AU2022201789B2 - Method for fabricating microbubbles using liquid-gas phase transition of CO2 and use of microbubbles - Google Patents
Method for fabricating microbubbles using liquid-gas phase transition of CO2 and use of microbubbles Download PDFInfo
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Abstract
The present invention discloses a method for fabricating microbubbles using liquid-gas
phase transition of C02 and use of microbubbles. Supercritical C02 and an oil-phase
floating-extraction agent are subjected to high-speed shear stirring in an autoclave to obtain a
homogeneous supercritical C02/oil-phase microemulsion. After the homogeneous
supercritical C02/oil-phase microemulsion is buffered and pressure-controlled, liquid
C02-in-oil nanoemulsion spheres are generated through a capillary channel distributor. The
liquid C02-in-oil nanoemulsion spheres are introduced into an aqueous phase to in situ
generate C02-in-oil microbubbles via a liquid-gas phase transition process of C02. The
microbubbles may react with target components in the aqueous phase, so that flash
enrichment and separation of the target components can be realized. This method has the
advantages including a high generation rate, high productivity, homogeneous and controllable
size of microbubbles, etc. The formed microbubbles can be widely used in the enrichment
and separation of rare and precious metals from minerals or solutions, removal of water
pollutants, upgrading and strengthening of difficult-to-float coal, etc., showing a good
industrial application prospect.
Nf.L
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I 23-2
21
11-2 21-3
I 11-1
21-1 22 21-2
23-1
11 11-4
12
12-1 13 |23
--------------------- 1- - ----------
II
FIG.1
Description
Nf.L
r -- -- -- -- -- -- -- -- -- - -- jr -- -- -- -- -- -- -- -- -- --
I 23-2
21
11-2 21-3
I 11-1
21-1 22 21-2 23-1 11 11-4
12 12-1 13 |23 --------------------- 1- - ---------- II
FIG.1
METHOD FOR FABRICATING MICROBUBBLES USING LIQUID-GAS PHASE TRANSITION OFCO 2 AND USE OF MICROBUBBLES
The present invention relates to a method for fabricating microbubbles, particularly relates to a method for fabricating microbubbles using liquid-gas phase transition of C02, and also relates to use of microbubbles for water pollutant removal or fine mineral enrichment and separation of a mineralized metallurgical system, or large-phase-ratio strategic metal ion enrichment and separation of a floating-extraction system, or lithium extraction from salt lakes or seawater, which belongs to the field of microbubble fabrication technologies in beneficiation and metallurgy applications.
Separation and enrichment technologies play an important role in chemical engineering, metallurgy, beneficiation and other industrial production processes. For example, the processes of enrichment and separation of strategic metal ions in minerals or solutions, removal of water pollutants, and upgrading and strengthening of difficult-to-float coal all require the enrichment and separation of target components. For the enrichment and separation of low-concentration solutions and fine mineral flotation upgrading, there are problems such as low process efficiency and difficulty in deep separation. In view of this, an oily bubble (i.e. bubbles coated with an oil film) technology is commonly used in the industry to enhance the large-phase-ratio extraction of dilute solutions and fine mineral flotation. Existing oily bubbles are mainly fabricated by two methods: bubble-in-oil film and microfluidics. For the bubble-in-oil film method, because oil vapor is coated on the surface of bubbles to fabricate oily bubbles, there is a potential risk in the heating process. The use of the microfluidics technology to fabricate oily bubbles has the problems of low generation rate of oily bubbles and low processing throughput. Both the two methods have the shortcomings of non-uniform size of oily bubbles, poor stability, complex equipment, etc. For example, Chinese Patent Application No. CN103949353A proposes a method and device for enhancing the flotation process of low-rank coal using oily bubbles, where oil vapor obtained by heating is coated on the surface of bubbles to fabricate oily bubbles. The device needs to heat the oil
I to vapor, posing a certain potential risk. Chinese Patent Application No. CN103736295A develops a large-phase-ratio extraction device via the organic liquid film coated on the bubble surface for separating low-concentration valuable metals from rare earth leachate. Due to the use of an intricate oily bubble distributor with inner and outer sleeves (capillary tubes), this device has the shortcomings such as complex equipment manufacture, low oily bubble generation rate, and low productivity of oily bubbles. Supercritical fluid is characterized as safe, environmentally friendly, efficient, etc. The use of the supercritical fluid to fabricate oily bubbles can effectively overcome the disadvantages of traditional oily bubble fabrication technologies, such as potential risks, low productivity of oily bubbles, and complex equipment, and this novel technology shows a good industrial application prospect. Therefore, it is of great significance to develop a supercritical surface-active oily bubble fabrication system.
