Adsorption and desorption integrated process for phosphorus-containing and fluorine-containing wastewater

Abstract

The invention relates to the technical field of industrial wastewater treatment, in particular to a phosphorus-containing and fluorine-containing wastewater adsorption and desorption integrated process which comprises the following steps: adding an inorganic polymeric flocculant into phosphorus-containing and fluorine-containing wastewater, and selectively adding a coagulant aid or coupling a Fenton oxidation module and a chelating adsorption module according to the type of wastewater pollutants; according to the constructed composite adsorbent system, through the synergistic effect of multiple components, the number and activity of adsorption sites are greatly improved, synchronous deep removal of phosphorus and fluorine is achieved, the adsorption efficiency is remarkably improved compared with that of an existing single adsorbent or a traditional composite adsorbent, and the concentration of phosphorus and fluorine in wastewater can be rapidly reduced to be within the emission standard. And in the aspect of desorption and cycle performance, the desorption efficiency is remarkably improved by combining the compound desorption agent with an ultrasonic or microwave auxiliary means, and the adsorbent can still keep relatively high adsorption capacity after being circulated for multiple times in cooperation with a targeted regeneration process, so that the replacement cost of the adsorbent is greatly reduced, and the service life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to an integrated adsorption and desorption process for phosphorus- and fluoride-containing wastewater. Background Technology

[0002] Phosphorus and fluoride-containing wastewater widely originates from various industrial sectors such as chemical, electroplating, photovoltaic, and semiconductor industries. Its discharge not only causes eutrophication of water bodies and corrosion of equipment but also harms the ecological environment and human health. Therefore, efficient treatment of this type of wastewater has become an important issue in the field of industrial environmental protection. Adsorption methods have become one of the mainstream technologies for treating phosphorus and fluoride-containing wastewater due to their simple operation and moderate cost; however, existing adsorption technologies still have many shortcomings that urgently need to be addressed.

[0003] In existing technologies, adsorbents often rely on single components or fixed composite systems, lacking categorized selection. This results in limited adsorption sites, making it difficult to achieve simultaneous and efficient removal of phosphorus and fluoride, and exhibiting poor adaptability to complex operating conditions. Desorption processes typically employ single alkaline or acidic solutions, resulting in limited desorption efficiency and insufficient disruption of the binding between adsorption sites and pollutants. This leads to insufficient adsorbent cycle stability and significant capacity decay after repeated use. Pretreatment stages often involve single flocculation processes, which are inadequate for handling industrial wastewater containing high COD, heavy metals, and high suspended solids, easily causing adsorbent pore blockage and affecting treatment effectiveness. Furthermore, existing process parameters are often fixed and cannot adapt to the treatment needs of wastewater with varying concentrations. This not only leads to high treatment costs but also potential resource waste. Additionally, there is a lack of effective treatment solutions for wastewater under extreme conditions such as low temperature, high salinity, and high acidity, limiting the technology's application scope. Therefore, developing an integrated process with high adsorption efficiency, good cycle stability, wide adaptability, and resource recovery capabilities has become an urgent need in this field. Summary of the Invention

[0004] The primary objective of this invention is to provide an integrated adsorption and desorption process for phosphorus- and fluoride-containing wastewater.

[0005] A further objective of this invention is to provide an integrated adsorption and desorption process for phosphorus- and fluoride-containing wastewater, comprising the following steps: (1) Pretreatment: Add inorganic polymer flocculant to phosphorus- and fluorine-containing wastewater. Depending on the type of pollutants in the wastewater, coagulant aid can be added, or a Fenton oxidation module or a chelation adsorption module can be coupled. The suspended solids in the wastewater after pretreatment are ≤10mg / L. (2) Adsorption: La-doped hydroxyphosphate-alumina composite adsorbent is added to the pretreated wastewater; the La-doped hydroxyphosphate-alumina composite adsorbent is composed of hydroxyphosphates, alumina and lanthanides in a mass ratio of 1:0.2-1:5:0.001-0.08; the adsorption temperature is 15-45℃, the pH is 3-9 and the time is 20-120min; (3) Desorption: The adsorption-saturated La-doped hydroxyphosphate-alumina composite adsorbent and the desorption agent are mixed at a solid-liquid ratio of 1:3-1:20; the desorption agent is an alkali, a carbonate, or a mixture of both; ultrasonic or microwave-assisted desorption is used; (4) Regeneration and resource recovery: The La-doped hydroxy phosphate-alumina composite adsorbent after desorption is washed, dried and activated for regeneration and can be recycled 3-10 times; the desorption solution is classified and treated according to concentration, and phosphorus and fluorine are recovered from the high-concentration desorption solution, while the low-concentration desorption solution is returned to the adsorption step for reuse.

[0006] Preferably, the hydroxyphosphate is selected from at least one of calcium hydroxyphosphate, magnesium hydroxyphosphate, zinc hydroxyphosphate, and strontium hydroxyphosphate; the hydroxyphosphate is industrial grade or self-made, with a particle size of 50-200 mesh and a specific surface area ≥30 m². 2 / g.

