阅读说明：本技术 一种处理含铬废水的粉煤灰基磁混凝剂及制备方法、应用和再生方法 (Fly ash-based magnetic coagulant for treating chromium-containing wastewater, preparation method, application and regeneration method ) 是由 齐立强 王旭 王吻 赵帅 于 2021-09-24 设计创作，主要内容包括：本发明属于混凝剂技术领域,公开了一种处理含铬废水的粉煤灰基磁混凝剂及制备方法、应用和再生方法。本发明将粉煤灰使用浓度为1～3mol/L的盐酸进行改性,并将改性粉煤灰与Fe-(3)O-(4)混合,得到粉煤灰基磁混凝剂。本发明利用盐酸对粉煤灰进行改性处理,可以使粉煤灰的表面变得更加粗糙,增大粉煤灰比表面积,提高粉煤灰对废水中重金属的吸附效果。本发明使用低浓度且较少量的盐酸即可实现粉煤灰的改性,制得的磁混凝剂在去除污水中悬浮物、污染物、降低浊度的同时,还可实现对于重金属铬离子的良好吸附效果,且再生后对于铬的去除率仍可达99％以上,磁混凝剂的重复再生性能较好,生产成本低。(The invention belongs to the technical field of coagulants, and discloses a fly ash-based magnetic coagulant for treating chromium-containing wastewater, and a preparation method, application and a regeneration method thereof. According to the invention, the fly ash is modified by using hydrochloric acid with the concentration of 1-3 mol/L, and the modified fly ash and Fe are mixed 3 O 4 And mixing to obtain the fly ash-based magnetic coagulant. According to the invention, the hydrochloric acid is used for modifying the fly ash, so that the surface of the fly ash becomes rougher, the specific surface area of the fly ash is increased, and the adsorption effect of the fly ash on heavy metals in wastewater is improved. The invention can realize the modification of the fly ash by using a small amount of hydrochloric acid with low concentration, and the prepared magnetic coagulant can remove the suspension in the sewageThe method can realize good adsorption effect on heavy metal chromium ions while reducing turbidity of substances and pollutants, the removal rate of chromium after regeneration can still reach more than 99%, and the magnetic coagulant has good repeated regeneration performance and low production cost.)

1. A preparation method of a fly ash-based magnetic coagulant for treating chromium-containing wastewater is characterized by comprising the following steps:

(1) modifying the fly ash by using hydrochloric acid with the concentration of 1-3 mol/L to obtain modified fly ash;

(2) mixing the modified fly ash with Fe₃O₄And mixing to obtain the fly ash-based magnetic coagulant.

2. The preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 1, wherein the mass-to-volume ratio of fly ash to hydrochloric acid in the step (1) is 1-2 g: 2-3 mL.

3. The preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 1 or 2, wherein the modification temperature in the step (1) is 20-30 ℃ and the modification time is 60-75 min.

4. The method for preparing the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 3, wherein the modified fly ash and Fe in the step (2)₃O₄The mass ratio of (A) to (B) is 2-3: 1.

5. The method for preparing the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 1, 2 or 4, wherein Fe in the step (2)₃O₄The particle size of (A) is 20 to 30 nm.

6. The preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 1 or 4, characterized in that the step (1) further comprises screening and drying the fly ash before modification, wherein the particle size of the screened fly ash is less than 61 μm, the drying temperature is 100-110 ℃, and the drying time is 1-2 h.

7. The fly ash-based magnetic coagulant for treating chromium-containing wastewater, which is prepared by the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to any one of claims 1 to 6.

8. The use of the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 7, wherein the fly ash-based magnetic coagulant is used for treating Cr-containing wastewater⁶⁺Waste water;

wherein the pH value of the wastewater is 3-4, and Cr in the wastewater⁶⁺The initial concentration is 5-15 mg/L, and the mass volume ratio of the fly ash-based magnetic coagulant to the wastewater is 10-15 g: 100mL, and the treatment time is 30-50 min.

9. The method for regenerating the fly ash-based magnetic coagulant for treating chromium-containing wastewater according to claim 7, which comprises the following steps:

washing the fly ash-based magnetic coagulant treated with the chromium-containing wastewater with water for 3-5 times, drying at 100-110 ℃ for 1-2 h, desorbing and regenerating with 1-1.5 mol/L nitric acid at room temperature for 20-60 min, washing with water for 3-5 times, and drying at 100-110 ℃ for 1-2 h to obtain the regenerated fly ash-based magnetic coagulant.

