DE1807609B2 - METHOD FOR PRODUCING MAGNESIUM - Google Patents

Description

The invention relates to a process for the production of magnesium by incorporating magnesium oxide and a metallic reducing agent in the reaction zone of the reduction furnace in the presence of a molten Oxydschlackenbades at a temperature of above 1300 ⁰ C, the resultant magnesium vapor from the reaction zone escapes into the condensation zone and is condensed there.

In such a method, which is known as "Magnetherm" process, the oxidation of silicon and the reduction of magnesia in the presence takes place of a bath of molten slag at a temperature above about 1300-1400 ⁰ C. Magnesium vapor develops under the high vacuum with a very low partial pressure and is then condensed into molten or solid magnesium metal. Periodically, "used" ferro-silicon alloy and a large amount of slag are tapped from the furnace in molten form. Since the furnace-condenser system is maintained under high vacuum to promote the desired reaction and evaporation of the magnesium, it is necessary that the vacuum be broken and operations stopped to periodically remove slag and spent alloy from the furnace . The process is therefore necessarily a batch process.

This procedure was carried out in a small ⁽ⁱ ° commercial scale, and it seems that it can not compete successfully with the now for the production of magnesium in large commercial-scale method used, namely the electrolysis of molten magnesium chloride. ^(L>

Another well-known metallothermal process for the production of magnesium, the "Pideeon" process, is also a batch process which has only been carried out on a comparatively small commercial scale. In this method, magnesium oxide is introduced in the form of calcined dolomite and metallic silicon in the form of ferrosilicon in batteries small externally heated retort, in which a solid phase reaction at temperatures on the order of 1100-1200 ⁰ C takes place. Under these conditions, metallic magnesium is released from the reaction zone as vapor with a very low partial pressure, and for this reason it is necessary to keep the retort battery under a very high vacuum.

It seems that this procedure except under special conditions and for special reasons not compete with the electrolysis process for the production of magnesium from magnesium chloride can.

DT-PS 10 53 791 describes a process for the production of magnesium by reducing magnesium oxide at temperatures above 1300 ⁰ C by means of a reducing agent such as ferrosilicon or silicoaluminum, in which a powdery reaction mixture of magnesium oxide and reducing agent with the surface of an im Slag of molten oxides located in the furnace is brought into contact, and which is characterized in that such an amount by weight of the reaction mixture is used that it is equal to the weight of the

liquid slag like

T-F

behaves, where T is the

Temperature of the liquid slag before the reaction mixture is added in ⁰ C and F means the melting temperature of the slag in ° C. In this DT-PS it is mentioned that the method according to the invention can be used without reducing the pressure, but that both a better output in the furnace

as well as a lower consumption of electrical energy is obtained when operating under reduced pressure is working.

Because: the slag bath used in this process is 415 to 50% due to its CaO content basic slag. This has the disadvantage that in relation to the amount of magnesium produced an undesirably large amount of slag is formed.

The object of the application is to create an improved metallothermal process for the production of magnesium, which has advantages over the prior art and in which with each unit of quantity of formed Magnesium only a relatively small amount of slag is formed.

This object was achieved according to the invention by the method specified in claim 1, in which the slag bath with a content of less than 30% calcium oxide, preferably about 10-20%, is an acidic slag which has the advantage that it is produced with each unit Magnesium, only about 1.6 to 2.5 units of slag can be formed, while 6 units of slag are produced with each unit of magnesium produced according to the above-described known method, which of course must be discarded.

The process of the invention is a continuous or batch process that takes place at or in the Near atmospheric pressure and which goes on in the following manner:

An aluminum-silicon alloy is used as a metallic reducing agent; a larger proportion the magnesium oxide required is supplied as magnesia and not as dolomite lime; a relatively high concentration of magnesia is maintained in the slag at all times; and the The proportions of metallic aluminum and silicon and the slag composition are determined in such a way mutually coordinated and maintained that the total amount - or nearly the total amount of the Aluminum oxide and silicon dioxide required for slag formation by the reduction from magnesia to metallic magnesium.