[0007] Preferably, the alumina is selected from at least one of activated alumina, mesoporous alumina, γ-alumina, and boehmite roasting products; the alumina is industrial grade, with a particle size of 20-150 mesh and a specific surface area ≥50 m². 2 / g, fluorine adsorption capacity ≥10mg / g.

[0008] Preferably, the lanthanide compound is selected from at least one of lanthanum nitrate, lanthanum chloride, lanthanum oxide, and lanthanum sulfate; the purity of the lanthanide compound is ≥95%, and the concentration is 0.05-2 mol / L; the lanthanum oxide needs to be dissolved in dilute hydrochloric acid with a volume ratio of 1:1 to prepare a solution before use.

[0009] Preferably, in the eluent, the alkali is selected from sodium hydroxide and potassium hydroxide, with a concentration of 0.1-3 mol / L; the carbonate is selected from sodium carbonate, sodium bicarbonate, and potassium carbonate, with a concentration of 0.1-2 mol / L; and the mass ratio of alkali to carbonate in the compound eluent is 1:0.1-1:5.

[0010] Preferably, in the pretreatment, the inorganic polymeric flocculant is selected from polyaluminum chloride, polyaluminum sulfate, polyferric chloride, and polyferric sulfate, with an effective component content ≥28% and a dosage of 0.01-0.5 g / L; the coagulant aid is anionic polyacrylamide with a molecular weight of 8 million-20 million and a dosage of 0.001-0.01 g / L.

[0011] Preferably, in the Fenton oxidation module, the amount of hydrogen peroxide added is 0.5-3 g / L, the amount of ferrous sulfate added is 0.1-0.5 g / L, the reaction temperature is 25-60℃, the reaction time is 30-60 min, and the pH is 2-4; in the chelation adsorption module, the amount of heavy metal chelating agent added is 0.1-1 g / L, the reaction time is 20-30 min, and the pH is 5-8.

[0012] Preferably, the phosphorus- and fluoride-containing wastewater has a phosphorus concentration of 5-500 mg / L and a fluoride concentration of 3-300 mg / L, and may contain COD of 10-500 mg / L, suspended solids of 5-200 mg / L, and coexisting ions of ≤500 mg / L; the coexisting ions are at least one of chloride ions, sulfate ions, and nitrate ions.

[0013] Preferably, in the regeneration step, the drying temperature of the calcium hydroxyphosphate-based adsorbent is 60-100℃ and the time is 3-8h, and the activation temperature is 120-200℃ and the time is 2-5h; the magnesium hydroxyphosphate or zinc hydroxyphosphate-based adsorbent needs to be soaked in 0.01-0.1mol / L dilute hydrochloric acid for 10-20min before regeneration.

[0014] Preferably, the high-concentration eluent has a phosphorus concentration ≥100mg / L and a fluoride concentration ≥50mg / L. Calcium chloride of 1-5g / L is added when recovering phosphorus, and sodium fluoride of 0.5-2g / L is added when recovering fluoride. The low-concentration eluent has a phosphorus concentration ≤50mg / L and a fluoride concentration ≤30mg / L, and must be filtered through a 0.45μm filter membrane before reuse.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The composite adsorbent system constructed in this invention significantly increases the number and activity of adsorption sites through the synergistic effect of multiple components, achieving simultaneous and deep removal of phosphorus and fluoride. The adsorption efficiency is significantly improved compared to existing single adsorbents or traditional composite adsorbents, rapidly reducing the concentration of phosphorus and fluoride in wastewater to within emission standards. Regarding desorption and recycling performance, the combination of the compound desorption agent and ultrasonic or microwave-assisted methods significantly improves desorption efficiency. Coupled with a targeted regeneration process, the adsorbent maintains a high adsorption capacity even after multiple cycles, greatly reducing adsorbent replacement costs and extending its service life.

[0016] 2. The wide range of parameters of this invention allows for flexible adjustment of process conditions according to wastewater concentration. The multi-module pretreatment system can specifically treat industrial wastewater containing high COD, heavy metals, and high suspended solids, effectively avoiding adsorbent clogging and ensuring that wastewater of different types and concentrations can be discharged stably in compliance with standards. At the same time, it can also achieve efficient treatment of wastewater under extreme conditions, significantly expanding the application scenarios of the process.

[0017] 3. The recycling of the adsorbent in this invention reduces solid waste emissions, the resource recovery design of the eluent enables the secondary utilization of phosphorus and fluorine resources, and the reuse of low-concentration eluent improves water resource utilization, which is in line with the concept of a circular economy. The overall process is simple to operate and stable, requiring no complex equipment modifications, and is easy to promote industrially. While reducing treatment costs, it achieves a balance between environmental and economic benefits. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0019] (1) Preparation of adsorbent: Weigh hydroxyphosphate and alumina in a mass ratio of 1:0.2-1:5. The hydroxyphosphate can be calcium hydroxyphosphate, magnesium hydroxyphosphate or zinc hydroxyphosphate, and the alumina can be activated alumina, mesoporous alumina or γ-alumina. Add 0.1-8% of lanthanide compounds to the mixture. If it is lanthanum oxide, dissolve it in dilute hydrochloric acid to prepare a 0.05-2 mol / L solution. Add deionized water to adjust the solid-liquid ratio to 1:3-1:25. Disperse the mixture in an ultrasonic generator (power 50-400W) for 15-90 min. Transfer the mixture to a vacuum drying oven with a vacuum degree of -0.08 to -0.1 MPa and dry it at 60-150℃ for 2-12 h. Grind the mixture through a 60-250 mesh sieve to obtain the La-doped composite adsorbent.

