A bridge fluid for microfine mineral oil agglomeration and a method of making the same

Abstract

The present application belongs to the technical field of mineral separation, and particularly relates to a bridge liquid for oil agglomeration separation of micro-fine particles and a preparation method thereof. The preparation method comprises two-step emulsification and two-step dilution. First, a W / O emulsion is prepared by using an oil phase, a lipophilic emulsifier and an inorganic salt solution. After dilution and adjustment of the internal water phase, an external water phase is prepared by using water, a hydrophilic emulsifier and an inorganic salt solution. Then, the W / O emulsion and the external water phase are mixed to obtain a W / O / W emulsion. Finally, the W / O / W emulsion is diluted by deionized water to obtain a high internal phase W / O / W emulsion. The emulsion prepared by the present application has good microdroplet dispersibility, high internal water phase ratio, stable internal structure and low viscosity. As the bridge liquid, the emulsion can construct high-water-content discrete oil bridges in situ between particles after adhesion to micro-fine particles, thereby improving dispersibility and strengthening stability control.

Description

Technical Field

[0001] This invention belongs to the field of mineral sorting technology, specifically relating to a bridging fluid for the sorting of fine mineral oil agglomerates and its preparation method. Background Technology

[0002] Fine-grained separation is a prominent challenge in mineral upgrading. Conventional flotation is insufficient for effectively processing minerals of this size. Current enhancement measures mainly include creating nanobubbles and increasing the apparent particle size, such as oil agglomeration and flocculation. Oil agglomeration separation selectively agglomerates target particles under the action of non-polar oil (bridging fluid), and then separates the agglomerates from non-target particles. However, its high oil consumption and cost severely restrict its widespread application. Currently, there are two main methods to reduce the cost of oil agglomeration: using inexpensive bio-oil as raw material and adding surfactants to reduce oil consumption. However, these two methods do not fundamentally solve the problem of high oil consumption, i.e., the need to fill the gaps between mineral particles with a large amount of oil to generate oil bridges of sufficient strength.

[0003] In the past two years, researchers have proposed using emulsions as bridging fluids to fill gaps between particles to reduce the cost of oil agglomeration. Emulsions are mainly divided into two types: water-in-oil (O / W) emulsions and oil-in-water (W / O) emulsions, with O / W emulsions widely used in the separation of fine-grained minerals. However, the water phase volume fraction in O / W and W / O / W emulsions prepared by the conventional two-step method can only reach a maximum of 50%, and they suffer from drawbacks such as high viscosity, poor dispersibility, and short stabilization time. Patent CN1482900A discloses a two-step method for preparing W / O / W composite emulsions, but the particle size range of emulsions prepared using this method fluctuates greatly, exhibiting low stability. Patent CN110142143A discloses a two-step method for preparing W / O / W multiphase emulsions for mineral separation, but this emulsion does not significantly improve mineral recovery rates when used for tungsten or cassiterite separation. Emulsions prepared using traditional methods are difficult to achieve stable control during mineral separation. This invention provides a novel emulsion with stable dispersion, high internal water phase ratio, and reduced oil agglomeration costs, and its preparation method is one of the keys to solving the problem of mineral sorting. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention first provides a method for preparing a bridging fluid for the separation and agglomeration of fine mineral oil particles.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for preparing a bridging fluid for the separation and sorting of fine mineral oil agglomerates includes the following steps:

[0007] Step 1. Preparation of W / O emulsion: Add a set amount of lipophilic emulsifier and inorganic salt solution to the oil phase, and stir gently at low speed to obtain a W / O emulsion; the oil phase is any one or a combination of several of straight-chain alkanes, branched-chain alkanes and cycloalkanes;

[0008] Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add the oil phase dropwise to the prepared W / O emulsion for dilution until the internal aqueous phase volume fraction is in the range of 45%~50%;

[0009] Step 3. Preparation of external aqueous phase: Add a set amount of hydrophilic emulsifier and inorganic salt solution to water, stir to obtain external aqueous phase, and adjust the osmotic pressure of external aqueous phase to be close to the osmotic pressure of the W / O emulsion;

[0010] Step 4. Preparation of W / O / W emulsion: The external aqueous phase prepared in step 3 is gently stirred at low speed and added dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%.

