The comprehensive treatment technology of mixing waste button batteries with other waste batteries mainly adopts a modular treatment method, that is, all batteries are first subjected to pretreatment such as crushing and screening, and then all batteries are sorted by category. The treatment technologies for mixed waste batteries are not the same, there are mainly three methods of pyrometallurgy, hydrometallurgy and mixed pyrometallurgy and hydrometallurgy.
At present, Switzerland, Japan, Sweden, the United States and other countries mainly use pyrometallurgy technology. Pyrometallurgical treatment of waste dry batteries is a process of oxidation, reduction, decomposition, volatilization and condensation of metals and their compounds in waste dry batteries at high temperatures. Fire method is divided into atmospheric metallurgy and vacuum metallurgy.
All operations of atmospheric metallurgy are carried out in the atmosphere; while vacuum metallurgy is carried out in a closed negative pressure environment. Most experts agree that the fire method is the best way to dispose of spent dry batteries and is the most efficient for mercury disposal and recycling.
(1) Atmospheric pressure metallurgy. At present, there are two main traditional atmospheric pressure metallurgy methods for the treatment of waste batteries: one is to heat the waste dry battery at a lower temperature, first to volatilize the mercury, and then to recover zinc and other heavy metals at a higher temperature; the second is to roast the waste battery at high temperature to volatilize the volatile metals and their oxides, and the residue is used as an intermediate product of metallurgy or treated separately.
When using a shaft furnace to treat waste dry batteries, the furnace is divided into three parts: an oxide layer, a reduction layer and a melting layer, which are heated with coke. Mercury is volatilized in the oxide layer, zinc is reduced and volatilized in the high-temperature reduction layer, and then recovered in different condensers respectively; most of the iron and manganese are reduced to manganese-iron alloy in the molten layer.
The Batrec waste battery treatment plant in Switzerland uses atmospheric pressure metallurgy treatment technology. Batrec Waste Battery Treatment Plant is located in the tourist area of Switzerland. It has been in operation since 1992. The annual processing capacity of waste batteries is 3000t. Currently, the annual processing capacity is 1500~2000t, and the processing cost is about 4750 Swiss francs/t. It mainly handles mercury-containing waste dry batteries (including mercury-containing button batteries), and now it can also handle other types of batteries, such as nickel-cadmium batteries, lithium-ion batteries, etc. In this process, the waste batteries do not need to be pretreated, and are directly put into the pyrolysis shaft furnace, and the organic matter in the waste batteries is pyrolyzed at 300-700 ℃. The pyrolyzed battery is sent to a melting furnace with a temperature of up to 1500 ℃, and metals such as Fe and Mn are melted, and the metal Zn is volatilized into vapor, and the vaporized metal Zn is condensed and recovered by a jet condenser, the molten manganese and iron form a ferromanganese alloy. Through this process, 95% of the metals or metal compounds in the spent batteries are recycled and regenerated, and the remaining slag after treatment is harmless to the environment. The recovered products are mainly mercury, zinc nuggets, and iron-manganese alloys. The advantage of this process is that waste batteries do not need pretreatment such as crushing and screening, the process flow is simple, and the pollution of waste batteries is greatly reduced after treatment. However, because the waste battery treatment is carried out at high temperature, the energy consumption is high, and the processing cost is as high as 4,000 US dollars per ton of waste battery; the melting furnace temperature is as high as 1500℃, and the refractory material requirements of the furnace body are high; in order to prevent secondary pollution, the requirements for waste water and waste gas treatment equipment are also very high. Therefore, the equipment investment cost is high, and the incineration substrate after the waste battery treatment needs to be landfilled.
Toita and Masaguki et al. used a method of heating waste batteries in an oxidation furnace to vaporize mercury and organic matter. The gas from the oxidation furnace is burned in the incinerator to completely decompose the recorded compounds and organic matter to generate elemental mercury and carbon dioxide. The battery treated in the oxidation furnace is heated at a high temperature in a melting furnace, and the low melting point zinc and its compounds are evaporated and then condensed in the condenser. The purity of the regenerated zinc is over 99.6%. After evaporating zinc, an alloy containing 37% manganese and 56% iron is obtained. This method is more thorough in removing mercury, and the purity of the regenerated zinc is also higher. The disadvantage is that the operating requirements are relatively strict, and iron should be added in a timely and appropriate amount, otherwise the ferromanganese alloy that meets the requirements will not be formed.
