RU2068017C1 - Method of refining aluminium from sodium and calcium - Google Patents

Abstract

FIELD: nonferrous metal engineering. SUBSTANCE: refinement of aluminium and its alloys from sodium and calcium is achieved by melting aluminium, eliminating dross, applying on the melt surface sodium chloride and aluminium fluoride (0.85-0.9 to 1 by weight) flux followed by agitation, ageing, dross elimination, and pouring out of aluminium. The process is carried out at the temperature 710-740 C. EFFECT: increased degree of refinement, shortened time of the process, reduced hygroscopicity and volatility of the flux. 1 tbl

Description

 The invention relates to the metallurgy of non-ferrous metals and can be used for refining aluminum and its alloys from sodium and calcium.

The following refining methods are known: thermal aging of aluminum [1] evacuation [2] gas purge [3] filtration [4] flux refining [4]
Closest to the claimed method in technical essence is the method of flux refining, in particular flux refining based on carnallite (MgCl ₂ • KCl) with the addition of aluminum fluoride (AlF ₃ ), taken as the basic version [4, p. 59]
The disadvantages of the basic method: insufficiently high degree of refining; the duration of the refining process; hygroscopicity of the flux, which leads to the hydrolysis of magnesium chloride with the formation of hydrogen chloride released into the atmosphere at the workplace, as well as to the formation of magnesium oxide deposited at the boundary of salt and metal melts, therefore, negatively affects the refining process; high volatility of flux, causing an increase in the content of harmful substances in the workplace.

 The aim of the invention is to increase the degree of refining, reducing the time of refining, reducing the hygroscopicity and volatility of the flux.

 This goal is achieved through the use of a flux containing potassium chloride and aluminum fluoride, with the following mass ratios (0.85-0.95): 1.

The inventive exothermic reaction of the interaction of aluminum fluoride with sodium and calcium, with the result that sodium and calcium are transferred to the salt phase. According to thermodynamic calculations, the reagent for sodium and calcium (at refining temperatures of 710-740 ^o C) is aluminum fluoride, potassium chloride at refining temperatures does not interact with sodium and calcium, but is used to reduce the melting point of the flux.

 An increase in the degree of refining is achieved due to a more vigorous interaction of aluminum fluoride (the proposed option) with sodium and calcium compared with carnallite (the basic version).

 Magnesium oxide formed during the hydrolysis of carnallite (basic version) is located at the metal-salt phase boundary and prevents the interaction of the refining reagent with impurities. In the proposed embodiment, there is no oxide film at the metal-salt interface, which greatly simplifies the delivery of the refining reagent to the impurity and reduces the refining time.

The use of potassium chloride (KCl) -based flux compared to carnallite-based flux (MgCl ₂ • KCl) reduces the tendency to evaporate and decreases the flux hygroscopicity [4] since the level of hygroscopicity of chloride-based fluxes is about 10 times lower compared to fluxes based on carnallite (in addition, the addition of aluminum fluoride reduces the hygroscopicity of potassium chloride). Chloride-based fluxes (NaCl, KCl) have a tendency to evaporate (volatility) 10 times less than carnallite-based fluxes [4, p.137]
It is proposed to use a flux of the composition (by weight) KCl: AlF ₃ = (0.85-0.95): 1. A smaller amount of KCl is impractical to use, since the volatility of the flux (mainly aluminum fluoride) increases, which leads to a decrease in the degree of refining and an increase in refining time. It is also impractical to use a larger amount of KCl, since in this case the melting temperature of the flux increases and solid aggregates (lumps) appear in the salt melt at refining temperatures. The transition of part of the flux to the solid phase reduces the degree of refining and increases the duration of the process.

Justification of the temperature range of the process. The selected refining temperature range (710-740 ^o C) slightly exceeds the melting temperature of the flux. When carrying out the process below 710 ^o With comes the pelletization of flux. This reduces the contact surface of the flux with the metal melt, which reduces the degree of refining and increases the duration of the process. At temperatures above 740 ^o With, the losses of aluminum fluoride in the gas phase sharply increase, which also reduces the degree of refining and increases the duration of the process.

The method was tested under industrial conditions. Refining was carried out in casting ladles with a capacity of 5 tons of aluminum. Liquid A7 grade aluminum or AK120CH grade alloy (previously prepared in the IAT-6 furnace) was poured into the ladle, slag was removed, a flux was applied to the aluminum surface at a temperature of 740 ^o C, after the flux was melted, stirring was carried out for 15 minutes, the melt was kept and removed again slag.

 For comparison, refining was performed according to the basic version. The flux consumption in all experiments (in the base case and in the proposed one) was assumed equal to 2 kg per ton of aluminum.

 The experimental results are shown in the table.

 Analysis of the refining results shown in the table shows that when refining according to the proposed method, in comparison with the base case, the degree of removal of sodium (6%) and calcium (3%) from aluminum increases and the refining time is reduced. TTT1

Claims (1)

A method of refining aluminum from sodium and calcium, including melting aluminum, removing slag from its surface, applying a flux containing potassium chloride and aluminum fluoride to the aluminum surface, melting and mixing the flux, removing slag and casting aluminum, characterized in that the potassium chloride and fluoride aluminum is used in a mass ratio of KCl AlF ₃ (0.85 0.95) 1.

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