Aluminum separation and recovery method for aluminum-containing metal-plastic composite materials

Abstract

This invention provides a method for separating and recovering aluminum from aluminum-containing metal-plastic composite materials, comprising: a preparation step of preparing a 20-40 wt% formic acid solution; a dissolution step of contacting the aluminum-containing metal-plastic composite material with the formic acid solution to dissolve the aluminum metal component in the composite material and generate aluminum formate, the chemical reaction of which is shown below; and a recovery step of recovering the generated aluminum formate from the formic acid solution. The method of this invention treats the composite material with a formic acid solution under specific operating conditions, causing the aluminum metal in the material to separate from the plastic component. The aluminum metal is dissolved and forms aluminum formate, which can then be recovered and reused by centrifugation or filtration. Furthermore, the formic acid solution used does not damage the plastic component, thus allowing for the recovery of the plastic component as well.

Description

Technical Field

[0001] This invention relates to a method for separating and recovering aluminum from aluminum-containing metal-plastic composite materials, which can separately recover the aluminum metal component and the plastic component in the aluminum-containing metal-plastic composite materials. Prior Technology

[0002] With the development of the chemical industry, since the development of plastics in the 1850s, plastic products have been increasingly widely used for various purposes. However, due to the limitations of plastics in terms of performance (such as insufficient strength and poor heat resistance), composite materials that combine plastics with other materials have been gradually developed to meet various application requirements.

[0003] Aluminum is a common component in various plastic components and packaging materials on the market. Due to its ease of processing, it can be combined with other plastic materials through plating or processing in sheet form. Furthermore, aluminum possesses excellent barrier properties (effectively blocking gases and light), is lightweight (density of only 2.7 g / cm³), has high strength, and good high / low temperature resistance, which can enhance product performance when combined with plastic materials.

[0004] However, when aluminum is combined with other materials to form composite materials, the recycling of aluminum and other components becomes more difficult. Unlike traditional single-material plastic products, these composites are not suitable for traditional plastic recycling processes. Furthermore, the metallic components are difficult to remove and recycle due to being encapsulated by the plastic components, which reduces their recycling value. Because of the difficulty in recycling these composite materials, they can mostly only be disposed of through incineration or landfill. However, both of these methods may produce toxic gases or cause environmental problems that are difficult to decompose, resulting in a waste of resources.

[0005] On the other hand, traditional aluminum recycling mainly focuses on processing pure aluminum components to recover materials with high aluminum content. However, this process usually requires high-temperature decomposition of impurities outside the metal, so the recycled product is mainly aluminum metal, and plastics or other components cannot be recovered. This results in excessively high processing costs, low recycling value, and waste of resources.

[0006] Moreover, the aluminum content in aluminum-plastic composites is usually low, and they may contain various types of plastics or other components. This makes the waste generated from these composites mostly non-recyclable and usually needs to be treated as general waste or converted into energy through thermal treatment.

[0007] However, in the above-mentioned treatment methods, the various plastic and metal components in aluminum-plastic composite materials do not actually return to the resource recycling cycle, and therefore are not ideal treatment methods. In particular, aluminum-plastic packaging materials often have a short service life, which in the long run not only wastes resources but also causes environmental and pollution problems.

[0008] Therefore, it is necessary to develop a recycling technology for aluminum-containing metal-plastic composite materials that can solve the above problems. Summary of the Invention

[0009] In view of this, the present invention aims to provide a recycling technology that can simultaneously recycle aluminum metal and plastic materials in aluminum-containing metal-plastic composite materials, and satisfies the requirements of low processing cost, high product recycling value, resource reuse, and avoidance of environmental problems.

[0010] To achieve the aforementioned objectives, the present invention provides a method for aluminum separation and recycling of aluminum-containing metal-plastic composite materials, comprising: Preparation steps: Prepare a 20 to 40 wt% formic acid solution; The dissolution step involves contacting the aluminum-containing metal-plastic composite material with a formic acid solution to dissolve the aluminum metal component in the composite material and generate aluminum formate. The chemical reaction is as follows: 2Al + 6HCOOH → 2Al(HCOO)3 + 3H2↑; and The recovery step involves recovering the aluminum formate generated from the formic acid solution.