[0011] Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction greater than 80%.

[0012] Preferably, in step 1, the lipophilic emulsifier is a surfactant with an HLB value between 4.3 and 8.6, and the mass ratio of the oil phase to the lipophilic emulsifier is (2-4):1.

[0013] Preferably, in step 2, the hydrophilic emulsifier is a surfactant with an HLB value of 10.5 to 16.7, and the mass ratio of water to hydrophilic emulsifier is (2 to 5):1.

[0014] Preferably, in steps 1 and 2, the inorganic salt solution is any one or a combination of NaCl, MgCl2, and AlCl3, the concentration of the inorganic salt solution is 0.2 to 0.3 mol / L, and the mass ratio of the inorganic salt solution to the oil phase in step 1 is (0.01 to 0.02):1.

[0015] Preferably, in step 5, during the dilution of the W / O / W emulsion with deionized water, hydrochloric acid or sodium hydroxide solution is added to adjust the pH value to 6-8.

[0016] Preferably, the low-speed gentle stirring speed is 100-300 r / min, and the stirring time is 30 min.

[0017] The present invention further provides a W / O / W emulsion, which is prepared by the preparation method described above; the W / O / W emulsion has an internal aqueous phase mass fraction greater than 80%, an emulsion particle size range of 0.543 to 1.34 μm, and an emulsion viscosity less than 4.45 mPa·s.

[0018] Finally, this invention provides an application of the W / O / W emulsion described above as a bridging fluid for the agglomeration and sorting of fine mineral oil particles.

[0019] The beneficial effects of this invention are as follows:

[0020] The W / O / W emulsion preparation method provided by this invention adds water dilution and osmotic expansion steps to the existing two-step method for preparing W / O / W emulsions, forming a new method of "two-step emulsification and two-step dilution". This new method increases the proportion of the inner aqueous phase by expanding the droplets through the osmotic pressure difference between the inner and outer aqueous phases, thereby increasing the structural stability of the aqueous phase. Furthermore, when used as a bridging fluid for the separation of fine-particle mineral oil agglomerates, it effectively reduces oil consumption, lowers production costs, and improves the flotation efficiency of fine-particle mineral agglomerates.

[0021] The novel bridging fluid prepared using this invention can reduce the amount of oil used during mineral oil agglomeration, significantly lowering production costs. The oil bridges formed between particles in the emulsion have high strength, significantly improving flotation recovery. Compared to the conventional two-step method for preparing high internal phase W / O emulsions and W / O / W emulsions, the novel bridging fluid of this invention has an internal aqueous phase ratio greater than 80%, an emulsion particle size range of 0.543–1.34 μm, an emulsion viscosity less than 4.45 mPa·s, and a long-term stability time greater than 30 days. It exhibits good microdroplet dispersibility, a high internal aqueous phase ratio, stable internal structure, and low viscosity. After adhering to fine mineral particles, it can construct high-water-content discrete oil bridges in situ between particles, enhancing both dispersibility and stability control. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, a method for preparing a bridging fluid for the separation of fine mineral oil agglomerates includes the following steps:

[0026] Step 1. Preparation of W / O emulsion: Add the lipophilic emulsifier and inorganic salt solution to the oil phase at a mass ratio of 2:1 (oil phase to lipophilic emulsifier). Stir gently at 250 rpm for 30 minutes to obtain a W / O emulsion. The oil phase is kerosene, the lipophilic emulsifier is a surfactant with an HLB value of 6.5, and the inorganic salt solution is a 0.2 mol / L NaCl solution, added at a rate of 1 / 100 of the oil phase mass.

