The precipitation and solubility of aluminium hydroxyfluoride hydrate between 30 and 70 °c

Ntuk, Ubong, Tait, Stephan, White, Edward T and Steel, Karen M (2015) The precipitation and solubility of aluminium hydroxyfluoride hydrate between 30 and 70 °c. Hydrometallurgy, 155 79-87. doi:10.1016/j.hydromet.2015.04.010

Author Ntuk, Ubong
Tait, Stephan
White, Edward T
Steel, Karen M
Title The precipitation and solubility of aluminium hydroxyfluoride hydrate between 30 and 70 °c
Journal name Hydrometallurgy   Check publisher's open access policy
ISSN 0304-386X
Publication date 2015-05
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.hydromet.2015.04.010
Volume 155
Start page 79
End page 87
Total pages 9
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2016
Language eng
Formatted abstract
This paper considers the recovery of fluoride from spent pot-lining (SPL) in the form of aluminium hydroxyfluoride (AHF), AlFx(OH)3 − x, with the intent of recycling the fluoride back into Al smelting pots. This study uses ion speciation equilibria calculations combined with dissolution experiments to examine the solubility (and thus potential yield of recovery) for the crystallization of AHF from synthetic solutions. Results suggest that when sodium hydroxide is used for pH adjustment, a high fluoride to aluminium (F:Al) ratio can be problematic because of the competitive co-precipitation of sodium fluoroaluminates. Further, for an F:Al ratio of 1.6 and pH of 4.9, the desired high purity AHF product can be produced. Results from solubility experiments strongly suggest that the AHF has a molecular formula of AlF2OH·H2O and yields a pKsp at 25 °C of 24.52 ± 0.05 and a heat of reaction (ΔHR) of − 23.48 ± 2.9 kJ/mol for the following reaction:


The primary means for inducing precipitation of AHF is pH adjustment/control, with temperature being a secondary means. The precipitation of AHF is beset by the competitive co-precipitation of other minerals, therefore restricting the operating conditions of the precipitation process for high purity AHF to a low pH (4–5). High temperatures (50–70 °C) are expected to be advantageous for precipitation owing to the solubility behaviour observed.
Keyword Spent potlining
Spent potliner
Aluminium hydroxyfluoride
Ionic speciation
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2016 Collection
Advanced Water Management Centre Publications
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Citation counts: TR Web of Science Citation Count  Cited 1 times in Thomson Reuters Web of Science Article | Citations
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