US3264097A - Method for producing magnesium - Google Patents

Description

Aug. 2, 1966 P. WEISS METHOD FOR PRODUCING MAGNESIUM 2 SheetsSheet 1 Filed Feb. 27, 1965 Wanna 5 fink 1956 P. wasss METHOD FOR PRODUCING MAGNESIUM 2 Sheets-Sheet 21 Filed Feb. 27, 1965 United States Patent 12 Claims. (or. 75-67) The present invention relates to a method and apparatus for producing magnesium.

Conventionally, magnesium is obtained from magnesium oxide or from magnesium-oxide-containing materials by reduction of the magnesium oxide with silicon, ferrosilicon, aluminum, calcium carbide or other reducing agents which upon oxidation will form non-volatile oxidation products. Of these reducing agents suitable for thermic reduction of magnesium, ferrosilicon containing about 75% silicon is the one that has found broadest industrial application. Burned or calcined dolomite is frequently used as the magnesium oxide-containing starting material. To speed up the reaction, it has been proposed to add fluorides of alkali or alkaline earth metals. The finely ground and intimately mixed components of the reaction mixture, i.e., burned dolomite, ferrosilicon and additives, are then briquetted under high pressure and thereafter the magnesium oxide component of the briquettes is subjected to reduction at elevated temperatures under vacuum or in an inert gas atmosphere. Although frequently available, magnesium silicate can be worked up in the above described manner only with great difficulties or not at all.

The difficulties and disadvantages of the above described methods include high labor and equipment requirements for the preparation and briquetting of the reaction mixtures, and the diflic-ulties which are involved in supplying to the briquetted reaction mixture the very considerable heat required for reaching the reaction temperature and for maintaining the reaction. These difficulties are considerable, particularly in view of the poor heat conductivity of the briquetted reaction mixture.

The difficulties connected with supplying the required heat, necessitate the use of furnaces including a large number of individual retorts of small cross-sectional di- 'iGIlSlOnS, or the use of rotatable furnaces with arrangements for electrically heating the interior thereof. Irrespective of whether rotatable furnaces or retorts are used, the discontinuous manner in which the process is to be carried out will further reduce the efficiency of the furnace so that per unit of time and furnace or retort volume only a relatively small yield of metallic magnesium is obtained.

The above difficulties are further increased when the ferrosilicon is to be replaced by calcium carbide as the reducing agent. This is due .to the fact that, particularly finely subdivided, calcium carbide in contact with the moisture of the air will easily form acetylene and, consequently, extensive precautions must be taken for the grinding of the calcium carbide and in connection with the mixing of the ground calcium carbide with the other reactants, and the briquetting of the thus formed mixture in order to avoid formation of acetylene.

Furthermore, a comparison of the theoretically required weight and volume of the reaction mixture which will yield 1 kilogram of magnesium, by using, on the one hand, ferrosilicon containing 75% by weight of silicon, and calcium carbide of technical quality containing about 80% of calcium carbide on the other hand, will show that the reaction mixture containing calcium carbide will have a weight equal to 1.6 times the weight of the corresponding reaction mixture containing ferrosilicon, and the volume of the calcium carbide-containing 3,264,097 Patented August 2, 1966 reaction mixture will be 2.7 times the volume of the corresponding ferrosilicon-containing reaction mixture. Assuming that the speed of reaction in both cases is the same, then the yield per unit of furnace volume and time which is obtained in accordance with the calcium carbide reduction method will be even smaller than the yield obtainable in accordance with the conventional ferrosilicon method. Although calcium carbide is an easily available and relatively inexpensive reducing agent, it thus did not lend itself for a technically and economically successful reduction of magnesium oxide.

It is therefore an object of the present invention to overcome the above discussed difficulties and disadvantages of conventional methods for reducing magnesium oxide under formation of metallic magnesium.

It is a further object of the present invention to provide a method of producing magnesium which can be carried out in a simple and economical manner.

It is yet another object of the present invention to provide a method for producing metallic magnesium in a simple and economical manner, whereby the reducing agent is provided by the decomposition of calcium carbide.

It is yet a further object of the present invention to provide a method of reducing magnesium oxide to metallic magnesium, which method can be easily carried out in a continuous manner and will give a large yield per unit of time and reaction space.

Other objects and advantages of the present invention will become apparent from a further reading of the description of the appended claims.

With the above and other objects in View, the present invention includes a method of producing magnesium, comprising the steps of reacting a magnesium oxidecontaining material with calcium vapor so as to reduce magnesium oxide of the material under formation of magnesium vapor, and subjecting the thus-formed magnesium vapor to condensation.

