System and method for removing fluorine and recycling calcium fluoride by using tubular membrane contactor

Abstract

The invention relates to the technical field of fluorine-containing wastewater treatment, in particular to a system for removing fluorine and recycling calcium fluoride by using a tubular membrane contactor, which comprises a first security filter, the tubular membrane contactor, a second security filter, a material separation membrane, a centrifugal machine and a drying machine, the first security filter, the tubular membrane contactor, the second security filter, the material separation membrane, the centrifugal machine and the drying machine are sequentially connected from front to back, and produced water of the material separation membrane and supernate of the centrifugal machine return to the tubular membrane contactor through a calcium-containing solution inlet of the tubular membrane contactor. The tubular membrane contactor is used for removing fluorine, the calcium-containing solution does not need to be in direct contact with the fluorine-containing wastewater, the hardness of the fluorine-containing wastewater is not increased, fluorine-containing sludge with complex components is not formed, the purity of obtained calcium fluoride is higher, the application range is wider, the economic benefit is higher, a large amount of lime, coagulant and flocculant do not need to be added, the cost is reduced, and the economic benefit is increased. And the risk of environmental pollution is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine-containing wastewater treatment, and in particular to a system and method for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor. Background Art

[0002] Fluoride-containing wastewater comes from a wide range of sources, including the smelting of non-ferrous metals and rare earth metals, aluminum electrolytic refining, glass and ceramic manufacturing, fluorosilicates, pesticides, stainless steel pickling, and the manufacturing of electronic products such as semiconductors and liquid crystal displays. If these fluoride-containing wastewaters are discharged without treatment, they are likely to adhere to soil, water and organic tissues, increase exposure risks, and cause harm to human health and safety.

[0003] Recycling calcium fluoride (CaF2) from high-concentration fluoride-containing wastewater can, on the one hand, cut off an important way for fluorine pollution to enter the natural environment, reduce the risk of fluorine pollution, and benefit environmental protection and ecological safety. On the other hand, the recovered calcium fluoride also has extremely high resource utilization value. After a series of purification and processing technology, calcium fluoride can be re-invested in various links of industrial production. This not only greatly reduces the dependence on natural fluorite resources and alleviates the pressure of resource shortage, but also reduces the company's raw material procurement costs, improves economic benefits, and forms a virtuous cycle model of environmental and economic win-win, which helps to promote the sustainable development of the industrial process and implement the modern resource recycling concept.

[0004] At present, the traditional method for treating high-concentration fluorine-containing industrial wastewater is lime flocculation and sedimentation. The basic process is as follows: fluorine-containing wastewater - reaction tank (add lime, coagulant or flocculant for stirring) - concentration tank (sludge is treated regularly) - supernatant is defluorinated wastewater. The traditional lime flocculation and sedimentation method for treating high-concentration fluorine-containing industrial wastewater has the disadvantages of large amount of calcium fluoride sludge, high water content, limited comprehensive utilization and difficult treatment and disposal, as follows: Difficulty in treating and disposing of fluorine-containing sludge: Fluorine-containing sludge has certain corrosive, toxic and other hazardous characteristics. The traditional treatment method is landfill, which may cause secondary pollution. Although calcium fluoride sludge produced by wastewater treatment is no longer a hazardous waste according to the 2016 version of the National List of Hazardous Wastes (hereinafter referred to as the List), due to its low calorific value and high leaching risk, it is generally not accepted by disposal units, resulting in an increasing accumulation of calcium fluoride sludge.

[0005] Adding excessive lime increases the hardness of wastewater and increases the burden of subsequent hardness removal of wastewater: In the process of treating fluoride-containing wastewater by the traditional lime flocculation and sedimentation method, in order to ensure the ideal fluoride ion removal effect and achieve rapid sedimentation and separation of sludge, operators usually take the means of adding excessive lime to the wastewater. From the perspective of chemical reaction, lime (the main component is calcium oxide or calcium hydroxide) reacts with fluoride ions in wastewater to form calcium fluoride precipitate, and this process follows a stoichiometric relationship. However, in actual operation, due to the complexity of wastewater components, fluctuations in reaction conditions, and considerations of the safety of treatment effects, lime is often added in an amount that exceeds the theoretical reaction requirement. When excess lime enters the wastewater system, in addition to reacting with fluoride ions, the calcium ions in it will dissolve in the water in large quantities, thereby significantly increasing the hardness of the wastewater, which is not conducive to the subsequent treatment and purification of the wastewater.

