Phosphate wastewater refining treatment and concentration recovery method

Abstract

The invention discloses a phosphate wastewater refining treatment and concentration recovery method, which comprises the following steps: conveying phosphate wastewater to a first reaction tank, adjusting the pH value, and carrying out a flocculation precipitation reaction to obtain a reaction liquid; performing circulating filtration through a plate-and-frame filtration device to obtain clarified filtrate; conveying to a second reaction tank, adjusting the pH again to form phosphate precipitate, and obtaining refined filtrate through a microporous filter; concentrating by adopting a high-pressure reverse osmosis membrane device to obtain a first concentrated solution and a first dialysate; the first dialysate is further concentrated through a low-pressure reverse osmosis membrane device, a second concentrated solution is returned to the second reaction tank for circular treatment, and the second dialysate is reused for the activated carbon production line; deeply refining the first concentrated solution through a multi-layer resin tower to obtain a high-purity sodium phosphate solution which is finally used as a raw material solution of a bipolar membrane electrodialysis system to electrolyze and recycle phosphoric acid and sodium hydroxide. According to the method, the whole-process recycling of the phosphate wastewater is realized.

Description

Technical Field

[0001] This invention relates to the field of chemical high-salt wastewater treatment technology, and in particular to a method for refining, concentrating and recovering phosphate wastewater. Background Technology

[0002] The production of activated carbon via the phosphoric acid process generates a large amount of wastewater, known as phosphate wastewater. This wastewater contains high concentrations of phosphates, along with small amounts of suspended particles and various divalent and higher-valence metal ions (such as calcium, magnesium, iron, and aluminum), and is characterized by high salinity and low pH. The high salinity and complex ionic composition make wastewater concentration difficult. Traditional evaporation and membrane separation technologies are susceptible to fouling and scaling, resulting in low concentration efficiency and difficulty in recycling. Traditional methods for producing phosphate wastewater via the phosphoric acid process involve simple alkali neutralization, flocculation, sedimentation, and filtration before discharge, still resulting in high-salinity wastewater environmental pollution. Alternatively, evaporation, concentration, and crystallization yield phosphate crystals, but due to low purity and low added value, these are difficult for the market to absorb. Summary of the Invention

[0003] In view of this, the purpose of this invention is to propose a method for the purification, treatment and concentration of phosphate wastewater, which solves the problem of the purification and membrane concentration of phosphate wastewater and its complete recycling. The phosphate wastewater from the phosphoric acid activated carbon production process can be collected and recycled. After purification and membrane concentration, a high-purity sodium phosphate concentrate is obtained, which can be used as a feed liquid for bipolar membranes.

[0004] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is: a method for refining, treating, concentrating, and recovering phosphate wastewater, comprising:

[0005] Phosphate wastewater is transported to the first reaction tank, where sodium hydroxide solution is added to adjust the pH to 3.0-6.0 to carry out flocculation and precipitation reaction, so that SiO2 and heavy metal ions form flocculated precipitates to obtain the reaction solution.

[0006] The reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate.

[0007] The clarified filtrate was transferred to the second reaction vessel, where sodium hydroxide solution and soda ash were added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, which further reduces the concentration of heavy metal ions. The filtrate is then filtered through a microporous filter to remove residual suspended solids, resulting in a purified filtrate.

[0008] The purified filtrate is sent to a high-pressure reverse osmosis membrane unit for concentration to obtain a first concentrate and a first dialysis solution;

[0009] The first dialysate is sent to a low-pressure reverse osmosis membrane unit for further concentration to obtain a second concentrate and a second dialysate.

[0010] The second concentrate is returned to the second reaction tank for recycling, and the second dialysis solution is reused in the activated carbon production line.

[0011] The first concentrate is sent to a multi-layer resin tower for deep purification to remove residual heavy metal ions and obtain a high-purity sodium phosphate solution.

[0012] High-purity sodium phosphate solution was used as the feed liquid for a bipolar membrane electrodialysis system to electrolyze and recover phosphoric acid and sodium hydroxide.

[0013] In some embodiments, phosphate wastewater is transported to a first reaction tank, where sodium hydroxide solution is added to adjust the pH to 3.0–6.0, and a flocculation and precipitation reaction is carried out to form flocculated precipitates of SiO2 and heavy metal ions, yielding a reaction solution comprising:

[0014] Polyaluminum chloride was added to the first reaction vessel as a flocculant at a dosage of 50 mg / L to 100 mg / L.

[0015] The reaction temperature was controlled at 25℃~50℃, the stirring speed at 60r / min~100r / min, and the reaction time at 30min~60min;

[0016] Flocculation and precipitation reaction to remove Fe 3+ Al 3 + Trivalent metal ions form phosphate precipitates, which co-precipitate SiO2 colloids.

[0017] In some embodiments, the reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate, comprising:

[0018] The reaction solution is pumped into a plate and frame filter device, and the filtration pressure is controlled at 0.4MPa to 0.6MPa. Filtration is carried out using a 150-200 mesh filter cloth. The initial filtrate is returned to the circulation filter. When the turbidity of the filtrate is ≤5NTU, the clear filtrate is collected.

