked Google Scholar™ search.

Full-text downloads:

195 since deposited on 27 May 2014
58 in the past twelve months

Full-text downloads displays the total number of times this work’s files (e.g., a PDF) have been downloaded from QUT ePrints as well as the number of downloads in the previous 365 days. The count includes downloads for all files if a work has more than one.

ID Code: 72155
Item Type: Conference Paper
Refereed: Yes
Keywords: red mud, bauxite residue, seawater neutralisation, reversion, calcium hydroxide
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > INORGANIC CHEMISTRY (030200)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2012 [please consult the author]
Deposited On: 27 May 2014 23:08
Last Modified: 13 Jun 2014 05:00

Export: EndNote | Dublin Core | BibTeX

Repository Staff Only: item control page