US2165742A - Process for separating magnesium and like metals which sublime from their ores and compounds - Google Patents

Description

y 1939- H. A. BLACKWELL ET AL 2,165,742

PROCESS FOR SEPARATING MAGNESIUM AND LIKE TADS WHICH SUBLIIE FROM THEIR ORES AND COMPOUNDS Filed Sept. 1, 1936 'atented July 11, 1939 PATENT OFFICE PROCESS FOR SEPARATING, MAGNESIUM AND LIKE METALS WHICH SUBLIME FROM THEIR ORES AND COMPOUNDS Harold Alexandre Blackwell and William Lawrence Turner, Garston, England Application September 1, 1936, Serial No. 98,994 In Great Britain September 4, 1935' 1 Claim. '(CI. 75-40) This invention relates to an improved process for separating magnesium, and like metals which sublime when they are reduced from their ores and compounds; in the following specification the term "magnesium ore is to be construed as including ores and compounds of the other metals which sublime like magnesium.

One of the objects of the present invention is to provide a process for the production of magnesium metal (a metal which is now in greater commercial demand than hitherto) which is simple and effective in operation.

Present processes such as, electrodeposition from solutions or from molten compounds contuining magnesium or by sublimating froma mixture, contained in a retort, consisting of calcium carbide and a compound of magnesium, which is heatedup with fuel or gas, are limited in their capacity and are methods not favorable for large production.

This invention makes use of the fact that carbonaceous material, silicon and its alloys'and like reducing agents which are electrical conductors, will reduce magnesium from its ores and compounds when the latter are in a direct mixture with the reducing agent if precautions are taken to prevent the vaporized magnesium from combining with any gas, such as oxygen, carbon monoxide, or the like, with which it might come in contact during the reaction and provided that a special heating method is employed. The reduction of magnesium by smelting with a reducing agent has been carried out in the presence of an inert gas or in a high vacuum to prevent oxidation 01' the reduced metal. The chief dii'll-v culty has been to maintain at the high temperature of reduction which is above the boiling point of magnesium the necessary conditions for along enough time to obtain any considerable quantity of magnesium metal. I

The possibility of producing magnesium on a commercial scale is governed by a number of factors. Otthese one of the most important is the securing and maintaining of an atmosphere, which, since the reduction of magnesium ore is carried out at temperatures above theboiling therefore is to provide a process and apparatus which makes'the obtaining of the aforesaid desirable-production-factors possible, since smelting ing from the smelting process present to attack the distilled metallic vapour, the gases resulting from the smelting process being drawn off at an early stage by a suction pump.

Another object of the invention is to obtain a high thermal efficiency in the process by smelting the metal-bearing ore by inter-mixing it with a reducing agent which can be heated by induced currents so that aiiiiiform and rapid heat is produced throughout thecharge.

Another object of the invention is to provide good conditions for the process of sublimation in that the smelting process being carried on by induced currents in the charge it is possible to locate a relatively cold surface close to the charge being smelted, and this accelerates sublimation.

Another object of the invention is to provide a continuous process in which the cold surface on which the distilled metallic vapour sublimes can be immediately removed when the charge is spent (for fusion of the condensate thereon) and a new cold surface or condenser located above the mouth of the crucible in which the smelting operation is carried on.

Accordingly the present invention provides a process for separating magnesium, and like metals -which sublime, from their ores or compounds which comprises mixing and reacting magnesium ore and a reducing agent in physical contact with a mediumffor heating the mix, which is of such a character that transitory or eddy currents can be generated therein (to heat the medium) by high frequency induction (e. g. from an induction coil) and under vacuum orpartial vacuum and elevating the temperature of the-heating medium by the high frequency induction to a value at which reduction of the magnesium ore and distillation of the resulting metal takes place.

According to a further feature of the present invention there is provided a processfor separating magnesium and like metals which sublime, from their ores or compounds which comprises ng and reacting magnesium ore with such a reducing agent that transitory or eddy currents can be generated thereimby which currents the reducing agent is heated, by a high frequency induction coil and under vacuum or partial vacuum and elevating the temperature of the mix by high frequency currents to a value at which reduction of the magnesium ore and distillation of theresulting metal take place.

