JPH02259092A - Production of calcium - Google Patents

Abstract

PURPOSE:To produce Ca with a small unit requirement of energy by using molten Zn, Sn, Cu or a molten alloy of Zn, Sn or Cu with Ca as the cathode, electrolyzing a molten salt mixture contg. Ca chloride or oxide and vacuum- distilling the resulting alloy of Ca with Zn, Sn, or Cu. CONSTITUTION:When Ca is produced through a Zn-Ca alloy, molten Zn is charged as the cathode, graphite is used as the anode 1 and a molten salt mixture of CaCl2 with CaK2 and CaF2 is used as an electrolytic bath 5, kept at a prescribed temp. and electrolyzed under a proper bath voltage to obtain a Ca-Zn intermediate alloy. This intermediate alloy is vacuum-distilled to produce Ca.

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a method for producing calcium, which is known as an active metal, by molten salt electrolysis and vacuum distillation.

[Conventional technology]

Calcium has conventionally been produced by molten salt electrolysis or aluminum thermal reduction. These are generally described, for example, in the Chemical Handbook (published by Maruzen). According to this, the former generally uses calcium chloride as an electrolytic bath;
Since calcium is lighter than the electrolytic bath, a method is used in which the produced calcium is solidified and pulled upwards. This method generally requires a high electrolytic sliding voltage, reaching 18-80V, and the power consumption of calcium is 30-50KWH/kg.
It is said to reach . The electrolysis voltage of calcium chloride at 850℃ is about 3.3V, and the theoretical electrolysis power is 4.4KWH.
/kg. Therefore, the conventional method performs electrolysis with an efficiency of 15% or less. In addition, there is Japanese Patent Publication No. 46-29250 which attempts to directly precipitate the solid state. In fact, since the electrolytic method is uneconomical, the aluminum thermal reduction method is said to be the mainstream at present. This involves mixing and molding quicklime powder and aluminum powder, causing them to react under vacuum at 1200°C in a heat-resistant steel crucible to distill calcium. This method is also said to have high energy costs. As a method similar to the present invention, Japanese Patent Publication No. 39-1309 discloses that an alloy of copper and alkaline earth metal is charged and the sulfide of the alkaline earth metal is electrolyzed to obtain a molten alloy of copper and alkaline earth metal. There is a plan to obtain alkaline earth metals by vacuum distilling this. [Problems to be Solved by the Invention] The first object of the present invention is to produce calcium by an electrolytic method with low energy consumption, instead of the conventional method which consumes a large amount of energy. The theoretical electrolytic power of magnesium, which is similar to calcium, is about 5.4 KW/kg, but it is actually carried out industrially at about 10 KW/kg. That is, the efficiency is 54%. Therefore, we sought to narrow the difference between the low efficiency of conventional methods and magnesium regarding calcium. One possible reason for the low efficiency of the conventional method is that calcium dissolves in the molten salt of the calcium halide. It appears that this molten salt reacts with chlorine generated at the anode, causing a loss in current efficiency. This problem needs to be overcome. [Means for Solving the Problems] The present invention uses zinc, tin, copper, or a composite liquid of these and calcium as the cathode, and electrolyzes a molten salt containing calcium chloride or oxide as a raw material to produce calcium. In this method, alloys of calcium and zinc, tin, or copper are obtained, and calcium is separated by vacuum distillation of these alloys. In the present invention, we believe that floating light calcium in the upper part of the electrolytic bath will cause highly active calcium to react with equipment materials and the electrolytic bath, and conversely, we considered making it heavier and taking it out from the bottom of the bath. Attempts were made to conduct electrolysis by using a molten material of zinc, tin, copper, or an alloy of these alloyed with calcium to have a low melting point as a cathode, and allowing the produced calcium to be absorbed by the cathode. As a result of the research, it was found that there is a concentration range because calcium does not become solid in the practical electrolysis temperature range described later and because calcium does not dissolve in the molten salt. Within this range, calcium easily mixes with these metals. It was found that electrolysis was possible with a low electrolytic sliding voltage. In copper, the lower limit of calcium is 20% due to melting point, and the upper limit is 7% due to dissolution.