According to a preferred manner of carrying out the method of the present invention, the same comprises in a method of producing magnesium, the steps of subjecting a material selected from the group consisting of dolomite and magnesium silicate to a calcining heat treatment; subjecting calcium carbide to a temperature sufiiciently high to decompose the calcium carbide under formation of calcium vapor, contacting the calcined material in the presence of a substance selected from the group consisting of the oxides of iron, manganese and chromium with the calcium vapor so as to cause an exothermic reaction between the calcium vapor and the iron oxide, and reduction of the magnesium oxide of the calcined material thereby substantially binding the calcium vapor and forming magnesium vapor, substantially separating the thusformed magnesium vapor, and condensing the separated magnesium vapor.

The present invention also contemplates in an appa ratus for the recovery of magnesium from magnesium oxide, in combination, electric are means for decomposing calcium carbide under formation of calcium vapor and a residue essentially consisting of graphite, first supply means for introducing calcium carbide into the electric arc means, first withdrawal means cooperating with the electric are means for withdrawing the highly graphite containing residue therefrom, a reaction vessel, heating means associated with the reaction vessel for maintaining therein a temperature sufficiently high for the reaction of calcium vapor with magnesium oxide under formation of magnesium vapor, second supply means for introducing magnesium oxide-containing material into the reaction vessel, conduit means communicating with the electric are means and the reaction vessel for passing calcium vapor from the electric are means into the reaction vessel, whereby upon reaction in the reaction vessel between the thus-introduced magnesium oxide and calcium vapor, magnesium oxide will be reduced under formation of magnesium vapor, second withdrawal means for withdrawing reaction products other than magnesium vapor from the reaction vessel, and condensing means operatively connected with the reaction vessel for condensing the magnesium vapor formed therein.

Thus, the present invention does not only overcome the difficulties which up to now stood in the way of the use of calcium carbide as the reducing agent for the thermic production of metallic magnesium, but it is also possible in accordance with the present invention to carry out the process in a particularly simple and economical manner, so as to obtain a high yield per unit of reaction space and time and, furthermore, under certain circumstances also to operate without additional heating of the reaction vessel. A further advantage of the present invention will be found in the fact that the same permits also the working up of magnesium silicate so as to obtain metallic magnesium from this raw material which up to now was of relatively little usefulness for such purpose.

According to the present invention, it is not the calcium carbide which is directly used as a reducing agent but, to the contrary, the calcium carbide is first decomposed under the formation of calcium vapor. The thus obtained calcium vapor is then brought in contact with the magnesium oxide-containing starting material and made to react with the same at elevated temperatures of between 1,000 and 1,300 C. The magnesium vapor which is produced in the reaction between calcium vapor and magnesium oxide is then condensed in conventional manner in a condenser communicating with the reaction vessel so as to obtain, as desired, either liquid or solid metallic magnesium. The method of the present invention can be carried out so as to reduce either magnesium oxide or magnesium silicate in an inert gas atmosphere or also under vacuum. When operating in an inert :gas atmosphere, it is advantageous to pass the inert gas first through the vessel in which calcium carbide is decomposed under formation of calcium vapor, and then to introduce the inert gas together with the calcium vapors into the reaction vessel in which the reduction of the magnesium oxide or magnesium silicate is to be carried out. Thereby it is possible in a simple manner to introduce the desired proportion of calcium vapor into the reaction vessel, either by controlling the vapor pressure of the calcium vapor or the amount of inert gas which flows per unit of time through the apparatus, i.e., from the vessel in which the calcium vapor is formed into the reaction vessel.

When it is desired to reduce magnesium oxide or magnesium silicate under vacuum, then, the calcium vapor will be drawn from the vessel in which the calcium carbide is decomposed into the reaction vessel in which the magnesium oxide or the like is to be reduced, due to the reduced pressure which is maintained in the last named reaction vessel. In other words, a pressure differential is then maintained so that there will be a higher degree of vacuum, or a lesser pressure, in the reaction vessel in which the magnesium oxide or the like is to be decomposed then in the device in which calcium vapor is formed by decomposition of calcium carbide, and it will follow that the freshly formed calcium vapor will flow into the communicating reaction vessel in which the decomposition of the magnesium oxide is to take place.

By properly choosing and controlling the temperature at which the calcium carbide is decomposed under formation of calcium vapor, which temperature preferably will be between 1,600 and 2,000 C., it is possible to control the vapor pressure of the calcium vapor and thus to obtain any desired speed of flow of the calcium vapor from the vessel wherein the same has been formed to the reaction vessel in which the calcium vapor is to react with magnesium oxide or magnesium silicate.