Japan's TDK Corporation and Nomura Xing Corporation have made great improvements to the regeneration process of waste dry batteries, that is, they no longer recycle individual metals, but instead recycle them as magnetic materials. Since the iron-coated oxygen raw materials used in color TVs and transformers are very close to the main components of dry batteries, the waste batteries are pulverized, heated at high temperature to remove impurities, and then oxidized to metal elements, and the product is the raw material for the production of iron oxide. The process simplifies the separation process, greatly reduces the cost of recycling resources, and has high added value and good sales of the product iron oxide. The method has a good development prospect.
(2) Vacuum metallurgy. Since all the operations of atmospheric metallurgy processing waste dry batteries are carried out in the atmosphere, air is involved in the operation, which has the disadvantages of long process, heavy pollution, consumption of energy and raw materials, and high production cost. Therefore, the emergence of the vacuum method makes up for these deficiencies.
The vacuum method is based on the fact that the components of the waste dry battery have different vapor pressures at the same temperature, and are separated from each other at different temperatures through evaporation and condensation in a vacuum, thereby realizing comprehensive recycling. During evaporation, components with high vapor pressure enter the vapor, and components with low vapor pressure remain in the residue or residue. When condensing, the vapor condenses into a liquid or solid at a lower temperature.
The German Alte company heats the waste battery after sorting out the nickel-cadmium battery in a vacuum, the mercury in it is quickly evaporated and recovered, and then the remaining raw materials are ground, and the iron is recovered by the magnetic separation method, and then extract zinc and manganese. With these methods, the mercury in the battery can be completely removed, thereby eliminating the harm of mercury.
Shigeo Mitsui and others heated the used waste dry batteries in a vacuum with a pressure of 200mmHg (26664Pa) at a temperature of about 300℃ for 2 hours, the mercury volatilized into the flue gas, the flue gas was condensed to recover mercury and remove dust, and the mercury in the residue is 1/5000~1/2000 of the original content, thus eliminating the harm to the environment.
Although there is still a lack of economic indicators for vacuum treatment of waste dry batteries, from the energy consumption per ton of refined zinc in the crude zinc refining process [Fire method (6~10)×106kJ; electrolysis method 3000~3500kW·h, namely (10.8~12.6)×106kJ; vacuum method not more than 1000kW·h, namely 3.6×106kJ], it can be indirectly seen that the energy consumption of the vacuum method must be lower than that of other methods, so its cost must be low.
The vacuum method has a short process, less pollution to the environment, and a high comprehensive utilization rate of various useful components. It has great advantages and is worthy of extensive promotion.
Hydrometallurgy is mainly based on the principle that zinc and manganese dioxide in waste batteries are soluble in acid, so that zinc and manganese dioxide in zinc-manganese batteries interact with acid to form soluble salts and enter the solution. After purification, the solution is electrolyzed to produce zinc and manganese dioxide or chemical products such as lithopone and zinc oxide fertilizer. The methods used are roasting leaching method and direct leaching method.
(1) Roasting and leaching method. The roasting and leaching method is to mechanically cut the waste battery, sort out carbon rods, copper caps, and plastics, and fully expose the internal powder and zinc cylinder of the battery (conducive to the volatilization of mercury vapor). Then under the condition of 600 ℃, roasting in a vacuum roasting furnace for 6~10 hours, so that metal mercury, NH4CI, etc. are volatilized into gas phase, which is recovered by condensation equipment. The exhaust gas must be strictly treated to minimize the mercury content; after grinding, the roasted product is subjected to magnetic separation and sieving to obtain iron sheets and zinc particles with higher purity. The sieved material is leached with acid (The high-valent manganese oxide in the battery is reduced to low-valent manganese oxide during the roasting process, which is easily soluble in acid), and then metal zinc and manganese dioxide are recovered from the leaching solution by electrolysis.
The method of Fuji Electric Corporation of Japan is as follows: after crushing the waste battery, remove the metal shell and zinc cylinder, pass the air in the furnace at 400~1000℃, calcinate for 3~20h, and burn the combustible material; the calcined product is subjected to magnetic separation after grinding, and the product with iron content of 75% is selected; the powder under the sieve contains 32.6% Mn, 28.1% Zn, Fe, Cu, Ni, Cd and other impurities, which are dissolved with 20% hydrochloric acid, and then adjusted to pH 5 with ammonia water, iron is removed, and filtered after precipitation. The clarified solution was adjusted to pH=9 with 28% ammonia water, and 130g/L of MnO2 with a particle size of 4~10μm was added. When the pH value was 9.0, manganese was precipitated in the form of Mn2O3. This method has complicated process and high recovery cost, but can directly obtain crude iron and crude zinc, which is worth learning from.
