Red mud-based magnetic defluorination agent, its preparation method and application

Abstract

The present invention relates to the field of water treatment, and discloses a red mud-based magnetic defluorination agent, a preparation method thereof and an application. The method comprises the following steps: (1) mixing red mud with coke and then roasting, and then leaching the roasted product in a sulfuric acid solution; (2) adjusting the pH value of the material obtained in step (1) to 5-7, then aging, and then drying and grinding the aged material. This method can successfully utilize red mud to prepare a defluorination agent, reduce the preparation cost of the defluorination agent, and the prepared defluorination agent has high defluorination efficiency, the preparation method is simple, and it has great industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and particularly to a red mud-based magnetic defluorination agent, a preparation method thereof and an application thereof. Background Art

[0002] Fluorine is an essential trace element for the human body. However, once excessive fluorine is ingested, it will endanger human health. If high-fluoride water is consumed for a long time, it will not only cause fluorosis symptoms such as dental fluorosis and skeletal fluorosis, but also damage the thyroid function of the human body and reduce the intelligence of children. The World Health Organization (WHO) stipulates that the mass concentration limit of fluoride ions in drinking water is 1.5 mg / L, and the hygienic standard for domestic drinking water in China stipulates that the mass concentration limit of fluoride ions in drinking water is 1.0 mg / L. In recent decades, the technology for removing fluorine from water bodies has been attracting much attention. Developing a high-efficiency and low-cost fluorine pollution treatment material and technology has great social, economic and environmental benefits.

[0003] Currently, the main technologies for treating fluoride-containing wastewater include coagulation sedimentation method, ion exchange method, membrane separation, electrochemistry method and adsorption method, etc. The coagulation sedimentation method and the adsorption method are widely used in the treatment of fluoride-containing wastewater due to their simple operation, stable effect, economic feasibility, etc. Currently, the coagulation sedimentation method mostly utilizes the adsorption of fluoride by aluminum hydroxide alternately generated by the hydrolysis of soluble aluminum salts, or the fluoride ions replace the hydroxyl groups in the aluminum hydroxy compounds to generate fluoroaluminum hydroxy compounds for removal. However, the capture ability of aluminum salts for fluoride is very limited, and often an excessive amount of aluminum salts needs to be added to achieve an ideal defluorination effect. At the same time, this also causes a significant increase in the concentration of aluminum ions or complex anions in the treated water. At the same time, due to the small specific gravity of the generated flocs, the sedimentation time of the treated flocs is long and the defluorination effect is poor. Currently, developing a defluorination material with high-efficiency defluorination, low metal ion residue, easy sedimentation, low cost and suitable for low-concentration fluoride-containing water is an urgent problem to be solved in this field.

[0004] Red mud is a solid industrial waste discharged during the production process of alumina. Due to its high alkalinity and large output, a large amount of stacking causes serious pollution to the surrounding water bodies, soil, atmosphere, etc. Red mud contains a large amount of elements such as iron, aluminum, silicon and calcium. If red mud is utilized, it can not only realize the recycling of waste resources of red mud, but also provide a new type of cheap treatment material for the field of fluoride-containing wastewater treatment, achieving the goal of treating waste with waste. Summary of the Invention

[0005] The object of the present invention is to overcome the problems existing in the prior art, such as low defluorination efficiency of defluorinating agents, high metal content in the treated water body, and difficulty in the resource utilization of red mud. The present invention provides a red mud-based magnetic defluorinating agent, its preparation method and application. This method can successfully utilize red mud to prepare a defluorinating agent, realizing the resource utilization of red mud, reducing the preparation cost of the defluorinating agent at the same time, and the prepared defluorinating agent has high defluorination efficiency, the preparation method is simple, and it has great industrial application prospects.

[0006] In order to achieve the above object, on the one hand, the present invention provides a preparation method of a red mud-based magnetic defluorinating agent, and the method includes the following steps:

[0007] (1) Mix red mud with coke and then carry out roasting, and then leach the roasted product in a sulfuric acid solution;

[0008] (2) Adjust the pH value of the material obtained in step (1) to 5-7, then carry out aging, and then dry and grind the aged material;

[0009] Wherein, the weight ratio of the dosage of red mud to coke is 20:1-4, and the weight ratio of the dosage of the roasted product to the sulfuric acid solution is 1:1-2.

[0010] The concentration of the sulfuric acid solution is 1-2 mol / L.

[0011] Preferably, the leaching conditions include: the leaching temperature is 20-40 °C, and the leaching time is 30-90 min.

[0012] Preferably, the drying conditions include: the drying temperature is 105-110 °C, and the drying time is 5-10 h.

