Irkutsk National Research Technical University (INRTU), Irkutsk, Russia:

N. V. Nemchinova, Head of the Department of Non-Ferrous Metallurgy, Doctor of Technical Sciences, Professor, e-mail: ninavn@yandex.ru
A. A. Tyutrin, Associate Professor at the Department of Non-Ferrous Metallurgy, Candidate of Technical Sciences (Eng.)
A. Е. Barauskas, Postgraduate Student at the Department of Non-Ferrous Metallurgy

The paper analyzes the formation of fine-grained fluorocarbon-containing technogenic materials the Irkutsk Aluminum Plant produces in large amounts (up to 9 thousand tons per annum per 1 ton of primary aluminum made in Soderberg-anode electrolyzers). It presents the analysis of the chemical composition of the sludge accumulated in the sludge dumps; the sludge consists of the electrolysis-produced cryolite-alumina melts of dust from electrofilters plus sludge from wet gas cleaning plus tailings of coal foam flotation. Samples of technogenic materials are analyzed by chemical, titrometric, and X-ray phase analysis using Russia-made DRON-3.0 X-ray diffractometer. Analysis reveals that sludge contains valuable elements such as fluorine, aluminum, and sodium. X-ray phase analysis reveals that the flotation tailings are 65% carbon, up to 15% cryolite, up to 10% chiolite and up to 10% aluminum oxide (α-Al₂O₃-corundum). Gas purification sludge samples are: 60% cryolite, 20% carbon, 10% corundum, possibly β-potassium cryolite, with traces of fluorite, quartz, and sodium sulfate. The electrofilter dust is 50% cryolite, 15% aluminum oxide (corundum) and chiolite, up to 10% carbon, with traces of fluorite and fluoric aluminum. Diffractogram analysis shows that the sludge from the sludge dumps is up to 78.7% cryolite, 11.9% carbon, 4.44% carbonate (dolomite), and traces of α-Al₂O₃-corundum and fluorite. Based on the analysis of the sludge elements and phases, the researchers propose a method to process it so as to extract the valuable components and to produce fluorine salts used in electrolysis, i. e. coprocessing by flotation with the coal foam removed off the electrolyte surface to produce secondary flotation cryolite.

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