The method of Nimara et al. is as follows: after the zinc-containing battery is treated with H2SO4, air is introduced to remove impurities under alkaline conditions, and the pH value is controlled to 7.5~8.0; add (NH4)2CO3 to precipitate basic zinc carbonate, and then calcine the precipitate at 600~800 ℃ to obtain ZnO with a purity of 99%. The recovery rate of zinc obtained by this method is 98%. The raw material consumption of this method is large, the cost is high, and it is not widely used. Its biggest feature is that high-purity ZnO can be obtained.
Hiroshi Ouchi roasts the waste battery to remove mercury from the residue (containing 30%~60% zinc, 23%~30% manganese) when the pH value is 1.0 with H2SO4 leaching the zinc and manganese in it, and then 95.4% of Zn was precipitated as ZnS with NaHS, and a very small amount of Mn was co-precipitated with Zn. This precipitate can be used as a raw material for metallurgy. The disadvantage of this method is that sulfur is introduced into the solution, and a large amount of waste water will be generated, so corresponding environmental protection measures need to be taken.
In 1984, Nomura Corporation successfully developed a complete set of experimental equipment for the recycling of mercury-containing wastes in Hokkaido, and in 1985, a 6000t/a recycling equipment was built. The industrial process is as follows: the dry cell is heated to 600~800℃ in a rotary furnace, the mercury is vaporized and then sent to a condenser to condense into powder, which is recovered and distilled into a finished mercury product with a purity of 99.9%. For metals such as zinc, manganese, potassium and iron contained in the slag from the rotary kiln, the zinc, potassium, iron and manganese are first separated from iron and manganese by a magnetic separator and then used as secondary raw materials respectively.
(2) Direct leaching method. The direct leaching method is a method of crushing, sieving and washing the waste dry batteries, and then taking appropriate measures to separate and purify the metals and their compounds, according to the nature of the metals and their compounds in the waste batteries being easily soluble in acid or salt.
The key link of the leaching method is the liquid leaching and the post-treatment of the leaching solution, which directly affect the recovery rate of various substances in the waste battery and the cost of the product. The liquids used for leaching are mostly acids (HCl, H2SO4, HNO3) and ammonium salts [(NH4)2CO3, (NH4)2SO4], and the treatment methods of the leaching solutions are also different.
1999 Japanese patent report: The waste battery is crushed and sieved. The fine slag under the sieve is leached with hydrochloric acid, and the small zinc flakes obtained during the sieving are continuously added during the leaching process to promote the dissolution of the manganese compound. The obtained leaching solution is filtered, and the filtrate is firstly removed from impurities such as Fe2+, SO42-, and then concentrated. The concentrated solution is oxidized by adding HClO4 to obtain a mixture of MnO2 and ZnCl2. The mixture was diluted with water and filtered to separate the water-insoluble MnO2 precipitate and the water-soluble ZnCl2. Wash the precipitate to get MnO2 fine product. After the filtrate is evaporated, ZnCl can be obtained as crude product, which is dissolved with alcohol or ketone, and after removing insoluble impurities, the organic solvent is distilled out to obtain ZnCl fine product. The method has low energy consumption, low cost and high purity of the obtained product.
A method reported in a Japanese patent is: leaching and filtering the waste battery with hydrochloric acid, then adding iron powder, on the one hand, reducing the mercury to remove the mercury; The pH value is adjusted to 10.0 by adding alkali, and oxidized with KCIO3 to obtain manganese-zinc ferrite with no mercury and excellent magnetic properties. The process of separating mercury by this method is relatively simple and has strong practicability, and the target product manganese-zinc ferrite powder can be directly used to manufacture magnetic heads, transformers and the like.
In 2000, the process of full wet acid leaching of waste batteries designed by Su Yongqing and others is as follows: after the shell is broken, the spent battery is successively leached with an acid solution with different acidity for three times and treated with the leaching solution, and then electrolyzed to obtain zinc with a purity of more than 98% and MnO2 with a content of 99.9%, and at the same time can also obtain available battery raw material carbon rods and other metals. The characteristic of this method is that it adopts three times of acid leaching process. During the process, the zinc excess is always maintained, so that the metal (such as mercury, iron, etc.) which is inactive than zinc in the acid leaching solution is replaced, and the zinc concentration in the acid leaching solution is gradually increased. This method has no three waste pollution and has strong practicability; but when there are many impurities, the electrolysis efficiency is low, and the cost of removing these impurities is high.
