CN1456507A

CN1456507A - Method for producing cryolite

Info

Publication number: CN1456507A
Application number: CN 02115819
Authority: CN
Inventors: 杨华春; 李世江; 李海生; 皇甫根利; 李克平; 侯红军; 张富山
Original assignee: DUOFUDUO CHEMICAL INDUSTRY Co Ltd JIAOZUO CITY
Current assignee: Duo Fluoride Chemicals Co Ltd
Priority date: 2002-05-10
Filing date: 2002-05-10
Publication date: 2003-11-19
Anticipated expiration: 2022-05-10
Also published as: CN1194897C

Abstract

A process for preparing cryolite includes such steps as reacting between ammonium fluoroaluminate and sodium carbonate in water plase at 90-100 deg.C, filtering, and drying at 150-300 deg.C. The gas generated by reaction can be absorbed to obtain by-product. Its advantages are simple process and no environmental pollution.

Description

Method for producing cryolite

Technical Field

The present invention relates to a method for producing cryolite, which can use ammonium fluoroaluminate which is waste residue obtained by treating the surface of an aluminum profile as a raw material.

Background

The cryolite is named as sodium fluoroaluminate in chemical name and has the molecular formula of Na₃AlF₆. It is natural and man-made, mainly used as a cosolvent in aluminium smelting in industry, as an opal agent in the silicate industry for making glass and enamel, and as an insecticide in agriculture. The aluminum industry in the world uses predominantly synthetic cryolite. The traditional production process of the artificial cryolite is a soda ash-fluoaluminic acid method, hydrofluoric acid and aluminum hydroxide are firstly reacted to generate fluoaluminic acid, then the fluoaluminic acid and soda ash are reacted to generate the cryolite, and the chemical reaction formula is as follows:

filtering and drying the obtained cryolite slurry to obtain a finished product. The process has the disadvantages that: (1) the method has the advantages of more process steps, more required equipment, higher requirements on equipment (acid resistance and high temperature resistance) and large equipment investment; (2) the reaction for synthesizing the fluoaluminic acid is violent, the operation is not easy to control, and the tank-caused injury accident is easy to occur; (3) the whole production process is carried out under a strong acid condition, the equipment is seriously corroded, and acid waste residues are generated to pollute the environment; (4) the raw materials are high in price and high in cost.

Disclosure of Invention

The invention aims to provide a method for producing cryolite, which has simple process and is easy to control.

In order to achieve the purpose, the invention adopts the following technical scheme: a process for preparing cryolite features that ammonium fluoroaluminate and sodium carbonate are used as raw materials and reacted in aqueous phase at 90-100 deg.C.

The molar ratio of the ammonium fluoroaluminate to the soda ash is 2: 3.

The concentration of the ammonium fluoroaluminate water-added slurry is 15-30%, the concentration of the soda aqueous solution is 15-30%, and the soda aqueous solution is continuously added into the ammonium fluoroaluminate slurry for reaction in the production process.

The ammonium fluoroaluminate is taken from the surface treatment waste residue of the aluminum profile; the cryolite slurry generated by the reaction is subjected to vacuum filtration, pressure filtration or centrifugal filtration and then is heated and dried by hot gas flow at the temperature of150 ℃ and 300 ℃ or a rotary kiln to obtain a finished product; the gas generated in the reaction is absorbed by an absorption system to obtain a byproduct.

The chemical reaction formula of the method is as follows:

the method has the advantages of one-step reaction, less required equipment, no special requirement on equipment, less equipment investment and low production cost; the reaction condition is mild, the operation and the control are easy, and the production safety is high; the gas generated in the reaction process is absorbed by an absorption system: if the ammonium carbonate solution is absorbed by water, the ammonium carbonate solid fertilizer can be obtained; such as ammonium fluoride or ammonium bifluoride solution by absorption with hydrofluoric acid. The production process has no three-waste discharge and is suitable for environmental protection requirements. Because the method can adopt the waste residue of aluminum profile surface treatment, namely the ammonium fluoroaluminate, as a raw material (the purity is more than or equal to 98 percent, and if the purity is low, the purity and the quality of the product are directly influenced), the waste is changed into valuable, the production cost can be greatly reduced, and the cost of the method is reduced by about 40 percent compared with that of the traditional process. Cryolite molecular ratio (NaF/AlF) produced by the method₃) 2.81, the product quality reaches the special grade standard of the national standard (GB/T4291-1999), and the chemical components are compared with the national standard and are shown in the table 1.

