US2559419A - Continuous production of volatilizable metals - Google Patents

Description

July 3, 1951 R. FOUQUET 2,559,419

CONTINUOUS PRODUCTION OF VOLATILIZABLE METALS Filed April 24, 1948 Wm-1'05 2 Robert Fouquet His Agent Patented July 3, 1951 CONTINUOUS PRODUCTION OF VOLATILIZABLE METALS Robert Fouquet, Paris, France Application April 24, 1948, Serial No. 22,977 In France March 1, 1948 g 1 Claim. 1

The present invention relates to a method for extracting magnesium from oxidized ores, and in particular from magnesia or dolomite, further for obtaining the metal so extracted in the liquid state so that it can be cast immediately into ingots, and lastly for achieving these results in a continuous manner. The extraction is effected by reduction according to the well-known chemical action, by means of solid reducers containing silicon or ferro-silicon.

Such a method has already been proposed in its main essentials in my pending patent application Serial No. 762,755, filed July 22, 1947, now abandoned, and in my pending divisional application Serial No. 11,592, filed February 27, 1948, of which this is a continuation in part.

The present invention has for its main object the provision of an improved method operating With a pulverulent mixture of the ore and reducer, preliminarily ground to suitable size and mixed together, but not briquetted or agglomerated, this method giving for a predetermined reaction temperature, on the one hand the metal in gaseous state with a definite vapor tension, and on the other hand residues not volatilized at that temperature, which residues can thus be readily separated from the gaseous metal. The gaseous metal is brought to the liquid state by cooling the said gaseous metal to a definite temperature, thus causing condensation of the metal, accordin to the known rules of distillation. The liquid metal can be collected by simple gravity flow at a place where there is maintained the temperature necessary for the persistence of the liquid state, the metal being tapped off from that place and cast in the ordinary conditions.

A further object of the invention is to provide continuity of operation by effecting the reducing reaction, the distillation and the storage of the liquid magnesium, in a medium such that neither the metallic vapor nor the liquid metal run the risk of being oxidized or nitrided at any point or at any time. This medium may be provided by a substantial vacuum or by an inert gas such as hydrogen or helium.

In View of the fact that the distilling operation normally causes a movement of the metallic gas toward the cooled condensation region, by virtue of the difference of vapor tensions of the gaseous magnesium at the respective temperatures, it

is not necessary to set up mechanically a current for conveying this metallic gas.

In order to fulfill these various conditions, it is desirable to provide a high temperature for the reaction; it has been found that in the case of magnesium extracted from dolomite reduced by ferro-silicon containing of silicon, at a temperature approximatin to 1400 C., the normal tension of the metallic gas produced was about 140 mm. of mercury. For the condensation, the cooling must be such that the gas is only liquefied and not solidified; it has been found that in the case of magnesium, at a temperature of 700 C., the normal state of the metal was liquid with a vapor tension not exceeding a few mm. of mercury. This difference of pressure (between 140 mm. and say 10 mm.) of about 130 mm., causes the desired movement of the metallic vapor towards the condensation chamber.

For securing the desired medium free from ordinary atmospheric gases (oxygen and nitrogen), it has been found that it is possible to employ columns of finely powdered material for establishing blockages substantially proof against passage of the gases, and thus isolating the metal from the ordinary atmosphere, both at the time of its production in gaseous state during the reducing reaction, and in the course of it condensation to liquid state and its storage. The height of these columns depends naturally upon the character of the pulverulent materials and their fineness, as well as upon the shape of the columns; there has been determined as a function of these parameters the minimum height necessary for the case of magnesium contained in a mixture of powdered dolomite and ferrosilicon, the dolomite employed having a, particle size of 1 to 10;, and the ferro-silicon a size of 10 to Profiting from these determinations, knowing also that pulverulent mixtures lose almost the whole of their entrained atmospheric gases and humidity, as well as their adsorbed atmospheric gases and humidity, at a temperature not exceeding 750 C., and lastly knowing that for powdered dolomite or magnesia, at a temperature of the order of 800 C., their decarbonation is complete under a pressure of 760 mm. of mercury, another object of the present invention accompanying diagrammatic drawing, which refers to an example of a furnace for treating mixtures of dolomite and ferro-silicon for the production of magnesium.

The drawing is a section of such a furnace,

showing the three zones, I being the charging zone, II the reducing, condensing and storage zone, and III the discharging zone, and showing also the complete lay-out according to the invention, without provision for movement of inert gas.

