A waste treatment method combining electrostatic adsorption and ultrafiltration

Abstract

The present invention discloses a waste treatment method combining electrostatic adsorption with ultrafiltration, and relates to the field of wastewater treatment. The present invention achieves particle size control of suspended particles in wastewater by adjusting the molar ratio of calcium fluoride particles in fluoride-containing wastewater to silicon dioxide nanoparticles in silicon-containing wastewater, and determines the adsorption state of particles by Zeta potential, thereby quickly and effectively reducing the turbidity of mixed wastewater, and achieving efficient removal of residual suspended particles under the condition of minimum membrane pollution in ultrafiltration. Since calcium fluoride particles in fluoride-containing wastewater are positively charged and silicon dioxide nanoparticles in silicon-containing wastewater are negatively charged, the adsorption and aggregation of particles are achieved by utilizing the opposite charge principle of the two suspended particles, thereby achieving the purpose of rapid sedimentation of colloidal particles. At the same time, the dosage of the reagent is greatly reduced, the pollution of the ultrafiltration membrane is effectively reduced, the operation stability of the membrane system is increased, and the cost is saved.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, and in particular to a wastewater treatment method combining electrostatic adsorption with ultrafiltration. Background Art

[0002] The rapid development of industries such as semiconductors, printed circuit boards, metal smelting, electroplating, chemicals and pesticides has generated a large amount of fluorine-containing wastewater and silicon-containing wastewater. For example, the photolithography and etching processes involved in the semiconductor manufacturing process require the use of hydrofluoric acid, which produces a large amount of fluorine-containing wastewater with a concentration range of 250mg / L to 1500mg / L, while the current industrial fluoride emission standard is limited to 10mg / L. In industries such as semiconductors and printed circuit boards, chemical mechanical polishing processes often use nanoparticles as abrasives, and the silicon-containing wastewater produced usually contains nanoparticles with a concentration of 500-2000mg / L. Therefore, the effective separation of fluoride from fluoride-containing wastewater and the effective separation of nanoparticles from silicon-containing wastewater have received widespread attention from researchers.

[0003] At present, adding calcium salts to fluoride-containing wastewater for chemical precipitation is the most widely used and economical method for fluoride removal, but this reaction often produces a large number of calcium fluoride suspended particles that are extremely difficult to settle. Similarly, nanoparticles in high-turbidity silicon-containing wastewater are suspended in the solution, making the solution appear milky white. Membrane separation technology is a new separation technology developed since the 21st century. It mainly uses the selective separation of membranes to achieve the separation, purification and concentration of different components in the feed liquid. Ultrafiltration shows great application potential in wastewater treatment because it can separate particles with a particle size between 0.002 and 0.1μm at low operating pressure. However, if fluoride-containing wastewater and silicon-containing wastewater are directly passed into the ultrafiltration device for solid-liquid separation, serious inorganic membrane pollution will be caused. Therefore, in industry, coagulants and flocculants such as polyaluminum chloride, polyferric sulfate, polyacrylic acid and polyacrylamide are often used for pre-sedimentation of calcium fluoride or nanoparticles to reduce the pollution of the later ultrafiltration membrane and improve the operation stability of the ultrafiltration membrane. Chinese patent (application number 201110082746.8) discloses a coagulation, sedimentation, ultrafiltration, and reverse osmosis method for treating fluorine-containing wastewater, achieving 95% recovery of fluorine-containing wastewater. Chinese patent (application number 202011612504.0) discloses a reuse water process for treating silicon-containing wastewater by inclined tube sedimentation (adding polyaluminium chloride and polyacrylamide), ultrafiltration and nanofiltration, achieving a nano-silicon dioxide particle removal rate of more than 95%. The above methods are effective in removing characteristic pollutants in fluorine-containing wastewater and silicon-containing wastewater. However, these methods require a large amount of coagulants and flocculants, and often require the establishment of a regulating tank. In addition, the flocs generated during the coagulation and flocculation process inevitably pollute the membrane system, seriously affecting the stability of the membrane system operation. The addition of coagulants can easily introduce impurity ions into the wastewater, making the conductivity of the wastewater too high, increasing the cost of chemical agents and affecting the effluent quality. Therefore, it is possible to consider studying the characteristic pollutants in fluorine-containing wastewater and silicon-containing wastewater, and to achieve simultaneous treatment of the two types of wastewater without adding any coagulants and flocculants, thereby effectively improving the comprehensive wastewater treatment capacity.

