Humic acid / bentonite composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of water treatment, and discloses a humic acid / bentonite composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing humic acid, ferrous salt and water, and then adding sodium borohydride to carry out reduction reaction; and after the reduction reaction is finished, adding magnetic bentonite, oscillating at constant temperature, carrying out suction filtration, and carrying out vacuum drying to obtain the humic acid / bentonite composite material. According to the invention, the humic acid is used for loading the nano zero-valent iron, so that the dispersity of the nano zero-valent iron is improved, and the humic acid also has an adsorption effect on chromium. The magnetic bentonite is subjected to microwave modification and has a relatively high specific surface area, while hexavalent chromium is adsorbed, trivalent chromium obtained by reducing nano zero-valent iron can be adsorbed among montmorillonite layers through a chemical adsorption effect, and the chemical adsorption effect is stable. The hexavalent chromium in the wastewater can be effectively removed through the dual effects of chemical reduction and adsorption.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a humic acid / bentonite composite material and a preparation method and application thereof. Background Art

[0002] Heavy metal wastewater refers to wastewater containing heavy metals discharged from industrial production processes such as mining, machinery manufacturing, chemical industry, electronics, and instrumentation. The heavy metals in heavy metal wastewater generally cannot be decomposed and destroyed, but can only be transferred to other locations and their physical and chemical forms. Among heavy metal wastewater, chromium-containing wastewater is a common type of heavy metal wastewater. Chromium pollution mainly comes from industrial activities such as leather making, electroplating, metal processing, and pigment manufacturing. Chromium mainly exists in trivalent and hexavalent forms in water, among which hexavalent chromium is the most toxic.

[0003] The existing treatment methods for chromium-containing wastewater mainly include chemical reduction, electrolysis, ion exchange, adsorption, etc. Among them, the chemical reduction method usually uses a reducing agent, has high requirements on the pH value of the wastewater, and has harsh reaction conditions; the electrolysis method consumes a large amount of anode and also produces a large amount of sludge, and the utilization value of the sludge is low; the ion exchange method has a high cost, and it has the disadvantage of limited adsorption capacity like the adsorption method. For example, patent CN105753237A discloses a method for treating chromium-containing wastewater, which adds alkali to the chromium-containing wastewater to adjust the pH to 12, then adds ferrous sulfate with 16 times the chromium content, and finally separates the precipitate. In this method, the amount of reducing agent used is large, and the utilization value of the sludge precipitate obtained in the end is small.

[0004] Therefore, how to treat chromium-containing wastewater efficiently and at low cost plays an important role in water pollution control. Summary of the invention

[0005] The object of the present invention is to provide a humic acid / bentonite composite material and a preparation method and application thereof, so as to solve the problems of high cost, large sludge output, limited adsorption capacity of adsorbent and the like in the existing chromium-containing wastewater treatment method.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a humic acid / bentonite composite material, comprising the following steps:

[0008] The humic acid, ferrous salt and water are mixed, and then sodium borohydride is added to carry out a reduction reaction; after the reduction reaction is completed, magnetic bentonite is added, and after constant temperature shaking, the mixture is filtered and vacuum dried to obtain a humic acid / bentonite composite material;

[0009] The preparation method of the magnetic bentonite comprises the following steps: modifying the bentonite by microwave irradiation to obtain modified bentonite; mixing the modified bentonite, ferrous sulfate heptahydrate and water, and then adding sodium hydroxide solution and potassium nitrate solution thereto for reaction, and obtaining the magnetic bentonite after the reaction is completed.

[0010] Preferably, in the above method for preparing a humic acid / bentonite composite material, the humic acid is weathered coal humic acid; and the ferrous salt is ferrous sulfate heptahydrate.

[0011] Preferably, in the above-mentioned method for preparing a humic acid / bentonite composite material, the usage ratio of humic acid, ferrous salt, sodium borohydride and magnetic bentonite is 10-50g: 1-3mol: 3-10mol: 5-60g.

[0012] Preferably, in the above-mentioned method for preparing a humic acid / bentonite composite material, the temperature of the reduction reaction is 10 to 30° C.; and the time of the reduction reaction is 10 to 120 min.

[0013] Preferably, in the above-mentioned method for preparing a humic acid / bentonite composite material, the power of the microwave irradiation is 1 to 3 kW; and the time of the microwave irradiation is 10 to 50 min.

