Recycling treatment method and system for removing silicon and fluorine from wastewater in photovoltaic industry

Abstract

The invention discloses a resourceful treatment method and a resourceful treatment system for removing silicon and fluorine from wastewater in the photovoltaic industry, which are characterized in that alkaline water in photovoltaic wastewater and other photovoltaic wastewater are respectively collected through an alkaline water collecting tank and a fluorine-containing wastewater regulating tank, and the alkaline water reacts with lime milk in a dosing tank to form calcium silicate sludge; the calcium silicate sludge enters a calcium silicate pickling tank and is subjected to pickling by a hydrochloric acid solution to generate a calcium chloride solution, and the calcium silicate sludge with the purity meeting the resource recycling requirement is obtained; clear water obtained after reaction in the chemical adding pool and other photovoltaic wastewater are mixed and enter the two-stage fluorine removal system together for fluorine removal treatment, fluorine ions and calcium ions are combined to form calcium fluoride sludge, the fluorine concentration of effluent of the two-stage fluorine removal system is lower than 8 ppm, and the effluent reaches the standard and is discharged. Meanwhile, resource recycling of calcium fluoride and calcium silicate sludge is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and system for resource-based treatment of wastewater for silicon and fluorine removal in the photovoltaic industry. Background Art

[0002] Under the general environment of global energy structure transformation, the market scale of photovoltaic industry continues to expand, generating a large amount of photovoltaic wastewater. According to the existing conventional treatment process, photovoltaic wastewater will produce a large amount of sludge containing calcium fluoride after defluorination. Calcium fluoride is called "the second rare earth" and has broad application prospects. However, the sludge produced after wastewater treatment has low purity and low utilization value. Through testing, it is found that in addition to calcium fluoride, the sludge produced after wastewater treatment also includes impurities such as silicon dioxide, calcium carbonate, calcium oxide and metal oxides. Among them, the content of silicon dioxide accounts for the largest proportion, generally 10-20%, which seriously affects the purity and resource utilization of sludge. It can be said that silicon is the main factor limiting the purity of sludge.

[0003] At present, there are many areas that can be improved in the treatment technology of fluoride-containing wastewater. First, photovoltaic wastewater is collected and treated uniformly, the amount of lime added is large, and the cost of reagents is high. Second, the existing treatment technology only focuses on the discharge of fluoride concentrations that meet the standards, but does not take into account the treatment cost and resource utilization of sludge. The large amount of sludge waste residue generated has poor reusability, high treatment cost, and may also cause secondary pollution.

[0004] Patent CN 112158983 A provides a system for efficient silicon removal and fluorine removal. First, calcium oxide is added to the primary unit to adjust the pH to 10-11, and then a sufficient amount of calcium chloride is added to remove silicon and fluorine; hydrochloric acid is added to the secondary unit to adjust the pH to 6.5-7.5, and then calcium chloride is added to introduce excess calcium ions for in-depth fluorine removal.

[0005] Although this type of process takes into account the removal of silicon, thereby improving the purity of the calcium fluoride sludge produced by the secondary defluorination unit, the integrated mode of primary silicon and fluorine removal will produce a large amount of low-purity fluorine-containing and silicon-containing sludge, which seriously affects the recovery of high-grade calcium fluoride sludge in the secondary defluorination. At the same time, it does not take into account the reduction or reuse of the sludge.

[0006] Patent CN 221344327 U invented a utility model photovoltaic wastewater treatment system, including a route for treating high-concentration acid and high-concentration alkali and a route for treating low-concentration acid and low-concentration alkali. This system collects and mixes high-concentration acid and high-concentration alkali to form high-concentration photovoltaic wastewater, and mixes low-concentration acid and low-concentration alkali to form low-concentration photovoltaic wastewater. Then, the low-concentration photovoltaic wastewater is treated for fluorine and silicon removal.

[0007] This process achieves separate silicon removal and fluorine removal, and classifies and collects photovoltaic wastewater, striving to achieve comprehensive treatment of photovoltaic wastewater, but the process is complicated, and the invention only focuses on the recycling and reuse of low-concentration fluorine-containing and silicon-containing photovoltaic wastewater. However, the traditional treatment mode is used for concentrated alkaline wastewater with a high silicon content and concentrated acid wastewater with a high fluorine content. The generated sludge has not escaped the low purity condition. Similarly, the invention does not take into account the reduction and recycling of sludge.