If, according to the method according to the invention, an aluminum-silicon alloy, which silicon and aluminum in a ratio of at least approximately 0.8: 1 (concentrations and ratios are expressed here by weight, unless otherwise specified) contains, for the reduction of magnesium oxide from one predominantly magnesia-containing oxidizing agent is used in the presence of a molten slag with a certain composition at a temperature above approximately 1400 ⁰ C, then magnesium vapor can be released in amounts even at atmospheric pressure, which correspond to a very high utilization of the silicon content of the alloy. Obviously, the presence of aluminum as a reactant in close physical association with silicon and the molten slag defined herein synergistically stimulates the reducing agent to react to such an extent that magnesium vapor evolves even at atmospheric pressure, thus eliminating the need to maintain a high vacuum in the System is avoided.

The use of aluminum-silicon alloys with a suitable composition thus creates a lot

important advantages over the use of ferrosilicon. A clear advantage is that Possibility of carrying out the reaction at or near atmospheric pressure. A second The advantage is that a predominant proportion of the silicon content of the reducing alloy can be used to reduce magnesium oxide. Furthermore, the aluminum oxide required in the slag can be obtained as a by-product of the reaction, thereby reducing the ratio of slag to formed magnesium metal can be reduced in a favorable manner.

It has also been found that the tendency of silicon to react with magnesia to form magnesium is greatly increased if the magnesia content of the slag is kept at a relatively high concentration, above about 5% and preferably between about 10 and about 20%. The increased rate of reaction of magnesia with both aluminum and silicon significantly increases the productivity capacity of a given size furnace. The high concentration of magnesium oxide in the slag plays an essential role in the process according to the invention.

To keep the ratio of slag to magnesium metal formed at the lowest practicable To maintain value, it is also desirable to have a relatively high concentration of alumina in the Maintain slag, namely greater than about 15% and preferably about 25-30%.

Furthermore, it has been found that the advantages of the pending process are best achieved thereby be able to avoid high concentrations of calcium oxide in the slag, during concentrations of silica of greater than about 25%, preferably about 30-45%, be used. The concentration of calcium oxide should be less than 30% and preferably around 10-20% can be held.

In the drawings shows

F i g. 1 a three-component diagram showing the possible and preferred amounts of calcium oxide, Represents alumina and silica components of the molten slag and

F i g. 2 is a three-component diagram showing the possible and preferred compositions of Represents reducing alloy.

In the inventive method, an aluminum-silicon alloy is used for the reduction of magnesium oxide prior to the reaction zone in a reducing furnace at a temperature above ungefähi 1400 ⁰ C and in the presence of a bath of molten slag Einei the following general composition:

component

CaO
MgO

Al ₂ O ₁
SiO>

Possible
area

0-30%

5-25%

15-35%

25-50%

Preferred area

10-20%
10-20%
25-30%
30-45%

An optimal composition of the molten slag is about 20% calcium oxide, about 15 ⁽

Magnesia, about 30% alumina, and about 35% silica.

Alternatively, the composition of the molten slag can be determined by the methods shown in FIG. 1 can be defined. Thus covered the possible range of the composition s the molten slag those compositions with about 5-25% of magnesium oxide and calcium oxide, silicon oxide and aluminum oxide in the by curve 10 of F i g. 1 specified quantities. Similarly, the ι ο preferred composition of the molten slag about 10-20% magnesium oxide, the remaining components in g by the curve 12 of R i. 1 are given. It should be noted that the in F i g. For the sake of simplicity, the percentages given in 1 relate to the molten slag without its magnesium oxide content, ie 5-25% and preferably 10-20% of the total slag. Thus the total amount of the three components is 100%, but only represents the> o part of the slag that remains when the amount of magnesium oxide is subtracted.

In a preferred embodiment of the invention the composition is the molten one Slag such that the ratio of aluminum oxide as and magnesia to .silica is less than 1.6: 1, the total amount of alumina and Magnesium oxide is less than 50% of the slag and the ratio of calcium oxide and magnesium oxide to silica is less than 1.6: 1. v>

Most metallurgical slags have a high CaO content of at least 40% and usually on the order of 50% and more. Such slags are called basic slags denotes, which are characterized by a relatively sharp melting point and which at low overheating form liquid slags with low viscosity. On the other hand, slags are mil classified as acidic slags in the above composition range, which are characterized by a somewhat.) i> characterized by a blurred melting point and form rather viscous "glassy" slags that need to be heated quite strongly to achieve a lower viscosity.

