Catalyst for purifying fluorine-containing groundwater and preparation method thereof

Abstract

The present invention discloses a catalyst for fluorine-containing groundwater purification and a preparation method thereof, that is, a cordierite honeycomb ceramic is used as a matrix, γ-Al2O3 formed after calcining hydroxyapatite and pseudo-boehmite with a higher specific surface area is used as a carrier, La, Ag and Ce are used as the main active components, and one or more oxides or composite oxidations of Cu, Fe, Mn and Ba are used as co-catalysts. The preparation method of the catalyst is as follows: pseudo-boehmite powder, hydroxyapatite powder, one or more of the auxiliary agents, and deionized water are mixed into a slurry in a certain proportion, and sodium hydroxide or calcium hydroxide solution is used to adjust the pH to 9-11, the ceramic matrix is ​​immersed in the slurry, and the catalyst required for the present invention is obtained after drying and roasting. The catalyst of the present invention has high fluoride ion removal efficiency and durability, and silver ion doping can inhibit microbial growth and reproduction.

Description

Technical Field

[0001] The present invention relates to a catalyst for purifying fluorine-containing groundwater and a preparation method thereof, in particular to a rare earth modified hydroxyapatite-honeycomb catalyst for purifying low-concentration fluorine-containing groundwater generated by coal mining and other mineral mining and a preparation method thereof. Background Art

[0002] With the intensification of mining of coal, fluorite, and other minerals, the aquifers in the underground rock formations have been damaged, causing the previously sealed fluoride-containing groundwater to gush out, turning into wastewater. This has also contaminated the drinking water sources of local residents, adversely affecting both businesses and residents. Furthermore, some residential areas are close to natural fluorite mines, phosphate mines, and other fluoride-containing associated minerals. These water sources are contaminated by dissolved and leaked fluoride, leading some residents to suffer from varying degrees of fluoride poisoning through long-term ingestion, such as typical dental fluorosis and skeletal fluorosis. Furthermore, long-term ingestion of fluoride ions can be toxic to the reproductive and nervous systems, posing a serious threat to health. Excessive fluoride not only poisons the human body through drinking water and air pollution, but also harms the growth and reproduction of plants and animals through groundwater systems, disrupting the development of local agriculture and animal husbandry.

[0003] Since the water quality and source of mine water are the same as those of groundwater, how to efficiently and cost-effectively reduce the fluoride ion concentration to below 1.0 mg / L in order to cooperate with the upgrading of enterprise wastewater treatment standards is a difficult problem that many water treatment industry workers need to solve. According to data, the fluoride content in coal mine water varies significantly according to different regions, and the content basically remains in the range of 5-20. In extreme areas such as the Huanglong Mining Area and the Mengdong Mining Area, the fluoride content in mine water reaches as high as 195 mg / L and 2320 mg / L respectively. However, unlike fluoride-containing wastewater from industrial production, fluoride from groundwater has the characteristics of low concentration, large water volume, and low organic matter content in the water. It is significantly different from the fluoride wastewater treatment methods in the electronics and chemical industries. It fully considers the economic efficiency and effluent stability, and actively reuses qualified discharged fresh water.

[0004] Currently, there are two main methods for removing fluoride ions from groundwater: physical and chemical. Physical methods are mainly based on membrane materials, ion exchange resins, etc., which can effectively remove fluoride, but the cost is relatively high and it is suitable for scenarios with small water volumes and high concentrations. Chemical methods are mainly based on traditional coagulation and sedimentation. This method is mature, but the fluoride ion concentration in the effluent fluctuates greatly. Due to its low cost and simple principle, it is widely used in water treatment. The above technologies are difficult to strike a balance between fluoride ion removal efficiency and cost. However, crystal catalysis methods based on hydroxyapatite materials can effectively reduce costs while improving the efficiency of fluoride ion conversion to fluorapatite.