[0011] According to one embodiment of the present invention, the pH value of the formic acid solution is between about 0.74 and 0.1.

[0012] According to one embodiment of the present invention, the formic acid solution has a formic acid concentration of 25 to 35 wt% and a pH value between 0.59 and 0.27.

[0013] According to one embodiment of the present invention, in the dissolution step, the formic acid solution is brought into contact with the aluminum-containing metal-plastic composite material at a temperature between 70 and 100 degrees Celsius.

[0014] According to one embodiment of the present invention, in the dissolution step, the mixture of the aluminum-containing metal plastic composite material and the formic acid solution is stirred or shaken.

[0015] According to one embodiment of the present invention, in the dissolution step, the pH value of the formic acid solution is monitored, and when the pH value is higher than 0.74, formic acid is added to the formic acid solution to control the pH value of the formic acid solution in the range of about 0.74 to 0.1.

[0016] According to one embodiment of the present invention, in the dissolution step, an aluminum-containing metal plastic composite material is continuously added to the formic acid solution so that the aluminum metal component therein continuously dissolves and generates aluminum formate, thereby saturating the formic acid solution with aluminum formate and causing it to precipitate; and in the recovery step, the precipitated aluminum formate is recovered from the formic acid solution.

[0017] According to one embodiment of the present invention, in the dissolution step, additional aluminum metal is further added to the formic acid solution to dissolve the additional aluminum metal and generate aluminum formate, thereby saturating the formic acid solution with aluminum formate and causing it to precipitate; and in the recovery step, the precipitated aluminum formate is recovered from the formic acid solution.

[0018] According to one embodiment of the present invention, in this recovery step, the precipitated aluminum formate is recovered from the formic acid solution by centrifugation or filtration.

[0019] According to one embodiment of the present invention, the supernatant or filtrate obtained after recovering the precipitated aluminum formate in the recovery step is used as the formic acid solution in the preparation step.

[0020] The advantages of this invention are that, compared with traditional recycling methods, the method of this invention operates at a lower temperature, which can reduce energy consumption during the recycling process, and the reaction process is simple, without the generation of complex or highly toxic substances.

[0021] In particular, the method of the present invention can not only recycle aluminum metal in the form of aluminum formate, but also recycle plastic components without generating other waste, and can achieve the best recycling effect for aluminum-plastic composite materials.

[0022] Furthermore, the method of the present invention can process various common plastic components, including PET, Nylon, PE, PP or PVE, and has a wide range of applications. Simple Explanation of the Diagram

[0023] Figure 1 shows a flowchart of the aluminum separation and recycling method of the aluminum-containing metal-plastic composite material of the present invention; Figure 2 shows the curve of pH value of formic acid solution as a function of formic acid concentration; Figure 3 shows a comparison of the dissolution efficiency of aluminum metal by formic acid solutions of different concentrations; Figures 4 and 5 show the recycling and treatment effectiveness of various aluminum-plastic composite materials; and Figure 6 shows the appearance of aluminum formate recovered by the method of the present invention. Implementation

[0024] In view of the above problems, this invention develops a recycling process for such aluminum-containing metal composite products. This process utilizes formic acid solution under specific operating conditions to dissolve the aluminum metal in the aluminum-plastic composite material, separating it from other components for aluminum recovery. The dissolved aluminum metal will form aluminum formate precipitate in the solution, which can then be recovered and reused through centrifugation or filtration.

[0025] In particular, the formic acid solution used in the recycling process will not dissolve or otherwise affect the plastic components in the aluminum-plastic composite material, so the plastic materials in the aluminum-plastic composite material can also be recycled and reused.

[0026] The technology of this invention relates to recycled materials including various aluminum-containing plastic packaging materials or plastic materials containing aluminum metal components. The recycling effect of this invention is not limited by the processing method of aluminum-plastic composite materials. Whether aluminum is combined with other materials through electroplating, vapor deposition, bonding, hot pressing or other processing methods, it does not affect the aluminum recycling effect of this invention.

[0027] Referring to Figure 1, the present invention provides a method for aluminum separation and recycling of aluminum-containing metal-plastic composite materials, comprising: a preparation step S1, a dissolution step S2, and a recycling step S3.

