A composite adsorbent and its preparation method

Abstract

This invention belongs to the field of wastewater treatment technology, specifically disclosing a composite adsorbent and its preparation method, comprising: mixing ferrous salt and magnesium salt in a container with water in a certain proportion to obtain a first mixed solution; mixing ammonium bicarbonate or sodium bicarbonate in a certain proportion with ferrous salt in a container with water to obtain a second mixed solution; heating the first mixed solution to a first preset temperature; adding the second mixed solution dropwise to the first mixed solution and stirring until completely mixed; allowing it to stand at the first preset temperature to obtain a mixture; and removing the precipitate to obtain the composite adsorbent. It has the following advantages: high purification efficiency, high purification intensity, large adsorption capacity, and excellent purification effect; it can efficiently purify phosphorus in wastewater to reduce the phosphorus concentration in the water.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a method for preparing composite adsorbents. Background Technology

[0002] Currently, wastewater purification methods mainly include chemical precipitation, biological methods, and adsorption methods. Biological phosphorus removal involves alternating between anaerobic and aerobic conditions with activated sludge, allowing polyphosphate-accumulating bacteria (PACs) to dominate. PACs release phosphorus under anaerobic conditions and absorb excess phosphorus under aerobic conditions. By discharging phosphorus-rich excess sludge, more phosphorus can be removed from the wastewater. The advantages of biological phosphorus removal are its cost-effectiveness, the absence of chemical reagents, utilization of existing carbon sources, and the avoidance of secondary hazards. However, its disadvantages include unstable phosphorus removal efficiency. Using biological phosphorus removal technology alone in wastewater treatment often fails to consistently meet discharge standards, frequently requiring supplementary chemical or adsorption phosphorus removal measures. Common chemical phosphorus removal methods mainly involve adding aluminum, iron, and calcium salts to remove phosphorus from wastewater. However, Al salts are generally toxic to organisms, while Fe salts are less toxic to aquatic organisms. Furthermore, Fe salts have a smaller impact on pH compared to Ca salts. The raw material for synthesizing polyferric sulfate is primarily ferrous sulfate heptahydrate, a byproduct of titanium dioxide production via the sulfuric acid process. Preparation methods are divided into catalytic oxidation and direct oxidation. Catalytic oxidation involves dissolving solid ferrous sulfate into a solution and mixing it with sulfuric acid. Under the action of a catalyst, the ferrous sulfate is catalytically oxidized under acidic conditions. Direct oxidation involves directly reacting oxidants such as H₂O₂, HNO₃, and KClO₃ with the ferrous sulfate solution. It can be seen that the oxidation process requires the consumption of catalysts and oxidants, resulting in higher costs and more complex processes. Commonly used phosphorus adsorption methods mainly involve adding adsorbents to water. Common phosphorus adsorbents include inorganic metal oxides and organic polymers. Among them, inorganic adsorbents have become a research hotspot due to their high adsorption efficiency, large specific surface area, and stable structure. In recent years, metal (hydrogen) oxide phosphorus adsorption materials have attracted widespread attention. Iron is one of the most abundant elements on Earth, and iron oxides and their hydrates exist widely on the Earth's surface in various forms. Currently, there are many reports on the adsorption of phosphorus by iron hydroxides and oxides. The main raw materials for the synthesis of iron hydroxides and oxides are ferric compounds such as ferric sulfate, ferric chloride, and ferric nitrate, or ferrous divalent compounds such as ferrous sulfate and ferrous chloride are used as raw materials to prepare intermediate products. Then, methods such as air passage are used to convert the ferrous divalent compounds into ferric compounds. It can be seen that the cost of using ferric compounds is relatively high, while the process of using ferrous divalent compounds as raw materials is relatively complex.

[0003] To address these issues, a composite adsorbent and its preparation method are proposed. Summary of the Invention

[0004] The present invention aims to provide a method for preparing composite adsorbents to solve or improve at least one of the above-mentioned technical problems.

[0005] In view of this, a first aspect of the present invention is to provide a method for preparing a composite adsorbent.

[0006] A second aspect of the present invention is to provide a composite adsorbent.

[0007] A first aspect of the present invention provides a method for preparing a composite adsorbent, comprising the following steps: placing ferrous salt and magnesium salt in a container in a certain proportion and mixing with water to obtain a first mixed solution; placing ammonium bicarbonate or sodium bicarbonate in a container in a certain proportion with the ferrous salt and mixing with water to obtain a second mixed solution; heating the first mixed solution to a first preset temperature; adding the second mixed solution dropwise to the first mixed solution and stirring until completely mixed; allowing the mixture to stand at the first preset temperature to obtain a mixture; and removing the precipitate from the mixture to obtain the composite adsorbent.

[0008] Further, the step of removing the precipitate from the mixture to obtain the composite adsorbent includes: filtering the precipitate from the mixture to obtain a semi-finished product; drying the semi-finished product at a second preset temperature to convert the ferrous ions in the semi-finished product into ferric ions; grinding the semi-finished product and screening out the composite adsorbent.

[0009] Furthermore, the first preset temperature is set to 50℃-90℃, and / or the second preset temperature is set to 60℃-100℃.

