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 an operating solution, which is a mixed solution of formic acid and lactic acid, wherein the operating solution contains 20 to 40 wt% formic acid, and the volume ratio of formic acid to lactic acid is 8:1 to 12:1; a dissolution step of contacting the aluminum-containing metal-plastic composite material with the operating solution to separate the aluminum metal component from the plastic component, dissolve it, and generate an aluminum salt containing aluminum formate, the chemical reaction of which includes the following reaction; and a recovery step of recovering the generated aluminum salt from the operating solution. The method of this invention treats the composite material with the operating solution under specific operating conditions, causing the aluminum metal in the material to separate from the plastic component, dissolve it, and form a soluble aluminum salt, which can then be recovered and reused by centrifugation or filtration. Furthermore, the operating 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. It can use a mixed solution of formic acid and lactic acid to demold and dissolve the aluminum metal component in the aluminum-containing metal-plastic composite material from the plastic component, thereby recovering the metal and plastic components separately. [Previous Technology]

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

[0003] Aluminum is one of the common components 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, because aluminum has 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, its combination with plastic materials can improve product performance.

[0004] However, when aluminum is combined with other materials to form composite materials, the difficulty of recycling aluminum and other components increases. Unlike traditional single-material plastic products, these composite materials are not suitable for traditional plastic recycling processes. Furthermore, the metal components are difficult to remove and recycle due to being encapsulated by the plastic components, which reduces their recycling value. Due to the difficulty of recycling these composite materials, they can mostly only be disposed of through incineration or landfill. However, these two 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 high-aluminum-content materials. However, this process usually requires high-temperature pyrolysis of impurities other than the metal, so the recycled product is mainly aluminum metal, and plastics or other components cannot be recovered, resulting in excessively high processing costs and low recycling value, and wasting resources.

[0006] Moreover, the aluminum content in aluminum-plastic composites is usually low, and they may contain various types of plastics or other components, which makes the waste derived from such composites mostly non-recyclable. They usually need 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 the aluminum-plastic composite material 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 material in aluminum-containing metal-plastic composite materials, and meets the requirements of low processing cost, high product recycling value, resource reuse, avoidance of environmental problems, and even extension of reaction vessel life.

[0010] To achieve the aforementioned objective, the present invention provides a method for aluminum separation and recovery from aluminum-containing metal-plastic composite materials, comprising: a preparation step, preparing an operating solution, which is a mixed solution of formic acid and lactic acid, wherein the operating solution contains 20 to 40 wt% formic acid, and the volume ratio of formic acid to lactic acid is 8:1 to 12:1; a dissolution step, contacting the aluminum-containing metal-plastic composite material with the operating solution to separate the aluminum metal component from the plastic component, dissolve it, and generate an aluminum salt containing aluminum formate, the chemical reaction comprising the following reaction: 2Al + 6HCOOH → 2Al(HCOO) 3 + 3H 2↑; and a recovery step, recovering the generated aluminum salt from the operating solution.

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

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

[0013] According to an embodiment of the present invention, in the dissolution step, the working 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 working solution is stirred or shaken.

[0015] According to one embodiment of the present invention, in the dissolution step, the pH value of the working solution is monitored, and when the pH value is higher than 0.74, formic acid and lactic acid are added to the working solution at a volume ratio of 8:1 to 12:1 to control the pH value of the working solution in the range of about 0.74 to 0.1.

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

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

[0018] According to an embodiment of the present invention, in the recovery step, the precipitated aluminum salt is recovered from the operating solution by centrifugation or filtration.

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

[0020] The advantage of the present invention is that, compared with traditional recycling methods, the method of the present invention uses mild formic acid and lactic acid as treatment agents, operates at a low temperature, reduces energy consumption in the recycling process, and the reaction process is simple and does not produce complex or highly toxic substances.

[0021] As the main component in the treatment agent, formic acid mainly functions to provide a stripping effect and helps maintain the acidity of the solution so that the aluminum component can react effectively, and also acts as a reactant in the aluminum formate formation reaction.

[0022] As an auxiliary component in the treatment agent, lactic acid has a structure similar to formic acid, which can promote the demolding effect and act as a stabilizer for the aluminum formate formation reaction, preventing the reaction from being too violent and preventing the metal container from rusting.

[0023] In particular, the method of the present invention can recycle not only aluminum metal in the form of soluble salts, but also plastic components without generating other waste, and can achieve the best recycling effect on aluminum-plastic composite materials.

