Review of Methods of Waste Lining Processing from Aluminum Electrolyzers

摘要

The spent lining (SL) of aluminum electrolyzers contains significant amounts of carbon, refractories, fluorides. In addition, in the SLcontains metals, nitrides, carbides, hydroxides, carbonates, and free cyanides and iron cyanides. The presence of cyanide refers the SL to toxic wastes, warehousing and storage of which is possible only in specially engineered landfills, in compliance with the precautionary measures to prevent ingress of cyanide and fluoride in the environment, including in water bodies. However, construction of specialized polygons requires significant capital costs, which in turn is an incentive to develop the technical solutions and technologies for the disposal and recycling of the SL, and a list of components, which can be returned to production, makes the development perspectives of these technologies economically attractive. SL processing technology developed IrNRTU can be implemented on existing shops equipment of fluoride salts production of aluminum smelters or on alumina production equipment or the equipment of chemical - metallurgical plants. SL technique involves its grinding, leaching with aqueous solutions of reagents of alkaline and acid nature, separation of liquid and solid phases of the pulp, the solution processing with releasing of fluoride product. Grinding and leaching are carried out in explosion-proof equipment. When grinding in an aqueous medium it is maintained at a pH of 6-8 and the temperature to 60°C, then the pulp is processed by caustic alkali solution at a temperature of 80-100 °C for 4-10 hours and the pH is maintained at 10-12. After phase separation solution treatment is carried out with an acids or salts. SL is grounded to a particle size of 50-200 microns. The solution processing may be carried out by aluminum sulfate in the presence of (or - without any) sulfuric acid, hydrofluoric acid or washing waters after purifying gases, containing fluorine, water. The developed in IRNRTU technology enables the SL treatment to produce high quality demanded product - cryolite with reduced sodium content and the possibility of the solid phase recycling onto energy products.