[0010] Furthermore, the ferrous salt is ferrous sulfate or ferrous chloride; and / or the magnesium salt is magnesium chloride or magnesium sulfate.

[0011] Furthermore, the ratio of the ferrous salt to the magnesium salt is 0.4-50.0, and the ratio of the ferrous salt to ammonium bicarbonate is 0.1-5.0.

[0012] Furthermore, the first mixed solution and the second mixed solution have a volume ratio, wherein the volume ratio is between 3 and 6.

[0013] Further, the step of adding the second mixed solution dropwise to the first mixed solution and stirring until completely mixed includes: adding the second mixed solution dropwise to the first mixed solution and stirring with a mixer to generate a mixture containing ferrous carbonate (FeCO3) and basic magnesium carbonate (Mg2(OH)2CO3).

[0014] Furthermore, the mixture also includes: a ferrous carbonate solid solution containing magnesium ions and a basic magnesium carbonate solid solution containing iron ions.

[0015] Furthermore, during the process of adding the second mixed solution to the first mixed solution, a preset rate is used to maintain the magnesium supersaturation of ferrous carbonate and basic carbonate in the first mixed solution, so that the particle size of the precipitated ferrous carbonate (FeCO3), basic magnesium carbonate (Mg2(OH)2CO3), magnesium-containing ferrous carbonate solid solution, and iron-containing basic magnesium carbonate solid solution is less than 5 μm; wherein, the preset rate is 2 ml / min-15 ml / min.

[0016] The composite adsorbent provided in the second aspect of the present invention comprises: ferrous carbonate (FeCO3) and basic magnesium carbonate (Mg2(OH)2CO3); wherein the ratio of ferrous carbonate (FeCO3) to basic magnesium carbonate (Mg2(OH)2CO3) is 4-10.

[0017] The beneficial effects of this invention compared to the prior art are as follows:

[0018] When treating phosphorus-containing wastewater, ensuring sufficient contact between the wastewater and the adsorbent allows for the removal of phosphorus pollutants through adsorption. This method offers advantages such as low cost, small equipment footprint, and simple operation. Adsorption can also remove recalcitrant pollutants from wastewater. Composite adsorbents offer better buffering performance, excellent adsorption capacity, are non-toxic and non-corrosive, and have excellent safety performance, preventing secondary pollution. Using composite adsorbents to purify phosphorus-containing wastewater is more effective than using single adsorbents.

[0019] It possesses high purification efficiency, high purification intensity, large adsorption capacity, and excellent purification effect, and can effectively purify phosphorus in wastewater to reduce the phosphorus concentration in the water.

[0020] Additional aspects and advantages of embodiments of the invention will become apparent in the following description or may be learned by practice of embodiments of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 This is a flowchart of the method of the present invention;

[0023] Figure 2 This is a flowchart illustrating the preparation method of the magnesium-iron composite adsorbent according to an embodiment of the present invention.

[0024] Figure 3 This is a phosphorus standard curve diagram of the present invention;

[0025] Figure 4 This is a graph showing the effect of the adsorbent dosage of the present invention on the purification rate of 10 mg / L phosphorus-containing wastewater;

[0026] Figure 5 This is a graph showing the effect of the adsorbent dosage of the present invention on the adsorption rate of 1 mg / L phosphorus-containing wastewater;

[0027] Figure 6 This is a graph showing the effect of solution pH on purification rate in this invention;

[0028] Figure 7 This is a graph showing the effect of reaction time on purification rate in this invention;

[0029] Figure 8 This is a graph showing the effect of the initial concentration on the purification rate in this invention;

[0030] Figure 9 This is the adsorption isotherm diagram of the present invention;

[0031] Figure 10 This is a diagram of the Langmuir equation of the present invention;

[0032] Figure 11 This is a diagram of the Freundich equation of the present invention;

[0033] Figure 12 This figure shows the effect of the dosage of magnesium-iron composite adsorbent and iron carbonate adsorbent of the present invention on the purification rate of 10 mg / L phosphorus-containing wastewater.

[0034] Figure 13 This is a scanning electron microscope image of the composite adsorbent of the present invention. Detailed Implementation

[0035] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0037] Please see Figure 1-13 The following describes some embodiments of the composite adsorbent and its preparation method.

[0038] The first aspect of this invention provides a method for preparing a composite adsorbent. In some embodiments of this invention, such as... Figure 1-12 As shown, the preparation method of this composite adsorbent includes:

[0039] Ferrous salt and magnesium salt were placed in a container in a certain proportion and water was added to mix them to obtain the first mixed solution.

[0040] A second mixed solution is prepared by mixing ammonium bicarbonate in a certain proportion with ferrous salt in a container and adding water.

[0041] The first mixed solution is heated to a first preset temperature, the second mixed solution is added dropwise to the first mixed solution and stirred until completely mixed, and the mixture is allowed to stand at the first preset temperature to obtain a mixture. The precipitate is then removed to obtain a composite adsorbent.