[0019] The moisture content of the filter cake produced during the filtration process is controlled at 60% to 70%.

[0020] In some embodiments, the clarified filtrate is transferred to a second reaction vessel, where sodium hydroxide solution and soda ash are added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, further reducing the concentration of heavy metal ions. The solution is then filtered through a microporous filter to remove residual suspended solids, yielding a purified filtrate, comprising:

[0021] The clarified filtrate is transferred to the second reaction vessel, and a 10% sodium hydroxide solution is added to adjust the pH to 9.0–10.5. Sodium carbonate solution is also added to control the carbonate ion concentration to 50 mg / L–100 mg / L.

[0022] The reaction temperature was controlled at 25℃~50℃, the stirring speed at 80r / min~120r / min, and the reaction time at 45min~90min;

[0023] After the reaction is complete, the mixture is filtered through a microporous filter with a pore size of 1μm to 5μm. The filtrate with SS ≤ 10mg / L is the purified filtrate.

[0024] In some embodiments, the purified filtrate is fed to a high-pressure reverse osmosis membrane device for concentration to obtain a first concentrate and a first dialysate, comprising:

[0025] The purified filtrate is pumped into a high-pressure reverse osmosis membrane device, and the operating pressure is controlled at 4.0 MPa to 6.0 MPa. The high-pressure reverse osmosis membrane device uses an acid-resistant polyamide composite reverse osmosis membrane as the first membrane element.

[0026] The high-pressure reverse osmosis membrane unit adopts a three-section arrangement, with the ratio of the number of first membrane elements in each section being 2:1:1;

[0027] During operation, the concentration factor is controlled at 10 to 15 times to obtain a first concentrate with a PO43- concentration ≥ 8% and a first dialysate with a TDS ≤ 2000 mg / L.

[0028] In some embodiments, the first dialysate is fed to a low-pressure reverse osmosis membrane device for further concentration to obtain a second concentrate and a second dialysate, comprising:

[0029] The first dialysate is pumped into the low-pressure reverse osmosis membrane device, and the operating pressure is controlled at 1.0MPa to 2.5MPa. The low-pressure reverse osmosis membrane device uses a polyamide composite reverse osmosis membrane as the second membrane element.

[0030] The low-pressure reverse osmosis membrane unit adopts a two-stage arrangement, with the ratio of the number of second membrane elements in each stage being 1:1;

[0031] During operation, the concentration factor is controlled at 5 to 6 times to obtain a second concentrate with a TDS of 8000 mg / L to 10000 mg / L and a second dialysate with a conductivity of ≤300 μS / cm.

[0032] In some embodiments, the second concentrate is returned to the second reaction tank for recycling, and the second dialysate is reused in the activated carbon production line, including:

[0033] The second concentrate is returned to the second reaction tank, mixed with the new clarified filtrate, and then subjected to pH adjustment and filtration again. The second concentrate accounts for 15% to 25% of the volume of the mixture.

[0034] The second dialysis solution is stored in a recycled water tank, disinfected with ultraviolet light, and then transported to the activated carbon production line via a metering pump.

[0035] In some embodiments, the first concentrate is fed to a multi-layer resin tower for deep purification to remove residual heavy metal ions, yielding a high-purity sodium phosphate solution, comprising:

[0036] The first concentrate is passed through a multilayer resin tower filled with chelating resin at a flow rate of 2 BV / h to 4 BV / h, and the operating temperature is controlled at 25℃ to 45℃. The chelating resin is an iminodiacetic acid type resin.

[0037] The multi-layer resin tower operates in series, consisting of a primary resin tower and a secondary resin tower. When the concentration of heavy metal ions in the effluent from the primary resin tower exceeds 0.1 mg / L, the system switches to operation of the secondary resin tower.

[0038] The resin regeneration of the multilayer resin tower is carried out by elution with 5% to 8% hydrochloric acid solution at a regeneration flow rate of 1 BV / h to 2 BV / h. After regeneration, it is transformed with 4% to 6% sodium hydroxide solution.

[0039] The total content of heavy metal ions in the refined high-purity sodium phosphate solution is ≤0.5mg / L, and the content of SiO2 is ≤10mg / L.

[0040] In some embodiments, a high-purity sodium phosphate solution is used as the feed solution in a bipolar membrane electrodialysis system for the electrolytic recovery of phosphoric acid and sodium hydroxide, including:

[0041] A high-purity sodium phosphate solution is pumped into the raw material chamber of the bipolar membrane electrodialysis system, and the solution temperature is controlled at 25℃~45℃.

[0042] Under the influence of a DC electric field, an operating voltage of 400V–450V is applied, and the current density is maintained at 800A / m. 2 ~1200A / m 2 ;

[0043] Through the hydrolysis effect of the bipolar membrane, a phosphoric acid solution with a concentration of 8% to 12% is obtained in the acid chamber, and a sodium hydroxide solution with a concentration of 8% to 10% is obtained in the alkali chamber.

[0044] Part of the sodium hydroxide solution is returned to the first reaction vessel for reuse as a pH adjuster, and the remainder is collected as a byproduct.

