Recovery of fluoride values from spent pot-lining: precipitation of an aluminium hydroxyfluoride hydrate product

Fernandez Lisbona, Diego and Steel, Karen M. (2008) Recovery of fluoride values from spent pot-lining: precipitation of an aluminium hydroxyfluoride hydrate product. Separation and Purification Technology, 61 2: 182-192. doi:10.1016/j.seppur.2007.10.012


Author Fernandez Lisbona, Diego
Steel, Karen M.
Title Recovery of fluoride values from spent pot-lining: precipitation of an aluminium hydroxyfluoride hydrate product
Journal name Separation and Purification Technology   Check publisher's open access policy
ISSN 1383-5866
Publication date 2008-07
Sub-type Article (original research)
DOI 10.1016/j.seppur.2007.10.012
Volume 61
Issue 2
Start page 182
End page 192
Total pages 10
Place of publication North Holland, Netherlands
Publisher Elsevier Science
Language eng
Subject 090404 Membrane and Separation Technologies
0904 Chemical Engineering
Formatted abstract
Treatment of spent pot-lining (SPL) from aluminium smelting cells by a two-stage leaching scheme comprising a water wash and an Al3+ each and fluoride recovery as an aluminium hydroxyfluoride product has been studied for extraction of fluoride and then recovery as smelter grade AlF3. The NaF content of a - 1. 18 mm size fraction was removed by the water wash, while the more refractory Na3AlF6 and CaF2 were removed by treatment with 0.34 M Al3+ solution at 25 degrees C for 24 h, which yielded an overall fluoride extraction of 76-86 mol%. Mathematical modelling using experimental stability constant data was carried out to predict the effect of combining solutions and identify ways to manipulate the solution equilibria to maximise fluoride precipitation yields. The predictions were then tested experimentally. In the 4.5-5.5 pH range, selective precipitation of fluoride as an aluminium hydroxyfluoride hydrate product was achieved by neutralisation of the combined solutions with addition of 2 M NaOH solution. Higher pH values lead to the co-precipitation of hydrolysed sodium fluoroaluminates. Characterisation of precipitates using X-ray diffraction, scanning electron microscopy coupled with energy-dispersive spectroscopy, thermogravimetric analysis, differential thermal analysis, aluminium and fluoride determination have pointed out both the AlF2(OH)center dot 1.4H(2)O Stoichiometry and possible thermal decomposition pathways to yield a dehydrated aluminium hydroxyfluoride product, AlF2(OH), that could be used for smelter grade AlF3 production. The kinetics of hydrolysis are such that nucleation dominates while particle growth is restricted. Techniques to allow slow hydrolysis are necessary to form smelter grade AlF3.
Keyword smelter grade aluminium fluoride
spent pot-lining
aluminium hydroxyfluoride hydrate
Q-Index Code C1
Q-Index Status Provisional Code

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Chemical Engineering Publications
 
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Created: Fri, 10 Jul 2009, 16:46:46 EST by Dr Karen Steel on behalf of Faculty Of Engineering, Architecture & Info Tech