Update on Spent Potliners Treatments:  Kinetics of Cyanides Destruction at High Temperature

Courbariaux, Yann; Chaouki, Jamal; Guy, Christophe

doi:10.1021/ie049775x

Cited by 44 publications

(33 citation statements)

References 20 publications

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“…The method of producing AHF starts by chemically leaching of SPL with a solution of Al 3+ , which can be produced by reacting H 2 SO 4 with Al(OH) 3 . The leachate is loaded with AlF 2 + and is then partially neutralized with a suitable base (usually NaOH) to preferentially crystallize AlF 2 OH.H 2 O (AHF).…”

Section: Al(oh)mentioning

confidence: 99%

“…This triggered the crystallization of aluminium hydroxyfluoride (AHF) crystals. AHF crystallization is believed to occur according to equation (3). Care was taken not to exceed this pH in order to prevent the co-precipitation of sodium-rich fluoroaluminates like cryolite and chiolite [7].…”

Section: Seed Crystal Preparationmentioning

confidence: 99%

“…The supersaturation driving force gets to a maximum at pH 5.0 ± 0.3 after which it starts to decline. This decline is due to OH competing successfully for Al over F. Above pH 5.0, other stable phases (typically Na 3 AlF 6 and Al(OH) 3 ) are more likely to co-precipitate. It is important to note that it is unlikely to get to the maximum (pH 5.0) supersaturation practically, without spontaneous AHF precipitation.…”

Section: Speciation Modellingmentioning

confidence: 99%

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Metastable zone width and nucleation threshold of aluminium hydroxyfluoride hydrate

Ntuk

Steel

2016

Crystal Research and Technology

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This paper considers the metastable zone width (MSZW) of aluminium hydroxyfluoride hydrate (AHF, AlF 2 OH.H 2 O) crystallizing solution, with a view to identifying suitable conditions for crystal growth. Speciation calculations combined with experimental validations have been used to estimate the degree of saturation at varying pHs leading to the identification of the metastable zone width (MSZW). From the results obtained, the solutions are saturated at pH 3.0 ± 0.3 and remain metastable until the nucleation threshold is reached at pH 5.0 ± 0.3. A narrowing of the MSZW at elevated temperatures has been observed and is attributed to the decrease in AHF solubility with increasing temperatures. This phenomenon was applied to obtain a tripling of the crystal particles in 30 minutes. The pH profile of the crystallizing solution is similar to that of acid/base titration curves and is found to be a quick and accurate method of estimating the MSZW. Using similar terminologies, the equivalent point corresponds to solution saturation while the midpoint corresponds to the nucleation threshold. These results are applicable in the recovery of fluoride values of spent pot lining.

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Section: Al(oh)mentioning

confidence: 99%

Section: Seed Crystal Preparationmentioning

confidence: 99%

Section: Speciation Modellingmentioning

confidence: 99%

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Metastable zone width and nucleation threshold of aluminium hydroxyfluoride hydrate

Ntuk

Steel

2016

Crystal Research and Technology

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“…Globally, about 1 million metric tons of SPL is produced annually. The lining is discarded when its integrity is compromised, which occurs in a variable period, usually 3-8 years from the time of installing a new lining (Courbariaux et al, 2004). Various factors contribute to cause this lining degradation including, mechanical stress, electrolyte penetration and side reactions (Lossius and Øye, 2000).…”

Section: Overview Of Splmentioning

confidence: 99%

“…There is also a refractory lining between the steel pot and the graphite cathode usually made from aluminosilicates (Al2O3-SiO2). (Courbariaux et al, 2004). 2 Al2O3 + 3 C → 4 Al + 3 CO2 (2.1)…”

Section: Overview Of Splmentioning

confidence: 99%

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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A Survey on Direct Search Methods for Blackbox Optimization and Their Applications

Audet

2014

Mathematics Without Boundaries

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Update on Spent Potliners Treatments: Kinetics of Cyanides Destruction at High Temperature

Cited by 44 publications

References 20 publications

Metastable zone width and nucleation threshold of aluminium hydroxyfluoride hydrate

Metastable zone width and nucleation threshold of aluminium hydroxyfluoride hydrate

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

A Survey on Direct Search Methods for Blackbox Optimization and Their Applications

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