The chemical reactions which are carried out in the process of the present invention can be represented by the following equations:

If magnesium oxide or magnesium oxide-containing materials are used as a starting material:

If the raw material consists of magnesium silicate, the reaction will be carried out according to the following equation:

With respect to Equation 1, it can be calculated, based on thermodynamic data, that by the metallothermic reduction of the oxide, for instance at the absolute temperature of 1,300 K., which equals 1,027 C., 555 kcaL/kg. magnesium will be evolved. The reaction in accordance with the Equation 2, similarly calculated, will show a yield of 829 kcaL/kg. magnesium. It has been found that upon reaching a sufiicient speed of reaction and by well insulating the reaction space against heat losses, the heat which is freed in these reactions will suffice to balance unavoidable heat losses in the reaction vessel. Thus, as discussed above, it is possible to reduce magnesium compounds in accordance with the present invention without additionally heating the reactions space. It suffices to preheat the starting material prior to introduction of the same into the reaction vessel and it is possible to control the temperature in the reaction vessel or reaction space by correspondingly changing the temperature at which the preheated starting material, i.e. the magnesium oxide or magnesium silicate is introduced into the same, and/ or by controlling the temperature and the speed of flow of the stream of calcium vapor into the reaction vessel.

Since, according to the present invention, the magnesium-containing starting material is introduced into the reaction vessel without having incorporated therein an oxidizable reducing agent, it is possible to preheat the magnesium-containing material in any desired manner and while exposed to the outer atmosphere.

When it is necessary to subject the magnesium compound-containing raw materials to a pretreatment by buming or calcining, such as is for instance required for working up magnesite or the generally preferred dolomite, or when it is required to heat the raw material, for instance, in the case of water-containing magnesium silicates, then the present invention can be carried out in a particularly economical manner by introducing the thus heated, burned or calcined starting material without intermediate cooling directly into the reaction vessel.

Another particularly advantageous method of carrying out the present invention provides for the heating up of the magnesium compounds-containing starting material in the reaction vessel itself, which heating in the reaction vessel to the reaction temperature is accomplished by incorporating in the starting materials a substance which will form with calcium in an exothermic reaction nonvolatile reaction products or volatile reaction products which will not interfere with the recovery of metallic magnesium. Iron oxide has been found to be particularly suitable as an additive to the starting material which will react with calcium in an exothermic reaction. Usually, iron oxide is already included in the preferred starting materials for thermic recovery of magnesium, such as magnesite, dolomite and magnesium silicates. On the other hand, when the starting materials are free of iron oxide or do not contain a sufiicient proportion thereof, the same is easily available at low cost and can be admixed without difficulty to the magnesium compoundcontaining starting material.

In accordance with the following equation:

and for instance at a temperature of 1300 K., equal to 1027 C., 2370 kcal./ kg. Fe O will be freed. Using, for instance, calcined dolomite as the magnesium oxide-conraining starting material,.the heating of the starting material from an ambient temperature of 298 K. to a reaction temperature of, for instance, 1300 K. will require 243 kcaL/lcg. starting material. In the case of magnesium silicate of the composition 2MgOSiO 204 kcal/kg. starting material are required. Thus, theoretically, the iron oxide concentration in the starting material would have to amount only to about in order to heat the starting material to the required reaction temperature.

This last feature of the present invention, namely to admix iron oxide or the like to the starting material which is to be reduced in contact with calcium vapor, is particularly important because it permits continuous introduction of the starting material in cold condition. Such continuous introduction of a starting material maintained at substantially ambient temperature into reaction vessel which is evacuated or filled with inert gas can be carried out without any difficulties.

The magnesium compounds-containing starting material may be introduced in coarse particulate form as well as in finely pulverulent condition. Finely pulverulent material is preferably reacted by passing the calcium vapors over the pulverulent starting material, for instance in known manner in a furnace similar to a story furnace. Or it can be worked according to the fluidized bed process, while in the case of coarse particulate starting material it is preferred to pass the calcium vapor through the mass of particulate material.

During the reaction between the magnesium oxide of the starting material and the calcium vapor, depending on the reaction temperature, a certain ratio of the vapor pressures of magnesium vapor relative to calcium vapor will be established which, however, in all cases will be such that the magnesium vapor leaving the reaction chamber will contain only insignificant proportions of calcium vapor.

The present invention also contemplates a continuous method of producing magnesium, which comprises the steps of subjecting calcium carbide to a temperature sufficiently high to decompose the calcium carbide under formation of calcium vapor and a highly graphite containing residue, separately recovering pure graphite from the residue, contacting magnesium-containing material with the thus-formed calcium vapor at a temperature sufficiently high to react the calcium vapor with the magnesium oxide under formation of magnesium vapor, substantially separating the thus-formed magnesium vapor from the reaction mixture, and condensing the separated magnesium vapor.