[0028] First, in preparation step S1, prepare a 20 to 40 wt% formic acid (HCOOH) solution. At this concentration, the pH value of the formic acid solution is between approximately 0.74 and 0.1.

[0029] The above concentration range represents the conditions under which formic acid solution can effectively dissolve aluminum metal. For example, the formic acid concentration of the formic acid solution can be 20wt%, 22.5wt%, 25wt%, 27.5wt%, 30wt%, 32.5wt%, 35wt%, 37.5wt%, or 40wt%. At these concentrations, the pH values ​​of the formic acid solution are approximately 0.74, 0.67, 0.59, 0.51, 0.43, 0.35, 0.27, 0.19, or 0.1, respectively.

[0030] The best dissolution effect was achieved when the formic acid concentration was 25 to 35 wt%, at which the pH value of the formic acid solution was between 0.59 and 0.27.

[0031] The solvent used to dilute formic acid in the formic acid solution can be water or other solvents miscible with formic acid. Since the operating temperature of the formic acid solution of this invention is between 70 and 100 degrees Celsius, considering operational feasibility and safety, the aforementioned solvents miscible with formic acid may include, for example, solvents with boiling points higher than 70 degrees Celsius such as ethanol, ethylene glycol, propanol, isopropanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and acetic acid.

[0032] Preferably, the formic acid solution can be an aqueous formic acid solution.

[0033] Unless otherwise specified, the formic acid solution mentioned in this specification can be any solution prepared from formic acid and water.

[0034] Subsequently, in the dissolution step S2, the aluminum-containing metal-plastic composite material (hereinafter referred to as aluminum-plastic composite material) is brought into contact with formic acid solution so that the aluminum metal component in the aluminum-plastic composite material dissolves and generates aluminum formate.

[0035] In this invention, the aluminum metal component is dissolved by reacting formic acid with aluminum-plastic composite material. One of the main recovered products in the reaction process is aluminum formate, which is a form of aluminum recovery. The above chemical reaction is as follows: 2Al + 6HCOOH → 2Al(HCOO)3 + 3H2↑ [Reaction 1]

[0036] The reason why formic acid can dissolve aluminum metal in aluminum-plastic composites but not other components is due to the selective chemical reaction of formic acid with aluminum metal. Formic acid is a mild weak acid that can react with aluminum metal to produce a soluble product, namely aluminum formate. Other components in aluminum-plastic composites (such as plastics) are usually polymers, which have high chemical stability to acids and therefore will not react with formic acid.

[0037] Although aluminum can be gradually dissolved by contacting formic acid with aluminum-plastic composite material at room temperature, the optimal aluminum dissolution temperature in the operation of the method of the present invention can be between 70 and 100 degrees Celsius. That is, in the dissolution step S2, the temperature of the formic acid solution can be controlled within this range so that the formic acid solution can contact the aluminum-plastic composite material at this temperature range, thereby achieving the best dissolution effect.

[0038] Since formic acid has a boiling point of 100.8 degrees Celsius, operating within a temperature range below this boiling point and above 70 degrees Celsius can balance dissolution efficiency and operational safety.

[0039] In the dissolution step S2, the formic acid solution can be brought into contact with the aluminum-plastic composite material at a temperature of 70, 75, 80, 85, 90, 95, or 100 degrees Celsius to dissolve the aluminum metal more effectively.

[0040] In the dissolution step S2, in order to ensure that the formic acid solution and the aluminum-plastic composite material can react uniformly, the mixture of the aluminum-plastic composite material and the formic acid solution can be stirred or shaken to promote the reaction between formic acid and aluminum metal, thereby improving the effect of dissolving aluminum metal in the aluminum-plastic composite material and separating it from the plastic components.

[0041] Besides temperature, the concentration of formic acid in the formic acid solution is also a key factor affecting the dissolution efficiency of aluminum. When the formic acid concentration is too low, aluminum cannot be effectively dissolved to form aluminum formate; while when the formic acid concentration is too high, a dense oxide layer (Al₂O₃) will form on the aluminum surface, preventing further reaction between the internal aluminum and formic acid. Therefore, when the formic acid concentration reaches 50 wt% or higher, the dissolution efficiency of aluminum becomes extremely poor.