[0006] Calcium fluoride is not pure and its comprehensive utilization is limited: In terms of resource utilization, there are many limitations on calcium fluoride sludge. Although calcium fluoride has certain application value in theory, such as being used as a raw material or additive in some industrial fields, the purity of calcium fluoride in sludge is not high, and it is often mixed with a large amount of unreacted lime, other metal ions, organic matter and other impurities, making it difficult to directly apply it to industrial production links with high purity requirements. For example, fluorine chemical industry usually requires the grade of CaF2 to be greater than 97%, and the content of harmful impurities such as CaCO3 and SiO2 is also required to be controlled within 1%.

[0007] The packing density of the hollow fiber membrane contactor is high, and the flow channels between the fiber bundles are relatively narrow. Calcium fluoride is difficult to dissolve in water. As the reaction proceeds, when the calcium fluoride particles gradually increase, it is easy to accumulate in these narrow channels, causing blockage, and thus affecting the performance of the entire membrane contactor. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a system and method for removing fluorine and recovering calcium fluoride using a tubular membrane contactor.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: A system for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor, comprising a first safety filter, a tubular membrane contactor, a second safety filter, a material separation membrane, a centrifuge and a dryer; The first security filter, tubular membrane contactor, second security filter, material separation membrane, centrifuge and dryer are sequentially connected from front to back, and the produced water of the material separation membrane and the supernatant of the centrifuge are returned to the tubular membrane contactor through the calcium-containing solution inlet of the tubular membrane contactor.

[0010] Furthermore, it also includes a wastewater lifting pump, a calcium-containing solution tank, a calcium-containing solution lifting pump, a calcium fluoride recovery tank, a calcium fluoride solution lifting pump, a calcium fluoride concentrated water tank, a centrifuge water inlet pump and a dryer mud inlet pump; The output end of the wastewater lifting pump is connected to the inlet of the first security filter, the outlet of the first security filter is connected to the fluorine-containing wastewater inlet of the tubular membrane contactor, the tubular membrane contactor is also provided with a calcium fluoride solution outlet, a calcium-containing solution inlet and a defluorinated wastewater outlet, the outlet of the calcium-containing solution tank is connected to the suction end of the calcium-containing solution lifting pump, the output end of the calcium-containing solution lifting pump is connected to the calcium-containing solution inlet of the tubular membrane contactor, the outlet of the calcium fluoride recovery tank is connected to the suction end of the calcium fluoride solution lifting pump, the output end of the calcium fluoride solution lifting pump is connected to the second security filter. The inlet of the first security filter is connected, the outlet of the second security filter is connected to the inlet of the material separation membrane, the material separation membrane is provided with a concentrated water outlet and a produced water outlet, the produced water outlet is connected to the inlet of the calcium-containing solution tank, the concentrated water outlet of the material separation membrane is connected to the inlet of the calcium fluoride concentrated water tank, the outlet of the calcium fluoride concentrated water tank is connected to the suction end of the centrifuge water inlet pump, the output end of the centrifuge water inlet pump is connected to the inlet of the centrifuge, the supernatant outlet of the centrifuge is connected to the inlet of the calcium-containing solution tank, and the mud outlet of the centrifuge is connected to the inlet of the dryer.

[0011] Preferably, the filtration accuracy of the first security filter is 5 to 10 microns.

[0012] Preferably, the membrane tube diameter of the tubular membrane reactor is 3 to 8 mm, and the pore diameter is 1 to 30 nm.

[0013] Preferably, the filtering accuracy of the second security filter is 5 to 10 microns.

