JPS6046192B2 - Manufacturing method of magnesium and chlorine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for electrochemically producing magnesium and chlorine useful in metallurgy.

Magnesium, a light metal, is used as a component of light alloys used in the manufacture of various buildings, as well as as a material for electrodes for cathodic protection against corrosion of metals, as a chemical reducing agent, e.g. as a reducing agent used in the production of titanium, and as a malleable material for iron. It is used as an additive to give

Chlorine, which is a chemically active gas, is used for example in vinyl chloride,
Useful in the production of carbon tetrachloride and calcium hypochlorite.

Salts accumulated in excess in the electrolytic bath are useful as -potassium fertilizers. [Prior Art] Several industrial methods of manufacturing magnesium and chlorine by electrolysis are known in the art.

These methods primarily involve electrolysis. They are distinguished from each other by the composition of the salt mixture containing magnesium chloride. In one method of the prior art, molten magnesium chloride containing small amounts of impurities is obtained when titanium tetrachloride is reduced by magnesium metal! is electrolyzed.

The molten salt electrolysis products, namely magnesium and chlorine, are used primarily in the production of titanium. Another method is to use an aqueous solution of magnesium chloride.
921 Request by Ken Ξ Judge Shibui Electrolyzes a melt of anhydrous salt, which is produced by a process of appropriation and contains magnesium chloride as a main component.

That is, in the first step, the magnesium chloride solution is spray-dried, and in the second step, the obtained powder is melted,
When the melt is heated to a temperature in the range of 800 to 900° C., the magnesium precipitates to form a molten anhydrous salt containing 70 to 80% by weight of magnesium chloride.
This salt is then sent to molten salt electrolysis. However, this method has not been implemented on an industrial scale because of the substantial loss of mayognesium chloride and the required capital investment. The method of manufacturing magnesium and chlorine that is most commonly used industrially is to produce magnesium,
Potassium and sodium chlorides are KCl:MgCl
.

■0.9■1 to 5, 0:1, preferably 1.05:
1 to 1.25: 1, and KCl:NaC1■4
．． It consists of electrolyzing a molten anhydrous salt mixture containing a molar ratio of 0:1 to 7.01. This molten salt mixture is produced by the following method. First, mainly Carnalite MgC12/KCl/Yu. A solid salt is prepared containing O, and also sodium chloride and usually an excess of potassium chloride. The solid salts can be prepared by recrystallizing naturally occurring carnalites or by reacting potassium chloride with an aqueous magnesium chloride solution. The solid salt is then dehydrated to a water content of 2 to 4% by weight by contacting the salt with flue gas. Since substantially all of the magnesium chloride is contained in the carnate and this magnesium chloride is not susceptible to hydrolysis, the solid salt can be dehydrated in a fluidized bed. The content of magnesia in the dehydrated solid salt does not exceed 2% by weight. The dehydrated salt is melted and treated with chlorine. The molten anhydrous salt mixture thus produced contains 6 to 1% by weight of magnesium chloride, 82 to 75% by weight of potassium chloride, and 8% by weight of sodium chloride.
The solution is poured into an electrolytic cell containing an anhydrous molten electrolyte containing 15% to 15% by weight from a ladle in a batchwise manner.

The electrolyte is maintained at a temperature in the range of 710 to 740° C. and a direct current is passed continuously, so that molten metal, ie magnesium, is generated at the Steele cathode and chlorine gas is liberated at the graphite anode. Magnesium is
It floats to the surface from the cathode and accumulates in the electrolytic cell, from where it is periodically drained via vacuum bottles and sent to the smelting and casting processes. The chlorine gas is continuously drawn from the electrolyzer and sent to the compressor. Since only magnesium chloride is molten salt electrolyzed, potassium and sodium chlorides accumulate in the electrolytic cell and the concentration of these electrolytes gradually increases. In order to keep the electrolyte in the cell below the maximum permissible amount, the excess accumulated molten salt is periodically pumped out and sent to a steel vessel where it is crystallized and cooled. temperature to 400
The salt, cooled below 0.degree. C., is ground and used for making carnalites or as potassium fertilizer. In order to reduce the amount of magnesium chloride lost, the excess accumulated salt is pumped out several hours after pouring the starting melt, when electrolysis (ElectrOlytic
As a result of MgCl
．． The amount decreases to %.

