Method of recycling lead-acid batteries separator waste based on purification by solvent and pyrolysis furnace

Abstract

The separator plate of lead-acid batteries is made of polyethylene, DOP oil, and micro-silica, and at present the separators are deposited in nature as waste after separation from worn-out batteries which in turn causes environmental pollution due to the existence of polyethylene, lead, and iron. In this invention, a new method for recycling these wastes based on purification with solvent and pyrolysis furnace is presented, which leads to the production of nanosilica with a purity of over 98%. In the first and second stages of purification using nitric acid, water, citric acid, and salt solvents, the metallic impurities of the separator are reduced from 6-9% to less than 0.2% and in the third stage of purification in the pyrolysis furnace, polymer impurities are separated from micro-silica in the form of soot, and nanosilica is removed from the furnace.

Description

DescriptionTitle of Invention : Method of recycling lead-acid batteries separator waste based on purification by solvent and pyrolysis furnaceTechnical Field

[0001] The technical field of this invention relates to the new process for recycling the wastes and residues of the separator plates from the old and worn-out lead-acid battery based on the purification method using solvent and pyrolysis, which allows the conversion of the lead-acid battery separator waste into nanosilica with a purity of more than 98%.Background Art

[0002] By searching the patents, it was found that Chambers et al in 2017, filed a patent entitled "Batteries, separators, components, and compositions with heavy metal removal capability and related methods". This patent is related to the formulation of PIMS mineral material (containing apatite) as a replacement for silica filler and heavy metals in lead acid battery separators. The purpose of the above invention is to improve the properties of separator plates for installation in lead-acid batteries, while the purpose of the new invention is to recycle the silica contained in waste separators of lead-acid batteries and produce nanosilica with a purity of more than 98%.

[0003] In another invention, Yoo Jong Sun in 2011 , filed a patent entitled "Silica waste recycling method and nanoporous or spherical material preparation method". This invention provides a new method to produce various types of porous nanosilica from silica waste resulting from the production process of nano-porous carbon. In this process, silica waste is first purified by ultrasound or filtration through fine filter paper. In this process, ionic surfactant, amphiphilic, or Pluronic polymer surfactant is utilized. In the new invention, nanosilica is produced from the separator waste of lead-acid batteries, such that two stages of purification are carried out using a solvent, and one stage of purification is carried out using a pyrolysis furnace.

[0004] A patent entitled "Separating and melting system and method for waste lead grid in waste lead acid storage battery recycling" was filed by Yang Chunming in 2022, which it is related to providing a device and method for separating lead from lead-acid batteries. The device components include a dust remover, a flue gas duct, a lead-containing liquid mixer, a lead grid circulation box, a lead grid barrier plate, an ash discharge pipe, an automatic ash collection machine, and a lead ash conveyor, a copper terminal separator, a lead mud tank, a lead mud stirrer, a copper parts collection box, a circulating water treatment device, a melting device, a spiral feeder and a drying drum. In this invention, lead is separated from the liquid waste of acid-lead batteries, while the purpose of the new invention is to provide a method to recycle battery separator waste and produce nanosilica with a purity of more than 98%.Technical Problem

[0005] Lead-acid batteries dominate a major part of the global battery market and have a short service life such that after reaching the end of their life cycle, they wear out and become unusable. These batteries are considered special waste, and because of the high level of poisoning nature and the threat to the health of humans and the environment, the recycling of lead-acid batteries is obligatory. At present, lead plates are recycled again and applied in the production of new batteries.

[0006] Another part of lead-acid batteries is the separator or separator (PE Separator), which is a polymer membrane that is placed between the anode with a positive charge and the cathode with a negative charge to prevent an electrical short circuit. These plates are made of polymer materials that have mesoporous pores and micro silica is usually used to make them (1 ).

[0007] After separation of old and worn-out batteries, separator plates are collected as waste and deposited in the environment. At present, there is no method for recycling these plates, as these plate due to having lead, sulfur, and iron cause environmental pollution. In the past years, ignoring the battery separators and improper disposal has caused environmental pollution on the one hand and the loss of a valuable source of silica on the other hand.

[0008] Separator plates of lead-acid batteries are produced of polyethylene, DOP oil, and micro-silica, which contains 55% of micro-silica. This invention aims to provide a method in order to recycle separator waste of lead-acid batteries, extract separator silica, and produce high-purity nanosilica. In this invention, several phases of the purification process of separator waste using different solvents to separate impurities such as lead, iron, etc. and the pyrolysis process to separate polymer from silica and produce nanosilica have been used. Finally, waste is converted to a valuable material.

