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1. Environmental issues of disposable waste batteries
Chemical substances in waste dry batteries will enter groundwater, soil and atmospheric environment through physical and chemical corrosion during simple storage and various treatment and disposal processes, and eventually enter the human body through the food chain, endangering health.
Waste dry batteries in municipal solid waste mainly come from batteries used in households, schools, factories, companies and government agencies. In China, the sorting and recycling of batteries only accounts for a small part, and most of the batteries are mixed with household waste and landfilled or incinerated.
The following are the two disposal methods of landfill and incineration to explain the ways that waste dry batteries pollute the environment.
(1) Landfill
Due to the lack of economical and effective recycling technology in China, the collected waste dry batteries usually still need to be disposed of in landfills or temporarily stored. There are three ways for landfill disposal: centralized landfill after classification and recycling (intermediate treatment); landfill after incineration; mixed landfill with domestic waste. The negative electrode zinc skin of the dry battery after landfill is an amphoteric metal, which is easy to react with water, as shown in the following equation.
Zn+2H2O→Zn(OH)2+2H2↑
Similarly, a similar reaction occurs with metal casings and metal base plates (iron). After the shell and zinc skin are corroded and perforated for a long time, the leakage of electrolyte and the outflow of heavy metals such as mercury will pollute the soil and groundwater.
In Japan, prior to the centralized landfill treatment of waste dry batteries, pretreatment such as cement curing is usually required to prevent the dissolution and leakage of mercury. After the dry cell is broken, add a curing agent sodium sulfide to form water-insoluble mercury sulfide with mercury. In order to avoid the re-reaction of mercury sulfide and sodium sulfide to form a soluble sodium disulfide complex when the sodium sulfide is excessive, add ferrous sulfate.
The above reaction occurs only when the mercury is in the divalent ion state. Since the mercury in the waste dry battery is mainly atomic metal mercury, it is difficult to generate water-insoluble mercury sulfide simply by adding a curing agent before landfilling. To achieve the desired purpose, processes such as mercury oxidation must be added.
In addition, the zinc and iron contained in the dry cell react with water to generate hydrogen, which expands the cured product and causes cracks or breakage of the cured product. Therefore, the landfill of waste dry batteries makes the landfill site a potential pollution area, which is not conducive to the development and utilization of land resources.
(2) Incineration
After the waste dry battery is incinerated at high temperature in the incinerator, the mercury in the dry battery is vaporized into the flue. Part of the mercury vapor is collected by the dust collector, the other part is absorbed by the exhaust gas wet treatment device, and the remaining part is diffused into the atmosphere. Research studies have shown that waste incineration produces mercury pollution in the atmosphere. Mercury pollution in Asia accounts for about half of the global mercury pollution, and mercury pollution from waste incineration accounts for about one-third of it. Of course, mercury from waste incineration also includes other sources, such as thermometers and fluorescent tubes.
The mercury-containing incineration ash and slag produced by waste dry batteries and other mercury-containing substances after high temperature treatment in incinerators must be disposed of in landfills, thus causing the possibility of soil and groundwater contamination.
2. Environmental impact of disposable waste batteries
If the waste dry batteries are mixed with domestic garbage and landfilled together, the exuded heavy metal substances may penetrate into the soil, pollute the groundwater, and then enter the human, animals and crops. When humans eat these animals and crops, metals will enter the human body and endanger human health. In 1981, a water pollution caused by waste dry batteries occurred in Japan, resulting in serious poisoning of more than a dozen people.
Commonly used disposable batteries such as zinc-manganese batteries, alkaline zinc-manganese batteries, and button-type silver oxide batteries, in addition to a small amount of mercury to the environment, there are also pollution from electrolyte solutions, other heavy metals (zinc, copper, iron, nickel) and manganese dioxide and other substances. However, the degree of impact of waste batteries on the environment should be evaluated objectively. Commonly used dry battery pollutants are mostly solid, and most of the harmful substances are insoluble in the battery or after being abandoned in the environment. The internal migration or diffusion of pollutants into the environment is a very slow process, especially mercury. Therefore, the scope and extent of its contamination is limited. As early as the early 1980s, the Japan Battery Industry Association commissioned Fufeng University to conduct research on the migration law of mercury in waste batteries for 15 years. They used different landfill methods to fill waste zinc-manganese batteries, alkaline zinc-manganese batteries, mercury oxide batteries, etc. in different landfill columns, monitor the mercury content in the leakage liquid and the air in the landfill column and the mercury concentration in the air when the landfill column disintegrates, and conduct a comparative analysis. In 10 years, the amount of mercury that migrated with the leachate in the experimental column only accounted for 0.08%-0.1% of the total mercury, and the amount of mercury diffused through the atmosphere only accounted for 0.05%-0.1% of the total mercury.
Of course, to objectively evaluate the environmental pollution of waste batteries is to better find scientific, economical and feasible ways of disposal and utilization. Due to the scattered use of civilian batteries, the difficulty of recycling and management, the high cost of recycling waste batteries, and the lack of scientific and economical treatment methods, it is more effective to focus on mercury-free civilian primary batteries than direct recycling.
3. Resource value of disposable waste batteries
After the dry battery is used up, part of the zinc powder and manganese powder in the battery will become zinc chloride, manganese trioxide and other substances in the chemical reaction, but they are still precious metal resources. According to China's production level, battery production consumes 250,000 tons of zinc, 240,000 tons of manganese, 4,500 tons of copper, and 60 tons of mercury every year; in addition, there are quite a lot of zinc chloride, graphite, iron, etc.
Primary metal resources are not infinite, and their resources will decrease and become depleted. According to the statistics of the United States Bureau of Mines, according to the estimated reserves of non-ferrous metals in the world, the useful life of zinc is 23 years and that of lead is 21 years. Faced with this severe situation, many countries in the world attach great importance to recovering metals from scrap metal secondary resources to make up for the growing demand for metals. China is a country whose per capita mineral resources are lower than the international average level. With the sustained and rapid economic development, the contradiction between the shortage of resources and the need for development will become more prominent. Accelerate the development of secondary resource recycling industry, including recycling and utilization of resource-rich waste dry batteries, to save and regenerate resources, save energy, construction funds, and reduce the amount of mining of primary resources, to form a virtuous cycle of "production-consumption-regeneration" for precious natural resources, and to maintain the sustainability of resources, which is of great significance to the national economic construction and development.
Due to management and technical reasons, the recovery rate of waste dry batteries in China has not been high. For example, the recovery rate of zinc in many small experiments in research work is generally 70%~80%, and the recovery rate of manganese is 80%~90%. Industrial production recovery rates will likely be lower. At this recovery rate, China still loses a considerable amount of metal every year.