Electrolysis tank used for aluminum electrolysis and electrolysis process using the electrolyzer

Abstract

An electrolytic cell for aluminum electrolysis includes a cell body, in which an anode and a cathode are arranged inside the cell body, the cell body is filled with an electrolyte, and at least a part of the anode is immersed in the electrolyte; the anode is arranged above the cell body, the cathode is arranged at the bottom of the electrolytic cell and is covered by aluminum liquid, the electrolyte is located between the anode and the cathode and covers the aluminum liquid; and an insulating layer is arranged on the inner sidewall of the cell body for isolating oxygen or the electrolyte from a carbon block. The anode contains Fe and Cu as primary components; and the electrolyte is composed of 30-38 wt % of NaF, 49-60 wt % of AlF₃, 1-5 wt % of LiF, 1-6 wt % of KF and 3-6 wt % of Al₂O₃, and the molar ratio of NaF to AlF₃ is 1.0-1.52.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an electrolytic cell for aluminum electrolysis and an electrolysis process using the electrolytic cell, belonging to non-ferrous metal smelting industry.BACKGROUND OF THE INVENTION[0002]In aluminum electrolysis industry, a traditional Hall-Heroult molten salt aluminum electrolysis process is typically adopted to perform electrolysis on the molten salts of cryolite-alumina in a prebaked carbon anode electrolytic cell typically by adopting, that is, cryolite Na3AlF6 fluoride salt melt is taken as flux, Al2O3 is dissolved in the fluoride salt, a carbon body is taken as an anode and vertically inserted into the electrolytic cell, a carbon body with aluminum liquid covering the bottom of the electrolytic cell is taken as a cathode, electrochemical reaction is carried out on the anode and cathode of the electrolytic cell at a high temperature ranging from 940 to 960° C. after a strong direct current is introduced, and the result...

AI Technical Summary

Benefits of technology

[0028]The anode containing metal Sn and composed of the aforementioned metal components is high in electric conductivity and low in overvoltage, the cell voltage in the electrolysis process of the electrolytic cell is about 3.1-3.4V, power consumption in the aluminum electrolysis process is small, the power consumption for per ton of aluminum is not more than 11000 kw·h, so the process cost is low; the anode material is alloy composed of Fe, Cu and Sn, so an oxide film formed on the surface of the anode in the electrolysis process is high in oxidation resistance and is hardly corroded by the electrolyte, and the formed oxide film is stable and not liable to fall off, therefore, the anode is imparted with quite high oxidation resistance and strong corrosion resistance so as to ensure the purity of aluminum products, that is, the purity of the produced aluminum can reach 99.8%. The following problems in the prior art are avoided: the alloy anode has high overvoltage, the oxide film on the alloy surface is low in oxidation resistance and liable to fall off, which leads to continuous consumption of the alloy anode and poor corrosion resistance, furthermore, the corroded or falling oxide film enters into liquid aluminum to degrade the purity of the final product aluminum. In addition, Fe and Cu serve as primary components of the alloy anode and their content proportions are quite high, and accordingly, the manufacturing cost of the anode material is lowered.

[0029]The used electrolyte employs a pure fluoride system, substance composition in the electrolyte is defined, the contents of these substances are further defined and the molar ratio of NaF to AlF3 is 1.0-1.52, so that the liquidus temperature of the electrolyte is lowered to 640-670° C., as a result, electrolysis can be carried out at 720-760° C. according to the electrolysis process, which reduces volatilization loss of fluoride salt, avoids corrosion to electrolysis devices and damage to human body, improves working environment, greatly reduces energy consumption in the electrolysis process and achieves the aim of energy saving and emission reduction; meanwhile, in the present invention, proper amounts of LiF and KF are added and can be combined with sodium ions and aluminum ions in the electrolyte to form lithium cryolite and potassium cryolite with low melting points, thus the crusting phenomenon is avoided in the electrolysis process; compared with the existing industry, the electrolyte for aluminum electrolysis in the present invention has no CaF2 and MgF2 added therein, instead, KF in an appropriate proportion, which has the function of increasing alumina solubility and dissolution velocity, is added to a system in which the molar ratio of NaF to AlF3 is 1.0-1.52, therefore, the shortcoming of low alumina solubility in the low-molar-ratio electrolyte is improved; in general, the electric conductivity of the electrolyte decreases as the temperature decreases, so typically, the electric conductivity at a low electrolysis temperature hardly meets the demand in a normal electrolysis process; the electrolysis temperature is lowered by lowering the liquidus temperature of the electrolyte in the present invention, however, the electric conductivity of the electrolyte at a low temperature can still meet the demand in the electrolysis process because LiF with a larger electric conductivity is added and component proportions in the electrolyte are optimized, thus enhancing the current efficiency in the electrolysis process. According to the invention, the content of LiF is defined as 1-5%, this is because too low content of LiF fails to improve electric conductivity and to prevent crusting, and too high content of LiF results in decrease of the alumina solubility, and the above two situations are effectively avoided by defining the content of LiF as 1-5% in the present invention; and there is no corrosion to a metal device when the electrolyte with the above proportions in the present invention is used, in this way, the service life of the electrolysis device is prolonged.

[0030]Similarly, the aforementioned inert alloy anode has the advantages of low material cost and high electric conductivity, in addition, the metal Al contained in the aforementioned inert alloy anode plays a role of oxidization resistance and can serve as a reducing agent for metallothermic reduction reaction with metal oxides in the inert anode alloy, thus preventing the metals in the inert alloy anode, i.e. primary components, from being oxidized, and causing reduction of the electric conductivity of the alloy anode; meanwhile, the metal Y added can be used for controlling a crystal structure for anode material formation in the preparation process of the inert anode, achieving the anti-oxidization purpose.

Problems solved by technology

Simultaneously, the second technical problem to be solved by the present invention is that, an alloy anode composed of metal components in the prior art is high in overvoltage, power consumption in the aluminum electrolysis process is large and the metal components employed are high in price, resulting in cost increment of the alloy anode; in addition, an oxide film on the surface of the alloy anode in the prior art is low in oxidation resistance and liable to fall off, which leads to continuous consumption of the alloy anode and poor corrosion resistance, furthermore, the corroded or falling oxide film enters into liquid aluminum to degrade the purity of the final product aluminum; and therefore, provided is an electrolytic cell for aluminum electrolysis, which is low in overvoltage of the used inert anode material, low in price, strong in oxidation resistance and stability of the oxide film formed on the surface thereof and resistant to electrolyte corrosion.

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