Technical Field

The invention relates to the technical field of coagulants, in particular to a fly ash-based magnetic coagulant for treating chromium-containing wastewater, and a preparation method, application and a regeneration method thereof.

Background

A large amount of heavy metals can be discharged in the processes of heavy metal mining, waste gas emission and the like, and the heavy metals are different from other organic pollutants, are difficult to degrade in the environment and are easy to enrich in the body. For example, Cr⁶⁺Can cause damage to the respiratory system and internal organs of human beings, and is more likely to cause respiratory tract cancer. And Pb²⁺It has toxic effects on many human systems, leading to hypertension and nephritis. Therefore, the method has important social significance for treating the heavy metal wastewater.

China is a big country of coal-fired power generation, a large amount of fly ash is generated every year, and the fly ash is prepared into a magnetic coagulant by combining a new wastewater treatment technology-a magnetic coagulation technology, so that the fly ash can be efficiently and quickly precipitated into floccules, heavy metals can be separated and removed, high-value utilization of the fly ash can be realized, and the fly ash has a positive effect on environmental ecology. Meanwhile, the magnetic coagulant is desorbed and regenerated, so that the heavy metal wastewater can be efficiently treated, and the sewage treatment cost can be further reduced.

At present, the preparation process of the existing fly ash-based magnetic coagulant is generally complex, and the proportion of silicon, aluminum and iron needs to be strictly controlled, for example, patent 201810479670.4 discloses a polysilicate aluminum iron composite coagulant prepared from fly ash, which is calcined and activated at high temperature, then subjected to acid leaching and alkali leaching, and in the process, an iron source, an aluminum source and other additives are required to be supplemented to maintain the proportion of silicon, aluminum and iron, the steps are complex, and the number of additives is large, so that the production cost of the coagulant is high, but the turbidity removal effect of the coagulant is not ideal. For another example, patent 201711262823.1 provides an inorganic coagulant comprising steel slag and fly ash, which is sequentially acidified and alkalized, and supplemented with an aluminum source, but has not high effect on removing heavy metals in wastewater.

Therefore, a fly ash-based magnetic coagulant which is simple and easy to operate in a preparation method and good in heavy metal treatment effect is needed to be provided.

Disclosure of Invention

The invention aims to provide a fly ash-based magnetic coagulant for treating chromium-containing wastewater, a preparation method, application and a regeneration method thereof, and solves the problems of complex preparation method, poor heavy metal wastewater treatment effect and poor recycling performance of the fly ash-based magnetic coagulant provided by the prior art.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of a fly ash-based magnetic coagulant for treating chromium-containing wastewater, which comprises the following steps:

(1) modifying the fly ash by using hydrochloric acid with the concentration of 1-3 mol/L to obtain modified fly ash;

(2) mixing the modified fly ash with Fe₃O₄And mixing to obtain the fly ash-based magnetic coagulant.

Preferably, in the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, in the step (1), the mass-to-volume ratio of fly ash to hydrochloric acid is 1-2 g: 2-3 mL.

Preferably, in the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, the modification temperature in the step (1) is 20-30 ℃ and the time is 60-75 min.

Preferably, in the above preparation method of fly ash-based magnetic coagulant for treating chromium-containing wastewater, the fly ash and Fe are modified in the step (2)₃O₄The mass ratio of (A) to (B) is 2-3: 1.

Preferably, in the above method for preparing a fly ash-based magnetic coagulant for treating chromium-containing wastewater, in the step (2), Fe is added₃O₄The particle size of (A) is 20 to 30 nm.

Preferably, in the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, the step (1) further comprises screening and drying the fly ash before modification, wherein the particle size of the screened fly ash is less than 61 μm, the drying temperature is 100-110 ℃, and the drying time is 1-2 hours.

The invention also provides a fly ash-based magnetic coagulant for treating chromium-containing wastewater, which is prepared by the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater.

The invention also provides an application of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, and the fly ash-based magnetic coagulant is used for treating Cr-containing wastewater⁶⁺Waste water;

wherein the pH value of the wastewater is 3-4, and Cr in the wastewater⁶⁺The initial concentration is 5-15 mg/L, and the mass volume ratio of the fly ash-based magnetic coagulant to the wastewater is 10-15 g: 100mL, and the treatment time is 30-50 min.

