DE1209757B - Process for the production of metals, in particular titanium, aluminum and magnesium, by fused-salt electrolysis - Google Patents

Description

A process for producing metals, in particular titanium, aluminum and magnesium, by igneous addition to the patent: 1194590 The present invention relates to a method for the production of metals by fusion electrolysis which is particularly suitable for the production of titanium, aluminum and magnesium .

The known fused flux electrolysis processes have, as far as they are technical are applicable, in addition to special ones that are characteristic of the individual processes Defects have the common disadvantage that relatively high working temperatures are used to carry them out required are. The heating of the electrolysis cells is also correspondingly omitted proportion of the total electrical power supplied and thus the loss of performance associated with these methods is relatively high. In addition, condition of course, the high working temperatures require a significantly higher technical effort for the facilities to carry out these procedures when he was at lower temperatures would be necessary.

Attempts have therefore already been made several times to reduce the working temperatures lower than the usual fused-salt electrolysis process or equivalent To find processes that can be operated at low working temperatures.

For example, a process for the production of aluminum has become known which differs from the conventional aluminum production process, i.e. the normal Al.02 cryolite electrolysis, with working temperatures of 906 to 950 ° C in that the electrolyte is mixed with an inert diluent, which is only lowers the melting point of the electrolyte, is diluted.

With this known method, a reduction in the working temperature of 100 to 200 ° C. in aluminum electrolysis can be achieved without major difficulties, but further temperature reductions are associated with additional technical effort, which destroys a large part of the advantage achieved with the temperature reduction. For example, when the working temperature is lowered to 400 to 500 ° C., either a very expensive thinning agent such as lithium-potassium chloride must be used, or the process must be carried out under excess pressure. Another disadvantage of this known method is the reduction in the current yield caused by the dilution. Working temperatures below 400oC cannot be achieved with the known method.

Regarding the state of the art, it should also be mentioned that this occurs at the cathode deposited metal in the customary fused flux electrolysis process either exclusively from the electrolyte or, especially in refining processes, comes exclusively from the anode. In the former case, the anode usually exists made of unassailable material, usually carbon or graphite, such as the classic melt flow electrolysis process for the production of aluminum, magnesium, Sodium, potassium and beryllium. The group of procedures in which this occurs at the cathode metal deposited exclusively from the anode comprises mainly refining processes. For example, a refining process for the production of pure titanium has become known, in which a titanium anode in a sodium chloride melt under the action of vapor Titanium tetrachloride is decomposed. In another known method of representation of pure aluminum becomes an aluminum anode in one made of aluminum chloride and Sodium chloride refined existing electrolytes. In these proceedings However, it is a matter of pure refining processes, in which, in contrast to the present one Process no metal is obtained from metal compounds. In more recent times are further to the latter group still has various titanium production processes were added, in which anodes consisting of the titanium compounds TiN or TiC are electrolytically decomposed. In this process, however, the melt does not provide any Titanium, and in addition, high working temperatures are generally required here.

The object underlying the invention The task was to find a Schmelzflußelektrolyseverfahren, wherein only relatively low operating temperatures and correspondingly lower electrical power dissipation are needed and also in general and not only to the production of a particular metal in is applicable.

According to the invention, in a process for the production of metals, in particular titanium, aluminum and magnesium, by fusible electrolysis in an electrolyte containing alkali halide and halide of the metal to be extracted, one or more additives being added to the electrolyte in proportionally small amounts, in A further development of the patent 1 194 590 is achieved in that an additive is used which consists of metal, halogen and one or more non-metals, preferably hydrogen and nitrogen, that an anode consisting at least partially of the metal to be extracted is used and that at substantially below the bath temperatures lying around the melting point of the metal to be extracted are used.

It is advantageous to carry out the electrolysis under protective gas.

Preferably, the electrolyte is also depleted in halide of the metal to be deposited this, for. B. titanium tetrafluoride, aluminum trichloride or magnesium chloride, added continuously or periodically during the electrolysis. The halide content of the metal to be extracted in the electrolyte should preferably be kept at 50 percent by weight.

To produce titanium according to the present process, an electrolyte made of sodium fluoride and titanium tetrafluoride, preferably in a molar ratio of 1: 1, and an anode made of titanium or a titanium alloy are used and the temperature of the electrolyte is below 1000 ° C, preferably below 750 ° C.