Conveniently in 'carrying\out the process the magnesium vapour, which "is distilled on, is collected in a constantly-evacuated condenser and a sufficiently reduced pressure is maintained in the vessel into which the magnesium vapour is distilled to prevent reverse reaction by the magnesium vapour with any of the gases liberated during .the reduction process. The reducing agent used in the process may be a carbonaceous compound, such as graphitic carbon, carbide compound, silicon, aluminium, calcium, or alloys thereof.

One form of apparatus by which the above process is carried out, comprises a crucible, for the ore to be reduced and a reducing agent, located within the field of a high frequency induction coil whereby the crucible or the contents thereof are heated by induction, and a collector located above the mouth of the crucible and the interior of which is maintained under vacuum or partial vacuum by an exhaust pump. The collector may be in the form of an inverted cone or dome, the exterior surface of which is maintained cool to permit the condensation of the magnesium vapour. Conveniently the collector is detachably mounted in an airtight manner on the mouth of the crucible to permit a new collector to be substituted and the old collector with condensed magnesium thereon removed for fusion of the condensed magnesium. A high frequency heating coil may be associated with the collector whereby the condensed metal can be fused and allowed to flow away therefrom. An internal channel may be provided in the interior of the collector at the lower part thereof, this channel being arranged to collect the fused magnesium metal condensed on the interior of the collector. Exit from this internal channel may be controlled by valve means so that the fused metal can be discharged directly into ingot moulds.

One form of apparatus suitable for use in carrying out the process will now be described with reference to the accompanying diagrammatic drawing which is a sectional elevation of a form of high frequency furnace and condenser collector for the magnesium.

The high frequency furnace is a well known type comprising a steel container i0 provided with an internal copper shield ill and external stiffening bands l2. The coil is shown at l3 with terminal coil connections l4. The refractory furn'ace lining i5 is supported by insulated blocks l6 and I1 and its external surface is cooled by water circulated through the coil l3 by the inlet and outlet conduits 36 and 31.

The collector-condenser I9 is in the form of an inverted dome and has a depending .skirt 24 which extends close to the furnace lining to direct the vapors towards the upper and cooler interior surface of the dome. The exterior of the dome is cooled by water flowing through a coil of copper piping 25 which may also serve as a high frequency coil for fusing magnesium which is condensed on the dome. The lower interior part of the dome may have an internal channel 20 (shown in dotted lines) the outlet of which is controlled by a valve 2| and this channel would serve to collect magnesium fused in situ on the dome and allowed to flow from the channel into ingot moulds. The crown of the dome is provided with a suction outlet 22 which is connected to an exhausting air pump 26.

The form of dome shown in full lines may be connected by water cooled dismountable joints 23 to the high frequency furnace. The purpose of this arrangement is to permit the dome withthe magnesium condensed thereon to beremoved for fusion of the magnesium and a fresh dome used for a new furnace charge. The cooling water may be allowed to flow on to the joints and collected in the trough 21 and be drained away therefrom to a sump. Where the apparatus is worked on continuous lines, that is to say the collector condenser I9 is removed after each charge and a new collector'condenser of similar construction substituted for condensing a new charge, then the coil 25 will not be used for fusing the condensed charge in situ; this fusing operation will be separately performed.

The high frequency alternating current generator used for an induction furnace is a wellknown apparatus. The generator which supplies the coil I3 is indicated generally at 28, and as is well-known comprises the usual thermionic valve generator. The mains are indicated at 29 and the leads 30 from the generator are connected to the terminals it forthe coil l3. A similar form'of L generator may be connected to the .coil 25 and this generator is indicated at 32, the leads 33 supplying the necessary energy to the coil 25.

