RU1840844C - Method of producing alkaline, alkaline earth metals and their alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises electrochemical extraction of oxide-halide melts. Concentration of produced metal oxide in melt is maintained equal to 1.0-17.0 wt%. Extraction is performed by composite-material anode made from sintered ceramic based on nickel and lithium oxides.

EFFECT: nonpolluting simplified process.

2 cl, 7 ex

Description

The invention relates to the field of electrochemistry and metallurgy, can be used to obtain alkaline and alkaline-earth metals and their alloys.

A known method of producing calcium by electrolysis on a liquid cathode (N. A. Doronin. "Calcium", M .: Gosatomizdat, 1962) Its essence is that the process is conducted by passing a constant electric current through a melt of calcium and potassium chlorides of eutectic composition at a temperature of 650-715 ° C. In this case, chlorine is released at the anode, and calcium at the cathode, which is used as copper or a copper-calcium alloy. A significant disadvantage of this method is the high consumption of graphite anodes (up to 500 kg per 1 ton of calcium produced). The consumption of anodes is primarily associated with their destruction. The presence of carbon particles in the electrolyte adversely affects the operation of the cell. Carbon foam floating on the surface of the electrolyte contributes to the leakage of current through the side walls of the bath. This leads to a decrease in current efficiency and violation of the technological regime. Carbon may settle to the bottom of the cell. In contact with the alloy, the carbon particles interact with it, forming calcium carbide. This negatively affects the electrolysis and the quality of the resulting product. Usually in these cases, replace the electrolyte with a new one.

To capture the chlorine released on the anode, a large amount of expensive equipment is required. However, even the presence of a chlorine capture system does not ensure its complete absorption. This leads to environmental pollution. It is possible that chlorine can accumulate in the electrolyzer and discharge it into the workshop’s working room, which poses a significant danger to workers’s lives.

A known method of producing lithium ("Applied Electrochemistry", edited by A.P. Tomilov, M .: Chemistry, 1984) Its essence is that the electrolysis process is carried out at a temperature of 400 ° C in a eutectic melt of lithium and potassium chlorides using a steel cathode and graphite anodes. This method has all of the above disadvantages. In addition, in the case of the use of solid cathodes, as graphite anodes are consumed, an increase in the interpolar distance and, as a result, an increase in the voltage across the electrolysis bath occurs.

Of the known closest in technical essence is the "Electrochemical method for producing calcium alloys" (ed. Certificate of the USSR No. 373325, 1970). The essence of this method lies in the fact that the process is carried out in melts containing fluoride (5-7 wt.% ), oxide (8-16 wt.%) and calcium chloride at a temperature of 700 ° C. Graphite is used as an anode.

This method has significant disadvantages. In the electrolytic production of calcium alloys, a chloride-fluoride-oxide electrolyte is used. The high oxide content in the melt (8-16 wt.%) Leads to an increase in the density of the electrolyte and at the same time reduces the allowable calcium content in the alloy. Otherwise, the resulting alloy will float to the surface of the electrolyte and oxidize. This leads to a decrease in the current efficiency of calcium and a decrease in its permissible content in the alloy. The addition of fluoride to the oxide-chloride melt further increases the density of the latter and reduces the process parameters.

It is not safe to carry out the process in such electrolytes. At the anode, the joint release of oxygen and fluorine, which interact with carbon, is possible. The product of such a reaction can be a highly toxic gas such as phosgene. In addition, to conduct the process for a long time, having graphite anodes and adding calcium oxide to the melt, is generally impossible. It is shown on industrial bathtubs and in laboratory conditions. Oxygen ions discharged at the anode interact with graphite to form carbon dioxide. As a result of the interaction of the released gas with the oxide, carbonate is formed, which is reduced at the cathode or in the volume of the melt by the dissolved metal to carbon. The resulting graphite foam and carbide increase the viscosity, the process temperature rises, the current yield of the target product sharply decreases. Typically, this process ends after 5-10 hours by stopping the bath and replacing the electrolyte. The interaction of oxide with graphite leads to increased consumption of anodes. Even theoretically, such a process is difficult to implement.

The aim of the present invention is the creation of environmentally friendly technology, its simplification and cost reduction of the resulting metal or alloy.

This goal is achieved by the fact that in the known method for producing alkali and alkaline-earth metals and their alloys by electrolysis of oxide-halide melts, electrolysis is carried out while maintaining the concentration of the oxide of the obtained metal 1-17 wt.%, With an anode of an electrically conductive composite material based on nickel oxides and lithium. The addition of lithium oxide to nickel oxide is 0.1-10.0 wt.%.

The electrolysis in oxide-halide melts can reduce the voltage on the bath and reduce energy consumption per unit of metal. This is due to the fact that the decomposition voltage of oxides of alkali and alkaline earth metals is lower than their halides. Therefore, oxide is first electrolyzed and oxygen is released at the anode, and the target metal is released at the cathode. Electrolysis is carried out while maintaining the oxide concentration constant in the range of 1-17 wt.%. Failure to comply with concentration limits leads to undesirable consequences. The oxide content below 1 wt.% Leads to an unstable mode of operation of the bath due to the difficulty of maintaining this concentration in the melt and low anode current densities. An increase in the current density above the limit leads to the joint evolution of oxygen and chlorine. Leading the process at an oxide concentration of the resulting metal below 1.0 wt.% Becomes economically unprofitable. The upper limit of the oxide content of the resulting metal in the electrolyte is due to the maximum solubility at the process temperature. An increase in this concentration leads to an increase in melt viscosity and a decrease in current efficiency. One of the main advantages of electrolysis in oxide-halide baths is the replacement of chlorine-releasing technology with oxygen-releasing. Such a technology will make it possible to solve a number of issues on the ecological situation of the environment and labor protection and safety measures. In addition, the technology for the production of alkali and alkaline earth metal oxides is simpler, less labor-consuming, than the production of their halides. In the case of calcium, its oxide can be obtained by calcining limestone at 900 ° C, while its chloride is obtained by complex chemical technology, requiring expensive stainless equipment and high labor costs (N.A. Doronin. "Calcium", M .: Gosatomizdat, 1962)

