Fundamental studies on electrochemical production of Al-Li alloys from oxyfluoride melts
AuthorNarayan, Ananth R.
AdvisorReddy, Ramana G.
Mining and Metallurgical Engineering
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A new process for the direct production of Aluminum lithium alloys in fluoride melts using low cost lithium oxide as a lithium source was investigated. Lithium was electrolytically deposited from 4LiF.CaF2 +Li 20(sat.) electrolyte using a graphite anode and liquid aluminum cathode. From the point of extraction of metals from oxides in fluoride melts, the solubility of the oxide in the fluoride melt is important since it is the dissolved oxide which reacts with the electrodes to form the metal. The solubility of Li 2o was found to increase from 10.6 wt.I at 1058K to 14.8 wt.I at 1133K and this was sufficient to attempt further experimental investigations on the electrolysis process. The overvoltage on the graphite anode was measured as a function of applied current density to obtain a deeper insight into the reaction mechanisms at the anode. A two electron charge transfer reaction at the anode in the Tafel region and a limiting current density phenomenon above 0.37 A/cm2 was observed. The oxyfluoride complex species was predicted to be predominantly Li0F2-. The effect of temperature and electrolyte composition on the cell efficiency was studied. An optimum temperature of 1121K with 4LiF.CaF2+Li 20(sat.) electrolyte showed the highest cathode current efficiency. The cathode current efficiency increased with increasing wt.I of LiF in the electrolyte and an optimum value of 361 was obtained for the cathode current efficiency at 1130K. The liquidus temperature of the electrolyte decides the process temperature and attempts to reduce the liquidus temperature by the addition of fluoride compounds would improve the efficiency of the cell. This would also reduce the redissolution of lithium in the electrolyte.
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