[0042] That is, the concentration of formic acid that can effectively dissolve aluminum metal falls between 20 and 40 wt%.

[0043] On the other hand, since the process of generating aluminum formate consumes formic acid in the solution, as the concentration of formic acid decreases, the pH value of the formic acid solution will gradually increase. When the pH value reaches above 2.2 (i.e., the formic acid concentration is below 20 wt%), the formic acid content in the solution can no longer dissolve aluminum metal.

[0044] Therefore, in order to maintain the solution at its optimal solubility during the recovery process, a pH meter can be used to monitor the pH changes of the formic acid solution and forcibly replenish the solution as needed to maintain the solubility efficiency.

[0045] Although the concentration of formic acid can be detected at any time during the operation, for example through titration, spectroscopy (visible light / UV / IR / NIR), chromatography (GL / HPLC), electrochemical methods, or enzymatic reactions, these detection methods all require waiting time or even additional pretreatment, and therefore cannot monitor the concentration of formic acid in real time.

[0046] Therefore, in order to monitor the concentration of formic acid in real time, using pH value as an indicator of formic acid concentration is a more efficient way, because compared with directly detecting the concentration, indirectly inferring the concentration by detecting the pH value with a pH meter can produce detection results more immediately.

[0047] Experimental tests showed that the pH value of formic acid solution with a concentration between 10 and 50 wt% exhibited a stable linear trend, thus allowing for accurate estimation of the formic acid concentration in the solution based on the pH value.

[0048] For example, when the pH value of a formic acid solution is higher than 0.74, it can be estimated from the linear trend of formic acid concentration and pH value (as shown in Figure 2) that the formic acid concentration is lower than 20 wt%. At this point, it is no longer effective in dissolving aluminum metal. Therefore, formic acid can be added to the formic acid solution to control the pH value of the formic acid solution in the range of about 0.74 to 0.1, and better maintained at around 0.6.

[0049] Subsequently, in the recovery step S3, aluminum formate generated in the dissolution step S2 is recovered from the formic acid solution.

[0050] In aluminum-plastic composites, aluminum metal does not immediately precipitate after dissolving in formic acid solution and forming aluminum formate. This is because aluminum formate is a soluble salt in formic acid solution, and it cannot precipitate before reaching saturation.

[0051] To separate and collect aluminum metal in the form of aluminum formate, the formic acid solution containing aluminum formate can be evaporated and crystallized or cooled and crystallized to allow aluminum formate to precipitate and form crystals, which can then be collected through solid-liquid separation.

[0052] In the above embodiments of recovering aluminum metal or aluminum formate by evaporation crystallization or cooling crystallization, the advantage is that it is not necessary to continuously add aluminum-plastic composite material or additional aluminum metal to the solution in order to saturate aluminum formate.

[0053] Alternatively, aluminum formate can be recovered through the following specific methods.

[0054] Specifically, in one embodiment, aluminum-plastic composite material can be continuously added to the formic acid solution in the dissolution step S2 so that the aluminum metal component therein can be continuously dissolved and aluminum formate can be generated, thereby saturating the formic acid solution and causing aluminum formate to precipitate.

[0055] Alternatively, in another embodiment, an additional suitable amount of aluminum metal may be added to the formic acid solution in the dissolution step S2 (either beforehand or during the dissolution process) so that the additional aluminum metal dissolves and generates aluminum formate, thereby promoting the saturation of aluminum formate in the formic acid solution and its precipitation (i.e., accelerating the process of reaching saturation).

[0056] The saturation of aluminum formate in formic acid solution is mainly affected by the volume of formic acid solution. The larger the solution volume, the more aluminum metal needs to be dissolved before saturation.

[0057] Experimental tests showed that 100 ml of formic acid solution can saturate the aluminum formate solution after dissolving 1.9 grams of aluminum.

[0058] In both of the above embodiments, the operation can be continued in the dissolution step S2 to dissolve aluminum metal or additional aluminum metal in the aluminum-plastic composite material and generate aluminum formate until the solution becomes turbid and white aluminum formate precipitate appears; when the aluminum formate precipitate accumulates to a certain amount, the aluminum formate precipitate can be separated from the formic acid solution in the subsequent recovery step S3 by solid-liquid separation (e.g., centrifugation or filtration), thereby recovering the aluminum metal in the form of aluminum formate generated in the dissolution step S2 to obtain the aluminum formate precipitate product.