[0004] Technical personnel in this field are committed to exploring the effective removal of suspended particulate matter by utilizing the interaction between characteristic pollutants in wastewater, and developing a simple and rapid waste treatment method combining electrostatic adsorption with ultrafiltration. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problems to be solved by the present invention are large dosage of coagulant and flocculant, complicated treatment steps, low wastewater treatment capacity, serious membrane pollution, etc.

[0006] To achieve the above-mentioned purpose, the present invention provides a waste treatment method combining electrostatic adsorption with ultrafiltration.

[0007] Step 1: adding calcium chloride to the fluoride-containing wastewater, adjusting the molar ratio of fluoride to calcium in the solution, stirring until the precipitation reaction is complete, and obtaining fluoride-containing wastewater I having calcium fluoride particles;

[0008] Step 2: adding the silicon-containing wastewater to the fluorine-containing wastewater I obtained in step 1, adjusting the molar ratio of silicon dioxide to calcium fluoride, slowly stirring and standing to obtain mixed wastewater after preliminary sedimentation, testing the Zeta potential of the mixed wastewater, and obtaining the particle size of the particles in the mixed wastewater;

[0009] Step 3: Pass the mixed wastewater after preliminary sedimentation into the ultrafiltration device for cross-flow filtration, and adjust the operating pressure and flow rate; stop the experiment when the system water production rate reaches 95%.

[0010] In a preferred embodiment of the present invention, in step 1, calcium chloride is added to the fluorine-containing wastewater and stirred at a speed of 150 rpm for 10 minutes, and then slowly stirred at a speed of 50 rpm for 10 minutes to complete the precipitation reaction.

[0011] In another preferred embodiment of the present invention, in step 1, the mixed wastewater is slowly stirred at a speed of 50 rpm for 10 minutes and allowed to stand for 40 minutes.

[0012] In another preferred embodiment of the present invention, the cross-flow filtration time in step 3 is 60-100 minutes.

[0013] In another preferred embodiment of the present invention, the fluoride ion concentration of the effluent in step 3 is lower than 9 mg / L, and the turbidity is reduced to lower than 0.02 NTU.

[0014] In another preferred embodiment of the present invention, in step 1, the calcium-fluoride molar ratio of the solution is adjusted to be 0.5-0.7.

[0015] In another preferred embodiment of the present invention, in step 2, the molar ratio of silicon dioxide to calcium fluoride is adjusted to 2-8.

[0016] In another preferred embodiment of the present invention, the average particle size of the particles in step 2 is 1100-1850 nm.

[0017] In another preferred embodiment of the present invention, in step 3, preferably, the turbidity is reduced to 0 NTU.

[0018] In another preferred embodiment of the present invention, in step 3, preferably, the filtration time is shortened to 60-70 minutes.

[0019] Technical Effects

[0020] (1) This method achieves efficient and simultaneous removal of suspended solids in fluorine-containing wastewater and silicon-containing wastewater by using the waste treatment method. The operation is simple and easy. Silicon-containing wastewater can completely replace traditional coagulants and flocculants. The turbidity removal efficiency is high, and the comprehensive wastewater treatment capacity is effectively improved. The dosage of chemicals is greatly reduced, which greatly saves the production cost of the enterprise and improves the economic benefits of the enterprise.

[0021] (2) The turbidity of the mixed effluent of fluoride-containing wastewater and silicon-containing wastewater meets the turbidity index far lower than that of the ultrafiltration inlet water, effectively reducing the pollution of the ultrafiltration membrane and increasing the stability of the membrane system operation. The ultrafiltration system can effectively remove the residual pollutants in the mixed wastewater at the same time, and the effluent water quality meets the "Comprehensive Discharge Standard for Fluoride Wastewater", which is in line with the sustainable development concept of ecological protection, and provides reference and technical support for new semiconductor, printed circuit board, metal smelting, electroplating, chemical and pesticide enterprises that adopt membrane technology.