It is 5%. The upper limit for tin is 20% due to its melting point. It was found that the upper limit for zinc is 85% due to penetration. A metal that meets the objectives of the present invention should form a low melting point alloy with calcium and have a sufficient boiling point difference with calcium. When searching for materials that meet this requirement, other materials include silver and cadmium, but these are rare resources and have drawbacks such as toxicity and are not practical, so they have been omitted. Calcium chloride or oxide is used as a raw material for the electrolytic bath, and if necessary, the melting point is lowered and melted with calcium or an alkali metal or alkaline earth metal halide to form an electrolytic bath. Metals other than calcium are used to lower the melting point, but of course they are included in the calcium, so they are limited to small amounts depending on the purpose. When calcium chloride is used as a raw material, it may be used alone, but calcium fluoride is preferably used to lower the melting point, but a bath with an even lower melting point can be obtained by adding a small amount of barium chloride or potassium chloride. On the other hand, agglomerated calcium is dissolved in a molten salt bath containing calcium chloride, calcium fluoride, or a certain amount of other alkaline earth metals or alkali metals as described above to form an electrolytic bath. In this case, a few substances such as calcium carbonate and calcium oxalate which decompose into calcium oxide by the temperature of the electrolytic bath may be substituted for calcium oxide. When calcium chloride is the raw material for electrolysis, graphite is used as an anode to generate chlorine, which can be recovered. Even when calcium oxide is the raw material, a carbon raw material such as graphite is used, but in this case it is a consumable electrode. Carbon monoxide or carbon dioxide gas is generated at the anode. Oxide electrolysis can lower the electric power consumption. Because calcium is active and is not attacked by the metals it is alloyed with, the cathode melt may be made of several metals such as molybdenum, niobium, tantalum, or calcium-resistant carbide or nitride ceramics such as titanium carbide; Running oxide or fluoride or contained in a self-lined vessel of coagulum of an electrolytic bath. The electrolytic sliding voltage was within the range of 4 to 7 at most, and the current efficiency was as high as about 90%. Since the data was obtained in an experimental reactor, actual use in a practical reactor will vary depending on the heating method of the furnace, the size of the furnace, the mode of electrolysis, etc. However, if this figure is maintained, the electricity consumption rate for electrolysis will range from 6 KWH/kg to 9.5 KWH/ kg
becomes. The temperature of the electrolytic melt varies depending on the type of solvent metal and molten salt used, but it is usually in the range of 600°C to 1000°C. Naturally, the temperature should be as low as possible. Therefore, when using copper as the solvent metal, Example 2.3 described below
It is best to leave some calcium behind and use it as a low-melting-point alloy, as shown in . In any case, by recycling the solvent metal, the loss of calcium is kept to a minimum. In this way, the required amount of calcium is electrolyzed and the dissolved metal is extracted from the electrolytic furnace. The alloy, either molten or once solidified, is charged into a vacuum furnace. The type of distillation in a vacuum furnace is different from that for zinc, copper, and tin. In the case of copper and tin, calcium is distilled and recovered,
In the case of zinc, the zinc is removed by distillation. The former method can be carried out in the same manner as the conventional distillation method for sodium, potassium, etc., or the distillation method for calcium by aluminum reduction method. The distillation temperature varies depending on the solvent metal and the distillation process, and is 750 to 1100°C. In the distillation of alloys with zinc, zinc evaporates, but this poses some problems because its boiling point is somewhat similar to that of calcium. It is distilled at a temperature of about 600°C assuming some loss of calcium, or it is separated by rectification in a rectification furnace made of materials that can withstand calcium. Although the apparatus used in the present invention is not special, two examples of electrolytic furnaces will be illustrated to facilitate understanding. In FIG. 1, 1 is an anode and 4 is an insulator. 