Magnesium, potassium and sodium chlorides,
The molar ratio of KCl:MgCl2 is 0.9:1 to 5.0
The process for preparing magnesium and chlorine as described above, which consists in feeding them in a ratio of 1:1 into an electrolyte containing similar chlorides, does indeed have fundamental drawbacks.

Since the melting point of the electrolyte containing the above amounts of magnesium, potassium and sodium chlorides exceeds 700°C,
Molten salt electrolysis cannot be carried out at electrolyte temperatures below 710°C.

At electrolyte temperatures below 710° C., the salts crystallize on the bottom and inner walls of the electrolytic cell, and the crystallized substances accumulate, thereby interfering with normal electrolytic operation.

The circulation of the electrolyte is thus impaired, the burning of the metallic magnesium on the surface of the electrolyte becomes severe, and short circuits occur between the electrodes through deposits. Furthermore, the operation of wiping the bottom of the electrolyzer from the ooze that has gradually accumulated as a result of the precipitation of solid particles of oxides and metals is also hindered. If the temperature of this electrolyte can be maintained at 720'C and above, the deposits will not grow on the walls and surfaces of the electrolytic cell.

However, other significant disadvantages arise. That is, as the temperature increases, the rate of magnesium chlorination increases,
And the current efficiency decreases due to harmful impurities such as metallic iron and its oxides. The decrease in current efficiency amounts to 0.2% per 1°C. Therefore, the power consumption per unit mass of magnesium obtained increases and the output of the electrolytic cell decreases. The useful life of the electrodes, graphite anodes and steel cathodes is also reduced. In the course of this, the electrodes wear unevenly, which disrupts the current distribution between the parallel connected electrochemical cells, leading to an increase in specific power consumption and a reduction in the output of the cells. Moreover, the presence of sodium and potassium chlorides in the electrolyte in the above amounts indicates that potassium chloride has insufficient conductivity (1.70 hm-1
of the order of cm-1) results in a further increase in specific power consumption.

A content of magnesium chloride of 6% by weight in the electrolyte is the minimum acceptable limit for this prior art process.

This is because when the content of magnesium chloride is low, the melting point of the electrolyte exceeds 730°C. As a result, it is necessary to ensure temperature conditions above 730° C. in order to avoid an increase in precipitates, which compromises substantial technical parameters. On the other hand, it is highly desirable to reduce said minimum content of MgCl2 in the electrolyte to less than 6% by weight. This will reduce the amount of magnesium chloride lost as well as excess salts accumulated in the electrolytic bath. PROBLEM TO BE SOLVED BY THE INVENTION The object of the invention is to overcome the aforementioned disadvantages inherent in the methods of the prior art.

The main object of the present invention is to provide a method for producing magnesium and chlorine that can reduce power consumption per unit mass of magnesium obtained.

Another object of the present invention is to provide a method for producing magnesium and chlorine which can extend the useful life of an electrolytic cell. It is yet another object of the present invention to provide a process for producing magnesium and chlorine which allows the specific consumption of starting materials to be reduced.

The present invention provides a method for producing magnesium and chlorine that utilizes an electrolyte composition that reliably reduces the specific consumption of power and starting materials and increases the useful life of the electrolyzer.

[Means for solving problems]

The above object is to supply an electrolytic bath with a melt of a mixture consisting of magnesium chloride, potassium chloride and sodium chloride in anhydrous state, the molar ratio of potassium chloride to magnesium chloride being in the range of 0.9 to 5.0. A method for producing magnesium and chlorine comprising electrolysis, wherein the molar ratio of potassium chloride to sodium chloride in the electrolytic bath is in the range of 1.2 to 2.7, and the sodium chloride content is 19 to 3% by weight. This is achieved by a method for producing magnesium and chlorine, which is characterized by electrolysis while maintaining the above range.

With this composition, the melting point of the electrolyte does not exceed 670°C, so this molten salt electrolysis can be carried out at temperatures in the range of 670 to 710°C without forming deposits on the bottom and inside walls of the electrolytic cell.

The molten salt electrolysis is preferably performed at a temperature in the range of 670 to 690°C.

As a result, compared to prior art methods, the electrolyte temperature was reduced by 3.
The current efficiency can be improved by 5 to 8%.