The carbon which is formed upon decomposition of the calcium carbide simultaneously with the formation of calcium vapor, accrues as graphite and can be easily separated and recovered in the form of pure graphite.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic, elevational view, partly in crosssection, of an apparatus according to the present invention; and

FIG. 2 is a schematic, elevational view, partly in crosssection, of another embodiment of the apparatus or device according to the present invention.

Referring now to the drawing, and particularly to FIG. 1, the apparatus of the present invention is shown to comprise an electric arc furnace 1 lined with refractory material and including electrodes 2 for forming therebetween an electric arc in furnace 1. The interior of furnace 1 communicates with vacuum pump 15 and thus may be maintained under vacuum. From a storage container 3 which also is maintained under vacuum, calcium carbide of technical quality is introduced through vacuumtight gate 4 into furnace 1 and is heated therein, by means of the electric arc formed between electrodes 2, to a temperature of preferably between 1600 and 2000 C., and most preferably to a temperature of between about 1750 and 1800 C., whereby the residual pressure within furnace 1 is preferably maintained below 20 millimeter mercury and most preferably between 0.1 and 1 millimeter mercury. Under these condition-s, calcium carbide will be decomposed into calcium vapor and graphite. The graphite and any undecomposed impurities or admixtures to the technical calcium carbide may be continuously withdrawn through vacuum-tight gate or charging valve 5 into vacuum-tight residue receptacle 6. The calcium vapor formed in electric arc furnace 1 passes through heat insulated conduit 7 into reaction vessel 8 into which through charging valve 9 the preheated magnesium compound-containing starting material is introduced from vacuum-tight storage container 10.

In reaction vessel 8, the reaction between the starting material and the calcium vapor will be carried out at a temperature of between about 1000 and 1300 C., preferably at about 1200 C. so as to produce magnesium vapors which will pass through conduit 11 into magnesium condenser 12. In magnesium condenser 12, the magnesium vapors are condensed to form liquid or solid magnesium metal which is then removed from condenser 12 in conventional manner (not illustrated).

The residue of the magnesium vapor-forming reaction in reaction vessel 8 will pass through vacuum-tight charge valve 13 into vacuum-tight residue container 14.

The reduction of pressure in the entire apparatus is achieved by means of vacuum pump 15 directly communicating with condenser 12 and through conduit 11 with reaction vessel 8 and from there through conduit 7 with electric arc furnace 1, as well as with storage and residue containers 3, 10, 6 and 14. The discharge of the magnesium-oxide-containing starting material into reaction vessel 8, of calcium carbide into electric arc furnace 1 and of the reaction residues into residue containers 6 and 14 is facilitated, and the rate of discharge controlled, by the operation of the, per se, conventional discharge plates 21, 22, 23 and 24. The starting material may also be heated to reaction temperature by means of resistance heater 18 associated with reaction vessel 8.

FIG. 2 illustrates an apparatus according to the present invention in which the reaction is carried out in an inert gas atmosphere and not under vacuum.

The charging and discharging of the various vessels and containers is carried out in FIG. 2 in a manner similar to that described in connection with FIG. 1. However, instead of maintaining a vacuum by operation of vacuum pump 15, according to the embodiment illustrated in FIG. 2, inert gas introduced by means of a valve V into the evacuated apparatus is passed through the entire apparatus by means of conduit 16 introducing the inert gas into electric arc furnace 1, from there through conduit 7, reaction vessel 8, conduit 11 and condenser 12 to blower 17 from which the inert gas then passes again through conduit 16 into electric arc furnace 1, so that the inert gas flows in a circular flow which is concurrent with the flow of calcium vapor from electric arc furnace 1 to reaction vessel 8 and with the flow of magnesium vapor from reaction vessel 8 to condenser 12.

The following examples are given as illustrative only of the present invention, without, however, limiting the invention to the specific details of the examples.

Example 1 In an apparatus such as illustrated in FIG. 1, container 10 is filled with 460 kg. of freshly calcined dolomite. The dolomite was calcined by burning at a temperature '17 of 1200 C. and, prior to calcining, had the following composition:

Percent CaO 30.4

MgO 21.3 SiO 0.3 A1 0.14 F203 Ignition loss 47.5

The calcined dolomite is used according to the present example in coarse particulate form, namely so that the diameter of the individual pieces of calcined dolomite generally will have a size or diameter of between 3 and cm. However, it is also possible to replace the particu late dolomite with briquetted dolomite whereby the individual briquettes, for instance, may be of a cylindrical shape having a height of between 4 and 5 cm. and a diameter of 5 cm.

Reaction vessel 8 at this point is still filled with partially reacted dolomite of the preceding charge.

