Electrolyzers used at present for the production of metallic magnesium from salt melts comprising magnesium chloride represent a lined chamber made in the form of a box of rectangular cross-section with a package of flat electrodes of alternating polarity and a partition separating the portion of the chamber intended for the collection of metallic magnesium arranged in it (see, for example, USA Patent No. 4,308,116 of December 29,1981; a book of Emley, E. F., Principle of Magnesium Technology, Pergamon Press, 1966 ; a review of Lupu, A., Present State of Magnesium Extractive Metallurgy, Technion, 1972).

Such electrolyzers are intended only for a single technological process-for electrolysis. As a rule, Joule heat generated at the current flow through the electrolyte is not used. The electrolyte is melted and purified from magnesium oxide and other impurities outside the electrolyzer, which involves the use of additional technological devices consuming large amounts of electric power and occupying a certain area in a workshop.

Summary of the invention In contrast to known devices, the present invention provides an apparatus which is multifunctional in that besides the electrolysis, the processes of melting and deep dehydration of salts and salt purification from magnesium oxide and impurities take place within the same apparatus and magnesium alloys can also be produced in said same apparatus. In addition, in accordance with the present invention, the Joule heat released at the electrolysis and magnetohydrodynamic (MHD) effects are used for melting and deep dehydration of salts and for heating the air fed into boiling-layer furnaces for chlorination and preliminary dehydration of salts.

Thus according to the present invention there is now provided a multifunctionai apparatus for the continuous electrolytic production of metallic magnesium from salts containing magnesium chloride, comprising a steel body serving as a housing and containing therein concentrically arranged annular sectionalized electrodes, wherein an annular cathode together with an annular anode form an annular chamber for metallic magnesium collection and magnesium alloy production and an internal central chamber for melting and secondary dehydration of salts and wherein Joule heat released by the electrolysis and magnetohydrodynamic effects is utilized for melting and dehydration of salts.

The ratio of the working surface of cathodes area to the area occupied by the apparatus in the workshop with the account for the area occupied by devices for purification and melting, equals 0.37 for known electrolyzers. For the proposed modifications shown in Figs. 1,2,11,12, this ratio is 0.34, and for the modifications in Figs. 3,4-0.68. Thus, the efficiency of the two said modifications per unit area occupied by the apparatus in the workshop practically does not differ from the efficiency of prototypes, whereas for the modifications in Figs. 3,4 it is twice that of prototypes.

Graphite anode blocks of the modified apparatus (Figs. 11,12) arranged on the lateral surface of said apparatus, rest on the lining and, thus, are totally free from bending stresses.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Brief description of the drawings Fig. 1 is a schematic vertical section AOB of the apparatus showing the arrangement of its principal units in the vertical plane.

Fig. 2 is a schematic horizontal section C-C of the apparatus and its top view showing the arrangement of its principal units in the horizontal plane and on the lid.

Fig. 3 is a schematic vertical section AidBi of an apparatus modification showing the arrangement of its principal units in the vertical plane and the difference between this design and that shown in Figs. 1, 2.

Fig. 4 is a schematic horizontal section Ci-Ci of the apparatus modification and its top view showing the arrangement of its principal units in the horizontal plane and on the lid and the difference between this modification and the design shown in Figs. 1,2.

Fig. 5 shows a cathode section used in the apparatus design shown in Figs. 1,2.

Fig. 6 shows a cathode section used in the apparatus design shown in Figs. 3,4.

Fig. 7 is a vertical section D-D of an electromagnet showing the shape of its core and the arrangement of coifs on the poles.

Fig. 8 is a vertical section E-E of the electromagnet.

Fig. 9 is a top view of the electromagnet.

Fig. 10 is a section F-F of the internal chamber of the apparatus by a horizontal plane showing the construction of graphite blocks of the additional anode, which makes it possible to form a solid annular wall, and the arrangement of conductive rods in the blocks.

Fig. 11 is a vertical section A202B2 of the apparatus modification with a lateral arrangement of anodes.

Fig. 12 is a horizontal section G-G of the apparatus modification with a lateral arrangement of anodes.

Detailed description of the preferred embodiments The embodiments of the present invention will now be described with reference to Figs. 1-12 of the drawings.

The multifunctional apparatus for the production of metallic magnesium comprises a steel body 1 thermally isolated by a double-layer lining 2, whose internal surface forms an annular working chamber. In said chamber a first annular sectionalized anode 3 made of graphite blocks with a current lead from below or a lateral current lead and a first aligned annular sectionalized cathode 4 made of low-carbon steel sheets are arranged. Working surfaces of the anode 3 and cathode 4 form an annular gap 40-70 mm wide. The shape of a section of the cathode is shown in Figs. 5,6 (items 4,24,25). In the upper portion of the working surface of the cathode there are windows for metallic magnesium overflow into an internal annular chamber 5.

