Method of producing lithium
US 3344049 A
Description (OCR text may contain errors)
United States Patent 3,344,049 METHOD OF PRODUCING LITHIUM Erich Thieler, Bad Homburg vor der Hohe, Germany, assignor to Foote Mineral Company, Exton, Pa., a corporation of Pennsylvania No Drawing. Filed Mar. 1, 1965, Ser. No. 436,263 Claims priority, application Germany, Mar. 6, 1964, M 60,174 3 Claims. (Cl. 20468) The present invention relates to a method for producing lithium through the electrolysis of molten salt mixtures.
It is well known how to produce metallic lithium through electrolysis of molten lithium salt mixtures, such as a mixture of LiCl and KCl. The prior art suggests the molten salt electrolysis of Li CO as well as a mixture of alkali chlorides with the addition of a small quantity of oxygen-containing alkali salts, for example Li CO Utilizing the methods suggested by the prior art has caused considerable technical difficulty in that the graphite anode is oxidized by the nascent oxygen produced in the electrolysis and is also mechanically destroyed, whereby undesirable foaming and contamination of the melt bath takes place and the electrolysis becomes inoperable.
However, it has been discovered that it is preferable to proceed directly to the lithium electrolysis from such oxygen-containing lithium salts as, preferably Li CO Oxygen-containing lithium salts such as Li CO may be made by the usual process for extracting lithium salts from lithium ores. Proceeding directly to the lithium electrolysis from such oxygen-containing lithium salts obviates the necessity for conversion of Li CO to LiCl as a separate process.
A method has been discovered of producing lithium through molten salt electrolysis of salt mixtures such that the chlorine produced in the electrolysis cell reacts with oxygen-containing lithium salts, particularly Li CO and the salt melt is renewed by the LiCl produced.
This process has the advantage that the continuous melt electrolysis of lithium-containing alkali salt mixtures can be carried out and maintained even with certain oxygen-containing lithium salts, which salts are made in the conventional processes for extracting lithium salts from ores, for example Li CO or LiOH. In addition, the anode is not attacked since the conversion of carbonate to chloride is completed before the molten mixture moves into the electrolysis zone. Furthermore, it is necessary to carry out the known reaction for conversion of Li CO with chlorine in the electrolytic cell itself since this eliminates the diificulties that have prevented the practical accomplishment of the direct conversion of Li CO with chlorine. The problem as evidenced by the prior art has been the lack of a technically suitable and economic material which will withstand attack by chlorine at the required reaction temperatures of between 400-480" C.
The process of this invention may be carried out in commonly used electrolytic cells operating with alkali salt mixtures at a temperature of 400480 C. The cell construction closely resembles that of sodium electrolysis in which the molten zone is separated by a diaphragm into an anode and cathode compartment, and the space above the molten salt is likewise separated into cathode and anode compartments which permits separation of the 3,344,049 Patented Sept. 26, 1967 "ice products of electrolysis, namely alkali metal and chlorine. According to the invention, well dried Li CO is put into th anodic collection compartment with the evolved chlorine which produces CO and 0 by the reaction:
The Li CO should be evenly distributed over the surface of the molten salt in the anodic compartment, and in such amount as is required by the depletion of the LiCl in the melt through production of lithium and chlorine.
The dried lithium carbonate reacts very quickly with the nascent chlorine due to the high temperature of the melt and of the chlorine gas itself. This results in only the newly formed lithium chloride being taken up by the melt. In this manner the disadvantages of the direct electrolytic conversion of Li CO are avoided. In addition, by maintaining an excess of lithium carbonate on the molten surface, practically all of the chlorine released by the electrolysis is used for conversion of the lithium carbonate.
Utilizing the process of the present invention, a continuous molten electrolytic process for obtaining lithium metal is provided which permits the required replenishment of the melt with LiCl continuously through use of an equivalent amount of Li CO which Li CO is converted by chlorine directly to LiCl in the collection space over the anode. Thus the previously required conversion of Li CO to LiCl in a separate process and by separate equipment can now be avoided.
Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the method may be made without departing from the spirit and the scope of the invention as hereinafter claimed.
What is claimed is:
1. In a process for producing lithium by electrolysis of a molten salt mixture containing LiCl in an electrolytic cell wherein the space above the molten salt is separated into chlorineand lithium-collecting spaces, the improvement comprising introducing an oxygen containing lithium compound selected from the group consisting of Li CO and LiOH onto the surface of the melt in the chlorine collecting space whereby the oxygen containing lithium compound is converted by the chlorine to LiCl which in turn replenishes the bath, and withdrawing lithium from the lithium collecting space.
2. Process of claim 1 characterized in that Li CO is converted in the anode collection space with chlorine to LiCl.
3. Process of 1 characterized in that the lithium chloride is formed on the surface of the melt.
References Cited UNITED STATES PATENTS 1,515,001 11/1924 Girsewald et a1. 20468 2,059,750 11/1936 Roder et al 20468 2,862,863 12/1958 Grifiith 20468 FOREIGN PATENTS 582,642 9/ 1959 Canada.
JOHN H. MACK, Primary Examiner.
D. R. VALENTINE, Assistant Examiner.