RU1775363C - Method for processing sodium silicon fluoride - Google Patents

Abstract

Usage: waste processing to obtain silicon-aluminum alloys. SUMMARY OF THE INVENTION: stoichiometric amounts of sodium silicofluoride and alumina are mixed, a reagent layer of 50-100 mm thick is placed on the crust of a working aluminum electrolyzer, an alumina layer of 70-150 mm thick is poured on top, the interactions are performed for at least 3 hours and the reaction products are immersed in electrolyte with continued electrolysis. 1 ill., 3 tablets

Description

The invention relates to the processing of sodium silicofluoride, as well as to the electrometallurgy of aluminum and the production of its alloys with silicon. The invention is related to the urgent problem of developing a non-waste technology of fluorine-containing products. Currently, such products in large quantities accumulate in dumps, because their processing methods are complex and environmentally friendly.

Currently, cryolite is prepared according to a method based on the interaction of solutions of aluminum fluoride and sodium fluoride, which are obtained from hydrofluoric acid by treating it with aluminum hydroxide and soda. Moreover, the quality of cryolite is inferior to the best foreign samples.

The closest in technical essence is a method in which with the aim

b /

more complete extraction of fluorine due to its double binding in the form of metal fluorides, sodium silicofluoride is processed in several stages:

a step of heating sodium silicofluoride to obtain sodium fluoride and tetrafluorosilane according to the reaction:

Na2 SiF6 2NaF + SIF4 (1)

and catching the latter:

passing tetrafluorosilane through alumina, obtaining metal fluoride

SiF / i + At203 AIF3 + SI02 (2)

product separation by reaction (2) due to sublimation followed by condensation of aluminum fluoride

A1F3 TV sublimation. A1 Far condensation. Rz then

(3)

It is proposed to use NaF and A1P3 processing products as cheaper components of the charge for electrolytic aluminum production. The authors propose reaction (1) to be carried out at a temperature not lower than 500 ° C.

For the 1st stage of the processes under consideration, obviously, complex technological equipment will be required.

The purpose of the invention is to reduce energy costs, simplify the process and ensure environmental cleanliness of the process due to the possibility of processing sodium silicofluoride in an existing and working device (aluminum electrolysis cell) using, which is not intended to achieve the goal, but which is released in the electrolyzer partially for losses in environment. Ensuring environmental cleanliness is achieved due to the possibility of double bonding of fluorine-containing products (chemical interaction in the mixture layer and adsorption - in the protective layer),

A stoichiometric mixture of sodium silicofluoride and alumina is poured onto the crust of the aluminum electrolyte electrolyte layer with a thickness of 50-100 mm, a layer of alumina 70-150 mm thick is poured over it, kept for several hours, after which, breaking the casing, the reaction products are immersed in the electrolyte,

The proposed method is based on the reaction

. 3Na2SiF6 + 2Al203 6NaF + 4A F3 + 3Si02 (4) This reaction occurs in a layer of a mixture of the starting components at temperatures of the order of 500 ° C. In this case, not the thermal decomposition product of sodium silicofluoride, as in the prototype, interacts with alumina, but sodium silicofluoride itself. The products of this interaction are immersed in the electrolyte melt, the fluorine salts of aluminum and sodium being the usual components of the cryolite-alumina melt, and the silicon goes to the cathode metal. With this processing method, the separation of silica and aluminum fluoride is avoided by laborious sublimation and condensation operations. The processing product is aluminum-silicon alloys widely used in industry. When conducting a patent search, no solutions were identified, which included the same set of features that distinguishes the solutions we offer. All the features inherent in the solution are organically involved in achieving the objective of the invention: for the processing of sodium cremofluoride, a well-functioning aluminum electrolysis mechanism is used, all the more so.

that some Siberian aluminum smelters are now experiencing difficulties with raw materials.

The implementation of the solution does not entail the need to develop and create apparatuses for the described stages (reactions 1-3), maintaining certain technological modes in them (temperature, pressure), which is inevitable

0 is associated with energy consumption, ensuring the tightness of apparatuses and communications, the use of their apparatus (electrolyzers) and the utilization of their heat allow us to talk about a reduction in material and energy costs. The products of reaction (4) are solid-phase, pollution of the atmosphere of the workshop, air near the plant is excluded. The presence of a protective layer of alumina reliably seals the reaction zone so that even in the case of decomposition of sodium cremofluoride gaseous tetrafluorosilane is formed by reaction (1), it will be bound in the protective layer with oxide (reaction (2). The environmental cleanliness is determined by the method itself process implementation.

To implement the method, we propose using a typical electrolytic cell for producing aluminum. To the electrolyte crust

0 available for normally working

electrolyzer, fill in a layer of stoichio.met. a mixture of sodium silicofluoride and

alumina. Oxide protective layer

aluminum over the reaction layer is necessary for sealing and warming the reaction layer. A bulk layer of alumina (omini actively adsorbs possible gaseous products, therefore it is necessary to have a thickness of about 10 cm. When the crust collapses, gaseous products will also be collected in the gas collection system.