[0008] The silicon removal and fluorine removal methods given in the above patents all focus on the removal of fluoride and operation issues, without considering the improvement of the purity of calcium fluoride sludge and the reduction of sludge treatment. At the same time, there are problems such as large dosage of defluorination agents, complex processes, and high treatment costs. Summary of the invention

[0009] In order to overcome the above-mentioned defects, the present invention provides a method and system for resource treatment of siliconization and fluorine removal from photovoltaic industry wastewater. The method and system for resource treatment of siliconization and fluorine removal from photovoltaic industry wastewater can not only improve the purity of calcium fluoride, but also achieve resource recovery and reuse.

[0010] The present invention adopts a technical solution to solve the technical problem: a method for resource treatment of wastewater for desiliconization and defluorination in the photovoltaic industry, comprising the following steps:

[0011] Step 1: Collect the alkaline water and other photovoltaic wastewater separately;

[0012] Step 2: Send alkaline water into the dosing tank, and add lime milk into the dosing tank, control the calcium-silicon molar ratio between 1-2, and react to form calcium silicate sludge;

[0013] Step 3: The precipitate formed after the reaction in step 2 enters the calcium silicate pickling tank, and hydrochloric acid solution is added to the calcium silicate pickling tank for pickling. The chloride ions in the hydrochloric acid react with the calcium ions in the sludge to generate a calcium chloride solution, and the calcium silicate sludge with a purity that meets the resource recycling demand is obtained. The sludge is pickled to dissolve the lime that has not participated in the reaction to form calcium chloride, which effectively reduces the amount of sludge and greatly reduces the cost of sludge treatment. At the same time, the purity of the calcium silicate sludge is guaranteed, and it can be used as cement, lime, and gypsum materials for construction to achieve resource recycling;

[0014] Step 4: The clean water after the reaction in step 2 is mixed with other photovoltaic wastewater in step 1, and enters the two-stage defluorination system for defluorination treatment, so that fluoride ions and calcium ions are combined to form calcium fluoride sludge. The fluoride concentration of the effluent from the two-stage defluorination system is lower than 8ppm, which meets the discharge standards. After the two-stage defluorination reaction, the fluoride ions and calcium ions in the fluoride-containing wastewater are fully combined to form calcium fluoride. The purity of calcium fluoride can be increased to 85%, which can be reused as a resource. At the same time, the fluoride ions in the wastewater are fully reacted, and the fluoride ion concentration in the effluent is greatly reduced to meet the discharge standards.

[0015] As a further improvement of the present invention, the calcium chloride solution generated in step three is fed into the two-stage defluorination system in step four for use as a calcium source. The calcium chloride solution generated in step three can be directly utilized in the two-stage defluorination system, saving the reagent cost of the defluorination process.

[0016] As a further improvement of the present invention, after the alkaline water is mixed with the lime milk in the dosing tank, it is sent to the reaction tank for stirring reaction to form calcium silicate sludge, the stirring speed is 20-60r / min, and the reaction time is 0.1-2h.

[0017] As a further improvement of the present invention, the reaction water from the reaction tank enters a flocculation sedimentation tank, PAM is added to the flocculation sedimentation tank for flocculation, and after the flocculation reaction, it enters the sedimentation tank of the flocculation sedimentation tank for sedimentation treatment to obtain precipitate and upper clear water, and the precipitate enters a calcium silicate pickling tank, and the upper clear water is mixed with other photovoltaic wastewater. The reaction water enters the flocculation sedimentation tank and, after flocculation, the precipitate is fully precipitated to avoid suspension in the wastewater, thereby ensuring the effective removal of silicon in the wastewater.

[0018] As a further improvement of the present invention, in step three, the amount of hydrochloric acid used is 0.5%-1.8% of the amount of alkaline water, the pickling time is 0.1-2h, and the dissolution rate of the sludge reaches 30-60%.

[0019] As a further improvement of the present invention, in step one, the alkaline water in the photovoltaic wastewater is collected separately into an alkaline water collection pool, and other photovoltaic wastewater enters a fluorine-containing wastewater regulating pool.

[0020] As a further improvement of the present invention, in step 4, the calcium fluoride sludge obtained in the two-stage defluorination system is recycled and utilized through a resource recovery treatment device. The calcium fluoride sludge is processed through the resource recovery treatment device to obtain high-purity calcium fluoride particles, which can improve the economic benefits of the enterprise.

[0021] As a further improvement of the present invention, in the step three, after the hydrochloric acid solution is added to the calcium silicate pickling tank for pickling, the pH value of the liquid in the calcium silicate pickling tank is neutral.

