Treatment system for high-phosphorus and high-fluorine wastewater

Abstract

The utility model relates to the technical field of wastewater treatment, and discloses a high-phosphorus-fluorine wastewater treatment system, which comprises a primary reaction device, a secondary reaction device, a secondary reaction device and a secondary reaction device, wherein the primary reaction device is used for adjusting the pH value of wastewater to be alkaline and assisting polyaluminum chloride to remove fluorine, so that phosphorus and fluorine in the wastewater are transferred to a solid phase; the first-stage membrane separation device is connected with the first-stage reaction device and is used for removing water-insoluble substances formed by the first-stage reaction; the second-stage reaction device is connected with the first-stage membrane separation device, calcium ions in the wastewater are transferred into a solid phase under an alkaline condition, and the risk of calcium sulfate scaling is reduced. By adopting the design of multi-stage reaction devices and multi-stage membrane separation, water and phosphorus and fluorine resources can be recovered to the greatest extent, the system recovery rate is high, the membrane, equipment and pipelines can be effectively prevented from scaling, the service life of the membrane is prolonged to the greatest extent, and the investment and the occupied area of the system are reduced.

Description

Technical Field

[0001] This utility model relates to the field of wastewater treatment technology, and in particular to a treatment system for high-phosphorus and high-fluoride wastewater. Background Technology

[0002] Phosphoric acid, a fundamental raw material in the phosphate chemical industry, is produced over 90% using the wet process. The wet process for producing phosphoric acid primarily involves the reaction of sulfuric acid with phosphate rock. The chemical reaction equation is as follows:

[0003] Ca(PO4)3F + 5H2SO4+ 10H2O → 5CaSO4·2H2O + 3H3PO4+ HF.

[0004] The wet process for producing phosphoric acid generates 4.5 to 5 tons of phosphogypsum for every ton of phosphoric acid produced. Currently, the national regulations require the harmless treatment of phosphogypsum produced during phosphoric acid production. The main harmless treatment measure is phosphogypsum washing, which produces acidic washing water rich in phosphates, sulfates, fluorosilicates, and fluorides. If this washing water is not effectively treated, it will pollute the environment. In addition, phosphogypsum stockpiles across the country also generate large amounts of leachate, polluting not only surface water bodies but also groundwater sources. National and provincial environmental protection departments have successively issued requirements for phosphogypsum disposal. Decades of accumulated phosphogypsum may take decades to process and utilize completely; however, the existing and future phosphogypsum leachate and washing water urgently need treatment.

[0005] Currently, the phosphorus chemical industry mainly uses lime neutralization, sedimentation separation of water-insoluble matter, sludge dewatering by pressure filtration, and acid back-conditioning of the supernatant before discharge when treating phosphogypsum washing water and slag yard leachate. Due to the incomplete solid-liquid separation and poor water quality, the phosphorus chemical industry urgently needs technological innovation to adopt more advanced technologies and equipment to treat phosphogypsum leachate and phosphogypsum washing water, thereby reducing environmental pressure while recovering phosphorus resources. Utility Model Content

[0006] The purpose of this invention is to solve the problems existing in the prior art and provide a treatment system for high phosphorus and fluoride wastewater. It is suitable for the current production and raw material status of the phosphorus chemical industry, and adopts lime neutralization, multi-stage membrane separation and concentration to recover phosphorus and fluoride resources, which also improves the quality of recycled water.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A treatment system for high-phosphorus and high-fluoride wastewater includes:

[0009] The primary reaction unit is used to adjust the pH of the wastewater to alkaline and assist in the removal of fluoride by polyaluminum chloride, so that the phosphorus and fluoride in the wastewater are transferred to the solid phase.

[0010] A primary membrane separation unit is connected to a primary reaction unit to remove water-insoluble substances formed in the primary reaction.

[0011] The secondary reaction unit is connected to the primary membrane separation unit. It uses alkaline conditions to transfer calcium ions in the wastewater into the solid phase, reducing the risk of calcium sulfate scaling.

[0012] A secondary membrane separation unit is connected to a secondary reaction unit to remove water-insoluble substances formed in the secondary reaction.

[0013] The RO membrane desalination unit uses a multi-stage membrane series configuration. The concentrate from the previous stage membrane is used as the feed water for the next stage membrane, and the permeate from each stage membrane is collected to form product water, which is then reused as pure water in the production system.