In view of the shortcomings of the existing technology for fabrication of microbubbles such as potential risks, low productivity of oily bubbles, non-uniform size, and poor stability, a first object of the present invention is to provide a method for fabricating microbubbles using liquid-gas phase transition of C02. This method has significant advantages including a high generation rate, high productivity, homogeneous and controllable size of microbubbles, etc. Besides, this method is safe and stable and has a simple process, showing a good industrial application prospect. A second object of the present invention is to provide an application method for fabricating microbubbles using liquid-gas phase transition of C02. In this method, the forming process of microbubbles is safe and stable, while the size of microbubbles is homogeneous and controllable. And the microbubbles are utilized for enrichment and separation of rare and precious metals from minerals or solutions, removal of water pollutants, upgrading and strengthening of difficult-to-float coal, etc. This method can realize the flash deep enrichment and separation of target components, showing a good industrial application prospect. In order to achieve the above technical objects, the present invention provides a method for fabricating microbubbles using liquid-gas phase transition of C02, including: performing high-speed shear stirring of supercritical C02 and an oil-phase floating-extraction agent in an autoclave to obtain a homogeneous supercritical C2/il-phase microemulsion, generating liquid C02-in-oil nanoemulsion spheres through a capillary channel distributor after buffering and pressure-controlling of the homogeneous supercritical C02/oil-phase microemulsion, and subjecting the liquid C02-in-oil nanoemulsion spheres into an aqueous phase to in situ generate C02-in-oil microbubbles via a liquid-gas phase transition process of C02. The key point of the technology for fabricating microbubbles using liquid-gas phase transition of CO2 in the present invention is to regulate the formation process of liquid C02 nanoemulsion spheres and in-situ generation process of C02-in-oil microbubbles by liquid-gas phase transition of liquid C02-in-oil nanoemulsion spheres. The present invention makes full use of the characteristics of the supercritical CO2 fluid, such as low surface tension and good flowability. Firstly, supercritical C02 and an oil-phase agent are subjected to high-speed shear stirring in an autoclave under high-pressure conditions to obtain a homogeneous supercritical C2/il-phase microemulsion. The quantity and size of the homogeneous supercritical C02/oil-phase microemulsion are regulated by a capillary channel distributor, generating a great volume of liquid C02-in-oil nanoemulsion spheres. Taking advantage of the special property of supercritical C02 fluid below critical conditions, liquid CO2 in inner cavities of the nanoemulsion spheres undergoes liquid-gas phase transition in an aqueous phase, with its volume being rapidly expanded by a factor of 200-1000, generating CO2-in-oil microbubbles in situ. By arranging the capillary channel distributor at the bottom of the reactor, a great volume of liquid CO2-in-oil nanoemulsion spheres are generated, which can be converted into microbubbles in situ for the flash separation and enrichment of target components. As a preferred embodiment, a flow ratio of the supercritical CO2 to the oil-phase floating-extraction agent is 1:5-20. As a preferred embodiment, the oil-phase floating-extraction agent includes a diluent and a