[0045] In some embodiments, the method further includes:

[0046] The phosphoric acid solution with a concentration of 8% to 12% generated by the bipolar membrane electrodialysis system is transported to the phosphoric acid refining unit, where it passes through an activated carbon adsorption tower to remove organic impurities and a precision filter to remove particulate matter, thus obtaining the final phosphoric acid product.

[0047] The sodium hydroxide solution, which is a byproduct, is processed by an evaporation and concentration unit to obtain the finished sodium hydroxide solution.

[0048] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0049] This invention provides a method for the purification, concentration, and recovery of phosphate wastewater, comprising: conveying phosphate wastewater to a first reaction tank, adjusting the pH, and performing a flocculation and precipitation reaction to obtain a reaction solution; circulating and filtering the wastewater through a plate and frame filter to obtain a clarified filtrate; conveying the wastewater to a second reaction tank, adjusting the pH again to form phosphate precipitate, and obtaining a purified filtrate through a microporous filter; concentrating the filtrate using a high-pressure reverse osmosis membrane device to obtain a first concentrate and a first dialysate; further concentrating the first dialysate using a low-pressure reverse osmosis membrane device, returning the second concentrate to the second reaction tank for recycling, and reusing the second dialysate in an activated carbon production line; deeply refining the first concentrate in a multi-layer resin tower to obtain a high-purity sodium phosphate solution, which is finally used as a feedstock for a bipolar membrane electrodialysis system to electrolyze and recover phosphoric acid and sodium hydroxide. This method achieves the full-process recycling of phosphate wastewater. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a schematic diagram of the method and apparatus described in the specific embodiments. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Please see Figure 1 This embodiment provides a method for refining, concentrating, and recovering phosphate wastewater, including:

[0054] Phosphate wastewater is transported to the first reaction tank, where sodium hydroxide solution is added to adjust the pH to 3.0-6.0 to carry out flocculation and precipitation reaction, so that SiO2 and heavy metal ions form flocculated precipitates to obtain the reaction solution.

[0055] The reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate.

[0056] The clarified filtrate was transferred to the second reaction vessel, where sodium hydroxide solution and soda ash were added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, which further reduces the concentration of heavy metal ions. The filtrate is then filtered through a microporous filter to remove residual suspended solids, resulting in a purified filtrate.

[0057] The purified filtrate is sent to a high-pressure reverse osmosis membrane unit for concentration to obtain a first concentrate and a first dialysis solution;

[0058] The first dialysate is sent to a low-pressure reverse osmosis membrane unit for further concentration to obtain a second concentrate and a second dialysate.

[0059] The second concentrate is returned to the second reaction tank for recycling, and the second dialysis solution is reused in the activated carbon production line.

[0060] The first concentrate is sent to a multi-layer resin tower for deep purification to remove residual heavy metal ions and obtain a high-purity sodium phosphate solution.

[0061] High-purity sodium phosphate solution was used as the feed liquid for a bipolar membrane electrodialysis system to electrolyze and recover phosphoric acid and sodium hydroxide.

[0062] In this embodiment, the apparatus used in the method includes a first reaction vessel, a plate and frame filter, a second reaction vessel, a microporous filter, a high-pressure reverse osmosis membrane device, a low-pressure reverse osmosis membrane device, a multilayer resin tower, and a bipolar membrane electrodialysis system. The first reaction vessel is used for initial pH adjustment and flocculation sedimentation, and is equipped with a stirring system to promote reaction uniformity. The plate and frame filter adopts a circulating filtration mode and has a backwashing function to ensure the clarity of the filtrate. The second reaction vessel is used for secondary pH adjustment and phosphate precipitation to optimize the removal of heavy metals. The microporous filter is used to retain residual suspended solids to ensure the quality of the purified filtrate. The high-pressure reverse osmosis membrane device uses an acid-resistant composite membrane to achieve high-fold concentration. The low-pressure reverse osmosis membrane device further concentrates the first dialysis solution to improve the reuse rate. The multilayer resin tower deeply adsorbs heavy metal ions through chelating resin. The bipolar membrane electrodialysis system is used to electrolyze sodium phosphate solution, simultaneously recovering phosphoric acid and sodium hydroxide.

[0063] This embodiment achieves efficient treatment and resource recovery of phosphate wastewater through the synergistic effect of multi-stage reaction, filtration, membrane separation, and resin purification. Two-stage pH adjustment and precipitation reactions target the removal of different metal ions and SiO2, while plate and frame filtration and microfiltration ensure filtrate clarity. The stepped concentration design of high-pressure and low-pressure reverse osmosis membranes improves phosphate recovery efficiency and enables dialysate reuse. Deep purification in a multi-layer resin tower further removes residual heavy metals, ensuring the sodium phosphate solution meets the purity requirements for bipolar membrane electrolysis. The bipolar membrane electrodialysis system converts the purified solution into phosphoric acid and sodium hydroxide, forming a complete resource recycling system. This embodiment not only solves the problems of membrane fouling, scaling, and low product purity in traditional processes but also achieves zero wastewater discharge, significantly reducing treatment costs and demonstrating significant environmental and economic value.