[0020] (2) Adsorption process: Take three types of wastewater (low concentration: phosphorus 10mg / L, fluorine 5mg / L; medium concentration: phosphorus 100mg / L, fluorine 80mg / L; high concentration: phosphorus 300mg / L, fluorine 200mg / L), add composite adsorbent, dosage 0.5-10g / L; adjust pH to 3-9, stir with a constant temperature stirrer (15-45℃, 50-500r / min) for 20-120min.

[0021] (3) Desorption process: The adsorbent saturated with the desorbent (single alkali: 0.1-3 mol / L sodium hydroxide / potassium hydroxide; compound: 0.1-2 mol / L sodium hydroxide + 0.1-2 mol / L sodium carbonate) is mixed at a solid-liquid ratio of 1:3-1:20; ultrasonic desorption (50-400W) at 20-50℃ for 15-90 min or microwave desorption (100-600W) for 5-30 min; filter to separate the desorbent from the adsorbent.

[0022] (4) Process results: The specific surface area of ​​the composite adsorbent is 50.2-150.8 m². 2 / g; after treatment, phosphorus ≤0.1mg / L and fluoride ≤1mg / L in low-concentration wastewater; adsorption capacity of phosphorus at medium concentration is 30.5-58.6mg / g and fluoride at medium concentration is 20.3-45.7mg / g; adsorption capacity of phosphorus at high concentration is 58.2-120.5mg / g and fluoride at high concentration is 45.3-80.2mg / g; desorption rate is 78.5-98.8%. Example

[0023] (1) Preparation of adsorbent: Using the same raw material system as in Example 1, the mass ratio of hydroxyphosphate to alumina was adjusted to 1:0.5-1:4, and the amount of lanthanide compound added was 0.5-5%; the total amount of modifier (silane coupling agent KH550 / KH560 + nano silica) added was 0.2-8%; the remaining steps were the same as in Example 1, and an optimized composite adsorbent was obtained.

[0024] (2) Adsorption process: Wastewater of full concentration as described in Example 1 was used, with temperature adjusted to 20-40℃ and pH 4-8; for low-concentration wastewater, stirring was performed for 20-60 min with a dosage of 0.5-3 g / L; for medium-concentration wastewater, stirring was performed for 45-90 min with a dosage of 1-5 g / L; for high-concentration wastewater, stirring was performed for 60-120 min with a dosage of 5-10 g / L; the wastewater contained Cl... - SO4 2- Adsorption is performed when the concentration is ≤500 mg / L.

[0025] (3) Desorption process: use compound desorption agent (0.3-1.8 mol / L potassium hydroxide + 0.2-1.5 mol / L potassium carbonate); low concentration adsorbent desorption solid-liquid ratio 1:3-1:10, time 15-45 min; high concentration adsorbent desorption solid-liquid ratio 1:10-1:20, time 45-90 min; microwave-assisted desorption (power 200-600W).

[0026] (4) Process results: The specific surface area of ​​the optimized adsorbent is 65.8-160.3 m². 2 / g; after treatment of low-concentration wastewater, phosphorus ≤0.05mg / L and fluoride ≤0.8mg / L; medium-concentration phosphorus adsorption capacity 40.2-65.3mg / g and fluoride adsorption capacity 28.5-50.7mg / g; high-concentration phosphorus adsorption capacity 65.8-135.2mg / g and fluoride adsorption capacity 50.6-88.5mg / g; desorption rate 85.6-99.2%; capacity retention rate after one cycle 82.3-95.1%. Example

[0027] (1) Pretreatment process: Three types of industrial wastewater were used (phosphorus chemical wastewater: phosphorus 250mg / L, fluorine 180mg / L, suspended solids 150mg / L; semiconductor wastewater: phosphorus 8mg / L, fluorine 15mg / L, COD 300mg / L; electroplating wastewater: phosphorus 60mg / L, fluorine 50mg / L, Cu 2+ (5 mg / L), select the pretreatment module according to type: For wastewater with high suspended solids: Add 0.05-0.5 g / L polyaluminum chloride / polyferric sulfate + 0.001-0.01 g / L polyacrylamide; adjust pH to 3-7; stir for 10-40 min; let stand for 20-60 min; filter by plate and frame press, and the suspended solids in the supernatant should be ≤10 mg / L; High COD wastewater: First undergo Fenton oxidation (H2O2 0.5-3g / L, Fe... 2+ (0.1-0.5 g / L, pH 2-4, reaction time 30-60 min), then pre-treat as high suspended solids wastewater, COD removal rate 20-60%; For wastewater containing heavy metals: first, chelate and adsorb (add 0.1-1 g / L heavy metal chelating agent, pH 5-8, stir for 20-30 min), then pretreat as wastewater with high suspended solids, with heavy metals ≤0.5 mg / L.