The invention also provides a regeneration method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, which comprises the following steps:

washing the fly ash-based magnetic coagulant treated with the chromium-containing wastewater with water for 3-5 times, drying at 100-110 ℃ for 1-2 h, desorbing and regenerating with 1-1.5 mol/L nitric acid at room temperature for 20-60 min, washing with water for 3-5 times, and drying at 100-110 ℃ for 1-2 h to obtain the regenerated fly ash-based magnetic coagulant.

Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:

according to the invention, the hydrochloric acid is used for modifying the fly ash, so that the surface of the fly ash becomes rougher, the specific surface area of the fly ash is increased, and the adsorption effect of the fly ash on heavy metals in wastewater is improved. The modification of the fly ash can be realized by using a small amount of hydrochloric acid with low concentration, the prepared magnetic coagulant can remove suspended matters and pollutants in sewage and reduce turbidity, and simultaneously can realize good adsorption effect on heavy metal chromium ions, the removal rate of chromium after regeneration can still reach more than 99%, the magnetic coagulant has good repeated regeneration performance and low production cost.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is an XRD representation diagram of chromium-containing wastewater treated by the fly ash-based magnetic coagulant in example 1;

figure 2 is an XRD characterization of the modified fly ash of example 1 and comparative example 5.

Detailed Description

The invention provides a preparation method of a fly ash-based magnetic coagulant for treating chromium-containing wastewater, which comprises the following steps:

(1) modifying the fly ash by using hydrochloric acid to obtain modified fly ash;

(2) mixing the modified fly ash with Fe₃O₄And mixing to obtain the fly ash-based magnetic coagulant.

In the invention, the mass-to-volume ratio of the fly ash to the hydrochloric acid in the step (1) is preferably 1-2 g: 2-3 mL; more preferably 1 to 1.8 g: 2.3-3 mL; more preferably 1 g: 3 mL.

In the invention, the concentration of hydrochloric acid in the step (1) is preferably 1-3 mol/L; further preferably 1.6-2.7 mol/L; more preferably 2 mol/L.

In the invention, the modification temperature in the step (1) is preferably 20-30 ℃, and the time is preferably 60-75 min; further preferably, the modification temperature is 22-29 ℃, and the time is 63-72 min; more preferably, the modification temperature is 25 ℃ and the modification time is 65 min.

In the invention, the step (1) also comprises screening and drying the fly ash before modification; wherein the particle size of the screened fly ash is less than 61 mu m; the drying temperature is preferably 100-110 ℃, more preferably 110 ℃, and the drying time is preferably 1-2 h, more preferably 1 h.

In the invention, the step (1) also comprises the steps of washing, drying and refining the modified fly ash after modification; wherein, the washing is preferably 3 to 6 times by water, and more preferably 5 times by water; the drying temperature is preferably 100-110 ℃, the drying time is preferably 1-2 h, and the drying time is preferably 2 h; the refining method is preferably grinding, and the particle size is less than 30 μm after grinding.

In the invention, the fly ash and Fe are modified in the step (2)₃O₄The mass ratio of (A) to (B) is preferably 2-3: 1; further preferably 2: 1.

In the present invention, Fe in step (2)₃O₄The particle size of (A) is preferably 20-30 nm; more preferably 20 nm.

The invention also provides a fly ash-based magnetic coagulant for treating chromium-containing wastewater, which is prepared by the preparation method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater.

The invention also provides an application of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, and the fly ash-based magnetic coagulant is used for treating Cr-containing wastewater⁶⁺Waste water;

wherein the pH value of the wastewater is 3-4, and Cr in the wastewater⁶⁺The initial concentration is preferably 5-15 mg/L, and more preferably 15 mg/L; the mass volume ratio of the fly ash-based magnetic coagulant to the wastewater is preferably 10-15 g: 100mL, more preferably 10: 100 mL; the treatment time is preferably 30 to 50min, and more preferably 40 min.

The invention also provides a regeneration method of the fly ash-based magnetic coagulant for treating chromium-containing wastewater, which comprises the following steps:

washing the fly ash-based magnetic coagulant treated with the chromium-containing wastewater for 3-5 times by using water, drying for 1-2 h at 100-110 ℃, then performing desorption regeneration by using nitric acid at room temperature, washing for 3-5 times by using water, and drying for 1-2 h at 100-110 ℃ to obtain the regenerated fly ash-based magnetic coagulant.

