Institute of Solid State Chemistry of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:

N. A. Sabirzyanov, Leading Researcher
V. M. Skachkov, Researcher
S. P. Yatsenko, Head of Laboratory, e-mail: yatsenko@ihim.uran.ru

There is described the method of purification of primary aluminum from sodium, using the graphitized materials (fabrics and felts) and sintered alundum filters (thickness is 10 mm, porosity is 85%, size of pores is 0.16 mm). Filtration of aluminum grades A-85 and A-7 was carried out under vacuum or by reladling. It is shown that sodium content is decreased by an order during the filtration with graphitized materials. Using the ceramic filter in the process of filtration, the content of sodium in aluminum is decreased by 2–3 times. Stability of filtering materials to metallic melt and their efficiency at repeated cycling are recognized as quite satisfactory. The filter do not loose its qualities after 10 filtrations, when primary aluminum was loaded and filtered aluminum was obtained. Possible mechanism of sodium removal from melt is discussed. Filtration of primary aluminum melt through the graphitized fabric reduces the content of suspended particles in melt, and catches the oxide films, concentrated with impurities, and large particles of intermetallic compounds, formed by impurities. Besides, the probability of formation of stratified intercalating compounds of sodium with carbon is high if aluminum melt is treated with carbon materials. These compounds are formed on the surface of filtering layer and then are displaced from the surface by aluminum atoms. As a result, sodium is transported from the bulk of melt to the surface of capillary streams, which promotes the evaporation of sodium and increases the purification efficiency. As the temperature of the melt rises, the contribution from this effect prevails. A ladle-to-ladle filtration through a pig-iron cell, lined with a graphitized fabric with a working zone of 240 mm in diameter, was successfully carried out at aluminum factory.

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