JPH0567570B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing magnesium chloride, and particularly to a method for producing magnesium chloride suitable for electrolyzing magnesium chloride and supplying it to an electrolytic cell for producing magnesium. (Prior technology) Magnesium is one of the lightest practical metals, and its uses are increasing, such as in the production of alloys with aluminum, as a contact agent in the production of ductile cast iron, and as a reducing agent in the production of titanium tetrachloride. I'm on my way. Currently, more than 90% of magnesium is produced by an electrolytic method that electrolyzes magnesium chloride, and the rest is produced by a reduction method using silicon. Conventionally, the following methods (1) to (4) have been used to produce magnesium chloride to be supplied to an electrolytic cell for producing magnesium.
method has been adopted. (1) A method of adding ammonium chloride to hydrated magnesium chloride and heating and dehydrating it. (2) A method of heating and dehydrating carnite (MgCl ₂・ KCl ・ 6H ₂ O). (3) hydrated magnesium chloride (MgCl ₂・ nH ₂ O) A method of adding hydrochloric acid to dissolve, evaporating, concentrating and dehydrating until n = 1.25 to 2, and then electrolyzing it as it is (Dow method) (4) Mixing magnesium (MgO) and a carbon material, such as pitch, etc. A method of obtaining anhydrous magnesium chloride by chlorinating magnesium with chlorine (problem to be solved by the invention) However, methods (1) and (4) above have complicated manufacturing processes and low productivity. However, method (2) above requires a large amount of energy for heating and dehydration, and KCl generated by decomposition of carnallite (MgCl ₂・ KCl ・ 6H ₂ O) accumulates in the electrolytic cell, causing periodic There was a problem in that it was necessary to remove the deposits, and there was no other way to use the deposits other than as fertilizer. In addition, the Dow method described in (3) above involves decomposition of the water contained during electrolysis, which causes high consumption of the graphite anode and requires a special electrolytic tank, and the chlorine concentration in the generated gas is low. Therefore, there was a problem that it was difficult to reuse. Furthermore, in any of the above conventional methods,
Because magnesium chloride has very high hygroscopicity,
Careful technical measures must be taken when supplying the produced magnesium chloride to the electrolytic cell. An object of the present invention is to provide a new method for producing magnesium chloride that does not have the problems of the above-mentioned conventional techniques, and its main purpose is to efficiently produce magnesium chloride that can be directly supplied to an electrolytic cell for producing magnesium. The aim is to provide a method to do so. (Means for Solving the Problems) The gist of the present invention is as follows. 2. A method for producing magnesium chloride, which is characterized by reacting magnesium oxide or/and magnesium carbonate with chlorine by passing a chlorine-containing gas through the suspension. The chlorine-containing gas passed through the suspension is
It means a gas containing enough chlorine to convert magnesium oxide into magnesium chloride according to the formula (2) below, and chlorine gas is usually used alone. However, a mixed gas of chlorine and carbon monoxide, or a gas that decomposes to generate _Cl2 , such as phosgene, can also be used. A carbon-containing substance may be added to the suspension, the chlorine-containing gas, or both to promote the reduction reaction. In the present invention, alkali metal chlorides include sodium chloride (NaCl), potassium chloride (KCl),
Lithium chloride (LiCl), etc., and alkaline earth metal chlorides include calcium chloride (CaCl ₂ ), magnesium chloride (MgCl ₂ ), and barium chloride (BaCl ₂ ).