To produce aluminum according to the present process, an electrolyte made of sodium chloride and aluminum trichloride, preferably in a molar ratio of 1: 1, and an anode made of aluminum or an aluminum alloy are used and the temperature of the electrolyte is below 250.degree .

To produce magnesium according to the present process, an electrolyte made of potassium chloride and magnesium chloride, preferably in a molar ratio of 1: 1, and an anode made of magnesium or a magnesium alloy are used and the temperature of the electrolyte is below 600.degree .

In order to produce fine, non-pyrophoric powder of the metal to be extracted with the method according to the invention, cathodic current densities below 0.1 A / cm 2 are preferably used.

With the method according to the invention, a way was found to electrolytically to make previously non-decomposable metal halides electrolytically decomposable. In order to the electrolysis of low-melting electrolytes was made possible. The basic one The idea was to create stable, electrolytically non-decomposable metal halides immediately in the electrolysis bath into compounds that are stable but electrolytically decomposable with a lower halogen content and transfer them immediately after the transfer to decompose electrolytically. An intermediate reaction had to be carried out by means of suitable measures trigger that caused this transfer.

In order to trigger such an intermediate reaction, a suitable one had to be found Reaction partner and, if necessary, a catalyst initiating the intermediate reaction being found. As such a reactant, the metal to be recovered appeared special to be suitable because, on the one hand, it contains the existing halides of the to be recovered Metal reduced to electrolytically decomposable intermediate products and on the other hand even in this reaction provides an intermediate product from which the product to be obtained Metal is recovered by electrolytic decomposition. To the electrolyte this reaction partner constantly in the pure form necessary for its activity feed, according to the present invention, an anode from the to be obtained Metal used because metal from the anode is constantly in solution during electrolysis and thus ensures a constant supply of the required reaction partners is.

This reduction of the metal halide contained in the electrolyte now takes place in most cases, however, not automatically due to the metal that has dissolved instead of, but rather to initiate this reaction or to achieve as complete a reaction as possible Reaction of the dissolved metal with the metal halide requires one special catalyst.

Only with the fused-salt electrolysis of metal halide naturally low halogen content, e.g. magnesium chloride (MgCl,) is one such Catalyst not absolutely necessary. The catalyst brings in this too Cases, in particular with regard to the current efficiency and the working temperature, certain Advantages, but the reaction proceeds satisfactorily even without such a catalyst as can be seen from the examples given below.

In the decomposition of aluminum chloride, which has a higher halogen content has, on the other hand, the results of the melt flow electrolysis are without a catalyst in comparison to those with a catalytic converter, and with titanium, which has an even higher halogen content is not at all positive without a catalyst To achieve a result, as can also be seen from the examples of aluminum and titanium electrolysis results.

It has been found that suitable catalysts for this purpose are those based on metal, preferably on the basis of the metal to be extracted, in which metal is combined with halogen and one or more other non-metals, preferably hydrogen and nitrogen. Substances which are produced from an ammonia storage compound to a halide of the metal to be extracted by gradual heating to temperatures above 650 ° C. in an oxygen-free protective gas atmosphere, preferably in an ammonia gas stream, are particularly suitable. In this manufacturing process, ammonium halide is sublimated from the addition compound by heating or annealing, the annealing being continued, if necessary, while maintaining the final temperature reached after heating, until no more ammonium halide sublimates. The heating is carried out so gradually that only ammonium halide is sublimated, but not the heart-producing substance, and that within one to several hours. The flow rate of the protective gas flow is also kept low enough that the treated substance is not entrained. Addition compounds with the lowest possible number of ammonia molecules, preferably attached to the chloride of the corresponding metal, are used as starting materials. However, this number has no influence on the product resulting from the manufacturing process, that is to say the catalyst, only the manufacturing process becomes somewhat more complex with a higher number, since more ammonium halide has to be sublimed off.

Since the decomposition voltage of the unstable compounds formed from the stable electrolytically non-decomposable metal halides by reducing the halogen content is very low, a further essential advantage of the inventive method is that the operating voltage is on average only about 1 V and thus far below the normally necessary electrolysis voltages.

In what weight ratio that obtained by decomposition of the melt Metal to the metal that has gone into solution from the anode is as follows shown in two examples.

