A method for preparing a persulfate activator using excess sludge, the obtained persulfate activator and its application

Abstract

The invention discloses a method for preparing a persulfate activator using excess sludge, the obtained persulfate activator and its application, and belongs to the technical field of sewage treatment. The method provided by the invention is as follows: the excess sludge is dried, ball-milled and sieved in sequence, and then placed in a high-temperature furnace and heated under an inert atmosphere; the mass fraction of the iron element in the excess sludge is 1-3wt%; when the temperature reaches 450-550°C, borane is introduced at a constant temperature for 5-20min; then the temperature is raised to 700-900°C for calcination to obtain a persulfate activator. The method provided by the invention does not require multiple calcination treatments and does not require the addition of exogenous metal salts and other substances, is simple to operate, has a short processing flow, and is low in cost; the obtained persulfate activator has a good degradation effect when activating persulfate to degrade organic pollutants, and can be recycled for multiple times.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for preparing a persulfate activator by utilizing excess sludge, the obtained persulfate activator and applications thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Persulfate advanced oxidation technology has the advantages of strong redox ability, low cost, and easy operation, and has shown application potential in water pollution control and soil remediation. It is difficult for persulfate to directly oxidize organic matter, and it needs to be activated by an activator to produce strong oxidizing sulfate radicals or hydroxyl radicals to degrade or even mineralize most organic matter.

[0004] There are a lot of studies on persulfate activators, such as the patent with authorization announcement number CN109912001B that discloses Ni 0.6 Fe 2.4 O 4 As a persulfate activator, the patent with the authorization publication number CN111135837B discloses a loaded Ni 2 SnO 4 Although the above patent has achieved good activation effect by using graphene sheets of nanoparticles as persulfate activators, it uses materials such as metals and graphene, has high preparation costs, and is not suitable for large-scale applications.

[0005] The carbonaceous material generated by thermal decomposition of sludge under high temperature and anoxic conditions has a large specific surface area, a stable graphite structure, a strong ion exchange capacity and a variety of oxygen-containing functional groups, which can be used as a persulfate activator. This method is more cost-effective and can be used as a resource for sludge. However, the surface active sites of sludge are limited after pyrolysis, resulting in its weak ability to activate persulfate, which limits its application. In addition, there are many types of sludge, and the components of different sludges are also quite different, so the activation effect may vary greatly. The patent with the authorization announcement number CN115608360B discloses a method for degrading antibiotic pollutants using a copper atom cluster modified sludge biochar catalyst. It uses industrial sludge as raw material, undergoes calcination, mixed calcination with alkaline substances, pickling, reaction with copper ion solution, calcination and other steps, and the operation is very cumbersome and energy-intensive. Patent with authorization announcement number CN113209970B discloses a carbon-based catalyst prepared from waste sludge as raw material and its application in degrading 4-chlorophenol in water by activated peracetic acid. The preparation process of the catalyst in this patent also undergoes two steps of high-temperature calcination, and additional ZnCl needs to be introduced. 2The activator needs to be immersed in a solution of ferric nitrate and cobalt nitrate at the same time, and the amount of metal salt used is large, the operation is complicated and the cost is high.

[0006] Therefore, how to provide a persulfate activator which uses sludge as raw material, has a simple preparation method and good activation effect is an urgent problem to be solved. Summary of the invention

[0007] In view of this, the present invention provides a method for preparing a persulfate activator using excess sludge, the obtained persulfate activator and its application. The method provided by the present invention can make the obtained persulfate activator have a better activation effect, thereby making the degradation efficiency of organic pollutants higher, while being simple to operate and low in cost.

[0008] In a first aspect, the present invention provides a method for preparing a persulfate activator using excess sludge, comprising the following steps:

[0009] The excess sludge is dried, ball-milled, sieved, placed in a high-temperature furnace, and heated under an inert atmosphere; the mass fraction of the iron element in the excess sludge is 1-3wt%;

[0010] When the temperature reaches 450-550°C, borane is introduced at a constant temperature for 5-20 minutes; then the temperature is raised to 700-900°C for calcination to obtain a persulfate activator.

[0011] In a second aspect, the present invention provides a persulfate activator prepared by the above method.

