US2134969A - Production of magnesium - Google Patents

Description

Nov. 1, 1938. K. ERDMANN PRODUCTION OF MAGNESIUM Filed Dec. 29, 1936 INVENTOIZ /Q0.04C adv-ham Patented Nov. 1, 1938 PATENT OFFICE 2,134,969 PRODUCTION or MAGNE IUM Konrad Erdmann, ltadenthein, Austria, assignor to American Magnesium Metals Corporation,

Pittsburgh, Pa.

Application December 29, 1936, Serial No. 118,076 In Austria January 10, 1936 Claims.

This invention relates to the electro-thermic production of magnesium from'oxidic magnesium compounds, particularly by smelting the said compounds with carbonaceous reducing agents.

It is an object of the invention to provide a charging method enabling the charge to be introduced with a minimum loss of temperature into a reduction process requiring the creation and maintenance of very high temperatures up to the discharge of the reduction chamber.

Another object of the invention is to simplify the charging operation without, however, .running the risk of introducing substantial amounts of air with the charge, or being exposed to loss and danger by substantial amounts of magnesium vapors escaping through the charging ,device.

Other objects of the invention will appear as the description proceeds. 1

In the electrothermic production by reduction of oxidic magnesium compounds with the use of carbonaceous reducing agent, the reaction only sets in at temperatures far above the boiling point of metallic magnesium; the liberated metal is therefore obtained in the form of vapors, and that in commixture with equimolecular quantities of carbon monoxide which is formed from the carbon used. Since, at temperatures but slightly below the lowest reduction temperature, magne- 30 sium vapors in the presence of carbon monoxide become violently re-converted into magnesium oxide with the liberation of carbon, all attempts to produce magnesium on these lines remained for along time unsuccessful. The problem thus presented was solved in principle by the adopting of a two-stage process in the first stage of which the magnesium vaporsare condensed to magnesium dust by abrupt chilling to below solidification point of magnesium, from which dust compact magnesium metal is then in the second stage recovered by heating of the dust to temperatures in the vicinity of the boiling point of magnesium until the metal particles coalesce, or by complete re-evaporation and condensation of MgO+C:Mg+CO I is practically displaced to the right of the equation, and, by the admixture of large quantities of the vapors to a liquiddeposit. A further ad-' cold inert or reducing gases, to dilute these products of reaction as they leave the hot reduction chamber while at the same time chilling them abruptly down to a temperature at which metallic magnesium and carbon monoxide are stable in the presence of each other.- It is only at temperatures above 2000 C. that the reduction proceeds at practically useful velocity, and the most favorable temperature conditions are in fact only reached when a temperature of 2500 C. is exceeded. In addition to this first condition for an economically successful reduction work it is necessary, in carrying out the above-mentioned process, to fulfill a second condition which consists in that the mixture of disengaged vapors and gases, rightup to the point of leaving the ,hot furnace chamber, shall not cool down to below the limit of temperature critical for the re-oxidation of the metal. These two conditions are fulfilled, to a hitherto unattained degree, by the method according to the present invention.

In accordance with this invention the mixture of oxidic magnesium compound and reducing agent, afterhaving been rendered plastic by the addition of slight quantities of a liquid binding agent, is so'fed through the bottom of the reaction chamber, with gradual expansion of the cross-section, that a plug of the plastic material fulfills the function of sealing the chamber.

It is already known in electrically heated furnaces to feed the charge in the form of a column of the dry mixture travelling from below upwards. Furthermore, it has also been proposed, and that more particularly in connection with the reduction of oxidic magnesium compounds with the aid of carbon, so to introduce the dry mixture to be charged from beneath into an electrode furnace that it is raised in the cold condition, with the aid of conveying meansjto the level of the horizontally disposed electrodes, to pass then, while acting as current carrying conductor, between the electrodes, after which the vaporous and gaseous reaction products are drawn off through an elongated conduit travers- 45 ing the brickwork of the furnace. With this method the feeding in of the charge is effected, as has already been proposed also for the feeding in of the charge from above, by means of a-locklike chamber interposed in the feed line to the furnace. However, in this manner only imperfect sealing of the furnace chamber is obtained, since the magnesium-vapors entrapped in the lock chambers escape into the open air every time the lock chambers are opened, which imll plies not only a loss but also, in view of the extreme readiness with which magnesium vapors ignite, a danger. On the other hand if excess pressure is maintained in the lock chambers by the introduction of hydrogen, with the view of forcing back the magnesium vapors, hydrogen escapes when the chambers are opened, and this gas is likewise readily ignitible; moreover, hydrogen also passes from the lock chambers kept under increased internal pressure, into the furnace, with the result that the economy of the process is impaired, since the hydrogen has to be heated in the furnace chamber up to the high reduction temperature and such additional heat has to be withdrawn again from the vaporous and gaseous products of reaction on their leaving the furnace. With the present process these drawbacks are obviated by virtue of the fact that the feed passage of the furnace is sealed by the charged plastic mixture itself.