The range of use given above covers a wide range of melting points. Many combinations are possible within this range, but they must be chosen carefully as necessary. to form a sip in which the mixture of oxides is so composed that a suitable combination of melting point and viscosity is obtained. For this purpose, a flux, such as. B. fluorite, Gewürischtenfalls be added to the slag.

The oxide introduced into the Rcakiionszonc is in a suitable manner an oxide mixture, such as. B. a mixture of magnesium oxide and calcium oxide. | cdoch is a predominant part of the oxide magnesia, ie magnesium oxyder ore. A smaller proportion of the oxide may be calcined dolomite, an equimolar amount. Combination of magnesium oxide and calcium oxide obtained from CnMg (COi) /. However, it is not necessary to use calcined dolomite in the oxide, and magnesium oxide allcine is satisfactory in some cases. In every I all the molar ratio of t <\ magnesium oxide to calcium oxide in the oxidizing agent is at least 2: 1

It is clear that if a Magncsilischcr dolomite stone with a relatively high ratio of magnesium oxide to calcium oxide is available, it may be desirable to replace ordinary dolomitic lime in whole or in part with lime made from such a stone, thereby reducing the amount of as Magnesia required magnesium oxide is reduced. On the other hand, if dolomitic lime is unavailable or undesirable, then it is clear that lime made from limestone can be used to produce the calcium oxide necessary to form a suitable slag.

In the process according to the invention, it is very desirable to maintain a temperature of at least about 1400 ^° C. in the reaction zone in order to create good reaction conditions, but temperatures of more than about 1700 ^° C. are undesirable because process engineering and operational difficulties arise here. For this reason, it is desirable to use a slag whose melting point is not higher than about 1600 ° C so that it can be sufficiently overheated to achieve sufficient fluidity of the slag without the need for excessively high temperatures. Thus, a temperature of about 1400-1700 ° C in the reaction zone is preferred, although in some cases higher or lower temperatures are suitable and may be desirable.

On the other hand, slags with a relatively high viscosity can be used in the process according to the invention can be used because there is no bed of solid material in the furnace through which the slag can pass Must find a way to reach the tap hole for emptying the furnace. So the problem is Slag viscosity is not as great as in most metallurgical processes, but it is nonetheless a Factor that needs attention.

In general, the composition of the slag in the present process is determined by the Ratio of aluminum to silicon, which are introduced as reducing agents, the degree of Use of silicon as a reducing agent, which is as high as possible for reasons of economy should be, and the amounts of Magncsiiimoxids, which as Magnesia and dolomilic lime are determined.

The term "aluminum / silicon alloy" as used herein includes reducing agents which, when added to the molten slag in the reaction zone of a reduction furnace in the manner described herein, yield metallic aluminum and silicon.

The use of Al-Si-Ic alloys as Reducing agents in the process according to the invention can be desirable, in particular in the With regard to the easy availability of such Aluinini umsilium · alloys. Aluminum can be produced in the form of such alloys by melting processes electric furnace, which are well known. When the aluminum content of the alloy increases, a small amount of iron is desirable and sometimes even necessary to avoid excessive iron Avoid volatilization of aluminum and silicon from the furnace. In general, the Aluminum content of these alloys should be limited to a maximum of about 60% for practical reasons. In in these cases the iron content is usually greater than about 5%.

On the other hand, it is for maximum utilization of the ; silicon content is desirable, a relatively low one To have iron content in the reducing agent used according to the invention. But this desideratum must counteract the beneficial effect of iron content on the cost of manufacturing the The induction agent, as already mentioned above, must be weighed. Hin iron content of about 10% appears satisfactory when these factors are taken into account, but it can be higher or lower, without deviating from the scope of the invention, for example 0-20%.

If you add all of these factors - the manufacturing cost, the concentration of aluminum and silicon; the exploitation of the silicon slag combination and properties, the ratio of slag to produced magnesium, the composition and the properties of the slag, the amount and composition of the consumed alloy - weighs against each other, then the desired range of composition of the alloy used at Invention methods are used, such as follows:

Metallic
component

Al
Si
Fe

Possible
area

25-50%

40-65%

0-20%

Preferred area

30 -

50-W) "/ ..

