US1861798A - Method of making metallic magnesium - Google Patents

Description

Patented June 7, 1932 UN lTE DSTA TES PATENT: ol-rlcla RALPH M. HUNTER AND SHELDON B. HEATH, F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, MIGBIGAN Nomawing.

The present invention concerns a method of producing metallic magnesium by the electrolysis of a fused bath containing mag-' essary to replenish the bath and maintain it of the desired character by feeding thereto 16 an equivalent of the magnesium and chlorine or other essential ingredients which, in the course of operations, have been or may-be removed therefrom.

It is well known that the ideal feed to such 20 a cell comprises anhydrous MgGl and that accompanying water will reduce the current and power efliciency of electrolysis. It is further known that inert constituents of the feed, such as MgO, tend to settle out of the bath, and unless removed therefrom, will accumulate and interfere with continuous operation. Such sediment must accordingly be removed, which is customarily done by dredging from time to time as re uired, but this operation removes also part 0 the bath along with the sediment or so-called sludge. In practice we have found that as high as two equivalents of bath may be removed in that way with one uivalent of sludie figured as MgO. The bat so removed wit the sludge must, of course, be returned by feeding to the cell the constituents so removed in addition to that required to replenish the MgCl converted to metal and chlorine.

Anhydrous MgCl is not only difiicult and expensive to prepare, but on account of its hygroscopic properties it is practically impossible to handle it without its taking up some moisture, and in practice, a content of 95 per cent MgCl in the chloride fed to the cell is considered obtainable good practice.-

In U. S. Patent No. 1,567,318 is disclosed a method of feeding MgCl containing water, whereby the detrimental effects of the water '0 are minimized.

or MIDLAND, moment, a coaroan'rron or un'rnon or name METALLIC menasruu Application mm m 27, 1929. Serial 110.886,!518.

In the copending application Serial No. 280,659, there is disclosed by Sheldon B. Heath, co-inventor herein, a method of utilizing magnesium chloride containing basic Itghlglride to replenish and maintain the fused We have discovered an improved method of introducing the MgCl fed to such an electrolytic cell having marked advantage as contrasted with methods heretofore disclosed or known to us, said improved method being ap plicable to introduction of MgCl containing water orsimilar introduction of MgCl containing basic salt.-

To the accomplishment of the foregoing and related ends, the invention, then, consists of the. steps hereinafter fully described and a particularly pointed out in the claim, the following description setting forth in detail one approved mode of carrying out our invention.

It has heretofore been customary to introduce the feed at one point in the cell and in accordance with the patent application referred to above, adjacent the anode. Such method of feeding gave improved results over previous practice 'on a relatively small scale, but when cells of large capacity were used, particularly cells employing a plurality of anodes which in certain cases may be distributed relative to a large bath area," that method of feeding was foundto produce large quantities of sludge, to involve over-cooling of the bath locally at the point of feed introduction, and to localize anode wear. The removal of this excessive quantity of sludge entailed the removal therewith of increased quantities of bath requiring increased added feed to maintain the bath, such feed carrying with it more basic salt or water or both, thereby adding still further to the sludge formation.

-We have now discovered that if the cell feed including MgCl containing basic salt or water or both be fed to the cell in a manner to distribute it relative to the active anode surface, a smaller amount of sludge is formed, local cooling of the bath is substantially avoided and the anode wear is distributed more evenly. The dredging is correspond- 100 ingly reduced as is. the loss of bath therewith and what is most important the requirement for feed is'likewise markedly reduced. The mechanics ofthe phenomenon of reduced sludge production are not definitely lmown.

It may be that thedistributed mode offeeding permits the solution in the bath of the face instead of allowing it to fall to the bottom of the bath where it becomes inert basic chloride adjacent "the activeanode sur and that the so dissolved basic salt is reacted upon by CO and chlorine to form M 1 CO and HCl. Whatever the cause 0 the said phenomenon the improved method of introducing the feed constitutes a valuable improvement in the art.

' 1 of the feed relative to the anode surface is to f A simple method of attaining distribution introduce said feed at a number of points instead of at one point. a The size, character and form of the cell will naturally determine the exact method of introduction and the number of points at'which' introduction may advisably be made, but very marked improvement is attained-by introducin at even but two points in a cell of upwa-r of 10000 ampere capacity m t still further improvement 1 the stepor steps stated by the may be expected by introducing such feed at more than two points,.the feed being in troduced in a fairly continuous manner.

We have found further that good results may be thus obtained when using a feed carrying as low or lower than 5 er cent equivalent MgO by introducing it into the bath at other points than adjacent the anode,

but we prefer, particularly with feeds running higher than 5 per cent equivalent MgO content, to introduce same adjacent the anode distributed relative to the anode surface. Other modes of applying the principle of our invention may be em loyed instead of the one explained, change being made as regards the-method herein disclosed, fprovided ollowin-g claim or the equivalent of such stated step or steps be employed. 7

We therefore particularly point out and distinctly claim as our invention e In the production of metallic magnesium by electrolyzing a molten bath containing magnesium chloride, wherein the raw mate-' rial fed tosaid bath consists of magnesium chloride containing some water or basic chlo.

ride, the improvement which consists in feed ing such raw material tosaid bath adjacent the anode at a plurality of points distributed with reference to the anode surface.

Signed by us this 23rd day of Ma 1929. RALPH M. HUNT R.

SHELDON B. HEATH.