National Mineral Resources University, Saint Petersburg, Russia:

A. A. Vlasov, Assistant of a Chair of Metallurgy

V. Yu. Bazhin, Dean of Chemical-Metallurgical Faculty, e-mail: bazhinalfoil@mail.ru

A. A. Pyaterneva, Post-Graduate Student, Chair of Metallurgy

Aluminum industry is a source of atmospheric pollutants, such as fluoride and sulfides, dust, carbon monoxide and tarry substance. There is only one way of industrial aluminum reduction process, which is the reduction process of aluminum oxide (alumina), dissolved in the melt of fluorides (cryolite, aluminum fluoride). The sources of harmful agent emissions in aluminum reduction process are raw and other materials. Main raw materials in aluminum reduction process are alumina, coal anode mass (prebaked coal anodes) and fluoride salts. During aluminium reduction process there is an emission of gaseous hydrogen fluoride. Hydrogen fluoride is generated mainly as a result of hydrolysis of fluoride salts at their interaction with the moisture, getting to electrolyte with raw materials (alumina, anode paste). Almost all generated fluoride is captured in the system of dry gas treatment, where metallurgical alumina is used as active adsorbent. This paper considers the problem of adsorptive ability of metallurgical alumina, closely connected with efficiency of gas treatment system of dry type for treatment from gaseous fluorides. Technology of dry gas treatment allows the fluoride recycling. However efficient catching of fluorides requires a detailed studying of physical and chemical alumina properties. There are carried out the experiments on laboratory setup with sand type alumina in a stream of flue gases from a surface of alumina cryolite melt. As a result, new data about the process of chemical sorption of fluorides on a sand type alumina surface are obtained, together with determination of dry gas treatment efficiency.

1. Chzhen V. A., Burkat V. S., Utkov V. A., Sambueva E. A. Minimizatsiya negativnogo vozdeystviya predpriyatiy alyuminievoy promyshlennosti na okruzhayushchuyu sredu (Minimization of negative impact of aluminium industry enterprises on environment). Metallurg = Metallurgist. 2008. No. 11. pp. 41–45.

2. Sleppy W. C. Aluminum compounds. Kirk-Othmer Encylopedia of Chemical Technology. Under the editorship of Kroschwitz J. I., Howe-Grant M. N. Y. : John Wiley & Sons, 1992. Vol. 2. pp. 252–267. 

3. Grjotheim K., Kvande H., Motzfeldt K., Welch B. The formation and composition of the fluoride emissions from aluminum cells. Canadian Metallurgical Quarterly. 2012. Vol. 11, No. 4. pp. 585–599. 

4. Patterson E. C. Hydrogen Fluoride Emissions From Aluminium Electrolysis Cells : PhD Thesis. The University of Auckland. New Zealand, 2002. 

5. Hyland М., Metson J., Haverkamp R., Welch B. Surface studies of hydrogen fluoride adsorption on alumina. Light Metals. 1989. pp. 113–118. 

6. Wagener J. B., Hancke J. J., Carstens P. A. Adsorption of HF on alumina. Journal of Thermal Analysis. 1993. Vol. 39. pp. 1069–1077. 

7. Dando N. R. Adsorption/entrainment of fluoride in smelting grade alumina: surface chemical speciation and adsorption mechanism. Light Metals. 2005. pp. 133–139. 

8. Gillespie A. R., Hyland M. M., Metson J. B. Irreversible HF adsorption in the dry-scrubbing process. Journal of the Minerals Metals & Materials society. 1999. Vol. 51, No. 5. pp. 30–32. 

9. Haupin W., Kvande H. Mathematical model of fluoride evolution from Hall-Heroult Cells. Light Metals. 1993. pp. 257–263. 

10. Grjotheim K., Welch B. J. Aluminium smelter technology. Second edition. Dusseldorf : Aluminium-Verlag, 1988.