The apparatus illustrated for carrying out the improved method comprises an elongated vertical column allowing the passage into a first heated zone I (known as the charging and preheating zone) of materials containing the oxidized metal and its reducer, in which zone there are eliminated the entrained, occluded and adsorbed gases and moisture, as well as the carbon dioxide gas which may be present from an incomplete preliminary decarbonation of these materials, all these gases expanded under the effect of the increase of temperature rising to the free surface at the top opening of the column, as

through a liquid. The materials continuing their downward movement reach the strongly heated reaction zone II (known as the reducing, condensing and storage zone), where there is produced and evolved the metallic vapor resulting from the reduction. In this position, the metallic vapor is absolutely protected from any oxidizing action by the blockage effect of the pulverulent column composed of the materials themselves, which isolates the vapor from the external atmosphere. The metallic vapor, of which the tension is 140 mm. if the temperature is 1400" C., becomes forced towards a condenser connected integrally with the reaction zone and consisting of a steel casing which is maintained at a temperature in the vicinity of 700 C. by the circulation in the interior of the casing of a bath of molten tin itself maintained at that temperature by a method which will be described in more detail hereinafter. As alreadystated, the metallic vapor evolved in the reaction zone under a tension which is about 140 mm. travels of itself towards the outer wall of the casing having a temperature of 700 0., on which it will condense. There is provided at the height of the reaction zone, a free space clear of the reacting materials, in such a way that the metallic vapor evolved will only have totraverse, as a maximum, in order to reach the condensing surface, the small thickness of the column of pulverulent material which is itself in downward movement.

The residual materials, already deprived of their metallic content, continue their movement through a lower column occupying the zone III (known as the discharging zone) the length of which is determined like that of the upper or charging zone I, so as to produce tightness against atmospheric gases which might tend to enter at the base of the column. During the descent of the residues, a device for recovery of their latent heat may be brought into action with the double object of avoiding losses of heat and lolwering their temperature as quickly as pos- Sl le.

Themetallic vapors condensed on the wall surface of the condenser casing flow down that surface and are collected in a semi-cylindrical gutter provided at the lower edge of the surface. This gutter has a slope which allows the liquid metal to be collected from the lowest point of the gutter into a receiver itself maintained by thermal insulation at a temperature higher than the melting point of the metal, namely above or in the vicinity of 650 C., from which receiver it is discharged very simply, by siphon effect, which allows of maintaining absolute tightness of the vacuum affecting the movement and reaction regions for the treated materials.

The metallic condenser casing is formed of welded iron or steel plates. The interior is filled with tin, at a temperature. of 700 C'., which is well above its melting point. This tin arrives through an iron pipe at the bottom of the casing and leaves through another iron pipe at the top. Having regard to the thermal expansibility of tin, there will thus be a movement of the liquid 1 bath by thermo-siphon effect at a speed determined by the temperature to which it is cooled. The flow and return pipes are continued externally of the condenser casing by a gilled tube coil itself immersed in a large iron casing through which there is circulated a cooling fluid, which may be water, steam or air. The speed of circulation of this fluid in the casing is controllable to allow of maintaining the temperature of the casing at such a value that the tin circulating through the coil gives up to the cooling fluid the heat units abstracted in the condenser casing. Thus by regulation of the speed of circulation of the cooling fluid it is possible to regulate the temperature of the tin in the condenser and thus to maintain the temperature of the walls of the condenser casing at 700 C. in a very simple manner.

It is to be noted that over the Whole distance travelled by the particles forming the mass of the materials under treatment, from the head of the charging column or zone I down to the foot of the discharge column or zone III, these particles are constantly rubbing against one another, which isa circumstance favorable to the evolution of the occluded, adsorbed and entrained gases, and moreover allows for evenly distributed heating of the particles, specially in the reducing zone.

The furnace illustrated is formed by a nonhomogeneous structure A made of brickwork, enclosed in a metallic sheathing B made of edgewelded plates, having external connections at only six points, viz. at I and I for the passage of a bar C or C transmitting a supersonic wave of relatively low frequency (1 to 2 kilocycles per second) intended to facilitate the descent of the charges at the base of the preheating zone I and at the top of the discharging zone III; at 2 and 2 for the admission of a current of fluid intended for the cooling of the condensing liquid; at 3 for the circulation of water for the recovery of latent heat from the residues; at 4 for the outlet of the liquid magnesium extraction siphon D; at 5, transversely, in the seating of a beam supporting a dihedral heating element E, for the lead-in and lead-out of the heating current; and at 6 and 5 for the heating of the preheating element L.

In this. brickwork structure A there are provided an upper shaft or flue for the descent of the charges in zone I, a heating chamber in zone II with seatings for the condensing and storage apparatus, and the pipes necessary for the movement of the liquid metal, and a lower shaft or flue for the discharge of residues in zone III.

Thebrickwork must be highly refractory in the and more porous naturezuntilthey make contact with the metallic sheathing.

The heating chamber is constituted by the "space inside a-widened out portion of the'brickwork, masked 'on the side towards the interior of the furnace bya curtain of refractory bricks F interrupted by staggered openings arranged in quincunx and sloping upwards. Through these multiple openings the magnesium vapor can easily reach the inner surface of the condenser casing G on which it liquefies, trickling down into the gutter I-I placed at the bottom of that surface, and flowing by gravity to the reservoir J, from which the liquid metal is tapped off in order to be cast into ingots at P. The casing G is filled with tin which circulates through a coil S immersed in the cooling fluid contained in the casing R. The widened-out portion or heating chamber is-traversed from one side to the other by a beam K made of long stifl slabs of fused and molded magnesia, set firmly in the brickwork but without rigid joints, so as to be able to play laterally in their seating in the brickwork.

