Method for flotation separation of micro-plastics

Abstract

The invention relates to a method for flotation separation of micro-plastics, and belongs to the field of water body micro-plastic separation. The method comprises the steps that in the presence of a foaming agent, a hydrophobic collecting agent and a water body containing the micro-plastics are mixed, and then the micro-plastics are subjected to bubbling flotation; the hydrophobic collecting agent contains dodecahexaenoic acid, eicosapentaenoic acid, cis-oleic acid, cis-linoleic acid and palmitic acid. The method is simple in procedure, easy to operate, low in cost and high in practicability.

Description

Technical Field

[0001] The invention relates to a method for flotation separation of microplastics, and belongs to the field of separation of microplastics in water bodies, and in particular to separation of microplastics in oceans, rivers, lakes and aquaculture farms. Background Art

[0002] Plastic waste will form microplastics with a diameter of less than 5 mm after aging and degradation in the environment. These microplastics are widely found in oceans, rivers, lakes, fish farms and urban water treatment systems, and appear in various forms such as fragments, particles, microbeads and fibers.

[0003] Common types of microplastics include polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, polyamide and polyurethane.

[0004] Microplastic pollution has become a serious public health problem. It can not only serve as a carrier of heavy metal ions and persistent organic pollutants, but also a colonization platform for potential pathogens, posing a significant threat to the ecological environment and human health. Through the enrichment effect of the food chain, microplastics are ingested by zooplankton and fish and then gradually accumulate in higher trophic level predators, ultimately affecting human health. Therefore, researchers are actively seeking efficient methods for the treatment of microplastics in water bodies.

[0005] At present, common microplastic treatment technologies include adsorption, electrocoagulation, membrane separation, advanced oxidation processes and biodegradation. However, these technologies all have certain limitations. For example, biodegradation takes a long time and has low efficiency; although the removal efficiency of filters can usually reach more than 90%, polymer substrates are mostly used, which may bring potential chemical risks, and surface particle blockage requires frequent cleaning; adsorption and magnetic separation technologies may cause ecological hazards due to desorption behavior after adsorbent saturation or release of nanomagnetic materials. Foam flotation process is used for microplastic separation, in which hydrophobic microplastics can adhere to rising bubbles to form microbubble-bubble aggregates and be removed from the liquid. However, for microplastics that have undergone natural aging, due to the decrease in surface hydrophobicity, their ability to bind to bubbles is weakened, resulting in reduced flotation efficiency. Therefore, it is usually necessary to use hydrophobic collectors to improve flotation efficiency.

[0006] A Chinese patent (publication number CN109909073A) discloses a method for separating microplastics based on air flotation, which specifically includes the following steps: (1) adding iodine-containing organic matter to a water body in which microplastics are dispersed and mixing thoroughly, (2) adding an inorganic acid to the dispersion obtained in step (1) and mixing thoroughly, and then continuously introducing air or oxygen, so that the introduced air or oxygen forms bubbles in the dispersion and rises, wherein the iodine-containing organic matter is triheptyl dodecyl ammonium iodide. This method has the problem of requiring a large amount of iodine-containing organic matter and having potential hazards to natural water bodies, which limits its practical application. Summary of the invention

[0007] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for flotation separation of microplastics. The method adopts a hydrophobic collector containing docosahexaenoic acid, eicosapentaenoic acid, oleic acid, linoleic acid and palmitic acid to float and separate microplastics in water. The method is simple in procedure, easy to operate, low in cost and highly practical.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present invention is to provide a method for flotation separation of microplastics, in the presence of a frother, a hydrophobic collector is mixed with water containing microplastics and then the microplastics are floated by bubbling; the hydrophobic collector contains docosahexaenoic acid, eicosapentaenoic acid, oleic acid, linoleic acid and palmitic acid.

[0009] The innovation of the present invention is that the hydrophobic collector containing docosahexaenoic acid, eicosapentaenoic acid, oleic acid, linoleic acid and palmitic acid can be adsorbed on the surface of microplastics to enhance the ability of bubbles to capture microplastics, and the hydrophobic collector can adsorb on the surface of microplastics and enhance the hydrophobicity of the surface of microplastics, thereby improving the flotation separation efficiency of microplastics in water. The method of the present invention has excellent flotation effects on both hydrophilic microplastics and hydrophobic microplastics in water.

[0010] In a preferred embodiment, in the hydrophobic collector, the content of docosahexaenoic acid is 0.3-1wt%, the content of eicosapentaenoic acid is 0.2-1wt%, the content of oleic acid is 1-3wt%, the content of linoleic acid is 1-3wt%, and the content of palmitic acid is 1-4wt%. When the content of docosahexaenoic acid, eicosapentaenoic acid, oleic acid, linoleic acid and palmitic acid is within this range, the surface adsorption of microplastics and the surface hydrophobicity of microplastics can be enhanced, thereby strengthening the ability of bubbles to capture microplastics, resulting in improved flotation separation efficiency of microplastics in water.