In the invention, the concentration of the nitric acid is preferably 1-1.5 mol/L; further preferably 1 mol/L.

In the invention, the mass-to-volume ratio of the fly ash-based magnetic coagulant to the nitric acid after the treatment of the chromium-containing wastewater is 0.5-3 g: 10-40 mL; more preferably 0.8 to 2 g: 20-35 mL; more preferably 1 g: 30 mL.

In the invention, the desorption regeneration time is preferably 20-60 min; further preferably 24-55 min; more preferably 30 min.

In the invention, the dried regenerated fly ash-based magnetic coagulant is subjected to refining treatment, wherein the refining treatment is preferably grinding, and the grain diameter after grinding is less than 30 μm.

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The embodiment provides a fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

(1) screening the fly ash by using a 240-mesh screen, and drying the undersize product at 110 ℃ for 1h to obtain dry fly ash;

(2) stirring 20g of dried fly ash and 60mL of 2mol/L hydrochloric acid at 25 ℃ for modification for 65min, performing suction filtration after modification, washing the product with water for 5 times, placing the product in an oven for drying at 100 ℃ for 2h, and grinding the product until the particle size is less than 30 microns to obtain modified fly ash;

(3) mixing the modified fly ash with Fe₃O₄Mixing according to the mass ratio of 2:1 to obtain the fly ash-based magnetic coagulant.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺The heavy metal wastewater treatment method comprises the following steps:

the volume of the heavy metal wastewater is 200mL, wherein the volume of Cr⁶⁺The initial concentration is 15mg/L, and the mass-volume ratio of the fly ash-based magnetic coagulant to the heavy metal wastewater is 10 g: 100 mL. Adjusting the pH value of the heavy metal wastewater to 3, adding a fly ash-based magnetic coagulant, oscillating for 40min, measuring by using a pervaporation TU-1901 double-beam ultraviolet spectrophotometer, and treating Cr in the heavy metal wastewater⁶⁺The concentration is 0.048mg/L, and the removal rate is 99.68%.

The mechanism of the fly ash-based magnetic coagulant for treating chromium-containing wastewater is as follows: cr in wastewater⁶⁺Is mainly Cr₂O₇ ^2-Is more easily reduced to Cr under acidic conditions³⁺Magnetic powder Fe₃O₄The reduced substance Fe contained in the alloy²⁺And Cr₂O₇ ^2-The following reaction was carried out:

6H⁺+Cr₂O₇ ^2-+6Fe²⁺→Cr₂O₄ ^2-+6Fe³⁺+3H₂O

produced Cr₂O₄ ^2-With an excess of Fe²⁺Combined to form FeCr with weak magnetism₂O₄Then precipitating with magnetic coagulant through adsorption bridging to realize Cr⁶⁺And (4) removing. In the invention, fly ash-based magnetic coagulant is used for treating Cr⁶⁺Not only has physical adsorption, but also has chemical adsorption.

The above treatment contains Cr⁶⁺XRD characterization is carried out on the fly ash-based magnetic coagulant of the heavy metal wastewater, and the result is shown in figure 1. As can be seen from figure 1, the fly ash-based magnetic coagulant adsorbs Cr⁶⁺After ionization, FeCr appears in XRD spectrogram₂O₄Characteristic peak of (C is FeCr)₂O₄Characteristic peak) indicating Cr in wastewater⁶⁺Ion transport by FeCr₂O₄The form of the chromium is precipitated through the adsorption and bridging effects, and the Cr is realized⁶⁺And (4) removing.

Example 2

The embodiment provides a fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

(1) screening the fly ash by using a 240-mesh screen, and drying the undersize product at 100 ℃ for 1.2h to obtain dry fly ash;

(2) stirring 20g of dried fly ash and 20mL of 3mol/L hydrochloric acid at 26 ℃ for modification for 61min, performing suction filtration after modification, washing the product with water for 3 times, drying the product in an oven at 106 ℃ for 2h, and grinding the product until the particle size is less than 30 microns to obtain modified fly ash;

(3) mixing the modified fly ash with Fe₃O₄Mixing according to the mass ratio of 2.3:1 to obtain the fly ash-based magnetic coagulant.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺The heavy metal wastewater treatment method comprises the following steps:

the volume of the heavy metal wastewater is 200mL, wherein the volume of Cr⁶⁺The initial concentration is 10mg/L, and the mass-volume ratio of the fly ash-based magnetic coagulant to the heavy metal wastewater is 12 g: 100 mL. Adjusting the pH value of the heavy metal wastewater to 3, adding a fly ash-based magnetic coagulant, oscillating for 35min, and measuring by using a pervaporation TU-1901 double-beam ultraviolet spectrophotometerCr in treated heavy metal wastewater⁶⁺The concentration is 0.041mg/L, and the removal rate is 99.59 percent.