[0012] In a third aspect, the present invention provides an application of the above-mentioned persulfate activator, wherein the application is: using the persulfate activator to activate persulfate to degrade organic pollutants.

[0013] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0014] (1) The present invention uses excess sludge as a raw material to prepare a persulfate activator. The iron element in the excess sludge can form an iron-oxygen complex after calcination. At the same time, the present invention introduces borane in the preparation process of the persulfate activator. Borane can modify biomass charcoal to form a boron-carbon covalent bond. Under the joint action of the iron, boron and carbon complex, the obtained persulfate activator greatly improves the degradation effect of organic pollutants when activating persulfate. Moreover, the persulfate activator can be recycled for multiple times.

[0015] (2) The preparation process of the persulfate activator of the present invention does not require multiple calcination treatments and does not require the addition of exogenous metal salts and other substances. The operation is simple and the processing flow is short. The cost is low and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 is the X-ray diffraction spectrum of the persulfate activator of Example 1 of the present invention;

[0018] Figure 2 is a scanning electron microscope image of the persulfate activator of Example 1 of the present invention;

[0019] Figure 3 It is a comparison chart of the degradation rates of atrazine degraded by sodium persulfate activated by the persulfate activator of Examples 1 to 3 of the present invention and Comparative Examples 1 to 6. DETAILED DESCRIPTION

[0020] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0021] As pointed out in the background technology, the method for preparing persulfate activator using sludge as raw material in the prior art has complicated operation steps and high cost. Therefore, the present invention provides a method for preparing persulfate activator using excess sludge, comprising the following steps:

[0022] The excess sludge is dried, ball-milled, sieved, placed in a high-temperature furnace, and heated under an inert atmosphere; the mass fraction of the iron element in the excess sludge is 1-3wt%;

[0023] When the temperature reaches 450-550°C, borane is introduced at a constant temperature for 5-20 minutes; then the temperature is raised to 700-900°C for calcination to obtain a persulfate activator.

[0024] Residual sludge refers to the activated sludge discharged from the secondary sedimentation tank (or sedimentation area) in the activated sludge system. The present invention preferably uses iron salt as the residual sludge produced by the flocculant. The residual sludge contains iron, which can provide an iron source to prepare iron-oxygen complexes and improve the effect of activating persulfate. The present invention limits the mass fraction of iron in the residual sludge to 1~3wt%. Too low iron content will lead to too few active sites, and too high iron content will lead to sintering (i.e., the phenomenon of inter-grain bonding at high temperature), which will lead to a decrease in the exposure of active sites. The iron element in the present invention is a metal element that exists in the residual sludge itself, and no external metal salt is required.

[0025] The present invention does not impose any special restrictions on the drying process of the excess sludge, as long as the moisture in the excess sludge is completely removed. The presence of moisture will affect the subsequent calcination process, and water will also react with borane, so it is necessary to ensure that the moisture is fully removed.

[0026] In the present invention, the ball milling time is 5 to 30 minutes, more preferably 8 to 15 minutes. The ball-to-material ratio in the ball milling process is (8 to 15):1, the ball milling speed is 400 to 800 rpm, and the ball milling adopts dry ball milling. The ball milling process has high energy and can promote the uniformity of the material.

[0027] In the sieving step of the present invention, the sieve size is 100 mesh or more, for example, it can be selected from 100 mesh, 200 mesh or 400 mesh, and the sieves with large apertures to small apertures can also be used for sieving, and the present invention does not impose any special restrictions on this. The sieved material is more uniform, which is conducive to the calcination process.

[0028] In the present invention, the inert atmosphere is selected from one or more of nitrogen or rare gases, and the rare gases can be selected from gases such as argon. The inert atmosphere is more preferably nitrogen to prevent borane from contacting with water and oxygen.

[0029] In the present invention, in the step of heating under an inert atmosphere and the step of heating to 700-900° C., the heating rate is 2-8° C. / min. The heating rates in the two steps may be the same or different, and the present invention does not impose any special limitation on this.

[0030] In the present invention, the flow rate of the borane is 5-20 mL / min, more preferably 8-15 mL / min; the borane is selected from diborane or diborane, more preferably diborane. In the process of calcining the residual sludge, borane is introduced to provide a boron source, which can interact with the biomass charcoal to form a boron-carbon covalent bond and induce electron transfer.