It may be noted in this connection that in the present example and in the following examples quantitative data are given which will lead to the production of about 100 kilograms of metallic magnesium. However, in actual operation, the process may be, and preferably is, carried out in a continuous manner.

Container 3 is filled with 370 kilograms of calcium carbide of technical quality, having a particle size of between 0.2 cm. and 1 cm. The composition of the calcium carbide is as follows:

Percent CaC C 2.0

CaO 11.3 MgO 0.1 A1203+F6203 SiO 5.1 S 0.3

Prior to starting the operation, petroleum coke or dolomite is placed on rotary discharge plate 24 in order to protect plate 24 against the effects of the heat which Will be generated in electric arc furnace 1. After the operation has proceeded for a certain length of time, the graphite flowing down toward rotary discharge plate 24 will protect the latter against exposure to excessive heat.

After thus charging storage containers and 3 with calcined dolomite and calcium carbide, respectively, vacuum pump is started and the entire apparatus is evacuated down to a residual pressure of between about 30 and 40 mm. mercury; then the electric arc is formed between electrodes 2, and the interior of electric arc furnace 1 is heated to about 1800 C. In the meantime, the contents of reaction vessel 8 are heated to about 1150 C. by means of electric resistance heating device 18.

Once the above temperatures have been reached, the pressures in the apparatus is further reduced to between 0.1 and 0.5 mm. mercury and calcium carbide is now permitted to drop from container 3 through charge valve 4 into electric furnace 1, wherein thermal decomposition of the calcium carbide will take place under formation of calcium vapor and a highly graphite containing residue. The calcium vapor flows through insulated conduit 7 into reaction vessel 8 in which now reaction of the magnesium oxide portion of the calcined dolomite with the calcium vapor takes place under formation of magnesium vapor. The temperature in reaction vessel 8, under the above indicated conditions, particularly with respect to residual pressure, will average about 1200 C., whereby a temperature drop of between 200 and 300 C. will be found between the portion of reaction vessel 8 into which the calcium vapor is introduced and the portion of the reaction vessel 8 from which magnesium vapors pass to the condenser. The temperature required for the reaction of magnesium oxide with calcium is maintained by suitably adjusting electric resistance heater 18.

8 The thus formed magnesium vapors then flow through conduit 11 into condenser 12 in which the magnesium vapor is condensed in conventional manner, for instance to form solid metallic magnesium.

At the time of starting the reaction, rotary discharge plates 21, 22, 23 and 24 are put in motion in order to continuously charge the starting materials, i.e. the calcined dolomite and the calcium carbide into reaction vessel 8 and electric arc furnace 1, respectively, and in order to with-draw from vessel 8 and electric arc furnace 1 solid reaction products into containers 6 and 14, respectively. The speed of rotation of discharge plate 22 is so adjusted that introduction of the 370 kilograms of calcium carbide into electric arc furnace 1 will require 10 hours, and the rotational speed of discharge plate 24 will be so adjusted that the upper level of the calcium carbide introduced into the electric arc furnace 1 is at a suitable distance under the electric arc between the electrodes 2 so the electric arc is able to burn without hindrance In the furnace 1 of Example 1 this distance is about 20 cm.

Discharge plate 21 is rotated at such speed that the 460 kilograms of calcined dolomite from container 10 will be introduced into reaction vessel 8 over a period of 10 hours, i.e. over the same length of time which is required for the 370 kilograms of calcium carbide in container 3 to be introduced into electric arc furnace 1, and to be decomposed therein so as to pass the corresponding amount of calcium vapor into reaction vessel 8.

During the same period of time, namely 10 hours, solid reaction products formed in reaction vessel 8 and amounting to about 5 30 kilograms are withdrawn, by rotation of discharge plate 23, into container 14.

Reaction of the above indicated quantities of calcium carbide and calcined dolomite will result in the production of kilograms metallic magnesium and, at the end of the (production run described above, the charge located in reaction vessel 8 will be similar to that which was located therein at the beginning of the production run. It is again noted that although in the examples the production of about 100 kilograms magnesium is described, in actual operation the process is preferably carried out in a continuous manner, for instance by providing a plurality of containers 3, 6, 10 and 14 which alternatingly may be operatively connected with electric arc furnace 1 and reaction vessel 3, respectively, or in other suitable manner, so as to maintain a continuous process.

The introduction of calcined dolomite into vessel 8 and withdrawal of solid reaction products therefrom is so arranged that reaction vessel 8 remains completely filled throughout the entire process.