On the other hand it has also already been proposed to introduce solid bodies into reaction chambers, for heating, in such a manner that the substances themselves act as sealing means, and for this purpose to stir up the substances to be introduced with a liquid, to form a paste. Since this known method solves the problem of feeding solid bodies into reaction chambers under high internal pressure, in an uninterrupted working process, it has for a pre-condition that the liquid evaporates more or less completely during the operation of forcing in tne charge, so that the mixture becomes solid by the time it enters the reaction chamber. The solid plug thus obtained is then thrust into the high pressure reaction chamber by the pressure of a piston. This plug thus represents the sealing member between the high pressure chamber and the space behind the piston, in which ordinary pressure prevails. In contrast thereto, in the method according to the present invention, the mixture to be charged is introduced into the furnace in a plastic state, which makes it possible for the material to be slowly brought right up into the hottest zone, in the form of a travelling column, without excessive increase of frictional resistance, and in this manner to pre-heat the material to a very high temperature. To the effects of the known method of introducing solid bodies into reaction chambers under high internal pressure there is hereby added the advantage that very considerably higher reduction temperatures can be attained under the same electrical working conditions. Furthermore, in consequence of the fact that the mixture to be charged is introduced into the furnace chamber from below, the gaseous and vaporous reaction products, which in the present process are drawn off close to the zone of greatest heat, in order to prevent gradual cooling off, do not encounter colder matter on their way to the discharge, so that reversal of the reaction within the furnace itself is more effectively avoided by the present process than has hitherto proved possible.

It is in conformity with the intentions underlying the present process that the material of the charge be introduced into the hottest zone at as high a temperature as possible, and this result may be achieved by bringing the column of charged mixture up to this zone with gradual enlargement of its cross-sectional area.

An electrode furnace suitable for carrying out the process according to the invention is shown in vertical section by way of example in the accompanying drawing.

The closed muffle I, through the top of which the electrodes 2 are inserted perpendicularly into the heating chamber, rests upon a pedestal 3, and is enclosed within a metallic shell 4 filled with heat-insulating loose material 5. The side walls and the bottom of the muffle I are supported against the shell 4 by means of struts 6. Into the bottom of the muffle there discharges an upwardly expanding or fiared passage 1, e. g., of conical form, to which thereis connected the feed pipe 8 receiving the charge from a tube 9 provided with a screw conveyor ID. The lower end II of the feed pipe takes the form of a cylinder in which there works a reciprocating piston H which is driven by the crank gear l3. The gaseous and vaporous products of reaction pass from the heating chamber I into a condenser ll.

The charge, consisting for example of an intimate mixture of finely ground magnesia and carbon, is rendered plastic and slippery with about 5% of tar or similar carbonizing binding agent and fed by the screw conveyor 9 to the piston chamber ll. At the up-stroke of the piston I2 the material is thrust into the feed pipe 8 and remains in the position to which it is pushed, owing to the tenacity of the mass, so that on the down-stroke of the piston a hollow space is left into which fresh material is introduced by the screw 9.

With the process according to the present invention there is no residue left behind in the reaction chamber. This is due to the fact that the gas yielding reaction MgO+C:Mg+CO proceeds at a temperature which is very considerably above the boiling point of magnesium, i. e., the reaction sets in only after the vapor pressure of the magnesium amounts to many atmospheres. The gases and vapors evolved being thus suddenly expanded can on account of their vehemence therefore carry over with them also the liquid and solid concomitant substances since the latter occur in extremely fine distribution.

According to the provisions of the patent statutes I have explained the principle and operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practised otherwise than as specifically illustrated and described.

I claim:

1. Process for the electro-thermic production of magnesium from oxidic magnesium compounds, of which no residue is left behind in the reaction chamber, comprising the steps of blending a mixture of the oxidic compound and a reducing agent with a slight amount of a liquid binder sufficient to convert the mixture into a fairly coherent plastic mass, and stuffing the so plastifled mixture, in the form of a confined vertical mass, from below upwards into the reduction chamber in such a manner that said mass fits tightly into the hole of the charging opening while remaining in a plastic condition, and introduction of substantial amounts of air with the charge is prevented.

2. Process for the electro-thermic production of magnesium from oxidic magnesium compounds, of which no residue is left behind in the reaction chamber, comprising the steps of blending a mixture of the oxidic compound and a reducing agent with a slight amount of a liquid binder sufficient to convert the mixture into a fairly coherent plastic mass, and stuffing the so plastified mixture, in the form of a confined

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