Discussion on recycling treatment process of waste zinc-manganese battery

I. Overview

China's battery industry originated in the 1920s. Today, the annual output of batteries has reached 14 billion, accounting for 1/3 of the world's total battery output. At present, the production of zinc manganese primary battery acid batteries, alkaline manganese batteries, lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries and lithium batteries, manganese batteries wherein 72% of the total battery. Zinc-manganese batteries are mainly made of about ten kinds of raw materials such as zinc, manganese, mercury , copper , iron , plastic and carbon.

According to the estimated raw materials consumption per 10,000 zinc-manganese batteries, the annual output of 10 billion zinc-manganese batteries is about to consume zinc, manganese dioxide, copper, ammonium chloride, zinc chloride, potassium hydroxide and carbon rods. 1, 6, 0, 0.14, 6, 2, 2, more than 30,000 tons, in addition to a considerable amount of mercury. However, since there is no waste recycling factory for zinc-manganese batteries in China, the discarded batteries are discarded at random, or long-term stacking is difficult to find a way out, or

Directly carrying out landfills, resulting in a lot of valuable resources wasted. From the perspective of environmental protection, manganese batteries, lead-acid batteries and nickel-cadmium batteries contain lead, mercury, cadmium and other metals, free to dispose of physical and mental health of the people can cause great harm. Therefore, the safety management of used batteries has attracted the attention of the government and the society. In Beijing, Shanghai and other places, activities have been carried out to recycle used batteries, and a large number of batteries have been collected, although safe landfill is also an effective method for safe disposal. Means, but due to the high cost of final disposal and the waste of a large amount of resources, the large amount of used batteries collected at present is simply stacked in the warehouse, and has not changed the current situation of waste batteries polluting the environment, so the construction of special waste zinc-manganese battery recycling The factory is imminent. This paper introduces the technology and treatment effect of the "baking-electrolysis" process for the treatment of waste zinc-manganese batteries, in order to obtain a magnified production test.

Second, the process, methods and results

(1) Process

The recycling of waste zinc-manganese batteries mainly solves two problems, firstly the recovery of metallic mercury and other useful substances, followed by the treatment of waste gas, waste liquid and waste residue. After many times of comparative experiments, we proposed a “roasting electrolysis” recycling process (see Figure 1), which mainly includes roasting, liquid refining, electrolysis, and waste gas and waste residue treatment.

Figure 1 shows the process of "baking-electrolysis"

(2) Test methods

Since mercury metal is mainly present on the paste paper and zinc cylinder, in order to facilitate the evaporation of mercury vapor, the waste zinc-manganese battery is first mechanically cut, and the carbon rod, copper cap and plastic are sorted to make the internal powder and zinc of the battery. The tube is fully exposed, and the carbon rod, copper cap, and plastic are recycled. The unrecovered components were sent to a closed roaster, and the air was calcined at 600 ° C for 3 h (the thermogravimetric analysis showed that the reaction was completed at 600 ° C). At this time, the manganese dioxide in the battery has been uniformly mixed with acetylene black, and is reduced to manganese monoxide during calcination, which is convenient for leaching with sulfuric acid (manganese dioxide must be dissolved with concentrated sulfuric acid and carbon powder at a temperature of 383 K) . The tail gas produced by roasting contains mercury, wax, ammonium chloride and ammonia. After being discharged from the roaster, it passes through the condensing tank, and most of the mercury vapor is coagulated and recovered. The tail gas enters the spray tank and is sprayed with water (pH=6) to absorb ammonia. Gas, ammonium chloride and wax. The spray water is recycled. When the ammonium chloride reaches saturation, the activated carbon is added to adsorb the residual mercury metal, and after filtering, the filtrate is evaporated to prepare ammonium chloride crystals. The residual exhaust gas is finally discharged through the bubble column purifier, and the filtered mercury concentration is 3-5 μg/m ³ , which can fully meet the national atmospheric emission standards.