[0013] Preferably, the carbon element content in the coke is ≥80%.

[0014] Preferably, the particle size of the coke is 80-120 mesh.

[0015] Preferably, in step (1), the roasting conditions include: the roasting temperature is 800-1100 °C, and the roasting time is 1-2 h.

[0016] Preferably, in step (2), the aging conditions include: the aging temperature is 80-100 °C, and the aging time is 20-30 h.

[0017] The second aspect of the present invention provides a defluorinating agent obtained by the above preparation method.

[0018] The third aspect of the present invention provides an application of the defluorinating agent in treating fluorine-containing wastewater.

[0019] Preferably, the concentration of fluoride ions in the fluorine-containing wastewater is 2-10 mg / L.

[0020] Advantages of the present invention:

[0021] (1) In the method of the present invention, red mud, an industrial waste, is fully utilized to prepare a defluorinating agent, which not only reduces the preparation cost of the defluorinating agent, but also enables the full recycling of red mud, providing a new way for the resource recycling of red mud and achieving the purposes of "treating waste with waste" and green development;

[0022] (2) The defluorinating agent prepared by the method of the present invention has high defluorination performance, can adsorb fluoride ions in the fluorine-containing wastewater, and can also complex with fluoride ions in the fluorine-containing wastewater to further improve the defluorination effect. Moreover, it will form flocs by itself, and the flocs can further reduce the fluoride ion content in the water through actions such as sweeping and bridging during the sedimentation process. Further, the defluorinating agent of the present invention also has excellent magnetism, and the flocs formed by the defluorinating agent can be quickly separated from solid to liquid by magnetic separation technology. While achieving a deep defluorination effect, it will not cause further metal ion pollution, and at the same time, it also improves the treatment efficiency of the fluorine-containing wastewater and reduces the floor area of the treatment facilities;

[0023] (3) The preparation process of the method of the present invention is simple, without organic solvent pollution, and the defluorinating agent of the present invention can not only treat fluorine-containing wastewater with a high concentration of fluoride ions, but also has excellent defluorination effect on fluorine-containing wastewater with a low fluoride ion concentration. It has a wide application range and great market economic benefits and broad application prospects. Specific embodiments

[0024] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0025] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] In the present invention, red mud refers to the solid industrial waste obtained from the production of alumina by the Bayer process, which contains 20-25 wt% of SiO 2 , 25-30 wt% of Al 2 O 3 , 10-15 wt% of CaO and 10-20 wt% of Fe2 O 3 。

[0027] The present invention provides a preparation method of a red mud-based magnetic defluorination agent, and the method comprises the following steps:

[0028] (1) Mix red mud with coke and then carry out roasting, and then leach the roasted product in a sulfuric acid solution;

[0029] (2) Adjust the pH value of the material obtained in step (1) to 5-7, then carry out aging, and then dry and grind the aged material.

[0030] In the method of the present invention, when the carbon element content in the coke is too low, the impurities contained in the coke will have an adverse effect on the subsequent reaction. Control the carbon element content in the coke ≥80%, preferably 80-85%.

[0031] In a preferred embodiment, the particle size of the coke is 80-120 mesh.

[0032] In a specific embodiment, in step (1), the roasting conditions include: the roasting temperature is 800-1100°C, preferably 800-1000°C, and the roasting time is 1-2 h. Specifically, the roasting temperature is 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C or 1100°C; the roasting time can be 1 h, 1.5 h or 2 h.

[0033] In a preferred embodiment, in step (1), the roasting conditions include: the roasting temperature is 900-1000°C, and the roasting time is 1-2 h.

[0034] In the method of the present invention, after mixing and calcining red mud with coke, the iron oxide in the red mud is reduced to magnetite, so that the prepared defluorination agent has magnetism. In the present invention, it is necessary to control the dosage ratio of coke to red mud so that the prepared defluorination agent has excellent magnetism and defluorination performance.

[0035] In a specific embodiment, the weight ratio of the dosage of red mud to coke is 20:1-4, preferably 20:1.5-4, and more preferably 20:1.5-3.5. Specifically, the weight ratio of the dosage of red mud to coke can be 20:1, 20:1.5, 20:2, 20:2.5, 20:3, 20:3.5 or 20:4.

[0036] In a specific embodiment, the weight ratio of the dosage of the roasted product to the sulfuric acid solution is 1:1-2. Specifically, the weight ratio of the dosage of the roasted product to the sulfuric acid solution can be 1:1, 1:1.5 or 1:2.

[0037] In a specific embodiment, the concentration of the sulfuric acid solution is 1 - 2 mol / L. Specifically, the molar concentration of the sulfuric acid solution can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L.