floating-extraction agent. The diluent is at least one of alcohols and mineral oils, and the floating-extraction agent is one of quaternary ammonium salts, organic phosphorus acids and carboxylic acids. A ratio of diluent to floating-extraction agent is 10:1-3. The floating-extraction agent and the diluent are common agents in the industry, and are selected depending on different applications of microbubbles in the enrichment and separation of rare and precious metals, removal of water pollutants, upgrading and strengthening of difficult-to-float coal, etc. As a preferred embodiment, an internal pressure of the autoclave in the high-speed shear stirring process is 8-20 MPa, and the high-speed shear stirring is performed at a rate of 10000-25000 r/min. The high-speed shear stirring under high-pressure condition can allow for the formation of a homogeneous supercritical C2/il-phase microemulsion. As a preferred embodiment, an upper part of the capillary channel distributor is of a cylindrical structure, and a lower part of the capillary channel distributor is of a hollow inverted cone structure. The cylindrical structure is composed of a capillary channel array and a micro-nano distributor. The capillary channel array is arranged perpendicularly to a surface of the micro-nano distributor. The process of converting the homogeneous supercritical C02/il-phase microemulsion into the liquid C02-in-oil nanoemulsion spheres by the capillary channel distributor is that: the homogeneous supercritical C02/oil-phase microemulsion enters the inverted cone structure for buffer diffusion; further enters the micro-nano distributor for uniform distribution; and then enters the capillary channel array for size adjustment to form the liquid C2-in-oil nanoemulsion spheres. Preferably, the micro-nano distributor is a glass frit. As a preferred embodiment, the capillary channel array is formed by a side-by-side arrangement of 200 to 5000 single-hole capillary channels having a diameter of 0.1-10 m. The quantity and size of the generated C2-in-oil microbubbles can be effectively controlled by regulating the single-hole capillary channels of the capillary channel array. As a preferred embodiment, the C02-in-oil microbubbles have a size of 0.2-50 m and an oil film thickness of 20-300 nm. After the C2-in-oil microbubbles are finally broken, escaping C02 may be recycled to a C02 storage tank for reuse. Oily bubbles fabricated in the present invention are small, uniform and controllable in size compared with oily bubbles fabricated by conventional oily bubble generation devices. Besides, the present invention has a higher productivity of microbubbles. As a preferred embodiment, the homogeneous supercritical C02/oil-phase microemulsion enters between the capillary channel distributors, and the pressure and the fluid velocity are regulated by a fluid buffer and a pressure control assembly, which is advantageous for obtaining size-controllable liquid C02-in-oil nanoemulsion spheres. The present invention also provides use of microbubbles fabricated by the method for water pollutant removal or fine mineral enrichment and separation of a mineralized metallurgical system, or large-phase-ratio metal ion enrichment and separation of a floating-extraction system, or lithium extraction from salt lakes or seawater. As a preferred embodiment, when the microbubbles are used for water pollutant removal or fine mineral enrichment and separation, C02-in-oil nanoemulsion spheres have a flow rate of 1-10 mL/min, the microbubbles have a size of 0.5-10 [m, and the process is performed for -60s.
