Improved understanding of Sodium hydroxide concentration role and kinetic model of cryolite reactive extraction in cathode Spent Pot Linings

Tropenauer, Blaž; Klinar, Dušan; Golob, Janvit

doi:10.2478/pjct-2021-0006

Abstract

Spent Pot Lining (SPL) cathode pot, waste from the aluminium smelting process needs detoxification from cyanides, washing out water-soluble salts and extraction of the cryolite (Na₃AlF₆) decomposition products to be recycled. Revealed cryolite decomposition mechanism with NaOH opens possibilities to explore its critical role in the reactive extraction process. Common Na⁺ ion from NaOH hinders the solubility of the product but also drives mass transfer to the reaction site. Reaction mass balance provides adequate liquid to solid ratio (L/S) and NaOH concentration range. A newly developed kinetic model based on Whitman film theory and NaOH mass flow enables prediction of the reaction time to decompose cryolite to a low enough level. Results show that the internal particle resistance to transport (1/k_s) is 19 times larger than the external (1/k_l) one and governs the whole process.

References

1. Holywell, G. & Breault, R. (2013). An overview of useful methods to treat, recover, or recycle spent potlining, JOM. 65, 1441–1451. DOI: 10.1007/s11837-013-0769-y.10.1007/s11837-013-0769-y
Search in Google Scholar Back to article
2. Pawlek, R.P. (2012). Spent Potlining: An Update, in: Light Met., 2012. DOI: 10.1002/9781118359259.ch227.10.1002/9781118359259.ch227
Search in Google Scholar Back to article
3. Chauke, L. & Garbers-Craig, A.M. (2013). Reactivity between carbon cathode materials and electrolyte based on industrial and laboratory data, Carbon N. Y. 58, 40–45. DOI: 10.1016/j.carbon.2013.02.023.10.1016/j.carbon.2013.02.023
Search in Google Scholar Back to article
4. Hop, J.G., Støre, A., Foosnæs, T. & Øye, H.A. (2004). Chemical and physical changes of cathode carbon by aluminium electrolysis, VII Int. Conf. Molten Slags Fuxes Salts. 775–782. DOI: 10.1179/037195505X63376.10.1179/037195505X63376
Search in Google Scholar Back to article
5. Østrem, Ø. (2013). Cathode wear in Hall-Héroult cells, Thesis for the degree of PhD, Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Materials Science and Engineering.
Search in Google Scholar Back to article
6. Silveira, B.I., Dantas, A.E., Blasquez, J.E. & Santos, R.K.P. (2002). Characterization of inorganic fraction of spent potliners: Evaluation of the cyanides and fluorides content, J. Hazard. Mater. 89, 177–183. DOI: 10.1016/S0304-3894(01)00303-X.10.1016/S0304-3894(01)00303-X
Search in Google Scholar Back to article
7. Mikša, D., Homšak, M. & Samec, N. (2003). Spent pot-lining utilisation possibilities, Waste Manag. Res. 21, 467–473. DOI: 10.1177/0734242X0302100509.10.1177/0734242X0302100509
Search in Google Scholar Back to article
8. Tropenauer, B., Klinar, D., Samec, N. & Golob, J. 2018. Circular economy model of cathode waste processing. DOI: 10.18690/978-961-286-211-4.8.10.18690/978-961-286-211-4.8
Search in Google Scholar Back to article
9. O’Neil, M.J. (ed.), (2001). The Merck Index – An Encyclopedia of Chemicals, Drugs, and Biologicals. 13th Edition, Whitehouse Station, NJ: Merck and Co., Inc., p. 456.
Search in Google Scholar Back to article
10. Cenčič, M., Kobal, I. & Golob, J. (1998). Thermal Hydro-lysis of Cyanides in Spent Pot Lining of Aluminium Electrolysis, Chem. Eng. Technol. 21, 523–532. DOI: 10.1002/(SICI)1521-4125(199806)21:6<;523::AID-CEAT523>3.0.CO;2-P.10.1002/(SICI)1521-4125(199806)21:6<;523::AID-CEAT523>3.0.CO;2-P
Search in Google Scholar Back to article
11. Ntuk, U., Tait, S. White, E.T. & Steel, K.M. (2015). The precipitation and solubility of aluminium hydroxyfluoride hydrate between 30 and 70^oC. Hydrometallurgy, 155, 79—87. DOI: 10.1016/j.hydromet.2015.04.010.10.1016/j.hydromet.2015.04.010