[0027] Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add kerosene dropwise to the prepared W / O emulsion for dilution until the internal water phase volume fraction is in the range of 45%~50%;

[0028] Step 3. Preparation of external aqueous phase: Add hydrophilic emulsifier and inorganic salt solution to water at a mass ratio of 3:1 and stir to obtain external aqueous phase. During the process, adjust the osmotic pressure of the external aqueous phase to be close to that of the W / O emulsion. The hydrophilic emulsifier is a surfactant with an HLB value of 12, and the inorganic salt solution is the same as in step 1.

[0029] Step 4. Preparation of W / O / W emulsion: Stir the external aqueous phase prepared in step 3 at low speed and gently, and add it dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%.

[0030] Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water, add hydrochloric acid to adjust the pH to 6.5, and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction of 87%, an emulsion particle size of 0.861 μm, and a viscosity of 1.13 mPa·s.

[0031] Example 2

[0032] like Figure 1 As shown, a method for preparing a bridging fluid for the separation of fine mineral oil agglomerates includes the following steps:

[0033] Step 1. Preparation of W / O emulsion: Add the lipophilic emulsifier and inorganic salt solution to the oil phase at a mass ratio of 3:1 (oil phase to lipophilic emulsifier). Stir gently at 250 rpm for 30 minutes to obtain the W / O emulsion. The oil phase is diesel oil, the lipophilic emulsifier is a surfactant with an HLB value of 6.5, and the inorganic salt solution is a 0.2 mol / L NaCl solution with a dropwise addition ratio of 0.01:1 to the oil phase mass.

[0034] Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add diesel oil dropwise to the prepared W / O emulsion for dilution until the internal water phase volume fraction is in the range of 45%~50%;

[0035] Step 3. Preparation of external aqueous phase: Add hydrophilic emulsifier and inorganic salt solution to water at a mass ratio of 3:1 and stir to obtain external aqueous phase. During the process, adjust the osmotic pressure of external aqueous phase to be close to that of W / O emulsion. The hydrophilic emulsifier is a surfactant with an HLB value of 12, and the inorganic salt solution is the same as in step 1.

[0036] Step 4. Preparation of W / O / W emulsion: Stir the external aqueous phase prepared in step 3 at low speed and gently, and add it dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%.

[0037] Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water, add hydrochloric acid to adjust the pH to 6.5, and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction of 90%, an emulsion particle size of 1.161 μm, and a pH of 1.32 mPa·s.

[0038] Example 3

[0039] like Figure 1 As shown, a method for preparing a bridging fluid for the separation of fine mineral oil agglomerates includes the following steps:

[0040] Step 1. Preparation of W / O emulsion: Add the lipophilic emulsifier and inorganic salt solution to the oil phase at a mass ratio of 2:1 (oil phase to lipophilic emulsifier). Stir gently at 250 rpm for 30 minutes to obtain the W / O emulsion. The oil phase is a mixture of kerosene and diesel oil. The lipophilic emulsifier is a surfactant with an HLB value of 6.5. The inorganic salt solution is NaCl with a concentration of 0.1 mol / L, and the addition ratio to the oil phase is 0.02:1.

[0041] Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add the mixed oil phase dropwise to the prepared W / O emulsion for dilution until the internal water phase volume fraction is in the range of 45%~50%;

[0042] Step 3. Preparation of external aqueous phase: Add hydrophilic emulsifier and inorganic salt solution to water at a mass ratio of 4:1 and stir to obtain external aqueous phase. During the process, adjust the osmotic pressure of the external aqueous phase to be close to that of the W / O emulsion. The hydrophilic emulsifier is a surfactant with an HLB value of 12, and the inorganic salt solution is the same as in step 1.

[0043] Step 4. Preparation of W / O / W emulsion: Stir the external aqueous phase prepared in step 3 at low speed and gently, and add it dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%.

[0044] Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water, add hydrochloric acid to adjust the pH to 6.5, and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction of 92%, an emulsion particle size of 1.182 μm, and a pH of 2.03 mPa·s.