[0028] (2) Adsorption-desorption process: The optimized adsorbent of Example 2 was used, and the parameters were adjusted according to the concentration (high concentration: dosage 8g / L, 40℃, desorption 60min; low concentration: dosage 1g / L, 25℃, desorption 20min); the rest were the same as in Example 2.

[0029] (3) Process results: All three types of wastewater met the standards; phosphorus adsorption capacity of phosphorus chemical wastewater was 110.5-130.2 mg / g, and desorption rate was 92.3-98.5%; after treatment, phosphorus in semiconductor wastewater was ≤0.08 mg / L and fluorine was ≤1.2 mg / L; Cu in electroplating wastewater... 2+ ≤0.1mg / L. Example

[0030] (1) Regeneration process: Collect the adsorbent after analysis in Example 3, and select the appropriate matrix: Hydroxyphosphate calcium group: Rinse with deionized water to pH 6-8; dry at 60-100℃ for 3-8 hours; activate at 120-200℃ for 2-5 hours; Magnesium hydroxyphosphate / zinc-based: Soak in 0.01-0.1 mol / L dilute hydrochloric acid for 10-20 min; rinse until pH 6-8; dry and activate to the same level as calcium hydroxyphosphate. The regenerated adsorbent has a specific surface area decrease rate of ≤20% and a mechanical strength of ≥8N / particle.

[0031] (2) Recycling and resource recovery: The regenerated adsorbent is recycled 3-10 times, repeating the process in Example 3; the eluent is sorted and treated: High-concentration eluent (phosphorus ≥100mg / L, fluoride ≥50mg / L): Adjust pH to 8-10; add 1-5g / L calcium chloride to generate calcium phosphate (phosphorus recovery ≥85%); then add 0.5-2g / L sodium fluoride to generate calcium fluoride (fluoride recovery ≥80%). Low-concentration eluent (phosphorus ≤ 50 mg / L, fluorine ≤ 30 mg / L): After filtration, return to the adsorption process for makeup water (reuse rate ≥ 70%).

[0032] (3) Process results: The capacity retention rate after 3 cycles is 80.5-93.2%; the retention rate after 10 cycles is 65.8-82.5%; the purity of recovered calcium phosphate is ≥90% and the purity of calcium fluoride is ≥95%. Example

[0033] (1) Extreme wastewater treatment: Take three types of extreme wastewater (low temperature wastewater: 5-15℃, phosphorus 30mg / L, fluoride 20mg / L; high salinity wastewater: NaCl 5000-15000mg / L, phosphorus 80mg / L, fluoride 60mg / L; high acidity wastewater: pH 2-3, phosphorus 50mg / L, fluoride 40mg / L), and adjust the process: Low-temperature wastewater: adsorbent with 0.5-2% nano titanium dioxide; adsorption time 60-120 min; ultrasonic power 300-600 W; High-salinity wastewater: Select γ-alumina-based adsorbent; increase dosage by 20-50%; add 0.1-0.5 mol / L sodium chloride as the desorbent; High acidity wastewater: Soak the adsorbent in 0.1-0.5 mol / L sodium hydroxide for 30-60 min; adsorption pH 3-4; desorption using 0.5-2 mol / L sodium carbonate.

[0034] (2) Process results: All three types of wastewater met the standards; the adsorption capacity fluctuation of low-temperature wastewater was ≤15%; the capacity retention rate of high-salt wastewater was 85-90%; the desorption rate of high-acidity wastewater was ≥80%; and the retention rate after 5 cycles was ≥70%.

[0035] Comparative Example 1: (1) Process steps: Only single hydroxyphosphate (without alumina composite, without La doping) is used as adsorbent; the adsorption parameters are the same as in Example 1 (medium concentration wastewater: phosphorus 100mg / L, fluorine 80mg / L, pH 3-9, 15-45℃); 0.1-3mol / L sodium hydroxide (single alkali) is used for desorption, and the desorption conditions are the same as in Example 1.

[0036] (2) Process results: The specific surface area of ​​the adsorbent is 25.3-38.6 m². 2 / g; phosphorus adsorption capacity 15.2-22.8mg / g, fluorine adsorption capacity 8.5-14.3mg / g; desorption rate 62.3-75.8%; after treatment, the phosphorus in medium-concentration wastewater is ≤3.8mg / L and the fluorine is ≤22mg / L, which does not meet the standards.

[0037] Comparative Example 2: (1) Process steps: The adsorbent is a composite of hydroxyapatite and activated alumina (without La doping and without modifier), with a mass ratio of 1:0.5-1:4; the adsorption parameters are the same as in Example 2 (medium concentration wastewater, temperature 20-40℃, pH 4-8); the desorption uses the compound desorption agent of Example 2.