[0022] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of the present invention;

[0024] Figure 2 is a surface morphology image (SEM) of the original ultrafiltration membrane of the present invention;

[0025] Figure 3 is a surface morphology image (SEM) of the ultrafiltration membrane of Comparative Example 1 of the present invention;

[0026] Figure 4 is a surface morphology image (SEM) of the ultrafiltration membrane of Example 2 of the present invention;

[0027] Figure 5 is a surface topography (AFM) of the original ultrafiltration membrane of the present invention;

[0028] Figure 6 is a surface morphology image (AFM) of the ultrafiltration membrane of Comparative Example 1 of the present invention;

[0029] Figure 7 This is a surface morphology image (AFM) of the ultrafiltration membrane of Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0031] In the drawings, components with the same structure are indicated by the same numerical reference numerals, and components with similar structures or functions are indicated by similar numerical reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the illustration clearer, the thickness of the components is appropriately exaggerated in some places in the drawings.

[0032] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0033] Figure 1 is a process flow chart of the method of the present invention, Figure 2 is a SEM image of the surface morphology of the ultrafiltration membrane used in the method of the present invention, Figure 5 It is an AFM image of the surface morphology of the ultrafiltration membrane used in the method of the present invention.

[0034] Example 1

[0035] Step 1. Calcium chloride is added to the fluoride-containing wastewater, and the calcium-fluoride molar ratio of the solution is adjusted to 0.5. The fluoride-containing wastewater is stirred at a speed of 150 rpm for 10 minutes, and slowly stirred at a speed of 50 rpm for 10 minutes to complete the precipitation reaction, and the fluoride ion concentration is reduced from 500 mg / L to 11 mg / L, and the turbidity of the wastewater is 143 NTU.

[0036] Step 2. Add the silicon-containing wastewater to the fluoride-containing wastewater obtained in step 1, and adjust the molar ratio of silicon dioxide to calcium fluoride to 2. At this time, the Zeta potential of the wastewater is 38mV, and the particle size of the particles in the water is 1156nm. The mixed wastewater is slowly stirred at a speed of 50 rpm for 10 minutes and allowed to stand for 40 minutes. The fluoride ion concentration is reduced to 10mg / L and the turbidity is reduced to 38NTU.

[0037] Step 3. The mixed wastewater after preliminary sedimentation was passed into the ultrafiltration device for cross-flow filtration, and the operating pressure was adjusted to 0.01MPa, the flow rate was 1.5L / min, and the experiment was stopped when the system water production rate was 95%. The filtration time was 100 minutes, the water production flux was 160LMH, the fluoride ion concentration of the effluent was 9mg / L, and the turbidity was reduced to 0.02NTU.

[0038] Example 2

[0039] Steps 1 to 3 refer to Example 1, except that in step 1 the calcium-fluoride molar ratio is 0.6, the fluoride ion concentration is reduced from 500 mg / L to 7 mg / L, and the turbidity is 177 NTU.

[0040] In step 2, the molar ratio of silica to calcium fluoride was adjusted to 5. At this time, the Zeta potential of the wastewater was -0.74 mV, the average particle size of the particles was 1844 nm, the fluoride ion concentration was reduced to 2 mg / L, and the turbidity was reduced to 12 NTU after standing for 40 minutes.

[0041] In step 3, the filtration time was 60 minutes, the water production flux was 267LMH, the fluoride ion concentration of the effluent was 2 mg / L, and the turbidity was reduced to 0 NTU.

[0042] Example 3

[0043] Steps 1 to 3 refer to Example 1, except that in step 1 the calcium-fluoride molar ratio is 0.7, the fluoride ion concentration is reduced from 500 mg / L to 5 mg / L, and the turbidity is 180 NTU.

[0044] In step 2, the molar ratio of silica to calcium fluoride was adjusted to 8. At this time, the Zeta potential of the wastewater was -11 mV, the average particle size of the particles was 1315 nm, the fluoride ion concentration was reduced to 1.7 mg / L, and the turbidity was reduced to 16 NTU after standing for 40 minutes.

[0045] In step 3, the filtration time was 70 minutes, the water production flux was 228LMH, the effluent fluoride ion concentration was 1.7 mg / L, and the turbidity was reduced to 0 NTU.

[0046] Comparative Example 1

[0047] Step 1. Calcium chloride is added to the fluoride-containing wastewater to adjust the solution calcium-fluoride molar ratio to 0.6. The fluoride-containing wastewater is stirred at a speed of 150 rpm for 10 minutes, and slowly stirred at a speed of 50 rpm for 10 minutes to complete the precipitation reaction, and the fluoride ion concentration is reduced from 500 mg / L to 7 mg / L, and the turbidity is 177 NTU.