As a preferred embodiment, when the microbubbles are used for large-phase-ratio metal ion enrichment and separation or lithium extraction from salt lakes or seawater, C02-in-oil nanoemulsion spheres have a flow rate of 0.5-8 mL/min, the microbubbles have a size of 0.2-5 [m, and the process is performed for 2-30 s. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to the present invention is mainly implemented based on a C02-in-oil microbubble system device. The system includes a supercritical C02/il-phase microemulsion generation device and a C02-in-oil microbubble generation device. The supercritical C02/il-phase microemulsion generation device includes an autoclave, a supercritical C02 generation device and an oil-phase storage tank. The supercritical C02 generation device and the oil-phase storage tank are both connected to the autoclave through pipelines. The C02-in-oil microbubble generation device includes a fluid buffer and a capillary channel distributor. An upper part of the capillary channel distributor is of a cylindrical structure, and a lower part of the capillary channel distributor is of a hollow inverted cone structure. The cylindrical structure is composed of a capillary channel array and a micro-nano distributor arranged at the bottom of the capillary channel array. The bottom of the inverted cone structure is sequentially connected to the fluid buffer and the autoclave through pipelines. The supercritical C02 generation device includes a C02 compressor, a C02 heater and a supercritical C02 storage tank sequentially connected in series. A shear stirring device is arranged in the autoclave. A constant-flow pump is arranged on a connecting pipeline of the supercritical C02 generation device and the autoclave. A constant-flow pump is arranged on a connecting pipeline of the oil-phase storage tank and the autoclave. A pressure control assembly is arranged on the fluid buffer. The pressure control assembly includes a first one-way valve, a second one-way valve and a pressure sensor. The pressure sensor is connected to the first one-way valve and the second one-way valve through pipelines. The first one-way valve and the second one-way valve are arranged at a fluid inlet and a fluid outlet at both ends of the fluid buffer, respectively. The fluid buffer has a spring-shaped helical structure. Preferably, the buffer may effectively regulate the flow rate of the supercritical C02/il-phase microemulsion. The capillary channel array is formed by a side-by-side arrangement of 200 to 5000 single-hole capillary channels having a diameter of 0.1-10 [m. The capillary channel array is arranged perpendicularly to a surface of the micro-nano distributor. After the C02-in-oil microbubbles according to the present invention are broken, escaping C02 is recycled to a C02 storage tank through a recovery device mounted at the top of the reactor. The buffer and pressure control process of the homogeneous supercritical C2/il-phase microemulsion according to the present invention is realized by the fluid buffer and the pressure control assembly, respectively, and the flow rate and pressure of the homogeneous supercritical C02/oil-phase microemulsion entering the capillary channel distributor can be controlled. Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects. (1) The present invention makes use of the liquid-gas phase transition principle of supercritical C02 for the first time, and generates " C02-in-oil microbubbles" in situ through the liquid-gas phase transition of liquid C02 in inner cavities of nanoemulsion spheres in an aqueous phase, with the volume expanded by a factor of 200-1000 instantaneously. The microbubbles are large in quantity, are small, homogeneous and controllable in size, and are environmentally friendly and safe in production process, which overcomes the potential risk that the common oily bubble fabrication technology needs to be heated to oil vapor. (2) The present invention makes full use of the characteristics of the supercritical C02 fluid, such as low surface tension and good flowability, and the supercritical C2/il-phase microemulsion passes through the capillary channel distributors arranged side by side, and a great volume of homogeneous liquid C02-in-oil nanoemulsion spheres with uniform and controllable size can be generated at a high productivity. (3) When the C02-in-oil microbubbles fabricated in the present invention are used for water pollutant removal, fine mineral flotation upgrading and large-phase-ratio enrichment and separation of metal ions in solutions, the microbubbles undergo a rapid rising and growing process, and an active agent in an oil film reacts with target components to realize flash deep enrichment and separation of the target components.
FIG. 1 is a schematic structure diagram of a C2-in-oil microbubble system device. In the figure, I: supercritical C02/oil-phase microemulsion generation device, II: C02-in-oil microbubble generation device, 11: supercritical C02 generation device, 11-1: C02 compressor, 11-2: C02 heater, 11-3: supercritical C02 storage tank, 11-4: constant-flow pump, 12: oil-phase storage tank, 12-1: constant-flow pump, 13: autoclave, 21: pressure control assembly, 21-1: first one-way valve, 21-2: second one-way valve, 21-3: pressure sensor, 22: fluid buffer, 23: capillary channel distributor, 23-1: micro-nano distributor, 23-2: capillary channel array.