[0014] Preferably, the primary membrane separation device uses one of the following: a polytetrafluoroethylene tubular membrane, an organic membrane made of cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, or polyethersulfone, or an inorganic membrane made of alumina or silicon carbide.

[0015] Preferably, the primary membrane separation device includes a water-insoluble matter output end and a water output end, with the water output end connected to the input end of the secondary reaction device and the water-insoluble matter output end connected to the first sludge dewatering device.

[0016] Preferably, the secondary membrane separation device uses one of the following: a polytetrafluoroethylene tubular membrane, an organic membrane made of cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, or polyethersulfone, or an inorganic membrane made of alumina or silicon carbide.

[0017] Preferably, the secondary membrane separation device includes a water-insoluble matter output end and a water output end, wherein the water output end is connected to the input end of the RO membrane desalination device, and the water-insoluble matter output end is connected to the second sludge dewatering device.

[0018] Preferably, the first sludge dewatering device and the second sludge dewatering device are plate and frame filter presses, vacuum belt filters or screw presses.

[0019] Compared with the prior art, the beneficial effects of this utility model are:

[0020] This invention employs a multi-stage reaction device and a multi-stage membrane separation design, which can maximize the recovery of water, phosphorus and fluorine resources. The system has a high recovery rate, effectively prevents scaling of membranes, equipment and pipelines, maximizes membrane life, and reduces investment and system footprint. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the composition of a high-phosphorus and fluoride wastewater treatment system proposed in this utility model.

[0022] Figure 2 This is a schematic diagram of the process in Example 1.

[0023] In the diagram: 1. Primary reaction unit; 2. Primary membrane separation unit; 3. Secondary reaction unit; 4. Secondary membrane separation unit; 5. RO membrane desalination unit; 6. First sludge dewatering unit; 7. Second sludge dewatering unit. Detailed Implementation

[0024] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0025] Reference Figures 1-2 A treatment system for high-phosphorus and high-fluoride wastewater includes:

[0026] The first-stage reaction unit 1 can be injected with lime slurry or carbide slag to adjust the pH of the wastewater to alkaline and assist in the removal of fluoride by polyaluminum chloride, so that the phosphorus in the wastewater is converted into dicalcium phosphate or calcium phosphate, and the fluoride ions in the wastewater are converted into calcium fluoride, thereby transferring phosphorus and fluoride to the solid phase. The first-stage reaction transfers most of the phosphorus and fluoride from the liquid phase to the solid phase and separates them from the water through membrane separation. The solid slag rich in dicalcium phosphate, calcium phosphate, and calcium fluoride can be used as raw material for phosphoric acid production.

[0027] The primary membrane separation device 2 is connected to the primary reaction device 1. It adopts one of the following organic membranes: polytetrafluoroethylene tubular membrane, cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, polyethersulfone, etc., and inorganic membranes: alumina, silicon carbide, etc. It mainly removes water-insoluble substances such as dicalcium phosphate or calcium phosphate, calcium fluoride, etc. formed in the primary reaction.

[0028] The primary membrane separation unit 2 intercepts the deposited dicalcium phosphate or calcium phosphate, calcium fluoride and other water-insoluble substances, which are then further dewatered by the first sludge dewatering unit 6 to obtain dicalcium phosphate or calcium phosphate, calcium fluoride sludge with a lower water content. This sludge can be returned to the production system as raw material. The filtrate is returned to the inlet of the primary reaction unit 1 to provide seed crystals for the primary reaction. The first sludge dewatering unit 6 can be equipped with plate and frame filter press, vacuum belt filter, screw press and other equipment.

[0029] The secondary reaction device 3 is connected to the primary membrane separation device 2. The secondary reaction device 3 is a calcium removal reaction device. Under alkaline conditions, carbonate ions react with calcium ions to form calcium carbonate, transferring calcium ions into the solid phase. This can reduce the concentration of calcium ions in the water and reduce the risk of calcium sulfate scaling. The wastewater after the secondary reaction enters the secondary membrane separation device 4.

[0030] The secondary membrane separation device 4 is connected to the secondary reaction device 3. It can be one of the following: organic membranes made of polytetrafluoroethylene tubular membrane, cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, polyethersulfone, etc., or inorganic membranes made of alumina and silicon carbide. It is mainly used to remove water-insoluble calcium carbonate formed in the secondary reaction.