[0005] Currently, there are many patents for agents, catalysts, and adsorbents targeting fluoride ions, mainly compound coagulants, such as:

[0006] CN1377841 discloses a method and apparatus for removing fluoride from groundwater. It uses a highly alkaline calcium-based polyaluminum-silicon composite coagulant to remove fluoride ions from the water. Fluoride is separated by forming flocculent precipitation, and the fluoride concentration in raw water of 5 mg / L can be reduced to 0.9 mg / L. However, the maximum dosage is 360 mg / L, which is too expensive for mine water with a daily output of tens of thousands of tons. Furthermore, the document does not provide a practical example of treating wastewater with a fluoride concentration of 5 mg / L, making it difficult to meet application scenarios with varying water quality.

[0007] CN115636493A discloses a wastewater defluoridation agent and its preparation and application methods. The agent uses polyferric sulfate and aluminum salt as main components, and utilizes the formation of complexes between ions to precipitate fluoride ions with polyferric sulfate. However, for high-concentration fluoride-containing wastewater, the defluoridation rate is only about 60%, and the fluoride content in the effluent does not meet the discharge requirements. Furthermore, during use, additional PAM flocculants and pH regulators need to be added.

[0008] CN114853109A discloses a deep defluorination agent and its preparation and use methods. It uses a variety of metal ions such as yttrium, cerium and calcium as chelating agents to form insoluble complexes with fluoride ions. However, the metal ions account for a high proportion, which will inevitably cause ion dissolution problems while increasing costs. Moreover, this type of agent has not been processed by molding, which will also cause excessively high cost burdens for subsequent recycling.

[0009] In addition, in other fluoride removal aspects, such as CN113772762A, CN113842871A, CN113578287A, etc., they all rely too much on the coagulation and complexation of metal ions such as aluminum ions, have weak binding effects with fluoride ions, and are mainly based on physical adsorption. Desorption is prone to occur when the fluoride concentration in the water changes. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to solve the problems of easy shedding of active coating and excessive bed pressure drop in current fluorine removal catalysts or filter materials, while being able to inhibit the growth and excessive reproduction of microorganisms in the water treatment process.

[0011] The present invention aims to provide a rare earth-modified hydroxyapatite-precious metal honeycomb catalyst with a robust active material coating, high fluoride removal efficiency, and high bed porosity. Specifically, it aims to provide a highly efficient and durable catalyst suitable for removing low-concentration inorganic fluoride ions from large volumes of water. The catalyst utilizes an organic compound that rapidly decomposes under conventional heat treatment conditions as a rare earth element precursor, a coating matrix made of a hydroxyapatite-like material with high fluoride adsorption capacity and high specific surface area, and special additives, resulting in a novel catalyst formulation.

[0012] Another object of the present invention is to provide a method for preparing the catalyst.

[0013] The technical solution of the present invention is:

[0014] A catalyst for purifying fluorine-containing groundwater, wherein the catalyst uses cordierite honeycomb ceramics as a carrier, La, Ag, and Ce as main active components, hydroxyapatite and alumina as a coating matrix, and one or more oxides or composite oxides of Cu, Fe, Mn, and Ba as a co-catalyst. The rare precious metal element precursors of the main active components of La, Ag, and Ce are:

[0015] Any of the lanthanum precursors La(NO3)3, La2(CO3)3 or La(PO4), or

[0016] Silver precursor AgNO3, or

[0017] Either of the cerium precursors Ce(NO3)2 or (NH4)2Ce(NO3)6.

[0018] In the coating matrix, the weight ratio of aluminum gel to hydroxyapatite is: aluminum gel: hydroxyapatite = 5:1-6. The additive contains wt.% (50% Mn-50% Ba) or wt.% (80% Mn-20% Cu) or wt.%

[0019] (40% Mn-30% Ba-30% Fe) composite oxide. The rare metal precursor is La(NO3)3, La2(CO3)3 or La(PO4) and Ce(NO3)2 or (NH4)2Ce(NO3)6 with a pH of 2-7 and a mass percentage concentration of 0.01-0.5%.

