Electrolyte used for aluminum electrolysis and electrolysis process using the electrolyte

Abstract

An electrolyte for aluminum electrolysis employs a pure fluoride salt system and includes the following components by mass percent: 20-29.9% of NaF, 60.1-66% of AlF3, 3-10% of LiF, 4-13.9% of KF and 3-6% of Al2O3, in which the molar ratio of NaF to AlF3 is 0.6-0.995; or the electrolyte includes the following components by mass percent: 30-38% of NaF, 49-60% of AlF3, 1-5% of LiF, 1-6% of KF and 3-6% of Al2O3, in which the molar ratio of NaF to AlF3 is 1.0-1.52.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an electrolyte for aluminum electrolysis and an electrolysis process using the electrolyte, belonging to non-ferrous metal smelting industry.BACKGROUND OF THE INVENTION[0002]Aluminum electrolysis refers to acquisition of aluminum by means of an electrolysis method. In the prior art, a traditional Hall-Heroult molten salt aluminum electrolysis process is typically adopted for aluminum electrolysis. This process is featured by use of a cryolite-alumina molten salt electrolysis method in which cryolite Na3AlF6 fluoride salt melt is taken as flux, Al2O3 is dissolved in fluoride salt, carbon body is taken as an anode, aluminum liquid is taken as a cathode, and electrolytic aluminum is obtained by performing electrochemical reaction at 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. Due to high electrolysis temperature, the traditional ...

AI Technical Summary

Benefits of technology

The present invention provides an electrolyte for aluminum electrolysis that has low liquidus temperature, does not corrode the electrolysis device, and is not liable to volatilization. The electrolyte has proper electric conductivity and alumina solubility, and does not have the crusting phenomenon. The invention also includes a process for preparing the electrolyte and using it in the electrolysis process. The technical effects of the invention are reducing energy consumption, improving economic efficiency, and prolonging the service life of the electrolytic cell device.

Problems solved by technology

Due to high electrolysis temperature, the traditional aluminum electrolysis process has such characteristics as large volatilization amount of electrolyte, large oxidization loss of a carbon anode, large energy consumption, large thermal loss and poor electrolysis working environment.

In the aforementioned electrolyte, however, BaF2 is liable to sedimentation in the electrolysis process due to large density, so it is hardly applied to industrial production in an extensive fashion; use of MgF2 and CaF2, which are high-melting-point substances, will increase the liquidus temperature of the entire system and will also degrade the electric conductivity and the alumina solubility of the electrolyte; because NaCl has a relatively low melting point, addition of NaCl is a way of lowering the liquidus temperature of the electrolyte, however, NaCl imposes a corrosion effect on such metals as Cu, Fe, Al and Ni at the aforementioned electrolysis temperature and will further lead to corrosion of metal parts like electrolytic cell accessories, this corrosion effect dramatically shortens the service life of electrolysis devices, furthermore, NaCl is extremely liable to volatilization in the electrolysis process so as to form HCl gas that is harmful to human body, so until now, NaCl has not been widely applied to industrial production; in addition to addition of NaCl, decrease of the molar ratio of NaF to AlF3 can also lower the liquidus temperature of the electrolyte in light of common knowledge in this art, but in the existing industry, the molar ratio of NaF to AlF3 is generally larger than 2.2, this is because an unsolvable problem will arise if the liquidus temperature of the electrolyte is further lowered and the electrolysis temperature is lowered correspondingly, namely, NaF and AlF3 will lead to a ‘crusting’ phenomenon of the cathode in the process of low-temperature electrolysis, the reason for this ‘crusting’ phenomenon is that sodium ions and aluminum ions in the electrolyte will gather at the cathode in the electrolysis process to generate sodium cryolite, which is seldom molten at a low temperature due to its high melting point, as a result, the surface of the cathode is covered by a layer of refractory cryolite crust to affect normal electrolysis in the electrolysis process tremendously.

Whether an electrolyte can be successfully applied to industrial production is based on comprehensive consideration for many factors like its liquidus temperature, volatility, electric conductivity, alumina solubility, preparation environment and whether stable electrolysis process can be guaranteed, however, due to the above problems in the prior art, industrial application of the electrolyte is significantly limited, and it is an unsolved problem in the prior art to find a way of avoiding corrosion to electrolysis devices and damage to human body and ensuring proper electric conductivity and alumina solubility as well as no ‘crusting’ phenomenon of the prepared electrolyte while the liquidus temperature of the electrolyte is further lowered.