2 is an iron shell of the lid, and 3 is graphite, which constitutes a compartment 7 and isolates chlorine generated from the anode. 5 is an electrolytic bath, and 6 is a molten metal of the cathode. The lining 8 is made of molybdenum or tantalum so that it is not attacked by the molten alloy, and the lining 9 is a steel plate. 10 is a heating furnace, 11 is a refractory heat insulating material, and 12 is a structure of the furnace. Reference numeral 13 denotes a cathode current-carrying rod, which is lined with molybdenum, tantalum, or at least the part that will be immersed in the molten metal. 14 is a charging port for raw materials, and 15 is a molten metal discharge port from which the molten metal is sucked and taken out through a pipe made of molybdenum or the like. 16 is a chlorine outlet. Figure 2 shows the furnace used for electrolyzing calcium oxide. 21
The anode is an anode, and although a power supply system and a device for moving the anode up and down are not shown, the anode is moved down as it wears out. 22 is the iron skin of the furnace lid, and 23 is a fireproof insulation material. Reference numeral 24 denotes a furnace shell, and 25 is stamped with calcium oxide and calcium fluoride to form a hearth. 26 is an electrolytic bath;
Reference numeral 27 is a cathode made of molten metal, and is supplied with electricity by a current-carrying rod 29 made of molybdenum, tantalum, or the like. Calcium oxide 28 is supplied from 32, is placed on the electrolytic bath or the hearth, and gradually dissolves in the electrolytic bath. 31 is a water-cooled high-frequency coil that heats the molten metal of the cathode and serves as a heating source for the furnace. Next, specific effects will be described using examples using these furnaces. (Example) Example-1 Production of calcium via zinc-calcium alloy The experimental apparatus shown in Fig. 1 was used. Zinc is charged into the cathode, graphite is used as the anode, and an electrolytic bath containing calcium chloride mixed with 10% potassium chloride and 15% calcium fluoride is used. The bath temperature was maintained at 750°C, and the electrolytic sliding voltage was set at 5. Electrolyze with Ov,
An alloy containing 70% calcium is obtained and removed from the furnace. The current efficiency was 85% based on the minute value of the intermediate alloy. The alloy is then placed in a tantalum crucible and distilled at 600°C. After the distillation is completed, argon gas is blown in and the temperature is raised to 850°C to dissolve the remaining calcium, and then it is cooled and taken out. The zinc content in the obtained calcium was 0.1% or less, the purity was 99.5% or more in calcium + magnesium content, and the yield of calcium from the alloy obtained by electrolysis was 95%. Example 2 Production of calcium via copper-calcium alloy The experimental apparatus shown in FIG. 1 was also used. A copper alloy containing approximately 20% calcium recovered by this method is used as the cathode, graphite is used as the anode, and a mixture of calcium chloride and calcium fluoride (12%) is used as the electrolytic bath. Bath temperature 900-95
Electrolysis is carried out at 0° C. with an electrolytic sliding voltage of 5.2 V to obtain an alloy containing approximately 70% calcium. During electrolysis, the consumed calcium chloride is supplied intermittently. The resulting alloy is distilled at 900-1000°C in a crucible lined with a mixture of calcium fluoride and calcium oxide. Distillation is stopped when the degree of vacuum rises rapidly, and the calcium condensed in the cold section is taken out. A copper alloy containing approximately 20% calcium remains in the crucible and is reused as a raw material for electrolysis. The purity of the calcium obtained was 99.8% or more in terms of calcium + magnesium. Example 3 Production of calcium via copper-calcium alloy The experimental apparatus shown in Fig. 2 was used. The lining uses a mixture of calcium oxide and calcium fluoride, and the cathode uses a copper-calcium alloy recovered by this method. Add 15% calcium fluoride to calcium chloride, and further mix and dissolve 15% calcium oxide. The bath temperature was maintained at 900°C and electrolysis was carried out at an electrolytic sliding voltage of 4.0V. During electrolysis, precipitated calcium carbonate is continuously supplied, the electrolytic sliding voltage is monitored, and the graphite anode is continuously lowered. The copper alloy containing approximately 