Although this temperature drop causes a certain decrease in the conductivity of the electrolyte, the conductivity is 0.15% lower than in the prior art method due to the increased sodium chloride content.
10.3? Hm-1 cm-1 increases. As a result, the specific power consumption during molten salt electrolysis is 1000-.00-./ton magnesium than in prior art methods. 15
It becomes lower by 00kW-Hr. The useful life of the electrodes is also increased, thus reducing the rate of electrode wear and the average ohmic resistance of the electrolytic bath, and contributing to further lower specific power consumption. The useful life of the electrolytic bath top and other structural components is also extended, and working conditions are improved. Ru. Further advantages and objects of the present invention will become more fully apparent from the detailed description and examples of this process for producing magnesium and chlorine below.

Magnesium, potassium and sodium chlorides, in solid or molten state, are added to the electrolytic bath periodically or continuously, together or separately, simultaneously or sequentially, in the form of KCl:MgCl.

is in the range of 0.9 to 5.0 (molar ratio), preferably 1.0
in the range of 5:1.25:1 (molar ratio), and KCl:N
aCl is introduced in a range of 2.7:1 to 1.2:1 (molar ratio). If the composition of the salt is subject to change over time, the molar ratios are determined over a time interval of 7 days or more. Most preferably, the chloride is supplied in the form of a molten anhydrous salt mixture simultaneously and in batches from the ladle to the electrolytic cell. The salt mixture is prepared in a conventional manner, with the proviso that the required amount of sodium chloride is added to the salt mixture during any step of its preparation in order to bring the KCl:NaCl ratio within the required range. It is desirable to add sodium chloride to the solid salt, which has been dehydrated to a water content of 2 to 4% by weight, before or during melting. In this way, potassium chloride can also be added at the same time, thus increasing the molar ratio of KCl:MgCl2 to 2:1 or higher, thereby reducing the consumption of chlorine for treating molten salt mixtures for magnesia and chlorination. can be done. However, if we take into account the increase in the amount of salt handled at the molten salt electrolytic treatment plant, this will definitely cause difficulties in transporting the molten salt in bottles. In this regard, in order to carry out said batch filling of the electrolyzer from the ladle, it is desirable to utilize a molten salt mixture of the following composition: MgCl.

48-3 mol% (39-31 mol%), KCl43-3
5% by weight (45-36 mol%), NaCl 2-24% by weight (16-32 mol%), MgOO. 2 to 0.5% by weight (a). 4 to 0.9 mol%), and other impurities contained within 1% by weight.

The amount of the molten salt mixture poured into the electrolytic cell is adjusted so that the electrolyte in the cell undergoing electrolysis has the following composition:

MgCl22.5-14% by weight (1.9-9.7 mol%
), KCl 76-5 mol% (73-46 mol%), Na
Cl9 to 3% by weight (1.7 to 4.3 mol%), other impurities (mainly CaCl2) 2% by weight or less (1.4 mol%).

Note that in the molten salt mixture to be electrolyzed, INaCl
It is significant that the amount is present at 19-3% by weight.

If the amount of NaCl is less than 1% by weight, the melting temperature of the mixture will be higher than 700'C, and salt will easily precipitate in the electrolytic cell.
If the amount of NaCl exceeds 3%, NaCl decomposes. A direct current is passed continuously through the electrolyte while maintaining its temperature preferably within the range of 670 to 690°C.

The molten metal, magnesium (its melting point is 650° C.), is generated at the Steil cathode, while gaseous chlorine is released at the graphite anode. Molten magnesium is 40 to 50k9/77t' less dense than an electrolyte of the above composition. Therefore, it accumulates and aggregates on the cathode surface, while the magnesium droplets float and merge to form a dense layer of liquid metal that floats on the electrolyte surface. This liquid and body metal are periodically discarded in vacuum bottles and sent to the smelting and casting process. The chlorine gas is continuously degassed from the electrolyzer and sent to a compressor for liquefaction or for the preparation of a molten salt mixture before being poured into the electrolyser for further production of magnesium and chlorine. . The time for pouring the molten salt into the electrolytic cell is determined by the chemical analysis data of the electrolyte and the liquid level in the bath.

