CN1225897A

CN1225897A - Production of high molecular-ration cryolite by sodium-fluorosilicate sodium-aluminate method

Info

Publication number: CN1225897A
Application number: CN 98118202
Authority: CN
Inventors: 李世江; 杨华春; 侯红军; 杨红亮; 李海生; 张富山; 杨晓英
Original assignee: 李世江
Priority date: 1998-08-29
Filing date: 1998-08-29
Publication date: 1999-08-18

Abstract

The new method for production of high-molecular cryolite uses sodium fluorosilicate, industrial ammonia water and sodium aluminate as raw material, at normal temp.a nd normal pressure uses the industrial ammonia water to decompose the sodium fluorosilicate to obtain the fluorosolution, then makes the fluorosolution and sodium aluminate solution react at normal pressure and 90-100 deg.C to form cryolite slurry, and makes the slurry undergo the processes of filtering and drying to obtain the high-molecular cryolite product. Said invention is smooth and stable in reaction process, its raw materials are easily available, its product is favourable for improving aluminium-smelting process, and its by-product is high-quality white carbon black.

Description

Sodium fluosilicate sodium aluminate method for producing cryolite with high molecular ratio

The present invention relates to a new method for producing cryolite with high molecular ratio-sodium fluosilicate-sodium aluminate method, and the cryolite is named sodium fluoroaluminate in chemical name, and its molecular formula is Na₃SiF₆。

The cryolite is natural cryolite and artificial cryolite, which are fluxing agents for aluminum smelting, and the artificial cryolite is mainly used in the aluminum smelting industry worldwide. The traditional process of the artificial cryolite is a soda-aluminum fluoride acid method, and the reaction formula is as follows:

filtering and drying the obtained cryolite slurry to obtain a finished cryolite product, wherein the national quality standard of the product is shown in the table: (GB4291-84)

	F	AL	Na	SiO₂+Fe₂O₃	SO^2- ₄	P₂O₅	H₂O
	F	AL	Na	SiO₂+Fe₂O₃	SO^2- ₄	P₂O₅	H₂O	Grade	Not less than		Not more than				Not more than
Special class	53	13	31	0.25	0.8	0.02	0.5	Grade	Not less than		Not more than				Not more than
Special class	53	13	31	0.25	0.8	0.02	0.5	First stage	53	13	31	0.40	1.2	0.05	0.8
Second stage	53	13	31	0.50	1.5	0.05	1.3	First stage	53	13	31	0.40	1.2	0.05	0.8

The production process has the defects that the used raw materials of aluminum hydroxide and soda ash are very short in China at present, the reaction for synthesizing the fluoroaluminic acid is violent, the operation is not easy to control, and the whole production process is carried out under an acidic condition, the temperature is high, the equipment is seriously corroded, and acidic waste residues are generated to pollute the environment; the raw materials are expensive and the cost is high.

Aiming at the problems, the invention provides a new method for producing cryolite by using sodium fluosilicate and sodium aluminate as raw materials, namely a sodium fluosilicate sodium aluminate method, the raw materials of the method are easy to obtain, the sodium fluosilicate is from a byproduct of phosphate fertilizer industry, the production is easy to control, the three-waste pollution is light, the produced polymer has lower cost than the cryolite, the quality of the cryolite is better, and the industrial utilization value of the byproduct white carbon black is high. The method takes sodium fluosilicate, industrial ammonia water and sodium aluminate solution as raw materials to synthesize cryolite (sodium fluoroaluminate), and the reaction formula is as follows:

(1)

(2)

the production process method comprises the following steps: sodium fluosilicate is prepared by using mother liquor filtered after synthesizing cryoliteAdding industrial ammonia water into 8% suspension at normal temperature and pressure to react to produce fluorine-containing solution, and settling and separating the solution to remove silica gel to obtain mixed solution of sodium fluoride and ammonium fluoride. Mixing the fluorine-containing solution with NaAlO at 90-100 deg.C₂The solution reacts to generate cryolite, and cryolite slurry is obtained; then filtering and drying the cryolite slurry to obtain the finished cryolite product.

In the raw material sodium fluosilicate, Na₂SiF₆The content is more than 98.5 percent. The ammonia content of the industrial ammonia water is more than 17 percent. Na in sodium aluminate solution₂O/Al₂O₃The gram equivalent ratio is less than 0.9.

When the ammonia water is used for decomposing the sodium fluosilicate, the temperature is normal temperature, and the addingamount of the ammonia water is 10-20% of the adding amount of the sodium fluosilicate. The excessive ammonia water is adopted to ensure that the sodium fluosilicate reacts completely, which is beneficial to improving the purity of the byproduct white carbon black, and simultaneously, the price of the sodium fluosilicate is higher than that of the ammonia water, and the excessive ammonia water can reduce the cost.

The synthesis reaction of the cryolite is carried out at the temperature of 90-100 ℃, the raw materials are fluorine-containing solution and sodium aluminate solution, the feeding ratio is 6F: Al =1.0-1.1 (molecular ratio), the fluorine-containing solution and the sodium aluminate solution are simultaneously added into a reaction kettle and react while adding to obtain cryolite slurry, and the synthesis reaction can be carried out discontinuously or continuously. The slurry can be filtered in vacuum, or by various filtering methods such as filter pressing or centrifugal filtration, and the filter cake is dried at the temperature of 150-300 ℃, and the drying can be carried out by airflow drying, or by direct heating or indirect heating drying in a rotary kiln, so as to obtain the finished product of the cryolite with high molecular ratio.

