Technology and development direction of hazardous waste treatment and disposal in China's electrolytic aluminum industry

The electrolytic aluminum industry has a relatively significant role in the social development process. Related research surveys show that there are now 100% metal aluminum processes, but this industry will produce a series of hazardous wastes during the production process. The research investigation shows that there is an average of 30-35kg of waste tank lining for every 1t of aluminum produced, and the soluble F-content in the waste tank lining excluded by China's electrolytic aluminum industry is about 2000mg / L and CN-content is 15mg / L And these wastes can be called hazardous waste. China's emphasis on the treatment of hazardous waste in the electrolytic aluminum industry is increasing. As early as 2007, China has considered the development of the "harmless treatment and comprehensive utilization of electrolytic aluminum solid waste" as one of the more important projects.

Dangerous waste treatment technology of electrolytic aluminum industry in China

1. Flotation-leaching process

This technology belongs to a technology that comprehensively recycles waste SiC-Si3N4 refractory insulation and carbonaceous waste cathode materials. When applying this technology, it mainly uses the flotation process to decompose the recovered carbonaceous material and electrolyte, and combines the two methods of chemical and physical to recycle the silicon carbide powder and electrolyte In practical application, the process steps are mainly grinding → flotation → acid leaching → evaporation.

When this technology is applied, the refractory insulation material will generate corresponding waste liquid during the process after the above steps. If lime water is added, it will generate calcium fluoride, and then it can be filtered and evaporated Eventually it becomes a harmless calcium slag; and the hydrogen fluoride gas generated in this process can be recycled using dry method.

2. Roasting process

This technology is a harmless technology for electrolytic aluminum waste tank lining developed for waste tank lining, including waste cathodes, and is one of China's independent research and development technologies. During the application of this technology, the calcium oxide-containing mineral is mainly used as a reactant, bituminous coal can be used as an external fuel, and the material containing silica is used as an additive; then it is heat-treated. Rotary kiln is mainly used for the treatment, and the tail gas can be adsorbed using alumina; after heat treatment of the material, it can be rinsed with lime water to generate a secondary reaction. Lime water can be recycled in one process. After applying this technology to the treatment of hazardous waste in the electrolytic aluminum industry, the content of soluble cyanide and fluoride in the waste tank lining can be significantly reduced, and the reduction can be greater than 95%, so that solid slag and Flue gas can meet China's emission standards.

Development direction of hazardous waste treatment and disposal technology in electrolytic aluminum industry

Although the above two processes can be technically harmlessly processed in practice, if considering from the perspective of recycling, the flotation-leaching process is more advantageous than the roasting process Therefore, in the future development process, China has more development prospects in the flotation-leaching process.

The main advantages of the roasting process in practical application are as follows: â‘  There is no need to classify and manage the hazardous waste in the electrolytic aluminum industry, and its processing objects are relatively extensive in the application process; â‘¡ After crushing, it can be Combining additives directly into the combustion kiln for roasting, cyanide can also be completely converted under high temperature conditions; â‘¢ In the actual treatment process, it is enough to perform proper purification treatment on the generated exhaust gas; â‘£ The entire operation process is relatively It is simple, and the technology is relatively mature, which is very suitable for promotion and use.

However, this technology also has certain shortcomings in the application process, which are mainly manifested in the following points: â‘ The rotary kiln consumes a lot of energy during use, and the energy utilization efficiency is relatively underground, only about 50%; â‘¡This technology Fluorine-containing waste gas generated in the application process will cause serious corrosion to the equipment; â‘¢In the application process, not only the recovery rate of fluoride is relatively underground, but the carbon in the waste tank lining is used as fuel for combustion and there is no good recycling value .

In the actual application process of the flotation-leaching process, its existing advantages are mainly as follows: in the application process, it has certain pertinence, and can effectively recycle and utilize the waste refractory insulation materials and waste cathode carbon blocks, and When the reagent is used, it will not participate in the reaction during the flotation process, so the flotation pulp can also be recycled during the application process. However, in the practical application of this process, electrolytic aluminum enterprises are required to classify and manage solid waste, and have strict standards and requirements for the two technical nodes of grinding and flotation. Relevant research investigations show that in the process of applying this technology, if the processing object is a waste cathode carbon block, the particle size of its grinding powder must be less than 0.45mm; in addition, in the flotation process, most of it is not a one-time process. If it is completed, it needs to be graded and floated, and there may be some toxic and flammable gases, so there are certain safety risks.

All in all, China ’s research on the treatment of hazardous waste in the electrolytic aluminum industry is still relatively late compared to other countries. However, from the current domestic research status, we can still clearly find that, for now, hazardous waste in the electrolytic aluminum industry In the process of development of processing technology, the wet method has replaced the fire method as the focus of research and is the future development direction. For this aspect of the research, it is mainly to study the flotation technology and chemical leaching technology.