[0048] Step 2. The fluoride-containing wastewater in step 1 was allowed to stand for 40 minutes, at which time the Zeta potential of the wastewater was 44 mV, the fluoride ion concentration was still 7 mg / L, and the turbidity was slightly reduced from 177 NTU to 164 NTU.

[0049] Step 3. The wastewater from step 2 was passed into the ultrafiltration device for cross-flow filtration, and the operating pressure was adjusted to 0.01 MPa, the flow rate was 1.5 L / min, and the experiment was stopped when the system water production rate was 95%. The filtration time was 210 minutes, the water production flux was 76 LMH, the fluoride ion concentration of the effluent was 7 mg / L, and the turbidity was reduced to 0.02 NTU.

[0050] By comparing Example 2 with Comparative Example 1, it is obvious that the turbidity of the solution after chemical precipitation of fluorine-containing wastewater alone is 164NTU, and the turbidity of the fluorine-containing wastewater and silicon-containing wastewater in Example 2 can be reduced to 12NTU after mixing, and the water flux after entering the ultrafiltration is reduced from 267LMH in Example 2 to 76LMH in Comparative Example 1, and the filtration time is extended from 60 minutes in Example 2 to 210 minutes in Comparative Example 1. It can be observed from the scanning electron microscope that the turbidity of Comparative Example 1 ( Figure 3 ) of the ultrafiltration membrane showed serious cake layer contamination, while the ultrafiltration membrane in Example 2 ( Figure 4 ) only slightly contaminated on the surface. From the atomic force microscope analysis of the ultrafiltration membrane surface contamination, it can be seen that the comparative example 1 ( Figure 6 ) is 170.8 nm, while the surface roughness of the ultrafiltration membrane in Example 2 is reduced to 117.6 nm ( Figure 7 ). Therefore, by using Example 2 to mix the fluorine-containing wastewater and the silicon-containing wastewater and adjusting the wastewater Zeta potential to about 0 mV, the turbidity of the wastewater can be rapidly reduced, and the ultrafiltration membrane pollution can be effectively alleviated, thereby increasing the water production flux.

[0051] Comparative Example 2

[0052] Step 1. The silicon-containing wastewater was stirred at a speed of 150 rpm for 10 minutes and slowly stirred at a speed of 50 rpm for 10 minutes, and the turbidity of the wastewater was 85 NTU.

[0053] Step 2. The silicon-containing wastewater in step 1 was allowed to stand for 40 minutes, at which time the Zeta potential of the wastewater was -16 mV, and the turbidity was slightly reduced from 85 NTU to 76 NTU.

[0054] Step 3. The wastewater from step 2 was passed into the ultrafiltration device for cross-flow filtration, and the operating pressure was adjusted to 0.01 MPa, the flow rate was 1.5 L / min, and the experiment was stopped when the system water production rate was 95%. The filtration time was 170 minutes, the water production flux was 94 LMH, and the turbidity was reduced to 2 NTU.

[0055] By comparing Example 2 with Comparative Example 2, it is obvious that the turbidity of silicon-containing wastewater alone after standing is 76NTU, and the turbidity of fluorine-containing wastewater and silicon-containing wastewater in Example 2 can be reduced to 12NTU after mixing, and the water flux after entering ultrafiltration is reduced from 267LMH in Example 2 to 94LMH in Comparative Example 2, the filtration time needs to be extended from 60 minutes in Example 2 to 170 minutes in Comparative Example 2, and the turbidity of water is increased from 0NTU in Example 2 to 2NTU in Comparative Example 2. Therefore, using Example 2 to mix fluorine-containing wastewater and silicon-containing wastewater and adjust the wastewater Zeta potential to about 0mV can achieve a faster reduction in wastewater turbidity, effectively alleviate ultrafiltration membrane pollution, and increase water flux.

[0056] Comparative Example 3

[0057] Step 1. Calcium chloride is added to the fluoride-containing wastewater, and the molar ratio of calcium to fluoride in the wastewater is adjusted to 0.6. The fluoride-containing wastewater is stirred at a speed of 150 rpm for 10 minutes, and slowly stirred at a speed of 50 rpm for 10 minutes to complete the precipitation reaction, and the fluoride ion concentration is reduced from 500 mg / L to 7 mg / L, and the turbidity is 177 NTU.