70% calcium is discharged from the furnace, placed in a lucium fluoride-based crucible, and distilled at 850-950°C. Distillation is stopped when the degree of vacuum rises rapidly, and the calcium condensed in the cold section is taken out. A copper alloy containing about 20% calcium remains in the crucible, and this is used as a raw material for electrolysis. In this method, carbon dioxide gas is mainly produced from the anode. The purity of the calcium obtained is 99.8% or more in terms of calcium + magnesium. Example 4 Production of calcium via tin-calcium alloy The experimental apparatus shown in FIG. 2 was used. The lining uses a mixture of calcium oxide and calcium fluoride, and the cathode uses recycled tin recovered by this method. 10% in calcium chloride
of calcium fluoride, 10% barium chloride and 10%
of calcium oxide and dissolve it. Bath temperature 850℃
Then electrolyze with an electrolytic sliding voltage of 4.0 to 4.5V. During electrolysis, calcium oxide is intermittently supplied, the electrolytic sliding voltage is monitored, and the graphite anode is lowered. Obtain a tin alloy containing approximately 15% calcium and place it in a molybdenum crucible to produce 850~9
Distill at 50°C. After the distillation is completed, the condensed calcium is taken out in the cold section, and the tin containing less than 3% calcium remaining in the crucible is reused. The purity of calcium is 99.5% or more in terms of calcium + magnesium. In Examples 2 to 4, calcium remains in the solvent metal, so the yield cannot be determined from the -th experiment, but from the balance calculation of the amount of calcium before and after, the yield is relative to the increased amount captured in the alloy by electrolysis. is 95% or more. Moreover, the current efficiency was 80 to 95%. [Effect of the invention] The above four examples are small experimental reactors, so there is a separate heating device.
If it is a large furnace, the electrolytic current will cover the heat balance of the electrolytic furnace. In either case, the electrolytic sliding voltage is sufficiently lower than that of conventional electrolytic methods, and the current efficiency is high. However, electricity is required for distillation, and this value is also theoretically 0.2.
It is approximately 1.2 KWH/kg, which is considered to be a small amount in a large experimental reactor, and even if both are added, the value is significantly lower than that of the conventional electrolytic method. As described above, the present method allows calcium to be produced with significantly lower energy consumption than conventional methods. Furthermore, when copper or bell is used as a solvent, non-volatile elements remain in the solvent metal, so there are fewer impurities as in conventional thermochemical production methods. On the other hand, when zinc is used as a solvent, volatile elements can be reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an electrolytic furnace for electrolytically producing an alloy of calcium, zinc, copper, and tin in the present invention, and this figure is used when calcium chloride is electrolyzed to produce chlorine as a by-product. FIG. 2 is a sectional view of another example of an electrolytic furnace, in which calcium chloride or the like is used, the anode is a consumable electrode, and carbon dioxide gas or carbon monoxide is produced as a by-product for electrolysis. 1... Anode 2... Lid 3... Graphite 4... Insulator 5... Electrolytic bath 6... Cathode metal bath 7... Partition wall 8... Molybdenum or tantalum Lining 9...
・Steel plate 1o... Heating furnace 1... Fireproof insulation material 12... Furnace structure 3... Cathode current carrying rod 14.
...Raw material charging port 5...Molten metal discharge port 16...Chlorine discharge port 1...Anode 22...Furnace lid shell 3
... Fireproof insulation material 24 ... Furnace shell 5 ... Hearth 26 ... Electrolytic bath 7 ... Molten metal cathode 2
8...Calcium oxide 9...Electricity rod 3o.
... Insulator 1 ... High frequency coil 2 ... Calcium oxide charging port 1: Positive exchange 2: Lid 3: Graphite 4: Insulator 5: Electrolytic bath 6: Cathode molten metal 9: Steel plate 1 port: Heating furnace 11: TFj Fire Insulation Heat Pumping Material Diagram 10+

Claims (1)

[Claims] 1. Using a melt of zinc, tin, copper, or an alloy of these and calcium as the cathode, electrolyzing a molten salt containing a chloride or oxide of calcium as a raw material to obtain an alloy of calcium and zinc, tin, or copper; A method for producing calcium, which comprises vacuum distilling this alloy to separate calcium.