[0038] (2) Process results: phosphorus adsorption capacity 26.5-35.7 mg / g, fluorine adsorption capacity 18.2-25.9 mg / g; desorption rate 76.5-85.2%; capacity retention rate after one cycle 62.3-70.5%.

[0039] Comparative Example 3: (1) Process steps: The optimized adsorbent of Example 2 is used, but the adsorption parameters are fixed (temperature 30℃, pH 6, dosage 3g / L) and are not adjusted according to the wastewater concentration; the analysis parameters are fixed (solid-liquid ratio 1:10, time 30min) and the degree of adsorbent saturation is not distinguished.

[0040] (2) Process results: Low-concentration wastewater (phosphorus 10mg / L) was over-adsorbed, with an adsorbent utilization rate of only 40-50%; high-concentration wastewater (phosphorus 300mg / L) was under-adsorbed, with phosphorus adsorption capacity of 45.2-55.8mg / g and fluorine adsorption capacity of 30.5-40.2mg / g; the desorption rate was 70.5-95.3%; after treatment, the phosphorus in low-concentration wastewater was ≤0.1mg / L and the fluorine was ≤1mg / L, while the phosphorus in high-concentration wastewater was ≤4.2mg / L and the fluorine was ≤15mg / L, which did not meet the standards.

[0041] Comparative Example 4: (1) Process steps: The semiconductor wastewater (high COD) of Example 3 was treated by using only polyaluminum chloride for single flocculation (without Fenton oxidation); the optimized adsorbent and parameters of Example 3 were used for adsorption-desorption.

[0042] (2) Process results: COD removal rate after pretreatment is 8-15%; adsorbent specific surface area decay rate is 40-50%; phosphorus adsorption capacity is 18.5-25.3 mg / g, fluoride adsorption capacity is 12.3-18.5 mg / g; desorption rate is 78.5-85.2%; the treated wastewater COD is ≤250 mg / L, phosphorus is ≤1.2 mg / L, and fluoride is ≤8 mg / L, which does not meet the standards.

[0043] Comparative Example 5: (1) Process steps: The adsorbent of Example 4 is used. After desorption, it is rinsed with deionized water only (without drying-activation step) and the adsorption-desorption process is directly repeated; resource recovery only collects the desorption liquid (without phosphorus and fluorine precipitation recovery).

[0044] Process results: After 3 cycles, the adsorption capacity retention rate was 45.2-55.8%; after 5 cycles, the capacity retention rate was ≤30%; the desorption rate was 75.6-82.3%; the phosphorus in the treated wastewater was ≤1.2mg / L and the fluoride was ≤12mg / L, but some of the samples did not meet the standards after some cycles.

[0045] Performance testing and results analysis: The performance testing method is as follows: (1) Phosphorus adsorption capacity: Low concentration phosphorus was detected by molybdenum antimony spectrophotometry, and high concentration phosphorus was detected by gravimetric method; when calculating, the initial phosphorus concentration of wastewater was subtracted from the phosphorus concentration at adsorption equilibrium, the difference was multiplied by the volume of wastewater, and then divided by the mass of adsorbent to obtain the phosphorus adsorption capacity. (2) Fluorine adsorption capacity: The fluorine concentration was detected by ion-selective electrode method; when calculating, the initial fluorine concentration of wastewater was subtracted from the fluorine concentration at adsorption equilibrium, the difference was multiplied by the volume of wastewater, and then divided by the mass of adsorbent to obtain the fluorine adsorption capacity. (3) Resolution: First, the concentration of phosphorus or fluorine in the eluent is detected. The concentration of the eluent is multiplied by the volume of the eluent to obtain the total mass of phosphorus or fluorine eluent. Then, the adsorption capacity is multiplied by the mass of the adsorbent to obtain the total mass of phosphorus or fluorine adsorbed by the adsorbent. Finally, the total mass eluent is divided by the total adsorbed mass and then multiplied by 100% to obtain the resolution. (4) Cycle retention rate: Calculate the ratio of the adsorption capacity at the nth cycle to the adsorption capacity at the first cycle, and then multiply by 100% to obtain the capacity retention rate at the nth cycle; (5) Concentration after treatment: Phosphorus in the treated wastewater was detected by the molybdenum-antimony spectrophotometric method, fluorine by the ion-selective electrode method, and COD by the potassium dichromate method. The corresponding concentration values ​​were read directly. (6) Adsorbent specific surface area decay rate: The specific surface area of ​​the adsorbent before and after use was measured by the BET method. The specific surface area decay rate was obtained by dividing (specific surface area before use minus specific surface area after use) by the specific surface area before use and then multiplying by 100%.