[0059] Furthermore, the advantage of the two implementation methods described above is that the precipitated product basically contains only aluminum formate, thus obtaining aluminum formate recovery products with extremely high purity.

[0060] Taking centrifugation as an example, a formic acid solution containing aluminum formate precipitate can be centrifuged at a speed of 2000 to 5000 RPM for 1 minute to separate the aluminum formate from the formic acid solution.

[0061] Taking filtration as an example, a formic acid solution containing aluminum formate precipitate can be filtered by using filter paper with a pore size of 2 to 10 µm through air filtration, thereby separating the aluminum formate from the formic acid solution.

[0062] The aluminum formate precipitate obtained from any of the above embodiments can be dried and reused as a primary recycling product.

[0063] In a preferred embodiment, the supernatant or filtrate obtained after separating and precipitating the aluminum formate solid precipitate in the recovery step S3 is a formic acid solution containing saturated aluminum formate, which can be continuously recovered and used in the treatment process. For example, it can be used as the formic acid solution in the preparation step S1.

[0064] In this case, since the aluminum formate in the formic acid solution is already saturated, the precipitated aluminum formate can be obtained immediately after dissolving the aluminum metal component in the aluminum-plastic composite material in dissolution step S2. Therefore, it is not necessary to continuously add aluminum-plastic composite material or add additional aluminum metal to the solution in order to make the aluminum formate saturate.

[0065] Furthermore, even if the remaining aluminum formate in the formic acid solution obtained after the separation and recovery of aluminum formate in the recovery step S3 is not saturated, it can be continuously recovered and used in the treatment process, for example, it can be used as the formic acid solution in the preparation step S1.

[0066] In this case, the amount of aluminum-plastic composite material continuously added to the solution to saturate the aluminum formate or the amount of additional aluminum metal can be reduced, or the need to prepare fresh formic acid solution can be reduced. [Experimental Data and Feasibility] [] [1.] [Formic acid concentration and] [pH] [Relationship of values] []

[0067] To verify whether there is a linear relationship between the concentration and pH value of formic acid solution, formic acid solutions with concentrations of 10wt%, 20wt%, 30wt%, 40wt%, and 50wt% were prepared, and the pH value of the formic acid solution at each concentration was measured. The distribution of formic acid concentration and pH value of formic acid solution was plotted based on the measurement results, and linear regression was performed. The results are shown in Figure 2.

[0068] In Figure 2, the solid line represents the distribution curve of formic acid solution concentration versus pH value, and the dashed line represents the regression line obtained from the regression analysis. The R² value of the regression line is as high as 0.9993, showing a highly stable linear relationship between formic acid solution concentration and pH value within the concentration range of 10wt% to 50wt%. Therefore, this linear relationship can be used as a calibration curve for formic acid concentration, allowing for the estimation of formic acid concentration simply by detecting the pH value of the formic acid solution. [2.] [Relationship between formic acid concentration and dissolution efficiency] []

[0069] To test the dissolving power of formic acid solutions of different concentrations on aluminum, formic acid solutions with concentrations of 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, and 50wt% were prepared. Aluminum metal sheets (aluminum foil) of similar volume were cut and weighed. The aluminum metal sheets were then placed in formic acid solutions of different concentrations and heated at 90 degrees Celsius for one hour. After the reaction was completed, the remaining aluminum metal sheets were removed and weighed. The residual weight of aluminum metal treated with formic acid solutions of different concentrations was calculated, and the results are shown in Figure 3.