[0020] The preparation method of the catalyst of the present invention comprises the following steps:

[0021] (1) Pseudo-boehmite powder, hydroxyapatite powder, one or more of the additives, and deionized water are mixed in a certain proportion to form a slurry, and the pH is adjusted to 9-11 using sodium hydroxide or calcium hydroxide solution. The mass percentage of the additive powder in the mixed slurry is 5%-30%, and the mass ratio of the mixed powder to deionized water is 1:0.8-2.5, to prepare a mixed coating slurry.

[0022] (2) Immerse the cordierite honeycomb ceramic carrier into the slurry mixed coating slurry prepared according to (1), take it out after 1-3 minutes, and use negative pressure to suck out the excess slurry, blow dry it at 120°C for 3-8 hours, and then calcine it at 300°C-500°C for 2-4 hours to obtain a coating carrier with a coating loading rate of 10-30% by mass in one go.

[0023] (3) Immerse the coated support prepared according to (2) in a noble metal precursor having a pH of 2-7:

[0024] Any of the lanthanum precursors La(NO3)3, La2(CO3)3 or La(PO4), or

[0025] Silver precursor AgNO3, or

[0026] The catalyst is immersed in a precursor solution of any one of the cerium precursors Ce(NO3)2 or (NH4)2Ce(NO3)6, and then stirred and immersed for 5-10 minutes. After being taken out, it is blown dried at 100°C for 1-3 hours. Then, it is immersed in any lanthanum and cerium precursor solution of La(NO3)3, La2(CO3)3 or La(PO4) and AgNO3 and Ce(NO3)2 or (NH4)2Ce(NO3)6 with a pH of 2-7 for 5-10 minutes. After being taken out, it is blown dried at 120°C for 1-3 hours and calcined at 300°C-500°C for 2-4 hours to obtain the catalyst for fluorine-containing groundwater purification of the present invention.

[0027] The catalyst of the present invention not only has a high fluorine adsorption capacity and high porosity, but also has a recyclable carrier, can inhibit microbial growth, has a simple preparation process, and is modular, making it widely applicable to various filtration devices and tower equipment. Compared with catalysts commonly used in the prior art, the catalyst of the present invention has the following advantages:

[0028] (1) The rare metal precursor solution used can be completely decomposed at a relatively low temperature, and no chemical reducing agent is required to obtain zero-valent active metal elements. Compared with the use of chlorochromate, the adsorption antagonism between chloride ions and fluoride ions is eliminated, and the thermal decomposition temperature of the precursor solution is reduced, thereby effectively reducing the preparation cost of the catalyst.

[0029] (2) A mixture of aluminum colloid prepared from pseudo-boehmite and hydroxyapatite dry powder is used as the coating matrix of the catalyst. Compared with the conventional γ-alumina bead defluoridation material, it has a higher fluoride ion adsorption capacity, which is due to the specific exchange ability of hydroxyl groups in hydroxyapatite with fluoride ions.

[0030] (3) Using one or more oxides or composite oxides of Cu, Fe, Mn, and Ba as co-catalysts has higher sintering resistance and improved coordination ability with fluoride ions compared with catalysts using only Cu, Fe, Mn, Ba and other elements. It can also reduce the proportion of precious metals and reduce costs.

[0031] (4) The catalyst of the present invention can effectively reduce the water flow pressure drop, improve the capture and fixation of fluoride ions, and play an important role in controlling the fluoride content in low-concentration and large-volume groundwater.

[0032] (5) The catalyst of the present invention can be used as an adsorbent, and can also be added to the high fluoride catalytic system with additional calcium and phosphorus sources, such as calcium chloride and disodium hydrogen phosphate, to greatly improve the fluoride ion removal efficiency, extend the service life, and improve the crystal catalytic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a simplified flow chart of a method for preparing a catalyst for purifying fluorine-containing groundwater.

