Treatment of Spent Pot-lining with Aluminum Anodizing Wastewaters: Selective Precipitation of Aluminum and Fluoride as an Aluminum Hydroxyfluoride Hydrate Product

Lisbona, Diego; Somerfield, Christopher; Steel, Karen M.

doi:10.1021/ie3013506

Cited by 30 publications

(7 citation statements)

References 9 publications

(34 reference statements)

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“…Fig. 4) suggested that AlF 3 (s), NaAl 3 F 6 (s) were unlikely to form, recently published solubility constants for the AlF 2 OH(s) phase 14,40 matched the low soluble Al values measured from gibbsite suspensions, as shown in Fig. 4.…”

Section: Resultssupporting

confidence: 70%

Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface

et al. 2016

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This study uncovers bifluoride-type (difluorohydrogenate(i); [HF2](-)) species formed at mineral/water interfaces. Bifluoride forms at [triple bond, length as m-dash]Al-F surface sites resulting from the partial fluoridation of gibbsite (γ-Al(OH3)) and bayerite (α-Al(OH3)) particles exposed to aqueous solutions of 50 mM NaF. Fluoride removal from these solutions is proton-promoted and results in a strongly self-buffered suspensions at circumneutral pH, proceeds at a F : H consumption ratio of 2 : 1, and with recorded losses of up to 17 mM fluoride (58 F nm(-2)). These loadings exceed crystallographic site densities by a factor of 3-4, yet the reactions have no resolvable impact on particle size, shape and mineralogy. X-ray photoelectron spectroscopy (XPS) of frozen (-155 °C) wet mineral pastes revealed coexisting surface F(-) and HF(0) species. Electron energy loss features pointed to multilayer distribution of these species at the mineral/water interface. XPS also uncovered a distinct form of Na(+) involved in binding fluoride-bearing species. XPS and solid state magic angle spinning (19)F nuclear magnetic resonance measurements showed that these fluoride species were highly comparable to a sodium-bifluoride (NaHF2) reference. First layer surface species are represented as [triple bond, length as m-dash]Al-F-H-F-Al[triple bond, length as m-dash] and [triple bond, length as m-dash]Al-F-Na-F-Al[triple bond, length as m-dash], and may form multi-layered species into the mineral/water interface. These results consequently point to a potentially overlooked inorganic fluorine species in a technologically relevant mineral/water interfacial systems.

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Section: Resultssupporting

confidence: 70%

Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface

et al. 2016

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“…It suggests that AlF2 + may be converting to AlF2OH, and this has been previously suggested by (Lisbona, 2012b) according to Equation 5.1.…”

Section: Preliminary Speciation Modellingsupporting

confidence: 52%

Crystallization of AlF2OH.H2O, for application in the recycle of fluoride from Spent Pot Lining (SPL)