[0070] The results in Figure 3 show that when the concentration of formic acid solution is between 20 wt% and 40 wt%, it exhibits significant aluminum dissolving power, with the best effect observed at a formic acid concentration of 25 to 35 wt%. If the formic acid concentration in the solution is too low (e.g., below 25 wt%), it is insufficient to dissolve aluminum. However, if the formic acid concentration in the solution reaches 50 wt% or higher, a dense oxide layer will form on the surface of the aluminum, thereby preventing the internal aluminum from reacting with the formic acid. [3.] [Estimated recovery rate of aluminum formate] []

[0071] Referring to the above reaction formula 1, the mole ratio of aluminum metal to formic acid is 1:3. That is, to dissolve 26.98 grams (1 mole) of aluminum metal, approximately 113 milliliters (3 moles) of formic acid are required, and 161.98 grams (1 mole) of aluminum formate and 3.024 grams (1.5 moles) of hydrogen byproduct (equivalent to a volume of 33.62 L of hydrogen gas) can be generated.

[0072] To test the recovery rate of aluminum formate by the method of the present invention, 100 ml of 25 wt% formic acid solution (excess reagent) was prepared, and a total of 3.0 g of aluminum metal (limit reagent) was gradually dissolved. The weight of aluminum metal before and after dissolution was recorded, and the weight of aluminum formate recovered was calculated.

[0073] To ensure the reaction is in optimal condition during the operation, a pH meter is used to monitor the pH value of the formic acid solution. If the pH value of the solution is detected to be higher than 0.74, formic acid is added to maintain the pH value of the solution at around 0.6.

[0074] This test was performed in two replicates, with recovered aluminum formate weights of 17.2 g and 17.4 g respectively, and an average recovered aluminum formate weight of 17.3 g. Based on reaction formula 1, 3 g of aluminum metal reacts with excess formic acid to produce approximately 18.0 g of aluminum formate (theoretical value). Calculations based on the actual recovered amount show that the aluminum formate recovery rate can reach approximately 96.1%, demonstrating excellent recovery efficiency.

[0075] The results show that although there are some errors and differences in the two repeated operations, the coefficient of variation is only 0.0058, indicating that the aluminum formate recovery operation carried out by the method of the present invention has good stability. [4.] [Recycling and processing effectiveness of various aluminum-plastic composite materials] []

[0076] To test the effectiveness of the method of the present invention in recycling various aluminum-plastic composite materials, various commercially available composite materials, including food packaging bags, aluminum-plastic packaging bags for precision electronic equipment, and cellophane, were prepared and subjected to aluminum dissolution tests. The results are shown in Figures 4 and 5.

[0077] Figures 4A through 4D show the aluminum dissolution test results for cellophane, food packaging bags, facial mask packaging bags, and medical material packaging bags, respectively; Figures 5E and F show the aluminum dissolution test results for electronic material packaging bags, while Figure 5G shows the aluminum dissolution test results for vehicle body components. In these figures, "Before" represents the photograph before processing, and "After" represents the photograph after processing.

[0078] As can be seen from the results in Figures 4 and 5, after treatment by the method of the present invention, the aluminum metal components in various composite materials can be dissolved in formic acid solution, thereby achieving the purpose of separating and recovering aluminum metal from aluminum-plastic composite materials. The plastic components in aluminum-plastic composite materials are not affected by the treatment (e.g., dissolution or degradation), so the purpose of separating and recovering plastic components can also be achieved during the operation.

[0079] The experimental results above show that the method of the present invention can be used to recycle aluminum metal from various types of aluminum-plastic composite materials. In particular, aluminum-plastic composite materials, regardless of how they are processed, can be processed using the method of the present invention.

[0080] Finally, referring to Figure 6, which shows the appearance of aluminum formate recovered by the method of the present invention, wherein A is the appearance of aluminum formate precipitated in formic acid solution, and B is the appearance of aluminum formate after separation and recovery and drying. The results show that the method of the present invention can indeed recover aluminum metal in the form of aluminum formate.

[0081] In summary, the method of the present invention treats aluminum-plastic composite materials (preferably after appropriate crushing) with formic acid solution under specific reaction conditions, so that the aluminum component in the aluminum-plastic composite material comes into full contact with the formic acid solution. This allows the aluminum metal, which is difficult to completely separate from the plastic in the prior art, to be fully dissolved in the solution. The dissolved aluminum will generate aluminum formate. When the aluminum formate in the solution reaches saturation, aluminum formate precipitate will be generated, which can then be separated and purified by centrifugation or filtration.