[0034] Figure 2 Results of continuous measurement of fluoride removal rate in simulated water supply for implementation case 4.

[0035] Figure 3 The data results of the fluoride removal efficiency measurement in an actual water sample in the implementation case 5 are shown.

[0036] Figure 4 This is an appearance diagram of the cordierite honeycomb ceramic carrier used in implementation examples 1-5. DETAILED DESCRIPTION

[0037] Example 1 (catalyst preparation):

[0038] See also Figure 1100g of aluminum gel (containing 70% pseudo-boehmite) powder, 30g of hydroxyapatite powder, and 20g of a (50% Mn-50% Ba) composite oxide were mixed. 200mL of a solution containing 20g of copper nitrate was added, the pH was adjusted to 10.0 with sodium hydroxide solution, and the mixture was stirred for 10 minutes to produce a coating slurry. A honeycomb ceramic support was immersed in the slurry for 5 minutes, and the excess slurry was removed using negative pressure. The support was then dried at 100°C for 3 hours and calcined at 350°C for 2 hours to obtain a firmly supported catalyst. The support was then immersed in a 0.01% by weight AgNO3 solution at pH 6 for 30 minutes, then dried at 100°C for 2 hours and calcined at 300°C for 2 hours. The catalyst was immersed again in a mixed solution of La(NO3)3 and Ce(NO3)2 with a pH of 6 and a mass percentage concentration of 0.3 for 30 minutes, dried at 100°C for 2 hours, and calcined at 300°C for 3 hours to obtain the final catalyst.

[0039] Example 2 (catalyst preparation):

[0040] See also Figure 1 300g of aluminum gel (containing 70% pseudo-boehmite) powder, 200g of hydroxyapatite powder, and 100g of a composite oxide (50% Mn-20% Ba-30% Fe) were mixed. 800mL of a solution containing 50g of copper nitrate was added. The pH was adjusted to 10.0 with sodium hydroxide solution and stirred for 15 minutes to produce a coating slurry. The honeycomb ceramic support was immersed in the slurry for 5 minutes, then dried at 100°C for 3 hours and calcined at 400°C for 2 hours to obtain a firmly supported catalyst. This was then immersed in a 0.01% by weight AgNO3 solution at pH 6 for 30 minutes, then dried at 100°C for 2 hours and calcined at 350°C for 2 hours. The catalyst was immersed again in a mixed solution of La(NO3)3 and Ce(NO3)2 with a pH of 6 and a mass percentage concentration of 1.0% for 30 minutes, dried at 100°C for 2 hours, and calcined at 350°C for 3 hours to obtain the final catalyst.

[0041] Example 3 (catalyst preparation):

[0042] See also Figure 1500g of aluminum gel (containing 70% pseudo-boehmite) powder, 300g of hydroxyapatite powder, and 150g of a composite oxide (20% Mn-30% Ba-50% Cu) were mixed, and 1000mL of deionized water was added. The pH was adjusted to 11.0 with sodium hydroxide solution, and the mixture was stirred for 20 minutes to produce a coating slurry. The honeycomb ceramic support was immersed in the slurry for 5 minutes, and the excess slurry was removed using negative pressure. The support was then dried at 100°C for 3 hours and calcined at 450°C for 2 hours to obtain a firmly supported catalyst. This support was then immersed in a 0.01% AgNO3 solution with a pH of 5 for 30 minutes, then dried at 100°C for 2 hours and calcined at 400°C for 2 hours. The catalyst was immersed again in a mixed solution of La(NO3)3 and Ce(NO3)2 with a pH of 6 and a mass concentration of 0.3% for 30 minutes, dried at 100°C for 2 hours, and calcined at 400°C for 2 hours to obtain the final catalyst.

