Regardless of the technology used, the acidic electrolyte produces complex chemical reactions when the lead is melted. Therefore, the acid of waste lead-acid batteries must be drained before entering the treatment process. After draining, the battery may or may not be broken, depending on the specific recycling process.
Typical lead recovery methods that do not require cell crushing prior to the melting stage include water jacket furnace, reverberatory furnace, electric furnace, and long/short rotary furnaces. Because high-temperature smelting technology can melt raw materials and other substances to form slag, the drained battery can be directly added to the processing process. However, it is best to shred the battery before entering the recycling process for the following reasons:
①Increase lead production and reduce the amount of slag;
② may produce soft lead and lead containing antimony;
③ Possibility of recycling polypropylene;
④ Simplification of furnace fume treatment;
⑤ High temperature smelting technology cannot allow the existence of acidic electrolyte.
In addition, as the battery industry has grown, it has become increasingly difficult to drain lead-sealed batteries and other types of battery electrolyte.
1. Disassembly of the battery
Before 1960, the dismantling of batteries was mainly with the help of axes, because organics were not allowed to enter the furnace during the processing process, and the battery could not be directly added to the furnace. While this situation has now improved in many countries, especially in developed countries, it unfortunately still exists in most developing countries. It must be emphasized that manual dismantling of batteries should be prohibited, not only because of the impact on human health, but also because it is not a suitable method of waste disposal. However, manual dismantling of large industrial batteries still exists in some modern smelting plants, of course partly because these batteries are too large to be replaced by normal appliances. If it is necessary to manually disassemble the battery, proper measures must be taken to protect the health of workers and the ecological environment.
From 1960 to 1970, the dismantling of batteries developed to the use of mechanical guillotine knives or saws, which largely reduced human contact with the crushing process.
Since 1980, most modern smelting plants have used a fully mechanically automated recovery system. In this system, in order to separate the various components of the battery, the battery is broken into small enough pieces.
It is generally believed that the dismantling of waste lead-acid batteries of standardized recycling manufacturers should go through the steps in Figure 1, that is, under the action of disassembly, rolling and gravity, the waste lead-acid batteries are disassembled into waste acid electrolyte, fine particles and electrode paste, metal Granules, bakelite and polypropylene etc.
Figure 1 Dismantling process of waste lead-acid battery
Irregular recycling plants generally use an axe to disassemble lead-acid batteries manually.
2. Battery preconditioning
To minimize human contact with the battery dismantling process, the spent batteries should be transported to the open apparatus by automatic conveyor belts or small vehicles as much as possible. Once the battery is placed in an open machine, a hammer grinder or other breaking tool breaks the battery into pieces. The crushing process ensures that all components in the battery, such as lead plates, connectors, plastic boxes and acidic electrolytes, are easily separated in subsequent steps (Figure 2). After crushing, because lead oxides and sulfates are usually crushed into very fine particles, they are generally separated from other raw materials by sieving, filtration or hydraulic sorting. After separation, these particles are sent directly to the furnace for processing using pyrometallurgical techniques or other processes such as hydrometallurgical smelting. After the first strong crushing, other crushing tools can sometimes be used to further reduce the particle size of the raw materials. The metals in lead-acid batteries mainly include lead plates, grids, connectors and bones, etc.; organic matter mainly includes plastic boxes ( PVC or hard rubber). Polyvinyl chloride separators etc. in organics are separated out in hydraulic sorting due to different densities.
Figure 2 Dismantling process of spent batteries
Other steps include separation of spent battery fragments by density and hydraulic sorting equipment into three parts: the first part is mainly lighter components such as plastics; the second part is mainly particles of lead oxides and sulfates; the third part is also the most The heavy parts are mainly lead plates and connectors. The method requires a filtration step to remove lead compounds mixed in with the plastic before it can be recycled. After the separation step, the organics are further separated into polypropylene waste (called light organics) and separators and hard rubbers called heavy organics. The light organics are then cut into small pieces according to their future use, while the hard rubber and spacers are simply stored. Unless the crushing system is directly connected to the furnace, lead-containing compounds as well as metal parts are stored for further processing in the future.
The specific conditions of the battery disassembly method are different in different processes, and new technologies are often available.
3. Environmental issues during battery disassembly and pretreatment
Various contaminations may exist in lead recycling. Several common situations that affect the environment during the battery disassembly and pretreatment process are: battery leakage, manual battery disassembly, mechanical battery disassembly, hydraulic sorting, and hard rubber fragments.
Source of acidic electrolyte and lead dust pollutants Because electrolyte is not only a strong corrosive solution, but also a carrier of soluble lead and lead particles. Therefore, battery leakage is a very common environmental pollutant and a source of pollution that endangers human health. If this solution spills into an unprotected area, it has the potential to contaminate the soil and injure people. In addition, in unprotected soil, when the spilled solution dries, the soil becomes a source of lead particle contamination. Combined with soil particles, lead may be blown up by the wind or contaminate it through media.
②Manual dismantling of batteries
Endangering human health and the environment through serious spills and lead dust Manual dismantling usually relies on original tools, and both the environment and workers are endangered. For sealed batteries, because it is difficult to break, it will cause leakage and endanger human health.
③Mechanical dismantling of batteries
The source of lead particles During the process of hammer mill crushing and dismantling batteries, lead-containing particles will be generated, but injecting water during hammer mill crushing can prevent the formation of particles.
Leakage of sewage Whether it is the separation of metal and organic matter, or the separation of heavy organic matter and light organic matter, sealed machines and closed water circulation systems are usually used in hydraulic separation. But if there is a leak in the water circulation system, lead compound contamination will be severe.
⑤ Ebony Chips
Contaminated Waste Because the ebonite chips usually contain 5% lead (mass fraction), when these chips are removed and disposed of, appropriate facilities must be designed in advance to control pollution.
The main materials in waste lead-acid batteries are lead, lead compounds, tin, antimony, sulfuric acid, plastics, and rubber, among which lead and lead compounds are the main materials. Batteries are disassembled into metal and plastic, all of which require ventilation systems to protect workers' health.
The waste electrolyte is usually treated by acid neutralization. The metal dissolved in the waste electrolyte can be separated and recovered by precipitation treatment, and the treated electrolyte can be properly discharged. In the waste lead-acid battery recycling technology, sludge treatment is the key. The sludge of waste lead-acid battery is mainly PbSO4, PbO2, PbO, Pb and so on. Among them, PbO2 is the main component, which accounts for 41%-46% and 24%-28% in the positive electrode filler and the mixed filler, respectively.