[0058] Step 2. 1300 mg / L polyaluminium chloride and 2 mg / L polyacrylamide were added to the fluoride-containing wastewater obtained in step 1, slowly stirred at 50 rpm for 10 minutes and allowed to stand for 40 minutes, the fluoride ion concentration was reduced to 2 mg / L, and the turbidity was reduced to 22 NTU.

[0059] Step 3. The mixed wastewater after preliminary sedimentation was passed into the ultrafiltration device for cross-flow filtration, and the operating pressure was adjusted to 0.01MPa, the flow rate was 1.5L / min, and the experiment was stopped when the system water production rate was 95%. The filtration time was 75 minutes, the water production flux was 213LMH, the fluoride ion concentration of the effluent was 1.8mg / L, and the turbidity was reduced to 0.02NTU.

[0060] By comparing Example 2 and Comparative Example 3, it is obvious that the turbidity is 22NTU after adding the traditional coagulant and flocculant to the fluorine-containing wastewater, and the turbidity can be reduced to 12NTU after the fluorine-containing wastewater and the silicon-containing wastewater are mixed in Example 2, and the water flux after entering the ultrafiltration is reduced from 267LMH in Example 2 to 213LMH in Comparative Example 3, and the filtration time needs to be extended from 60 minutes in Example 2 to 75 minutes in Comparative Example 3. Therefore, the use of Example 2 to mix the fluorine-containing wastewater and the silicon-containing wastewater and adjust the wastewater Zeta potential to about 0mV can achieve a faster reduction in wastewater turbidity, effectively alleviate ultrafiltration membrane pollution, and increase water flux.

[0061] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A waste treatment method combining electrostatic adsorption and ultrafiltration, characterized in that: The following steps are involved: Step 1: adding calcium chloride to the fluoride-containing wastewater, adjusting the molar ratio of fluoride to calcium in the solution, stirring until the precipitation reaction is complete, and obtaining fluoride-containing wastewater I having calcium fluoride particles; Step 2: adding the silicon-containing wastewater to the fluorine-containing wastewater I obtained in step 1, adjusting the molar ratio of silicon dioxide to calcium fluoride, slowly stirring and standing to obtain mixed wastewater after preliminary sedimentation, testing the Zeta potential of the mixed wastewater, and obtaining the particle size of the particles in the mixed wastewater; Step 3: Pass the mixed wastewater after preliminary sedimentation into the ultrafiltration device for cross-flow filtration, and adjust the operating pressure and flow rate; stop the experiment when the system water production rate reaches 95%.

2. The waste treatment method of electrostatic adsorption combined with ultrafiltration as claimed in claim 1, characterized in that: In the step 1, calcium chloride is added to the fluorine-containing wastewater and stirred at a speed of 150 rpm for 10 minutes, and then slowly stirred at a speed of 50 rpm for 10 minutes to complete the precipitation reaction.

3. The waste treatment method of electrostatic adsorption combined with ultrafiltration as claimed in claim 1, characterized in that: In the step 2, the mixed wastewater is slowly stirred at a speed of 50 rpm for 10 minutes and allowed to stand for 40 minutes.

4. The waste treatment method of electrostatic adsorption combined with ultrafiltration as claimed in claim 1, characterized in that: The cross-flow filtration time in step 3 is 60-100 minutes.

5. The waste treatment method of combining electrostatic adsorption with ultrafiltration as claimed in claim 1, characterized in that: In step 3, the fluoride ion concentration of the effluent is lower than 9 mg / L, and the turbidity is reduced to lower than 0.02 NTU.

6. The waste treatment method of electrostatic adsorption combined with ultrafiltration as claimed in claim 1, characterized in that: In step 1, the calcium-fluoride molar ratio of the solution is adjusted to be 0.5-0.

7.

7. The waste treatment method of combining electrostatic adsorption with ultrafiltration as claimed in claim 1, characterized in that: In step 2, the molar ratio of silicon dioxide to calcium fluoride is adjusted to 2-8.

8. The waste treatment method of combining electrostatic adsorption with ultrafiltration as claimed in claim 1, characterized in that: The average particle size of the particles in step 2 is 1100-1850nm.

9. The waste treatment method of combining electrostatic adsorption with ultrafiltration as claimed in claim 1, characterized in that: In step 3, the turbidity is reduced to 0 NTU.

10. The waste treatment method of combining electrostatic adsorption with ultrafiltration as claimed in claim 1, characterized in that: In step 3, the filtration time is shortened to 60-70 minutes.

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