A trivalent arsenic adsorbent and preparation method thereof

Abstract

The invention discloses a trivalent arsenic adsorbent and a preparation method thereof. The trivalent arsenic adsorbent is MnO x ‑CeO x The modified activated carbon preparation method comprises the following steps: S1, adding deionized water and anhydrous ethanol to a container, adding activated carbon, and performing ultrasonic dispersion to obtain a uniform suspension; S2, sequentially adding potassium permanganate and cerium nitrate to the suspension, stirring and dissolving, and then adding urea; S3, placing the mixed solution into a polytetrafluoroethylene liner, and then placing the mixed solution into a high-temperature reaction kettle, sealing it, and placing it in an oven for reaction; S4, cooling the reaction product, washing it with deionized water, centrifuging it, drying the precipitate, cooling it, and grinding it; S5, placing the dried precipitate into a tubular furnace for heating and roasting, and naturally cooling it to obtain MnO x ‑CeO x Modified activated carbon adsorbent. The present invention MnO x ‑CeO x The modified activated carbon adsorbent has a wide pH application range, the best removal effect under neutral conditions, good stability, and a small amount of manganese and cerium released after the reaction. It is significantly better than other methods for preparing activated carbon-loaded manganese-cerium oxide adsorbents.

Description

Technical Field

[0001] The invention belongs to the technical field of water pollution control, and particularly relates to a trivalent arsenic adsorbent and a preparation method thereof. Background Art

[0002] Arsenic pollution is currently one of the top ten public health issues, and at least 50 million people are facing the threat of endemic arsenic poisoning. With the development of the industrial economy, a large amount of arsenic-containing wastewater is discharged into natural water bodies, affecting the safety of human drinking water. Among the many arsenic compounds, As2O3, commonly known as arsenic trioxide, is the most toxic. Its toxicity is 25 to 60 times that of pentavalent arsenic and several hundred times that of organic arsenic. After arsenic enters the body through the respiratory tract and skin, it is rapidly distributed throughout the body through the blood, endangering the human nervous system, digestive system, and cardiovascular and cerebrovascular system. The latest revised "Standards for Drinking Water Hygiene" (GB5749-2022) stipulates that the arsenic content in drinking water shall not exceed 10μg / L. The safety standard is relatively high, which shows that the research on arsenic pollution prevention and control technology is of great significance.

[0003] At present, the main methods for treating arsenic-containing wastewater include adsorption, ion exchange, biological method, membrane separation, coagulation and sedimentation. Among these methods, adsorption is considered to be a promising technology due to its advantages of low cost, simple operation, wide application range, and no need for expensive reagents. However, the treatment effect of traditional adsorbents is not ideal, and there are problems such as low adsorption capacity and slow adsorption rate. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a trivalent arsenic adsorbent and a preparation method thereof, using CeN3O9·6H2O, KMnO4, CON2H4 and activated carbon as raw materials, and preparing MnO4 by hydrothermal method. x -CeO x The modified activated carbon has a wide pH application range, the best removal effect under neutral conditions, good stability, and a small amount of manganese and cerium released after the reaction. It is significantly better than other methods for preparing activated carbon-loaded manganese-cerium oxide adsorbents.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A trivalent arsenic adsorbent, the adsorbent is MnO x -CeO x Modified activated carbon is prepared by high pressure reactor hydrothermal synthesis method using CeN3O9·6H2O, KMnO4 and activated carbon as raw materials. The adsorbent particle size is 10-100nm and the specific surface area of ​​the adsorbent is 200-220m 2 / g.

[0007] A method for preparing a trivalent arsenic adsorbent comprises the following steps:

[0008] S1. Mix deionized water and anhydrous ethanol in a volume ratio of 1:1 and add to a container, then add activated carbon and ultrasonically disperse for 15 to 30 minutes to obtain a uniform suspension;

[0009] S2, adding potassium permanganate and cerium nitrate to the suspension obtained in step S1 in sequence, stirring and dissolving to obtain a mixed solution, then adding urea to the mixed solution, and continuing to stir for 20 to 40 minutes;

[0010] S3, placing the mixed solution obtained in step S2 into a polytetrafluoroethylene liner, then placing it into a high-temperature reaction kettle, sealing it, and placing it in an oven at 80-120° C. for reaction for 1-3 hours;

[0011] S4, cooling the reaction product in step S3, washing it with deionized water, centrifuging it, and drying the precipitate obtained after centrifugation in an oven at 55-65°C for 10-12 hours, and grinding it to 50-70 mesh after cooling;

[0012] S5. Place the dried precipitate in a tube furnace and heat it to 380-420°C for 2-4 hours. After cooling naturally, obtain MnO x -CeO x Modified activated carbon.