[0038] In a specific embodiment, the conditions for leaching include: the leaching temperature is 20 - 40°C, and the leaching time is 30 - 90 min. Specifically, the leaching temperature can be 20°C, 25°C, 30°C, 35°C or 40°C; the leaching time can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min.

[0039] In a preferred embodiment, the conditions for leaching include: the leaching temperature is 35°C, and the leaching time is 60 min.

[0040] In the method of the present invention, after leaching with the sulfuric acid solution, it is not necessary to filter the material obtained after leaching. All the materials after leaching in step (1) are directly put into the subsequent reaction. The components that are not leached will form a porous structure on the surface during the subsequent reaction. When applied to the defluorination process, fluoride ions can also be removed through physical adsorption, which can also help with deep defluorination. Thus, all the red mud can be recycled and reused, and no new industrial solid waste will be generated, providing a very good path for the resource recovery and utilization of red mud.

[0041] In the method of the present invention, in step (2), an alkaline solution is selected to adjust the pH value of the material obtained in step (1) to 5 - 7, preferably 5 - 6. Specifically, an alkaline solution can be selected to adjust the pH value of the material obtained in step (1) to 5, 5.5, 6, 6.5 or 7.

[0042] In a specific embodiment, the alkaline solution is selected from one or more of NaOH solution, KOH solution and ammonia water solution.

[0043] In a preferred embodiment, the molar concentration of hydroxide ions in the alkaline solution is 0.5 - 2 mol / L, preferably 1 - 2 mol / L.

[0044] Specifically, the molar concentration of hydroxide ions in the alkaline solution can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L.

[0045] In a specific embodiment, the specific steps of adjusting the pH value of the material obtained in step (1) to 5 - 7 with an alkaline solution include: first, dropping the alkaline solution into the material obtained in step (1), oscillating to fully mix them, then standing for 3 - 5 min to completely settle the large particles in the system, and then using a pH meter to measure the pH value of the supernatant. Repeat this operation until the pH value of the system reaches 5 - 7.

[0046] In a specific embodiment, in step (2), the conditions for aging include: the aging temperature is 80 - 100 °C, preferably 80 - 90 °C, and the aging time is 20 - 30 h, preferably 23 - 28 h. Specifically, the aging temperature can be 80 °C, 85 °C, 90 °C, 95 °C or 100 °C, and the aging time can be 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 29 h or 30 h.

[0047] In the method of the present invention, the calcined product is leached with a sulfuric acid solution, and after adjusting the pH value of the leached material, aging is carried out. The obtained defluorinating agent can simultaneously have the functions of adsorbing, complexing and coagulating and settling fluoride ions. This may be because the defluorinating agent prepared in the present invention contains components such as polyaluminum sulfate, polyferric sulfate and polyaluminum ferric silicate. When the defluorinating agent is applied to treat fluoride-containing wastewater, polyaluminum sulfate will form polynuclear hydroxy complexes in aqueous solution, for example, it will form [Al 2 (OH) 2 4+ 、[Al 3 (OH) 4 5+ 、[Al 6 (OH) 15 3+ 、[Al 7 (OH) 17 4+ 、[Al 8 (OH) 20 4+ and other cationic substances. Adsorption, ion exchange and complexation reactions will occur between fluoride ions and these cations to generate [Al x (OH) c-y F y z+ ​​​​​​Fluorine-substituted polynuclear hydroxy complex ions, so as to achieve the purpose of reducing the concentration of fluoride ions in fluoride-containing wastewater. In addition, polyferric sulfate can form [Fe 2 (H 2 O) 8 (OH) 2 4+ 、[Fe 3 (H 2 O) 6 (OH) 3 6+ and other cations in aqueous solution. These cations also have a strong attraction to fluoride ions and there are also adsorption and complexation effects with fluoride ions, and can also produce beneficial effects in the process of removing fluoride ions from wastewater. Further, polyaluminum ferric silicate can also be used to remove fluoride ions in aqueous solution. There is a strong bonding effect between aluminum-fluorine, iron-fluorine, silicon-aluminum and silicon-iron. Therefore, polyaluminum ferric silicate can effectively lock fluoride ions in the silicon-aluminum-oxygen and silicon-iron-oxygen skeletons to achieve the purpose of deep fluoride removal. And after adsorbing fluoride ions, the cations themselves are neutralized and will form flocs. The flocs can further remove fluoride ions in water through actions such as sweeping and bridging during the sedimentation process to form coprecipitation. Subsequently, the solid-liquid separation can be quickly realized by using the magnetism of the defluorinating agent described in the present invention. The various active ingredients in the defluorinating agent described in the present invention cooperate with each other to jointly improve the maximum defluorination ability and defluorination efficiency of the defluorinating agent.