[0031] The present invention is more preferably heated to 750-850 ° C for calcination. The calcination temperature will have a significant effect on the performance of the persulfate activator. If the calcination temperature is too low, the biomass carbonization degree will be low, and if it is too high, the inorganic matter will be sintered, and the persulfate activator will not be able to fully play its role. The calcination time is 1-5 h, more preferably 1.5-3 h. During the calcination process, the biomass is gradually carbonized, iron gradually forms an iron-oxygen complex, and boron is doped in the biomass charcoal.

[0032] The present invention also provides a persulfate activator prepared by the above method, which has a specific surface area of ​​200 m 2 / g or above.

[0033] The present invention also provides an application of the persulfate activator, wherein the application is to use the persulfate activator to activate persulfate to degrade organic pollutants. The persulfate activator of the present invention has a good effect of activating persulfate and can degrade organic pollutants more efficiently; at the same time, the persulfate activator of the present invention has a good recycling effect and can still maintain a high degradation rate when degrading organic pollutants after multiple uses.

[0034] In the present invention, the specific method of using the persulfate activator for activating persulfate to degrade organic pollutants is: adding the persulfate activator and persulfate to a water body containing organic pollutants, stirring and reacting; the mass ratio of the persulfate activator to the persulfate is 1:(0.8~1.2), the concentration of the persulfate activator is 80~200 mg / L, and the concentration of the organic pollutants is 2~20 mg / L.

[0035] In the present invention, the persulfate is selected from one or more of sodium persulfate, potassium persulfate or ammonium persulfate, and sodium persulfate is preferably used in the present invention.

[0036] The present invention does not place any special restrictions on the types of organic pollutants, and may be refractory organic pollutants, such as chlorophenol, nitrobenzene, atrazine, bisphenol A, etc. In one or more embodiments of the present invention, the organic pollutant is selected from atrazine, which is a triazine herbicide, mainly used for the removal of annual grasses and broadleaf weeds. Studies have shown that atrazine remaining in water can seriously affect the growth and reproduction of species, and atrazine is also an endocrine disrupting and carcinogenic compound that can destroy the immune system of an organism. The persulfate activator prepared by the present invention can achieve a degradation rate of more than 90% in 2 h when activating persulfate to degrade atrazine.

[0037] The technical solution of the present invention is further described below in conjunction with specific embodiments. In the following embodiments, the mass fraction of iron in the residual sludge is the mass fraction of iron in the dry sludge, which is determined by inductively coupled plasma mass spectrometry (ICP-MS). Unless otherwise specified, the residual sludge is the residual sludge of the secondary sedimentation tank using iron salt as a flocculant.

[0038] Example 1

[0039] This embodiment provides a method for preparing a persulfate activator using excess sludge.

[0040] 1 L of residual activated sludge (iron mass fraction of 2.4wt%) was dried at 80℃ in a blast drying oven for 18h, then ball-milled for 10 min using a planetary ball mill, where the ball-to-material ratio was 10:1, the ball-to-cavity ratio was 1:12, and the ball milling speed was 600rpm. The ball-milled powder was sieved with 100 mesh, 200 mesh, and 400 mesh sieves in turn and placed in a high-temperature tube furnace; the temperature was raised to 500℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and then diborane was introduced at a constant temperature, with a flow rate of 10 mL / min and an introduction time of 10 min. Then, the temperature was raised to 800℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcined for 2 h, and the persulfate activator was obtained by cooling to room temperature with the furnace.

[0041] Figure 1 This is the X-ray diffraction (XRD) diagram of the persulfate activator prepared in this example. It can be seen that the valence state of Fe in the obtained persulfate activator is divalent and trivalent.

[0042] Figure 2 This is a scanning electron microscope image of the persulfate activator prepared in this example. It can be seen that the persulfate activator presents fragments and block morphologies with uneven shapes and sizes.

[0043] Example 2

[0044] This embodiment provides a method for preparing a persulfate activator using excess sludge.