[0013] Preferably, in step S2, the molar ratio of potassium permanganate, cerium nitrate and urea is 1:1-3:8-12.

[0014] Preferably, in step S3, the mixed solution is reacted in a high pressure reactor at 100° C. for 2 h.

[0015] Preferably, in step S5, the precipitate is calcined at 400° C. for 3 h.

[0016] Preferably, MnO x -CeO x MnO in modified activated carbon x The loading rate is 20-30%, of which Mn 4+ , Mn 3+ , Mn 2+ The ratio of CeO is 12:10:5; x The load rate is 20-60%, of which Ce 4+ With Ce 3+ The ratio is 3:1.

[0017] Beneficial effects of the present invention:

[0018] The present invention mixes CeN3O9·6H2O and KMnO4 in a certain molar ratio, uses CON2H4 as a precipitant, and prepares a metal oxide with small particle size and controllable morphology through hydrothermal method, and loads it through activated carbon to obtain a trivalent arsenic adsorbent, which has a wide pH application range, the best removal effect under neutral conditions, good stability, and a small amount of manganese and cerium released after the reaction, which is significantly better than other methods for preparing an adsorbent of manganese-cerium oxide loaded on activated carbon. The present invention utilizes the high temperature and high pressure conditions of the reactor to make the particles of the metal oxide smaller, the activated carbon is more stripped, and the metal oxide is more evenly distributed on the surface of the activated carbon. The surface of the adsorbent of the present invention has rich active sites, and the supporting effect of the activated carbon avoids the agglomeration problem of the metal oxide, reducing the cost of the material. The specific surface area and pore volume of the adsorbent of the present invention are greatly increased, which are 22 times and 51 times of those of the activated carbon alone, respectively. The aggregation degree of manganese and cerium oxide particles is significantly reduced, and the anti-interference ability is strong when removing As(III), Cl - 、F - 、NO3 - 、SO4 2- The effects on the removal of As(III) are relatively small. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 The MnO prepared in Example 1 of the present invention x -CeO x N2 adsorption-desorption isotherms of modified activated carbon adsorbent;

[0021] Figure 2 The MnO prepared in Example 1 of the present invention x -CeO x SEM image of modified activated carbon adsorbent;

[0022] Figure 3 The MnO prepared in Example 1 of the present invention x -CeO x Removal efficiency of As(III) by modified activated carbon adsorbent under different pH conditions;

[0023] Figure 4 The MnO prepared in Example 1 of the present invention x -CeO x The concentrations of Mn and Ce in the solution after the modified activated carbon adsorbent reacted under different pH conditions;

[0024] Figure 5 MnO prepared in Example 1 of the present invention x -CeO x The adsorption capacity of As(III) by modified activated carbon adsorbent in the presence of different concentrations of ions;

[0025] Figure 6 MnO prepared in Example 1 of the present invention x -CeO x Adsorption isotherms of modified activated carbon adsorbents;

[0026] Figure 7 MnO prepared in Example 1 of the present invention x -CeO x Full XPS spectra of modified activated carbon adsorbent before and after reaction with As(III);

[0027] Figure 8 MnO prepared in Example 1 of the present invention x -CeO x XPS decomposition spectra of modified activated carbon adsorbent before and after reaction with As(III);

[0028] Fig. 9 MnO prepared in Example 1 of the present invention x -CeO x Mechanistic diagram of As(III) removal by modified activated carbon adsorbent. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inside", "all around" and the like indicating orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0031] Example 1

[0032] A trivalent arsenic adsorbent, the adsorbent is MnO x -CeO xThe modified activated carbon is prepared by hydrothermal synthesis using CeN3O9·6H2O, KMnO4 and activated carbon as raw materials. The preparation method comprises the following steps:

[0033] S1. Mix deionized water and anhydrous ethanol in a volume ratio of 1:1 and add to a container, then add 0.3 g of activated carbon and ultrasonically disperse for 15 min to obtain a uniform suspension;

[0034] S2, adding 0.4272 g potassium permanganate and 1.1735 g cerium nitrate to the suspension obtained in step S1, stirring and dissolving to obtain a mixed solution, then adding 1.6227 g urea to the mixed solution, and continuing to stir for 40 min;

[0035] S3, placing the mixed solution obtained in step S2 into a polytetrafluoroethylene liner, then placing it into a high-temperature reaction kettle, sealing it, and placing it in an oven at 80° C. for reaction for 3 hours;

[0036] S4, cooling the reaction product in step S3, washing it with deionized water, centrifuging it, and drying the precipitate obtained after centrifugation in a 65°C oven for 10 hours, and grinding it to 60 mesh after cooling;

[0037] S5. The dried precipitate is placed in a tube furnace and heated to 380°C for 4 hours. After natural cooling, MnO is obtained. x -CeO x Modified activated carbon adsorbent, the obtained product is marked as Mn-Ce / AC3.

[0038] The N2 adsorption-desorption isotherms of Mn-Ce / AC3 obtained in this example are shown in Figure 1 , where 1(a) is activated carbon and 1(b) is Mn-Ce / AC3. Figure 1 It can be seen that the specific surface area and pore volume of Mn-Ce / AC3 obtained by modification with Mn and Ce are greatly improved. The specific surface area of ​​Mn-Ce / AC3 (213.25m 2 / g) is activated carbon alone (9.63m 2 / g) is 22 times that of Mn-Ce / AC3; the pore volume (0.5862cm 3 / g) is activated carbon alone (0.01144cm 3 / g) is 51 times.

[0039] Scanning electron microscopy images of activated carbon alone and Mn-Ce / AC3 are shown in Figure 2 As shown in the figure, 2(a) is activated carbon and 2(b) is Mn-Ce / AC3. It can be seen from the figure that the surface of activated carbon alone is relatively smooth; after modification by Mn and Ce, CeO x 、MnO x The particles are evenly distributed on the surface of the activated carbon, and the surface of the activated carbon becomes rougher.

[0040] Example 2

[0041] A trivalent arsenic adsorbent, the adsorbent is MnO x -CeO x The modified activated carbon is prepared by hydrothermal synthesis using CeN3O9·6H2O, KMnO4 and activated carbon as raw materials. The preparation method comprises the following steps:

[0042] S1. Mix deionized water and anhydrous ethanol in a volume ratio of 1:1 and add to a container, then add 0.45 g of activated carbon and ultrasonically disperse for 20 min to obtain a uniform suspension;

[0043] S2, adding 0.6408 g potassium permanganate and 5.2809 g cerium nitrate to the suspension obtained in step S1, stirring and dissolving to obtain a mixed solution, then adding 1.9472 g urea to the mixed solution, and continuing stirring for 30 min;

[0044] S3, placing the mixed solution obtained in step S2 into a polytetrafluoroethylene liner, and then placing it into a high-temperature reaction kettle, sealing it, and placing it in an oven at 100° C. for reaction for 2 hours;

[0045] S4, cooling the reaction product in step S3, washing it with deionized water, centrifuging it, and drying the precipitate obtained after centrifugation in a 60° C. oven for 10 h, and grinding it to 70 mesh after cooling;

[0046] S5. The dried precipitate is placed in a tube furnace and heated to 400°C for 3 hours. After natural cooling, MnO is obtained. x -CeO x Modified activated carbon adsorbent, the obtained product is marked as Mn-Ce / AC3.