etc. Any one of the above alkali metal chlorides and alkaline earth metal chlorides can be used. However, since the main purpose of the present invention is to supply the obtained molten salt containing magnesium chloride as it is to an electrolytic cell for producing magnesium, the composition of the molten salt is not suitable for the bath composition of the electrolytic cell. It is desirable to leave it there. When producing magnesium by electrolyzing magnesium chloride, a salt having a structure such as magnesium chloride-sodium chloride-calcium chloride (barium chloride)-magnesium fluoride is usually used. Therefore, the composition of the molten salt used in the method of the present invention is as follows: (a) NaCl: 10-60%, _ClCl2 : 10-40%, _MgCl2 : 5-70%, _MgF2 : 5% or less ( b) NaCl: 10-60%, BaCl ₂ : 10-40%, MgCl ₂ : 5-70%, MgF ₂ : 5% or less (c) NaCl: 10-60%, KCl: 10-60%, CaCl ₂ : 10 to 40%, MgCl ₂ : 10 to 60%, and MgF ₂ : 5% or less. In the present invention, "molten salt mainly composed of chlorides of alkali metals and/or alkaline earth metals" means that it may contain some amount of MgF ₂ and impurities as described above. The molten salt having the above composition (used as a bath salt, henceforth referred to as "molten bath salt" or simply "bath salt" or "bath") contains one or two of solid powdered magnesium oxide and magnesium carbonate. suspend. These may be added to the bath in the form of MgO, _MgCO3 , or ores such as magnesite containing MgO, _MgCO3 , or primary products such as heavy-burnt magnesia or light-burnt magnesia. good. When MgCO ₃ is added to the bath, it is decomposed by the reaction MgCO ₃ →MgO+CO ₂ (1), producing MgO in the bath, which is converted to MgCl ₂ according to equation (2) described below. As the magnesium oxide, those with relatively high MgO purity, such as magnesia obtained by firing magnesite (magnesium carbonate) or magnesium hydroxide, are suitable for use. If MgO is chlorinated in a molten bath salt with the above composition to generate MgCl ₂ and the MgCl ₂ concentration in the bath is increased to higher than the concentration before chlorination, for example to about 40% to 50%, the bath It can be supplied as it is to an electrolytic cell for producing magnesium, and it is possible to obtain metallic magnesium by floating or settling and separating it from the electrolytic bath salt, depending on the comparative difference in the magnesium produced by electrolysis. Gases containing chlorine include chlorine gas (Cl ₂ ) as mentioned above, mixed gases of chlorine and carbon monoxide (CO), phosgene (COCl ₂ ), etc., or mixtures of these gases with carbon-containing substances. It's gas. In addition to coke powder, petroleum pitch, etc., gases such as methane (CH ₄ ) and ethane (C ₂ H ₆ ) can also be used as carbon-containing substances. When the carbon-containing substance is a solid powder such as coke powder, good results can also be obtained by directly adding and suspending it in the molten bath salt. (Function) The method for producing magnesium chloride of the present invention uses the above-mentioned materials, and based on the reaction formula (2) below, MgO + Cl ₂ → MgCl ₂ + 1/2O ₂ ... (2), magnesium oxide reacts with chlorine to form chloride. It takes advantage of the fact that it changes into magnesium. When a mixed gas of chlorine and carbon monoxide is used, magnesium chloride is generated according to the reaction formula (3) below: MgO+Cl ₂ +CO→MgCl ₂ +CO ₂ (3). In addition, when a carbon-containing substance is added to the gas to be passed, the molten salt, or both, for example, the following reaction formulas (4) and (5) MgO + Cl ₂ + 1/2C → MgCl ₂ + 1/2CO ₂ ... …(4) 4MgO＋4Cl ₂ ＋CH ₄ →4MgCl ₂ ＋CO ₄ ＋2H ₂ O
...(5) produces magnesium chloride. The attached figure is a schematic cross-sectional view showing an example of an apparatus for carrying out the method for producing magnesium chloride of the present invention. In the figure, 1 is a chlorination furnace made of refractories, 2 is its upper cover, and the upper part of the furnace wall of the chlorination furnace 1 contains magnesium oxide as a raw material (hereinafter, it will be explained as using magnesium oxide). A raw material inlet 4 is provided at the bottom of the chlorination furnace 1, and a gas inlet 8 through which chlorine-containing gas is passed is provided. A gas outlet 3 is attached to the upper lid 2 for discharging gas after the chlorine and magnesium oxide reacted through the gas inlet 8. In order to produce magnesium chloride using the apparatus configured as described above, first, a molten bath salt 5 is prepared as shown in the attached drawing. This may be supplied by melting a suitable mixture of alkali metal and alkaline earth metal chlorides as described above, but bath salt with a reduced concentration of magnesium chloride may be supplied from an electrolytic cell for magnesium production. You can also bring your own and supply it. The temperature of the molten bath salt 5 is maintained at 600 to 900°C, but the higher the bath