Excess accumulated molten salt is pumped out of the electrolytic bath several hours after pouring the molten salt mixture to the highest permissible level of the electrolyte and lowered to the lowest permissible level. The molten salt is pumped with a centrifugal pump or a vacuum bottle and poured into a steel container where it is crystallized. This crystalline salt is ground and used as potassium fertilizer or for the production of carnalites. When salt excessively accumulated in an electrolyte is used as a potassium fertilizer, Na is added to the electrolyte.
It is preferred to supply potassium chloride at the upper limit of the molar ratio of KCl to Cl, ie close to 2.7.

When the salt is used for the production of carnalites, Na
It is desirable to set the molar ratio of KCl to Cl close to its lower limit, that is, 1.2. In both cases, the excess accumulated molten chloride should preferably be discharged within the range of 2.5 to 4.5% by weight of magnesium chloride in the electrolyte, thus reducing the amount of magnesium chloride for said chloride. Losses can be minimized as much as possible. This is of paramount importance for use as potassium fertilizer, considering the double expense and unavoidable extra loss of magnesium chloride in preparing the recovered stock for molten salt electrolysis. , its use in carnalite production is also important. If the molar ratio of KCl:NaCl deviates from the above-mentioned limits, either the disadvantages present in the prior art methods arise or (when KCl:NaCl is greater than 2.7) the amount of sodium chloride used to adjust the electrolyte composition increases. leading to decomposition (when KCl:NaCl is less than 1.2).

Preferably, the KCl:NaCl ratio is maintained within the range of 2.2 to 1.5. Exceeding the preferred limits of the temperature of the electrolyte according to the present invention results in a decrease in current efficiency (T = 6
(when T is higher than 90°C), or electrolyte precipitation and sludge formation on the bottom and inner walls of the electrolytic cell (when T is lower than 670°C).

Exceeding the preferred limit of the magnesium chloride content in the molten salt withdrawn from the electrolyzer will either lead to an increased amount of magnesium chloride loss (if this content is greater than 4.5% by weight) or a severe reduction in current efficiency. (if this content is less than 2.5% by weight).

〔Example〕

Example 1 The composition of the main components is MgCl243±1% by weight (about 36 mol%), KCl38±1% by weight (about 40 mol%), NaC
An anhydrous molten salt mixture (KCl:MgCl2=1 at 700±10°C) with Il8±1% by weight (about 24 mol%)
．． 13, corresponding to an average molar ratio of KC1:NaCl=1.65) was periodically poured from the bottle into the electrolytic cell.

When a direct current was constantly passed through the electrolyte while keeping the temperature at 680±5°C, the composition was as follows. MgCl. 3 to 14% by weight (2.2 to 10
．． 4 mol%), KCl65-59% by weight (60.8 to 55.8%), NaCl3l-2 heel weight% (37.0
to 33.8 mol%). KCl/NaCl molar ratio=approximately 1.650 The obtained metal, namely magnesium, was periodically discharged from the electrolytic cell in a vacuum bottle and transferred to the refining and casting process.

The gaseous chlorine compressed by the compressor was mainly delivered to the manufacturing of chemicals. The current efficiency could be increased by about 7% due to a 30-40° C. reduction in electrolyte temperature compared to the prior art process.

Furthermore, the specific power consumption in the molten salt electrolysis was reduced by 1300 kWt-Hr per ton of magnesium obtained. MgCl. The excess accumulated molten salt containing 3.0±0.2% by weight was removed from the electrolytic cell once a day and transferred to the carnalite manufacturing process. Example 2 Solid anhydrous carnalites, solid sodium chloride and solid potassium chloride were charged separately into an electrolytic cell: only the anhydrous carnalites were charged over a period of 3 hours and during the next 3 hours sodium chloride and potassium chloride were charged. I just loaded it.

This loading cycle was then repeated. The molar ratio of the amounts of chloride fed to the electrolyzer in both carnal and free form over a period of 7 days was KCl:MgC.
l2=1.1, KC1:NaCl=2.7.

The composition of this electrolyte is as follows. MgCl24.
3-7. Saliva volume% (3.2-5.3 mol%), KCl74
~7 heel weight% (71-70 mol%), NaCl2l~2 mol% (26-25 mol%), KCl/NaCl molar ratio =
2.7.

When the temperature of this electrolyte is 68°C, the direct current passed through the electrolyte is
The temperature was adjusted to be maintained at 5±5°C.