[0045] 1L of excess activated sludge (iron mass fraction of 1.8wt%) was dried at 80℃ in a blast drying oven for 18h, then ball-milled in a planetary ball mill for 10min, where the ball-to-material ratio was 10:1, the ball-to-cavity ratio was 1:12, and the ball-milling speed was 600rpm. The ball-milled powder was sieved with 100 mesh, 200 mesh, and 400 mesh sieves in turn and placed in a high-temperature tube furnace; heated to 500℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, and then diborane was introduced at a constant temperature, with a flow rate of 10mL / min and an introduction time of 10min. Then, the temperature was raised to 800℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, calcined for 2h, and cooled to room temperature with the furnace to obtain a persulfate activator.

[0046] Example 3

[0047] This embodiment provides a method for preparing a persulfate activator using excess sludge.

[0048] 1L of residual activated sludge (iron mass fraction of 2.4wt%) was dried at 80℃ in a blast drying oven for 18h, then ball-milled in a planetary ball mill for 10min, where the ball-to-material ratio was 10:1, the ball-to-cavity ratio was 1:12, and the ball-milling speed was 600rpm. The ball-milled powder was sieved with 100 mesh, 200 mesh and 400 mesh sieves in turn and placed in a high-temperature tube furnace; heated to 500℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, and then diborane was introduced at a constant temperature, with a flow rate of 10mL / min and an introduction time of 10min. Then, the temperature was raised to 900℃ at a heating rate of 5℃ / min in a nitrogen atmosphere and calcined for 3h, and the persulfate activator was obtained by cooling to room temperature with the furnace.

[0049] Comparative Example 1

[0050] This comparative example is different from Example 1 in that diborane is not introduced. The specific preparation method is as follows:

[0051] 1L of residual activated sludge (with an iron mass fraction of 2.4wt%) was dried at 80℃ in a forced air drying oven for 18h, and then ball-milled for 10min using a planetary ball mill, wherein the ball-to-material ratio was 10:1, the ball-to-cavity ratio was 1:12, and the ball-milling speed was 600rpm. The ball-milled powder was sieved using 100-mesh, 200-mesh and 400-mesh sieves in turn and placed in a high-temperature tubular furnace; the temperature was raised to 800℃ at a heating rate of 5℃ / min in a nitrogen atmosphere and calcined for 2h, and then cooled to room temperature with the furnace to obtain a persulfate activator.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the mass fraction of iron in the residual activated sludge of this comparative example is 0.8wt%.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that the mass fraction of iron in the residual activated sludge of this comparative example is 3.5wt%.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 1 is that the calcination temperature of this comparative example is 600°C.

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 1 is that the calcination temperature of this comparative example is 1000°C.

[0060] Comparative Example 6

[0061] Compared with Example 1, the difference between this comparative example and Example 1 is that the residual sludge in this comparative example is the residual sludge of the secondary sedimentation tank using non-iron salt as flocculant, the mass fraction of iron element is less than 0.2wt%, and this comparative example is not subjected to borane treatment. The specific steps are as follows:

[0062] 1L of residual activated sludge (the mass fraction of iron element is less than 0.2wt%) was dried at 80℃ in a forced air drying oven for 18h, and then ball-milled for 10min using a planetary ball mill, wherein the ball-to-material ratio was 10:1, the ball-to-cavity ratio was 1:12, and the ball-milling speed was 600rpm. The ball-milled powder was sieved using 100-mesh, 200-mesh and 400-mesh sieves in turn and placed in a high-temperature tubular furnace; the temperature was raised to 800℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and calcined for 2h, and then cooled to room temperature with the furnace to obtain a persulfate activator.

[0063] Test example

[0064] 1. Determination of physical parameters:

[0065] The specific surface area, pore volume and pore diameter of the persulfate activators prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were measured by gas adsorption method. The test results are shown in Table 1.

[0066] It can be seen from Table 1 that both temperature and iron content have a significant effect on the specific surface area; as the temperature increases, the specific surface area gradually increases, reaching a maximum value at 800°C, and then the specific surface area shows a downward trend; the iron content is negatively correlated with the specific surface area; boron doping has no obvious effect on the specific surface area.