Example 3

The embodiment provides a fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

(1) screening the fly ash by using a 240-mesh screen, and drying the undersize product at 102 ℃ for 1.5h to obtain dry fly ash;

(2) stirring 20g of dry fly ash and 30mL1.4mol/L hydrochloric acid at 28 ℃ for modification for 69min, performing suction filtration after modification, washing the product with water for 4 times, drying the product in an oven at 110 ℃ for 1h, and grinding the product until the particle size is less than 30 mu m to obtain modified fly ash;

(3) mixing the modified fly ash with Fe₃O₄Mixing according to the mass ratio of 2.5:1 to obtain the fly ash-based magnetic coagulant.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺The heavy metal wastewater treatment method comprises the following steps:

the volume of the heavy metal wastewater is 100mL, wherein the volume of Cr⁶⁺The initial concentration is 5mg/L, and the mass-volume ratio of the fly ash-based magnetic coagulant to the heavy metal wastewater is 15 g: 100 mL. Adjusting the pH value of the heavy metal wastewater to 4, adding a fly ash-based magnetic coagulant, oscillating for 30min, measuring by using a pervaporation TU-1901 double-beam ultraviolet spectrophotometer, and treating Cr in the heavy metal wastewater⁶⁺The concentration is 0.023mg/L, and the removal rate is 99.53 percent.

Example 4

The embodiment provides a regenerated fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

20g of the fly ash-based magnetic coagulant obtained after chromium-containing wastewater treatment in the embodiment 1 is washed by water for 4 times, is placed in an oven to be dried for 1h at 110 ℃, is stirred and desorbed at room temperature by using 600mL of 1mol/L nitric acid for regeneration for 30min, is washed by water for 3 times, is placed in the oven to be dried for 1h at 110 ℃, and is ground until the particle size is less than 30 mu m, so that the regenerated fly ash-based magnetic coagulant is obtained.

Use of the regenerated fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Heavy metal wastewater treatment method, refer to implementationExample 1 Cr in treated heavy Metal wastewater⁶⁺The concentration was 0.059mg/L and the removal rate was 99.61%.

Example 5

The embodiment provides a regenerated fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

30g of the fly ash-based magnetic coagulant obtained after chromium-containing wastewater treatment in the embodiment 2 is washed with water for 4 times, is placed in an oven to be dried at 100 ℃ for 1.5h, is stirred and desorbed at room temperature by using 400mL1.3mol/L nitric acid for regeneration for 50min, is washed with water for 4 times, is placed in the oven to be dried at 110 ℃ for 1h, and is ground until the particle size is less than 30 mu m, so that the regenerated fly ash-based magnetic coagulant is obtained.

Use of the regenerated fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 2, Cr in treated heavy metal wastewater⁶⁺The concentration is 0.066mg/L, and the removal rate is 99.34%.

Example 6

The embodiment provides a regenerated fly ash-based magnetic coagulant, and a preparation method thereof comprises the following steps:

20g of the fly ash-based magnetic coagulant obtained after chromium-containing wastewater treatment in the embodiment 3 is washed with water for 4 times, is dried in an oven at 110 ℃ for 2 hours, is stirred and desorbed at room temperature by using 400mL1.5mol/L nitric acid for regeneration for 60 minutes, is washed with water for 3 times, is dried in an oven at 107 ℃ for 1.8 hours, and is ground until the particle size is less than 30 mu m, so that the regenerated fly ash-based magnetic coagulant is obtained.

Use of the regenerated fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 3, Cr in treated heavy metal wastewater⁶⁺The concentration was 0.04mg/L, and the removal rate was 99.2%.

Comparative example 1

The present comparative example provides a fly ash-based magnetic coagulant, the preparation method of which is described in example 1, except that the fly ash is not subjected to hydrochloric acid modification treatment.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 1, in treated heavy metal wastewaterCr⁶⁺The concentration was 1.107mg/L, and the removal rate was 92.62%.

