HS CODE 28263000
HS CODE 28263000 (Cryolite) is a white or colorless crystalline solid, powder. The sodium hexafluoroaluminate crystalline solid and natural cryolite (A compound found in large quantities in Greenland.) may be colored reddish or brown or even black but loses this discoloration on heating; synthetic product is an amorphous powder. Odorless.
According to the ratio of its sodium fluoride to aluminum fluoride, cryolite can be divided into high molecular weight Cryolite HS CODE 28263000 and low molecular weight Cryolite HS CODE 28263000. Most of the electrolytic aluminum plants use low molecular weight Cryolite HS CODE 28263000 with a molecular ratio of 1.8 to 2.2 as the electrolyte for aluminum electrolysis. Since the use of the high molecular weight is superior to cryogenic Cryolite HS CODE 28263000 in environmental protection and economic benefits, high molecular Cryolite HS CODE 28263000 is commonly used as an electrolyte for aluminum electrolysis in various electrolytic aluminum plants. Cryolite HS CODE 28263000 can be divided into sand-shaped Cryolite HS CODE 28263000, granular Cryolite HS CODE 28263000, and powdered Cryolite HS CODE 28263000 according to its physical properties.
• The characteristics of sand-shaped Cryolite HS CODE 28263000 are:
1. low melting point, fast melting speed, can shorten the time to enter normal working conditions;
2. molecular ratio can be adjusted in a large range, and can adapt to different requirements of the molecular ratio of Cryolite HS CODE 28263000 in different periods of the electrolytic cell;
3. low water content, low fluorine loss;
4. granular, good fluidity, conducive to transportation;
5. raw materials are easy to obtain, and the production cost is low.
• The characteristics of granular Cryolite HS CODE 28263000 are:
1. good fluidity, dust pollution, suitable for mechanized cutting;
2. The high yield in electrolytic production can reduce the cost of electrolytic aluminum;
3. The molecular ratio is between 2.5 and 3.0, which is especially suitable for the opening of electrolytic aluminum.
4. particles are mostly 1 to 10 mm.
• The characteristics of powdered Cryolite HS CODE 28263000 are:
1. can achieve a higher particle size, usually more than 200 mesh;
2. molecular ratio can reach 1.75 ~ 2.5, with good adjustability;
3. ultra-fine products, 325 mesh pass rate of 98% or more, to meet the requirements of Cryolite HS CODE 28263000 in special industries.
2. Industrial quality requirements
Cryolite HS CODE 28263000 is the largest used in the aluminum industry, with an annual consumption of about 700,000 tons in the world. As a flux for electrolytic aluminum smelting, Cryolite HS CODE 28263000 must meet certain requirements in terms of sodium-to-aluminum molecular ratio, impurity content, and water content. First, the ratio of sodium to aluminum in Cryolite HS CODE 28263000 should be as high as possible. The higher the molecular ratio, the higher the current efficiency of electrolytic aluminum smelting, the less the fluorine loss, the smaller the environmental pollution, and the higher the polymer is than the Cryolite HS CODE 28263000. In addition to the use of industries other than the aluminum industry, secondly, the content of impurities such as silicon oxide, iron oxide and phosphorus pentoxide in Cryolite HS CODE 28263000 is low, and the presence of these impurities directly affects the quality of the aluminum ingot and the current efficiency of the aluminum smelting.
Third, the water content of Cryolite should also be as low as possible, and the presence of water will increase the consumption of Cryolite.
3. Synthesis method
The production of Cryolite at home and abroad mainly has the following processes:
Hydrofluoric acid method: The dry method and the wet method are formed by reacting gaseous hydrofluoric acid with aluminum hydroxide at 400 to 700 ° C to form (H3AlF6), which is then reacted with soda ash at a high temperature. The wet method is prepared by reacting 40 to 60% of hydrofluoric acid with aluminum hydroxide and then adding soda ash.
Fluorosilicic acid method: The ammonium fluoride intermediate product and the sodium fluorosilicate intermediate product method can be divided, and the former is formed by reacting fluorosilicic acid with ammonia water and then reacting with sodium aluminate. The latter is obtained by recovering fluorine-containing exhaust gas in the production of phosphate fertilizer by recovering sodium fluorosilicate and then performing ammoniacal synthesis.
Carbonation method: Cryolite can also be obtained by using carbon dioxide in sodium aluminate and sodium fluoride solution. Aluminum industry recycling method: Dilute hydrofluoric acid recovered from the waste gas produced by aluminum production can react with sodium aluminate to recover Cryolite.
Alkali method: Soda ash, fluorite, silica sand are calcined, pulverized, leached and reacted with aluminum sulfate, which is rarely used in the industry.
4. (LOI)Loss of Ignition
LOI is an important test indicator for Na3AlF6. It is a percentage of the amount of ignition loss in the environment of cryolite material 550 ° C / 0.5 h. The Loss of Ignition of Na3AlF6 is a new indicator when the national standard was established in 1999. There is no such thing as the national standard in 1984. With the advancement of society and the development of the aluminum electrolysis industry, the automation level of industrial production and environmental protection have received attention and there is an urgent need to improve the performance of Cryolite as a raw material for aluminum electrolysis. The acrophobic reduction directly affects its use in aluminum electrolysis production. The high Loss of Ignition will cause problems such as hydrotalcite hydrolysis, flying, low material utilization, and aggravation of environmental pollution. The lower the burning, the better the effect. Therefore, reducing the Loss of Ignition is the primary problem to improve the quality of Cryolite products to produce high-quality Cryolite.