Manufacturing Cryolite Products By Utilizing Wastewater Containing Fluorine.

During the aluminum fluoride and other fluorine-containing chemical products, fluorine-containing wastewater is generated through the absorption of tail gas.

To effectively recycle fluorine resources, when the fluorine content in the fluorine-containing wastewater exceeds 0.5%, it can be converted into cryolite products.

Cryolite, also known as sodium hexafluoroaluminate or sodium aluminum fluoride, has a chemical formula of Na3AlF6.

By converting fluorine-containing wastewater into cryolite products, valuable resources can be recovered and put to further use.

Cryolite serves as a flux in the production of electrolytic aluminum, which reduces the melting point of alumina and improves the electrolyte's conductivity.

Under ideal conditions, the production process of electrolytic aluminum does not consume fluorine, but during the electrolysis process, cryolite is electrolyzed or hydrolyzed into fluorine, aluminum, sodium, and other elements, with the fluorine either adsorbed by the electrolytic cell lining material or discharged into the atmosphere.

To compensate for fluorine loss, aluminum fluoride and cryolite are added. The amount of fluorine-containing materials required depends on various factors, including the type of cathode and anode materials, electrolyzer size, alumina raw materials, additives, and electrolyzer service life.

In addition to its use in the production of electrolytic aluminum, cryolite has other applications.

It can serve as a wear-resistant filler for resin grinding wheels, an opacifier and solvent for glass and enamel production, a whitening agent for enamel, and a pesticide for crops.

It is also used in the production of aluminum alloys, iron alloys, and boiling steel.

The production of cryolite (Na3AlF6) uses fluorine-containing wastewater, sodium hydroxide, and aluminum hydroxide as raw materials.

When it is combined with an aluminum fluoride production line, it is capable of achieving zero wastewater discharge.

The collection tank is used to pump the absorption liquid of aluminum fluoride tail gas or other fluorine-containing wastewater.

The solid content and hydrofluoric acid content of the liquid are analyzed and sampled to determine the required dosage of aluminum hydroxide and sodium hydroxide to be added.

The fluorine-containing wastewater is then reacted with either waste aluminum oxide or aluminum hydroxide and sodium hydroxide in the pre-reactor and synthesis reactor to generate cryolite. Cryolite crystals are grown by aging and reacting, and then precipitated. Cryolite solids are separated by centrifuge or vacuum filter to obtain wet cryolite products.

The wet product enters the airflow dryer, where it is dehydrated at high temperature.

After cooling, the cryolite products are packaged and made ready for use.

This process enables the production of cryolite using fluorine-containing wastewater and achieves zero discharge of wastewater when used in combination with an aluminum fluoride production line.

The separated liquid from cryolite production, which makes up the majority (80%), is returned to the tail gas absorption device of aluminum fluoride as absorption water.

A small part (20%) is sent to the Fluorine Wastewater Treatment System at the sewage treatment station.

After treatment, the F- content is lowered to ≤10 ppm to meet the discharge standard.

Otherwise, it goes through a reclaimed water recycling device for further purification and is used as purified water in the production line, replacing tap water, to realize zero wastewater discharge.

The cryolite product is a fine powder that can be utilized as a welding additive, grinding tool, ceramic glaze material, and more.

When used in the electrolytic aluminum industry, pressing equipment is required to turn the powdery product into flake or granular products.