temperature, the better the reactivity, and 800 to 900°C is particularly desirable. Although not shown in the figure, the chlorination furnace 1 is equipped with a bath salt heating device. Next, a required amount of raw material magnesium oxide powder is introduced through the raw material inlet 4 and suspended in the bath salt 5 by a method such as mechanical stirring or gas bubbling. Next, a chlorine-containing gas is passed through the gas inlet 8 to rise in the bath salt 5 as bubbles 6 and react with the suspended magnesium oxide 7. Since the reactivity of the chlorine-containing gas is better when the bubbles are as small as possible, it is preferable to attach a porous plate or a small-hole nozzle to the gas inlet 8. The content of magnesium oxide in bath salt 5 is 5~
It is best to set it to 40%, especially 15 to 25%. The reason for this is that if it is less than 5%, the reaction rate decreases, especially if it is less than 1%, it decreases rapidly, while if it exceeds 40%, the viscosity of the bath salt increases. If only the productivity of magnesium chloride is to be improved, it is better to increase the concentration of magnesium oxide as high as possible, but if the handling of the bath salt and the dispersibility of the bubbles of the chlorine-containing gas passed through the gas inlet 8 are also considered, the viscosity will increase. is not preferred, and a particularly desirable concentration range of magnesium oxide is 15 to 25%. In the bath salt 5 in which magnesium oxide is suspended in this way, the magnesium oxide 7 and chlorine react as shown in equation (2) above, producing magnesium chloride, which dissolves in the bath salt 5 and increases the magnesium chloride concentration. increase. In this case, as mentioned above, a carbon-containing substance may be added at the same time to the gas to be passed and/or the bath salt, or the gas to be passed may be a mixed gas of chlorine and carbon monoxide, etc. That's right. The reacted gas is discharged from a gas outlet 3 provided in the refractory top cover 2, but if there is unreacted chlorine, it is desirable to recover it. When magnesium oxide is chlorinated by the method of the present invention, the reaction rate begins to decrease when the concentration of magnesium oxide in the bath salt 5 becomes 5% or less, and the lower the concentration, the lower the reaction rate. In particular, when it falls below 1%, it decreases rapidly. Therefore, while measuring the concentration of unreacted chlorine, it was determined that the concentration of magnesium oxide was 1% just before the chlorine reaction rate suddenly deteriorated.
It is sufficient to stop the reaction before the amount reaches below, allow unreacted magnesium oxide to settle at the bottom of the furnace by natural sedimentation, and take out only the supernatant from the furnace. What is thus extracted is a mixed salt containing magnesium chloride at a higher concentration than before chlorination, with the remainder consisting of other alkali metals and/or alkaline earth metals. The most preferable usage method is to supply this mixed salt in a molten state to an electrolytic cell for producing magnesium. In addition, when chlorinating magnesium oxide,
The higher the concentration of magnesium chloride in the bath salt, the slower the reaction rate becomes, and this tendency becomes especially noticeable when the magnesium chloride content exceeds 70%.
It is necessary to avoid increasing the magnesium chloride concentration of the bath salt 5 more than necessary. The concentration of magnesium chloride is determined by the amount of magnesium oxide in the bath salt 5, so for example, if the bath salt 5 before chlorination does not contain magnesium chloride, the magnesium oxide added will be 50% MgO and 10% magnesium chloride. 45% as MgO when it contains, MgO when it contains 15% magnesium chloride
The limit is 44%. In the above description, magnesium oxide was used, but the same effect can be obtained by using magnesium carbonate or by using a mixture of magnesium carbonate and magnesium oxide. Furthermore, the principle is exactly the same when using ores containing magnesium oxide and magnesium carbonate. Hereinafter, description will be given based on examples. Examples 1 to 4 Inner diameter 500 mm and height having the configuration shown in the attached drawings
A test for producing magnesium chloride was conducted using the method of the present invention using a 2500 mm chlorination furnace. Magnesia was used as a raw material. The production conditions and the magnesium chloride concentration in the bath salt after the chlorination reaction are also shown in Table 1. Note that the bath salt used was extracted from an electrolytic cell for producing magnesium, so it contained 15% MgCl ₂ from the beginning. From Table 1, the concentration of magnesium chloride in the bath salt significantly increased from 15% to 41% in all of Examples 1 to 4, which indicates that magnesium chloride is efficiently produced by the method of the present invention. Recognize.
