RU2241073C2 - Carbon anode of electrolyzer - Google Patents

Abstract

FIELD: production of calcium by electrolysis, different branches of non-ferrous metallurgy at using metal chlorides as raw material during electrolysis.

SUBSTANCE: carbon anode includes electric current supply lead in the form of metallic crosspiece; secured to it anode unit with protective corrosion-proof coating applied onto it. Anode unit is secured to crosspiece through sizing electrically conducting layer made of graphite powder with phenol binder. Protective corrosion-proof layer is made of aluminosilicate powder with chrome-aluminum phosphate binder. Graphite powder has particle size no more than 100 micrometers. Electrically conducting layer includes as phenol resin as binder. Mass relation of graphite powder and phenol resin is 3 : 2. Particle size of aluminosilicate powder is no more than 100 micrometers. 30 % aqueous solution of chrome-aluminum phosphate binder of protective corrosion-proof layer is used as chrome-aluminum phosphate binder of said layer. Mass relation of aluminosilicate powder and solution of chrome-aluminum phosphate binder is 1 : 1.

EFFECT: increased useful life period of anode unit of electrolyzer, less loss of power in contact current supply unit.

4 cl, 2 dwg

Description

The invention relates to the production of calcium by the electrolytic method and can be used in other non-ferrous metallurgy industries using metal chlorides as raw materials for electrolysis.

The anode of the calcium electrolyzer is an assembly of carbon blocks 300 × 300 × 900 mm in size with a rectangular prism in the upper part, to which a current-carrying metal crosshead is attached using bolted connections. An anode assembly consisting of twelve carbon blocks is assembled on a common metal traverse.

The applied designs of anode assemblies (Doronin N.A. Calcium metallurgy, M .: Atomizdat, 1959, Doronin N.A. Calcium, M .: Atomizdat, 1962) have two significant drawbacks:

- loss of electricity in the contact zone of the beam - graphite, which increases during operation of the cell from 70-100 to 300 mV after 1 month of operation;

- insufficient resource for the operation of the anode assembly, due to both destruction and burnout of graphite over the electrolyte “mirror” zone — chlorine-air gas mixture. At an electrolysis temperature of ~ 700 ° C, the life of the anode assembly is on average 3 months. Further burning of graphite leads to uneven destruction of individual carbon blocks of the anode assembly and its precipitation into the electrolysis bath, which creates an emergency.

Also known is the design of the carbon anode of the electrolyzer with a surface protective layer consisting of boron compounds (boric acid, boron oxide, salts of boric acid). For the formation of such a layer, it is necessary to carry out special firing of the anode with a protective layer (patent No. 2155826, class C 25 C 3/12, 7/02, 2000). The disadvantages of this design in relation to electrolysis for the production of calcium are the presence in the boron layer, which is unacceptable when receiving calcium, as well as the need for special burning of the anode, which increases energy costs, increases the pre-start period and requires special equipment.

Also known is the design of the carbon anode of the electrolyzer with a surface protective layer of a mixture of aluminum with aluminum oxide. During operation, ductile aluminum is held in an aluminum oxide frame. Design disadvantages are the difficulty of obtaining a uniform protective layer applied by spraying liquid aluminum in air, as well as the complexity and unreliability of existing spray equipment (USSR Author's Certificate No. 583199, class C 25 C 7/00, C 25 V 11/12, C 01 B. 1977).

The closest analogue is the carbon anode of the electrolyzer, containing a current-carrying unit in the form of a metal traverse and an anode block attached to it, the surface layer of which is impregnated with orthophosphoric acid (Rodyakin V.V. Calcium, its compounds and alloys. M: Metallurgy, 1967, p. 84-85).

The claimed invention solves the problem of increasing the service life of the anode assembly of the electrolyzer and reducing energy losses in the contact conductive assembly.

The technical result is achieved by the fact that, in contrast to the prototype, which contains a lead-in assembly in the form of a metal traverse and an anode block attached to it with an orthophosphoric acid-impregnated surface layer, a special conductive layer is located between the current-conducting surfaces of the metal cross-arm and the graphite anode, and for protection a protective anticorrosion layer 0.3-0.4 mm thick is applied against oxidation.

The technical result is also achieved due to the fact that the conductive bonding interlayer with a thickness of 0.5-1.0 mm consists of a conductive graphite powder with a particle size of less than 100 microns and a phenolic binder. The ratio of graphite filler and binder 3: 2. A pre-prepared graphitophenol mixture is applied to the entire surface of the anode assembly in contact with the traverse. The traverse is coupled with graphite blocks by bolting. When mounting the contact node, preliminary surface preparation and subsequent special heat treatment of the joint zone are not required. The specific electrical resistance of the bonding layer is (10-15) · 10 ^-6 Ohm · m, which is almost equal to the electrical resistance of the graphite anode material and actually does not change during the operation of the electrolyzer.