[0031] The water-insoluble calcium carbonate deposited in the secondary membrane separation unit 4 is further dewatered by the second sludge dewatering unit 7 to obtain calcium carbonate sludge with a lower water content. The filtrate is returned to the inlet of the secondary reaction unit 3 to provide seed crystals for the secondary reaction. The second sludge dewatering unit 7 can be equipped with a plate and frame filter press, a vacuum belt filter, a screw press, or other similar equipment.

[0032] The RO membrane desalination unit 5 uses a multi-stage membrane series configuration. The concentrate from the previous stage membrane is used as the feed water for the next stage membrane. The permeate from each stage membrane is collected to form permeate water, which is then reused as pure water in the production system. The concentrate from the last stage membrane, which is rich in phosphorus and fluorine, is returned to the phosphorus chemical production system as raw material.

[0033] The system works as follows:

[0034] The first-stage reaction unit 1 adjusts the pH of the wastewater to 9-11 by adding lime slurry or carbide slag slurry, and adds polyaluminum chloride at 0.01-0.1‰. The reaction is stirred for 0.5-1 hours, causing most of the phosphorus and fluoride to crystallize and precipitate as water-insoluble substances in the form of dicalcium phosphate, calcium phosphate, and calcium fluoride. The wastewater after the reaction enters the first-stage membrane separation unit 2, which can use a polytetrafluoroethylene (PTFE) membrane filter. The wastewater after the first-stage reaction is pumped or pumped into the PTFE membrane filter, where the water-insoluble substances are retained by the membrane, and the clean water permeates through the membrane into the second-stage reaction unit 3. Alternatively, the wastewater after the reaction can flow by gravity into a membrane tank, where a hollow fiber submerged membrane made of materials such as cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, or polyethersulfone is used for solid-liquid separation via external filtration. The water-insoluble substances are retained on the outer surface of the membrane, and the water permeates through the membrane and flows out from the product water end. The retained water-insoluble substances are washed off from the membrane surface by the water flow and discharged periodically. The water-insoluble matter trapped by the membrane is deposited at the bottom of the filter and discharged periodically. It is then pumped to the first sludge dewatering unit 6 via a slurry pump. The first sludge dewatering unit 6 can be dewatered using equipment such as a plate and frame filter press, a vacuum belt filter, or a screw press, to obtain sludge with low water content, such as dicalcium phosphate or calcium phosphate and calcium fluoride sludge. This sludge can be returned to the production system as raw material. The filtrate is returned to the inlet of the first-stage reaction unit 1 to provide seed crystals for the first-stage reaction.

[0035] The secondary reaction device 3 further removes calcium by adding caustic soda solution, sodium carbonate solution, or ammonium carbonate solution, adjusting the pH of the wastewater to 10-11, and adding sodium carbonate solution or ammonium carbonate solution according to a residual calcium ion concentration molar ratio of 1:1. Carbon dioxide gas can also be introduced, and the reaction is stirred for 1-1.5 hours to make most of the calcium ions react into calcium carbonate precipitate with low solubility. The wastewater after the reaction enters the secondary membrane separation device 4. The secondary membrane separation device 4 can use polytetrafluoroethylene membrane filtration. The wastewater after the secondary reaction is sent to the polytetrafluoroethylene membrane filter by pump or differential pressure, and water-insoluble matter is intercepted by the membrane; or the wastewater after the secondary reaction flows into the membrane tank by gravity, using hollow fiber submerged membranes made of materials such as cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, polyethersulfone, etc., for solid-liquid separation by external filtration. Water-insoluble matter is intercepted on the outer surface of the membrane, and water flows out from the product water end through the membrane. The intercepted water-insoluble matter is washed off from the membrane surface by the water flow and discharged periodically. The membrane filtration permeate is adjusted to pH 6-7 by adding sulfuric acid or nitric acid before entering the RO raw water tank. The water-insoluble matter trapped by the membrane is deposited at the bottom of the filter and discharged periodically. It is then pumped to the second sludge dewatering device 7 via a slurry pump. The second sludge dewatering device 7 can be dewatered using equipment such as a plate and frame filter press, a vacuum belt filter, or a screw press to obtain calcium carbonate sludge with low water content. The filtrate is returned to the inlet of the secondary reaction device 3 to provide seed crystals for the secondary reaction.