[0047] Example 3

[0048] A trivalent arsenic adsorbent, the adsorbent is MnO x -CeO x The modified activated carbon is prepared by hydrothermal synthesis using CeN3O9·6H2O, KMnO4 and activated carbon as raw materials. The preparation method comprises the following steps:

[0049] S1. Mix deionized water and anhydrous ethanol in a volume ratio of 1:1 and add to a container, then add 0.24 g of activated carbon and ultrasonically disperse for 30 min to obtain a uniform suspension;

[0050] S2, adding 0.3418 g potassium permanganate and 1.8776 g cerium nitrate to the suspension obtained in step S1, stirring and dissolving to obtain a mixed solution, then adding 1.5578 g urea to the mixed solution, and continuing stirring for 20 min;

[0051] S3, placing the mixed solution obtained in step S2 into a polytetrafluoroethylene liner, then placing it into a high-temperature reaction kettle, sealing it, and placing it in an oven at 120° C. for reaction for 1 hour;

[0052] S4, cooling the reaction product in step S3, washing it with deionized water, centrifuging it, and drying the precipitate obtained after centrifugation in a 55°C oven for 12 hours, and grinding it to 50 mesh after cooling;

[0053] S5. The dried precipitate is placed in a tube furnace and heated to 420°C for 2 hours. After natural cooling, MnO is obtained. x -CeO x Modified activated carbon adsorbent, the obtained product is marked as Mn-Ce / AC3.

[0054] Performance Testing

[0055] 1. pH effect experiment

[0056] The Mn-Ce / AC3 prepared in Example 1 was applied to remove As(III) in the solution, and the specific steps were as follows:

[0057] (1) Weigh 0.01 g of Mn-Ce / AC3 into a 100 mL iodine volumetric flask, add 50 mL of 20 mg / L As(III) solution, adjust the pH of the solution to 2-11, and then place the iodine volumetric flask in a constant temperature shaker;

[0058] (2) The temperature of the constant temperature shaker is 25°C, the rotation speed is 200 rpm, and the reaction time is 300 min;

[0059] (3) After the reaction is completed, the solution is separated using a 0.45 μm filter membrane to remove As(III) from the aqueous solution, and the concentrations of arsenic in the initial solution and the remaining solution, as well as the concentrations of Mn and Ce in the remaining solution, are measured.

[0060] The effect of solution pH on the removal of As(III) by Mn-Ce / AC3 is shown in Figure 3 ,from Figure 3 It can be seen that at pH 3 to 9, Mn-Ce / AC3 maintains a high removal rate for As(III), and Mn-Ce / AC3 has a wide pH range of application for removing As(III). Figure 4 As can be seen from the figure, when the pH is 3-11, almost no Ce ions leak into the solution; when the pH is ≥ 6, the concentration of Mn ions in the solution is less than the manganese emission limit (2 mg / L) in the comprehensive sewage discharge standard. Therefore, Mn-Ce / AC3 has good stability.

[0061] 2. Experiment on the influence of coexisting ions on adsorption effect

[0062] In the presence of different interfering ions, the adsorption amount of As(III) in the solution by the adsorbent was compared. The specific steps are as follows:

[0063] (1) Take several conical flasks and add 50 mL of As(III) with an initial concentration of 20 mg / L. In order to test the adsorption selectivity of the Mn-Ce / AC3 composite material, Cl - 、F - 、NO3 - 、SO4 2- solutions (10 mg / L and 50 mg / L) as coexisting anions.

[0064] (2) Adjust the pH to 7.0 ± 0.1 using NaOH and HCl solutions.

[0065] (3) Add 0.5 g / L of Mn-Ce / AC composite material and react in a constant temperature oscillator at 25°C for 300 min.

[0066] (4) After the reaction is completed, the determination method in Example 2 is repeated to determine the concentration of arsenic in the initial solution and the remaining solution, and the adsorption amount and removal rate of arsenic are calculated.

[0067] from Figure 5 It can be seen that at the experimental concentration (20 mg / L), Cl - 、F - 、NO3 - and SO4 2- The presence of has no obvious effect on the adsorption of As(III), indicating that the Mn-Ce / C3 composite material exhibits good anti-interference ability against a variety of coexisting anions, proving that the material can be used in different water environments.

[0068] 3. Isotherm adsorption experiment

[0069] At different reaction temperatures and initial concentrations, the adsorption amount of As(III) in the solution by the adsorbent was compared. The specific steps are as follows:

[0070] (1) Take several conical flasks and add 50 mL of As(III) solution with initial concentrations of 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 80 mg / L, and 100 mg / L, respectively. Adjust the pH value with NaOH and HCl solutions. The pH value of the As(III) solution is 7.0±0.1.