The content of the present invention will be further described below with reference to specific embodiments. It should be noted that these embodiments are used merely for a better understanding of the content of the present invention, and are not intended to limit the protection scope of the claims of the present invention. The C02-in-oil microbubble system device provided by the present invention is shown in FIG. 1. The C02-in-oil microbubble system is mainly composed of a supercritical C02/oil-phase microemulsion generation device I and a C02-in-oil microbubble generation device II. The supercritical C02/oil-phase microemulsion generation device is mainly used to generate a homogeneous supercritical C02/oil-phase microemulsion, while the C02-in-oil microbubble generation device is mainly used to obtain C02-in-oil microbubbles by buffering, uniform distribution and capillary control of the supercritical C02/il-phase microemulsion. The supercritical C02/oil-phase microemulsion generation device includes an autoclave 13 with a stirring device, a supercritical C02 generation device 11 and an oil-phase storage tank 12. The supercritical C02 generation device includes a C02 compressor 11-1, a CO2 heater 11-2 and a supercritical C02 storage tank 11-3 sequentially connected in series. The supercritical C02 generation device may fabricate supercritical C02 using C02 raw materials. The supercritical C02 generation device and the oil-phase storage tank are both connected to an inlet of the autoclave through pipelines, and constant-flow pumps are arranged on connecting pipelines of the supercritical C02 generation device with the oil-phase storage tank and the autoclave respectively. Supercritical C02 generated by the supercritical C02 generation device is conveyed into the autoclave through the constant-flow pump 11-4, while an oil-phase agent in the oil-phase storage tank is conveyed into the autoclave through the constant-flow pump 12-1. The supercritical C02 and the oil-phase agent form a uniform supercritical C02/oil-phase microemulsion under the strong shear stirring action of the stirring device in the autoclave. An outlet of the autoclave is connected to the C02-in-oil microbubble generation device. The C02-in-oil microbubble generation device includes a fluid buffer 22 and a capillary channel distributor 23. The fluid buffer is a spring-like helical structure and is mainly used to control the rate of the supercritical C02/oil-phase microemulsion. A pressure control assembly 21 is arranged on the fluid buffer to intelligently regulate a pressure of the supercritical C02/oil-phase microemulsion. The pressure control assembly is composed of a first one-way valve 21-1, a second one-way valve 21-2 and a pressure sensor 21-3. An inlet end and an outlet end of the fluid buffer are respectively provided with the first one-way valve and the second one-way valve. The pressure sensor is connected to the first one-way valve and the second one-way valve through pipelines. The pressure control assembly is mainly used to control the pressure of the supercritical C02/oil-phase microemulsion. An upper part of the capillary channel distributor is of a cylindrical structure which is composed of a capillary channel array 23-2 and a micro-nano distributor 23-1 arranged at the bottom of the capillary channel array. A lower part of the capillary channel distributor is of an internally hollow inverted cone structure, and the bottom of the inverted cone structure is sequentially connected to the fluid buffer and the outlet of the autoclave through pipelines. The capillary channel array is formed by a side-by-side arrangement of 200 to 5000 single-hole capillary channels having a diameter of about 0.1-10 [m. The capillary channel array is arranged perpendicularly to a surface of the micro-nano distributor. The diameter and quantity of the single-hole capillary channels of the capillary channel array can be regulated according to the quantity and size of the C02-in-oil microbubbles actually required. The homogeneous supercritical C02/oil-phase microemulsion generated in the autoclave slowly enters the C02-in-oil microbubble generation device through the slow control of the fluid buffer. In the C02-in-oil microbubble generation device, the supercritical C02/oil-phase microemulsion is uniformly distributed via the micro-nano distributor and controlled by the capillary channel to generate a large volume of homogeneous liquid C02-in-oil nanoemulsion spheres. The capillary channel distributor may be directly arranged at the bottom of an aqueous solution system to be treated. During the rising process of the liquid C02-in-oil nanoemulsion spheres in an aqueous phase, liquid CO2 in the inner cavities undergoes liquid-gas phase transition and is rapidly expanded in volume to generate C02-in-oil microbubbles in situ. Example 1 Based on a floating-extraction system, this technology was used to enrich and separate low-concentration strategic metal tungsten, and the