[0064] In some embodiments, phosphate wastewater is transported to a first reaction tank, where sodium hydroxide solution is added to adjust the pH to 3.0–6.0, and a flocculation and precipitation reaction is carried out to form flocculated precipitates of SiO2 and heavy metal ions, yielding a reaction solution comprising:

[0065] Polyaluminum chloride was added to the first reaction vessel as a flocculant at a dosage of 50 mg / L to 100 mg / L.

[0066] The reaction temperature was controlled at 25℃~50℃, the stirring speed at 60r / min~100r / min, and the reaction time at 30min~60min;

[0067] Flocculation and precipitation reaction to remove Fe 3+ Trivalent metal ions such as Al3+ form phosphate precipitates, which co-precipitate SiO2 colloids.

[0068] In this embodiment, phosphate wastewater undergoes flocculation and sedimentation in the first reaction tank by adding polyaluminum chloride. The reaction is carried out for 30-60 minutes at 25℃~50℃ and 60r / min~100r / min, effectively removing Fe. 3+ Al 3 + Trivalent metal ions and SiO2 colloids form easily filtered precipitates.

[0069] This embodiment optimizes the flocculation and sedimentation conditions of the first reaction tank, using polyaluminum chloride as a flocculant to achieve efficient co-precipitation of trivalent metal ions and SiO2 under controlled temperature and rate conditions. This not only improves the density of the flocs for subsequent plate and frame filtration, but also ensures the destabilization effect of the colloids through molecular weight control, significantly reducing the turbidity and heavy metal content of the reaction solution. This creates favorable conditions for subsequent membrane concentration and resin purification, while avoiding secondary pollution problems caused by excessive reagent addition.

[0070] In some embodiments, the reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate, comprising:

[0071] The reaction solution is pumped into a plate and frame filter device, and the filtration pressure is controlled at 0.4MPa to 0.6MPa. Filtration is carried out using a 150-200 mesh filter cloth. The initial filtrate is returned to the circulation filter. When the turbidity of the filtrate is ≤5NTU, the clear filtrate is collected.

[0072] The moisture content of the filter cake produced during the filtration process is controlled at 60% to 70%.

[0073] In this embodiment, by optimizing the operating parameters of the plate and frame filter device and employing filter cloth with a specific pore size in conjunction with precise pressure control, stable turbidity compliance is achieved while ensuring filtration efficiency. The filter cake moisture content is controlled within a reasonable range of 60% to 70%, ensuring solid-liquid separation while avoiding energy waste caused by excessive dehydration. This embodiment significantly improves the reliability and economy of the filtration process, providing a high-quality clarified filtrate guarantee for subsequent reaction tank processing and membrane concentration.

[0074] In some embodiments, the clarified filtrate is transferred to a second reaction vessel, where sodium hydroxide solution and soda ash are added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, further reducing the concentration of heavy metal ions. The solution is then filtered through a microporous filter to remove residual suspended solids, yielding a purified filtrate, comprising:

[0075] The clarified filtrate is transferred to the second reaction vessel, and a 10% sodium hydroxide solution is added to adjust the pH to 9.0–10.5. Sodium carbonate solution is also added to control the carbonate ion concentration to 50 mg / L–100 mg / L.

[0076] The reaction temperature was controlled at 25℃~50℃, the stirring speed at 80r / min~120r / min, and the reaction time at 45min~90min;

[0077] After the reaction is complete, the mixture is filtered through a microporous filter with a pore size of 1μm to 5μm. The filtrate with SS ≤ 10mg / L is the purified filtrate.

[0078] In this embodiment, the pH of the clarified filtrate was adjusted to 9.0–10.5 in the second reaction vessel using a 30% sodium hydroxide solution, and the carbonate ion concentration was controlled at 50 mg / L–100 mg / L. The reaction was carried out at 25°C–50°C and 80–120 r / min for 45–90 minutes to allow the Ca2+ ions to react. 2+ Mg 2+After sufficient precipitation, the solution is processed through a 1-5 μm microporous filter until SS ≤ 10 mg / L to obtain a purified filtrate that meets the requirements.

[0079] This embodiment achieves efficient precipitation of divalent metal ions by controlling the alkalinity adjustment and precipitation conditions of the second reaction tank and using a specific concentration of sodium hydroxide and sodium carbonate in synergistic action under optimized temperature and stirring conditions. Combined with microporous filtration with precise pore size, it ensures that the suspended solids content of the purified filtrate consistently meets the standards. This process design not only guarantees the deep removal of heavy metal ions but also effectively prevents the risk of membrane system scaling through the introduction of carbonate ions. It provides a feed solution with extremely low impurity content for subsequent reverse osmosis concentration and resin purification, while avoiding the salt accumulation problem caused by excessive reagent addition.

[0080] In some embodiments, the purified filtrate is fed to a high-pressure reverse osmosis membrane device for concentration to obtain a first concentrate and a first dialysate, comprising:

[0081] The purified filtrate is pumped into a high-pressure reverse osmosis membrane device, and the operating pressure is controlled at 4.0 MPa to 6.0 MPa. The high-pressure reverse osmosis membrane device uses an acid-resistant polyamide composite reverse osmosis membrane as the first membrane element.