The fly ash-based magnetic coagulant after the treatment of the chromium-containing wastewater is regenerated according to the method of the embodiment 4, and the regenerated fly ash-based magnetic coagulant is treated according to the method of the embodiment 1 to contain Cr⁶⁺Heavy metal wastewater, Cr in treated heavy metal wastewater⁶⁺The concentration was 1.458mg/L, and the removal rate was 90.28%.

Comparative example 2

This comparative example provides a fly ash-based magnetic coagulant, the preparation method of which is described in example 1, except that Fe₃O₄Replacement by gamma-Fe₂O₃。

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 1, Cr in treated heavy metal wastewater⁶⁺The concentration was 3.64mg/L, and the removal rate was 75.73%.

The fly ash-based magnetic coagulant after the treatment of the chromium-containing wastewater is regenerated according to the method of the embodiment 4, and the regenerated fly ash-based magnetic coagulant is treated according to the method of the embodiment 1 to contain Cr⁶⁺Heavy metal wastewater, Cr in treated heavy metal wastewater⁶⁺The concentration is 4.229mg/L, and the removal rate is 71.81%.

Due to gamma-Fe₂O₃Color in the presence of Cr in a spectrophotometer⁶⁺The measurement has an influence on the result, and gamma-Fe₂O₃For Cr⁶⁺The removal of (A) is physical adsorption mainly based on electrostatic action, Fe₃O₄For Cr⁶⁺Not only has physical adsorption, but also has more important chemical adsorption.

Comparative example 3

The present comparative example provides a fly ash-based magnetic coagulant, the preparation method of which is described in example 1.

The fly ash-based magnetic coagulant is used for treating Pb-containing²⁺Heavy metal wastewater treatment method, see example 1, except that Cr-containing wastewater of example 1 is treated⁶⁺Replacement of heavy metal wastewater with Pb-containing wastewater²⁺Heavy metal wastewater, Pb in treated heavy metal wastewater^{2 +}At a concentration of2.327mg/L, the removal rate is 84.49%.

The fly ash-based magnetic coagulant after the lead-containing wastewater treatment is regenerated according to the method of the embodiment 4, and the regenerated fly ash-based magnetic coagulant is used for treating Pb-containing wastewater according to the method of the embodiment 1²⁺Heavy metal wastewater, Pb in treated heavy metal wastewater²⁺The concentration is 2.869mg/L, and the removal rate is 80.87%.

Comparative example 4

The present comparative example provides a fly ash-based magnetic coagulant, the preparation method of which is described in example 2, except that the hydrochloric acid concentration is 10 mol/L.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 2, Cr in treated heavy metal wastewater⁶⁺The concentration was 1.858mg/L, and the removal rate was 81.42%.

The fly ash-based magnetic coagulant after the treatment of the chromium-containing wastewater is regenerated according to the method of the embodiment 5, and the regenerated fly ash-based magnetic coagulant is treated according to the method of the embodiment 2 to contain Cr⁶⁺Heavy metal wastewater, Cr in treated heavy metal wastewater⁶⁺The concentration was 2.162mg/L, and the removal rate was 78.38%.

Comparative example 5

The present comparative example provides a fly ash-based magnetic coagulant, the preparation method of which is described in example 1, except that hydrochloric acid is replaced by sodium hydroxide.

Use of said fly ash-based magnetic coagulant to treat Cr-containing⁶⁺Method for treating heavy metal wastewater, see example 1, Cr in treated heavy metal wastewater⁶⁺The concentration was 2.397mg/L, and the removal rate was 84.02%.

The fly ash-based magnetic coagulant after the treatment of the chromium-containing wastewater is regenerated according to the method of the embodiment 4, and the regenerated fly ash-based magnetic coagulant is treated according to the method of the embodiment 1 to contain Cr⁶⁺Heavy metal wastewater, Cr in treated heavy metal wastewater⁶⁺The concentration is 2.665mg/L, and the removal rate is 82.23%.

XRD characterization is carried out on the sodium hydroxide modified fly ash and the hydrochloric acid modified fly ash in example 1, and the result is shown in figure 2. As can be seen from FIG. 2, the acidThe modification and the alkali modification do not change the material composition of the fly ash, but only change the structure of the fly ash, but the acid modification leads the fly ash to contain H⁺Ions, in the case of coagulant, of Cr⁶⁺Has an accelerating effect on reduction.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.