SU145228A1 - The mercury method of obtaining caustic alkalis - Google Patents

Description

Mercury processes are known for producing caustic alkalis by incomplete decomposition of alkali metal amalgam in decomposing agent.

These methods do not allow to obtain the target product of high purity, such as, for example, necessary in semiconductor technology.

In the present invention, in order to obtain a product of high purity, the amalgam is subjected to multiple purification on bipolar electrodes in an alkaline solution, while the bipolar electrodes are connected in a single countercurrent cycle. Compensation of the difference in current yields in anodic processes is made by feeding the electrodes with a refiner with incompletely decomposed amalgam from the decomposing agent.

The drawing shows a schematic diagram of a device for producing caustic soda in accordance with the proposed method.

A device for producing caustic soda contains an electrolyzer /, refiners 2, 3, 4, 5, a sodium amalgam decomposer 6, a predispenser 7, a mercury deep purification unit 8, and mercury pumps 9.

Electrolytic decomposition of sodium chloride with the formation of sodium amalgam and chlorine is going on in the electrolyzer / with graphite or any other anodes. Each refiner has a cathode and anode compartment through which sodium amalgam circulates. Electrolyte is a 15-20% solution of caustic soda. Under the action of an electric current, sodium is dissolved on the amalgam anode and deposited on the amalgam cathode of the refiner, forming sodium amalgam. The mercury cathode of the electrolysis cell (a) and the amalgam anode of refiner 2 are electrically connected to each other by means of women 10 and the flow of sodium amalgam; thus, they act as an amalgam bipolar electrode. In the same way, the amalgam electrodes of neighboring portions of Finers form biopolar electrodes. The cathode bus of the DC source is connected to the amalgam cathode of the refiner 5. The sodium amalgam decomposer 6 is filled with a graphite nozzle and is fed with clean water. The distributor 7 is a conventional decomposer, in which the weak sodium amalgam entering it is completely decomposed. As a unit for deep cleaning of mercury 8, any device can be used that guarantees sufficiently deep cleaning of it. For example, a well-known method for purifying mercury with nitric acid can be used.

The sodium amalgam formed in the electrolyzer 1 enters the anode compartment of refiner 2. The sodium amalgam slab from the anode compartment of refiner 2 is sent to predisperse 7, where it is completely decomposed. Mercury from pre-distributor 7 enters purification unit 8, and from there pure mercury is sent to the cathode compartment of refiner 5, in which pure sodium amalgam is formed, which is sent to decomposer 6. The sodium amalgam slab from the decomposer 6 enters the cathode compartment of refiner 4, where it enriched with sodium and sent to the anodic compartment of the refiner 5 n.d. Amma, pyc:; 1 sodium from the anodic compartment of the refiner 3 enters the electrolyzer and the cycle repeats.

Part of the caustic soda obtained in the decomposer 6 is displayed as finished product, and part is sent to the refiner 5, where it is diluted with pure water supplied thereto to the concentration of electrolyte used. All the refiners are interconnected by electrolyte transfer 1L. Thus, the electrolyte initially enters the refiner 5, then all the other refiners pass sequentially and are withdrawn from the refiner 2 as low-grade caustic soda.

In the process of sodium salt electrolysis, sodium amalgam is contaminated with impurities of various metals. When refining sodium on amalgam electrodes, some of the impurities go to the amalgam cathode, some remain in the electrolyte, and some go along with the weak sodium amalgam. Thus, the removal of the primer is accomplished by feeding the weak sodium amalgam and refining electrolytes from a higher refining stage to a lower one. Since the anodic separation of refiner 2 feeds on sodium amalgam with a high content of impurities, most of these impurities remain in the weak sodium amalgam and in the electrolyte.

The electrolyzer / and all the refiners are connected in series, as a result of which the same electric current passes through the entire device. However, the cathode current output in both the electrolaser / and in each refiner is not equal to lOCVo. In addition, the presence of predistributor 7 reduces the current efficiency in the system at the first stage 1 and rafp p: ppr, ip kc how many percent. Therefore, it is necessary to aiyHiKpCisaib part of the current at the Kansda stage of the anodic process, or to feed each amalgam anode with sodium amalgmoid. In this scheme, the compensation of the output differences to the current is obtained due to the incomplete decomposition of the sodium amalgam in decomposer 5. The decomposition with sodium amalgam is used to feed the amalgam anodes. So, for example, from the decomposer 6 vigurum, sodium amalgale is led from the concentration of 0.05% and is sent to pa-finer 4, in which it is enriched with sodium to a concentration of 0.25% and enters the anode compartment of the refiner 5. There, turn, the sodium concentration in the amalgam decreases to 0.045%, etc. The process is controlled by changing the sodium amalgam concentration at the outlet of the decomposer 6. The concentration change is regulated by the amount of water supplied or the amount of nozzle in the decomposer 6.

Subject invention

A mercurial method of producing caustic alkalis by incomplete decomposition of alkali metal amalgam in a decomposer, characterized in that, in order to obtain a product of high purity, the amalgam is subjected to repeated purification on bipolar electrodes in an alkaline solution, connected in a single countercurrent cycle, and compensation for the difference of yields by the current in the anodic processes is produced by feeding the refiner electrodes with incompletely decomposed amalgam from the decomposing agent.

№ 145228

2

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