[0046] The test results are shown in Table 1 below:

[0047] It should be noted that Comparative Example 1, due to the lack of alumina composite and La doping, has a single adsorption site, and its phosphorus and fluoride adsorption capacity is only 40-50% of that of Example 1, with a lower resolution rate of 15-23 percentage points. The phosphorus and fluoride concentration after treatment far exceeds the first-level standard, highlighting the synergistic advantages of the composite adsorbent. The table does not measure "cycle retention rate," "post-treatment COD," or "specific surface area decay rate" for this comparative example because its process design goal is only to verify the core differences between "single adsorbent vs. composite adsorbent," without involving adsorbent recycling, wastewater COD treatment, or adsorbent clogging and decay; therefore, additional testing of irrelevant indicators is unnecessary.

[0048] Comparative Example 2: Lack of La 3+The strong coordination effect of La resulted in a phosphorus adsorption capacity 30-35% lower than that of Example 2, and a retention rate 20-25 percentage points lower after one cycle, demonstrating the key role of La doping in improving adsorption activity and stability. The retention rates after 3 / 5 cycles, post-treatment COD, and specific surface area decay rate were not measured because this comparative study only focused on the impact of La doping. The cycle test used one cycle as the core verification period and did not involve COD wastewater treatment or long-term decay testing. The test range of the indicators matched the design objectives.

[0049] Comparative Example 3: Without adjusting parameters according to wastewater concentration, high-concentration wastewater showed insufficient adsorption, while low-concentration wastewater resulted in wasted adsorbent, highlighting the necessity of the wide-range parameter design in this invention. "Recycling retention rate," "post-treatment COD," and "specific surface area decay rate" were not measured because the process design focuses on the difference in adsorption effect between "fixed parameters vs. wide-range adjustment," and does not involve adsorbent recycling or COD treatment; therefore, testing these non-related indicators is unnecessary.

[0050] Comparative Example 4: Without the Fenton oxidation module, the COD removal rate was 12-45 percentage points lower, the adsorbent surface area decreased by 40-50% due to COD blockage, and the phosphorus capacity was 60-70% lower than in Example 3, verifying the industrial applicability value of multi-module pretreatment. The "cycle retention rate" was not measured because this comparative example primarily verifies the impact of "pretreatment module integrity" on single adsorption. Cycle testing requires "adsorbent regeneration" as a prerequisite, and its process did not include a regeneration step; therefore, no cycle data was available.

[0051] Example 1: "Retention rate", "COD after treatment", and "specific surface area decay rate" were not measured because, as a basic verification step of this invention, the focus was only on "the core performance of adsorption-desorption of the composite adsorbent". Recycling and COD treatment were specifically verified in subsequent Examples 4 and 3, respectively, to avoid repeated testing and to conform to the progressive process design logic. Example 3: "Retention rate" was not measured because the focus was on verifying the industrial adaptability of "multi-module pretreatment + adsorption". The recycling performance was specifically tested in Example 4. Example 5: "Retention rate after 3 / 10 cycles" and "COD after treatment" were not measured because, as the core verification was "the ability to meet standards under extreme conditions", only 5 cycles were required, and high-COD wastewater was not selected, so there was no COD data. The indicators not measured in each example and comparative example were all based on "focused process design goals". Only indicators related to the core innovation points were tested, with no redundancy or missing data, and the data completeness and relevance were consistent.

[0052] As shown in the performance test data in Table 1, this invention, through the modification of composite adsorbents, optimization of process parameters and integration of functional modules, comprehensively surpasses traditional solutions in the core indicators of phosphorus and fluoride wastewater treatment. It not only solves the limitations of existing technologies, but also achieves multi-scenario adaptability and long-term stable operation.

[0053] (1) Regarding adsorption capacity, the phosphorus adsorption capacity of all embodiments remained between 24.5 and 135.2 mg / g, and the fluorine adsorption capacity was between 15.6 and 88.5 mg / g. This adsorption efficiency was significantly better than that of the comparative examples. Taking Comparative Example 1 as an example, it only used a single hydroxyapatite as the adsorbent and did not undergo alumina composite and La doping treatment. The phosphorus adsorption capacity was only 15.2-22.8 mg / g, and the fluorine adsorption capacity was even lower at 8.5-14.3 mg / g, which was about 50% of that of Example 1. The synergistic adsorption system constructed in this invention has the core advantage: La 3+ Can be used with PO4 3- Strong coordination bonds are formed, and hydroxyphosphate achieves selective adsorption of phosphorus through ion exchange, while alumina captures fluoride ions through electrostatic interactions. The synergistic effect of these three agents significantly increases the number and activity of adsorption sites. Example 2 further adds a silane coupling agent and nano-silica to the above system, further enhancing the adsorption capacity. The core reason for this is that the modifier effectively optimizes the dispersibility of the adsorbent, increases the specific surface area, promotes effective contact between pollutants and adsorption sites, and thus improves adsorption efficiency.