[0045] Example 4

[0046] like Figure 1 As shown, a method for preparing a bridging fluid for the separation of fine mineral oil agglomerates includes the following steps:

[0047] Step 1. Preparation of W / O emulsion: Add the lipophilic emulsifier and inorganic salt solution to the oil phase at a mass ratio of 2:1 (oil phase to lipophilic emulsifier). Stir gently at 250 rpm for 30 minutes to obtain the W / O emulsion. The oil phase is diesel oil, the lipophilic emulsifier is a surfactant with an HLB value of 6.5, and the inorganic salt solution is a 0.2 mol / L NaCl solution with a dropwise addition ratio of 0.01:1 to the oil phase mass.

[0048] Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add the oil phase dropwise to the prepared W / O emulsion for dilution until the internal aqueous phase volume fraction is in the range of 45%~50%;

[0049] Step 3. Preparation of external aqueous phase: Add hydrophilic emulsifier and inorganic salt solution to water at a mass ratio of 2:1 and stir to obtain external aqueous phase. During the process, adjust the osmotic pressure of the external aqueous phase to be close to that of the W / O emulsion. The hydrophilic emulsifier is a surfactant with an HLB value of 12, and the inorganic salt solution is the same as in step 1.

[0050] Step 4. Preparation of W / O / W emulsion: Stir the external aqueous phase prepared in step 3 at low speed and gently, and add it dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%.

[0051] Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water, add hydrochloric acid to adjust the pH to 6.5, and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction of 83%, an emulsion particle size of 0.761 μm, and a pH of 0.86 mPa·s.

[0052] Experiment 1

[0053] Low-order kerosene agglomeration flotation tests were conducted using the high internal phase W / O / W emulsion prepared in Example 1 as a bridging fluid.

[0054] The low-rank coal pure mineral (low-ash clean coal) particles used accounted for 85% of the mass of the -45μm particle size. The flotation test was conducted using a 1.0LXFD type hanging flotation machine with a spindle speed of 1700r / min.

[0055] 30g of coal sample was weighed and poured into a flotation cell containing ultrapure water. A high internal phase W / O / W emulsion was added at a dosage of 1500g / t and stirred for 3 minutes. A frother (2-octanol) was added at a dosage of 150g / t and stirred for 30 seconds. Gas was then introduced to scrape off the foam for 3 minutes. The scraped-off foam and the residue at the bottom of the cell were filtered, dried, and weighed to obtain the ash content and combustible gas recovery rate of the product. In addition, the same dosage of kerosene, high internal phase W / O emulsion, and ordinary W / O / W emulsion were selected as collectors. The high internal phase W / O emulsion had an internal water ratio of 59%, a particle size of 1.69μm, and a viscosity of 0.42mPa·s. The ordinary W / O / W emulsion had an internal water ratio of 78%, a particle size of 0.617μm, and a viscosity of 0.69mPa·s. All other experimental conditions were the same, and a control experiment was conducted. The experimental results are shown in Table 1.

[0056] Table 1. Experimental Results

[0057]

[0058] As can be seen from Table 1, the clean coal recovery rate of the novel bridging fluid of the present invention is significantly higher than that of kerosene and high internal phase W / O emulsion, indicating that the novel bridging fluid provided by the present invention has good recovery ability for low-rank coal. At the same time, compared with kerosene, W / O emulsion and ordinary W / O / W emulsion, the actual oil consumption of the novel bridging fluid provided by the present invention is reduced by 87%, 28% and 9%, respectively.

[0059] Experiment 2

[0060] The high internal phase W / O / W emulsion prepared in Example 2 was used as a bridging fluid for molybdenum ore agglomeration flotation tests.

[0061] The molybdenite used was a single mineral sample with a particle size of -38μm. The flotation test was conducted using a 1.0LXFD hanging flotation machine with a spindle speed of 1700r / min.