The condensed metallic magnesium which is obtained in solid form in condenser 12 has a calcium content of between about 0.1 and 0.2%. The exact proportion of calcium in the metallic magnesium depends on the location within condenser 12 at which condensation of the respective portion of the metallic magnesium takes place. Magnesium which is solidified in the immediate vicinity of conduit 11 will have a higher calcium content than magnesium which is solidified farther distant from conduit 11 and closer to vacuum pump 15.

Example 2 The process is carried out substantially as described in Example 1, however, according to the present example, it is desired to maintain the residual pressure of the apparatus below 0.1 mm. mercury since by thus lowering the residual pressure it is possible to lower the temperature at which the calcium carbide will be decomposed. For instance, at a residual pressure of 0.04 mm. mercury, calcium carbide can be effectively decomposed at a temperature of about 1700 C., while the temperature conditions in reaction vessel 8 may be about the same as indicated in Example 1, in order to maintain the desired reaction speed. Under the conditions described in the present example, the length of time required for obtaining 100 kilogram magnesium by working up the quantities of starting materials described in Example 1 will be extended to about 13 hours.

While it would be more desirable to operate at such low residual pressure, frequently practical considerations and technical limitations of the apparatus will prevent lowering of the residual pressure below 0.1 mm.

Example 3 When it is desired to work with a residual pressure of about 5 mm. mercury, it will be necessary to heat electric arc furnace 1 to about 1900 C. in order to obtain the desired decomposition of the calcium carbide. However, by otherwise proceeding as described in Example 1, 100 kilogram magnesium will be obtained in about 9 hours.

While the preceding examples refer to a process which is to be carried out in an apparatus such as is illustrated in FIG. 1 of the drawing, the Examples 4-6 should be considered with reference to FIG. 2 of the drawing.

Example 4 Calcined dolomite and calcium carbide of the composition and in the quantities described in Example 1 are reacted in an apparatus as illustrated in FIG. 2. The temperature conditions in electric furnace 1 and reaction vessel 8 are about the same as described in Example 1, namely about 1800 C. in electric arc furnace 1 and about 1200 C. in reaction vessel 8.

The entire apparatus of FIG. 2 is first evacuated down to a residual pressure of 0.1 mm. mercury and thereafter filled with hydrogen gas so as to restore atmospheric pressure in the apparatus. Thereafter, the process is carried out as described in Example 1 with the exception that the hydrogen pressure of 1 atmosphere absolute is maintained and the hydrogen gas is circulated by means of blower 17 during the 10 hour production run so that the hydrogen gas passes from the upper portion of condenser 12 through blower 17 and conduit 16 into electric arc furnace 1 and from there through reaction vessel 8 to condenser 12. The hydrogen gas is circulated at a speed of 21 standard cubic meters per minute.

Example 5 The process is carried out substantially as described in Example 4, however, the temperature in electric arc furnace 1 is reduced to 1700 C. In this case, a speed of circulation of a hydrogen gas of 38 standard cubic meters per minute is required in order to produce 100 kilograms of magnesium in ten hours. On the other hand, if the temperature in electric arc furnace 1 is reduced to 1700 C. and the speed of circulation of the hydrogen gas is maintained at 21 standard cubic meters per minute, production of 100 kilograms of metallic magnesium will require hours.

Example 6 Again following the process of Example 4, but increasing the temperature in electric arc furnace 1 to 1900 C. it will be possible to produce 100 kilograms metallic magnesium in ten hours by circulating the hydrogen gas at a rate of 13 standard cubic meters per minute, while maintaining the rate of circulation at 21 standard cubic meters per minute, will reduce the time required for the production of 100 kilograms magnesium to 7 hours.

Example 7 The process described in Example 1 is substantially repeated, however, magnesite is used as the starting material in place of the dolomite of Examples 1-6.

The magnesite is to the following composition:

Percent MgO 46.4 CaO 0.8 SiO 0.3 A1 0 0.8 Pe O 0.4 Ignition loss 51.6

The magnesite, prior to introduction into the apparatus is burned at 1100 C.

Duringa ten hour production run, 200 kilograms of the calcined magnesite are introduced into reaction vessel 8. The process conditions remain the same as de scribed in Example 1. However, in this case, the amount of solid reaction products which is discharged from reaction vessel 8 during the ten hour production run will be equal to about 270 kilograms.

kilograms of solid magnesium containing an average of 011% calcium will be recovered from condenser 12.

Example 8 The process of Example 1 is carried out with serpentine, i.e. a magnesium silicate mineral.