[0011] In a preferred embodiment, the hydrophobic collector is fish feed and / or fish feed residue. Fish feed and fish feed residue can be used as a natural and harmless hydrophobic collector to enhance the flotation efficiency of aged microplastics. The method is simple in procedure, easy to operate, low in cost and highly practical. At the same time, the method can not only efficiently separate microplastics in water bodies, but also avoid the risk of secondary pollution of natural water bodies by traditional collectors. It has no biological toxicity, and the presence of an appropriate amount of fish feed and / or fish feed residue in open waters will not have a negative impact on the environment. This strategy achieves the combination of environmental protection and efficient governance, and provides a new idea for the improvement of microplastic separation technology.

[0012] In a preferred embodiment, the concentration of the hydrophobic collector in the water body is 40-150 g / L.

[0013] In a preferred embodiment, the concentration of the foaming agent in the water body is 0.01-0.05 mg / L.

[0014] In a preferred embodiment, the foaming agent is sodium lauryl sulfate.

[0015] In a preferred embodiment, the hydrophobic collector is fish feed residue. Fish feed residue refers to the edible part of fish feed that is preferentially consumed by fish after the fish feed is put into the water body, and the fish feed that is not completely consumed is called fish feed residue. Using the fish feed residue in the water body can not only play the role of waste utilization, but also reduce the flotation cost.

[0016] In a preferred embodiment, the flotation operation includes: flotation using a flotation column, blowing air from the bottom of the flotation column, and the air flow rate is 40-60 L / h. Too low a flow rate will result in low bubble density, and a low probability of collision and capture of bubbles and microplastics. Too high a flow rate will result in poor stability of bubbles in the flotation column, reducing flotation efficiency.

[0017] In a preferred embodiment, the flotation operation further comprises: starting to scrape bubbles 10 to 20 seconds after bubbling, and the total scraping time is 300 to 500 seconds.

[0018] Compared with the prior art, the present invention has at least the following advantages: (1) The method provided by the present invention is simple in procedure, easy to operate, and low in cost, and can effectively remove microplastics from water bodies (oceans, rivers, lakes, and fish farms).

[0019] (2) The present invention can fully utilize fish feed and / or fish feed residues in aquaculture water, has no biological toxicity, is highly practical, and can be directly applied to natural waters and aquaculture waters.

[0020] (3) The method of the present invention can float not only hydrophobic microplastics but also hydrophilic microplastics at a low dosage of frother, and the flotation efficiency is high.

[0021] (4) This method can not only efficiently separate microplastics from water bodies, but also avoid the risk of secondary pollution of natural water bodies by traditional collectors. It is non-biotoxic and will not have a negative impact on the environment even if there is a moderate amount of fish feed and / or fish feed residues in open waters. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a graph showing the flotation results of microplastics at various particle size levels in Example 1; Figure 2 This is a graph showing the flotation results of microplastics at various particle sizes in Example 2; Figure 3 This is a graph showing the flotation results of microplastics at various particle size levels in Example 3; Figure 4 This is a graph showing the flotation results of microplastics at various particle size levels in comparative example 1. DETAILED DESCRIPTION

[0023] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0024] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without creative work still belong to the protection scope of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] The unsaturated fatty acids in fish feed residues were determined using the national standard "GB5009.168-2016". The results are as follows: Fish feed residues: the content of docosahexaenoic acid is 0.59wt%, the content of eicosapentaenoic acid is 0.47wt%, the content of oleic acid is 1.83wt%, the content of linoleic acid is 1.95wt%, and the content of palmitic acid is 2.03wt%.

[0027] In the following examples, the microplastics were treated to be hydrophilic. Since the stronger the hydrophobicity of the microplastics, the better the flotation effect, the following examples all used hydrophilic microplastics that are more difficult to float for flotation experiments.

[0028] Example 1 (1) Select discarded polystyrene plastic as raw material, crush the polystyrene plastic to 0.125-0.45 mm, 48-72 μm, and 35-48 μm to obtain microplastics of different particle sizes; (2) 0.5 g of microplastics of different particle sizes were treated with 100 mL of 1000 mg / L tannic acid for hydrophilization, the pH was adjusted to 7, and the treatment time was 1 h; (3) filtering and separating the above liquid to obtain hydrophilic microplastics of different particle sizes; (4) Floatation of microplastics of different particle sizes: Add 1000 mL of deionized water to the flotation column, add 50 g of fish feed, stir evenly, then add hydrophilic microplastics to the flotation column, and add 0.02 mg of sodium dodecyl sulfate as a foaming agent; (5) Use an air pump to inject gas from the bottom of the flotation column, set the air pump flow rate to 50 L / h, and set the flotation time to 480 s. The flotation column has a volume of 1 L, a height of 30 cm, and is equipped with a porous medium with a pore size of 10-30 μm. Scrape the bubbles 15 seconds after bubbling, and collect the flotation microplastics at 30, 60, 120, 180, 240, and 480 seconds. Filter, dry, and weigh the flotation-separated microplastics.