[0071] (2) Add 0.5 g / L of Mn-Ce / AC3 composite material and place it in a constant temperature oscillator at 25°C for 300 min.

[0072] (3) After the reaction was completed, the initial concentration and residual concentration of As in the solution were determined according to the method in Example 2, and the adsorption amount and removal rate of arsenic were calculated.

[0073] (4) Repeat the above experimental steps at 35°C and 45°C respectively.

[0074] The results of the test are as follows Figure 6 As shown in the figure, the composite material has a good adsorption effect on arsenic. At 25°C, the maximum adsorption capacity of Mn-Ce / AC3 for As(III) is 70.97 mg / g calculated according to the Langmuir model, which is much higher than the currently available adsorbents, and the saturated adsorption capacity of Mn-Ce / AC3 gradually increases with the increase of reaction temperature.

[0075] XPS characterization of Mn-Ce / AC3 before and after reaction at 25°C is shown in Figure 7 and Figure 8 , where 8(a): As 3d, 8(b): Mn 2p, 8(c): Ce 3d, 8(d): O 1s; From the figure, we can see that before the reaction, Mn(IV), Mn(III) and Mn(II) exist in Mn-Ce / AC3, and their proportions are 43.94%, 37.88% and 8.18% respectively; Ce(IV) and Ce(III) exist at the same time, and their proportions are 75.19% and 24.81% respectively; O1s is decomposed, and it is known that the content of hydroxyl (-OH) is 37.73%. During the reaction, Mn(IV), Mn(III) and Ce(IV) undergo redox reactions with As(III), and -OH undergoes substitution reaction with As(III), resulting in a decrease in the proportion of Mn(IV), Ce(IV) and -OH in Mn-Ce / AC3 after the reaction.

[0076] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0077] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A trivalent arsenic adsorbent, characterized in that: The adsorbent is MnO x -CeO x Modified activated carbon is prepared by high pressure reactor hydrothermal synthesis method using CeN3O9·6H2O, KMnO4 and activated carbon as raw materials. The adsorbent particle size is 10-100nm and the specific surface area of ​​the adsorbent is 200-220m 2 / g; The preparation method of the trivalent arsenic adsorbent comprises the following steps: S1. Mix deionized water and anhydrous ethanol in a volume ratio of 1:1 and add to a container, then add activated carbon and ultrasonically disperse for 15 to 30 minutes to obtain a uniform suspension; S2, adding potassium permanganate and cerium nitrate to the suspension obtained in step S1 in sequence, stirring and dissolving to obtain a mixed solution, then adding urea to the mixed solution, and continuing to stir for 20 to 40 minutes; S3, placing the mixed solution obtained in step S2 into a polytetrafluoroethylene liner, then placing it into a high-temperature reaction kettle, sealing it, and placing it in an oven at 80-120° C. for reaction for 1-3 hours; S4, cooling the reaction product in step S3, washing it with deionized water, centrifuging it, and drying the precipitate obtained after centrifugation in an oven at 55-65°C for 10-12 hours, and grinding it to 50-70 mesh after cooling; S5. Place the dried precipitate in a tube furnace and heat it to 380-420°C for 2-4 hours. After cooling naturally, obtain MnO x -CeO x Modified activated carbon; The adsorbent contains MnO x The loading rate is 20-30%, of which Mn 4+ , Mn 3+ , Mn 2+ The ratio of CeO is 12:10:5; x The load rate is 20-60%, of which Ce 4+ With Ce 3+ The ratio is 3:

1.

2. The trivalent arsenic adsorbent according to claim 1, characterized in that: In step S2, the molar ratio of potassium permanganate, cerium nitrate and urea is 1:1-3:8-12.

3. The trivalent arsenic adsorbent according to claim 1, characterized in that: In step S3, the mixed solution is reacted in a high pressure reactor at 100° C. for 2 h.

4. The trivalent arsenic adsorbent according to claim 1, characterized in that: In step S5, the precipitate is calcined at 400° C. for 3 hours.

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