[0022] A treatment system for desiliconization and defluorination of photovoltaic wastewater, characterized in that it comprises an alkaline water collection tank, a fluorine-containing wastewater regulating tank, a dosing tank, a reaction tank, a flocculation sedimentation tank, a calcium silicate pickling tank and a two-stage defluorination system, wherein the alkaline water collection tank is used to collect alkaline water in photovoltaic wastewater, the fluorine-containing wastewater regulating tank is used to collect other photovoltaic wastewater, the drain outlet of the alkaline water collection tank is connected with the water inlet of the dosing tank through a pipeline, the alkaline water collected in the alkaline water collection tank can be quantitatively delivered to the dosing tank by a lifting pump, the dosing tank is provided with a dosing device, the dosing device can quantitatively add lime milk to the dosing tank, the water outlet of the dosing tank is connected with the water inlet of the reaction tank through a pipeline, the mixed liquid in the dosing tank can be discharged into the reaction tank by a lifting pump or gravity flow, the reaction tank is provided with a stirrer, the stirrer can stir the mixed liquid entering the reaction tank, the drain outlet of the reaction tank is connected with the water inlet of the flocculation sedimentation tank through a pipeline, the fully mixed liquid in the reaction tank can be delivered to the reaction tank by a lifting pump or gravity flow, The sludge is discharged into the flocculation sedimentation tank in a flowing manner. The water outlet at the upper end of the flocculation sedimentation tank is connected with the water inlet of the fluorine-containing wastewater regulating tank. The upper clear water in the flocculation sedimentation tank can flow into the fluorine-containing wastewater regulating tank through the water outlet. The sludge discharge outlet at the lower end of the flocculation sedimentation tank is connected with the calcium silicate pickling tank through a pipeline. The lower sludge of the flocculation sedimentation tank can be pumped into the calcium silicate pickling tank through a sludge pump. The calcium silicate pickling tank is provided with a hydrochloric acid doser, which can quantitatively add hydrochloric acid to the calcium silicate pickling tank. The water outlet of the calcium silicate pickling tank is connected with the drug inlet of the two-stage defluorination system through a pipeline. The calcium chloride generated by the reaction in the calcium silicate pickling tank is quantitatively discharged into the two-stage defluorination system along with the outlet water through a lifting pump. The drain outlet of the fluoride-containing wastewater regulating tank is connected with the water inlet of the two-stage defluorination system through a pipeline. The fluoride-containing wastewater in the fluoride-containing wastewater regulating tank is quantitatively discharged into the two-stage defluorination system through a lifting pump for defluorination treatment. The two-stage defluorination system can convert fluoride ions in the fluoride-containing wastewater into calcium fluoride precipitates through two-stage defluorination.

[0023] As a further improvement of the present invention, the two-stage defluorination system comprises a primary defluorination system, a secondary defluorination system, a calcium source dosing device and a calcium fluoride source.

[0024] The drain outlet of the fluorine-containing wastewater regulating tank is connected with the water inlet of the primary defluorination system through a pipeline to supply fluorine-containing wastewater. The water outlet of the primary defluorination reaction tank is connected with the water inlet of the secondary defluorination reaction tank. The calcium source dosing device can quantitatively add calcium source to the primary defluorination system and the secondary defluorination system through the drug inlet respectively. The calcium source reacts with fluoride ions in the fluoride-containing wastewater to generate calcium fluoride. The calcium fluoride discharge outlets of the primary defluorination system and the secondary defluorination system are connected with the calcium fluoride resource recovery device. The calcium fluoride resource recovery device can perform resource treatment on calcium fluoride to obtain calcium fluoride particles that meet the resource recovery requirements. The secondary effluent of the secondary defluorination reaction tank meets the discharge standards.

[0025] The beneficial effects of the present invention are as follows: the present invention adopts a novel process method of one-stage silicon removal and two-stage fluorine removal, and formulates different silicon removal and fluorine removal process routes according to the difference in the proportion of substances contained in the acid and alkali solution. The process is simple and the operating cost is low. The sludge after silicon removal is treated separately, and the interference of silicon dioxide on the purity of calcium fluoride can be eliminated, so that a high-purity calcium fluoride product can be obtained, and the resource recovery and utilization of calcium fluoride can be realized. At the same time, after the silicon removal sludge is acid-washed, not only can the sludge be reduced, but the obtained cleaning liquid can be used as a calcium source in the two-stage fluorine removal process, and the cleaned calcium silicate sludge can be used as a building material, so as to realize the purpose of resource utilization of calcium silicate sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the principle diagram of the two-stage defluorination system of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example: The silicon content in the alkaline water of a certain enterprise's photovoltaic wastewater is 2107 mg / L. The steps for treating the enterprise's photovoltaic wastewater are as follows:

[0029] Step 1: Alkaline water in photovoltaic wastewater is collected separately into the alkaline water collection pool, and other photovoltaic wastewater enters the fluorine-containing wastewater regulating pool;

[0030] Step 2: The alkaline water collected in the alkaline water collection tank enters the dosing tank, and lime milk is added to make the calcium-silicon molar ratio 1.5. The alkaline water and lime milk are mixed and reacted in the reaction tank with a stirring speed of 30r / min. After reacting for 1 hour, it enters the flocculation tank, and flocculants are added to the flocculation tank. Then the solution enters the sedimentation tank; the silicon content of the supernatant in the sedimentation tank is 30.87mg / L, which flows from the overflow weir into the fluorine-containing wastewater regulating tank and mixes with other photovoltaic wastewater; the sludge in the flocculation sedimentation tank is discharged from the bottom and enters the calcium silicate pickling tank;

[0031] Step 3: Add hydrochloric acid solution to the calcium silicate pickling tank for pickling. The dosage of 36% hydrochloric acid is 0.8% of the amount of alkaline water. After reacting for about 1 hour, the dissolution rate of the sludge can reach 39%; the concentration of calcium chloride in the supernatant is 11000 mg / L;

[0032] Step 4: After acid washing, the calcium silicate sludge is filtered and washed with water before being used as cement material for construction.

[0033] Step 5: The effluent from the silicon removal process in the fluorine-containing wastewater regulating tank enters the two-stage defluorination system together with other photovoltaic wastewater for defluorination treatment. Lime is added to the two-stage defluorination system to make the pH of the wastewater in the two-stage defluorination system neutral. At the same time, the calcium chloride solution generated in step 3 is used as a supplement of the calcium source to combine fluoride ions with calcium ions to form calcium fluoride. The purity of calcium fluoride can be increased to 85%;

[0034] Step 6: The clarified supernatant of the secondary defluorination system of the two-stage defluorination system flows out from the outlet, and the fluorine concentration is lower than 8ppm, which can meet the discharge standards.

[0035] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for resource treatment of wastewater for desiliconization and defluorination in the photovoltaic industry, characterized by: The following steps are involved: Step 1: Collect the alkaline water and other photovoltaic wastewater separately; Step 2: Send alkaline water into the dosing tank, and add lime milk into the dosing tank, control the calcium-silicon molar ratio between 1-2, and react to form calcium silicate sludge; Step 3: The precipitate formed after the reaction in step 2 enters the calcium silicate pickling tank, and hydrochloric acid solution is added to the calcium silicate pickling tank for pickling. The chloride ions in the hydrochloric acid react with the calcium ions in the sludge to generate a calcium chloride solution, thereby obtaining calcium silicate sludge with a purity that meets the resource recycling requirements; Step 4: The clean water after the reaction in step 2 is mixed with other photovoltaic wastewater in step 1, and enters the two-stage defluorination system for defluorination treatment, so that fluoride ions and calcium ions are combined to form calcium fluoride sludge. The fluoride concentration of the effluent from the two-stage defluorination system is less than 8ppm, which meets the discharge standards.

2. The method for resource treatment of photovoltaic industry wastewater for desiliconization and defluorination according to claim 1, characterized in that: The calcium chloride solution generated in step three is fed into the two-stage defluorination system in step four for use as a calcium source.

3. The method for resource treatment of photovoltaic industry wastewater for desiliconization and defluorination according to claim 1, characterized in that: After the alkaline water is mixed with lime milk in the dosing tank, it is sent to the reaction tank for stirring reaction to form calcium silicate sludge. The stirring speed is 20-60r / min and the reaction time is 0.1-2h.

4. The method for resource treatment of photovoltaic industry wastewater for desiliconization and defluorination according to claim 3 is characterized in that: The reaction water from the reaction tank enters the flocculation sedimentation tank, and PAM is added to the flocculation sedimentation tank for flocculation. After the flocculation reaction, it enters the sedimentation tank of the flocculation sedimentation tank for sedimentation treatment to obtain sediment and upper clear water. The sediment enters the calcium silicate acid washing tank, and the upper clear water is mixed with other photovoltaic wastewater.

5. The method for resource treatment of photovoltaic industry wastewater for desiliconization and defluorination according to claim 1, characterized in that: In step 3, the amount of hydrochloric acid used is 0.5%-1.8% of the amount of alkaline water, the pickling time is 0.1-2h, and the dissolution rate of the sludge reaches 30-60%.

