The electrowinning of lithium from chloride-carbonate melts
- PDF / 1,023,762 Bytes
- 11 Pages / 603.28 x 783.28 pts Page_size
- 51 Downloads / 213 Views
I.
INTRODUCTION
L I T H I U M metal is usually prepared by the electrolysis of an anhydrous 44 to 50 wt pct LiCl and 66 to 50 wt pct KC1 electrolyte at a temperature of 730 to 770 K, with an anode to cathode spacing of 5 - 1 0 cm, to give a metal purity of 99 pet with the major contaminant being sodium, fl-61 The cells operate at 6 - 9 V, with current efficiencies of 90 pct, giving the energy requirement of 3 5 - 4 0 kWh kg- Li. As both the products of the electrolysis process, liquid lithium and chlorine, are less dense than the electrolyte, it is necessary to reduce the chance of back reactions by having a steel wire mesh diaphragm between the anode and the cathode. The production of anhydrous lithium chloride feed material is an expensive energy intensive process involving the reaction of lithium carbonate with hydrochloric acid and heating the solution above 368 K where anhydrous lithium chloride crystallizes, m The lithium chloride must then be stored in completely dry atmospheres to prevent it absorbing moisture. It would he a considerable advantage if lithium could be electrowon from cells fed with lithium carbonate instead of anhydrous lithium chloride. As well as the economic attractions of having a cheaper feed material, there should also be energy savings in the cell as the decomposition potential should be significantly lower. This is shown in Table I. The most favorable reaction is the reaction with carbon to form CO2 which, as well as having a potential significantly lower than the decomposition potential of lithium chloride, requires a much lower heat input. In a LiC1-KC1 eutectic melt, lithium deposition occurs at - 2 . 5 4 3 V v s a Ag/Ag (I) reference eleclrode~9Jthrough the reaction Li (1) + e = Li (1) [1] However, against the same reference, the reaction t~~ CO~- (1) + 4e- = C (s) + 302- (1) [2] WILLIAM H. KRUESI, Senior Scientist, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, England, is with Interpm, Golden, CO 80403. DEREK J. FRAY, formerly University Lecturer, Department of Materials Science and Metallurgy, University of Cambridge, is Professor of Mineral Engineering and Head of Department, Department of Mining and Mineral Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom. Manuscript submitted November 25, 1992. METALLURGICAL TRANSACTIONS B
occurs at - 2 . 5 V. S t u d i e s U1A2,13] of the cathodic reduction process in carbonate melts have shown that alkali metal is deposited from binary melts consisting of sodium and potassium carbonate but melts containing lithium carbonate always resulted in the deposition of carbon by the reaction CO32- (1) + 4e- = C (s) + 302- (1)
[3]
Possible solutions to this problem are either to lower the activity of the electrowon lithium sufficiently so that its reduction potential is less negative than the reduction of the carbonate ion or to isolate the catholyte by use of a porous diaphragm which hinders the transport of carbonate ions to the cathode. The concept of using lithium carbonate was fi
Data Loading...