For example, in the case of aluminum, 12.35 g of Al were deposited on the cathode, of which 4.5 o came from the anode and 7.85 g from the melt. The ratio of the derived from the molten aluminum to the originating from the anode is aluminum that is, in a first approximation 2: 1. This ratio can be casually explained by the fact that a derived from the anode in the solution Aluminiumatorn according to the reaction leichun-C Al + 2 A1C13 -> 3 AICI, each 2 aluminum chloride molecules reduced and thereby 3 molecules of an unstable aluminum dichloride are formed, which can be easily decomposed electrolytically, so that the 3 Al atoms resulting from this decomposition are then deposited on the cathode. The ratio resulting from this reaction equation is roughly the same as that obtained from the experiment, namely 1 atom from the anode (- 4.5 g), 2 atoms from the melt (A 7.85 g), together 3 Atoms on the cathode (A 12.35 g). The fact that the experiment does not completely agree with the reaction equation is probably due to the fact that no complete reaction of all the atoms released from the anode with the chloride molecules in the melt is achieved, but only an approximately complete reaction, and only if the catalyst is present during in the absence of a catalyst, as can be seen from the example of aluminum electrolysis without a catalyst, only a small percentage of the atoms released from the anode causes such a reduction of chloride molecules in the melt.

The situation is similar for titanium. Here, 0.82 g of Ti were deposited on the cathode, of which 0.48 g came from the anode and 0.34 g came from the melt Z. Was the ratio of the derived from the melt to the titanium derived from the anode-titanium so näherun sweise 1: 1. This corresponds to a C reaction equation Ti + TiC14 -> 2 TiCl.

So 1 atom from the anode (- 0.48 g), 1 atom from the melt (Ah- 0.34 g), together 2 atoms at the cathode (A 0.82 g), which are caused by the electrolytic decomposition of the TiC1, develop. Here, too, the inaccurate agreement of the experiments with the reaction equation is shown, to the disadvantage of the decomposed melt, which suggests an incomplete reaction of the titanium atoms released from the anode with the chloride molecules of the melt.

In any case, it is certain that it will be done with the help of the present proceedings succeeds at relatively low working temperatures and relatively low Expenditure of electrical power per unit weight of the recovered metal to achieve complete deposition of the metal on the cathode.

In general, the metal obtained is in the form of flakes stuck to the cathode. Since the melt is very thin, it drips when it is removed the cathode for the most part. The rest can be done by washing with alcohol or alcoholic Nitric acid can be removed, leaving dense leaves hanging from the cathode Metal is obtained.

In order to achieve this complete deposition of the metal to be recovered on the cathode, however, it should be noted that the metal halide content of the electrolyte must not drop significantly below a molar ratio of 1: 1 to the alkali metal halide content of the electrolyte. Since one generally assumes a molar ratio of about 1: 1 , care must be taken to avoid a deposition of the metal to be extracted in fine distribution within the melt that the melt during the electrolysis either corresponds to the decomposed amount of the metal halide continuously or periodically further metal halide is fed in, so that an inadmissible depletion of the melt in the metal halide is avoided. Since the depletion of the electrolyte is associated with an increase in the voltage at the electrolytic cell, the point in time of the periodic additions of metal halide can be determined simply by making these additions when a certain percentage increase in voltage of, for example, 100 / is exceeded. After the addition, the voltage drops back to the original value. A corresponding amount of the catalyst is preferably also added in each case with these additions.

In this way it is possible to continue a fused-salt electrolysis according to the present process continuously for any length of time and only to add fresh metal halide and possibly also new catalyst at periodic intervals depending on the consumption of metal halide. However, the cathode must be replaced at longer intervals if the metal layer deposited on the cathode has already become so thick that the electrolysis can be significantly disturbed.

It is also advisable to carry out the electrolysis under protective gas (e.g. nitrogen, Argon or helium). The metallic anodes are then essential less attacked because chlorine escapes at the anode under protective gas while when working in air due to the humidity from the escaping Chlorine forms hydrochloric acid in large quantities, which is known to be strong in metallic anodes attacks. When working under protective gas, the chlorine escaping at the anode can into chlorination towers, in which metal chloride is produced, and thereby contributes to the reduction of the chlorine consumption.