[0054] (2) Desorption and cycling performance are key indicators for evaluating the economic efficiency of the process, and the embodiments of the present invention excel in this regard. The desorption rates of the embodiments are generally between 75.6% and 99.2%, especially in Examples 2 to 5, which use a desorption agent composed of alkali and carbonate, supplemented by ultrasonic or microwave assistance, resulting in a desorption rate 15-23 percentage points higher than that of Comparative Example 1, which uses only a single alkali. The compound desorption system can precisely destroy the bonds between the adsorption sites and phosphorus and fluorine, while ultrasonic or microwave assistance can accelerate the mass transfer rate. The synergistic effect of the two significantly improves the desorption efficiency. In terms of cycling stability, the advantages of the present invention are even more prominent: after 10 cycles, the capacity retention rate of the adsorbent in Example 4 is still maintained at 65.8%-82.5%; even in the face of extreme conditions such as low temperature, high salt, and high acid in Example 5, the capacity retention rate is still not less than 70% after 5 cycles. In contrast, in the comparative examples, Comparative Example 2, lacking La doping, saw its capacity retention drop to 62.3-70.5% after only one cycle; Comparative Example 5, without the drying-activation regeneration process, experienced a capacity retention below 30% after five cycles, essentially losing its adsorption efficiency. These results demonstrate that La doping enhances the structural stability of the adsorbent, while the drying-activation process effectively restores the activity of adsorption sites, ensuring long-term reusability of the adsorbent and significantly reducing process operating costs.

[0055] (3) Compliance with standards is the core prerequisite for the practical application of the process. The wastewater treated in all examples met the Class I standard of GB8978-1996 "Integrated Wastewater Discharge Standard", namely, phosphorus concentration ≤0.5mg / L and fluoride concentration ≤10mg / L. However, most comparative examples failed to meet this requirement. For example, Comparative Example 3 fixed the adsorption parameters to a temperature of 30℃, pH 6, and adsorbent dosage of 3g / L without adapting the parameters according to the wastewater concentration. As a result, the phosphorus concentration of the high-concentration wastewater after treatment reached 4.2mg / L, far exceeding the standard limit. In contrast, Examples 1 to 5 can flexibly adjust the process parameters according to the wastewater concentration. For low-concentration wastewater, the adsorbent dosage is reduced and the stirring time is shortened. For high-concentration wastewater, the adsorbent dosage is increased and the stirring time is extended, thus achieving precise treatment of wastewater with different concentrations. In Comparative Example 4, when treating high-COD semiconductor wastewater, only polyaluminum chloride was used for flocculation treatment without Fenton oxidation pretreatment. The final effluent COD was still 250 mg / L and the phosphorus concentration was 1.2 mg / L, which did not meet the discharge standards. Example 3 designed differentiated pretreatment modules for wastewater with different pollutant types: for high-COD wastewater, Fenton oxidation was used to degrade recalcitrant organic matter. For wastewater containing heavy metals, chelation adsorption was used to fix heavy metal ions, and then flocculation was combined to remove suspended solids. In the end, not only was a COD removal rate of 20-60% achieved, but the adsorbent was also effectively prevented from being blocked by impurities, ensuring that the final effluent met the standards.

[0056] (4) The stability of the adsorbent directly affects the long-term operation of the process. The specific surface area decay rate of the adsorbents in Examples 3 to 5 did not exceed 20%, while the decay rate of Comparative Example 4 was as high as 40-50%. The reason for this is that Comparative Example 4 did not carry out Fenton oxidation pretreatment, and the COD components in the wastewater easily adhered to the surface of the adsorbent, causing pore blockage and resulting in a significant decrease in specific surface area. Example 3 pre-degraded the difficult-to-degrade COD components through Fenton oxidation, while Examples 4 and 5 used regeneration processes to remove residual pollutants on the surface of the adsorbent, effectively protecting the structural integrity of the adsorbent and reducing performance decay. In addition, in Example 4, the mechanical strength of the hydroxymagnesium phosphate or zinc hydroxyphosphate-based adsorbent after pretreatment with dilute hydrochloric acid can reach more than 8N / particle, which can meet the requirements for long-term cyclic use and avoid breakage failure due to repeated use.

[0057] In summary, this invention effectively solves the core technical problems of existing technologies, such as the functional limitations of single adsorbents, rigid process parameters, poor adaptability to industrial wastewater, and insufficient cycle stability, through an integrated design that combines composite adsorbent modification, wide-range parameter control, multi-module pretreatment, and closed-loop regeneration and recycling. Whether it is wastewater of conventional concentration or wastewater under extreme conditions such as low temperature, high salinity, or high acidity, and whether it is wastewater with a single pollutant or industrial wastewater with multiple pollutants, this invention can achieve efficient treatment and compliant discharge. Furthermore, the design for recycling the adsorbent and recovering the desorption liquid reduces solid waste emissions and raw material consumption, demonstrating significant practical application value and environmental benefits.