[0014] Preferably, in the above-mentioned method for preparing a humic acid / bentonite composite material, the usage ratio of the modified bentonite, ferrous sulfate heptahydrate, sodium hydroxide in the sodium hydroxide solution, and potassium nitrate in the potassium nitrate solution is 1-10 g: 0.1-1 g: 0.01-0.1 mol: 0.01-0.05 mol.

[0015] Preferably, in the above-mentioned method for preparing a humic acid / bentonite composite material, the reaction temperature is 50-70° C.; and the reaction time is 1-3 hours.

[0016] The invention also provides a humic acid / bentonite composite material prepared by a preparation method of the humic acid / bentonite composite material.

[0017] The present invention also provides a humic acid / bentonite composite material prepared by a preparation method of the humic acid / bentonite composite material or an application of the humic acid / bentonite composite material in treating wastewater containing Cr(VI).

[0018] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention uses humic acid to load nano zero-valent iron, and then combines it with magnetic bentonite to effectively remove hexavalent chromium from wastewater through the dual effects of chemical reduction and adsorption. On the one hand, the loading of humic acid improves the dispersibility of nano zero-valent iron, so that nano zero-valent iron can reduce hexavalent chromium more effectively. Humic acid also has a good adsorption effect on hexavalent chromium, further improving the removal rate of hexavalent chromium in wastewater; on the other hand, the magnetic bentonite is modified by microwaves and has a higher specific surface area. While physically adsorbing hexavalent chromium, it can also adsorb the trivalent chromium obtained by reducing nano zero-valent iron in the interlayer of montmorillonite through chemical adsorption. The chemical adsorption is stable, and magnetism is used for solid-liquid separation, which solves the problem that the conventional magnetic coagulant and the trivalent chromium adsorption are unstable, making it difficult to completely separate the trivalent chromium in wastewater.

[0020] (2) The humic acid / bentonite composite material of the present invention has mild preparation conditions, a simple preparation process, uses low-cost raw materials, has no secondary pollution to water bodies, and has broad application prospects. DETAILED DESCRIPTION

[0021] The present invention provides a method for preparing a humic acid / bentonite composite material, comprising the following steps:

[0022] The humic acid, ferrous salt and water are mixed, and then sodium borohydride is added to carry out a reduction reaction; after the reduction reaction is completed, magnetic bentonite is added, and after constant temperature shaking, the mixture is filtered and vacuum dried to obtain a humic acid / bentonite composite material;

[0023] The preparation method of the magnetic bentonite comprises the following steps: modifying the bentonite by microwave irradiation to obtain modified bentonite; mixing the modified bentonite, ferrous sulfate heptahydrate and water, and then adding sodium hydroxide solution and potassium nitrate solution thereto for reaction, and obtaining the magnetic bentonite after the reaction is completed.

[0024] In the present invention, the humic acid is preferably weathered coal humic acid.

[0025] In the present invention, the humic acid also includes pretreatment before use; the method of the pretreatment is preferably: humic acid and sodium hydroxide solution with a pH of 11 are stirred and mixed at a ratio of 1g:20mL for 2h, the lower layer insoluble matter is filtered to remove, 5mol / L hydrochloric acid solution is added to the upper layer solution until the system pH is 2, and then the solution is allowed to stand to produce precipitation, and the precipitation is washed with water and dried in turn. The humic acid used in the embodiments of the present invention has been pretreated as described above.

[0026] In the present invention, the ferrous salt is preferably ferrous sulfate heptahydrate.

[0027] In the present invention, the bentonite is preferably sodium bentonite.

[0028] In the present invention, the usage ratio of humic acid, ferrous salt, sodium borohydride and magnetic bentonite is preferably 10-50g:1-3mol:3-10mol:5-60g, more preferably 15-40g:2-3mol:5-8mol:20-50g, and more preferably 30g:3mol:7mol:40g.

[0029] In the present invention, the mass ratio of humic acid to water is preferably 10-50 g:100-300 g, more preferably 20-40 g:100-200 g, and even more preferably 30 g:100 g.

[0030] In the present invention, the temperature of the reduction reaction is preferably 10-30°C, more preferably 15-25°C, and more preferably 20°C; the time of the reduction reaction is preferably 10-120 min, more preferably 40-80 min, and more preferably 50 min.

[0031] In the present invention, the reduction reaction is carried out under a protective atmosphere; the protective atmosphere is preferably nitrogen.