[0024] In addition, 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.

Implementation Method

[0025] In view of the above problems, the present invention develops a recycling process for such aluminum-containing metal composite products. This process involves using an operating solution under specific operating conditions to dissolve the aluminum metal in the aluminum-plastic composite material, separating it from other components for aluminum metal recovery. Lactic acid is added to promote the reaction and stabilize the process. The dissolved aluminum metal will form an aluminum salt precipitate containing aluminum formate in the solution, which can then be recovered and reused via centrifugation or filtration.

[0026] In particular, the operating solution used in the recycling process will not cause dissolution or other effects on 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.

[0027] In addition, lactic acid can be recovered almost without loss during the decoction process of aluminum-containing metal composite products.

[0028] The recycled materials involved in the technology of this invention include 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 recycling effect of aluminum in this invention.

[0029] Referring to Figure 1, the present invention provides a method for aluminum separation and recycling of aluminum-containing metal-plastic composite materials, including: a preparation step S1, a dissolution step S2 and a recycling step S3.

[0030] First, in preparation step S1, an operating solution is prepared, which is a mixed solution of formic acid (HCOOH) and lactic acid (CH3CH(OH)COOH), wherein the operating solution contains 20 to 40 wt% formic acid, and the volume ratio of formic acid to lactic acid added is 8:1 to 12:1, preferably 10:1. At this concentration, the pH value of the operating solution is between about 0.74 and 0.1.

[0031] Aluminum metal can be effectively dissolved when the formic acid concentration in the operating solution is 20 to 40 wt%. For example, the formic acid concentration in the operating solution can be 20 wt%, 22.5 wt%, 25 wt%, 27.5 wt%, 30 wt%, 32.5 wt%, 35 wt%, 37.5 wt%, or 40 wt%, and the pH values ​​of the operating solution at these concentrations are approximately 0.74, 0.67, 0.59, 0.51, 0.43, 0.35, 0.27, 0.19, or 0.1, respectively.

[0032] The best dissolution effect is achieved when the formic acid concentration is 25 to 35 wt%, and at this concentration, the pH value of the solution is between 0.59 and 0.27.

[0033] Since lactic acid (pKa is 3.86) is weaker than formic acid (pKa is 3.75), and the volume ratio of lactic acid in the operating solution is only one-tenth that of formic acid, the effect of lactic acid on the pH of the operating solution can be ignored. The pH value of the operating solution is basically determined by the concentration of formic acid in the solution.

[0034] The solvent used to dilute formic acid and lactic acid in the operating solution can be water or other solvents miscible with formic acid and lactic acid. Since the operating temperature of the operating solution of the present invention is between 70 and 100 degrees Celsius, considering operational feasibility and safety, the aforementioned solvents miscible with formic acid and lactic 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.

[0035] Preferably, the operating solution can be a mixed aqueous solution of formic acid and lactic acid.

[0036] Unless otherwise specified, the operating solutions mentioned in this specification can be solutions prepared from formic acid and lactic acid and water.

[0037] 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 the working solution so that the aluminum metal component in the aluminum-plastic composite material is separated from the plastic component, dissolved and generates an aluminum salt containing aluminum formate.

[0038] In this invention, the aluminum metal component is mainly removed from the plastic component and dissolved by reacting formic acid with aluminum metal in the aluminum-plastic composite material. One of the main recycled products in the reaction process is aluminum formate, which is the recycled form of aluminum component. The above chemical reaction is as follows: 2Al + 6HCOOH → 2Al(HCOO)3 + 3H2↑ [Reaction Formula 1]

[0039] As the main component in the working solution, the reason why formic acid can dissolve the aluminum metal in the aluminum-plastic composite material but not other components is that formic acid has the selective chemical reaction characteristics of aluminum metal, that is: formic acid is a mild weak acid that can react with aluminum metal to produce a soluble product, namely, aluminum formate; while other components in the aluminum-plastic composite material (such as plastic) are usually polymers, which have high chemical stability to acids, and therefore will not react with formic acid.

[0040] On the other hand, lactic acid, due to its molecular structure characteristics, can be used as an auxiliary component in the working solution. First, since lactic acid has a structure similar to formic acid, that is, it has a similar core structure and both have a carboxyl group, it has the same effect as formic acid in demolding metal components.

[0041] In addition, lactic acid has a hydroxyl group compared to formic acid. Since the hydroxyl group has the effect of enhancing the penetration ability, it can penetrate into the aluminum-plastic interface and react effectively, thereby helping the aluminum metal components to be demolded and separated.