[0042] The composite adsorbent preparation method provided by this invention allows for full contact between the wastewater and the adsorbent when treating phosphorus-containing wastewater. The adsorption effect of the adsorbent is used to remove phosphorus pollutants from the phosphorus-containing wastewater. The advantages of this treatment method are that it requires less capital, the equipment occupies a small area, and it is simple and easy to operate. The adsorption method can also remove pollutants that are difficult to biodegrade in wastewater.

[0043] The carbonate and hydroxide ions in basic magnesium carbonate can neutralize acids in water, providing a certain buffering capacity. This enhances the buffering performance of the composite adsorbent, resulting in excellent adsorption capacity, non-toxicity, non-corrosiveness, and superior safety without causing secondary pollution. Using composite adsorbents to purify phosphorus-containing wastewater is more effective than using single adsorbents.

[0044] In any of the above embodiments, the step of removing the precipitate from the mixture to obtain the composite adsorbent includes:

[0045] Filter the sediment from the mixture to obtain a semi-finished product.

[0046] The semi-finished product is dried at a second preset temperature to convert the ferrous ions in the semi-finished product into ferric ions.

[0047] Grind the semi-finished product and screen out the composite adsorbent.

[0048] In this embodiment, existing phosphorus purifiers generally use expensive ferric iron to prepare adsorbents containing ferric iron. This method uses cheaper ferrous iron to prepare adsorbents containing ferric iron, which can reduce the manufacturing cost of phosphorus adsorbents containing ferric iron.

[0049] After the filter cake is dried, particles with an initial particle size of less than 5 μm will aggregate together to form larger particle aggregates. Grinding is mainly to make the particle aggregates smaller. The particle aggregates are formed by the aggregation of original particles with a particle size of less than 5 μm. There are gaps between the original particles. The phosphorus-containing solution can contact the particles smaller than 5 μm through the gaps. The small particle size of the original particles can increase the adsorption area. Reducing the particle aggregates helps to accelerate the contact between the phosphorus-containing solution and the original particles.

[0050] In any of the above embodiments, the first preset temperature is 50℃-90℃, and / or the second preset temperature is 60℃-100℃.

[0051] In this embodiment, the first preset temperature should be lower, as a lower temperature is conducive to the formation of adsorbents with smaller particle sizes, and the second preset temperature should be higher, as this is conducive to the reaction of ferrous ions with oxygen in the air to convert them into ferric ions.

[0052] In any of the above embodiments, the ferrous salt is ferrous sulfate or ferrous chloride.

[0053] Magnesium salts include magnesium chloride and magnesium sulfate.

[0054] In this embodiment, the composite adsorbent of this application can be prepared using any of the above-mentioned salts.

[0055] In any of the above embodiments, the ratio of ferrous salt to magnesium salt is 0.4-50.0, and the ratio of ferrous salt to ammonium bicarbonate is 0.1-5.0.

[0056] In any of the above embodiments, the first mixed solution and the second mixed solution have a volume ratio, which is 3-6.

[0057] In this embodiment, the higher the ratio, the lower the dilution of solution two on solution one, which is more conducive to forming a higher supersaturation. However, if the ratio is too high, the concentration of ammonium bicarbonate in solution two will be too high, which will make it difficult for ammonium bicarbonate to dissolve.

[0058] In any of the above embodiments, the step of adding the second mixed solution dropwise to the first mixed solution and stirring until completely mixed includes:

[0059] The second mixed solution is added dropwise to the first mixed solution and stirred with a stirrer to generate a mixture containing ferrous carbonate (FeCO3) and basic magnesium carbonate (Mg2(OH)2CO3).

[0060] In this embodiment, the adsorbent consists of spherical and irregularly shaped precipitate particles. The spherical precipitate is ferrous carbonate (FeCO3), and the irregularly shaped precipitate is basic magnesium carbonate (Mg2(OH)2CO3).

[0061] In any of the above embodiments, the mixture further includes: a ferrous carbonate solid solution containing magnesium ions and a basic magnesium carbonate solid solution containing iron ions.

[0062] In this embodiment, a magnesium-containing ferrous carbonate solid solution or an iron-containing basic magnesium carbonate solid solution may also be formed during the adsorbent preparation process. The synergistic effect of iron and magnesium enhances the adsorption efficiency of the adsorbent. Magnesium ions in the solution can also cause ferric carbonate to form smaller particles. The smaller particle size indicates that the adsorbent has a larger specific surface area, which can effectively purify phosphorus in water.

[0063] In any of the above embodiments, the second mixed solution is added dropwise at a preset rate during the process of adding the first mixed solution, and the ferrous carbonate and basic magnesium carbonate are kept supersaturated in the first mixed solution so that the particle size of the precipitated ferrous carbonate (FeCO3), basic magnesium carbonate (Mg2(OH)2CO3), magnesium ion-containing ferrous carbonate solid solution and iron ion-containing basic magnesium carbonate solid solution is less than 5 μm.

[0064] The preset rate is set to 2 ml / min - 15 ml / min.

[0065] In this embodiment, the second mixed solution is added dropwise to the first mixed solution mainly to improve the utilization rate of ammonium bicarbonate and reduce the amount of ammonium bicarbonate decomposed.