process was as follows: (1) A kerosene solution containing 5% of hexadecyl trimethyl ammonium bromide was introduced into an autoclave at a flow rate of 10 mL/min, and a supercritical fluid generated by a supercritical fluid generation device was injected at a flow rate of 1 mL/min and stirred at 15000 r/min for 5 min to obtain a supercritical C02/il-phase microemulsion. (2) 10 L of a solution with a tungstate concentration of 5 mg/L was added into a mineralized metallurgical reactor, the microemulsion was slowly controlled by a fluid buffer, and then a great volume of liquid C02-in-oil nanoemulsion spheres were generated through a capillary channel distributor arranged at the bottom of the mineralized metallurgical reactor. The diameter of a capillary tube was 1 m, the quantity of channels was 1000, and the size of the nanoemulsion spheres was 500 nm. (3) In the rising process of the nanoemulsion spheres in an aqueous phase, the liquid C02 in inner cavities vaporized, resulting in rapid volume expansion and in-situ generation of "C02-in-oil microbubbles" having a size of 2 m. In the rising process of the microbubbles in the reactor, hexadecyl trimethyl ammonium bromide in an oil film reacted with tungstate in the solution by complexation and floats for 15 s, thus realizing the super-normal enrichment of tungstate. (4) After the microbubbles were broken, CO2 was recycled to a C02 storage tank through a recovery device mounted at the top of the reactor. Tungstate enriched at the top of the reactor was collected by an overflow device with a recovery rate of 99.8%, a concentration as high as 4.9 g/L, and an enrichment ratio of 980. Example 2 Based on a floating-extraction system, this technology was used to enrich and separate low-concentration strategic metal tungsten, and the process was as follows: (1) A kerosene solution containing 2% of hexadecyl trimethyl ammonium bromide was introduced into an autoclave at a flow rate of 10 mL/min, and a supercritical fluid generated by a supercritical fluid generation device was injected at a flow rate of 2 mL/min and stirred at 20000 r/min for 3 min to obtain a supercritical C02/il-phase microemulsion. (2) 20 L of a solution with a tungstate concentration of 2 mg/L was added into a mineralized metallurgical reactor, the microemulsion was slowly controlled by a fluid buffer, and then a great volume of liquid C02-in-oil nanoemulsion spheres were generated through a capillary channel distributor arranged at the bottom of the mineralized metallurgical reactor. The diameter of a capillary tube was 2 m, the quantity of channels was 2000, and the size of the nanoemulsion spheres was 300 nm. (3) In the rising process of the nanoemulsion spheres in an aqueous phase, the liquid C02 in inner cavities vaporized, resulting in rapid volume expansion and in-situ generation of "C02-in-oil microbubbles" having a size of 2 m. In the rising process of the microbubbles in the reactor, hexadecyl trimethyl ammonium bromide in an oil film reacted with tungstate in the solution by complexation and floats for 30 s, thus realizing the super-normal enrichment of tungstate.
(4) After the microbubbles were broken, CO2 was recycled to a C02 storage tank through a recovery device mounted at the top of the reactor. Tungstate enriched at the top of the reactor was collected by an overflow device with a recovery rate of 99.5%, a concentration as high as 3.8 g/L, and an enrichment ratio of 1900. Example 3 Based on a mineralized metallurgical reactor, this technology was used to float and separate clean coal from low-rank coal, and the process was as follows: (1) A diesel oil collector solution was introduced into an autoclave at a flow rate of 10 mL/min, and a supercritical fluid generated by a supercritical fluid generation device was injected at a flow rate of 2 mL/min and stirred at 20000 r/min for 3 min to obtain a supercritical C02/oil-phase microemulsion. (2) 10 L of low-rank coal slurry with a pulp concentration of 100 g/L was added into a mineralized metallurgical reactor, the microemulsion was slowly controlled by a fluid buffer, and then a great volume of liquid C02-in-oil nanoemulsion spheres were generated through a capillary channel distributor arranged at the bottom of the mineralized metallurgical reactor. The diameter of a capillary tube was 5 m, the quantity of channels was 2000, and the size of the nanoemulsion spheres was 800 nm. (3) In the rising process of the nanoemulsion spheres in an aqueous phase, the liquid C02 in inner cavities vaporized, resulting in rapid volume expansion and in-situ generation of "C02-in-oil microbubbles" having a size of 5 m. In the rising process of the microbubbles in the reactor, diesel oil in an oil film chemically reacted with coal in the coal slurry, and floats for 60 s, thus realizing the super-normal enrichment of low-quality coal. (4) After oily bubbles were broken, CO2 was recycled to a C02 storage tank through a recovery device mounted at the top of the reactor. Clean