STUDY OF FLUORINE RECOVERY FROM THE SPENT LINING REFRACTORY PART OF ALUMINUM PRODUCTION ELECTROLYSERS

The PURPOSE of the paper is to study the chemical composition of the research object represented by the refractory part of the spent lining (SL) of aluminum electrolysers and to investigate the process of fluorine recovery from the spent lining refractory part by a hydro-metallurgical method. The study is also given to the influence of aqueous leaching parameters (duration and temperature) on the fluorine recovery into solution and the evaluation of the thermodynamic probability of reactions between the lining components and various solvents under leaching. METHODS. The methods of x-ray fluorescence and x-ray phase analysis as well as scanning electron microscopy are used to study the composition of samples. The liquid analyzer EXPERT-001 with a combined pH electrode ESK-10601/7 K80.7 and an ion selective electrode ELITE-221 of Nika company are used to measure the pH and concentration of water-soluble forms of fluorides. RESULTS. The chemical composition of the research object has been studied. The influence of process temperature and duration on fluorine recovery from the spent lining under water-soluble NaF dissolution has been investigated. The thermodynamic calculations of interaction reactions of the main fluorine-containing components of lining such as cryolite Na₃AlF₆, chiolite Na₅Al₃F₁₄, calcium fluoride CaF₂ with the solutions of sodium hydroxide, carbonate and hydro-carbonate under leaching have been performed. CONCLUSION. Conducted laboratory studies allowed to determine that the maximum fluorine recovery of 62.95% is achieved under water leaching at the temperature of 60°C and process duration of 120 minutes. Based on thermodynamic calculations and performed experiments a basic technological scheme is proposed for regenerative cryolite production from leaching solutions using either the solutions of sodium bicarbonate or the solutions of gas purification and slime waters of operating plants of primary aluminum production.

electrolyser, spent lining, refractory part of lining, leaching, thermodynamics, regenerative cryolite

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