This beam supports the element E, which is of very acutely pointed dihedral shape, made of wide and smooth molded plates of fused magnesia, having their outer surfaces polished so as not to oppose any resistance to the sliding of the particles of reacting materials which pass down over them. At its lower part, the supporting beam K is fashioned to a more obtuse dihedral shape serving as a guide for the movement of the descending pulverulent material.

The plates of the dihedral element E are heated internally by electrical means due to an electric current flowing through metallic resistances placed in recesses made beforehand in the thickness of these plates, the resistances being such that they are not affected by their contact with magnesia at temperatures of about 1400" C. at which the operation is carried out. It is easy to determine the amounts of current which are necessary for developing and maintaining the desired temperature on the surface of the plates of the dihedral element; it will be remembered on this point that the reaction of the reduction of magnesia by silicon is slightly exothermic, and account will be taken of that circumstance in calculating the amounts of electrical energy required.

Account will also be taken of the variation of electrical conductivity of magnesia, which is a function of its temperature, increasing at first and then diminishing when the temperature of 1400 C. is reached. In fact magnesia then behaves like a high-resistance conductor and becomes heated by Joule efiect. The current connections of the heating metallic conductors with the external supply are ensured by baths of molten metal which afford perfect tightness of the whole electrical heating circuit.

The preheating device L may be provided by an insulated heating ring sunk in the brickwork of the shaft or fiue in which the charges descend, the ring being made up in the same manner as the plates of the dihedral element E described above.

The descent of the charges may .be held up either by the-formation of blocksdue to the establishment of bridges in .the. charging and preheating zone or in the discharging zone, or 'by initial agglomeration of the particles after reaction due to the formation of silicatesv fusible at the reaction temperature. In bothcases thefreeclom of each particle in the charge will be greatly increased by a vibratory movement traversingthe mass-of the charge-and being transmitted to the same. This vibration may be caused mechanically by the emission of asupersonic flux produced by a magneto-striction emitter ofwhich the-vibrating bar will be welded to the main-sheathing and will therefore notprevent its gas-tightness. Two of these'emitter groups are shown provided, one-T C near the base of =ithe-charging zone, tlie :other C"-'at'the.top of the discharging zone. 'LCalculation of the relations of the frequency and intensity of vibration with the size of the particles Will allow of bringing the parameters to their optimum value. For the same object the charging and discharging columns in the zones I and III may present a slight widening out downwards.

Thermo-electric couples (not shown) allow of observing constantly and recording the temperatures developed:

(1) In the preheating column at the level of the heating ring L.

(2) At the outer surface of the dihedral heating element E.

(3) At the surface of the condenser casing G turned towards the reaction column.

(4) In the coil S for cooling the tin from the condenser casing.

(5) At the top of the discharging column or zone III.

(6) At the base of this same column.

The charging-of the materials to be treaced takes place freely at the top of the charging column. The discharging of the spent materials takes place at the base by the operation of a horizontal worm conveyor M which delivers into a hopper N open at its base for the removal of the residues. A device for the recovery of the latent heat of these residues is provided at T.

Modifications can naturally be applied to the apparatus described and illustrated without departing from the scope of the invention.

What I claim is:

In a method of producing magnesium by the thermal reduction of magnesium ores by nongasforming solid reducing agents, the steps of forming a finely divided particulate intimate mixture of said ore and reducing agent, introducing said mixture into a vertical elongated reaction chamber comprising three superimposed vertical zones, heating said mixture to degas and dry it and simultaneously feeding the same by gravity to form a self-packed substantially gas impervious enclosed column of said mixture in the first zone, allowing said gas impervious column to descend by gravity from said first zone into a reduction zone, reducing the ore in said reduction zone by heating to reaction temperature to vaporize the resulting magnesium, causing the magnesium vapors to pass from said reduction zone substantially laterally into a condensation chamber to be condensed into liquid state therein by virtue of the pressure dilferential established between said condensation chamber and said reduction zone as a result of the cooling of said magnesium vapors in said condensation chamber, allowing the spent solid reaction materials to form by gravity the third zone beneath said reduction zone, said columns of raw and spent materials in said first and third zones being substantially continuous and having a length sufficient to render them substantially impervious to the passage of gas vertically therealong, whereby the ingress of air through said columns into said reduction zone is prevented. 7

ROBERT FOUQUET.

Name Date Number V Curtis NOV. 11, 1884:

Number Name Date 2,011,288 Kemmer Aug. 13, 1935 2,123,990 Erdmann July 19, 1938 2,148,358 Lang et al Feb. 21, 1939 2,219,059 Suchy et a1. Oct. 22, 1940 2,251,906 Hanawalt Aug. 12, 1941 2,337,042 Gloss Dec. 21, 1943 2,362,718 Pidgeon Nov. 14, 1944 FOREIGN PATENTS Number, Country Date 543,399 Great Britain Feb. 24, 1942 OTHER REFERENCES Langes Handbook of Chemistry, published in 1937 by Handbook Publishers, Inc., Sandusky, Ohio. Pages 1173-1175.

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