The composition of the serpentine is as follows:

Percent MgO 41 C210 0.4

FeO 1.4 F6203 A1 0 0.5 S10 41 3 H O 13 3 The serpentine is first calcined at 1050 C. Thereafter 415 kilograms of the calcined serpentine are charged into reaction vessel 8 over a period of ten hours as described in Example 1. The amount of calcium carbide and the temperature and pressure conditions are again the same as in Example 1. About 480 kilograms of solid reaction products are withdrawn from reaction vessel 8 during the ten hour process. During the same time, \98 kilograms of solid magnesium containing 0.12% calcium are obtained in condenser 12.

Example 9 In a further modification of the process as described in Example 1, 460 kilograms of calcined dolomite are mixed with 60 kilograms of burned and ground hematite containing 87.1% Fe O so that the mixture of the starting materials will contain 10% Fe O This mixture is charged over ten hours into preheated reaction vessel 8 which at the beginning of the process is still filled with material from the preceding charge. Upon starting the reaction by introduction of calcium vapor from electric arc furnace 1, electric resistance heating 18 is discontinued and the required temperature of about 1200 C. in reaction vessel 8 is maintained by the exothermic reaction between calcium vapor and the 10% admixture of iron oxide.

In order to pnoduce 100 kilograms metallic magnesium, it is required in this case to decompose 460 kilograms of technical calcium carbide in electric arc furnace 1.

The quantity of solid reaction residue which is discharged from reaction vessel 8 during the ten hour reaction period equals 625 kilograms.

Instead of using Fe O it is also possible to produce the required heat by providing in reaction vessel 8 for an exothermic reaction between calcium vapor and oxides of other metals such as manganese, chromium and the like.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of metal recovery devices differing from the types described above.

Example 10 In another modification of the process as described in Example 1 460 kg. of dolomite being freshly calcined at a temperature of 1200 C. is filled in the container 3 without cooling the dolomite which is thus preheated for the process. From the container 3 the dolomite is charged over ten hours into the preheated reaction vessel 8 which at the beginning of the process is still filled with material from the preceding charge. Upon starting the reaction by introducing of calcium vapor from electric arc furnace 1 electric resistance heating 18 is discontinued as the heat which is freed by the exothermic reaction be tween calcium vapor and preheated dolomite as indicated above suffices to maintain the temperature in the reaction vessel 8 at about 1200 C.

While the invention has been illustrated and described as embodied in an apparatus for the recovery of magnesium from magnesium oxide, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptions should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufliciently high to decompose said calcium carbide under formation of calcium vapor; contacting magnesium oxidecontaining material with the thus-formed calcium vapor at a temperature sufficiently high to react said calcium vapor with said magnesium oxide under formation of magnesium vapor; substantially separating the thusformed magnesium vapor from the reaction mixture; and condensing said separated magnesium vapor.

2. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature of between 1600 and 2000 C. being sufficiently high to decompose said calcium canbide under formation of calcium vapor; heating magnesium oxide-containing material to a temperature sufliciently high to cause reduction of magnesium oxide in contact wit-h calcium vapor; contacting the thus-heated magnesium oxide-containing material with said calcium vapor while maintaining a temperature of between 1000 and 1300 C. being sufiiciently high to react said calcium vapor with said magnesium oxide under formation of magnesium vapor; substantially separating the thus-formed magnesium vapor from the reaction mixture; and condensing said separated magnesium vapor.

3. A method of producing magnesium, comprising the steps of subjecting a material selected from the group consisting of dolomite and magnesium silicate to a calcining heat treatment; subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; contacting said calcined material at substantially its calcining temperature with said calcium vapor so as to cause reaction between said calcium vapor and the magnesium oxide of said calcined material thereby substantially binding said calcium vapor and forming magnesium vapor; substantially separating the thus-formed magnesium vapor; and condensing said separated magnesium vapor.

4. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; contacting a material containing magnesium oxide and also containing a substance adapted to react exothermically with calcium vapor with the thus-formed calcium vapor so as to react said calcium vapor with said substance and said magnesium oxide under formation of magnesium vapor; substantially separating the thus-formed magnesium vapor from the reaction mixture; and condensing said separated magnesium vapor.

5. A method of producing magnesium, comprising the steps of subjecting a material selected from the group consisting of dolomite and magnesium silicate to a calcining heat treatment; subjecting calcium carbide to a temperature sufliciently high to decompose said calcium carbide under formation of calcium vapor; contacting said calcined material in the presence of iron oxide with said calcium vapor so as to cause an exothermic reaction between said calcium vapor and said iron oxide, and reduction of said magnesium oxide of said calcined material thereby substantially binding said calcium vapor and forming magnesium vapor; substantially separating the thus-formed magnesium vapor; and condensing said separated magnesium vapor.

6. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufiiciently high to decompose said calcium carbide under formation of calcium vapor; passing thus-formed calcium vapor through a mass of particulate magnesium oxidecontaining material at a temperature sufficiently high to cause reaction between said calcium vapor and the magnesium oxide of said material so as to reduce said magnesium oxide under formation of magnesium vapor; withdrawing the thus-formed magnesium vapor; and condensing said withdrawn magnesium vapor.

7. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; passing thus-formed calcium vapor in contact with a mass of finely subdivided magnesium oxide-containing material at a temperature sufiiciently high to cause reaction between said calcium vapor and the magnesium oxide of said material so as to reduce said magnesium oxide under formation of magnesium vapor; withdrawing the thus-formed magnesium vapor; and condensing said withdrawn magnesium vapor.

8. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; reacting under a vacuum of below 20 mm. mercury a magnesium oxide-containing material with thus-formed calcium vapor so as to reduce magnesium oxide of said material under formation of magnesium vapor; and subjecting the thus-formed magnesium vapor to condensation.

9. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufriciently high to decompose said calcium carbide under formation of calcium vapor; reacting in an inert gas atmosphere a magnesium oxide-containing material with thus-formed calcium vapor so as to reduce magnesium oxide of said material under formation of magnesium vapor; and subjecting the thus-formed magnesium vapor to condensation.

10. A method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; reacting in an hydrogen gas atmosphere a magnesium oxide-containing material with thus-formed calcium vapor so as to reduce magnesium oxide of said material under formation of magnesium vapor; and subjecting the thus formed magnesium vapor to condensation.

11. A method of producing magnesium, comprising the steps of subjecting a material selected from the group -consisting of dolomite and magnesium silicate to a calcining heat treatment; subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor; contacting said calcined material in the presence of a substance selected from the group consisting of the oxides of iron, manganese and chromium with said calcium vapor so as to cause an exothermic reaction between said calcium vapor and said iron oxide, and reduction of said magnesium oxide of said calcined material thereby substantially binding said calcium vapor and forming magnesium vapor; substantially separating the thus-formed magne- 13 sium vapor; and condensing said separated magnesium vapor.

12. A continuous method of producing magnesium, comprising the steps of subjecting calcium carbide to a temperature sufficiently high to decompose said calcium carbide under formation of calcium vapor and a highly graphite containing residue separately recovering pure graphite from said residue; contacting magnesium oxidecontaining material with the thus formed calcium vapor at a temperature sufiiciently high to react said calcium vapor with said magnesium oxide under formation of magnesium vapor; substantially separating the thusformed magnesium vapor from the reaction mixture; and condensing said separated magnesium vapor.

References Cited by the Examiner UNITED STATES PATENTS 1,811,021 6/1931 Patart 75-10 2,213,170 8/1940 Peake 75-67 2,222,585 11/1940 Riggs 23-208 2,398,443 4/1946 Munday 75-67 1 4!- 2,45 0,057 9/ 1948 Reik 7567 2,650,160 8/1953 Totzek 7591 X 2,831,760 4/1958 Rejdak 7527 2,839,380 6/1958 Iaife 7510 2,847,295 8/ 1958 Bretsohneider 75-67 2,889,218 6/ 1959 Hiskey 75-27 2,920,951 1/ 1960 Bretschneider 75-67 2,931,719 4/1960 Menegoz 75--67 2,965,475 12/1960 Wilson 75--67 2,992,095 7/1961 Li 75-27 OTHER REFERENCES Mikulinskii: Preparation of Calcium by the Dissociation of Calcium Carbide, AEC-t r-4405, United States Atomic Energy Commission, 1961, pp. 18, translated from Zhurnal Prikladnoi Khimi 33, 835-41 (1960).

HYLAND BIZOT, Primary Examiner.

BENJAMIN HENKIN, DAVID L. RECK, Examiners.

H. W. CUMMINGS, H. W. TARRING,

Assistant Examiners.

Claims (1)

1. A METHOD OF PRODUCING MAGNESIUM, COMPRISING THE STEPS OF SUBJECTING CALCIUM CARBIDE TO A TEMPERATURE SUFFICIENTLY HIGH TO DECOMPOSE SAID CALCIUM CARBIDE UNDER FORMATION OF CALCIUM VAPOR; CONTACTING MAGNESIUM OXIDECONTAINING MATERIAL WITH THE THUS-FORMED CALCIUM VAPOR AT A TEMPERATURE SUFFICIENTLY HIGH TO REACT SAID CALCIUM VAPOR WITH SAID MAGNESIUM OXIDE UNDER FORMATION OF MAGNESIUM VAPOR; SUBSTANTIALLY SEPARATING THE THUSFORMED MAGNESIUM VAPOR FROM THE REACTION MIXTURE; AND CONDENSING SAID SEPARATED MAGNESIUM VAPOR.

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