coal enriched at the top of the reactor was collected by an overflow device with a recovery rate of 96.3%, and the grade of the clean coal is increased from 21.2% to 83.4%. Example 4 Based on a mineralized metallurgical reactor, this technology was used to float and separate clean coal from low-rank coal, and the process was as follows: (1) A diesel oil collector solution was introduced into an autoclave at a flow rate of 15 mL/min, and a supercritical fluid generated by a supercritical fluid generation device was injected at a flow rate of 1 mL/min and stirred at 25000 r/min for 5 min to obtain a supercritical C02/oil-phase microemulsion. (2) 20 L of low-rank coal slurry with a pulp concentration of 60 g/L was added into a mineralized metallurgical reactor, the microemulsion was slowly controlled by a fluid buffer, and then a great volume of liquid C02-in-oil nanoemulsion spheres were generated through a capillary channel distributor arranged at the bottom of the mineralized metallurgical reactor. The diameter of a capillary tube was 5 m, the quantity of channels was 5000, and the size of the nanoemulsion spheres was 500 nm. (3) In the rising process of the nanoemulsion spheres in an aqueous phase, the liquid C02 in inner cavities vaporized, resulting in rapid volume expansion and in-situ generation of
" C02-in-oil microbubbles" having a size of 2 m. In the rising process of the microbubbles in the reactor, diesel oil in an oil film chemically reacted with coal in the coal slurry, and floats for 45 s, thus realizing the super-normal enrichment of low-quality coal. (4) After oily bubbles were broken, CO2 was recycled to a C02 storage tank through a recovery device mounted at the top of the reactor. Clean coal enriched at the top of the reactor was collected by an overflow device with a recovery rate of 97.6%, and the grade of the clean coal is increased from 21.2% to 85.4%. Comparative Example 1 Based on a floating-extraction system, a common oily bubble generation device was used to enrich and separate low-concentration strategic metal tungsten: (1) A kerosene solution containing 5% of hexadecyl trimethyl ammonium bromide was slowly injected into an oily bubble generator, and air was introduced by an air compressor to obtain oily bubbles having a size of 20-100 [m. (2) 10 L of a solution with a tungstate concentration of 5 mg/L was added into a mineralized metallurgical reactor while injecting the oily bubbles obtained in (1) into the mineralized metallurgical reactor at a flow rate of 10 mL/min. (3) In the rising process of the oily bubbles in the reactor, hexadecyl trimethyl ammonium bromide in an oil film reacted with tungstate in the solution by complexation and floated for 5 min, thus realizing the separation and enrichment of tungstate. Tungstate enriched at the top of the reactor was collected by an overflow device with a recovery rate of only 85.2%, a concentration as high as 3.2 g/L, and an enrichment ratio of 640. Comparative Example 2 Based on a mineralized metallurgical reactor, bubbles in oil vapor were used to float and separate clean coal from low-rank coal: (1) A diesel collector solution was placed in a flask of an oil gas generator and heated to 230°C to generate oil vapor while introducing air by an air compressor to obtain oily bubbles having a size of 50-200 [m. (2) 10 L of low-rank coal slurry with a pulp concentration of 100 g/L was added into a mineralized metallurgical reactor while injecting the oily bubbles obtained in (1) into the mineralized metallurgical reactor at a flow rate of 10 mL/min. (3) In the rising process of the oily bubbles in the reactor, diesel oil in an oil film chemically reacted with coal in the coal slurry, and floated for 20 min, thus realizing the separation and enrichment of low-quality coal. Clean coal enriched at the top of the reactor was collected by an overflow device with a recovery rate of only 87.1%, and the grade of the clean coal was increased from 21.2% to 73.2%. In conclusion, a method for fabricating microbubbles using liquid-gas phase transition of C02 and use thereof are widely applicable to the process of enrichment and separation of strategic metal ions in minerals or solutions, removal of water pollutants, upgrading and strengthening of difficult-to-float coal, and can significantly improve the efficiency of separation and enrichment. In addition, the process has the significant advantages including safe and stable microbubble manufacturing process, small size and high productivity of microbubbles, flash deep enrichment and separation, etc. compared with common low-concentration target component separation methods, showing a good industrial application prospect. In addition, it should be noted that the present invention is not limited to the foregoing embodiments. Any variation made to the present invention within the scope of technical conception of the principles of the present invention shall fall within the protection scope of the present invention.