Ntuk¹

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Spent pot lining (SPL) is a major waste generated in the process of producing primary aluminium (7-30 kg SPL per tonne of primary aluminium). It is the discarded carbon cathode and refractory lining of the smelting pots in the electrolytic process. This waste is classified as hazardous, mainly due to its leachable cyanide and fluoride content. This has led to a ban from disposal in landfills or water bodies by several environmental laws. Currently, about 1 million tonnes per annum of this waste is produced globally. This figure is projected to increase by 6 % per year by 2016.Over the years, much research has been carried out to offer an economic method of handling this waste, but to date no such method is widely accepted. Previous methods have aimed at inertization, but current efforts are driven towards recycling. Chemical leaching, followed by product recovery has been found to be a promising option. Previous work has successfully recovered up to 86 % of the fluoride values in the form of aluminium hydroxyfluoride hydrate, AlF2OH (AHF). Which could be subsequently converted to AlF3 for re-use in the smelters. There is currently very little information available on the properties or methods for obtaining AHF that is suitable for subsequent conversion.This project aimed at developing a controlled crystallization process for aluminium hydroxyfluoride hydrate from model solutions using established techniques of crystallization to improve the crystal properties. It also aimed to provide information on this compound for standard references. Model solutions were made to mimic the spent pot lining leachate solution and used throughout the studies.AHF was isolated and studied, and useful information of its solubility, supersaturation, metastability, crystal habit, nucleation and crystal growth kinetic are obtained. The obtained data is needed for the design of a suitable crystallizer/crystallization process.Co-precipitation of impurities is a major problem in crystallizing AHF. Major co-precipitates are cryolite (Na3AlF6), gibbsite (Al(OH)3) and sodium sulphate (Na2SO4). Results from this study have found that when NaOH is used for pH adjustment, a high fluoride to aluminium (F:Al) molar ratio favoured cryolite co-precipitation due to increased sodium (Na) in solution. While a low F/Al molar ratio favoured gibbsite co-precipitation due to the excess Al in solution. An optimum F/Al molar ratio was 2.0 ± 0.2. Solubility tests showed that AHF solubility was dependent mainly on the solution pH and to a lesser extent on temperature. It decreased with increasing pH/temperature and vice versa. The solubility product constant (log Ksp) at 25 o C was obtained as -24.3 ± 0.05. This value holds true for the definition of the solubility constant product in terms of the dissociation of AHF into its composing III ions. The heat of reaction (ΔHR) was obtained as −25.0 ± 2.9 kJ/mol while the enthropy (∆S) was obtained as -549 ± 9 J/K.The metastable zone width (MSZW) in the mother liquor was found to be narrow. The nucleation ...

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“…The response experimental results based on BBD are listed in Table 6. The comparison and analysis of models 15,24,25 No. Equation…”

Section: Model Fitting and Anovamentioning

confidence: 99%

Optimization of purification treatment of spent cathode carbon from aluminum electrolysis using response surface methodology (RSM)

Yuan

Xiao

Tian

et al. 2017

Asia-Pacific J Chem Eng

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Purification treatment and carbon recovery of the spent cathode carbon (SCC) from aluminum electrolysis were optimized using response surface methodology (RSM) in caustic leaching process and purified further by acid leaching. The purity of treated SCC was 96.43%. A Box-Behnken design based on a single-factor experiment was utilized to model 3 independent variables, namely, temperature (55-85°C), time (70-110 min), and initial alkali-material ratio (0.15-0.35), to investigate their responses to the carbon content of caustic leaching residue. A multivariate quadratic regression equation model was established according to RSM principles. Results revealed that the carbon content of caustic leaching residue was significantly influenced by the initial alkali-material ratio, temperature, and time, sorted from big to small. Interactions of any 2 of the 3 factors significantly affected the response. RSM is thus successfully applied in the optimization of the SCC impurities removal process.

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Treatment of Spent Pot-lining with Aluminum Anodizing Wastewaters: Selective Precipitation of Aluminum and Fluoride as an Aluminum Hydroxyfluoride Hydrate Product

Cited by 30 publications

References 9 publications

Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface

Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface

Crystallization of AlF2OH.H2O, for application in the recycle of fluoride from Spent Pot Lining (SPL)

Optimization of purification treatment of spent cathode carbon from aluminum electrolysis using response surface methodology (RSM)

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Treatment of Spent Pot-lining with Aluminum Anodizing Wastewaters: Selective Precipitation of Aluminum and Fluoride as an Aluminum Hydroxyfluoride Hydrate Product

Cited by 30 publications

References 9 publications

Bifluoride ([HF2]−) formation at the fluoridated aluminium hydroxide/water interface

Bifluoride ([HF2]−) formation at the fluoridated aluminium hydroxide/water interface

Crystallization of AlF2OH.H2O, for application in the recycle of fluoride from Spent Pot Lining (SPL)

Optimization of purification treatment of spent cathode carbon from aluminum electrolysis using response surface methodology (RSM)

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Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface

Bifluoride ([HF₂]⁻) formation at the fluoridated aluminium hydroxide/water interface