RU2096530C1 - Method of roasting electrolysers for electrocytical production of aluminium - Google Patents

Abstract

FIELD: aluminum industry. SUBSTANCE: method of roasting electrolyzer for aluminium production comprises warming bottom, pouring in liquid aluminium and connecting electrolyzer to direct current circuit. Charged salts contain melt of chiolite and/or barium chloride or fluoride. Ratio of these components is as follows, %: chlorite, 75-80 and/or barium fluoride. EFFECT: more efficient roasting method. 4 cl

Description

 The invention relates to the production of aluminum by electrolytic method and can be used in the preparation of electrolyzers for industrial use.

 The purpose of the invention is to increase the service life of the cell due to the uniform heating of the hearth and reduce the saturation rate of the lining of the cathode device with sodium during the firing period.

A known method of preparing the bottom of the cell to obtain aluminum for operation [1]
Significant losses of fluoride salts, unstable process in the starting period when using the method.

 The firing technology consists of two stages. At the first stage, the hearth heating is carried out by known methods, for example, on metal or burners. At the second stage, in the cell of the electrolyzer insulated at the first stage of firing, a mixture of salts containing, wt.

chiolite 75 80
barium chloride and / or fluoride 20 85
The loading of salts in the form of a dry mixture is carried out on the periphery of the mine and aluminum is poured.

 Processing of the bath occurs from the periphery to the center as the salt is melted.

 When pouring the molten salt, the anode is simultaneously lifted, then liquid aluminum is poured.

 Barium salts are used to increase the density of the molten salt, which is necessary to keep the molten salt under a layer of molten metal and prevent mixing with it.

 The formation of refractory barium compounds filling the pores in the blocks, cracks in the joints and blocks, leaks at the contact points of the hearth and blocks.

 The molten salt is either prepared in a special furnace, or an electrolyte produced by high frequency synthesis is used. Filling and pouring of the molten salt from the electrolyzer is carried out by a vacuum ladle, which reduces the complexity of the technology. Pouring can be carried out from the calcined electrolyzer to another, prepared for this stage of firing.

 As a mixture of salts (molten salts), a chiolite (K.O. 1.2 - 1.5) 75 80 wt. barium chloride and / or fluoride 20 25 wt. With less than 75 wt. the content of chiolite increases the number of heavy barium-containing salts - more than 25 wt. which land on the bottom and reduce electrical conductivity. At large 80 wt. the content of chiolite decreases the content of heavy barium-containing salts of less than 20 wt. the density of molten salts decreases, their mixing in aluminum is possible, and the loss of fluorine salts increases, due to the lack of barium-containing salts, the effect of hardening of the lining is not fully achieved and the current distribution in the hearth is worsened.

The use of barium-containing salts is most appropriate in a mixture of barium chloride + barium fluoride at a ratio of 1: 1. In this case, a more refractory compound barium fluorochloride (BaCl ₂ • BaF ₂ ) is formed during the firing process.

Maintaining a density of molten salts of 2.6 2.8 g / cm ³ ensures its constant location below the metal level, in a layer ratio of 1: 2 1: 4 provides protection against loss of fluorine salts during the firing process.

 The method is implemented as follows.

Example 1. The firing of the electrolyzer was carried out in two stages. At the first stage, conventional non-metal calcination (5 t) was carried out. A day later, when the metal temperature reached 750 ^o C, the salt melt containing 25 wt. barium chloride and 75 wt. a chiolite having a melting point of 660 ^° C., in an amount of 4 tons, and a voltage of 5.0 V is set. After 4 hours, the voltage is set to 4.5 V, after 10 hours, 4.0 V and maintained until start up. After 2 days, the starting charge was melted and the electrolyzer was in start-up mode.

 In the post-start-up period, a study was conducted of the operation of the electrolyzer: the voltage drop in the hearth was 320 mV, there were no cracks in the joints and blocks, a constant decrease in the content of iron (from 1.30 to 0.35 for 40 days), silicon (from 0, 60 to 0.12 for 40 days).

 The cell is stable.

Example 2. At the first stage, firing was performed on metal (6 t). A day later, at a temperature of 730 ^° C., a salt melt containing 13 wt. barium chloride, 10 wt. barium fluoride, 77 wt. chiolite having a melting point of 700 ^o C, in an amount of 2.5 tons. A voltage of 5.5 V.

 After 4.5 hours the voltage is 5.0 V, after 10 hours it is 4.5 V, after 12 hours it is 4.0 V and it is maintained until the start.

Example 3. On the periphery of the bath load a dry mixture having a composition of wt. chiolite 75, barium chloride 15, barium fluoride 10. Pour liquid aluminum (5 t, 750 ^o C), connect the electrolyzer and set the voltage to 5V, then after 5 hours 4.8 V, after 10 hours -4.5 V, after 12 h 4.0 V and support until start. Melting the charge, the formation of an electrolyte layer and entering the start-up mode occurs one day after loading the charge. In the future, the cell operates in a normal steady state.

 The proposed technology provides, in addition to uniform high-temperature firing of the lining, a more uniform distribution of current loads in the hearth.

 The service life of the electrolyzer increases, the current distribution by blooms improves.

 The post-launch period showed the stable operation of baths fired by this technology, the absence of cracks in the joints and blocks, a stable decrease in the content of iron and silicon in raw aluminum.

Claims (3)

 1. A method of firing an electrolyzer for aluminum production, including heating the hearth, loading onto the bottom of salts containing fluorides and / or metal chlorides, pouring liquid aluminum and connecting the electrolyzer to a direct current circuit, characterized in that as the loaded salts use a mixture of salts containing chiolite and / or barium fluoride, in the following ratio, wt. Chiolite 75 80
Barium chloride and / or fluoride 20 85
2. The method according to claim 1, characterized in that the loaded salt is used in the form of a molten salt. 3. The method according to claim 2, characterized in that the ratio of the layers of the molten salt
the molten metal is supported within 1 2 1 4. 4. The method according to claim 2, characterized in that the density of the molten salt is maintained equal to 2.6 2.8 g / cm ³ .