Determination of Optimal Fluorine Leaching Parameters from the Coal Part of the Waste Lining of Dismantled Electrolytic Cells for Aluminum Production

• Published in: Zapiski Gornogo instituta (1999) Vol. 239; no. 5; pp. 544 - 549
• Main Authors: Nemchinova, N. V., Tyutrin, A. A., Somov, V. V.
• Format: Journal Article
• Language: English
• Published: Saint-Petersburg Mining University 01.01.2019
• ISSN: 2411-3336; 2541-9404
• DOI: 10.31897/pmi.2019.5.544

When aluminum is obtained by electrolysis of cryolite-alumina melts when the baths are sent for  capital repairs, a solid technogenic product is formed – waste lining of electrolytic cells (WLEC). The volume of formation of WLEC is 30-50 kg per 1 ton of aluminum. Currently, it is mainly stored at landfills near industrial enterprises, causing harm to the environment. However, this technogenic raw material contains valuable components (fluorine, aluminum, sodium) that can be extracted to produce fluoride salts, which are in demand during the electrolytic production of aluminum. The objects of research were samples of the coal part of the waste lining of dismantled S-8BM (E) type electrolytic cells of «RUSAL Krasnoyarsk» JSC (Krasnoyarsk) of RUSAL company. According to the X-ray experiment diffraction analysis (using a Bruker D8 ADVANCE diffractometer) of the phase composition of the samples, it was found that the main fluorine-containing compounds are cryolite, chiolite, sodium and calcium fluorides. The total fluorine  content  in  the  studied  samples  averaged  13.1  %.  We  conducted  studies  on  the  leaching  of fluorine from WLEC with a solution of caustic alkali (NaOH concentration – 17.5 g/dm3). The process was  carried out in a mechanically agitated reactor using a BIOSAN MM-1000 top drive laboratory stirrer with a two-blade nozzle. By the method of mathematical planning of a three-factor experiment, the mutual influence of three leaching conditions on the optimization parameter was established – the extraction of fluorine in solution (in percent). The maximum recovery of fluorine from WLEC to the leach solution averaged 86.4 % and was achieved with the following indicators:processtemperature–95°C,theratio ofliquidtosolidphase–9:1,duration– 210 min.