[0042] In addition, since lactic acid has carboxyl and hydroxyl groups, it can form a stable chelate with aluminum ions, namely aluminum lactate, thereby avoiding excessive reaction and preventing the formation of other aluminum compounds such as aluminum hydroxide, thus helping to stabilize the synthesis reaction of aluminum formate.

[0043] Furthermore, if the reaction vessel is made of metal, the mild reaction characteristics of lactic acid can also prevent the reaction vessel from rusting, thus extending the life of the operating vessel.

[0044] It should be noted that although lactic acid also reacts with aluminum in aluminum-plastic composites (as shown below), because the reactivity of lactic acid is milder than that of formic acid, only a trace amount of lactic acid reacts with aluminum to produce trace amounts of aluminum lactate, which is negligible compared to aluminum formate. Al + 3CH₃CH(OH)COOH → Al(CH₃CH(OH)COO)³⁺² / 3H₂↑ [Reaction Equation 2]

[0045] Although aluminum can be gradually dissolved by contacting the working solution with the 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 working solution can be controlled within this range so that the working solution can contact the aluminum-plastic composite material at this temperature range, thereby achieving the best dissolution effect.

[0046] Since the boiling point of formic acid is 100.8 degrees Celsius and the boiling point of lactic acid is 122 degrees Celsius, operation within a temperature range below the above boiling points and above 70 degrees Celsius can balance dissolution efficiency and operational safety.

[0047] In the dissolution step S2, the working 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.

[0048] In the dissolution step S2, in order to enable the working solution and the aluminum-plastic composite material to react uniformly, the mixture of the aluminum-plastic composite material and the working solution can be stirred or shaken to promote the reaction of formic acid and lactic acid with aluminum metal, thereby improving the effect of dissolving aluminum metal in the aluminum-plastic composite material and separating it from the plastic component.

[0049] In addition to temperature, the concentration of formic acid in the operating solution is also a major key factor affecting the aluminum formate formation reaction (lactic acid, due to its weak acidity and reactivity and low concentration, mainly plays the role of assisting demolding and stabilizing the reaction, and its influence can be ignored).

[0050] When the formic acid concentration is too low, it cannot effectively dissolve aluminum metal to form aluminum formate; while when the formic acid concentration is too high, a dense oxide layer (Al₂O₃) will form on the surface of the aluminum metal, which will prevent the internal aluminum metal from reacting further with formic acid. Therefore, when the formic acid concentration reaches 50 wt% or more, the dissolution efficiency of aluminum metal will become extremely poor.

[0051] That is, the concentration of formic acid that can effectively dissolve aluminum metal falls between 20 and 40 wt%.

[0052] On the other hand, since the process of generating aluminum formate will consume formic acid in the solution, as the concentration of formic acid decreases, the pH value of the operating solution will gradually increase. When the pH value reaches 2.2 or above (i.e., the formic acid concentration is below 20wt%), the formic acid content in the operating solution can no longer dissolve aluminum metal.

[0053] Therefore, in order to maintain the solution in a state with optimal solubility during the recovery operation, a pH meter can be used to monitor the pH value change of the operating solution, and formic acid and lactic acid can be added to the solution appropriately (the mixed volume ratio of formic acid and lactic acid is 10:1) to maintain the solubility efficiency.

[0054] Although the concentration of formic acid can be detected at any time during the operation, for example by titration, spectroscopy (visible light / UV / IR / NIR), chromatography (GL / HPLC), electrochemical method or enzyme reaction method, these detection methods all require waiting time or even additional pretreatment, and therefore cannot monitor the concentration of formic acid in real time.

[0055] Therefore, in order to monitor the concentration of formic acid in real time, it is more efficient to use pH value as a measure to indicate the concentration of formic acid, 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 instantly.

[0056] Experimental tests showed that the pH value of the operating solution at concentrations between 10 and 50 wt% exhibited a stable linear trend, thus enabling accurate estimation of the formic acid concentration in the operating solution based on the pH value.

[0057] For example, when the pH of the operating solution is higher than 0.74, it can be estimated from the linear trend of the formic acid concentration and pH value of the operating solution (as shown in Figure 2) that the formic acid concentration is lower than 20 wt%. At this time, it is no longer possible to effectively dissolve aluminum metal. Therefore, formic acid and lactic acid can be added to the operating solution (the mixed volume ratio of formic acid and lactic acid is 8:1 to 12:1, preferably 10:1) to control the pH value of the operating solution in the range of about 0.74 to 0.1, preferably maintained at about 0.6.

