1. Comparison of wet and pyro recovery technologies
It can be seen from the comparison between the wet method and the fire method of cadmium metal recovery technology that there are many technological methods for realizing wet recovery of cadmium metal and each has its own characteristics. For the selective leaching process, although it has the advantages of simple operation and simple process, it also brings the disadvantages of low product purity and unsatisfactory leaching rate. For the selective precipitation process, although the nickel-cadmium metal separation effect is good, the operation of the process is difficult, and the selected reagents are easier to decompose. Similarly, the process of selective extraction and ion exchange separation of nickel-cadmium metal also has the disadvantages of expensive reagents and high equipment cost in continuous operation. For the emerging biodecomposition method to recover nickel-cadmium batteries, although it has the characteristics of low pollution and simple operation, its process flow and cycle are too long, which is not suitable for large-scale production operations. It can be seen that the wet recycling process has the advantages of relatively complete separation and flexible operation, and is currently a commonly used recycling process in the world.
Compared with the wet process, the pyro process has the advantages of short process flow, complete recovery of cadmium and high product purity. In addition, some pyrotechnic processes can also use other industrial waste materials as recycling raw materials while recovering cadmium metal, reducing costs and obtaining higher commercial value.
From this point of view, the shortcomings of the long cycle and complex pretreatment of the wet process cannot be overcome with a small investment cost in industrial production. The choice of fire method or wet method mainly depends on the conditions and cost of recovery.
2. Development trend of recycling technology of waste nickel-cadmium batteries
The recycling and regeneration technology of waste nickel-cadmium batteries was produced with the industrial production of nickel-cadmium batteries in the early 20th century. At that time, the main application range and usage of nickel-cadmium batteries were small, so until the 1950s and 1960s, the technological development in this area was very slow. The waste nickel-cadmium battery recycling technology is mainly used to recycle the production waste of nickel-cadmium batteries, and the research is limited to the manufacturers of nickel-cadmium batteries. After the 1960s, human's awareness of the environmental hazards of cadmium led to a climax of research and development of waste nickel-cadmium battery recycling technology. A large number of recycling technologies emerged during this period, including wet and fire methods. Since the environmental protection requirements were not strict at that time, the main focus of recycling technology was the recycling rate; and because the production volume of nickel-cadmium batteries was not large at that time, there were very few examples of waste nickel-cadmium battery recycling technology that has achieved industrialization, especially commercialization. After entering the 1980s and 1990s, the production technology of nickel-cadmium batteries has gradually matured, the production volume and application range have expanded unprecedentedly, especially people's concerns about the environment and human health have promoted the rapid development of waste battery management, and also promoted the application of various recycling technologies. The development direction of waste nickel-cadmium battery recycling technology is more economical and environmentally friendly. In recent years, the pyro-recycling process of waste nickel-cadmium batteries has developed rapidly and has become the mainstream of industrial applications.
With the increasingly strict environmental emission standards, the waste nickel-cadmium battery recycling technology is required not only to achieve a high resource recovery rate, but also to avoid secondary pollution during the recycling process. At present, the research focus of waste nickel-cadmium battery recycling technology focuses on process improvement, new technology development, improving recycling rate and reducing waste discharge.