[0082] The high-pressure reverse osmosis membrane unit adopts a three-section arrangement, with the ratio of the number of first membrane elements in each section being 2:1:1;

[0083] During operation, the concentration factor is controlled at 10 to 15 times to obtain a first concentrate with a PO43- concentration ≥ 8% and a first dialysate with a TDS ≤ 2000 mg / L.

[0084] In this embodiment, the purified filtrate is concentrated using a high-pressure reverse osmosis membrane device. An acid-resistant polyamide composite reverse osmosis membrane is used as the first membrane element, operating at a pressure of 4.0 MPa to 6.0 MPa, with the membrane flux controlled at 15 L / (m²). 2 ·h)~25L / (m 2 The device adopts a three-stage arrangement (membrane element ratio 2:1:1), with the concentration factor controlled at 10 to 15 times, and finally obtains a first concentrate with PO43- concentration ≥8% and a first dialysate with TDS ≤2000mg / L.

[0085] This embodiment optimizes the operating parameters of the high-pressure reverse osmosis membrane unit, employing an acid-resistant polyamide composite membrane with a three-stage arrangement design. This ensures system stability while achieving highly efficient phosphate concentration. Precisely controlled concentration ratios ensure that the PO43- concentration meets subsequent treatment requirements while avoiding the risk of membrane fouling due to excessive pressure. The resulting low-TDS dialysate can be directly reused, while the high-concentration concentrate provides ideal raw material for subsequent resin refining. This embodiment fully leverages the selective separation characteristics of the reverse osmosis membrane, significantly reducing system energy consumption while achieving resource recovery, providing crucial assurance for the economical operation of the entire wastewater treatment process.

[0086] In some embodiments, the first dialysate is fed to a low-pressure reverse osmosis membrane device for further concentration to obtain a second concentrate and a second dialysate, comprising:

[0087] The first dialysate is pumped into the low-pressure reverse osmosis membrane device, and the operating pressure is controlled at 1.0MPa to 2.5MPa. The low-pressure reverse osmosis membrane device uses a polyamide composite reverse osmosis membrane as the second membrane element.

[0088] The low-pressure reverse osmosis membrane unit adopts a two-stage arrangement, with the ratio of the number of second membrane elements in each stage being 1:1;

[0089] During operation, the concentration factor is controlled at 5 to 6 times to obtain a second concentrate with a TDS of 8000 mg / L to 10000 mg / L and a second dialysate with a conductivity of ≤300 μS / cm.

[0090] In this embodiment, by optimizing the operating parameters of the low-pressure reverse osmosis membrane unit and employing a polyamide composite membrane with a two-stage arrangement design, advanced treatment of the dialysate is achieved at a relatively low operating pressure. Precisely controlled concentration ratios ensure that the second concentrate meets reuse standards while also guaranteeing that the conductivity of the second dialysate meets industrial water requirements. This process design fully leverages the energy-saving advantages of low-pressure reverse osmosis, significantly reducing energy consumption while maintaining treatment effectiveness and achieving efficient water reuse. Through the rational configuration of the cascade membrane concentration process, advanced treatment of the high-pressure reverse osmosis dialysate is achieved, along with the reuse of the concentrate and the resource utilization of the dialysate, providing crucial assurance for the economic and sustainable operation of the entire wastewater treatment system.

[0091] In some embodiments, the second concentrate is returned to the second reaction tank for recycling, and the second dialysate is reused in the activated carbon production line, including:

[0092] The second concentrate is returned to the second reaction tank, mixed with the new clarified filtrate, and then subjected to pH adjustment and filtration again. The volume ratio of the second concentrate to the mixed liquid is 15% to 25%.

[0093] The second dialysis solution is stored in a recycled water tank, disinfected with ultraviolet light, and then transported to the activated carbon production line via a metering pump.

[0094] In this embodiment, the second concentrate is returned to the second reaction tank at a volume ratio of 15% to 25%, and after being mixed with the clarified filtrate, it is re-involved in pH adjustment and filtration. The second dialysate is stored in a recycled water tank after being disinfected by ultraviolet light, and is precisely delivered to the activated carbon production line as recycled production water through a metering pump.

[0095] This embodiment establishes a closed-loop circulation system for the second concentrate, achieving deep treatment of residual pollutants under strict control of the reflux ratio. This avoids the accumulation of harmful substances and improves resource utilization. Standardized disinfection treatment of the second dialysis solution and the establishment of a precise metering and reuse mechanism ensure stable and reliable reclaimed water quality. By constructing a complete material recycling system, this embodiment incorporates all membrane concentration products into the resource utilization channel, eliminating the environmental risks of wastewater discharge and significantly reducing fresh water and reagent consumption. This achieves a synergistic improvement in environmental and economic benefits, providing practical and feasible technical support for the sustainable development of activated carbon production.

[0096] In some embodiments, the first concentrate is fed to a multi-layer resin tower for deep purification to remove residual heavy metal ions, yielding a high-purity sodium phosphate solution, comprising:

[0097] The first concentrate is passed through a multilayer resin tower filled with chelating resin at a flow rate of 2 BV / h to 4 BV / h, and the operating temperature is controlled at 25℃ to 45℃. The chelating resin is an iminodiacetic acid type resin.