[0014] A method for removing fluorine and recovering calcium fluoride using a tubular membrane contactor comprises the following steps: S1, high concentration fluoride-containing wastewater passes through the security filter and enters the tubular membrane contactor; S2. In the tubular membrane contactor, fluoride ions pass through the membrane and react with calcium ions on the other side of the membrane to form calcium fluoride particles, which promotes the defluorination of wastewater; S3, the calcium fluoride solution is filtered and concentrated through a material separation membrane, and the produced water is reused to continue reacting with fluoride ions; S4. The concentrated water from the material separation membrane is centrifuged and dried to obtain calcium fluoride powder.

[0015] Preferably, in step S2, a calcium chloride solution provides calcium ions.

[0016] Preferably, in step S2, a calcium hydroxide solution provides calcium ions.

[0017] The beneficial effects of the present invention are: 1. High purity of calcium fluoride: The calcium-containing solution and the fluoride-containing wastewater react in the tubular membrane contactor. The calcium-containing solution and the fluoride-containing wastewater do not need to be in direct contact. This design avoids the complex chemical reactions and impurity doping problems that may be caused by the direct mixing of the two solutions. The membrane acts as a selective barrier, allowing fluoride ions to migrate from the fluoride-containing wastewater to the calcium-containing solution side driven by the concentration difference. Other metal ions and organic matter in the fluoride-containing wastewater are restricted by the membrane layer and it is difficult to enter the area where the calcium-containing solution reacts with the fluoride ions. Therefore, the generated calcium fluoride precipitate contains almost no other metal ions and organic matter, or its content can be controlled at a very low level, and the concentration of calcium fluoride can reach more than 98%.

[0018] 2. Does not increase the hardness of wastewater: Due to the barrier of the membrane layer between the calcium-containing solution and the fluoride-containing wastewater, calcium ions do not pass through the membrane layer into the fluoride-containing wastewater, and will not cause a significant increase in the hardness of the wastewater.

[0019] 3. No fluoride-containing sludge is generated: the calcium fluoride solution is concentrated, centrifuged and dried to become high-purity calcium fluoride powder, which can be widely used in various fields and is conducive to alleviating the pressure of fluorite resource shortage.

[0020] 4. Reduce the dosage of chemicals and reduce the risk of environmental pollution: Reduce the dosage of lime, coagulants and flocculants, and reduce the cost of chemicals for fluoride-containing wastewater treatment. At the same time, reducing the dosage of chemicals means reducing the amount of these chemicals entering the wastewater and the environment, reducing the risk of chemical pollution to the water environment.

[0021] 5. Compared with hollow fiber membrane, it is more resistant to pollution: Compared with ordinary hollow fiber, tubular membrane separation system integration can withstand higher sludge concentration and more extreme pH environment. In the process of fluoride ion recovery and generation of calcium fluoride particles, the hollow fiber membrane will intensify the interaction between particles due to its narrow channels and large specific surface area, and its anti-clogging ability is weak. The calcium fluoride particles in the tubular membrane have a larger diffusion space and will not quickly accumulate on the membrane to cause blockage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a system for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor proposed by the present invention; Figure 2 The present invention provides a flow chart of a method for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor.

[0023] In the figure: 1-wastewater lifting pump; 2-first safety filter; 3-tubular membrane contactor; 4-calcium solution tank; 5-calcium solution lifting pump; 6-calcium fluoride recovery tank; 7-calcium fluoride solution lifting pump; 8-second safety filter; 9-material separation membrane; 10-calcium fluoride concentrated water tank; 11-centrifuge water inlet pump; 12-centrifuge; 13-dryer mud inlet pump; 14-dryer. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Embodiment 1: Reference Figure 1 A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor includes a wastewater lifting pump 1, a first security filter 2, a tubular membrane contactor 3, a calcium-containing solution tank 4, a calcium-containing solution lifting pump 5, a calcium fluoride recovery tank 6, a calcium fluoride solution lifting pump 7, a second security filter 8, a material separation membrane 9, a calcium fluoride concentrated water tank 10, a centrifuge water inlet pump 11, a centrifuge 12, a dryer mud inlet pump 13 and a dryer 14.