[0066] The first aspect of the present invention provides a composite adsorbent. In some embodiments of the present invention, such as... Figure 13 As shown, the composite adsorbent comprises:

[0067] Ferrous carbonate (FeCO3) and basic magnesium carbonate (Mg2(OH)2CO3);

[0068] The ratio of ferrous carbonate (FeCO3) to basic magnesium carbonate (Mg2(OH)2CO3) is 4-10.

[0069] The composite adsorbent provided by this invention can completely transform the white filter cake into a red filter cake containing ferric oxide during the drying process. In the magnesium-iron composite adsorbent, the ferrous iron is fully converted into ferric iron during the drying process. Since the adsorption efficiency of ferric iron for phosphorus is greater than that of ferrous iron, the adsorption effect of the composite adsorbent is better than that of the single-component adsorbent.

[0070] The research content of this embodiment is to determine the purification effect of adsorbents prepared with ferrous sulfate and magnesium chloride on phosphorus-containing wastewater. First, different magnesium-iron adsorbents were synthesized. By comparing the adsorption effects under the same conditions, an adsorbent with the highest purification rate was found. By controlling the variable method, the dosage of adsorbent, pH during solution reaction, shaking time and initial concentration conditions were changed to obtain the highest adsorption rate and optimal adsorption conditions of this adsorbent for purifying phosphorus-containing wastewater.

[0071] Comparative Example 1:

[0072] Add a certain amount of water to 0.2 mol ferrous sulfate and 0.1 mol magnesium chloride to make a total volume of 600 ml. Adjust the pH to 11 with 3 mol / L sodium hydroxide, seal and let stand for 24 hours, filter and wash, dry at 70℃, grind and sieve with a 100 mesh sieve.

[0073] Comparative Example 2:

[0074] Add a certain amount of water to 0.2 mol ferrous sulfate and 0.1 mol magnesium chloride to make a total volume of 600 ml. Adjust the pH to 11 with 3 mol / L sodium hydroxide, heat to 60°C, purge with air for 30 min, let stand at 60°C for 2 hours, filter and wash, dry at 70°C, grind and sieve with a 100 mesh sieve.

[0075] Comparative Example 3:

[0076] 0.2 mol ferrous sulfate was added to water to make a total volume of 400 ml, labeled A. 0.1 mol magnesium chloride was added to water to make a total volume of 200 ml, labeled B. 3 mol / L sodium hydroxide was added to solution A to adjust the pH to 11. The solution was heated to 60°C, aerated for 30 min, and allowed to stand at 60°C for 2 hours to induce magnetism. Then solution B was added to the solution, and the pH was adjusted to 11 with 3 mol / L sodium hydroxide. The solution was allowed to stand at 60°C for 2 hours, filtered and washed, dried at 70°C, ground, and sieved using a 100-mesh sieve.

[0077] 1. Experimental apparatus:

[0078] Electronic balance, HH-2 digital display constant temperature water bath, T9 UV-Vis spectrophotometer, ZD-85 constant temperature shaking box, PHS-3C pH meter, drying oven, TDL-5A benchtop low-speed centrifuge, optical microscope, EM-30AX scanning electron microscope, agate mortar, 100-mesh sieve, glass rod, conical flask, centrifuge tubes, beakers, volumetric flasks.

[0079] 2. Experimental methods:

[0080] 2.1 Plotting the phosphorus standard curve

[0081] Take seven 50ml volumetric flasks or colorimetric tubes and add 0.00, 1.00, 3.00, 5.00, 10.00, 15.00, and 20.00mL of 2mg / L phosphate standard solution to each flask. Add 1mL of ascorbic acid solution to each volumetric flask, mix well, and after 30s, add 2mL of molybdate solution. Dilute to the mark with distilled water, mix thoroughly at room temperature, and let stand for 15min to develop color. Then, using a 10mm cuvette, measure the absorbance of the solution at a wavelength of 700nm, with zero concentration as a blank reference.

[0082] 2.2 Phosphorus Adsorption Experiment

[0083] Experiment to determine the optimal adsorbent: Pre-prepared simulated phosphorus-containing wastewater was added to a beaker, and the pH of the solution was uniformly adjusted to 6. Equal volumes of the solution were transferred into 250mL Erlenmeyer flasks, and then different types of adsorbents of the same mass were added to each flask. After a period of shaking in a constant-temperature shaker at 25℃ and 130r / min, the mixture was removed and allowed to stand. Solid-liquid separation was achieved using a membrane filter, followed by centrifugation. The supernatant was collected, and the absorbance of each solution after the reaction was measured. The purification rate was calculated to obtain the optimal adsorbent.

[0084] Effect of adsorbent dosage on purification rate: Simulated wastewater containing phosphate with the same content was transferred into 250mL conical flasks. Then, 0.05g, 0.06g, 0.07g, 0.08g, 0.09g, 0.10g, 0.12g, and 0.14g of the optimal adsorbent were weighed and added to the conical flasks respectively. After shaking and reacting for a period of time in a constant temperature shaker at 25℃ and 130r / min, the flasks were removed and allowed to stand. Solid-liquid separation was performed by filtration using a filter membrane, followed by centrifugation. The supernatant was collected, its absorbance was measured, and the purification rates were calculated to obtain the optimal dosage.

