SU918336A1 - Electrolyte for producing aluminium-silicon alloys - Google Patents

Description

I.:. -.:. This invention relates to the electrolytic production of aluminum and its. alloys from cryolite-alumina melts. A cryolite-alumina -, electrolyte is known for producing aluminum – silicon-silicon alloys of the following composition, wt .: AtaO-b 3.5–8.0; SiO, 1,, 0; LEG 8.0-25.0; - The rest The disadvantages of this electrolyte are increased volatility and low electrical conductivity of it. with a high content of aluminum fluoride. A large amount of SiO also contributes to a decrease in electrical conductivity and an increase in the viscosity of the electrolyte. Cryolite-alumina electrolytes are known with NaC6 additives to produce aluminum O. 2.2-3.2; CaFj 6–9% and NaCe 4–9% and aluminum-silicon alloys (NaCE up to 18) 2j. The disadvantage of this electrolyte is its increased volatility and its reduced electrical conductivity at low cryolite ratios: an increased content of sodium ions in the electrolyte at high cryolite ratios and high NaCE contents, which leads to an increase in the sodium content in the metal and a decrease in the service life of the cathode (electrolyzer ). A cryolite-alumina electrolyte is also known for producing aluminum-silicon alloys with KF additives ranging from 15 to about 0 wt.% Z. The main disadvantage of such an electrolyte is a high content of KF, which negatively affects the carbon hearth of the electrolyzer, which reduces its service life. The closest to the present invention is the following electrolyte composition for producing aluminum-silicon alloys, May.: AEP-j 39.1 "5; NaF 52.8-58.7; AEaO 0.3-3.5; Sio

0.2 + -0.38, Silicon oxide enters the electrolyte either with high-siliceous alumina or from waste, for example, with new slag .kj.

A disadvantage of the known electrolyte is the increased resistance of the electrolyte due to the content of oxides in it, which leads to an increased consumption of electricity, an elevated temperature of the electrolyte and, as a result, to a decrease in current efficiency and increased consumption of fluoride salts.

The purpose of the invention is to improve the technical and economic indicators of electrolysis (reduction of electricity consumption, fluoride salts and alumina increase in current efficiency, reduction in the cost of the resulting alloy) for. by improving the physicochemical properties of the electrolyte (an increase in the electrical conductivity, a decrease in the melting point of the electrolyte, etc.) and the use of cheaper lithium-containing raw materials.

The goal is achieved by the fact that the electrolyte for producing aluminum-silicon alloys containing sodium fluoride, aluminum fluoride, aluminum oxide and silicon oxide, additionally contains calcium fluoride, magnesium fluoride, lithium fluoride, fluoride and lithium-containing concentrate in the following ratio of components, masd : Aluminum fluoride 29-37 Calcium fluoride 1-7 Magnesium fluoride 5 Potassium fluoride Oh, Lithium fluoride 1-5 Aluminum oxide 0.5-7 Silicon oxide 0.1-0.5 Lithium-containing concentrate Q, 01-1 Sodium fluoride Balance the molecular ratio of sodium fluoride to aluminum fluoride is between 2.6 and 3 ,.

Lithium containing concentrates (spodumenic, lepidolite, muscovite, petalitic, mica, etc.) have the following content of main components, masD: 1-8; SiOj 35-60; KO 0,5-10; 15-30; F 0.5-10.

Minerals (spodumene, petalite, etc.) or their mixtures can be used as lactitic raw materials.

The introduction of lithium-containing concentrate into the electrolyte from 0.01 to 1 mPD is due to the following: when the concentrate is loaded less than 0.01%, the positive effect of using lithium compounds decreases, since it is not possible to maintain the required concentration of lithium fluoride; when loading more than 1%, the resistance of the electrolyte increases dramatically due to the large amount of oxides.

In the process of electrolysis of alumina and lithium-containing concentrate dissolved in an electrolyte consisting of sodium fluoride, aluminum, calcium,. magnesium and lithium; liquid aluminum-silicon alloy containing Si 0.2–5 is released on the cathode. The lithium-containing concentrate may be loaded into the electrolyte continuously, semi-continuously or periodically; together with alumina or with fluoride salts separately; on the crust of the electrolyte or directly into the melt. As a result of the interaction of the oxides with the components of the electrolyte, active alumina () is formed which is better dissolved in the electrolyte. Correction of electrolyte by cryolite ratio is made by cryolite, aluminum fluoride or sodium fluoride. Additives (CaF, MgF / j., MgO and others) are loaded periodically. With their large supply with concentrate in the form of priyesy (CaO, MgO), the loading of additives is not performed at all. To create the initial desired concentration, lithium can be introduced into the electrolyte in the form of pure salts (fluoride, carbonate, aluminate) or in the form of a lithium-containing concentrate. To compensate for the loss of lithium during electrolysis and the introduction of silica, as well as partially alumina, a lithium-containing concentrate is added to the electrolyte in an amount of 0.01-1 wt.%.

Some compositions of the proposed electrolyte and their properties are given

e table.

Impurities (Na O, CaO, TiO, MgO, Mho, Fe 0 and others)

Si content in the alloy, mas

Changes in the properties of the proposed electrolyte relative to limestone

Lower start temperature

16.5 17.5

13.5

17

0.6 0.6

5.0

0.2 1.0

So, when used for electrolysis electrolyte with a cryolite ratio of 2.7 of known composition, m.s.%: der NaF 56; SiO 0.3, process temperature is 970-980 ° C, voltage 65 V, alumina consumption 1930 kg / t AK, fluoride salt consumption 32 kg (in terms of fluorine) per ton of aluminum.

Claims (3)

When using an electrolyte with a cryolite ratio of 3.2 of the proposed composition, masd: NaF 52.7 32.9; CaFi 2.5; MgFi 3.5; LiF i; KF 1; AEp, 3; Si02.0.2, and also Q., 2% of lithium-containing concentrate, the process temperature decreases by (with a decrease in the temperature of the onset of crystallization on), the average voltage, S B, the consumption of alumina is 1880 kg / t AB (i.e., lower tia 50 kg), the consumption of fluoride salts is reduced by 2.5 kg of fluorine per ton of aluminum. In addition, the proposed electrolyte contributes to the formation of active alumina (5-10% of the alumina being contaminated), which also leads to a decrease in the operating voltage; the cost of lithium raw materials is also reduced by 20%, all this contributes to the improvement of technical and economic indicators and the reduction of the cost of the resulting alloy. : .- ..,. . Electrolyte for aluminum-silicon alloys containing sodium fluoride, aluminum fluoride, aluminum oxide and silicon oxide, which is also due to the fact that, in order to improve the technical and economic performance of electrolysis, the electrolyte also contains calcium fluoride, fluoride. magnesium, potassium fluoride, lithium fluoride and lithium-containing concentrate in the following ratio, wt .: Aluminum fluoride 29-37 Calcium fluoride 1-7 magnesium fluoride 1-5 Potassium fluoride 0.5-6. Lithium fluoride 1-5 Aluminum oxide 0.5-7 Silicon oxide O, 1-0.5 Lithium-containing concentrate 0.01-1 Sodium fluoride The remaining molecular ratio of sodium fluoride to aluminum fluoride is 2.6 to 3, . Sources of information taken into account in the examination 1. The author's certificate of the USSR If A9172t, cl. C 25 C 3/36, 1973. 2. US Patent No., cl. publish 1957. 3. Authors certificate of the USSR N, cl. C 25 C 3/36, 197. if. USSR author's certificate, class .. C 25 C 3 / 3b, 1976.