[0058] Subsequently, in the recovery step S3, the aluminum salt generated in the dissolution step S2 is recovered from the operating solution.

[0059] The aluminum metal in the aluminum-plastic composite material does not immediately precipitate after dissolving in the working solution and forming aluminum salt. This is because aluminum salt is a soluble salt in the working solution and cannot precipitate before reaching saturation.

[0060] At this time, if it is necessary to separate and collect aluminum metal in the form of soluble salt, the working solution containing aluminum salt can be evaporated and crystallized or cooled and crystallized so that aluminum salt precipitates and forms crystals, and aluminum salt crystals can be collected by solid-liquid separation.

[0061] In the above embodiments of recovering aluminum metal or aluminum salt 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 the aluminum salt.

[0062] Alternatively, aluminum salts can be recovered through the following specific methods.

[0063] Specifically, in one embodiment, aluminum-plastic composite material can be continuously added to the operating solution in the dissolution step S2 so that the aluminum metal component therein continuously separates from the plastic component, dissolves and generates aluminum salt containing aluminum formate, thereby saturating the aluminum salt in the operating solution and causing it to precipitate.

[0064] Alternatively, in another embodiment, an additional appropriate amount of aluminum metal may be added to the operating solution in the dissolution step S2 (either before or during the dissolution process) so that the additional aluminum metal dissolves and generates an aluminum salt containing aluminum formate, thereby promoting the aluminum salt in the operating solution to reach saturation and precipitate (i.e., accelerating the process of reaching saturation).

[0065] The saturation of aluminum salts in the operating solution is mainly affected by the volume of the operating solution. When the volume of the solution is larger, the amount of aluminum metal that needs to be dissolved before saturation is reached is greater.

[0066] Experimental tests showed that 100 ml of the operating solution could saturate the aluminum salts (especially aluminum formate) in the solution after dissolving 1.9 g of aluminum.

[0067] In the above two 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 salt until the solution becomes turbid and white aluminum salt (especially aluminum formate) precipitates. When the aluminum salt precipitate accumulates to a certain amount, the aluminum salt precipitate can be separated from the operating solution in the subsequent recovery step S3 by solid-liquid separation (e.g., centrifugation or filtration) to recover the aluminum metal in the form of aluminum salt generated in the dissolution step S2 and obtain the aluminum salt precipitate product.

[0068] Furthermore, the advantage of the above two embodiments is that the precipitated product basically contains only aluminum formate, so that aluminum formate recovery product with extremely high purity can be obtained.

[0069] Taking centrifugation as an example, the working solution containing aluminum salt precipitate can be centrifuged at a speed of 2000 to 5000 RPM for 1 minute to separate the aluminum salt from the working solution.

[0070] Taking filtration as an example, the solution containing aluminum salt precipitate can be filtered by air filtration using filter paper with a pore size of 2 to 10 µm, so that the aluminum salt is separated from the solution.

[0071] The aluminum salt precipitate (which basically only contains aluminum formate) obtained by any of the above embodiments can be used as a primary recycling product for reuse after drying.

[0072] In a preferred embodiment, the supernatant or filtrate obtained after separating and precipitating the aluminum salt solid precipitate in the recovery step S3 is an operating solution containing saturated aluminum salt (especially saturated aluminum formate), which can be continuously recovered and used in the processing process, for example, it can be used as the operating solution in the preparation step S1.

[0073] In this case, since the aluminum salt in the operating solution is already saturated, the precipitated aluminum salt product can be obtained immediately after dissolving the aluminum metal component in the aluminum-plastic composite material in the 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 salt saturate.

[0074] Furthermore, even if the remaining aluminum salt in the operating solution obtained after separating and recovering aluminum salt in the recovery step S3 is not saturated, it can be continuously recovered and used in the processing, for example, it can be used as the operating solution in the preparation step S1.