[0085] Effect of pH on purification rate: Simulated wastewater containing the same amount of phosphate was transferred into 250mL Erlenmeyer flasks. The pH was adjusted to 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0, respectively, and the optimal dosage of the chemical was added. The flasks were shaken for a certain period of time at 25℃ and 130r / min, then removed and allowed to stand. Solid-liquid separation was achieved by filtration through a membrane filter, followed by centrifugation. The supernatant was collected, its absorbance was measured, and the purification rates were calculated to obtain the optimal pH conditions.

[0086] Effect of shaking time on purification rate: Simulated wastewater containing phosphate with the same content was transferred into 11 250mL Erlenmeyer flasks, the pH was adjusted to the optimal conditions, and the optimal dosage of the reagent was added. The flasks were shaken at 25℃ and 130r / min for 5min, 10min, 20min, 30min, 60min, 90min, 120min, 150min, 180min, 210min, and 240min, respectively. After shaking, the flasks were removed and allowed to stand. Solid-liquid separation was performed by filtration through a filter membrane, followed by centrifugation. The supernatant was collected, the absorbance of the filtrate was measured, and the purification rate of each filtrate after the reaction was calculated to obtain the optimal shaking time.

[0087] Effect of initial concentration on purification rate: Seven 250mL conical flasks were filled with the same volume of simulated phosphate-containing wastewater at concentrations of 10mg / L, 20mg / L, 30mg / L, 40mg / L, 50mg / L, 60mg / L, and 70mg / L, respectively. The pH was adjusted to the optimal conditions, the optimal dosage was added, and the flasks were shaken in a constant temperature shaker at 25℃ and 130r / min for the optimal reaction time. After the reaction time, the flasks were removed and allowed to stand. Solid-liquid separation was performed by membrane filtration, followed by centrifugation. The supernatant was collected, the absorbance of the filtrate was measured, and the purification rates were calculated to obtain the optimal initial concentration.

[0088] 3. Data processing and calculation

[0089] By substituting the data measured by the T9 UV-Vis spectrophotometer into the phosphorus standard curve, the concentration of phosphate in the purified solution can be calculated, and then the adsorption efficiency can be calculated by substituting it into formula (1):

[0090] Adsorption rate = (c0 - c) e ) / c0 (1)

[0091] c0 — Initial concentration, mg / L

[0092] c e —Phosphate concentration after purification, mg / L

[0093] 4. Research Results and Data Analysis

[0094] Typical domestic wastewater containing phosphorus has a total phosphorus content of 3–15 mg / L. Therefore, this study mainly focuses on wastewater containing phosphorus with a concentration of 10 mg / L. Furthermore, since domestic sewage is generally neutral, the pH of the simulated phosphorus-containing wastewater was adjusted to approximately 6 before the reaction, except in special cases. HCl and NaOH solutions were used to adjust the pH.

[0095] 4.1 Plotting the phosphorus standard curve

[0096] This experiment used spectrophotometry to determine the absorbance of each filtrate in the phosphorus standard curve. The data are shown in Table 1 below (phosphorus standard curve), and the trend is shown in [the table below]. Figure 2 ;

[0097] Table 1. Phosphorus Standard Curve

[0098]

[0099] Depend on Figure 2 The equation of the standard curve can be obtained from Table 1:

[0100] y = 0.345x + 0.002

[0101] y—Absorbance A; x—Phosphate concentration (mg / L)

[0102] 4.2 Selection of the optimal adsorbent

[0103] The 20ml stock solution was diluted to 1000ml, and the pH was adjusted to 7. 100ml of each solution was then added to five conical flasks, labeled 0, 1, 2, 3, and 4. 0.1g of each of the prepared adsorbents 1, 2, 3, and 4 was added to the corresponding numbered flasks, shaken for 120min, filtered through a membrane filter, and then centrifuged to collect the supernatant. The absorbance was measured, and the data are shown in Table 2.

[0104] Table 2 Selection of Optimal Adsorbent

[0105]

[0106]

[0107] The data in Table 2 show that the adsorbent in this embodiment has a good adsorption effect. Therefore, the adsorbent in this embodiment is selected as the optimal adsorbent, with an adsorption rate of 96.46%.

[0108] 4.3 Effect of Dosage on Purification Rate

[0109] 4.3.1 Selection of the optimal dosage for 10 mg / L phosphorus-containing wastewater

[0110] 100 ml of simulated phosphate-containing wastewater (10 mg / L) was placed in a 250 mL Erlenmeyer flask, and the pH was adjusted to 6. Then, 0.05 g, 0.06 g, 0.07 g, 0.08 g, 0.09 g, 0.10 g, 0.12 g, and 0.14 g of adsorbent 4 were weighed and added to the respective Erlenmeyer flasks. The mixture was purified for 2 hours in a constant-temperature shaker at 25°C and 130 r / min. The mixture was then removed, and solid-liquid separation was achieved using a membrane filter. After centrifugation, the supernatant was collected, and the absorbance was measured. The purification rates were calculated to obtain the optimal dosage of adsorbent 4. The measured data are shown in Table 3.