The annular chamber 5 is formed by the annular cathode 4 and an additional annular sectionalized anode 6 made of graphite blocks with copper rods 20 connected by an annular bus bar feeding current to each block. The construction of the anode 6 is shown in Fig. 10. The anode 6 also forms a central chamber 19. On the bottom of the chamber 19 a metal (steel) central second cathode 7 is aligned, whose upper portion is covered with a ceramic conical tip 8, on which a steel box 31 is mounted. The current is fed to the cathode 7 from below. The central chamber 19 is hydraulically connected with the annular working gap by an annular gap formed by the bottom of the central chamber, cathode 7,8 and thin-wall channels fixed in the gaps of electromagnets 10, the construction of which is shown in Figs. 7-9. The electromagnets consist of a core 27 made of cobalt steel with the Curie point ~950°C and windings 28 made of a copper bus bar insulated by quartz fabric 29.

Such a structure allows long-term operation of electromagnets at the temperature ~700°C without cooling. At the outlet of the channels 9 there are receptacles 30 for the accumulation of precipitated impurities.

Between the body and the lining windings 13 are arranged made of air-cooled copper tube of a rectangular cross-section. The windings are connected in series either to the current flowing in the working gap or to the current flowing in the annular chamber 5.

The lining is cooled by a coil pipe 23 made of a copper or brass tube of a rectangular cross-section that feeds compressed air. The distance between the coil pipe and the internal surface of the lining is chosen so that the air heated up to the temperature of 150-180°C.

The chamber formed by the working annular cathode is covered from above by a lid consisting of a metal structure 17,22 and lining 18. The metal structure consists of a central portion 22 made of nonmagnetic metal (for instance, steel or pig iron) and a welded annular frame 17 made of low-carbon magnetic steel. A double-cone charging device 16 is established on the lid, as well as insulators, on which current leads to the cathode 4 and to the internal annular anode 6 are fixed.

In the upper portion of the lining there are channels uniformly arranged along the circumference, with incorporated branch pipes 14 connected with the annular collector 15. This system is intended for a uniform removal of gaseous chlorine released during the electrolysis out of the annular working gap.

The apparatus operates as follows : Salt pre-dehydrated in boiling-layer furnaces and containing magnesium chloride is fed using a double-cone charging device 16 into the box 31 arranged in the central chamber 19, which is hydraulically coupled with the annular working gap and filled with molten electrolyte. The salt entering the chamber 19 is melted by heat released at the electrolysis and MHD action, dehydrated and fed into the channels 9 through the annular gap. The molten electrolyte in the channels becomes"lighter"due to the interaction of the magnetic field excited by electromagnets 10 with the electric current flowing along the channel from the central cathode 7 to the annular anode 3, which leads to the intensification of the sedimentation process of magnesium oxide and other impurities in the electrolyte transferred by the flow and accumulated in the receptacles 30. The purified electrolyte is fed into the annular working gap, where magnesium chloride electrolysis takes place. Gaseous chlorine released on the anode is sucked out by a system of branch pipes 14,15 and can be used after refining in boiling-layer furnaces for the preliminary dehydration of salts containing magnesium chloride.

Metallic magnesium released on the cathode is transferred into the annular chamber 5 by a convective flow arising due to airlift under the action of chlorine.

The metallic magnesium is sucked out of the chamber 5 by a vacuum pump or a MHD pump.

When passing a current through the windings 13, an axial magnetic field is excited in the annular gap and chamber 5, its flux density reaching the values-0. 1 T at the current-50 kA and the number of winding turns-4. Here the steel body 1 serves as a core. The interaction of the axial magnetic field with the radial current density field in the annular gap and chamber 5 leads to the appearance of azimutal body forces. Under their action, differential rotation of the electrolyte and metallic magnesium with respect to the apparatus axis arises.

At a current density in the annular gap-0. 4 A/cm2, the azimutal velocity of the electrolyte flow is-6 mm/s. The azimutal electrolyte flow smoothes all the inhomogeneities of the technological process of electrolysis, including a nonuniform distribution of current and magnesium production rate in the horizontal plane.

The azimutal velocity of liquid magnesium flow in the annular chamber 5 depends on the current density in said chamber, which is regulated by the voltage applied to the anode 6 and depends on the technology of centrifugal magnesium purification and production of magnesium alloys in the chamber 5.

Centrifugal forces acting on liquid magnesium in the annular gap promote its overflow into the chamber 5.

The air that cools the lining is heated up to the temperature-150-180°C and can be used in boiling-layer furnaces.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.