[0032] In the present invention, the temperature of the constant temperature oscillation is preferably 30-50°C, more preferably 35-45°C, and more preferably 40°C; the time of the constant temperature oscillation is preferably 1-5h, more preferably 2-5h, and more preferably 3h.

[0033] In the present invention, the constant temperature oscillation is carried out under a protective atmosphere; the protective atmosphere is preferably nitrogen.

[0034] In the present invention, the vacuum drying temperature is preferably 70-90°C, more preferably 85-90°C, and more preferably 90°C; the vacuum drying time is preferably 6-12h, more preferably 8-12h, and more preferably 10h.

[0035] In the present invention, the power of the microwave irradiation is preferably 1-3 kw, more preferably 2-3 kw, and more preferably 3 kw; the time of the microwave irradiation is preferably 10-50 min, more preferably 20-40 min, and more preferably 30 min.

[0036] In the present invention, the usage ratio of the modified bentonite, ferrous sulfate heptahydrate, sodium hydroxide in the sodium hydroxide solution, and potassium nitrate in the potassium nitrate solution is preferably 1-10 g: 0.1-1 g: 0.01-0.1 mol: 0.01-0.05 mol, more preferably 3-9 g: 0.2-0.8 g: 0.02-0.08 mol: 0.01-0.03 mol, and more preferably 7 g: 0.5 g: 0.06 mol: 0.02 mol.

[0037] In the present invention, the mass ratio of the modified bentonite to water is preferably 1-10 g:50-200 g, more preferably 2-7 g:50-100 g, and even more preferably 5 g:70 g.

[0038] In the present invention, the concentration of the sodium hydroxide solution is preferably 5 to 8 mol / L, more preferably 5 to 7 mol / L, and more preferably 5 mol / L.

[0039] In the present invention, the concentration of the potassium nitrate solution is preferably 2 to 5 mol / L, more preferably 2 to 3 mol / L, and more preferably 2 mol / L.

[0040] In the present invention, the reaction temperature is preferably 50-70°C, more preferably 55-70°C, more preferably 60°C; the reaction time is preferably 1-3h, more preferably 2-3h, more preferably 2h.

[0041] The invention also provides a humic acid / bentonite composite material prepared by a preparation method of the humic acid / bentonite composite material.

[0042] The present invention also provides a humic acid / bentonite composite material prepared by a preparation method of the humic acid / bentonite composite material or an application of the humic acid / bentonite composite material in treating wastewater containing Cr(VI).

[0043] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0044] Example 1

[0045] This embodiment provides a humic acid / bentonite composite material, and the preparation method thereof comprises the following steps:

[0046] The sodium-based bentonite is modified by microwave irradiation at a power of 1 kW for 20 minutes to obtain modified bentonite; the modified bentonite, ferrous sulfate heptahydrate and water are stirred and mixed evenly in a mass ratio of 7g:0.4g:100g, and then a 6 mol / L sodium hydroxide solution and a 2 mol / L potassium nitrate solution are added thereto so that the ratio of the modified bentonite, sodium hydroxide and potassium nitrate is 7g:0.06mol:0.03mol, and the mixture is reacted at a temperature of 60°C for 3 hours. After the reaction is completed, the mixture is filtered and dried to obtain magnetic bentonite;

[0047] Weathered coal humic acid, ferrous sulfate heptahydrate and water were stirred and mixed in a dosage ratio of 40g:2.5mol:150g, and then sodium borohydride was added to make the molar ratio of ferrous sulfate heptahydrate and sodium borohydride 2.5mol:7mol, and reduction reaction was carried out at 20°C in a nitrogen atmosphere for 60min; after the reduction reaction, magnetic bentonite was added to make the dosage ratio of weathered coal humic acid and magnetic bentonite 40g:30g, and the mixture was shaken at a constant temperature of 40°C for 2h in a nitrogen atmosphere, and then filtered and vacuum dried at 90°C for 8h to obtain a humic acid / bentonite composite material.

[0048] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 0.027mg / L, and the removal rate is 99.91%.