10%

Within the above ranges of the classification summary the ratio of silicon to aluminum is at least 0.8: 1, preferably more than 1: 1 and in particular at least 1.4: L

Alternatively, the composition of the aluminum-silicon reducing agent may be of the present invention by the pressure component diagram of FIG. 2 being represented. Thus, the possible composition of the negative effects falls within the range indicated by curve 20 of FIG. 2 surrounding area. Preferably the falls Reduction agent composition within the by the curve 22 of Γ i g. 2 surrounded! 'Laugh.

The following examples are given to demonstrate the technical and economic advantages of the invention Procedure to show; however, the examples are not to be interpreted in a restrictive sense.

Examples

The following works are carried out in an electric reduction furnace which is connected to a condensing chamber. The procedure consists in this. that the furnace is charged with a slag and that heat is applied until a proper viscosity is reached at a temperature above about 1400 ^° C. whereupon the oxide and the reducing agent are introduced in small batches. The molten slag and any ferro-silicon alloy that may be present are tapped off periodically. The addition of oxide and reducing agent and the tapping off of slag and spent crrosilicon have been carried out in such a way that the composition of the slag is kept essentially constant. The process is carried out essentially continuously.

The oxide and reducing agent are placed in the furnace. The tapped slag possesses the composition given in the table. The reaction takes place at temperatures that are also given in the table. The magnesium vapor was developed and condensed at atmospheric pressure. The compositions of the Slag are also given in the table.

Reducing agent
Al
Si

Oxidizing agent: Mutincsin *) Dolomitic KuIk * ¹ )

Sips:

CuO

ΜμΟ

Al, O ₁

SiO-

Tempcralur, I Alloy used) Formed sips ⁴¹ ) I e-Si-Ncbcnprodukl *) CaO 4 MgD / SK), ΜμΟ ♦ Al, O, / SiO.

40 40 30th 30th 30th .M! 40 40 M) 50 M) M) M) 60 M) 50 0 10 10 H) 10 10 IO IO 1.7 ') 1.41 1.50 1.66 1.68 κ% 1.46 K6. ¹ 0.30 1.14 0.92 0.45 K14 0.15 K (K) 0.56 10 30th 26th 15th 27 S. 28 18th 15th 10 10 10 20th 20th 10 10 30th 35 30th 35 25th 35 30th 35 45 25th 34 40 28 40 32 37 1500 1625 1525 1550 1625 1650 1525 1600 0.68 1.06 0, «W KU K07 KOl 0.84 0.83 1.72 2.20 2.05 1.76 2.46 1.76 2.10 1.80 0 0..Vi ^{1 y} 0.44 ') 0.44 ') 0.44 ') 0.44 ') O.I ') ¹ ) O.I ')') 0.55 1.60 1.06 0.63 1.68 0.63 1.15 () .7 (i KOO 1.81) KI8 K12 1.60 K37 1 .. " ¹ p 1. ¹ I 709 629/180

(I nilsct / ιιημ)

Reducing agent:

Ie O \ wLiiionsmillcl:

Magnesia*)

Dolomilic lime *)

Slag: CaO MgO Λ 1.0, SiO,

Temperature, C Alloy used *) Formed slag *) Fe-Si by-product *) GaO -t MgQVSiOi MgO + Αί, Ο, / SiOj

*) Expressed as the weight unit of magnesium formed per unit. ') 72% silicon. -) 757η silicon. S 56% silicon. ⁴ I (OK% silicon.

II. · Ι ·> | ΐΐι.Ί in Il 0 I. ' i .; 0 I I 0 IS 1" 30th 30th 10 30th 30th 20th 30th 18th H) 30th .Ul 01) W) 33 () () 00 30th 00 30th 50 00 (.0 IO 10 57 Kl IO 50 K) 32 K) 10 IU 1.73 1.81 1600 1, SK 1450 l. ^l > 5 1560 1.03 1.01 1.5o 0.25 0 0.84 0.3 ') 0 0.83 0 0.84 0.83 0.75 0.72 ') 1.44 12th 1.59 1.58 23 21 M. 10 0.21 ⁴ ) 20th 0.2 I ⁴ ) 0.2I ⁴ ) 15th 15th IO 30th 0.17 25th 0.40 0.34 30th 30th 25th 51 0.75 43 1.00 0.92 32 34 43 1400 1525 1575 1575 1400 0.85 0.83 0.84 1.09 0.85 1.59 1.91 2.10 2.05 1, ¹ st 0.21 ⁴ ) 0.21 ⁴ ) 0.19 ¹ ) 0.441 0.21 ⁴ ) 0.37 0.74 1.19 1.06 0.74 0J8 1.05 1.09 1.06 0.81

the

erchlHch. d.0 the AusnuBiin, V.kuumartai.swcisc isl and in

_k »"