[0062] 300g of ore sample was weighed and poured into a flotation cell containing ultrapure water. A high internal phase W / O / W emulsion was added at a dosage of 200g / t and stirred for 3 minutes. A frother (2-octanol) was added at a dosage of 100g / t and stirred for 30 seconds. Gas was then introduced for skimming and foaming for 3 minutes. The resulting concentrate and tailings were filtered, dried, and weighed separately to obtain the molybdenum grade and recovery rate of the concentrate. In addition, a control experiment was conducted using the same dosage of kerosene, high internal phase W / O emulsion, and ordinary W / O / W emulsion. The high internal phase W / O emulsion used had an internal water ratio of 59%, a particle size of 1.69μm, and a viscosity of 0.42mPa·s. The ordinary W / O / W emulsion used had an internal water ratio of 78%, a particle size of 0.617μm, and a viscosity of 0.69mPa·s. All other experimental conditions were the same. The experimental results are shown in Table 2.

[0063] Table 2 Experimental Results

[0064]

[0065]

[0066] It can be seen that the concentrate recovery rate of the novel bridging fluid of the present invention is significantly higher than that of kerosene and high internal phase W / O emulsion, indicating that the novel bridging fluid provided by the present invention has a good recovery capacity for molybdenite. At the same time, compared with kerosene, W / O emulsion and ordinary W / O / W emulsion, the actual oil consumption of the novel bridging fluid provided by the present invention is reduced by 90%, 31% and 12%, respectively.

[0067] Experiment 3

[0068] The high internal phase W / O / W emulsion prepared in Example 3 was used as a bridging fluid for gasification ash residue oil agglomeration flotation tests.

[0069] The gasification ash used is a typical gasification fine ash, with -45μm particle size content reaching 80%. A 1.0LXFD type hanging tank flotation machine was used, with a spindle speed of 1700 r / min.

[0070] 30g of ore sample was weighed and poured into a flotation cell containing ultrapure water. A high internal phase W / O / W emulsion was added at a dosage of 5000g / t and stirred for 3 minutes. A frother (2-octanol) was added at a dosage of 100g / t and stirred for 30 seconds. Gas was then introduced for skimming and foam removal for 3 minutes. The concentrate and tailings were filtered, dried, and weighed separately to obtain the concentrate and tailings recovery rates. In addition, a control experiment was conducted using the same dosage of kerosene, high internal phase W / O emulsion, and ordinary W / O / W emulsion as collectors. The high internal phase W / O emulsion used had an internal water ratio of 59%, a particle size of 1.69μm, and a viscosity of 0.42mPa·s. The ordinary W / O / W emulsion used had an internal water ratio of 78%, a particle size of 0.617μm, and a viscosity of 0.69mPa·s. All other experimental conditions were the same. The experimental results are shown in Table 3.

[0071] Table 3. Experimental Results

[0072]

[0073] It can be seen that the concentrate recovery rate of the novel bridge fluid of the present invention is higher than that of kerosene and high internal phase W / O emulsion, indicating that the novel bridge fluid provided by the present invention has a good recovery ability for gasification ash residue. At the same time, compared with kerosene, W / O emulsion and ordinary W / O / W emulsion, the actual oil consumption of the novel bridge fluid provided by the present invention is reduced by 92%, 33% and 14%, respectively.

[0074] Experiment 4

[0075] The high internal phase W / O / W emulsion prepared in Example 4 was used as a bridging fluid for graphite oil agglomeration flotation experiments.

[0076] The graphite particles with a diameter of -74μm accounted for 94.25%, and those with a diameter of -38μm accounted for 16.8%. The experiment used a 1.0LXFD type hanging tank flotation machine with a spindle speed of 2100 r / min.

[0077] 100g of ore sample was weighed and poured into a flotation cell containing ultrapure water. A high internal phase W / O / W emulsion was added at a dosage of 200g / t and stirred for 3 minutes. A frother (2-octanol) was added at a dosage of 100g / t and stirred for 30 seconds. Gas was then introduced for skimming and foam removal for 3 minutes. The concentrate and tailings were filtered, dried, and weighed separately to obtain the concentrate and tailings recovery rates. In addition, a control experiment was conducted using the same dosage of kerosene, high internal phase W / O emulsion, and ordinary W / O / W emulsion as collectors. The high internal phase W / O emulsion used had an internal water ratio of 59%, a particle size of 1.69μm, and a viscosity of 0.42mPa·s. The ordinary W / O / W emulsion used had an internal water ratio of 78%, a particle size of 0.617μm, and a viscosity of 0.69mPa·s. All other experimental conditions were the same. The experimental results are shown in Table 4.