The calcined material is cooled under air-tight conditions to prevent re-oxidation of manganese monoxide. After cooling, the iron is removed by magnetic separation, washed with water, filtered (to obtain filtrate 1) to remove chloride ions, and filtrate 1 is obtained by recrystallization. Manganese chloride and zinc chloride. The generated filter residue l is first dissolved in sulfuric acid, and then filtered to obtain filtrate 2 (mixed liquid of manganese sulfate and zinc sulfate), and finally the residue (filter residue 2) is solidified (after several times of high temperature and pickling treatment, the residue 2 is no longer Harmful Substance). A mixed liquid of manganese sulfate and zinc sulfate (filtrate 2) is electrolyzed in the same electrolytic cell, manganese dioxide is obtained at the electrolytic anode, metal zinc is obtained by the cathode, and the electrolyte can be reused.

(3) Test results

The recycling process can completely recover the mercury metal in the waste zinc-manganese battery, and the exhaust gas and waste residue can be fully treated to fully meet the emission standards. The test results are shown in Tables 1-3.

Table 1 Comparison of mercury content before and after roasting (mg/kg)

Table 2 Comparison of metal content before and after water leaching of zinc-manganese battery after roasting (%)

Table 3 Comparison of metal content before and after leaching of filter residue 1 by sulfuric acid (mg/L)

Third, feasibility analysis

Using the PGA51 thermogravimetric analyzer produced by DuPont of the United States, we conducted a thermogravimetric analysis on the cut and sorted waste zinc-manganese battery. It was found that the temperature of the material from room temperature to 600 °C was fast F-fall, 600~ The material quality is basically unchanged between 760 °C, and the material quality is decreased between 760 and 810 °C. This indicates that the mercury metal, ammonium chloride and the like are completely evaporated in the material before 600 °C (mercury boiling point 356.57 ° C, ammonium chloride boiling point 520 °C), the reduction reaction was completed, and the material quality decreased near 800 ° C because of the evaporation of zinc chloride (zinc chloride boiling point 756 ° C). Therefore, we set the calcination temperature at 600 °C, and used the muffle furnace to expand the humanity experiment, and achieved good results. The mercury content of the baked powder after calcination fell below 15 mg/L, and the removal rate reached over 97%. It shows that in industrial production, the material is subjected to cycle roasting, and the mercury metal content can reach the standard. The calcined material is magnetically etched, immersed in water, and dissolved in sulfuric acid, leaving only about 10% of the residue, mainly re-oxidized divalent manganese and some impurities, which can be placed in the roasting furnace for roasting, and finally the residue is solidified. , can achieve the requirements of harmless. The mixture of zinc sulfate and manganese sulfate is electrolyzed in the same electrolytic cell, and the manganese dioxide obtained by the electrolytic anode meets the national standard for secondary electrolytic manganese dioxide, and the discharge performance far exceeds that of natural manganese dioxide. Currently, China's alkaline The zinc-manganese battery industry is developing rapidly, and the demand for electrolytic manganese dioxide is very large. This is a driving force for the construction of waste zinc-manganese battery back to the animal husbandry factory; the zinc quality obtained by the electrolytic cathode meets the national third-grade zinc standard and meets the light industry. The requirements for zinc cakes used in the Ministry of Zinc. Therefore, it is feasible to recycle and treat the waste zinc-manganese battery by this process.

From an economic point of view, the benefits are also quite rich. Assuming that 30% of zinc-manganese batteries, or 3 billion, can be recycled each year, electrolytic manganese dioxide, zinc, ammonium chloride and zinc chloride can be recovered separately for 4, 3, 1.5, and 0.6 million tons, in addition to a large number. The necessary raw materials for the production of batteries such as carbon rods, copper caps, iron sheets and waxes.

Fourth, the conclusion

Under laboratory conditions, the "baking-electrolysis" process can recover the mercury metal in the waste zinc-manganese battery, and the exhaust gas and waste residue can be treated to meet the emission standards, which is of great help to solve the problem of battery pollution. Therefore, the above-mentioned recycling process is worthy of expanding the productivity test to turn the laboratory results into productivity, and actually apply it to the recycling process of waste zinc-manganese batteries.

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