S i Ϊ SÄ b In J..S «! "Lic can be a " -csel. become I de Viskos. · «/ u ^ n. without the »Qberml«. High le .., _K r..un »are required. Arheilshedingun

gen des ^0Γ ' ^ιη , 3 ^ 7ιηΐ JeVhiiinissc der / tigeftlhrten / "sunimen e./ungcn .mi VwMHn. J,

i KÄn w « c Z adjust, dall

'deTiediikionsmiiicls .ml den, ^kS ^ "' _{Mll | J} , _{K. slll} , _n rcag.c

UIer? FfenheMHfcrm, U-rN »he Ϊ anÄnsth. liniks "chul.cn. , .Imuhl iw Ben procedure.,. You. These metals can be removed or removed by suitable meiallurgical processes

of the SiIu

the most varied combinations of Ic ^ "" Mmmenwuungen and Schlackc./t.sa.n.nense./nnic niJtigchen. while iroi / dem the Desulerata cim _{nift | r} , SchUtckenverhlllinisses and cii.es high degree of Ausnu./un «eier .neialhsvhen R, uli.kii» i.sni. ^{lcl mil llcm} ge ^ hlussrncM furnace condenser Svste. μ, which works at essentially atmospheric Ιΐηκ, can be maintained, wmhinh the furnace is operated in a continuous W * v ermoglk-hl w.rd D, work tempo · »... * wr1

desirably kept above about 1400 C, and / was low enough that serious work difficulties should be avoided, and high enough that there is sufficient volume of the slag.

Hs is also possible instead of the one described for Purposes used alloys mixtures

l'errosilicon or silicon and very red aluminum to use and a lime with a high magnef oxide content completely or partially for dolomilis To use lime and magnesia without deviating from the invention.

I licivii .- IiI.ill

Claims (6)

i8 07 Patent claims: • 1. Metallothermal «« Process for the production of magnesium by introducing magnesium oxide and a metallic reducing agent, e.g. B. an alloy of silicon and aluminum, which has a ratio of silicon to aluminum of at least 0.8: 1, in the presence of a molten oxide slag bath at a temperature of ι ο at least about 1400 ⁰ C, the resulting magnesium vapor from the reaction zone escapes into the condensation zone and is condensed there, characterized in that the molten oxide slag bath in the reaction zone contains approximately 25-50% by weight of silicon dioxide and less than 30% by weight of calcium oxide. 2. The method according to claim 1, characterized in that a metallic alloy is used which is about 30-40% by weight aluminum, about 50-60% by weight silicon, and about 10% by weight Has a weight percent iron and a silicon to aluminum ratio of at least 1.0: 1. 3. The method according to claim 1 or 2, characterized in that a molten slag with about 10-20% by weight calcium oxide, about 10-20% by weight magnesium oxide, approximately 25-30 wt% alumina and approximately 30-45 wt% silica are maintained will. 4. The method according to any one of claims 1 to 3, characterized in that the temperature of the charge in the molten furnace is approximately 1400-1700 ⁰ C and that the furnace is operated at approximately atmospheric pressure. 5. The method according to any one of claims 1 to 4, characterized in that in the vapor space of the called furnace an inert gas atmosphere consisting of argon. Helium or hydrogen will. 6. The method according to any one of claims 1 to 5, characterized in that a slag is maintained in which the ratio of aluminum oxide and magnesium oxide to silicon dioxide in the slag is less than 1.6, the aluminum oxide and magnesium oxide less than It accounts for 50% of the slag, and the ratio of calcium oxide and magnesium oxide to silicon dioxide in the slag is less than 1.6.