In using the apparatus above described dolomite or magnesite ore is mixed with coke and charged into the space surrounded by the lining B5. The condenser portion is is adjusted and sealed by suitable means such as bolts 39 and nuts 40 and then with the use of the air pump the reaction chamber formed when the condenser is mounted in position is evacuated of air and gas to a degree sufficient to prevent reverse reaction between the magnesium vapor and any gases liberated during the reduction process. The dissociation pressure here defined is meant to be a sufficiently reduced pressure to prevent reverse reaction between the magnesium vapor and any of the gases liberated during the reduction process. The high frequency valve is tuned in to give the desired frequency of current the periodicity of which is sufliciently high to heat the reducing agent and immediately the carbon reducing agent is increased in temperature. The heat generated in the carbon reducing agent is localized and in intimate contact with the ore to be reduced, thereby providing ahigh thermal efficiency. The gases initially resulting from the application of heat (when the coke is raised to a red heat) may be carbonic acid gas, carbon-monoxide and aqueous vapour. These are quickly eliminated by the suction pump, and the temperature of the reducing agent is increased to above the boiling point of magnesium which at normal pressure is of the order of 1100 C. The magnesium metal resulting from the reduction of the ore distils and the vapour rises into contact with the cold surface of the collector condenser l9 and is condensed on the inside surface thereof. From there the distillate can be removed by fusion and cast into ingot moulds. It will be observed that with the localized heat generated in the charge and the comparatively cool collector condenser used for the sublimation of the metallic vapour the process of sublimation is accelerated by the large temperature drop between the furnace and the collector condenser.

The barometric reading must not be allowed to rise above 2 mm. with the reducing agents and ores described, namely, cokeor calcium carbide and dolomite or magnesite) or no magnesium vapour will condense but it will reduce carbon from the carbon-monoxide instead. If the vapour density of the mixed vapours is insufficiently reduced (under certain circumstances) this reverse reaction may occur. -It will be understood that there is no objection to maintaining a much higher vacuum and in somecases this is a decided advantage. The magnesium metal will be condensed in large quantities inside the condenser part I9 while carbon monoxide will be carried away by the pump.

In order to show how such a process can be carried out we now give examples of the process:

Example I 12 parts by .weight .of coke and 39 parts by weight of magnesite (93% MgO dead burnt) were mixed together, of which 8 parts by weight coke and 39 parts by weight magnesite were crushed and mixed intimately and 4 parts by weight of coke added in the form of lumps approximately 1 inches in diameter. These were placed in the container or crucible, the casing closed and suitably sealed. The whole was evacuated by the air pump until the pressure indicated was 0.01 mm. barometric reading. The H. F. valve was tuned in and in a few minutes when the temperature reached a red heat, magnesium vapour began; to distil off. At 1200 C. magnesium ceased to distiloif and 20 parts by weight of magnesium crystals were recovered in the condenser.

Example II In a further example in which ferro silicon was used as the reducing agent instead of coke,

were crushed and mixed intimately and 12 parts by weight of ferro silicon were added in the form of lumps approximately inch in diameter. These were" placed in the container or crucible and the casing sealed. The casing was evacuated by an air pump until the pressure indicated was equal to 0.01 mm. barometric reading. The H. F. valve was tuned in and in a few minutes when the temperature reached a red heat, magnesium vapour began to distil ofif. At, approximately 1200 C. magnesium ceased to distil off and 41.8 parts of magnesium crystals Were recovered in the condenser. A bullet of ferro silicon containing approximately 18% silicon, 82.0% iron remained in the container with the spent charge.

The examples hereinbefore described are given by way of illustration and are not to be construed as a limitation of the invention which is defined in the following claim.

We claim:

A process for separating magnesium and like metals which sublime from magnesium and like ores which can be reduced, comprising mixing and reacting magnesium and like ore in subdivided form with graphitic carbon in sub-divided form and heating the reaction mix by high frequency induction, the periodicity of which is sufficiently high to heat the reducing agent quickly to the temperature at which reduction of the magnesium ore and distillation of the resulting metal takes place without liquefaction or-fusing of the reaction mix, and carrying out the reaction in a continuously evacuated container, pressure of the atmosphere within the container not being permitted to rise above 2 mm. mercury pressure, and condensing the vaporized metal. H. A. BLACKWELL.

W. L. TURNER.

Images