[0075] In this case, the amount of aluminum-plastic composite material continuously added to the solution to saturate the aluminum salt or the amount of additional aluminum metal can be reduced, or the need to prepare fresh operating solutions can be reduced. Experimental Data and Feasibility

[0076] To verify the recycling effect of a mixed solution of formic acid and lactic acid on aluminum-containing metal-plastic composites, pure lactic acid, equivalent to 1 / 10 the volume of pure formic acid, was added to the operating solutions in the following experiments, so that the volume ratio of formic acid to lactic acid in the operating solutions was 10:1. 1. Relationship between formic acid concentration and pH value

[0077] To verify whether there is a linear relationship between the formic acid concentration and pH value in the operating solution, operating solutions with formic acid concentrations of 10wt%, 20wt%, 30wt%, 40wt%, and 50wt% were prepared respectively, and the pH value of the operating solutions at each concentration was measured. The distribution graph of formic acid concentration and pH value of the operating solution was plotted based on the measurement results, and linear regression was performed. The results are shown in Figure 2.

[0078] In Figure 2, the solid line represents the distribution curve of formic acid concentration and pH value in the operating solution, 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 very stable linear relationship between the formic acid concentration and pH value in the operating solution within the range of 10 wt% to 50 wt%. Therefore, this linear relationship can be used as a calibration curve for formic acid concentration, and thus, the formic acid concentration can be estimated by simply detecting the pH value of the operating solution. 2. Relationship between formic acid concentration and dissolution efficiency

[0079] To test the dissolving power of operating solutions with different formic acid concentrations on aluminum metal, operating solutions with formic acid concentrations of 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, and 50wt% were prepared respectively. Aluminum metal sheets (aluminum foil) with similar volumes were cut and their weights were recorded. Then, the aluminum metal sheets were placed in the operating solutions of each formic acid concentration and heated at 90 degrees Celsius for one hour. After the reaction was completed, the remaining aluminum metal sheets were taken out and their weights were recorded. The residual weight of aluminum metal after treatment with operating solutions of different formic acid concentrations was calculated. The results are shown in Figure 3.

[0080] The results in Figure 3 show that when the formic acid concentration in the operating 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 the 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. Estimation of Aluminum Formate Recovery

[0081] Referring to the above reaction formula 1, it can be seen that the mole ratio of aluminum metal to formic acid is 1:3, that is, for every 26.98 grams (1 mole) of aluminum metal dissolved, approximately 113 ml (3 moles) of formic acid is 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.

[0082] To test the recovery rate of aluminum salt by the method of the present invention, 100 ml of 25 wt% operating solution (excess reagent) was prepared, and a total of 3.0 g of aluminum metal (limit reagent) was gradually dissolved, and the weight of aluminum metal before and after dissolution was recorded, thereby calculating the weight of recovered aluminum salt.

[0083] In order to keep the reaction in the operation process in the best condition, the pH value of the operation solution is monitored using a pH meter. If the pH value of the solution is detected to be higher than 0.74, formic acid and lactic acid are added (the volume ratio of formic acid to lactic acid is 10:1) to keep the pH value of the solution at around 0.6.

[0084] This test was performed in two replicates, with recovered aluminum salt weights of 17.2 g and 17.4 g respectively. The average recovered aluminum salt weight was 17.3 g. According to reaction formula 1, 3 g of aluminum metal reacts with excess formic acid to produce approximately 18.0 g of aluminum salt (theoretical value). Based on the actual recovered amount, the aluminum salt recovery rate is approximately 96.1%, demonstrating an excellent recovery rate (since the recovered aluminum salt basically only contains aluminum formate, the recovery rate is calculated based on the theoretical value of aluminum formate).

[0085] 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 salt recycling operation carried out by the method of the present invention has good stability. 4. Recycling and treatment effectiveness of various aluminum-plastic composite materials

[0086] 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 electronic precision equipment, and cellophane, were prepared and subjected to aluminum dissolution tests. The results are shown in Figures 4 and 5.

[0087] Figures 4A to D 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 photo before processing, and "After" represents the photo after processing.

[0088] As can be seen from the results in Figures 4 and 5, after being processed by the method of the present invention, the aluminum metal components in various composite materials can be dissolved in the operating 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.

[0089] As can be seen from the above experimental results, the method of the present invention can be used to recycle aluminum metal in 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.

[0090] Finally, referring to FIG6, which shows the appearance of aluminum salt recovered by the method of the present invention, wherein A is the appearance of aluminum salt precipitated in the operating solution, and B is the appearance of aluminum salt 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 salt.

[0091] In summary, the method of the present invention treats aluminum-plastic composite material (preferably after appropriate crushing) with an operating solution under specific reaction conditions, so that the aluminum component in the aluminum-plastic composite material is in full contact with the operating solution. This allows the aluminum metal, which is difficult to completely separate from the plastic in the prior art, to be demolded and fully dissolved in the solution. The dissolved aluminum will generate aluminum salt containing aluminum formate. When the aluminum salt in the solution reaches saturation, aluminum salt precipitate will be generated, which can then be separated and purified by centrifugation or filtration.