The oxygen released during electrolysis should not interact with the anode material in order to eliminate the above disadvantages characteristic of other methods. Such material is nickel oxide with lithium oxide additives. The introduction of lithium oxide significantly increases the electrical characteristics of the anode. A small content of lithium oxide leads to an increase in the resistance of the anode and an increase in the voltage drop across it. At concentrations less than 0.1 wt.%, The voltage drop reaches a value when the study of such anodes becomes economically unprofitable. Over 10 wt.% Lithium oxide in the anode reduces the resistance of the anodes in the melt and complicates their synthesis. In the study of other known technical solutions in the art, the features that distinguish the claimed invention from the prototype were not identified and, therefore, ensure the invention meets the criterion of "Significant differences".

EXAMPLE 1

In an open type electrolyzer, an electrolyte consisting of calcium chloride with the addition of 17 wt. % calcium oxide. The anode was material sintered from nickel and lithium oxides. The content of lithium oxide, determined analytically, was 0.1 wt.%. Lead was used as the cathode. The process temperature was maintained between 750-800 ° C. The anodic current density in this case was 0.5 A / cm ² , the cathodic 0.05 A / cm ² . Electrolysis was carried out for 16 hours. The voltage on the bath did not exceed 4.5 V. Calcium was obtained with a current efficiency of 80-85%. During electrolysis, calcium oxide was immersed in the bath, maintaining a concentration of 17 wt.%. After the end of the process, the anode remained unchanged. An alloy of calcium with lead is obtained. The calcium content in the alloy was 10 wt. %

EXAMPLE 2

This experiment is presented as a negative example. Under the electrolysis conditions described in example 1, a method using a graphite anode is implemented. The electrode collapsed within 40 minutes. The mirror of the bath was covered with fine graphite. The voltage on the bath increased to 8 V. The current output of calcium fell to zero. The electrolysis was stopped, thus showing the unsuitability of the graphite anode for the oxide-chloride electrolyte in the production of calcium.

EXAMPLE 3

The example of lithium production shows the production of pure metals. Potassium and lithium chlorides were deposited in an open type electrolyzer in the ratio 1: 1 and lithium oxide was added in an amount of 1.0 wt.%, The process temperature was 400 ° C. The synthesized material of the following composition was used as the anode: nickel oxide 90.0 wt.%, Lithium oxide 10.0 wt.%. The process was conducted for 16 hours. The anode remained unchanged. The voltage on the bath is 4.0 V. The current output is 96%. Received lithium satisfying T.U.

EXAMPLE 4

Under the conditions specified in example 1, an experiment was conducted on the long-term operation of the ceramic anode (synthesized from nickel and lithium oxides). The duration of the test is 120 hours. The anode remained unchanged.

EXAMPLE 5

In an open cell, calcium chloride and 0.5 wt.% Calcium oxide were deposited. Ceramics with a content of 10.0 wt.% Lithium oxide served as an anode. At a current density at the anode of 0.3 A / cm ² , chlorine was detected in the anode gases (up to 10.0%). Chlorine was absent in the anode gases at current densities not exceeding 0.02 A / cm ² . Process temperature 780 ° C. After 10 hours of electrolysis, pits and roughness appeared on the anode, indicating corrosion of the electrode. Analysis of the electrolyte showed the presence of nickel and lithium in it.

EXAMPLE 6

In an open cell, lithium and potassium chlorides were deposited in a ratio of 1: 1 and lithium oxide was added in an amount of 8.5 wt.%. Process temperature 450 ° C. Ceramics of the composition were used as the anode: nickel oxide 94.6 wt.%, Lithium oxide 5.4 wt.%. The process was 8 hours. The anode remained unchanged. The voltage on the bath is 4.2 V. The current output is 92%. Received lithium satisfying T.U.

EXAMPLE 7

In an open type electrolyzer, calcium chloride was deposited and 8 wt.% Calcium oxide was added. Process temperature 720 ° C. Electrolytic copper was used as a cathode. The anode - sintered - ceramics contained 95 wt.% Nickel oxide and 5 wt.% Lithium oxide. An alloy of calcium with copper is obtained. During the electrolysis, the concentration of calcium oxide in the electrolyte was maintained constant and equal to 8.0 wt.%. Current efficiency 75%. The process was 8 hours. The anode remained unchanged.

Using the proposed method provides, in comparison with existing methods, the following advantages:

1. Replacing chlorine-releasing technology with oxygen-releasing. Improving the environmental situation, working conditions and safety.

2. Reducing energy costs per unit of production due to the introduction of oxide, the resulting metal.

3. Simplification of technology. Lack of complex and expensive equipment for producing chlorides.

4. Improvement of technological parameters and the quality of the resulting metal by eliminating the destruction of the anodes and accurately maintaining the process parameters.

Claims (2)

1. The method of producing alkaline, alkaline-earth metals and their alloys by electrolysis of oxide-halide melts, characterized in that, in order to create an environmentally friendly technology and its simplification, the concentration of oxide of the obtained metal in the melt is maintained at 1.0-17.0 wt. % and electrolysis is carried out with an anode of a composite material made of sintered ceramic based on nickel and lithium oxides. 2. The method according to claim 1, characterized in that they use ceramic composition, wt.%:
lithium oxide 0.1-10.0 nickel oxide rest