[0026] The output end of the wastewater lifting pump 1 is connected to the inlet of the first security filter 2, the outlet of the first security filter 2 is connected to the fluorine-containing wastewater inlet of the tubular membrane contactor 3, the tubular membrane contactor 3 is also provided with a calcium fluoride solution outlet, a calcium-containing solution inlet and a defluorinated wastewater outlet, the outlet of the calcium-containing solution tank 4 is connected to the suction end of the calcium-containing solution lifting pump 5, the output end of the calcium-containing solution lifting pump 5 is connected to the calcium-containing solution inlet of the tubular membrane contactor 3, the outlet of the calcium fluoride recovery tank 6 is connected to the suction end of the calcium fluoride solution lifting pump 7, and the output end of the calcium fluoride solution lifting pump 7 is connected to the second security filter 8, the outlet of the second security filter 8 is connected to the inlet of the material separation membrane 9, the material separation membrane 9 is provided with a concentrated water outlet and a produced water outlet, and its produced water outlet is connected to the inlet of the calcium-containing solution tank 4, the concentrated water outlet of the material separation membrane 9 is connected to the inlet of the calcium fluoride concentrated water tank 10, the outlet of the calcium fluoride concentrated water tank 10 is connected to the suction end of the centrifuge water inlet pump 11, the output end of the centrifuge water inlet pump 11 is connected to the inlet of the centrifuge 12, the supernatant outlet of the centrifuge 12 is connected to the inlet of the calcium-containing solution tank 4, and the mud outlet of the centrifuge 12 is connected to the inlet of the dryer 14.

[0027] In this embodiment, the calcium-containing solution is a calcium chloride solution.

[0028] High-concentration fluoride-containing wastewater enters the first security filter 2 (filtration accuracy 5-10 microns) through the wastewater lifting pump 1, and then enters the tubular membrane reactor 3. A relatively high-concentration calcium chloride solution is configured in the calcium-containing solution tank 4 and injected into the tubular membrane reactor 3 through the calcium-containing solution lifting pump 5.

[0029] In the tubular membrane reactor 3, the fluorine-containing wastewater flows through the tube side, and the calcium chloride solution flows through the shell side. The membrane tube diameter is 3-8 mm, and the pore size is 1-30 nm. The fluoride ions in the wastewater pass through the membrane and react with the calcium ions in the calcium chloride solution to generate CaF2 that is insoluble in water, which is collected in the calcium fluoride recovery tank 6.

[0030] The calcium fluoride solution enters the second security filter 8 (filtration accuracy 5-10 microns) through the calcium fluoride solution lifting pump 7, and then enters the material separation membrane 9 for separation and concentration. The clarified produced water is transported to the calcium-containing solution tank 4 for reuse, and the concentrated calcium fluoride concentrated water is collected in the calcium fluoride concentrated water tank 10.

[0031] The calcium fluoride concentrated water is transported to the centrifuge 12 by the centrifuge inlet pump 11, the supernatant is transported to the calcium solution tank 4 for reuse, and the deposited calcium fluoride is transported to the dryer 14 by the dryer mud pump 13, and finally the calcium fluoride powder is obtained after dehydration and drying.

[0032] Reference Figure 2 , a method for removing fluorine and recovering calcium fluoride using a tubular membrane contactor, comprising the following steps: S1, high concentration fluoride-containing wastewater passes through the security filter and enters the tubular membrane contactor; S2. In the tubular membrane contactor, fluoride ions pass through the membrane and react with calcium ions on the other side of the membrane to form calcium fluoride particles, which promotes the defluorination of wastewater; S3, the calcium fluoride solution is filtered and concentrated through a material separation membrane, and the produced water is reused to continue reacting with fluoride ions; S4. The concentrated water from the material separation membrane is centrifuged and dried to obtain calcium fluoride powder.

[0033] Embodiment 2:

[0034] Different from the first embodiment, the calcium-containing solution is a calcium hydroxide solution, which recovers calcium fluoride when treating acidic fluoride-containing wastewater and neutralizes H+ in the wastewater, thereby adjusting the pH to a certain extent and reducing the dosage of the commonly used pH regulator sodium hydroxide.