[0092] The advantages of the present invention are that the reaction process of aluminum dissolving to generate aluminum salt 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 salt, plastic components and aluminum salt solution). Furthermore, since the aluminum salt (which basically only contains aluminum formate) after separation and drying has high purity, it can be recycled as a primary recycling product.

[0093] Compared with traditional recycling methods, which can only recover aluminum from high-aluminum-content materials, require high-temperature pyrolysis of impurities outside the metal during the processing, and have the main recycled product being a single aluminum metal, the method of the present 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.

[0094] In particular, the operating 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 salt, the plastic component can also be appropriately separated and recycled without generating waste during the processing.

[0095] In addition, since lactic acid can prevent the reaction of aluminum formate from being too violent and no undesirable reactants are produced during the reaction, adding lactic acid to the mixed solution helps to stabilize the reaction.

[0096] Specifically, the common plastic components in the aluminum-plastic composite plastic products currently tested, including PET, Nylon, PE, PP or PVE, can all be recycled and reused after being processed by the method of the present invention.

[0097] In particular, since the formic acid component 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.

[0098] Without causing contradictions, the technical features of any embodiment or example of the present invention may be combined with other embodiments or examples of the present invention. [Simplified Explanation of the Diagram]

[0099] Figure 1 shows a flowchart of the aluminum separation and recovery method of the aluminum-containing metal-plastic composite material of the present invention; Figure 2 shows the curve of pH value of the operating solution changing with formic acid concentration; Figure 3 shows the comparison results of the dissolution efficiency of aluminum metal by formic acid of different concentrations; Figures 4 and 5 show the recycling effect of various aluminum-plastic composite materials; and Figure 6 shows the appearance of aluminum formate recovered by the method of the present invention.

Claims

1. A method for aluminum separation and recycling in aluminum-containing metal-plastic composite materials, comprising: The preparation step involves preparing an operating solution, which is a mixed solution of formic acid and lactic acid, wherein the operating solution contains 20 to 40 wt% formic acid, and the volume ratio of formic acid to lactic acid is 8:1 to 12:1; the dissolution step involves contacting the aluminum-containing metal-plastic composite material with the operating solution to allow the aluminum metal component in the aluminum-containing metal-plastic composite material to separate from the plastic component, dissolve, and generate an aluminum salt containing aluminum formate, the chemical reaction of which includes the following reaction: 2Al + 6HCOOH → 2Al(HCOO)3 + 3H2↑; and the recovery step involves recovering the generated aluminum salt from the operating solution.

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

1.

3. The aluminum separation and recycling method as described in Request 1, wherein, The formic acid concentration in the solution used in this procedure is 25 to 35 wt%, and the pH value is between 0.59 and 0.

27.

4. The aluminum separation and recycling method as described in Request 1, wherein, In this dissolution step, the working solution is brought into contact with the aluminum-containing metal-plastic composite material at a temperature between 70 and 100 degrees Celsius.

5. 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 working solution is stirred or shaken.

6. The aluminum separation and recycling method as described in Request 1, wherein, During the dissolution step, the pH value of the working solution is monitored. When the pH value is higher than 0.74, formic acid and lactic acid are added to the working solution at a volume ratio of 8:1 to 12:1 to control the pH value of the working solution within the range of approximately 0.74 to 0.

1.

7. 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 operating solution so that the aluminum metal component therein continuously separates from the plastic component, dissolves and generates an aluminum salt containing aluminum formate, thereby saturating the aluminum salt in the operating solution and causing it to precipitate, and in the recovery step, the precipitated aluminum salt is recovered from the operating solution.

8. The aluminum separation and recovery method of claim 1, wherein in the dissolution step, additional aluminum metal is further added to the operating solution to dissolve the additional aluminum metal and generate an aluminum salt containing aluminum formate, thereby saturating the aluminum salt in the operating solution and causing it to precipitate, and in the recovery step, the precipitated aluminum salt is recovered from the operating solution.

9. The aluminum separation and recycling method as described in request item 7 or 8, wherein, In this recovery step, the precipitated aluminum salt is recovered from the operating solution by centrifugation or filtration.

10. The aluminum separation and recycling method as described in claim 9, wherein, The supernatant or filtrate obtained after recovering the precipitated aluminum salt in this recovery step is used as the operating solution in this preparation step.

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