Search in Google Scholar Back to article
12. Schönfelder, I., Gock, E. Tochtrop, E. & Schmidt Rieder, E. 2015. Recycling von Elektrolyseausbruch (SPL) aus der Primäraluminiumgewinnung, (n.d.). http://www.vivis.de/phocadownload/Download/2015_rur/2015_RuR_385-404_Gock.pdf (accessed June 15, 2018).
Search in Google Scholar Back to article
13. Zhao, L.C. 2001. Comprehensive recovery of waste linings of aluminium electrolysers, CN patent 1,320,491 (Appl. date 28 February 2001). https://patents.google.com/patent/CN1320491A/en.
Search in Google Scholar Back to article
14. Shi, Z., Li, W. Hu, X., Ren, B., Gao, B. & Wang, Z. (2012). Recovery of carbon and cryolite from spent pot lining of aluminium reduction cells by chemical leaching, Trans. Nonferrous Met. Soc. China, 22, 222–227. DOI:10.1016/S1003-6326(11)61164-3.10.1016/S1003-6326(11)61164-3
Search in Google Scholar Back to article
15. Kasireddy, V., Bernuer, J.L. & Kimmerle, F.M. (2003). Recycling of spent pot linings, US patent No.: US 6,596,252 B2, Date of Patent: Jul. 22, 2003.
Search in Google Scholar Back to article
16. Lisbona, D.F. & Steel, K.M. (2008). Recovery of fluoride values from spent pot-lining: Precipitation of an aluminium hydroxyfluoride hydrate product, Sep. Purif. Technol. 61(2), 182–192. DOI: 10.1016/j.seppur.2007.10.012.10.1016/j.seppur.2007.10.012
Search in Google Scholar Back to article
17. NIOSH – The National Institute for Occupational Safety and Health. 2016, Solubility of Cryolite, (2016). access on 10. Jun 2018 https://www.cdc.gov/niosh/npg/npgd0559.html.
Search in Google Scholar Back to article
18. Staffan Sjoeberg, Chemical Specification in Aqueous Al³⁺-F^–-OH^– Systems of relevance to Natural Waters and Body Fluids: The dissolution of AlF3 and Na3AlF6 (cryolite). Department of Inorganic Chemistry, Umeå University, Sweden. Unpublished report for Toxicon AB, (2002). (Committee for Risk Assessment RAC Annex 1 Background Document to the Opinion proposing harmonised classification and labelling at Community level of Trisodium hexafluoroaluminate (cryolite), natural and synthetic; 2010).
Search in Google Scholar Back to article
19. Averill, B. & Eldredge, P. (2016). General Chemistry: Principles, Patterns, and Applications 1.0 |Flat World Education, Flat World Educ.
Search in Google Scholar Back to article
20. Reynolds, J.G. & Belsher, J.D. (2017). A Review of Sodium Fluoride Solubility in Water. J. Chem. Eng. 62(6), 1743–1748. DOI: 10.1021/acs.jced.7b00089.10.1021/acs.jced.7b00089
Search in Google Scholar Back to article
21. Selvaraj, D., Toghiani, R.K. & Lindner, J.S. (2017). Solubility in the Na + F + NO₃ and Na + PO₄+ NO₃ Systems in Water and in Sodium Hydroxide Solutions. J. Chem. Eng. 53(6), 1250–1255.DOI:10.1021/je700597m.10.1021/je700597m
Search in Google Scholar Back to article
22. Weber, C.F., Beahm, E.C., Lee, D.D. & Watson, J.S. (2000). A Solubility Model for Aqueous Solutions Containing Sodium, Fluoride, and Phosphate Ions, Ind. Eng. Chem. Res. 39(2), 518–526. DOI: 10.1021/ie990457l.10.1021/ie990457l
Search in Google Scholar Back to article
23. Xiping, C. & Wangxing, L. (2007). Research on crushing character of spent cathode, in: TMS Light Materials.
Search in Google Scholar Back to article
24. Tropenauer, B., Klinar, D., Samec, N., Golob, J. & Kortnik, J. (2019). Sustainable waste-treatment procedure for the spent potlining (SPL) from aluminium production. Mater. Tehnol. 53(2), 277–284. DOI: 10.17222/mit.2018.147.10.17222/mit.2018.147
Search in Google Scholar Back to article
25. Patent application No.: P-201900265, Slovenian Intellectual Property Office (SIPO), (January 6. 2020).
Search in Google Scholar Back to article

Improved understanding of Sodium hydroxide concentration role and kinetic model of cryolite reactive extraction in cathode Spent Pot Linings

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