[0029] The flotation results of this example are shown in Figure 1 At 300s, the flotation separation rate of microplastics in the particle size range of 0.125~0.45 mm was 85wt%, the flotation separation rate of microplastics in the particle size range of 48~72 μm was 80wt%, and the flotation separation rate of microplastics in the particle size range of 35~48 μm was 75wt%.

[0030] Example 2 (1) Select discarded polystyrene plastic as raw material, crush the polystyrene plastic to 0.125-0.45 mm, 48-72 μm, and 35-48 μm to obtain microplastics of different particle sizes; (2) 0.5 g of microplastics of different particle sizes were treated with 100 mL of 1000 mg / L tannic acid for hydrophilization, the pH was adjusted to 7, and the treatment time was 1 h; (3) filtering and separating the above liquid to obtain hydrophilic microplastics of different particle sizes; (4) Floatation of microplastics of different particle sizes: Add 1000 mL of deionized water to the flotation column, add 100 g of fish feed, stir evenly, then add hydrophilic microplastics to the flotation column, and add 0.02 mg of sodium dodecyl sulfate as a foaming agent; (5) Use an air pump to inject gas from the bottom of the flotation column, set the air pump flow rate to 50 L / h, and set the flotation time to 480 s. The flotation column has a volume of 1 L, a height of 30 cm, and is equipped with a porous medium with a pore size of 10-30 μm. Scrape the bubbles 15 seconds after bubbling, and collect the flotation microplastics at 30, 60, 120, 180, 240, and 480 seconds. Filter, dry, and weigh the flotation-separated microplastics.

[0031] The flotation results of this example are shown in Figure 2 At 300s, the flotation separation rate of microplastics in the particle size range of 0.125~0.45 mm was 65wt%, the flotation separation rate of microplastics in the particle size range of 48~72 μm was 90wt%, and the flotation separation rate of microplastics in the particle size range of 35~48 μm was 90wt%.

[0032] Example 3 This example is carried out in a similar manner to Example 1, except that the fish feed is replaced with fish feed residues of equal mass.

[0033] The flotation results of this example are shown in Figure 3 At 300s, the flotation separation rate of microplastics in the particle size range of 0.125~0.45 mm was 50 wt%, the flotation separation rate of microplastics in the particle size range of 48~72 μm was 79wt%, and the flotation separation rate of microplastics in the particle size range of 35~48 μm was 77wt%.

[0034] Comparative Example 1 This comparative example was carried out in a similar manner to Example 1, except that no fish feed was added in step (4).

[0035] The flotation results of this comparative example are shown in Figure 4 At 300s, the flotation separation rate of microplastics in the particle size range of 0.125~0.45 mm was 10wt%, the flotation separation rate of microplastics in the particle size range of 48~72 μm was 5wt%, and the flotation separation rate of microplastics in the particle size range of 35~48 μm was 30wt%.

[0036] Test Case The fish feed was crushed into 200-300 meshes, sieved and separated, 50 g of the powder under the sieve was placed in water, and rotated and stirred to obtain a fish feed suspension, and the suspension was separated by a centrifuge, and the supernatant was taken to obtain the fish feed residual liquid.

[0037] Deionized water and residual liquid in fish feed were added dropwise to the surface of hydrophilic microplastics, blown dry with an ear bulb, and the contact angles were measured. The contact angle of the hydrophilic microplastics was 25.4°, and the contact angle of the residual liquid in fish feed was 37.5°.

[0038] From the above results, it can be seen that after adding residual liquid of fish feed to the surface of hydrophilic microplastics, its surface contact angle increases and its hydrophobicity is enhanced. The unsaturated fatty acids in the fish feed are adsorbed on the surface of hydrophilic microplastics and enhance the hydrophobicity, thereby improving the flotation separation efficiency of microplastics.

[0039] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for flotation separation of microplastics, characterized in that: In the presence of a frother, a hydrophobic collector is mixed with water containing microplastics and then the microplastics are floated by bubbling; the hydrophobic collector contains docosahexaenoic acid, eicosapentaenoic acid, oleic acid, linoleic acid and palmitic acid.

2. A method for flotation separation of microplastics according to claim 1, characterized in that: In the hydrophobic collector, the content of docosahexaenoic acid is 0.3-1wt%, the content of eicosapentaenoic acid is 0.2-1wt%, the content of oleic acid is 1-3wt%, the content of linoleic acid is 1-3wt%, and the content of palmitic acid is 1-4wt%.

3. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The hydrophobic collector is fish feed and / or fish feed residue.

4. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The concentration of the hydrophobic collector in the water body is 40-150 g / L.

5. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The concentration of the foaming agent in the water body is 0.01-0.05 mg / L.

6. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The foaming agent is sodium lauryl sulfate.

7. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The hydrophobic collector is fish feed residue.

8. A method for flotation separation of microplastics according to claim 1 or 2, characterized in that: The flotation operation includes: flotation using a flotation column, blowing air from the bottom of the flotation column, and the flow rate of the air is 40-60 L / h.

9. A method for flotation separation of microplastics according to claim 8, characterized in that: The flotation operation also includes: scraping bubbles starting from 10 to 20 seconds after bubbling, and the total scraping time is 300 to 500 seconds.

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