[0058] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A phosphorus-containing fluorine-containing wastewater adsorption and desorption integrated process, characterized in that, Includes the following steps: (1) Pretreatment: Add inorganic polymer flocculant to phosphorus- and fluorine-containing wastewater. Depending on the type of pollutants in the wastewater, coagulant aid can be added, or a Fenton oxidation module or a chelation adsorption module can be coupled. The suspended solids in the wastewater after pretreatment are ≤10mg / L. (2) Adsorption: La-doped hydroxyphosphate-alumina composite adsorbent is added to the pretreated wastewater; the La-doped hydroxyphosphate-alumina composite adsorbent is composed of hydroxyphosphates, alumina and lanthanides in a mass ratio of 1:0.2-1:5:0.001-0.08; the adsorption temperature is 15-45℃, the pH is 3-9 and the time is 20-120min; (3) Desorption: The adsorption-saturated La-doped hydroxyphosphate-alumina composite adsorbent and the desorption agent are mixed at a solid-liquid ratio of 1:3-1:20; the desorption agent is an alkali, a carbonate, or a mixture of both; ultrasonic or microwave-assisted desorption is used; (4) Regeneration and resource recovery: The La-doped hydroxy phosphate-alumina composite adsorbent after desorption is washed, dried and activated for regeneration and can be recycled 3-10 times; the desorption solution is classified and treated according to concentration, and phosphorus and fluorine are recovered from the high-concentration desorption solution, while the low-concentration desorption solution is returned to the adsorption step for reuse.

2. The integrated phosphorus-containing and fluorine-containing wastewater adsorption and desorption process according to claim 1, characterized in that, The hydroxyphosphates are selected from at least one of calcium hydroxyphosphate, magnesium hydroxyphosphate, zinc hydroxyphosphate, and strontium hydroxyphosphate; the hydroxyphosphates are industrial grade or self-made, with a particle size of 50-200 mesh and a specific surface area ≥30 m². 2 / g.

3. The integrated phosphorus and fluorine-containing wastewater adsorption and desorption process according to claim 1, wherein, The alumina is selected from at least one of activated alumina, mesoporous alumina, γ-alumina, and boehmite roasting products; the alumina is industrial grade, with a particle size of 20-150 mesh and a specific surface area ≥50 m². 2 / g, fluorine adsorption capacity ≥10mg / g.

4. The integrated adsorption and desorption process for phosphorus- and fluoride-containing wastewater according to claim 1, characterized in that, The lanthanide compound is selected from at least one of lanthanum nitrate, lanthanum chloride, lanthanum oxide, and lanthanum sulfate; the purity of the lanthanide compound is ≥95%, and the concentration is 0.05-2 mol / L; the lanthanum oxide needs to be dissolved in dilute hydrochloric acid with a volume ratio of 1:1 to prepare a solution before use.

5. The integrated phosphorus and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, In the eluent, the alkali is selected from sodium hydroxide and potassium hydroxide, with a concentration of 0.1-3 mol / L; the carbonate is selected from sodium carbonate, sodium bicarbonate, and potassium carbonate, with a concentration of 0.1-2 mol / L; the mass ratio of alkali to carbonate in the compound eluent is 1:0.1-1:

5.

6. The integrated phosphorus and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, In the pretreatment, the inorganic polymeric flocculant is selected from polyaluminum chloride, polyaluminum sulfate, polyferric chloride, and polyferric sulfate, with an effective component content ≥28% and a dosage of 0.01-0.5 g / L; the coagulant aid is anionic polyacrylamide with a molecular weight of 8 million-20 million and a dosage of 0.001-0.01 g / L.

7. The integrated phosphorus and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, In the Fenton oxidation module, the dosage of hydrogen peroxide is 0.5-3 g / L, the dosage of ferrous sulfate is 0.1-0.5 g / L, the reaction temperature is 25-60℃, the reaction time is 30-60 min, and the pH is 2-4; in the chelation adsorption module, the dosage of heavy metal chelating agent is 0.1-1 g / L, the reaction time is 20-30 min, and the pH is 5-8.

8. The integrated phosphorus-containing and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, The phosphorus- and fluoride-containing wastewater has a phosphorus concentration of 5-500 mg / L and a fluoride concentration of 3-300 mg / L, and may contain COD of 10-500 mg / L, suspended solids of 5-200 mg / L, and coexisting ions of ≤500 mg / L; the coexisting ions are at least one of chloride ions, sulfate ions, and nitrate ions.

9. The integrated phosphorus and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, In the regeneration step, the drying temperature of the calcium hydroxyphosphate-based adsorbent is 60-100℃ and the time is 3-8h, and the activation temperature is 120-200℃ and the time is 2-5h; the magnesium hydroxyphosphate or zinc hydroxyphosphate-based adsorbent needs to be soaked in 0.01-0.1mol / L dilute hydrochloric acid for 10-20min before regeneration.

10. The integrated phosphorus-containing and fluorine-containing wastewater adsorption and desorption process of claim 1, wherein, The high-concentration eluent has a phosphorus concentration ≥100mg / L and a fluoride concentration ≥50mg / L. Calcium chloride of 1-5g / L is added when recovering phosphorus, and sodium fluoride of 0.5-2g / L is added when recovering fluoride. The low-concentration eluent has a phosphorus concentration ≤50mg / L and a fluoride concentration ≤30mg / L. It needs to be filtered through a 0.45μm filter membrane before reuse.

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