In 1999, Rabah et al. studied in detail the effects of leaching time, temperature, pH value and liquid-solid ratio on the leaching rate during the acid leaching process, and concluded that the ideal conditions for the treatment of waste batteries by acid leaching are: the leaching temperature was 30℃, the leaching time was 60 min, the pH value was 4.0, and the liquid-solid ratio was 35.
There is also a method of using lye as the leachate. Hexi Dazhi and others removed the shell of the waste battery, dissolved it in an alkaline (NH4)2CO3 solution containing 80~300g/L of NH4+ and 80~140g/L of CO32-, and oxidized it to form manganese oxide (Mn2O3, MnO2) precipitate. MnO can be obtained by heat-treating the above-mentioned precipitation at a temperature of 900-1000 ℃. ZnCl2 can be obtained by adding hydrochloric acid after removing manganese from the solution, and ZnO can be obtained by heating and calcining ZnCl2 at 800℃.
The "wet treatment" device in the suburbs of Magdeburg, Germany, uses sulfuric acid to dissolve various types of batteries other than lead storage batteries, and then uses ionic resin to extract various metals from the solution. The raw material obtained in this way is purer than the heat treatment method, so it is more expensive in the market, and 95% of the various substances contained in the battery can be extracted. Wet processing eliminates sorting (which increases costs because sorting is manual). The annual processing capacity of this device in Magdeburg can reach 7,500 tons. Although its cost is slightly higher than that of landfill methods, the precious raw materials will not be discarded and will not pollute the environment.
3. Pyro-hydrometallurgical hybrid treatment
The main metals in the waste batteries have significantly different boiling points, so the metals to be separated can be vaporized by accurately heating the waste batteries to a certain temperature, and then the gas can be collected for cooling. Metals with higher boiling points are recovered in the molten state at higher temperatures.
The boiling points of cadmium and mercury are relatively low, the boiling point of cadmium is 765 ℃; while mercury is only 357 ℃, so they can be separated and recovered by pyrometallurgical technology. Mercury is usually recovered by pyrometallurgy, followed by hydrometallurgical recovery of the remaining metal mixture. Among them, iron and nickel are generally recovered as iron-nickel alloys.
The Swiss Recytec company uses a combination of fire and wet methods to treat mixed waste batteries that are not sorted and recover various heavy metals respectively. First, the mixed waste batteries were heat-treated under negative pressure conditions of 600~650 ℃. The waste gas from the heat treatment is condensed to convert most of its components into condensate. The condensate is centrifuged into three parts, water containing ammonium chloride, liquid organic waste, and mercury and cadmium. The wastewater is replaced with aluminum powder to remove the trace mercury and then discharged.
The solid material remaining after the heat treatment is firstly crushed, and then washed with water at a temperature ranging from room temperature to 50° C., so that the manganese oxide forms a suspension in water; at the same time, the lithium salt, sodium salt and potassium salt are dissolved. The wash water is precipitated to remove manganese oxide (which contains trace amounts of zinc, graphite and iron) and then evaporated to partially recover the alkali metal salts. The wastewater is treated in other processes, and the remaining solids are recovered by magnetic separation. The final remaining solids go into a process system known as the "RecytecTM Electrochemical System and Solution". These solids are the metal-rich fraction of mixed waste batteries, mainly zinc, copper, cadmium, nickel, and silver, with trace amounts of iron. In this system, electrolytic deposition is carried out using aerobic acid. Different metals are recovered using different electrodeposition methods, each with its own operating parameters. The acid is recycled throughout the system, and the sediment is treated electrochemically to remove manganese oxide from it.
In this process, no secondary waste is generated during the entire treatment process, water and acid can achieve closed-circuit circulation, and 95% of the waste battery components can be recovered, but the recycling cost of this process is also high.
Judging from the mixed treatment process of these waste batteries, generally speaking, the hydrometallurgical process is long, and the waste gas, waste liquid, and waste residue are difficult to treat. The hydrometallurgical recycling method is gradually reducing the use. Pyrometallurgy and combined wet and pyrometallurgical treatment are the best directions for the mixed treatment of waste button batteries and other batteries.