TABLE 1 comparison of the products of the invention with the national standard

Product(s)	Chemical composition (%)
	Chemical composition (%)										Not less than		Not more than
	F	Al	Na	SiO₂	Fe₂O₃	SO₄ ^2-	CaO	P₂O₅	H₂O	Reduced burning at 550 deg.C	Not less than		Not more than
	F	Al	Na	SiO₂	Fe₂O₃	SO₄ ^2-	CaO	P₂O₅	H₂O	Reduced burning at 550 deg.C	Special class	53	13	32	0.25	0.05	0.7	0.10	0.02	0.4	2.5
First stage	53	13	32	0.36	0.08	1.2	0.15	0.03	0.5	3.0	Special class	53	13	32	0.25	0.05	0.7	0.10	0.02	0.4	2.5
First stage	53	13	32	0.36	0.08	1.2	0.15	0.03	0.5	3.0	Second stage	53	13	32	0.40	0.10	1.3	0.20	0.03	0.8	3.0
The invention	53.87	13.09	31.33	0.141	0.034		0.05			1.55	Second stage	53	13	32	0.40	0.10	1.3	0.20	0.03	0.8	3.0

Drawings

FIG. 1 is a schematic view of the process of the present invention.

Detailed Description

Example 1, a method of producing cryolite, comprising the steps of: (1) preparing a sodium carbonate aqueous solution, and preparing the sodium carbonate solution with the sodium carbonate content of 20% by using deionized water or circulating mother liquor in the reaction process; (2) synthesizing cryolite, namely adding deionized water or partial mother liquor into a synthesis tank, adding aluminum profile surface treatment waste residue-ammonium fluoroaluminate (purity 98%) under continuous stirring to enable the concentration of the ammonium fluoroaluminate to reach 20%, then opening a steam valve, introducing steam to enable the temperature of the ammonium fluoroaluminate to rise to 90 ℃, slowly adding a sodium carbonate solution into the synthesis tank from a metering tank for reaction, wherein the feeding time is 40 minutes, the molar ratio of the ammonium fluoroaluminate to the sodium carbonate is 2: 3, and obtaining cryolite slurry after the reaction is finished; (3) filtering the cryolite slurry with a horizontal spiral centrifuge to obtain an ointment (with a water content of below 40%); (4) drying the ointment at150 deg.C with flash evaporation drier until the water content is below 1%, to obtain cryolite product, and its chemical component analysis is shown in Table 1. Carbon dioxide and oxygen generated in the reaction process are absorbed by water to obtain ammonium bicarbonate solution.

Example 2 in this example, the soda ash concentration was 15%, the ammonium fluoroaluminate concentration was 15%, the cryolite synthesis reaction temperature was 95 ℃, the addition time was 50 minutes, and the ointment drying temperature was 200 ℃. The rest is the same as example 1.

Example 3 in this example, soda concentration 25%, ammonium fluoroaluminate concentration 25%, cryolite synthesis reaction temperature 95 ℃, addition time 45 minutes, and ointment drying temperature 300 ℃. The rest is the same as example 1.

Claims

1. The present invention features that ammonium fluoroaluminate and sodium carbonate are reacted in water phase at 90-100 deg.c.

2. The process according to claim 1, wherein the molar ratio of ammonium fluoroaluminate to soda ash is 2: 3.

3. The method as claimed in claim 1 or 2, wherein the ammonium fluoroaluminate slurry is added with water at a concentration of 15 to 30% and the aqueous soda solution is added at a concentration of 15 to 30%, and the aqueous soda solution is continuously added to the ammonium fluoroaluminate slurry during the production process to carry out the reaction.

4. The method according to claim 3, wherein the ammonium fluoroaluminate is obtained from surface treatment waste of the aluminum profile; the cryolite slurry generated by the reaction is subjected to vacuum filtration, pressure filtration or centrifugal filtration and then is heated and dried by hot gas flow at the temperature of 150 ℃ and 300 ℃ or a rotary kiln to obtain a finished product; the gas generated in the reaction is absorbed by an absorption system to obtain a byproduct.