[0009] Generally, the major objectives of the present invention are as follows:

[0010] 1. Designing and developing an optimal process for recycling the separator plates waste of lead-acid batteries and disappear environmental problems

[0011] 2. Production of valuable nanosilica products through a cost-effective and safe processSolution to Problem

[0012] As mentioned above, the main issues are the environmental pollution caused by the improper disposal of PE battery separators from lead-acid batteries, as well as the lack of a suitable and cost-effective method to recycle such lead-acid battery wastes.

[0013] In this invention, to solve the environmental issues of lead-acid battery separator waste and also to manufacture a valuable material from the waste, a process based on solvent purification and pyrolysis furnace is presented. The conventional method of producing nanosilica is from the reaction of silicon tetrachloride, SiCI4 with hydrogen and oxygen at high temperatures, which is a very sensitive and dangerous method. However in the new method, for the first time, the risks of conventional methods have been reduced to a great extent, and the process includes the following steps:

[0014] 1) Washing and preparation of raw materials: In this step, to separate impurities and dust from lead-acid battery separators, raw materials are washed inside an industrial bath using water.

[0015] 2) Crushing of raw materials: In this step, to improve the efficiency of the purification process, decrease the surface-area-to-volume ratio, and shorten thetime of separation of metal impurities, the separators are crushed to less than 5 cm using a grinder.

[0016] 3) The first stage of purification: In this stage, the metal impurities in the polyethylene separator, including lead oxides, iron oxides, and calcium oxide, are reduced from 9-6 to 2-3% with the abrasion mechanism. At this stage, the ground plates enter a tank with a mixer, which contains sand and water. In this device, a process similar to the sandblasting process is performed in the presence of water solvent for 1 hour, which reduces the mentioned oxide impurities to about 2-3%.

[0017] 4) The second stage of purification: in this stage, as one of the main stages of recycling separator plates and producing nanosilica, metal impurities including lead oxide, sulfur compounds, manganese, and iron oxides present in polyethylene separator plates from 2-3% is reduced to less than 0.2%. At this stage, first, nitric acid, water, citric acid solvent in a ratio of 1 :2:1 is poured into the tank, and after the solution becomes uniform, the crushed plates are poured into the flat tank and for 4 to 5 hours are stirred inside the tank and these solvents reduce the interaction between metal impurities and the polymer and silica substrate, and on the other hand, by increasing the solubility of these impurities, it separates the impurities from silica and polymer. Subsequently, for selective extraction, salt is added to the flat tank in the amount of 10% of the weight of the solvents, and after 1 hour, the crushed parts are removed from the tank.

[0018] 5) Drying of materials: In this step, continuous dryers are used to dry and decrease the humidity of the crushed plates. Decreasing the humidity of the parts also has a great effect on the efficiency of the pyrolysis furnace and the humidity of the final nanosilica, which is carried out at a temperature of 55 to 70 C for 3 to 5 hours.

[0019] 6) The third stage of purification: This stage is also one of the main stages of separator recycling, in which the polymer is separated from silica and the microsilica in the separator waste is converted into nanosilica. At this stage, the crushed pieces are put inside the pyrolysis furnace and placed under a temperature of 800 to 900 C for 5 hours so that the polymers are burned and separated from the microsilica in the separators in the form of soot, andsimultaneously, the size of the particles is reduced from micro to nanoscale. Subsequently, nitrogen gas and argon gas are injected into the furnace with a ratio of 2:1 to adjust the atmosphere of the furnace, which prevents the sintering and agglomeration process of nanoparticles due to superficial melting and maintains the size of the particles in the nano-scale. After 1 hour of nitrogen and argon gas injection, oxygen gas is blown into the furnace to remove soot and polymer impurities in a controlled manner from inside the furnace, because soot resulting from burning polymer materials inside the furnace react with the nanosilica particles and causes color change and impurity in the produced nanosilica.

[0020] 7) milling: In this step, the materials are ground in a hammer mill and nanosilica is produced with a purity of more than 98%.

[0021] In this process, the separator of lead-acid batteries, which is currently disposed of as unused waste in nature, is converted into a valuable material of nanosilica, which has many applications in various industries, such as rubber, plastic, construction materials, pharmaceuticals, catalysts, fillers in composite materials, etc.

[0022] The most important parameter in the technical specifications of nanosilica is its purity, particle size, and specific surface area, and the most final properties of nanosilica are related to these three parameters and according to the results of analyzes and microscopic images, the nanosilica resulted from this process has a purity of more than 98%, size of 25-30 nm and specific surface area of 100-120 m2 / g.Advantageous Effects of Invention

[0023] The innovations of this invention are as follows:

[0024] One of the innovations of the claimed invention is to provide a new method for recycling separator waste of lead-acid batteries and producing nanosilica with a purity of over 98%, while currently lead-acid battery separators after separation are deposited in nature as unused waste.

[0025] The prior art of nanosilica production is based on the reaction of silicon tetrachloride, SiCI4 with hydrogen and oxygen at a temperature above 1800 C,which is a very sensitive and risky method, but one of the innovations of the new method is the production of nanosilica according to the safe method and it does not require high pressure and temperature.