[0036] The reverse osmosis unit consists of a membrane, membrane housing, membrane frame, high-pressure pump, and supporting pipes, valves, and instruments. The reverse osmosis membrane is an artificial semi-permeable membrane with certain characteristics, made to mimic biological semi-permeable membranes, and is the core component of reverse osmosis technology. The principle of reverse osmosis technology is that, under pressure higher than the osmotic pressure of the solution, other substances cannot pass through the semi-permeable membrane, thus separating these substances from water. The membrane pore size of the reverse osmosis membrane is very small, thus it can effectively remove dissolved salts, colloids, microorganisms, organic matter, etc. from water. The leachate from the phosphogypsum slag field and gypsum wash water, after ultrafiltration pretreatment, are pumped into the reverse osmosis membrane module through a high-pressure pump. Water permeates through the membrane and flows out from one end through a collection pipe, resulting in permeate with lower levels of phosphates, sulfates, and fluorosilicates. The phosphates, sulfates, and fluorosilicates retained by the membrane flow out with the water from the concentrate end, resulting in concentrate with higher levels of phosphates, sulfates, and fluorosilicates.

[0037] The reverse osmosis membrane needs to retain phosphates, sulfates and fluorosilicates under weakly acidic conditions of pH 6-7.

[0038] The purpose of the secondary membrane separation device 4 is to pretreat the reverse osmosis unit.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) Use membranes for pretreatment of reverse osmosis to provide safe and qualified feed water for each stage of reverse osmosis unit, and ensure the stable operation of reverse osmosis membranes and the quality of produced water.

[0041] (2) Use multi-stage reverse osmosis units in series to improve the water production rate and recovery rate of the reverse osmosis unit.

[0042] (3) By adding carbonate to convert calcium ions into calcium carbonate, and then adding acid to adjust the calcium carbonate after separation, the carbonate ions are converted into bicarbonate ions, so that the calcium carbonate, calcium sulfate, calcium fluoride and other substances in the wastewater are all in an unsaturated state, which prolongs the cleaning cycle and life of the reverse osmosis membrane.

[0043] (4) The number of reverse osmosis stages is set according to the raw water quality. The final stage reverse osmosis concentrate will concentrate phosphate, sulfate, fluorosilicate, etc. to meet the production requirements and be directly returned to the phosphoric acid production unit.

[0044] (5) The reverse osmosis permeate is collected and returned to the production process for recycling.

[0045] (6) The recovered dicalcium phosphate, calcium phosphate, and calcium fluoride can be reused as phosphoric acid raw materials. Calcium carbonate can also be used as a raw material for cement production and can also replace some lime milk and carbide slag to neutralize high-concentration wastewater.

[0046] Example 1

[0047] Pilot-scale treatment of leachate from gypsum slag yard of a manganese metal production enterprise

[0048] China accounts for more than 90% of the world's manganese metal production, with enterprises mainly located in the border area of ​​Chongqing, Hunan, Guizhou and Guangxi provinces and western Ningxia.

[0049] The production of metallic manganese, especially the preparation of electrolyte, is similar to that of phosphoric acid production. It also uses sulfuric acid extraction to convert manganese in manganese ore into manganese sulfate. In this process, calcium in the manganese ore reacts with sulfuric acid to form a large amount of gypsum. The separated manganese gypsum is also piled up in a fixed slag yard. Since the four provinces of Chongqing, Hunan, Guizhou and Guangxi are also in the subtropical climate and have a lot of rain, rainwater seeps through the gypsum slag layer and collects at the bottom of the slag yard dam, forming acidic slag yard leachate. This leachate contains high concentrations of calcium and magnesium ions, sulfate ions, manganese ions, ammonia nitrogen, etc., which seriously pollutes surface and groundwater resources.

[0050] To address this global environmental challenge, extensive laboratory research determined that a dual-membrane treatment process combining ultrafiltration and reverse osmosis was employed. A pilot-scale test with a capacity of 2 m³ / h was conducted. The process flow is as follows: Figure 2 As shown.

[0051] The leachate from the manganese slag plant is treated by ultrafiltration to remove water-insoluble substances. The permeate then enters the first-stage reverse osmosis system, where the recovery rate is 80% and the manganese ion removal rate is 90%. The permeate from the first-stage reverse osmosis system enters the second-stage reverse osmosis system, where it is reused in the production system. The concentrate from the second-stage reverse osmosis system is returned to the inlet of the first-stage reverse osmosis system, and the concentrate from the first-stage reverse osmosis system, which is rich in manganese sulfate, is reused as a raw material in the extraction section.