Filling the layer of the reaction mixture can be arranged along the longitudinal sides of the electrolyzer, where the technological operation of punching the crust is periodically performed, as well as along the transverse sides of the electrolyzer. In the latter case, the technologically necessary crust punching operation and the proposed operation

0 sublimation of the electrolyte with reaction products (4) can be divided. As a result, it is possible to more accurately control the composition of aluminum-silicon alloy according to the silicon content and to obtain alloys in

5 a wide range of its contents (from low to high silicon).

The processing of sodium silicofluoride may be batchwise, in one bath, in several baths, or batchwise. When implementing the method, it becomes necessary to prepare a stoichiometric mixture of sodium cremofluoride and alumina. It can be made using known methods for mixing noupou-shaped materials. The mixture can be used in the introduction of automatic alumina (APG) electrolysis systems at the plants. The drawing shows a schematic section of an aluminum electrolyzer. The cell consists of anode 1. immersed in molten electrolyte 5, and a cathode casing lined with hearth 3 and side 4 carbon-graphite blocks. The cathode product - an alloy of aluminum and silicon - is located on the bottom 2 under a layer of electrolyte. Garnissage 6, additionally insulating the side lining, and the crust of the frozen electrolyte 7 over the working space are technologically necessary. An additional layer of a mixture of sodium silicofluoride with alumina 8 is proposed to be placed on the formed hardened crust, sprinkled on top of an alumina layer 9 for sealing and warming. PRI me R. In a C 8-BM electrolyzer with an anode width of 2800 mm and an overhead current supply, when alumina is again filled, instead of alumina, a stoichiometric mixture of sodium silicofluoride with alumina in the amount of 10 kg is filled with a 50 mm thick layer along the longitudinal sides of the bath instead of alumina. Mass ratio of components in the mixture, kg Na2SiF6 7.3; A120s 2.7. A protective layer of alumina with a thickness of 100 mm is poured over the reaction layer, after which this bath continues to operate in the usual technological mode at 950–960 ° С and, when the crust is pierced again after 3.3 hours, 3.3 KrNaF, 4.4 kgA1Rzi2.3 kg of Si02 and the product are immersed electrolysis is a low silicon alloy of aluminum. Examples for other thicknesses of the reaction mixture layer (hi) with the same thickness of the protective layer (h2) of 0.1 m and a time of 3 hours are presented in Table 1. In the table. Figure 2 shows the amount of reaction mixture (mi) that provides the required layer thickness over an area of 2.5 m. An area of 2.5 m is taken for reasons that the mixture will be poured onto the crust of the electrolyte between the anode and the side wall (this is a distance of about 0.5 m) over a length of 5 m on one side of a conventional electrolyzer with an upper S8-BM type TOKOPODODOD. A suitable range of the thickness of the reaction mixture is within the range of 0.05-0.1 m. The lower limit is determined by the fact that irrationally small amounts of the reaction mixture must be used, and the upper limit by the fact that the bath will be supersaturated with silicon (). Because in the claims, it is assumed that the thickness of the protective layer (h2) of alumina varies from 0.07 m to 0.15 m, we show the advisability of choosing this range for a time of 3 hours on the same area 2.5 m after calculating the amount of alumina in the protective layer (t 2), providing backfilling of the layer of the required thickness (Table 2). In order to bind all the fluorine introduced into the reaction mixture with a thickness of 0.07 m, 424 kg of A1203 are required. and the minimum thickness of the reaction sgr of 0.05 m requires filling in the area under consideration of 320 kg AI203. This indicates a reasonable range of 350-750 kg of A1203 and a layer thickness of 0.07-0.15 m, respectively. The maximum value of the protective layer is 0.15 m with an average reaction layer of 0.07 m that provides an excess of ABO3 and is evidence of the possibility of complete binding of fluorine, which guarantees the ecological purity of the process specified in the purpose of the invention. Achieving the objective of the invention to reduce material costs shows a small calculation. To produce 1 ton of aluminum, about 72 kg of cryolite and fluorosols are required. The use of sodium silicofluoride, which gives these electrolyte components, will additionally produce a certain amount of aluminum (Table 3). The possibility of obtaining additional metal through the use of sodium silicofluoride for various thicknesses of the reaction mixture layer is shown in Table 5. Achieving the objective of the invention to reduce energy costs illustrates an example. For the production of 1 ton of silumin, about 140 kWh of power is consumed, and 1 ton of aluminum more than 110 kWh, i.e. production of 1 ton of silumin, and an aluminum electrolyzer will save 140 kWh of electricity. Thus, the method allows to process a product (sodium fluorosilicate), which is currently going to dumps, using existing technological equipment, to obtain the alloys needed in the domestic economy. The transshipment process is environmentally friendly, energy and resource efficient.

Claims (1)

The claims A method of processing sodium cremofluoride, comprising reacting cremnefluors containing a substance with alumina). when heated, characterized in that, in order to reduce energy consumption, simplify the process and improve its environmental friendliness. a mixture of stoichiometric amounts of sodium silicofluoride and aluminum oxide is fed into the interaction, the interaction is carried out for at least three hours in a reagent layer 50-100 mm thick having a coating of a 70-150 mm thick aluminum oxide layer, the process being carried out on a working aluminum electrolyte crust the cell and the reaction products are immersed in the electrolyte while continuing the electrolysis. Table 1 table 2 Table 3