[0026] Another innovation is to present a purification method with the abrasion mechanism and using sand, which, in combination with water as a solvent, removes the metal impurities of the separator plates and impurities include lead oxides, iron oxides, and calcium oxides. It reduces impurities from 6-9 % to 2-3% so that the simultaneous use of sand as an abrasive method along with the solvent to increase the speed of separation of impurities is one of the innovations of this stage that was not observed in the prior art.

[0027] The other innovation of the new method is presenting a purification process and using nitric acid, water, and citric acid solvents to reduce the metal impurity percentage from 2-3 to below 0.2%, as well as using salt to separate surface impurities.

[0028] Designing the process within the pyrolysis furnace to burn polymer and separate microsilica from polymer impurities and using argon and nitrogen gases to adjust the furnace atmosphere and convert microsilica to nanosilica is another innovation of the new method, while in the prior art high-pressure nitrogen and oxygen is used as a burner fuel to provide the required temperature of 1800 C.

[0029] One of the other innovations of the new invention is the addition of oxygen gas to the pyrolysis furnace to quickly remove soot from the furnace, as the soot resulting from the burning of polymer materials reacts with nanosilica particles and causes color change and impurities in the produced nanosilica and should be taken out of the furnace quickly, while in the prior art, oxygen is used as fuel and to supply the temperature of the burner, which is very dangerous and sensitive.

[0030] The mentioned innovations have led to the following advantages:• Conversion of waste to a valuable and imported material• Reduction of environmental pollution caused by improper disposal of battery separator waste• Production of nanosilica with a purity of more than 98%• Production of nanosilica with particle size of 30-35 nm and specific surface area of 100-120 m2 / g• Lower cost of nanosilica production compared to conventional methods• Production of nanosilica by a safe and secure methodBrief Description of Drawings

[0031] Fig 1 : Illustrates lead-acid battery;

[0032] Fig 2: Production process of nanosilica from lead-acid battery waste;

[0033] Fig 3: Test images;

[0034] Fig 4: IPC-OES analysis sheet.Description of Embodiments

[0035] Figure 1 ) this figure illustrates a schematic of the different parts of the lead- acid battery so that the separator is embedded between the positive and negative plates of a polymer membrane and is placed between the anode with a positive charge and the cathode with a negative charge to prevent electrical short circuit.

[0036] Terminal (1), Fill Cap (2), Strap (3), Negative (4), Separator (5), Positive plate (6), Glass mat (7), Battery enclosure (8), Minimum liquid fill line (9), Maximum liquid fill line (10).

[0037] Figure 2) this figure shows the new production process of nanosilica from lead-acid battery waste. This process involves the stages of washing the plates with water to separate the dust, crushing the plates with a grinder, the first stage of purification using water and sand solvent, second stage of purification by nitric acid solvent, water, citric acid, and salt, the stage of drying plates in a continuous dryer, the process of separating micro-silica from polymer and converting the size of particles from micro to nano scale inside the pyrolysis furnace and finally crushing using a hammer mill.

[0038] Figure 3) In this figure, part a is related to the image of nanosilica extracted from separator plates, part b is related to the FESEM test from the scanning electron microscope, and parts c and d are related to the results of the TEM test,which shows that the size of the extracted silica particles are 25-30 nm, implying that the silica particles are nanoparticles.

[0039] a) Appearance, b) FESEM, c) TEM images, d) TEM images,

[0040] Figure 4) this figure shows the IPC-OES analysis sheet that, as can be seen, the purity of nanosilica produced in this method ranged from 98-99%.

[0041] Table 1 presents the technical specifications of nanosilica extracted from the wastes of lead-acid battery separator plates by the new method.Examples

[0042] To implement this method, first, separator wastes from lead-acid batteries are purchased from battery manufacturing and recycling companies. In the first step, the plates are washed with water to remove dust. Then, using a grinder, the plates are crushed into smaller sizes and poured into a tank with a mixer containing sand and water, so that a percentage of the metal impurities of the separator plates are dissolved in the solvent by combining the dissolvation and abrasion methods. In the next step, the plates are placed into a tank with anothermixer to reduce their metal impurities below 0.2% with nitric acid, water, citric acid, and salt.

[0043] After drying the crushed plates in a continuous dryer, the plates are placed into the pyrolysis furnace to be separated from the polymer at a temperature of 800 to 900 C for 6 hours exposed to argon, nitrogen, and oxygen gases, and the size of the silica particles is reduced from micro to nanoscale and in the last step, nanosilica is converted into powder using a hammer mill and finally, it is packed in 10 kg bags.Industrial Applicability

[0044] Nanosilica produced in this process is used in many fields, including rubber, plastic, construction materials, pharmaceuticals, catalysts, fillers in composite materials, etc. Some of the uses of this product are as follows:

[0045] • Rubber industry: In this industry, nanosilica is used as a filler, which eliminates the environmental problems caused by soot and also improves the physical and mechanical properties of rubber.