[0035] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor, characterized in that: It comprises a first safety filter (2), a tubular membrane contactor (3), a second safety filter (8), a material separation membrane (9), a centrifuge (12) and a dryer (14); The first security filter (2), the tubular membrane contactor (3), the second security filter (8), the material separation membrane (9), the centrifuge (12) and the dryer (14) are connected in sequence from front to back, and the produced water of the material separation membrane (9) and the supernatant of the centrifuge (12) are returned to the tubular membrane contactor (3) through the calcium-containing solution inlet of the tubular membrane contactor (3).

2. A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor according to claim 1, characterized in that: It also includes a wastewater lifting pump (1), a calcium-containing solution tank (4), a calcium-containing solution lifting pump (5), a calcium fluoride recovery tank (6), a calcium fluoride solution lifting pump (7), a calcium fluoride concentrated water tank (10), a centrifuge water inlet pump (11) and a dryer mud inlet pump (13); The output end of the wastewater lifting pump (1) is connected to the inlet of the first security filter (2), the outlet of the first security filter (2) is connected to the fluorine-containing wastewater inlet of the tubular membrane contactor (3), the tubular membrane contactor (3) is further provided with a calcium fluoride solution outlet, a calcium-containing solution inlet and a defluorinated wastewater outlet, the outlet of the calcium-containing solution tank (4) is connected to the suction end of the calcium-containing solution lifting pump (5), the output end of the calcium-containing solution lifting pump (5) is connected to the calcium-containing solution inlet of the tubular membrane contactor (3), the outlet of the calcium fluoride recovery tank (6) is connected to the suction end of the calcium fluoride solution lifting pump (7), the output end of the calcium fluoride solution lifting pump (7) is connected to the outlet of the second security filter (8), and the outlet of the calcium fluoride recovery tank (6) is connected to the suction end of the calcium fluoride solution lifting pump (7). The inlet of the second security filter (8) is connected, the outlet of the second security filter (8) is connected to the inlet of the material separation membrane (9), the material separation membrane (9) is provided with a concentrated water outlet and a produced water outlet, the produced water outlet of the material separation membrane (9) is connected to the inlet of the calcium-containing solution tank (4), the concentrated water outlet of the material separation membrane (9) is connected to the inlet of the calcium fluoride concentrated water tank (10), the outlet of the calcium fluoride concentrated water tank (10) is connected to the suction end of the centrifuge water inlet pump (11), the output end of the centrifuge water inlet pump (11) is connected to the inlet of the centrifuge (12), the supernatant outlet of the centrifuge (12) is connected to the inlet of the calcium-containing solution tank (4), and the slurry outlet of the centrifuge (12) is connected to the inlet of the dryer (14).

3. A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor according to claim 1 or 2, characterized in that: The filtering accuracy of the first security filter (2) is 5 to 10 microns.

4. A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor according to claim 1 or 2, characterized in that: The membrane tube diameter of the tubular membrane reactor (3) is 3 to 8 mm, and the pore diameter is 1 to 30 nm.

5. A system for removing fluorine and recovering calcium fluoride using a tubular membrane contactor according to claim 1 or 2, characterized in that: The filtering accuracy of the second security filter (8) is 5 to 10 microns.

6. A method for removing fluorine and recovering calcium fluoride using a tubular membrane contactor, characterized in that: The following steps are involved: S1, high concentration fluoride-containing wastewater passes through the security filter and enters the tubular membrane contactor; S2. In the tubular membrane contactor, fluoride ions pass through the membrane and react with calcium ions on the other side of the membrane to form calcium fluoride particles, which promotes the defluorination of wastewater; S3, the calcium fluoride solution is filtered and concentrated through a material separation membrane, and the produced water is reused to continue reacting with fluoride ions; S4. The concentrated water from the material separation membrane is centrifuged and dried to obtain calcium fluoride powder.

7. The method for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor according to claim 6, characterized in that: In step S2, a calcium chloride solution provides calcium ions.

8. The method for removing fluorine and recovering calcium fluoride by using a tubular membrane contactor according to claim 6, characterized in that: In step S2, a calcium hydroxide solution provides calcium ions.

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