[0078] Table 4. Test Results

[0079]

[0080] It can be seen that the concentrate recovery rate of the novel bridging fluid of the present invention is higher than that of kerosene and high internal phase W / O emulsion, indicating that the novel bridging fluid provided by the present invention has good recovery ability for graphite. At the same time, compared with kerosene, W / O emulsion and ordinary W / O / W emulsion, the actual oil consumption of the novel bridging fluid provided by the present invention is reduced by 83%, 24% and 5%, respectively.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bridging fluid for the separation and agglomeration of fine mineral oil particles, characterized in that, Includes the following steps: Step 1. Preparation of W / O emulsion: Add a set amount of lipophilic emulsifier and inorganic salt solution to the oil phase, and stir gently at low speed to obtain a W / O emulsion; the oil phase is any one or a combination of several of straight-chain alkanes, branched-chain alkanes and cycloalkanes; Step 2. Internal oil phase dilution: Maintain the W / O emulsion temperature at 22℃~26℃, and add the oil phase dropwise to the prepared W / O emulsion for dilution until the internal aqueous phase volume fraction is in the range of 45%~50%; Step 3. Preparation of external aqueous phase: Add a set amount of hydrophilic emulsifier and inorganic salt solution to water, stir to obtain external aqueous phase, and adjust the osmotic pressure of external aqueous phase to be close to the osmotic pressure of the W / O emulsion; Step 4. Preparation of W / O / W emulsion: The external aqueous phase prepared in step 3 is gently stirred at low speed and added dropwise to the diluted W / O emulsion in step 2 to form a W / O / W emulsion with an internal aqueous phase volume fraction of 45% to 50%. Step 5. Dilution and swelling: Dilute the W / O / W emulsion with deionized water and stir to obtain a high internal phase W / O / W emulsion with an internal aqueous phase volume fraction greater than 80%.

2. The method for preparing a bridging fluid for the agglomeration and sorting of fine mineral oil particles as described in claim 1, characterized in that, In step 1, the lipophilic emulsifier is a surfactant with an HLB value between 4.3 and 8.6, and the mass ratio of the oil phase to the lipophilic emulsifier is (2-4):

1.

3. The method for preparing a bridging fluid for the agglomeration and sorting of fine mineral oil particles as described in claim 1, characterized in that, In step 2, the hydrophilic emulsifier is a surfactant with an HLB value of 10.5 to 16.7, and the mass ratio of water to hydrophilic emulsifier is (2 to 5):

1.

4. The method for preparing a bridging fluid for the agglomeration and sorting of fine mineral oil particles as described in claim 1, characterized in that, In steps 1 and 2, the inorganic salt solution is any one or a combination of NaCl, MgCl2, and AlCl3, the concentration of the inorganic salt solution is 0.2 to 0.3 mol / L, and the mass ratio of the inorganic salt solution to the oil phase in step 1 is (0.01 to 0.02):

1.

5. The method for preparing a bridging fluid for the agglomeration and sorting of fine mineral oil particles as described in claim 1, characterized in that, In step 5, during the process of diluting the W / O / W emulsion with deionized water, hydrochloric acid or sodium hydroxide solution is added to adjust the pH value to 6-8.

6. The method for preparing a bridging fluid for the agglomeration and sorting of fine mineral oil particles as described in claim 1, characterized in that, The low-speed, gentle stirring is performed at a speed of 100–300 r / min for 30 min.

7. A W / O / W emulsion, prepared by the preparation method according to any one of claims 1-6; wherein the W / O / W emulsion has an internal aqueous phase mass fraction greater than 80%, an emulsion particle size range of 0.543-1.34 μm, and an emulsion viscosity less than 4.45 mPa·s.

8. The application of the W / O / W emulsion as described in claim 7 as a bridging fluid for the separation of fine mineral oil agglomerates.

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