[0098] The multi-layer resin tower operates in series, consisting of a primary resin tower and a secondary resin tower. When the concentration of heavy metal ions in the effluent from the primary resin tower exceeds 0.1 mg / L, the system switches to operation of the secondary resin tower.

[0099] The resin regeneration of the multilayer resin tower is carried out by elution with 5% to 8% hydrochloric acid solution at a regeneration flow rate of 1 BV / h to 2 BV / h. After regeneration, it is transformed with 4% to 6% sodium hydroxide solution.

[0100] The total content of heavy metal ions in the refined high-purity sodium phosphate solution is ≤0.5mg / L, and the content of SiO2 is ≤10mg / L.

[0101] In this embodiment, the first concentrate is deeply purified by a multi-layer resin tower filled with iminodiacetic acid chelating resin, with the flow rate controlled at 2BV / h to 4BV / h and the operating temperature at 25℃ to 45℃. The first and second resin towers are operated in series, and the process is switched to the second resin tower when the concentration of heavy metal ions in the first-stage effluent exceeds 0.1mg / L. The resin is regenerated by elution with 5% to 8% hydrochloric acid solution followed by transformation with 4% to 6% sodium hydroxide solution, finally obtaining a high-purity sodium phosphate solution with a total heavy metal ion content ≤0.5mg / L and a SiO2 content ≤10mg / L.

[0102] This embodiment optimizes the operating parameters and series switching mechanism of the multi-layer resin tower to fully utilize the selective adsorption characteristics of iminodiacetic acid-type resin, achieving deep removal of heavy metal ions under mild operating conditions. The innovative resin regeneration process maintains resin exchange capacity while ensuring regeneration efficiency, guaranteeing long-term stable system operation. The refined high-purity sodium phosphate solution not only meets the raw material requirements of the bipolar membrane system, but its extremely low heavy metal and SiO2 content also provides quality assurance for subsequent resource-based products. This embodiment effectively solves the technical bottleneck of traditional treatment methods' difficulty in deep impurity removal by establishing a precisely controlled resin refining system, laying a solid foundation for the high-value utilization of phosphate wastewater, while significantly reducing the risk of membrane system failure due to heavy metal pollution.

[0103] In some embodiments, a high-purity sodium phosphate solution is used as the feed solution in a bipolar membrane electrodialysis system for the electrolytic recovery of phosphoric acid and sodium hydroxide, including:

[0104] A high-purity sodium phosphate solution is pumped into the raw material chamber of the bipolar membrane electrodialysis system, and the solution temperature is controlled at 25℃~45℃.

[0105] Under the influence of a DC electric field, an operating voltage of 400V–450V is applied, and the current density is maintained at 800A / m. 2 ~1200A / m 2 ;

[0106] Through the hydrolysis effect of the bipolar membrane, a phosphoric acid solution with a concentration of 8% to 12% is obtained in the acid chamber, and a sodium hydroxide solution with a concentration of 8% to 10% is obtained in the alkali chamber.

[0107] Part of the sodium hydroxide solution is returned to the first reaction vessel for reuse as a pH adjuster, and the remainder is collected as a byproduct.

[0108] In this embodiment, a high-purity sodium phosphate solution is pumped into the raw material chamber of the bipolar membrane electrodialysis system, and the solution temperature is controlled at 25°C to 35°C; the system operates at a voltage of 400V to 450V and an A / m... 2 ~1200A / m 2Under current density conditions, through the bipolar membrane water dissociation effect, an 8%–12% phosphoric acid solution is obtained in the acid chamber and a 6%–10% sodium hydroxide solution is obtained in the alkali chamber; part of the sodium hydroxide solution is returned to the first reaction vessel as a pH adjuster, and the remainder is collected as a by-product.

[0109] This embodiment achieves highly efficient electrolytic conversion of sodium phosphate solution by precisely controlling the operating conditions of the bipolar membrane electrodialysis system while optimizing energy consumption. A reasonable voltage and current density ratio ensures electrolysis efficiency while avoiding membrane damage due to overload. The generated phosphoric acid and sodium hydroxide solutions have appropriate concentrations, directly meeting industrial application requirements. Furthermore, the partial reuse of sodium hydroxide creates an internal material cycle, significantly reducing the consumption of fresh sodium hydroxide. This embodiment organically combines wastewater treatment with resource recovery, achieving not only complete resource utilization of phosphate wastewater but also constructing an internal circular economy system through product reuse. It provides activated carbon production enterprises with a wastewater treatment solution that combines environmental and economic benefits, effectively improving the overall sustainability of the process.

[0110] In some embodiments, the method further includes:

[0111] The phosphoric acid solution with a concentration of 8% to 12% generated by the bipolar membrane electrodialysis system is transported to the phosphoric acid refining unit, where it passes through an activated carbon adsorption tower to remove organic impurities and a precision filter to remove particulate matter, thus obtaining the final phosphoric acid product.

[0112] The sodium hydroxide solution, which is a byproduct, is processed by an evaporation and concentration unit to obtain the finished sodium hydroxide solution.