[0111] Table 3. Effect of adsorbent dosage on the purification rate of 10 mg / L phosphorus-containing wastewater

[0112]

[0113] from Figure 3 The data and trends in Table 3 show that when the adsorbent dosage is 0.14g, the purification rate reaches 98.93%, and the equilibrium concentration of phosphorus in the purified water is 0.107mg / L. Adsorption equilibrium is reached when the adsorbent dosage exceeds 0.14g, and the increase in phosphorus purification rate gradually decreases with increasing adsorbent dosage. Therefore, the optimal dosage for purifying 10mg / L phosphorus-containing wastewater is 0.14g, i.e., 0.14g of adsorbent is added per 100ml of phosphorus-containing wastewater (10mg / L).

[0114] 4.3.21 mg / L Optimal Dosage Selection for Phosphorus-Containing Wastewater

[0115] 1000 ml of simulated phosphate-containing wastewater (1 mg / L) was added to each of the six 1000 ml agitators of the six-unit coagulant, and the pH was adjusted to 6. Then, 0.05 g, 0.06 g, 0.07 g, 0.08 g, 0.09 g, and 0.10 g of adsorbent 4 were weighed and added to each agitator, respectively. The mixture was stirred for 120 min at 130 r / min and 25 °C. Solid-liquid separation was achieved using a membrane filter, followed by centrifugation. The supernatant was collected, absorbance was measured, and the purification rates were calculated to determine the optimal dosage of adsorbent 4. The measured data are shown in Table 4.

[0116] Table 4. Effect of adsorbent dosage on the purification rate of 1 mg / L phosphorus-containing wastewater

[0117]

[0118] from Figure 4 The data and trends in Table 4 show that when the adsorbent dosage is 0.06g, the equilibrium concentration of phosphorus in the purified water is 0.4576mg / L, which is less than the first-level discharge standard limit (0.5mg / L) in GB 8978-1996. Therefore, the optimal dosage for purifying 1mg / L phosphorus-containing wastewater is 0.06g, i.e., 0.06g of adsorbent is added per 100ml of phosphorus-containing wastewater (1mg / L).

[0119] 4.4 Effect of pH value on purification rate

[0120] 100 ml of a pre-prepared 10 m³ / L simulated phosphorus-containing wastewater was added to nine 250 mL Erlenmeyer flasks. The pH values ​​were adjusted to 3, 4, 5, 6, 7, 8, 9, 10, and 11, respectively. 0.14 g of the optimal adsorbent was added to each flask. After adsorption reaction for 120 min in a constant temperature shaking incubator at 25 °C and 130 r / min, solid-liquid separation was achieved by membrane filtration. The flasks were then centrifuged, and the supernatant was collected. The absorbance was measured, and the purification rates were calculated to obtain the pH conditions for the adsorbent.

[0121] Table 5 Effect of solution pH on purification rate

[0122]

[0123] From Table 5, Figure 5The data and trends show that the purification effect of the adsorbent in the pre-prepared simulated phosphorus-containing wastewater remained relatively stable under different pH conditions, with purification rates ranging from 95.58% to 98.93%. As the pH value increased, the purification trend of the adsorbent generally rose slowly to a certain maximum value, and then gradually decreased. The purification rate reached its highest point at pH 6, at 98.93%, with a phosphorus equilibrium concentration of 0.107 mg / L after purification. The purification rate reached its lowest point at pH 11, at 95.58%, with a phosphorus equilibrium concentration of 0.442 mg / L after purification. The experimental results indicate that the optimal pH value for the adsorbent to purify phosphorus in water is 6.0, which also conforms to the wastewater discharge standard of pH 6-9 in actual production.

[0124] 4.5 Effect of Oscillation Time on Purification Rate

[0125] 100 ml of simulated phosphate-containing wastewater (10 mg / L) was placed in 11 250 mL Erlenmeyer flasks. The pH was adjusted to 6. 40.14 g of adsorbent was added to each flask, and the flasks were shaken at 25°C and 130 rpm for 5 min, 10 min, 20 min, 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 210 min, and 240 min, respectively. The flasks were then removed and allowed to stand. Solid-liquid separation was achieved using a membrane filter, followed by centrifugation. The supernatant was collected, and the absorbance of the filtrate was measured. The purification rate under each condition was calculated, and the optimal shaking time for the adsorbent was determined.

[0126] Table 6. Effect of reaction time on purification rate

[0127]

[0128] From Table 6, Figure 6 The data and trends show that the purification rate continuously increases as the shaking time increases from 5 min to 120 min during the reaction. The purification rate reaches a stable state between 120 min and 240 min. From an economic perspective, the optimal shaking time for purifying phosphorus-containing simulated wastewater is 120 min, with a purification rate of approximately 98.93% and a phosphorus equilibrium concentration of 0.107 mg / L after purification. Furthermore, the adsorbent exhibits rapid adsorption, reaching a purification rate of 74.59% after only 5 min of shaking. Adsorption reaches equilibrium after 180 min, with a purification rate of 99.25% and a phosphorus equilibrium concentration of 0.075 mg / L after purification. The adsorption time for the experiment investigating the effect of initial concentration was 3 hours.

