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

Lisbona, Diego; Steel, Karen M.

doi:10.1016/j.seppur.2007.10.012

Cited by 131 publications

(50 citation statements)

References 17 publications

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“…In this case, lithium was precipitated as LiF, evaporating the solutions above the solubility product constant (Ksp) of LiF [16,17,[19][20][21][22][23]. The recovery efficiency of each element was calculated by gravimetric analysis.…”

Section: Recovery Assaysmentioning

confidence: 99%

Recovery Process of Li, Al and Si from Lepidolite by Leaching with HF

et al. 2017

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This work describes the development of a new process for the recovery of Li, Al and Si along with the proposal of a flow sheet for the precipitation of those metals. The developed process is comprised of lepidolite acid digestion with hydrofluoric acid, and the subsequent precipitation of the metals present in the leach liquor. The leaching operational parameters studied were: reaction time, temperature and HF concentration. The experimental results indicate that the optimal conditions to achieve a Li extraction higher than 90% were: solid-liquid ratio, 1.82% (w/v); temperature, 123 • C; HF concentration, 7% (v/v); stirring speed, 330 rpm; and reaction time, 120 min. Al and Si can be recovered as Na 3 AlF 6 and K 2 SiF 6 . LiF was separated from the leach liquor during water evaporation, with recovery values of 92%.

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Section: Recovery Assaysmentioning

confidence: 99%

Recovery Process of Li, Al and Si from Lepidolite by Leaching with HF

et al. 2017

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“…The average AHF/H2O ratio has been calculated to be 1.43. This was comparable to the 1.40 previously reported by Lisbona and Steel (2008). In the light of the results obtained (while still working out the error margin), my preliminary conclusion will be that the AHF samples synthesised, contains ~1 water of crystallization per mole.…”

Section: Characterization Of Functional Groups and Structural Watersupporting

confidence: 85%

“…Previous studies have shown that the recovery of SPL in the form of aluminium hydroxyfluoride hydrate may be one of the most economical processing route (Lisbona and Steel, 2008). The process is simple, uses cost effective reagents, has relatively low energy demand, and produces economically viable products.…”

Section: Justification For Methodsmentioning

confidence: 99%

“…This was thought to be due to the formation of the very stable aluminium complex AlF 2+ . Experimental results from Lisbona and Steel (2008) showed that 76 -86 % of the fluoride in SPL could be recovered through this process, and that the residual graphite is more than 87 wt. % carbon.…”

Section: Recovery As Aluminium Hydroxyfluoride Hydrate (Ahf)mentioning

confidence: 99%

“…A majority of the previous publications agree that an F/Al molar ratio of 2 is optimum for the starting solutions (Bush and Gaydoski, 1985, Lisbona, 2009, Kaaber and Mollgaard, 1996. There is also a general agreement that partial neutralization should only be used up to pH ~ 5.0 to avoid co-precipitates (Bush andGaydoski, 1985, Lisbona andSteel, 2008 Furthermore, it is likely that the solution will get past the point of saturation into a supersaturated region, prior to the labile region where spontaneous precipitation occurs. It is the object of this chapter to identify these regions, thereby identifying the metastable zone width (MSZW).…”

Section: Supersaturated Solutions Are Known To Have Regions Where Spomentioning

confidence: 99%

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

Cited by 131 publications

References 17 publications

Recovery Process of Li, Al and Si from Lepidolite by Leaching with HF

Recovery Process of Li, Al and Si from Lepidolite by Leaching with HF

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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