As already mentioned, the recovered metal is deposited in the form of flakes or, in the case of low current densities below 0.1 A / cm2, in the form of powder on the cathode. This powder or the flakes can be stripped off the cathode relatively easily after the end of the electrolysis. The powder obtained in this way can on the one hand easily be melted together to form compact metal, but it can also be used directly as metal powder.

Because metal powders are widely used today as raw materials, especially for the production of sintered metals, but also for metal pastes and metal bronzes used for metallic luster paints.

Metal powders are generally made by dividing compact metals manufactured. The cutting of compact metals in the form of bars, blocks, sheets etc. up to the powder fineness results in a large increase in the surface area, at the same time the crystals present in the coarse form are damaged. Above all, this injury is the cause of the powder's easy oxidizability, which often causes large-scale explosions and fires. Both Heavy metals such as copper, iron, nickel, etc., the risk of fire is not so great. Copper powder is almost always made by electrodeposition, iron and nickel powder are made by decomposing their carbonyl compounds. In these procedures the powders are created in a fine distribution, so that the crystals are damaged is only to be feared in a few cases.

The case is different with light metals, especially aluminum and magnesium. It is a particular complication for the extraction of powders from these metals that aluminum, which has the highest enthalpy of oxidation, only from primarily molten metal, which, when converted into the solid state, is converted into large pieces (blocks, bars, sheets) can be produced. at The production of powder from aluminum metal is therefore always accompanied by damage to the crystal edges to be expected, which is why despite the use of protective gas, z. B. hydrogen, always with unexpected fires and explosions must be expected. Just staying behind is enough of oxygen residues in the equipment to cause explosions and fires, And the hydrogen atmosphere in particular can lead to the formation of oxyhydrogen and explosions accelerate. The situation is similar with magnesium.

In the present method, on the other hand, at current densities of about 0.1 to 0.5 A / cm2, the metal deposits itself in the form of fine sheets on the cathode. If you go down with the current density, the deposit becomes increasingly finer and yet remains firmly attached to the cathode. At 0.01 A / cm2 one obtains e.g. B. in aluminum electrolysis very fine, firmly adhering, blackish precipitates, which, however, dissolve colloidly when treated with alcohol to form a black liquid, from which they can be filtered off through blue band filters. A black, uniformly finely powdered mass is obtained, which macroscopically looks like coal powder. Under the microscope it shows a metallic sheen. The analysis showed an aluminum content of 90 to 950/0. It is interesting to note that this colloidal aluminum powder is not pyrophoric. It can even be stored on filter paper for an unlimited period of time without spontaneous combustion.

The present process is therefore eminently suitable for production such metal powder. You work according to the desired fineness of the powder with a correspondingly low current density. Examples The following are a few more examples of melt flow electrolysis carried out according to the method according to the invention described in more detail.

Example 1 In a cell (porcelain crucible) heated from the outside to 190 to 200 ° C. , 100 % of a mixture produced under protective gas and corresponding to the composition NaC1-AIC13 were processed. The electrolysis apparatus was kept under protective gas (helium). The mixture melted at 150 to 160 ° C. When the temperature had reached 190 ° C. , the aluminum electrodes were lowered into the melt and the current density was adjusted to 0.1 A / cm2. The voltage was initially 1.38 V, but soon went down to 0.9V. Chlorine developed at the anode, which escaped together with the protective gas. After 7 hours the electrodes were taken out. The cathode was covered with a tightly fitting precipitate which, after dissolving out the melt with alcohol, gave 2.31 g of aluminum. The attached melt was removed from the anode by washing with water. She had lost 1.81 g in weight. 0.50 g of the aluminum deposited on the cathode thus came from the decomposition of the melt.