Claims (10)
1. A method for fabricating microbubbles using liquid-gas phase transition of C02, comprising: performing high-speed shear stirring on supercritical C02 and an oil-phase floating-extraction agent in an autoclave to obtain a homogeneous supercritical C02/il-phase microemulsion, generating liquid C02-in-oil nanoemulsion spheres through a capillary channel distributor after buffering and pressure-controlling of the homogeneous supercritical C02/oil-phase microemulsion, and introducing the liquid C02-in-oil nanoemulsion spheres into an aqueous phase to in situ generate C02-in-oil microbubbles via a liquid-gas phase transition process of C02.
2. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 1, wherein a flow ratio of the supercritical C02 to the oil-phase floating-extraction agent is 1:5-20.
3. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 1 or 2, wherein the oil-phase floating-extraction agent comprises a diluent and a floating-extraction agent.
4. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 1, wherein an internal pressure of the autoclave in the high-speed shear stirring process is 8-20 MPa, and the high-speed shear stirring is performed at a rate of 10000-25000 r/min.
5. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 1, wherein an upper part of the capillary channel distributor is of a cylindrical structure, and a lower part of the capillary channel distributor is of a hollow inverted cone structure; the cylindrical structure is composed of a capillary channel array and a micro-nano distributor, and the capillary channel array is arranged perpendicularly to a surface of the micro-nano distributor; and the process of converting the homogeneous supercritical C02/oil-phase microemulsion into the liquid C02-in-oil nanoemulsion spheres by the capillary channel distributor is that: the homogeneous supercritical C2/il-phase microemulsion enters the hollow inverted cone structure for buffer diffusion; further enters the micro-nano distributor for uniform distribution; and then enters the capillary channel array for size adjustment to form the liquid C02-in-oil nanoemulsion spheres.
6. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 5, wherein the capillary channel array is formed by a side-by-side arrangement of 200 to 5000 single-hole capillary channels having a diameter of 0.1-10 m.
7. The method for fabricating microbubbles using liquid-gas phase transition of C02 according to claim 5, wherein the C02-in-oil microbubbles have a size of 0.2-50 m and an oil film thickness of 20-300 nm.
8. Use of microbubbles fabricated by the method according to any one of claims 1 to 7 for water pollutant removal or fine mineral enrichment and separation of a mineralized metallurgical system, or large-phase-ratio metal ion enrichment and separation of a floating-extraction system, or lithium extraction from salt lakes or seawater.
9. The use of microbubbles fabricated by the method according to claim 8, wherein when the microbubbles are used for water pollutant removal or fine mineral enrichment and separation, C02-in-oil nanoemulsion spheres have a flow rate of 1-10 mL/min, the microbubbles have a size of 0.5-10 [m, and the process is performed for 5-60 s.
10. The use of microbubbles fabricated by the method according to claim 8, wherein when the microbubbles are used for large-phase-ratio metal ion enrichment and separation or lithium extraction from salt lakes or seawater, C02-in-oil nanoemulsion spheres have a flow rate of 0.5-8 mL/min, the microbubbles have a size of 0.2-5 m, and the process is performed for 2-30 s.
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