[0049] Example 2

[0050] This embodiment provides a humic acid / bentonite composite material, and the preparation method thereof comprises the following steps:

[0051] The sodium-based bentonite is modified by microwave irradiation with a power of 2 kW for 15 minutes to obtain modified bentonite; the modified bentonite, ferrous sulfate heptahydrate and water are stirred and mixed evenly in a mass ratio of 3g:0.6g:50g, and then 5 mol / L sodium hydroxide solution and 2 mol / L potassium nitrate solution are added thereto so that the ratio of the modified bentonite, sodium hydroxide and potassium nitrate is 3g:0.02mol:0.01mol, and the mixture is reacted at a temperature of 50°C for 2 hours. After the reaction is completed, the mixture is filtered and dried to obtain magnetic bentonite;

[0052] Weathered coal humic acid, ferrous sulfate heptahydrate and water were stirred and mixed evenly in a dosage ratio of 30g:2mol:100g, and then sodium borohydride was added so that the molar ratio of ferrous sulfate heptahydrate and sodium borohydride was 2mol:3mol, and reduction reaction was carried out at 30°C for 40min under a nitrogen atmosphere; after the reduction reaction, magnetic bentonite was added so that the dosage ratio of weathered coal humic acid and magnetic bentonite was 30g:40g, and the mixture was shaken at a constant temperature of 30°C for 3h under a nitrogen atmosphere, and then filtered and vacuum dried at 70°C for 8h to obtain a humic acid / bentonite composite material.

[0053] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 0.041mg / L, and the removal rate is 99.86%.

[0054] Example 3

[0055] This embodiment provides a humic acid / bentonite composite material, and the preparation method thereof comprises the following steps:

[0056] The sodium-based bentonite is modified by microwave irradiation at a power of 2 kW for 20 minutes to obtain modified bentonite; the modified bentonite, ferrous sulfate heptahydrate and water are stirred and mixed evenly at a mass ratio of 5g:0.1g:100g, and then 5mol / L sodium hydroxide solution and 2mol / L potassium nitrate solution are added thereto so that the ratio of the modified bentonite, sodium hydroxide and potassium nitrate is 5g:0.07mol:0.02mol, and the mixture is reacted at a temperature of 70°C for 1 hour. After the reaction is completed, the mixture is filtered and dried to obtain magnetic bentonite;

[0057] The weathered coal humic acid, ferrous sulfate heptahydrate and water were stirred and mixed evenly in a dosage ratio of 20g:1mol:100g, and then sodium borohydride was added so that the molar ratio of ferrous sulfate heptahydrate and sodium borohydride was 1mol:5mol, and the reduction reaction was carried out at 30°C in a nitrogen atmosphere for 80min; after the reduction reaction, magnetic bentonite was added so that the dosage ratio of weathered coal humic acid and magnetic bentonite was 20g:50g, and the mixture was shaken at a constant temperature of 30°C for 4h in a nitrogen atmosphere, and then filtered and vacuum dried at 70°C for 10h to obtain a humic acid / bentonite composite material.

[0058] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 0.056mg / L, and the removal rate is 99.81%.

[0059] Example 4

[0060] This embodiment provides a humic acid / bentonite composite material, and the preparation method thereof comprises the following steps:

[0061] The sodium-based bentonite is modified by microwave irradiation at a power of 1 kW for 50 minutes to obtain modified bentonite; the modified bentonite, ferrous sulfate heptahydrate and water are stirred and mixed evenly in a mass ratio of 10 g: 0.1 g: 200 g, and then 5 mol / L sodium hydroxide solution and 2 mol / L potassium nitrate solution are added thereto so that the ratio of the modified bentonite, sodium hydroxide and potassium nitrate is 10 g: 0.1 mol: 0.03 mol, and the mixture is reacted at a temperature of 70° C. for 3 hours. After the reaction is completed, the mixture is filtered and dried to obtain magnetic bentonite;

[0062] Weathered coal humic acid, ferrous sulfate heptahydrate and water were stirred and mixed evenly in a dosage ratio of 50g:3mol:200g, and then sodium borohydride was added so that the molar ratio of ferrous sulfate heptahydrate and sodium borohydride was 3mol:8mol, and reduction reaction was carried out at 10°C in a nitrogen atmosphere for 50min; after the reduction reaction, magnetic bentonite was added so that the dosage ratio of weathered coal humic acid and magnetic bentonite was 50g:30g, and the mixture was shaken at a constant temperature of 50°C for 3h in a nitrogen atmosphere, and then filtered and vacuum dried at 90°C for 6h to obtain a humic acid / bentonite composite material.

[0063] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 0.039mg / L, and the removal rate is 99.87%.

[0064] Comparative Example 1

[0065] This comparative example provides a humic acid / bentonite composite material, which is specifically referred to Example 1, except that the bentonite is not modified by microwave irradiation.