[0113] In this embodiment, the 8%–12% phosphoric acid solution generated by the bipolar membrane electrodialysis system is purified by an activated carbon adsorption tower and a precision filter to obtain industrial-grade phosphoric acid product; the 6%–10% sodium hydroxide solution is concentrated to a 30%–32% sodium hydroxide solution product by evaporation at 70℃–90℃; the system does not generate wastewater and realizes full-process material recycling.

[0114] This embodiment constructs a complete product purification chain, purifying the crude phosphoric acid produced by electrodialysis through two stages of activated carbon adsorption and precision filtration, effectively removing organic impurities and particulate matter to obtain a directly marketable phosphoric acid product. The byproduct sodium hydroxide solution is concentrated by gentle evaporation, achieving efficient concentration of sodium hydroxide while avoiding excessive energy consumption due to high temperatures. No wastewater is discharged, and precise recycling maintains the system's water balance while preventing the loss of valuable components. This embodiment transforms all electrodialysis products into high-value-added commodities through a multi-stage resource recovery pathway, not only achieving the goal of zero discharge in the wastewater treatment process but also establishing a complete value conversion chain of "wastewater-resource-product," significantly improving the overall economic feasibility of the process and providing a technological model for maximizing resource recovery in phosphate wastewater treatment.

[0115] By adopting the above technical solution, the present invention differs from the prior art and has the following beneficial effects:

[0116] This invention achieves efficient purification and resource recovery of phosphate wastewater by constructing a multi-stage synergistic treatment system. First, two-stage pH adjustment and flocculation sedimentation reactions are used to specifically remove heavy metal ions of different valence states and SiO2. Plate and frame filtration and microfiltration ensure the clarity of the filtrate. A stepped concentration design using high-pressure and low-pressure reverse osmosis membranes improves phosphate recovery efficiency and enables graded reuse of the dialysis solution. Deep purification in a multi-layer resin tower further removes residual heavy metals, ensuring the sodium phosphate solution meets the purity requirements for bipolar membrane electrolysis. The bipolar membrane electrodialysis system converts the purified solution into phosphoric acid and sodium hydroxide. Combined with subsequent activated carbon adsorption, precision filtration, and evaporation crystallization processes, commercially viable phosphoric acid and sodium hydroxide products are finally obtained. This technical solution, through closed-loop circulation and partial reuse of sodium hydroxide, forms a complete resource recycling system. It not only solves the problems of membrane fouling, scaling, and low product purity in traditional processes but also achieves zero wastewater discharge and maximizes resource utilization, significantly reducing treatment costs. This provides activated carbon production enterprises with a sustainable development solution that combines environmental and economic benefits.

[0117] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0118] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods of various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0119] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for refining, treating, concentrating, and recovering phosphate wastewater, characterized in that, include: Phosphate wastewater is transported to the first reaction tank, where sodium hydroxide solution is added to adjust the pH to 3.0-6.0 to carry out flocculation and precipitation reaction, so that SiO2 and heavy metal ions form flocculated precipitates to obtain the reaction solution. The reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate. The clarified filtrate is transferred to a second reaction vessel, where sodium hydroxide solution and soda ash are added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, which further reduces the concentration of heavy metal ions. The filtrate is then filtered through a microporous filter to remove residual suspended solids, resulting in a purified filtrate. The purified filtrate is fed to a high-pressure reverse osmosis membrane device for concentration to obtain a first concentrate and a first dialysate; The first dialysate is sent to a low-pressure reverse osmosis membrane device for further concentration to obtain a second concentrate and a second dialysate. The second concentrate is returned to the second reaction tank for recycling, and the second dialysis solution is reused in the activated carbon production line; The first concentrate is sent to a multi-layer resin tower for deep purification to remove residual heavy metal ions and obtain a high-purity sodium phosphate solution. The high-purity sodium phosphate solution is used as the feed solution for a bipolar membrane electrodialysis system to electrolyze and recover phosphoric acid and sodium hydroxide.

2. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, Phosphate wastewater is transported to the first reaction tank. Sodium hydroxide solution is added to the first reaction tank to adjust the pH to 3.0–6.0, causing SiO2 and heavy metal ions to form flocculated precipitates, yielding a reaction solution comprising: Polyaluminum chloride is added to the first reaction vessel as a flocculant at a dosage of 50 mg / L to 100 mg / L. The reaction temperature was controlled at 25℃~50℃, the stirring speed at 60r / min~100r / min, and the reaction time at 30min~60min; Flocculation and precipitation reaction removes Fe 3+ Al 3 + Trivalent metal ions form phosphate precipitates, which co-precipitate SiO2 colloids.

3. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The reaction solution is fed to a plate and frame filter for circulating filtration to obtain a clear filtrate, comprising: The reaction solution is pumped into a plate and frame filter device, and the filtration pressure is controlled at 0.4MPa to 0.6MPa. Filtration is carried out using a 150-200 mesh filter cloth. The initial filtrate is returned to the circulation filter. When the turbidity of the filtrate is ≤5NTU, the clear filtrate is collected. The moisture content of the filter cake produced during the filtration process is controlled at 60% to 70%.

4. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The clarified filtrate is transferred to a second reaction vessel, where sodium hydroxide solution and soda ash are added to adjust the pH to 9.0–10.5, so that Ca... 2+ Mg 2+ Phosphate precipitate is formed, further reducing the concentration of heavy metal ions. The solution is then filtered through a microporous filter to remove residual suspended solids, yielding a purified filtrate, comprising: The clarified filtrate is transferred to a second reaction vessel, and a 10% sodium hydroxide solution is added to adjust the pH to 9.0–10.

5. Sodium carbonate solution is also added to control the carbonate ion concentration to 50 mg / L–100 mg / L. The reaction temperature was controlled at 25℃~50℃, the stirring speed at 80r / min~120r / min, and the reaction time at 45min~90min; After the reaction is complete, the mixture is filtered through a microporous filter with a pore size of 1μm to 5μm. The filtrate with SS ≤ 10mg / L is the purified filtrate.

5. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The purified filtrate is fed to a high-pressure reverse osmosis membrane device for concentration to obtain a first concentrate and a first dialysate, comprising: The refined filtrate is pumped into a high-pressure reverse osmosis membrane device, and the operating pressure is controlled at 4.0 MPa to 6.0 MPa. The high-pressure reverse osmosis membrane device uses an acid-resistant polyamide composite reverse osmosis membrane as the first membrane element. The high-pressure reverse osmosis membrane device adopts a three-section arrangement, with the ratio of the number of first membrane elements in each section being 2:1:1; During operation, the concentration factor is controlled at 10 to 15 times to obtain a first concentrate with a PO43- concentration ≥ 8% and a first dialysate with a TDS ≤ 2000 mg / L.

6. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The first dialysate is fed to a low-pressure reverse osmosis membrane device for further concentration to obtain a second concentrate and a second dialysate, comprising: The first dialysate is pumped into a low-pressure reverse osmosis membrane device, and the operating pressure is controlled at 1.0 MPa to 2.5 MPa. The low-pressure reverse osmosis membrane device uses a polyamide composite reverse osmosis membrane as the second membrane element. The low-pressure reverse osmosis membrane device adopts a two-section arrangement, with the ratio of the number of second membrane elements in each section being 1:1; During operation, the concentration factor is controlled at 5 to 6 times to obtain a second concentrate with a TDS of 8000 mg / L to 10000 mg / L and a second dialysate with a conductivity of ≤300 μS / cm.

7. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The second concentrate is returned to the second reaction tank for recycling, and the second dialysis solution is reused in the activated carbon production line, including: The second concentrate is returned to the second reaction tank, mixed with the new clarified filtrate, and then subjected to pH adjustment and filtration again. The volume ratio of the second concentrate to the mixed liquid is 15% to 25%. The second dialysis solution is stored in a recycled water tank, disinfected with ultraviolet light, and then transported to the activated carbon production line via a metering pump.

8. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, The first concentrate is fed to a multi-layer resin tower for deep purification to remove residual heavy metal ions, yielding a high-purity sodium phosphate solution, comprising: The first concentrate is passed through a multilayer resin tower filled with chelating resin at a flow rate of 2 BV / h to 4 BV / h, and the operating temperature is controlled at 25℃ to 45℃. The chelating resin is an iminodiacetic acid type resin. The multi-layer resin tower operates in series, including a primary resin tower and a secondary resin tower. When the concentration of heavy metal ions in the effluent from the primary resin tower exceeds 0.1 mg / L, the system switches to operate in the secondary resin tower. The resin regeneration of the multilayer resin tower is carried out by elution with 5% to 8% hydrochloric acid solution at a regeneration flow rate of 1 BV / h to 2 BV / h. After regeneration, it is converted with 4% to 6% sodium hydroxide solution. The total content of heavy metal ions in the refined high-purity sodium phosphate solution is ≤0.5mg / L, and the content of SiO2 is ≤10mg / L.

9. The method for refining, concentrating, and recovering phosphate wastewater according to claim 1, characterized in that, Using the high-purity sodium phosphate solution as the feed solution in a bipolar membrane electrodialysis system, the electrolytic recovery of phosphoric acid and sodium hydroxide includes: The high-purity sodium phosphate solution is pumped into the raw material chamber of the bipolar membrane electrodialysis system, and the solution temperature is controlled at 25℃~45℃. Under the influence of a DC electric field, an operating voltage of 400V–450V is applied, and the current density is maintained at 800A / m. 2 ~1200A / m 2 ; Through the hydrolysis effect of the bipolar membrane, a phosphoric acid solution with a concentration of 8% to 12% is obtained in the acid chamber, and a sodium hydroxide solution with a concentration of 8% to 10% is obtained in the alkali chamber. Part of the sodium hydroxide solution is returned to the first reaction tank for reuse as a pH adjuster, and the remainder is collected as a byproduct.

10. The method for refining, concentrating, and recovering phosphate wastewater according to claim 9, characterized in that, The method further includes: The phosphoric acid solution with a concentration of 8% to 12% generated by the bipolar membrane electrodialysis system is transported to the phosphoric acid refining unit, where it passes through an activated carbon adsorption tower to remove organic impurities and a precision filter to remove particulate matter, thus obtaining the final phosphoric acid product. The sodium hydroxide solution, which is a byproduct, is processed by an evaporation and concentration unit to obtain the finished sodium hydroxide solution.

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