[0082] The advantages of this invention are that the reaction process of aluminum dissolving to generate aluminum formate is simple, low-pollution, and produces a single product. There are no other derivative products in the reaction process, which simplifies the subsequent reuse process of each substance (e.g., aluminum formate, plastic components, and aluminum formate solution). Furthermore, since the aluminum formate after separation and drying has high purity, it can be recycled as a primary product.

[0083] Compared to traditional recycling methods that can only recover aluminum from high-aluminum-content materials, require high-temperature pyrolysis of impurities outside the metal during the processing, and whose main recycled products are aluminum metal, the method of this invention operates at a low temperature, which can reduce energy consumption during the recycling process. Moreover, the reaction process is simple, without the generation of complex or highly toxic substances, and can achieve the best recycling effect on aluminum-plastic composite materials.

[0084] In particular, the formic acid solution used in the method of the present invention does not damage the plastic component in the aluminum-plastic composite material. Therefore, the aluminum metal and the plastic component can be separated during the processing. Thus, in addition to recycling the aluminum metal in the form of aluminum formate, the plastic component can also be appropriately separated and recycled without generating waste during the processing.

[0085] Specifically, common plastic components in aluminum-plastic composite plastic products currently being tested, including PET, Nylon, PE, PP, or PVE, can all be recycled and reused after being processed by the method of this invention.

[0086] In particular, since the formic acid in the solution will be consumed during the reaction, the formic acid concentration can be easily monitored by detecting the pH value of the solution, so that the solution is in a condition with optimal reaction efficiency.

[0087] Without creating contradictions, any technical feature of any embodiment or example of the present invention may be combined with other embodiments or examples of the present invention.

[0088] S1: Preparation Steps S2: Dissolving Step S3: Recycling Steps

Claims

1. A method for aluminum separation and recycling in aluminum-containing metal-plastic composite materials, comprising: The preparation step involves preparing a 20 to 40 wt% formic acid solution; the dissolution step involves contacting the aluminum-containing metal plastic composite material with the formic acid solution at a temperature between 70 and 100 degrees Celsius to dissolve the aluminum metal component in the aluminum-containing metal plastic composite material and generate aluminum formate, the chemical reaction of which is as follows: 2Al + 6HCOOH → 2Al(HCOO)3 + 3H2↑; and the recovery step involves recovering the generated aluminum formate from the formic acid solution.

2. The aluminum separation and recycling method as described in Request 1, wherein, The pH value of this formic acid solution is between approximately 0.74 and 0.

1.

3. The aluminum separation and recycling method as described in Request 1, wherein, The formic acid solution has a formic acid concentration of 25 to 35 wt% and a pH value between 0.59 and 0.

27.

4. The aluminum separation and recycling method as described in Request 1, wherein, In this dissolution step, the mixture of the aluminum-containing metal-plastic composite material and the formic acid solution is stirred or shaken.

5. The aluminum separation and recycling method as described in Request 1, wherein, In this dissolution step, the pH value of the formic acid solution is monitored. When the pH value is higher than 0.74, formic acid is added to the formic acid solution to control the pH value of the formic acid solution in the range of approximately 0.74 to 0.

1.

6. The aluminum separation and recovery method of claim 1, wherein in the dissolution step, an aluminum-containing metal plastic composite material is continuously added to the formic acid solution to continuously dissolve the aluminum metal component therein and generate aluminum formate, thereby saturating the formic acid solution with aluminum formate and causing it to precipitate, and in the recovery step, the precipitated aluminum formate is recovered from the formic acid solution.

7. The aluminum separation and recovery method of claim 1, wherein in the dissolution step, additional aluminum metal is further added to the formic acid solution to dissolve the additional aluminum metal and generate aluminum formate, thereby saturating the formic acid solution with aluminum formate and causing it to precipitate, and in the recovery step, the precipitated aluminum formate is recovered from the formic acid solution.

8. The aluminum separation and recycling method as requested in item 6 or 7, wherein, In this recovery step, the precipitated aluminum formate is recovered from the formic acid solution by centrifugation or filtration.

9. The aluminum separation and recycling method as described in request item 8, wherein, The supernatant or filtrate obtained after recovering the precipitated aluminum formate in this recovery step is used as the formic acid solution in this preparation step.

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