[0046] • Cement and concrete industry: The filling properties of nanosilica in the pores of cement paste increase the compressive strength of concrete.Nanosilicas are placed between hydrated calcium silicate gel particles and fill the gel particles due to their high fineness and good adhesion of the particles. This improves the integrity of hydrated calcium gel and increases the durability of concrete.

[0047] • Paint and resin industries: Nanosilica in the three forms of powder, gel, and colloid are utilized in the paint industry as a flatting agent, and concentrator and enhances environmental resistance and wear properties.

[0048] • Plastic industry: They are used as fillers to improve the quality of the surface and increase the strength and dimensional stability of the product.

[0049] • Food industry: It is used as a powder flow enhancer in the food industry.

[0050] • Stone industry: stable nanosilica particles are used to polish stone surfaces and fill voids.

[0051] • Cosmetics industry

[0052] • Thermal and electrical insulation

[0053] • Medicines and cosmetics

[0054] • Pigments and catalysts and batteries

[0055] • Pharmaceutical industry

[0056] • Ceramic Industry

[0057] • Corrosion-resistant coatings

Claims

Claims

1. Process for recycling the separator waste from lead-acid batteries to separate nanosilica which comprising: a. - Washing and preparing and crushing raw materials b. - Two-stage purification c. - Drying and the third stage of purification and millingIn the first stage, after washing the waste separator plates with water and crushing it into less than 5 cm with a grinder, purification, and separation of metal impurities from the crushed separator is carried out using sand and water inside the tank at the same time and then in the second stage, purification and separation of metal impurities from the crushed separator is performed using nitric acid, water, citric acid, and salt solvents inside the tank, and then the crushed plates are dried, and then in the third stage the purification of polymer impurities from the separator and the production of nanosilica is conducted in the pyrolysis furnace in the presence of noble gases argon, nitrogen, oxygen, and finally the nanosilica is crushed and powdered using a hammer mill.

2. The process for recycling the separator waste from lead-acid batteries to separate nanosilica which according to claim 1 , in the first stage of purification, the tank is equipped with a mixer, sand and water solvent, and the crushed plates are stirred inside the tank for 2 hours to remove metal impurities including lead oxides, iron oxides and calcium oxide and reduce them from 6- 9% to 2-3%.

3. The process according to claim 2, in which sand is used as an abrasion mechanism, and the simultaneous use of sand as an abrasion method along with the solubility method increases the speed of separating impurities and dissolving them in the solvent.

4. The process for recycling the separator waste from lead-acid batteries to separate nanosilica which according to claim 1 , in the second stage of purification, nitric acid, water, and citric acid solvent in a ratio of 1 :2:1 arepoured into the tank so that separators plates for 4 to 5 hours are stirred inside the tank and these solvents reduce the interaction between metal impurities and the polymer and silica substrate, and on the other hand, by increasing the solubility of these impurities, it separates the impurities from silica and polymer and metal impurities should be reduced from 2- 3% to less than 0.2%.

5. The process that according to claim 4, in which to separate surface impurities in a selective extraction salt is used, which is added to the flat tank at the rate of 10% of the weight of the solvents, and after 1 hour, the crushed parts are removed from the tank.

6. The process for recycling the separator waste from lead-acid batteries to separate nanosilica which according to claim 1 , in the third stage of purification the crushed pieces are put inside the pyrolysis furnace and exposed to 800 to 900 C for 6 hours in the presence of noble gases argon, nitrogen and oxygen to burn the polymers and separate them as soot from the silica in the separators and simultaneously reduce the size of the silica particles from micro to nanoscale.

7. The process for recycling the separator waste from lead-acid batteries to separate nanosilica which according to claim 1 , in the third stage of purification the crushed pieces are put inside the pyrolysis furnace and exposed to 800 to 900 C for 6 hours in the presence of noble gases argon, nitrogen and oxygen to burn the polymers and separate them as soot from the silica in the separators and simultaneously reduce the size of the silica particles from micro to nanoscale.

8. The process in which according to claim 7, after 5 hours, nitrogen gas is injected into the furnace in a ratio of 2:1 to adjust the atmosphere of the furnace to prevent the sintering process and adhering of nanoparticles to each other due to surface melting and keep the particle size in the nanoscale.

9. The process that according to claims 7 and 8, one hour after nitrogen and argon gas injection, oxygen gas is blown into the furnace to remove sootand polymer impurities from inside the furnace in a controlled manner so that the soot resulting from the burning of polymer materials does not react with silica nanoparticles and does not cause color change and impurity in nanosilica.

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