[0129] 4.6 Effect of initial concentration on purification rate

[0130] Using a pipette, 2 ml, 4 ml, 6 ml, 8 ml, 10 ml, 12 ml, and 14 ml of phosphate stock solution were added to seven volumetric flasks, respectively. These were then diluted to the mark with distilled water to obtain simulated wastewater concentrations of 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, and 70 mg / L. This was then transferred to seven 250 ml Erlenmeyer flasks, and each flask was adjusted to the optimal pH of 6. The optimal dosage of 0.14 g of phosphate stock solution was added, and the mixture was shaken and adsorbed at 25°C and 130 rpm for 180 min. The flasks were then removed, and the solid-liquid mixture was separated by membrane filtration, followed by centrifugation. The supernatant was collected, and its photometric properties were measured.

[0131] Table 7. Effect of initial concentration on purification rate

[0132]

[0133]

[0134] From the above table 7, Figure 7 The data and trends show that the initial concentration has a significant impact on the phosphorus purification rate. The adsorption rate of the adsorbent for phosphate decreases continuously with the increase of the initial concentration of the phosphorus-containing simulated wastewater. Since the mass of the adsorbent itself does not change, the initial concentration of the simulated wastewater continuously increases, and the concentration of phosphate also continuously increases. The amount of adsorbent added cannot completely adsorb the excess phosphate, thus leading to a continuous decrease in the adsorption rate. When the initial concentration of the phosphate-containing simulated wastewater is 10 mg / L, its purification effect reaches its highest value, with a purification rate of 99.25% after 180 minutes. The equilibrium concentration of phosphorus in the purified water is 0.075 mg / L.

[0135] 4.6 Adsorption Isotherm

[0136] The values ​​of ce and qe were calculated based on the data on the effect of concentration, as shown in Table 8.

[0137] Table 8. Data Processing of Adsorption Isotherms

[0138]

[0139] From Table 8, Figure 8 The data and trends show that the equilibrium adsorption capacity of the adsorbent increases with the increasing initial concentration of the simulated wastewater. Representative models describing adsorption isotherms are the Langmuir model and the Freundlich model. Therefore, regression analysis was performed using these two models, and the following figure was plotted:

[0140] Langmuir equation: c e / q e =1 / (Q0k) L )+ce / Q0

[0141] Freundlich equation: lnq e =lnk f +lnc e / n

[0142] ce — equilibrium mass concentration (mg / L);

[0143] qe — equilibrium adsorption capacity (mg / g);

[0144] kL — adsorption equilibrium constant;

[0145] Q0—Maximum adsorption capacity (mg / L);

[0146] kf — adsorption capacity (mg / L);

[0147] n – Adsorption strength (mg / g).

[0148] From the data in the table and the trend in the graph above, we obtain the Langmuir equation: Y = 0.0431x + 0.0643, and the Freundlich equation: Y = 0.1903x + 2.465. Calculations show Q0 = 23.202 mg / g and n = 5.255. This indicates that the adsorbent has a large adsorption capacity and intensity for phosphate, making it an excellent purifier with high purification efficiency. Furthermore, the entire purification process is simple and easy to operate. The results of this experiment demonstrate that this adsorbent can be used as a phosphorus adsorbent for purifying phosphorus in wastewater.

[0149] 4.8 Effect of Magnesium on the Purification Efficiency of Adsorbents

[0150] In the experiment, the adsorbent for Comparative Example 5 was further prepared to investigate whether the presence of magnesium affected the purification efficiency.

[0151] (1) Add a certain amount of water to 0.3 mol ferrous sulfate to make a total volume of 600 ml, and label it A. Add water to 0.6 mol ammonium bicarbonate to make a total volume of 200 ml, and label it B. Heat solution A to 60°C, and add solution B dropwise to solution A while stirring. Then let it stand at 60°C for 1 h, filter and wash, dry at 70°C, grind and sieve, and select a 100 mesh sieve.

[0152] (2) Take 100ml of simulated phosphate wastewater with a concentration of 10mg / L and place it in a 250mL conical flask. Adjust the pH to 6. Then weigh 0.05g, 0.06g, 0.07g, 0.08g, 0.09g, 0.10g, 0.12g, and 0.14g of adsorbent 5 into each conical flask. After purification and adsorption in a constant temperature shaking oven at 25℃ and 130r / min for 2 hours, let it stand. Use a filter membrane to filter and separate the solid and liquid. Then centrifuge, take the supernatant, measure the absorbance, and calculate the purification rate to obtain the optimal dosage of adsorbent for comparative example 5. The measured data are shown in Table 9.

[0153] Table 9 shows the dosage of adsorbent 5 at 10 mg / L. -1 Impact of phosphorus-containing wastewater purification rate

[0154]

[0155]

[0156] pass Figure 11 The comparison shows that adsorbent 4 has a significantly higher purification efficiency than adsorbent 5, meaning that the iron-magnesium composite adsorbent is more effective than a single adsorbent. This is presumably because the composite solid solution formed by magnesium and iron creates more active sites than the aggregate of iron alone, resulting in changes in its crystal structure and chemical properties, thus making the composite adsorbent more effective than a single adsorbent.