6. The method for resource treatment of photovoltaic industry wastewater for desiliconization and defluorination according to claim 1, characterized in that: In step one, the alkaline water in the photovoltaic wastewater is collected separately into the alkaline water collection pool, and the other photovoltaic wastewater enters the fluorine-containing wastewater regulating pool.

7. The method for removing silicon and fluorine from photovoltaic wastewater according to claim 1, characterized in that: In step 4, the calcium fluoride sludge obtained in the two-stage defluorination system is recycled and utilized through resource recovery processing equipment.

8. The method for removing silicon and fluorine from photovoltaic wastewater according to claim 1, characterized in that: In the step 3, the calcium silicate pickling tank is added with hydrochloric acid solution for pickling so that the pH value of the liquid in the calcium silicate pickling tank is neutral.

9. A system for treating wastewater from the photovoltaic industry for silicon removal and fluorine removal as a resource, used in the method for treating wastewater from the photovoltaic industry for silicon removal and fluorine removal as a resource, according to claims 1 to 8, characterized in that: It includes an alkaline water collection tank, a fluorine-containing wastewater regulating tank, a dosing tank, a reaction tank, a flocculation sedimentation tank, a calcium silicate pickling tank and a two-stage defluorination system. The alkaline water collection tank is used to collect alkaline water in photovoltaic wastewater, the fluorine-containing wastewater regulating tank is used to collect other photovoltaic wastewater, the drain outlet of the alkaline water collection tank is connected with the water inlet of the dosing tank through a pipeline, the alkaline water collected in the alkaline water collection tank can be quantitatively sent to the dosing tank through a lifting pump, the dosing tank is provided with a dosing device, the dosing device can quantitatively add lime milk to the dosing tank, the water outlet of the dosing tank is connected with the water inlet of the reaction tank through a pipeline, the mixed liquid in the dosing tank can be discharged into the reaction tank by a lifting pump or gravity flow, the reaction tank is provided with a stirrer, the stirrer can stir the mixed liquid entering the reaction tank, the drain outlet of the reaction tank is connected with the water inlet of the flocculation sedimentation tank through a pipeline, the fully mixed liquid in the reaction tank can be discharged into the flocculation sedimentation tank by a lifting pump or gravity flow, The water outlet at the upper end of the flocculation sedimentation tank is connected with the water inlet of the fluorine-containing wastewater regulating tank, and the upper clear water in the flocculation sedimentation tank can flow into the fluorine-containing wastewater regulating tank through the water outlet. The sludge discharge outlet at the lower end of the flocculation sedimentation tank is connected with the calcium silicate pickling tank through a pipeline, and the lower sludge of the flocculation sedimentation tank can be pumped into the calcium silicate pickling tank through a sludge pump. The calcium silicate pickling tank is provided with a hydrochloric acid doser, which can quantitatively add hydrochloric acid to the calcium silicate pickling tank. The water outlet is connected with the drug inlet of the two-stage defluorination system through a pipeline. The calcium chloride generated by the reaction in the calcium silicate pickling tank is quantitatively discharged into the two-stage defluorination system along with the outlet water through a lifting pump. The drain outlet of the fluoride-containing wastewater regulating tank is connected with the water inlet of the two-stage defluorination system through a pipeline. The fluoride-containing wastewater in the fluoride-containing wastewater regulating tank is quantitatively discharged into the two-stage defluorination system through a lifting pump for defluorination treatment. The two-stage defluorination system can convert fluoride ions in the fluoride-containing wastewater into calcium fluoride precipitates through two-stage defluorination.

10. The system for treating wastewater for photovoltaic industry for silicon removal and fluorine removal as claimed in claim 9, characterized in that: The two-stage defluorination system includes a primary defluorination system, a secondary defluorination system, a calcium source dosing device and a calcium fluoride source. The drain outlet of the fluorine-containing wastewater regulating tank is connected with the water inlet of the primary defluorination system through a pipeline to supply fluorine-containing wastewater. The water outlet of the primary defluorination reaction tank is connected with the water inlet of the secondary defluorination reaction tank. The calcium source dosing device can quantitatively add calcium source to the primary defluorination system and the secondary defluorination system through the drug inlet respectively. The calcium source reacts with fluoride ions in the fluoride-containing wastewater to generate calcium fluoride. The calcium fluoride discharge outlets of the primary defluorination system and the secondary defluorination system are connected with the calcium fluoride resource recovery device. The calcium fluoride resource recovery device can perform resource treatment on calcium fluoride to obtain calcium fluoride particles that meet the resource recovery requirements. The secondary effluent of the secondary defluorination reaction tank meets the discharge standards.

Images