US1820022A - Method of producing substantially pure metallic magnesium directly by electrolysis of a fused bath - Google Patents

Description

Patented Aug. 25, 1931 UNITED STATES P'A'TENTi oFF cr.

RALPH I. HUNTER, OF MIDLAND, MICHIGAN, ASSIGNOB T THE'DOW CHEMICAL CO!- PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN .EETHOD OF PRODUCING SUBSTANTIALLY PURE METALLIC @MAGN ESIUM DIRECTLY A BY ELECTBOLY SIS OF A FUSE!) BATH Io Drawing.

The present invention relates to the production of metallic magnesium by the electrolysisof a fused bath containing magnesium chloride.

An object of the invention is to separate the metal directly from the bath in a sufficiently pure condition to enable its use in the arts without further refining.

It has been considered necessary and has been the practice heretofore, so far as I am aware, to subject metallic magnesium produced in the electrolytic process to a subse-'- quent refining procedure. Various modes of such procedure have been used or proposed.

One of the least costly procedures is to remelt the crude metal in the presence of a limited amount of a suitable flux with which it is then agitated, said flux being of a character to coat the surface of the metal ex posed to the air so as to protect it from oxidation. After a period of such washing, the

basic magnesium compounds present in the 1 r'aw metal are largely washed out and transferred to the flux whereupon the metal may i be dipped or" otherwise separated from the flux and cast into ingots or disposed of as desired. 7

Such practice requires arehandling and rem'elting of the metal and provision of associated plant and apparatus for the refining step. I

I have invented a method of producing Jhe equivalent of the so refined metal directly in the electrolytic cell whereby such rel andling', remelting and plantcosts are saved.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the method hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail one mode of carrying out the invention, such disclosed mode illustrating, however, but one of various ways in zsliph the principle of the invention may be scribed.

Application filed Kay 31, 1929. serial in. 867,251.

4 I electrolyze a suitable fused bath contain-' ing magnesium chloride and sodium chloride. The exact composition of the bath appears to be unimportant. Any bath suited to liberate magnesium upon electrolyzing will serve as a washing agent in my process, as hereinafter described. I prefer to use for the electrolysis a type of cell in which the liberated metal floats upon the bath, I prefer in any event a type of cell in which the metal is gathered together .into a compact molten mass. Such an electrolytic cell is disclosed in co-pending application Serial Number 210,785 by Louis E. Ward and the applicant herein. In the cell therein described the metal is automaticall led into a gathering or collecting well. ther forms of construction than therein disclosed may obviously be employed, and it is further obvious that in some such, the collecting well or zone may be at one, side or one end, i. e. along the margin of the fused bath, thereby permi ing. easy access for the operations hereig aften de-y' v I permit the metal to collect in such well by the gathering together of the separate globules of metal pre erably under restricted contact with the air or in an atmosphere of hydrogen, if the metal be floating upon the bath, which latter gas may accompany the metal'liberated due to the presence of water or basic chloride in the chloride fed to the bath. After the metal has collected to a substantial depth, which may be several inches, I find that it has acquired a -consistent character, the separate globules having coalesced and squeezed out the bathor flux. I agitate or mix it with the cell bath which may be readily done by removing the cover above the metal, if one be used, insert- 4 ing a ladle, dipping and pouring the metal over and over whereby it is contacted with the bath. Mechanical a 'tating means may, however, be employed, riven by power, if 00 desired, to impart relative motion to the bath and the metal whereby freshsurfaces of metal are brought successively into contact with the bath. After a'short period of such washing I withdraw the metal and cast it into molds. This may be done by ladling or other procedure convenient or desirable. I find the metal so treated before withdrawing from the cell to have substantially the same" degree of purit as the metal heretofore produced by with rawing from the bath without such treatment, casting into crude ingots, subsequently remelting, washing with a flux and again casting into ingots. The metal may be obtained by means of my simplified procedure with a purity of 99.85 per cent or better.

The impurities in the metal are washed out by the bath, and inasmuch as such in crement of impurity in the bath is a small one, substantiall no additional burden is placed upon the redging of the sludge from .the cell incident to its normal operation.

.Much effort has been directed to the development of thetechnicaldetails of after refining, i.-e. remelting in a refining flux. The fused bath, which is used in the cell, may or may nothave the ideal composition indicated by such research. I find, however, that equivalent results are readily and cheaply obtained emplo g the cell bath itself as refining flux. fter refining usually has been done by washing the remelted .metal with a quite limited weight of flux,

whereas in my method I wash it with a relatively very large weight of flux. The use of flux to the extent of one-half (.or less) the weight of metal is a customary ratio for after refining. In my method the weight of the flux or bath relative to the metal may be several hundred times that of thelattcr. The dredging of the sediment is a normal operation in the electrolytic step which pro 'cedure keeps the bath effectively clean and active as a washing agent for the metal. The advantage of a large ratio of flux to metal appears to outweigh any disadvantage which may be inherent in the. bath composition relative to an ideal composition thereof.

- In after refining the bathbeing small from to" percent dependin upon the type of'cell used. I find that i the metal I be gathered into a area to a substantial. .depth enablingit to aggregate into the bath.

a consistent mass and be then washed, as herein described, the purification is unexpectedly improved and ametalin excess of 99 percent pure is readily obtained.

I find further that practicing washing upon such an aggregated mass of metal there results a prompt and effective separation of the metal from the flux and that the withdrawal of the metal from the cell with a minimum amount of flux, is easily done the total impurity including the flux being less than one percent of the total withdrawn.

Although my method of producing a substantially pure metal is more readily applicable when employed in large scale wor ing i. c. with electrolytic cells using current in excess of 10,000 amperes, it may be employed in small scale production with advantage.

It is obvious that myvimproved method eliminates the requirement for separate melting pots, furnaces and associated e uipment incident to and connected with a er refining. It saves the cost of rehandl ng, labor and fuel for reinelting. It also consolidates the production and refining steps at one'point in one vessel regllnring a minimum of supervision, labor, el and equipment and hence constitutes a valuable ad- Vance in the art.

Other modes of applyin the principle of my invention may be emp oyed instead of the one explained, change bein made as regards the method herein disc osed, provided the step or steps stated by any of the following claims or 'the equivalent of suc stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invent1on:

1. In a method of the character described, the step which consists in washing molten metallic magnesium with the fused bath containing magnesium chloride from which it has been liberated byelectrol sis before removal of said metal from said ath.

2. In a method of the character described, the steps which consist in electrolyzin a fused bath containing magnesium chloride, gathering together the globules of the liberated metal into a consistent mass substantially free from inclusionsof bath, agitating andwashing the so gathered metal with the bath and removing the purified metal from the'bath. 1

3. In a method of the character described, the steps which consist in electrolyzing a fused bath containing magnesium chloride under conditions permitting the liberated nietal to float thereon, gathering the liberated metal into a consis nt mass floating on said bath, agitating a (1 Washing the so collected metal with [the bath upon which it floats and removing the purified metal from 4. In a method of a substantially pure magnesium metal by electrolysis of a fused bath containing magnesmm chloride, the steps which consist in gathering together the globules of metal so liberated into a consistent mass substantially free from inclusion of bath and then setting up relative motion between said gathered metal and the bath whereby fresh surfaces of the metal are brought successively into contact with the bath.

Signed by me this 28th day of May, 1929.

RALPH M. HUNTER.