[0157] Scanning electron microscope image of adsorbent 4 is as follows Figure 12 As shown, the adsorbent exhibits both spherical aggregates and irregular sheet-like aggregates. The spherical aggregates are ferrous carbonate, while the irregular sheet-like aggregates are basic magnesium carbonate. During adsorbent preparation, magnesium-containing ferrous carbonate solid solutions or iron-containing basic magnesium carbonate solid solutions may also be formed. The synergistic effect of iron and magnesium enhances the adsorption efficiency of the adsorbent. Magnesium in the solution can also cause ferric carbonate to form smaller particles. The smaller particle size indicates that the adsorbent has a larger specific surface area, which can effectively purify phosphorus in water.

[0158] During the experiment, it was also found that during the drying process, the white filter cake of adsorbent 4 could be completely transformed into a red filter cake containing ferric oxide. During the drying process, only the outer thin layer of the white filter cake of adsorbent 5 was transformed into red, and the inside was not transformed. This indicates that the ferrous iron in the magnesium-iron composite adsorbent was fully transformed into ferric iron during the drying process. Since the adsorption efficiency of ferric iron for phosphorus is greater than that of ferrous iron, the adsorption effect of the composite adsorbent is better than that of the single-component adsorbent.

[0159] This experiment first compared the purification rates of four different adsorbents, finding that the mixed adsorbent prepared with ammonium bicarbonate was the optimal adsorbent and yielded the best dosage. Subsequently, other factors affecting the adsorption effect were investigated, such as purification time, reaction pH, and the initial concentration of the simulated solution, ultimately determining the optimal adsorption conditions for the best adsorbent. Specifically, the mixed adsorbent prepared with ammonium bicarbonate achieved excellent adsorption performance under the conditions of pH 6, a dosage of 0.14 g, and 10 mg / L phosphorus-containing wastewater, after shaking for 120 minutes, with a purification efficiency of approximately 98.93%. Furthermore, calculations yielded Q0 = 23.202 mg / g and n = 5.255, indicating that this optimal adsorbent possesses high purification efficiency, high purification intensity, large adsorption capacity, and excellent purification effect, effectively purifying phosphorus from wastewater to reduce its concentration.

[0160] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a composite adsorbent, characterized in that, Includes the following steps: Ferrous salt and magnesium salt were placed in a container in a certain proportion and water was added to mix them to prepare the first mixed solution; A second mixed solution is prepared by placing ammonium bicarbonate or sodium bicarbonate in a container in a certain proportion with the ferrous salt and adding water. The first mixed solution is heated to a first preset temperature, the second mixed solution is added dropwise to the first mixed solution and stirred until completely mixed, and the mixture is allowed to stand at the first preset temperature to obtain a mixture. The precipitate in the mixture is then removed to obtain the composite adsorbent. The step of removing the precipitate from the mixture to obtain the composite adsorbent includes: Filter the precipitate from the mixture to obtain a semi-finished product; The semi-finished product is dried at a second preset temperature to convert the ferrous ions in the semi-finished product into ferric ions. The semi-finished product is ground, and the composite adsorbent is screened out. The first preset temperature is 50℃-90℃, and the second preset temperature is 60℃-100℃. The ferrous salt is ferrous sulfate or ferrous chloride; The magnesium salt is magnesium chloride or magnesium sulfate; The ratio of the ferrous salt to the magnesium salt is 0.4-50.0, and the ratio of the ferrous salt to ammonium bicarbonate is 0.1-5.

0. The first mixed solution and the second mixed solution have a volume ratio, wherein the volume ratio is between 3 and 6; The step of adding the second mixed solution dropwise to the first mixed solution and stirring until completely mixed includes: The second mixed solution is added dropwise to the first mixed solution and stirred with a stirrer to generate a mixture containing ferrous carbonate FeCO3 and basic magnesium carbonate Mg2(OH)2CO3; The mixture also includes: ferrous carbonate solid solution containing magnesium ions and basic magnesium carbonate solid solution containing iron ions. During the process of adding the second mixed solution to the first mixed solution, a preset rate is used for addition. The first mixed solution is kept supersaturated with ferrous carbonate and basic magnesium carbonate so that the particle size of the precipitated ferrous carbonate FeCO3, basic magnesium carbonate Mg2(OH)2CO3, magnesium ion-containing ferrous carbonate solid solution and iron ion-containing basic magnesium carbonate solid solution is less than 5 μm. The preset rate is between 2 ml / min and 15 ml / min. The ratio of ferrous carbonate (FeCO3) to basic magnesium carbonate (Mg2(OH)2CO3) is 4-10.

2. The composite adsorbent obtained by the preparation method described in claim 1, characterized in that, The obtained semi-finished products include: Ferrous carbonate (FeCO3) and basic magnesium carbonate (Mg2(OH)2CO) 3； The ratio of ferrous carbonate (FeCO3) to basic magnesium carbonate (Mg2(OH)2CO3) is 4-10.

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