The resulting magnesium and chlorine were removed from the electrolyte.
Compared to the prior art process, the current efficiency could be increased by about 7% because the electrolyte temperature was lowered by about 30°C. The specific power consumption in the molten salt electrolysis was reduced by 1300 kwt-Hr per ton of magnesium.
The excessively accumulated molten salt is removed when the magnesium chloride content in the electrolyte is 4.3±0. The electrolyte was pumped once a day in % slag. The salt obtained after crystallization and grinding was used as potassium fertilizer. Example 3 Composition is MgCl242±1% by weight
(approximately 34 mol%), KCl 35 ± 1% by weight (approximately 36 mol%), NaCl 23 ± 1% by weight (approximately 30 mol%) (70
At a temperature of 0±10'C, the average molar ratio is KCl:Mg
An anhydrous molten salt mixture (corresponding to Cl2=1.05, KC1:NaCI=1.2) was poured batchwise into the electrolytic cell.

A direct current is continuously passed through this electrolytic cell to raise its temperature to 675.
It was kept at ±5°C. This electrolyte had the following composition:
MgCl22.5-1.2% by weight (2-9 mol%), K
CI59-5 heel weight% (54-50 mol%), NaCl3
8-34 wt% (44-41 mol%), KCl/NaC
l molar ratio = 1.2. The obtained magnesium and chlorine were further sent to the next treatment step. Excess accumulated molten salt
Twice a day MgCl2 content 2.7±0. 1 in weightage%
The electrolyzer was pumped out twice a day and recycled into the carnalite manufacturing process. Advantages similar to those described in Examples 1 and 2 above were achieved in the operation of this example.
Example 4 The following composition: MgCl244±1% by weight (approximately 37 mol%), KCl43±1% by weight (approximately 46%), NaCl
l2±1% by weight (approximately 17%) (at a temperature of 700±10°C, the average molar ratio is KCl:MgCl.=1.25, K
An anhydrous molten salt of C1 (corresponding to NaCl=2.7) was poured into the electrolytic cell in a batch manner.

A direct current is constantly passed through the electrolyte to raise its temperature to 685±5.
It was kept at °C. The composition of this electrolyte is as follows. N
4gCl24.3-1% (3-9mol%), KCl
74-6 heel weight% (72-67 mol%), NaCl2l-
1 heel weight% (25-24 mol%), 9KC1/NaCl molar ratio = 2.7.

The obtained magnesium and chlorine were sent to the next processing step. MgCl2 content 4.5±
At 0.2% by weight it was pumped from the electrolyzer once a day. After crystallization and grinding, the salt thus produced was used as potassium fertilizer. In this example the same advantages as described in Examples 1 and 2 above were achieved with 1ζ. Example 5 The following composition: KCl45±1% by weight (approximately 50 mol%), N
aCl8±1% by weight (approximately 11 mol%), MgCI246
Anhydrous molten salt at 700±10° C. with ±1% by weight (approximately 39 mol%) was poured into the electrolytic cell in batches, and solid sodium chloride was additionally charged.

The molar ratios of chloride fed to the electrolysis in both molten and solid state over a period of 7 days were as follows:
KCl:MgCl2=1.25; KCl:NaCl=1
．． 2. The direct current passing through the electrolyte was regulated to maintain the electrolyte temperature at 675±5°C. The electrolyte had the following composition. MgCl22.5~1 heel amount% (2~
9 mol%), KCl52-5 mol% (51-50 mol%
), NaCl38-34% by weight (47-41 mol%),
KCl/NaCl molar ratio = 1.2.

Claims (1)

[Claims] 1. Supplying a molten mixture of anhydrous magnesium chloride, potassium chloride and sodium chloride, in which the molar ratio of potassium chloride to magnesium chloride is in the range of 0.9 to 5.0, to an electrolytic bath. In the method for producing magnesium and chlorine by electrolysis, the content of sodium chloride in the electrolytic bath is 19 to 38% by weight, and the molar ratio of potassium chloride to sodium chloride is 1.
A method for producing magnesium and chlorine, which comprises performing electrolysis while maintaining the concentration in the range of 2 to 2.7. 2. The method according to claim 1, wherein the electrolysis is carried out at a temperature in the range of 670 to 690°C.