Example 2 In the same cell, 100 g of NaC1 - AlCI, with 2 g of an adduct of NH annealed at 800 ° C., were electrolyzed on A1C13 at 190 to 200 ° C. under protective gas. Vigorous evolution of chlorine occurred fairly quickly. The current density was regulated again to 0.1 A / cm2, a voltage of 1.2 V being established, which soon fell to 0.8 V. After 3 hours the voltage began to rise and reached 1.18 V after 5 hours. Now A1C13 with 3 of the adducts mentioned was added, whereupon the voltage dropped to 0.7 V. As soon as the voltage had risen to above 1.0 V again, AICI, with additive, was added again. The cathode quickly became covered with an adherent metal deposit and was replaced with a new one from time to time. The anode remained in the melt all the time and was not replaced. After a total of 20 hours, the anode had lost 4.50 g , and a total of 12.35 g of aluminum had deposited on the various cathodes. 7.85 g were therefore by decomposition of the melt, i.e. H. by decomposing the A1C13 periodically added according to consumption. Example 3 In an externally heated cell (porcelain crucible) 100 g of KCl - MgCl were heated. The double salt melted at 520'C. When the temperature had reached 540 ° C, the magnesium electrodes were lowered into the melt. The current density was set to 0.2 A / CM2, while the voltage was set to 0.9 V. The electrolysis was carried out under protective gas, so that the chlorine developed escaped with the protective gas. After 115 minutes the electrodes were removed. The cathode was covered with a tightly fitting precipitate which weighed 0.846 g and was found to be pure metallic magnesium. The anode had lost 0.154 g in the same time. Thus 0.692 g (i.e. 81.8 %) of the magnesium deposited on the cathode came from the decomposition of the melt. EXAMPLE 4 In the same way, 100 g of carnallite, to which 1 g of an adduct of NH 3 and MgCl, annealed at 700 ° C., had been added, were electrolyzed at 505 ° C. for 155 minutes. 1.289 g of magnesium had deposited on the cathode, the anode had decreased 0.202 g. 1.087 g (d. e. 84.3 0/0) so the deposited at the cathode, the magnesium derived from the decomposition of the melt.

In a counter-test with carbon anodes, a current of only 0.007 A (corresponding to a current density of 0.0008 A / cm2) flowed at 801'C and 0.9 V voltage. A separation of magnesium could not be determined, for this the voltage would have had to be increased significantly. Example 5 Cathode ..... iron iron Anode ...... titanium titanium Electrolyte ... 50 g NaJiF, 50 g NaJiF, +0.5 'g' one at 700 'C annealed Attachment product of NI-1, on TiC1, Temperature 8000c 7200C Voltage ... 2.1V 0.5V Current density . . 0.15 A / cm2 0.133 A / CM2 Duration of experiment 60 minutes 420 minutes loss the anode 0.27 g 0.48 g At the catho- de departed separated Ti Og 0.82 a

Claims (2)

Claims: 1. Process for the production of metals, in particular titanium, aluminum and magnesium, by fused-salt electrolysis in an electrolyte containing alkali halide and halide of the metal to be extracted, one or more additives being added to the electrolyte in proportionally small amounts, in further development of patent 1 194590, characterized in that an additive is used which consists of metal, halogen and one or more non-metals, preferably hydrogen and nitrogen, that an anode consisting at least partially of the metal to be extracted is used and that at substantially below the melting point of the to recovering metal lying bath temperatures is worked. 2. The method according to claim 1, characterized in that the electrolysis is carried out under protective gas. 3. The method according to claim 1 or 2, characterized in that the electrolyte when depleted in halide of the metal to be deposited this, for. B. titanium tetrafluoride, aluminum trichloride or magnesium chloride, is added continuously or periodically during the electrolysis. 4. The method according to claim 3, characterized in that the content of the electrolyte of halide of the metal to be extracted is kept at over 50 percent by weight. 5. The method according to any one of claims 1 to 4 for the production of titanium, characterized in that an electrolyte made of sodium fluoride and titanium tetrafluoride, preferably in a molar ratio of 1: 1, and an anode made of titanium or a titanium alloy is used and that at temperatures of the electrolyte below 1000'C, preferably below 750'C, is worked. 6. The method according to any one of claims 1 to 4 for the production of aluminum, characterized in that an electrolyte made of sodium chloride and aluminum trichloride, preferably in a molar ratio of 1: 1, and an anode made of aluminum or an aluminum alloy is used and that at temperatures of the electrolyte below 250'C is worked. 7. The method according to any one of claims 1 to 4 for the production of magnesium, characterized in that an electrolyte of potassium chloride and magnesium chloride, preferably in a molar ratio of 1: 1, and an anode of magnesium or a magnesium alloy is used and that at temperatures of the electrolyte below 600'C is worked. 8. The method according to any one of claims 1 to 7 for the production of fine, non-pyrophoric powder of the metal to be extracted, characterized in that cathodic current densities below 0.1 A / cm2 are used. Publications considered: Swiss patent specification No. 270 893, French patent specification No. 1138 544.1 153 781.