[0052] The pilot test results are shown in the table below:

[0053]

[0054] Since the leachate contains saturated calcium sulfate, preventing calcium sulfate scaling during membrane separation and concentration is crucial for this pilot test. To this end, a submerged ultrafiltration membrane was used in the pilot test, with a high concentration of calcium sulfate particles in the membrane tank to disrupt the supersaturation of calcium sulfate. Regular chemical cleaning was also employed to maximize the stable operation of the ultrafiltration and reverse osmosis membranes. The pilot test ran continuously for one month without any membrane scaling, and the pilot test achieved its expected goals.

[0055] Comparative Example 1

[0056] Comparative Example 1 is from the same company as Example 1. Comparative Example 1 uses lime neutralization, gravity clarification, and acid addition to adjust pH to treat the leachate from the manganese gypsum slag field. The purpose is to reuse the permeate or discharge it in compliance with standards. Comparative Example 1 already has an industrial application device. Water samples after treatment were taken for analysis and compared with the secondary reverse osmosis permeate from Example 1. The results are shown in the table below:

[0057]

[0058] The above analysis results show that Comparative Example 1 cannot meet the emission standards for manganese, ammonia nitrogen, SS, CODCr, etc. Even if it is allowed to be reused in the production process without external discharge, the continuous accumulation of TDS will cause crystallization or scaling blockage of equipment and pipelines. This is the main reason why companies in the industry are looking for new technologies to solve the environmental pollution problem of leachate from storage yards.

[0059] The results above show that the dual-membrane process in Example 1 can not only obtain high-quality permeate, but also return the concentrate to the production system, achieving resource recycling and regeneration. The technology is advanced. It is important to note that the reverse osmosis device pretreatment should be well designed, and the membrane should be cleaned and maintained during operation.

[0060] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A system for treating high phosphorus fluorine wastewater, characterized by comprising: The application relates to a wastewater treatment device, which comprises: a primary reaction device for adjusting the pH of wastewater to alkaline and assisting in removing fluorine from the wastewater by using polyaluminum chloride, so that phosphorus and fluorine in the wastewater are transferred to a solid phase; a primary membrane separation device connected with the primary reaction device and used for removing water-insoluble substances formed in the primary reaction; a secondary reaction device connected with the primary membrane separation device and used for transferring calcium ions in the wastewater to the solid phase by using an alkaline condition, so as to reduce the risk of calcium sulfate scaling; a secondary membrane separation device connected with the secondary reaction device and used for removing water-insoluble substances formed in the secondary reaction; an RO membrane desalination device, wherein the reverse osmosis membrane is arranged in the form of multiple-stage membrane series connection, the concentrated solution of a front-stage membrane is used as the water inlet of a rear-stage membrane, and the percolate of each stage of membrane is collected as product water and reused as pure water to a production system.

2. The system for treating high phosphorus and fluorine wastewater according to claim 1, characterized in that: The primary membrane separation device is made of one of polytetrafluoroethylene tubular membrane, cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, polyether sulfone, inorganic membrane made of aluminum oxide and silicon carbide.

3. The system for treating high phosphorus and fluorine-containing wastewater according to claim 2, characterized in that: The primary membrane separation device comprises a water-insoluble substance output end and a water body output end, the water body output end is connected with the input end of the secondary reaction device, and the water-insoluble substance output end is connected with the first sludge dewatering device.

4. The system for treating high phosphorus and fluorine-containing wastewater according to claim 3, characterized in that: The secondary membrane separation device is made of one of polytetrafluoroethylene tubular membrane, cellulose acetate, cellulose acetate ester, polyethylene, PVDF, polysulfone, polyether sulfone, inorganic membrane made of aluminum oxide and silicon carbide.

5. The system for treating high phosphorus and fluorine-containing wastewater according to claim 4, characterized in that: The secondary membrane separation device comprises a water-insoluble substance output end and a water body output end, the water body output end is connected with the input end of the RO membrane desalination device, and the water-insoluble substance output end is connected with the second sludge dewatering device.

6. The system for treating high phosphorus and fluorine-containing wastewater according to claim 5, characterized in that: The first sludge dewatering device and the second sludge dewatering device are plate-and-frame filter presses, vacuum belt filter machines or screw presses.

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