[0048] In a preferred embodiment, the drying conditions include: the drying temperature is 105-110 °C, and the drying time is 5-10 h. Specifically, the drying temperature can be 105 °C, 106 °C, 107 °C, 108 °C, 109 °C or 110 °C; the drying time can be 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0049] In a specific embodiment, the dried product is ground to a particle size of 80-120 mesh to obtain the defluorinating agent.

[0050] In a specific embodiment, in step (2), the aged material is in a solid-liquid mixed state. Before drying the aged material, it is not necessary to filter the material, and the aged material can be directly dried. After drying, the obtained solid is ground to obtain the defluorinating agent.

[0051] The present invention further provides a defluorinating agent obtained by the above preparation method.

[0052] In the method of the present invention, the defluorinating agent simultaneously has the functions of adsorbing, complexing and coagulating and sedimenting fluoride ions, which can greatly improve the defluorination ability of the defluorinating agent and improve the defluorination effect.

[0053] ​​The present invention can further provide an application of the defluorinating agent in treating fluoride-containing wastewater.

[0054] In the method of the present invention, the defluorinating agent of the present invention can be applied to the treatment of high-concentration or low-concentration fluoride-containing wastewater. Preferably, the concentration of fluoride ions in the fluoride-containing wastewater is 2-10 mg / L.

[0055] The present invention further provides a method for treating fluoride-containing wastewater, which includes: adding the above-mentioned defluorinating agent to the fluoride-containing wastewater, then stirring for 5-10 min at a stirring speed of 100-200 r / min, and then stirring for another 20-30 min at a stirring speed of 5-10 r / min. After the stirring is completed, let it stand, and then perform solid-liquid separation using a magnetic field.

[0056] In a preferred embodiment, the solid-liquid ratio of the dosage of the defluorinating agent to the fluoride-containing wastewater is 2-5 mg:100 mL.

[0057] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0058] In the following examples and comparative examples, the red mud used contains 21 wt% of SiO 2 , 26 wt% of Al 2 O 3 , 15 wt% of CaO and 15 wt% of Fe 2 O 3 ; the red mud comes from a certain alumina plant in Henan, and the coke is industrial coke purchased.

[0059] Example 1

[0060] (1) Mix 100 g of red mud with 15 g of coke (C content is 85 wt%, particle size is 80-120 mesh), then perform roasting at a roasting temperature of 1000 °C for 2 h. Then leach the roasted product in a sulfuric acid solution with a concentration of 1.5 mol / L (the weight ratio of the roasted product to the sulfuric acid solution is 1:1), the leaching temperature is 25 °C, and the leaching time is 60 min;

[0061] (2) Add NaOH solution (molar concentration is 1 mol / L) to adjust the pH value of the material obtained in step (1) to 5, then perform aging at an aging temperature of 85 °C for 24 h. Then dry the aged material at 105 °C for 6 h, and then grind it to 80-120 mesh to obtain the defluorinating agent.

[0062] Example 2

[0063] (1) Mix 100 g of red mud with 10 g of coke (C content is 82 wt%, particle size is 80 - 120 mesh), then carry out roasting. The roasting temperature is 800 °C and the roasting time is 1.5 h. Then leach the roasted product in a sulfuric acid solution with a concentration of 1 mol / L (the weight ratio of the roasted product to the sulfuric acid solution is 1:1.5). The leaching temperature is 20 °C and the leaching time is 70 min;

[0064] (2) Add NaOH solution (molar concentration is 1.5 mol / L) to adjust the pH value of the material obtained in step (1) to 5.5, then carry out aging. The aging temperature is 80 °C and the aging time is 28 h. Then dry the aged material at 105 °C for 8 h, and then grind it to 80 - 120 mesh to obtain the defluorinating agent.

[0065] Example 3

[0066] (1) Mix 100 g of red mud with 20 g of coke (C content is 85 wt%, particle size is 80 - 120 mesh), then carry out roasting. The roasting temperature is 1100 °C and the roasting time is 1 h. Then leach the roasted product in a sulfuric acid solution with a concentration of 2 mol / L (the weight ratio of the roasted product to the sulfuric acid solution is 1:2). The leaching temperature is 30 °C and the leaching time is 80 min;

[0067] (2) Add KOH solution (molar concentration is 2 mol / L) to adjust the pH value of the material obtained in step (1) to 6, then carry out aging. The aging temperature is 90 °C and the aging time is 24 h. Then dry the aged material at 110 °C for 8 h, and then grind it to 80 - 120 mesh to obtain the defluorinating agent.