The quality index is as follows;

component (A)	F	Al	Na	SiO₂	Fe₂O₃	SO^2- ₄	P₂O₅	H₂O
component (A)	F	Al	Na	SiO₂	Fe₂O₃	SO^2- ₄	P₂O₅	H₂O	Content (wt.)	53.5	13.2	31.9	0.3	0.01	0.2	0.05	0.43

FIG. 1 is a process flow chart of producing cryolite with high molecular ratio by sodium fluosilicate and sodium aluminate method.

The sodium fluosilicate-sodium aluminate method for producing high-molecular-ratio cryolite is characterized by that it uses sodium fluosilicate and sodium aluminate to substitute the scarce raw materials of aluminium hydroxide, soda ash and fluorite, and can reduce production cost, and its by-product white carbon black also has high economic value, and the main component of ice mother liquor produced by reaction is ammonia water, and can be cyclically used, so that it has obvious economic benefit. The method has simple process and stable reaction, and the whole production process can be carried out under the conditions of normal temperature and normal pressure or not too high temperature, thereby being beneficial to the improvement of labor conditions and the corrosion prevention of equipment. The process has the outstanding advantages that the process solves the problem of utilization of byproducts in the phosphate fertilizer industry and simultaneously protects precious fluorite resources in China. The technological process is carried out under the condition of alkalescence, and mother liquor (main component ammonia water) generated in the technological process can be recycled, so that the production cost is reduced, and the environment is protected. The cryolite produced by the method is used as a fluxing agent, which is beneficial to the improvement of an aluminum smelting process, reduces the cost of the original aluminum, can improve the labor condition and the environmental condition and is unavailable in aluminum smelting. Cryolite is used agriculturally as an insecticide, as an opal agent in the silicate industry for the manufacture of glass and enamel, and the like.

Example (b): (1) ammonolysis: preparing sodium fluosilicate into 8% suspension with circulating ice mother solution, adding industrial ammonia water under continuous stirring for 60min, stirring for 20min, settling for 20min, filtering, and washing the silica gel filter cake with hot water (more than 80 deg.C) for 3 times. And then feeding the silica gel filter cake into a rinsing pool for rinsing for 3 times, and drying and crushing to obtain the white carbon black. (2) Synthesizing cryolite: under the condition of continuously stirring at 90-100 ℃, the fluorine solution and the sodium aluminate solution are added into the reaction kettle from the elevated tank according to the mixture ratio at the same time, and the reaction is carried out while adding, wherein the adding time is not less than 60 min. After the feeding is finished, stirring is continuously carried out for 20min, the reaction is finished, cryolite slurry is obtained, and the synthesis is carried out in a discontinuous mode. (3) The cryolite slurry is vacuum filtered without washing, and the filtrate can be used as diluent for preparing sodium fluosilicate suspension for recycling. (4) The filtrate is at the temperature of 150-300 ℃. Drying with hot air until the water content is below 1% to obtain cryolite product with high molecular ratio.

Claims

1. A process for preparing high-molecular-ratio cryolite (Na-fluoroaluminate) with Na molecular formula₃AlF₆The method is characterized in that:

(1) the raw materials are sodium fluosilicate, industrial ammonia water and sodium aluminate;

(2) preparing sodium fluosilicate into turbid liquid, adding industrial ammonia water for reaction to prepare a mixed solution of sodium fluoride and ammonium fluoride, settling and separating to obtain a fluorine-containing solution as a liquid phase and silicon dioxide as a solid phase, and washing, drying and crushing to obtain the high-quality white carbon black.

(3) Reacting the fluorine solution with the sodium aluminate solution at 90-100 ℃ to generate cryolite, so as to obtain cryolite slurry;

(4) then filtering and drying the cryolite slurry to obtain the finished product of the cryolite with high molecular ratio.

2. The sodium fluorosilicate sodium aluminate process of claim 1 wherein the sodium fluorosilicate contains Na₂SiF₆≥98.5％。

3. The sodium fluorosilicate sodium aluminate process of claim 1, characterized in that the industrial ammonia water contains NH₃Not less than 17 percent (mass percentage)

4. The sodium fluorosilicate sodium aluminate process of claim 1 wherein the sodium fluorosilicate is decomposed with ammonia in an amount of 1.1 to 1.2 times the stoichiometric amount.

5. The fluorine of claim 1The sodium silicate-sodium aluminate method is characterized in that Na in the raw material sodium aluminate solution₂O/Si₂O₃Is less than 0.9.

6. The sodium fluorosilicate sodium aluminate process of claim 1, wherein the temperature of the reaction system during the cryolite synthesis reaction is between 90 ℃ and 100 ℃. The mass ratio of 6F to AL is 1.0-1.1. The pH value of the reaction system is preferably controlled to be 8-12, and indirect or continuous synthesis can be adopted.

7. The sodium fluorosilicate sodium aluminate process of claim 1, wherein the filtering of the cryolite slurry may be by vacuum filtration or by pressure filtration, centrifugal filtration, or other filtration means.

8. The sodium fluorosilicate sodium aluminate method as set forth in claim 1, wherein the drying temperature is 150 ℃ and 300 ℃, and various drying methods such as pneumatic drying or direct heating drying in a rotary kiln can be adopted.

9. The sodium fluorosilicate sodium aluminate process of claim 1 wherein the filtrate from the cryolite slurry filtration is recycled for use in the preparation of the suspension of sodium fluorosilicate.

10. The sodium fluorosilicate sodium aluminate process of claim 1 wherein ammonia gas generated during the cryolite synthesis reaction is recycled for decomposition of sodium fluorosilicate.