[0066] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 4.108mg / L, and the removal rate is 86.31%.

[0067] Comparative Example 2

[0068] The present comparative example provides a humic acid / bentonite composite material, see Example 1 for details, except that the bentonite does not contain nano zero-valent iron, and the corresponding preparation method is: weathered coal humic acid and water are stirred and evenly mixed in a dosage ratio of 40g:150g, magnetic bentonite is added so that the dosage ratio of weathered coal humic acid to magnetic bentonite is 40g:30g, and the mixture is shaken at a constant temperature of 40°C for 2h under a nitrogen atmosphere, and then filtered and vacuum dried at 90°C for 8h to obtain a humic acid / bentonite composite material.

[0069] The method for treating Cr(VI)-containing wastewater using the above humic acid / bentonite composite material is as follows: 2g of humic acid / bentonite composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 7.33mg / L, and the removal rate is 75.57%.

[0070] Comparative Example 3

[0071] This comparative example provides a humic acid composite material, which is specifically referred to in Example 1, except that no magnetic bentonite is added.

[0072] The method for treating Cr(VI)-containing wastewater using the above humic acid composite material is as follows: 2g of the humic acid composite material is added to 100mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30mg / L, and the reaction is carried out under oscillation conditions for 1h. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 6.763mg / L, and the removal rate is 77.46%.

[0073] Comparative Example 4

[0074] This comparative example provides a bentonite composite material, which is magnetic bentonite. The preparation method of the magnetic bentonite is specifically described in Example 1.

[0075] The method for treating Cr(VI)-containing wastewater using the bentonite composite material is as follows: 2 g of the bentonite composite material is added to 100 mL of Cr(VI)-containing wastewater with a pH of 5.5 and an initial Cr(VI) concentration of 30 mg / L, and the reaction is carried out under oscillation conditions for 1 hour. The residual Cr(VI) content in the wastewater is measured using an ultraviolet spectrophotometer, and the concentration of Cr(VI) after treatment is 10.214 mg / L, and the removal rate is 65.95%.

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a humic acid / bentonite composite material, characterized in that: The following steps are involved: The humic acid, ferrous salt and water are mixed, and then sodium borohydride is added to carry out a reduction reaction; after the reduction reaction is completed, magnetic bentonite is added, and after constant temperature shaking, the mixture is filtered and vacuum dried to obtain a humic acid / bentonite composite material; The preparation method of the magnetic bentonite comprises the following steps: modifying the bentonite by microwave irradiation to obtain modified bentonite; mixing the modified bentonite, ferrous sulfate heptahydrate and water, and then adding sodium hydroxide solution and potassium nitrate solution thereto for reaction, and obtaining the magnetic bentonite after the reaction is completed.

2. The method for preparing a humic acid / bentonite composite material according to claim 1, characterized in that: The humic acid is weathered coal humic acid; and the ferrous salt is ferrous sulfate heptahydrate.

3. The method for preparing a humic acid / bentonite composite material according to claim 1, characterized in that: The usage ratio of humic acid, ferrous salt, sodium borohydride and magnetic bentonite is 10-50g: 1-3mol: 3-10mol: 5-60g.

4. The method for preparing a humic acid / bentonite composite material according to claim 3, characterized in that: The temperature of the reduction reaction is 10-30° C.; the time of the reduction reaction is 10-120 min.

5. The method for preparing a humic acid / bentonite composite material according to claim 1 or 4, characterized in that: The power of the microwave irradiation is 1-3kw; the time of the microwave irradiation is 10-50min.

6. The method for preparing a humic acid / bentonite composite material according to claim 5, characterized in that: The usage ratio of the modified bentonite, ferrous sulfate heptahydrate, sodium hydroxide in the sodium hydroxide solution, and potassium nitrate in the potassium nitrate solution is 1-10g: 0.1-1g: 0.01-0.1mol: 0.01-0.05mol.

7. The method for preparing a humic acid / bentonite composite material according to claim 6, characterized in that: The reaction temperature is 50-70° C.; the reaction time is 1-3 hours.

8. A humic acid / bentonite composite material obtained by the method for preparing a humic acid / bentonite composite material according to any one of claims 1 to 7.

9. Use of a humic acid / bentonite composite material obtained by the preparation method of a humic acid / bentonite composite material according to any one of claims 1 to 7 or a humic acid / bentonite composite material according to claim 8 in treating wastewater containing Cr(VI).