[0067] Table 1 Physical properties of the persulfate activators of Examples 1 to 3 and Comparative Examples 1 to 6

[0068]

[0069] 2. Experiment on degradation of atrazine:

[0070] At 25±2°C, sodium persulfate was added to a 4 mg / L atrazine solution to control the concentration of sodium persulfate to 100 mg / L, and then the persulfate activator of the embodiment or comparative example was added to control the concentration of the persulfate activator to 100 mg / L; the reaction was stirred for 2 hours, and the degradation within 2 hours was measured and recorded. The results are as follows: Figure 3 As shown in Table 2, Figure 3 In the vertical axis, C t represents the concentration of atrazine at time t, in mg / L; C 0 represents the initial atrazine concentration in mg / L; C t / C 0 represents the residual rate of atrazine at time t, and the degradation rate of atrazine at time t = (1-Ct / C 0 )×100%.

[0071] Table 2 Test data of the degradation of atrazine by activating sodium persulfate with persulfate activators in the examples and comparative examples

[0072]

[0073] from Figure 3 As can be seen from Table 2, temperature, iron content, and the presence or absence of boron treatment all have a significant effect on the activation and degradation of atrazine by the material. The results show that under the conditions of 800°C, 2.4wt% iron content and boron doping, the degradation rate of atrazine in 2h is the highest, up to 96%; when the persulfate activator of the embodiment activates sodium persulfate to degrade atrazine, the degradation rate within 2h can reach more than 90%. Under the conditions where the iron content in the persulfate activator is very low and no borane treatment is performed, the degradation rate is only 16% (Comparative Example 6). When the temperature is too low (600°C), the degradation rate is only 28%, which is mainly because the carbonization is incomplete at this temperature, the specific surface area is small, and it is difficult to give full play to the activation effect. When the temperature is too high (1000°C, Comparative Example 5), the activator will cause sintering, which will greatly reduce the specific surface area, thereby reducing the degradation efficiency. Excessive iron content will also lead to sintering, which will reduce the exposure of active sites and reduce the final degradation rate.

[0074] 3. Cyclic performance of the persulfate activator of Example 1:

[0075] The persulfate activator of Example 1 was used to activate sodium persulfate to degrade atrazine. The experiment was the same as the above-mentioned degradation experiment. After the degradation experiment, the retained material was filtered out, washed with deionized water and filtered until no atrazine was detected in the filtrate. The retained material was then dried and used for the next cycle degradation experiment.

[0076] Table 3 Cyclic performance data of the persulfate activator of Example 1

[0077]

[0078] It can be seen from Table 3 that after three cycles, the degradation rate of atrazine by activated sodium persulfate of the persulfate activator of Example 1 is still maintained at more than 80%, and the iron ion dissolution rate is less than 1%, indicating that it has good stability in use.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a persulfate activator using excess sludge, characterized in that: The steps include: The excess sludge is dried, ball-milled, sieved, placed in a high-temperature furnace, and heated under an inert atmosphere; the mass fraction of the iron element in the excess sludge is 1-3wt%; When the temperature reaches 450-550°C, borane is introduced at a constant temperature for 5-20 minutes; then the temperature is raised to 750-850°C for calcination; the calcination time is 1-5 hours, and a persulfate activator is obtained; The flow rate of the borane is 5-20 mL / min; the borane is diborane.

2. The method according to claim 1, characterized in that The ball milling time is 5-30 min, the ball-to-material ratio in the ball milling process is (8-15):1, and the ball milling speed is 400-800 rpm.

3. The method according to claim 1, characterized in that In the sieving step, the sieve hole size is greater than 100 meshes; the inert atmosphere is selected from one or more of nitrogen or rare gases.

4. The method according to claim 1, characterized in that In the step of heating under an inert atmosphere and the step of heating to 750-850° C., the heating rate is 2-8° C. / min.

5. The persulfate activator prepared by the method according to any one of claims 1 to 4.

6. The use of a persulfate activator as claimed in claim 5, characterized in that: The application is: using the persulfate activator to activate persulfate to degrade organic pollutants.

7. The use according to claim 6, characterized in that The specific method of using the persulfate activator to activate persulfate to degrade organic pollutants is as follows: adding the persulfate activator and persulfate to a water body containing organic pollutants, stirring and reacting; the mass ratio of the persulfate activator to the persulfate is 1:(0.8~1.2), the concentration of the persulfate activator is 80~200 mg / L, and the concentration of the organic pollutants is 2~20 mg / L.

8. The use according to claim 7, characterized in that The persulfate is selected from one or more of sodium persulfate, potassium persulfate or ammonium persulfate.

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