In addition, compared to Example 1 which did not use a porous plate for the gas inlet, Example 2 used a porous plate.
It can be seen that the chlorine gas blowing time is slightly shorter in this case, indicating that the use of a porous plate is effective. In this example, where the temperature of the bath salt is 800°C, the effects of Example 3 using a mixed gas of chlorine and carbon monoxide and Example 4 adding coke powder to the bath salt are not as noticeable. Nakatsuta. Examples 5 to 10 A magnesium chloride production test was conducted using the chlorination furnace used in Examples 1 to 4 by changing only the bath temperature.
When only chlorine gas is used, when a mixed gas of chlorine and carbon monoxide is used, and when coke is added as a carbon-containing substance to bath salt (same conditions as Example 4)
The reaction rates between magnesia and chlorine were compared in the following cases. The test results are shown in Table 2. In the same table, the reaction rate is expressed as a reaction rate ratio, with the reaction rate under the conditions of Example 5 being 1. From Table 2, when the temperature of the bath salt decreases to 700°C or even 650°C, compared to when only chlorine gas is used, when using a mixed gas of chlorine and carbon monoxide, and when coke powder is used, It can be seen that the reaction rate increases when added to bath salt. Example 11 Chlorination was carried out using magnesium carbonate using the apparatus used in Examples 1-4. The bath salt and chlorine gas were the same as in Example 1, and the amount of magnesium carbonate input was 100 kg. When magnesium carbonate was added, a large amount of bubbles were generated and the bath salt turned black, but it quickly became transparent after chlorine gas was introduced, and the magnesium chloride concentration was 29.5 after 9 hours of chlorine gas.
It was %.

【table】

[Table] (Effects of the Invention) The method of the present invention is an extremely excellent method for producing magnesium chloride from magnesium oxide or/and magnesium carbonate. In particular, when producing magnesium chloride in an electrolytic cell for producing magnesium by electrolyzing magnesium chloride, as mentioned above, the bath salt for electrolysis and the bath salt are used, and magnesium oxide or/and magnesium carbonate is added to the bath salt. The concentration of magnesium chloride in the bath salt can be increased by suspending it and passing a chlorine-containing gas through it to generate magnesium chloride. Therefore, when used in an electrolytic cell, if the bath salt with a high concentration of magnesium chloride is returned directly to the electrolytic cell, there is no need to take out the magnesium chloride as a solid, but magnesium chloride has high hygroscopicity and is extremely difficult to handle. The problem of being is solved. Further, the method of the present invention has a simple manufacturing process and does not require a large amount of energy, and the equipment for carrying out the method is very simple and can be installed near the electrolytic cell. Since the produced magnesium chloride does not contain any water, there is no problem of the graphite anode being severely consumed due to the decomposition of water during electrolysis.

[Brief explanation of drawings]

The accompanying drawing is a schematic cross-sectional view showing an example of an apparatus for carrying out the present invention.

Claims (1)

[Scope of Claims] 1 Solid powdered magnesium oxide or/and magnesium carbonate is suspended in a molten salt mainly composed of chlorides of alkali metals and/or alkaline earth metals, and chlorine is added to this suspension. A method for producing magnesium chloride, which comprises reacting magnesium oxide or/and magnesium carbonate with chlorine by passing a gas containing the above. 2. The method for producing magnesium chloride according to claim 1, wherein the gas to be passed is a mixed gas of chlorine and carbon monoxide. 3. Claim 1 or 2, characterized in that a carbon-containing substance is added to the gas and/or molten salt to be passed.
The method for producing magnesium chloride described in .