[0068] Comparative Example 1

[0069] Carry out according to the method of Example 1, the difference is that the addition amount of coke is 4 g.

[0070] Comparative Example 2

[0071] Carry out according to the method of Example 1, the difference is that the addition amount of coke is 25 g.

[0072] Comparative Example 3

[0073] Carry out according to the method of Example 1, the difference is that the weight ratio of the roasted product to the sulfuric acid solution is changed to 1:0.5.

[0074] Comparative Example 4

[0075] Carry out according to the method of Example 1, the difference is that the weight ratio of the roasted product to the sulfuric acid solution is changed to 1:3.

[0076] Test Example

[0077] Test Example 1

[0078] The defluorination performance of the defluorinating agents obtained in Examples 1 - 3 and the products prepared in Comparative Examples 1 - 4 was tested.

[0079] Test method: The samples prepared in the examples and comparative examples were respectively added to simulated fluorine - containing wastewater with the same fluoride ion concentration. Then, it was stirred for 5 min at a stirring speed of 100 r / min, and then stirred for another 25 min at a stirring speed of 5 r / min. After stirring, it was left to stand for 2 h. The treated liquid was subjected to solid - liquid separation using a magnetic field. The supernatant was taken, and the concentration of fluoride ions in the solution was measured using ion chromatography (Thermo Fisher ICS - 1100). Then, the removal rate of fluoride ions was calculated respectively. The test results are shown in Table 1.

[0080]

[0081]

[0082] Where: c 0 and c e are respectively the initial concentration of fluoride ions in the solution and the concentration of fluoride ions in the treated solution, with the unit of mg / L, m is the mass of the defluorinating agent, with the unit of mg; V is the volume of the simulated fluorine - containing wastewater, with the unit of L;

[0083] Test parameters: The mass of the defluorinating agent used was 2 mg, the volume of the simulated wastewater was 100 mL, and the fluoride ion concentration in the simulated fluorine - containing wastewater was 5 mg / L.

[0084] Table 1

[0085] Example number Concentration of fluoride ions in the treated solution / mg / L Removal rate / % Equilibrium adsorption capacity / mg / g Example 1 0.55 89 222.5 Example 2 0.67 86.6 216.5 Example 3 0.82 82 209 Comparative example 1 0.95 81 202.5 Comparative example 2 1.51 69.8 174.5 Comparative example 3 1.25 75 187.5 Comparative example 4 1.05 79 197.5

[0086] From the results in Table 1, it can be seen that the defluorinating agent prepared by the method described in the present invention has excellent defluorination performance, high removal rate of fluoride ions in fluorine - containing wastewater, large equilibrium adsorption capacity, and can be well applied to the field of fluorine - containing wastewater treatment. Moreover, the preparation method of the defluorinating agent prepared in the present invention is simple, and rapid solid - liquid separation can be achieved through magnetic separation technology, further improving the defluorination efficiency, and having great application prospects.

[0087] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of a red mud-based magnetic defluorination agent, characterized in that, the method comprises the following steps: (1) Mix red mud and coke and then carry out roasting, and then leach the roasted product in a sulfuric acid solution; (2) Adjust the pH value of the material obtained in step (1) to 5-7, then carry out aging, and then dry and grind the aged material; wherein, the weight ratio of the dosage of red mud to coke is 20:1-4, and the weight ratio of the dosage of the roasted product to the sulfuric acid solution is 1:1-2; the concentration of the sulfuric acid solution is 1-2 mol / L; the carbon element content in the coke is 80-85%; The red mud contains 20-25 wt% of SiO 2 , 25-30 wt% of Al 2 O 3 , 10-15 wt% of CaO and 10-20 wt% of Fe 2 O 3 .

2. The preparation method of the red mud-based magnetic defluorination agent according to claim 1, characterized in that, in step (1), the roasting conditions include: the roasting temperature is 800-1100 °C, and the roasting time is 1-2 h.

3. The preparation method of the red mud-based magnetic defluorination agent according to claim 1, characterized in that, the leaching conditions include: the leaching temperature is 20-40 °C, and the leaching time is 30-90 min.

4. The preparation method of the red mud-based magnetic defluorination agent according to claim 1, characterized in that, in step (2), the aging conditions include: the aging temperature is 80-100 °C, and the aging time is 20-30 h.

5. The preparation method of the red mud-based magnetic defluorination agent according to claim 1, characterized in that, the drying conditions include: the drying temperature is 105-110 °C, and the drying time is 5-10 h.

6. The preparation method of the red mud-based magnetic defluorination agent according to claim 1, characterized in that, the particle size of the coke is 80-120 mesh.

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