The ratio of graphite filler and phenolic binder is determined experimentally. For a given particle size and the content of graphite powder in the bonding layer, graphite electrically conductive “bridges” are formed evenly over the entire bonding area with good adhesion of the bonding layer both to the surface of the anode and to the surface of the metal cross-beam provided by the phenolic binder.

The achievement of the technical result is also facilitated by the fact that the protective anticorrosion layer consists of an aluminosilicate powder filler with a particle size of less than 100 microns and a 30% aqueous solution of an aluminochromophosphate binder. The ratio of filler and binder is 1: 1. The aluminosilicate filler provides high heat resistance of the protective anticorrosive layer in a chlorine-air gas medium up to a temperature of 700-900 ° C, and the aluminochromophosphate binder, along with high heat resistance, provides good adhesion of the protective anticorrosive layer to the graphite base. The curing of the layer occurs either at room temperature or by heating with an open flame simultaneously with the starting heating of the electrolysis bath, provided for by the operation mode of the electrolyzer. The use of a 30% aqueous binder solution ensures uniform distribution of the mixture over the graphite surface when it is applied, and the use of a filler with a particle size of less than 100 microns reduces the porosity of the protective anti-corrosion layer. The selected ratio of aluminosilicate filler and aluminochromophosphate binder provides optimal heat resistance of the coating at the operating temperature of the electrolyzer and good adhesive properties of the protective anticorrosive layer with the surface of the graphite anode.

The application of a protective anti-corrosion layer is as follows. The surface of the anode blocks is cleaned of adhering particles of graphite and foreign objects. A pre-prepared mixture of aluminosilicate and a 30% aqueous solution of aluminochromophosphate binder in a ratio of 1: 1 is applied with a brush to the cleaned surface of the anode. After drying at room temperature, the second and third layers are applied alternately so that the total thickness of the layer is 0.3-0.4 mm. Then, in the process of starting heating of the electrolysis bath with an open flame, curing and formation of a protective layer occurs. Furthermore, the temperature does not exceed 600 ° C. The final formation of the anticorrosion layer occurs during the operation of the electrolyzer.

The advantages of the claimed invention are illustrated by the following examples.

Example 1: In industrial electrolysis baths No. 31 and No. 32 of the enterprise, graphite anode blocks were installed with phosphoric acid impregnation and current-carrying traverses with a gluing current-conducting strip from waste from the food industry (molasses). Electrolyzer operation mode: current 22-23 kA, voltage 8-9 V. The service life was 94 days. Losses (voltage drop) in the contact current-supply unit at the beginning of operation amounted to 110-140 mV, and after 90 days of operation - 300 mV. Thus, the voltage drop increased by almost 3 times.

Example 2: In industrial electrolysis baths No. 29 and No. 30, graphite anode blocks made according to the invention were installed with a protective anticorrosive layer based on aluminosilicate and an aluminum chromophosphate binder and current-carrying metal cross beams using adhesive conductive gaskets based on graphite filler and phenolic binder. The operation mode of the electrolyzer: current 22-23 kA, voltage 8-9 V. The service life was 120 days. Losses (voltage drop) in the contact current-supply unit at the beginning of operation amounted to 100-110 mV and practically did not change over the entire period of operation.

As can be seen from the above examples, when using the invention:

- the life of the anode assembly of the cell increased by 20%;

- Electricity losses in the contact current-supplying unit during the operation of the electrolyzer decreased by almost 1.5-2.0 times.

In addition, the raw materials used are cheap and non-deficient, the manufacturing technology of a protective anticorrosive layer and a bonding conductive layer is simple and does not require special equipment.

Claims (4)

1. A carbon anode of an electrolyzer containing a current-carrying unit in the form of a metal cross-arm and an anode block attached to it with a protective anticorrosive layer deposited on its surface, characterized in that the anode block is attached to the cross-arm through a bonding conductive layer made of graphite powder on a phenolic binder, and the protective anticorrosive layer is made of aluminosilicate powder on an aluminochromophosphate binder. 2. The anode according to claim 1, characterized in that the particle size of the graphite powder does not exceed 100 microns, as a phenolic binder, the conductive layer contains a phenolic resin, and the mass ratio of graphite powder to phenolic resin is 3: 2. 3. The anode according to claim 1, characterized in that the particle size of the aluminosilicate powder does not exceed 100 μm, and its 30% aqueous solution is used as the aluminum chromophosphate binder protective anticorrosive layer. 4. The anode according to claim 3, characterized in that the mass ratio of the aluminosilicate powder and the aluminochromophosphate binder solution is 1: 1.