[0043] Example 4 (Wastewater Defluoridation):

[0044] Use sodium fluoride chemicals and deionized water to prepare 500mL of 6.0mg / L fluoride-containing water, take 10g of ceramic catalyst grinding powder and place it in the wastewater for room temperature oscillation, take samples at regular intervals, and use a fluoride ion selective electrode to measure the fluoride ion concentration. After 90 minutes of oscillation, the fluoride ion concentration in the wastewater is measured to be 0.876mg / L. The removal rate continuous measurement results are as follows Figure 2 shown.

[0045] Example 5 (Wastewater Defluoridation):

[0046] A 10L sample of fluoride-containing groundwater near a coal mine in a certain place was used, and the fluoride ion content was measured to be 13.762mg / L and the pH was 8.95. A fluoride removal test was carried out using a homemade filtration device. Five 300-mesh φ80 cylindrical honeycomb ceramic catalysts were placed in a plexiglass column and continuously fed with water through a peristaltic pump. At the same time, additional calcium chloride 5.5g and disodium hydrogen phosphate 4.3g were added to the raw water. The calcium-phosphorus ratio was about 5:3. The inlet flow rate was 1.0L / h and the residence time was 60min. The effluent was monitored using an online fluoride ion monitoring system. The water quality is as follows: Figure 3 shown.

Claims

1. A catalyst for purifying fluorine-containing groundwater, characterized in that: The catalyst uses honeycomb ceramics as a carrier, La, Ag and Ce as active components, hydroxyapatite and aluminum gel as a coating matrix, and one or more oxides or composite oxides of Cu, Fe, Mn and Ba as co-catalysts; the metal precursors of the La, Ag and Ce active components are: Lanthanum precursor La(NO3)3, or Silver precursor AgNO3, or Either of the cerium precursors Ce(NO3)2 or (NH4)2Ce(NO3)6.

2. The catalyst according to claim 1, characterized in that: The honeycomb ceramic carrier is a cordierite honeycomb ceramic carrier.

3. The catalyst according to claim 1, characterized in that: In the coating matrix, the weight ratio of aluminum gel to hydroxyapatite is: aluminum gel:hydroxyapatite=5:1-10.

4. The catalyst according to claim 1, characterized in that: The co-catalyst contains the following composite oxides in percentage by mass: 50%Mn-50%Ba or 80%Mn-20% Cu or 40%Mn-30%Ba-30%Fe.

5. The catalyst according to claim 1, characterized in that: The pH value of the metal precursor is 2-7, and the mass percentage concentration is 0.01-0.5%.

6. A method for preparing a catalyst for purifying fluorine-containing groundwater according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Pseudo-boehmite powder, hydroxyapatite powder, and additive powder are formed into a mixed powder, the mixed powder is mixed with deionized water in a certain proportion to form a slurry, and the pH is adjusted to 9-11 using sodium hydroxide or calcium hydroxide solution; (2) dipping the cordierite honeycomb ceramic carrier into the slurry mixed with the coating slurry prepared in step (1) for a period of time, taking it out, and using negative pressure to suck out excess slurry, and then drying and calcining it in one go to obtain a coating carrier with a coating loading rate of 10-30% by mass; (3) Immerse the coated support prepared in step (2) in a metal precursor solution having a pH of 2-7, wherein the metal precursor is: Lanthanum precursor La(NO3)3, or Silver precursor AgNO3, or Cerium precursor Ce(NO3)2 or (NH4)2Ce(NO3)6, Then, the mixture is stirred and immersed, taken out and dried by air, immersed in the precursor solution for a period of time, taken out and dried by air again, and finally calcined to obtain the catalyst for purifying fluorine-containing groundwater.

7. The preparation method according to claim 6, characterized in that In step 1: The mass percentage of the auxiliary powder in the mixed slurry is 5%-30%; The mass ratio of the mixed powder to deionized water is 1:0.8-2.

5.

8. The preparation method according to claim 6, characterized in that In step 2: The immersion is carried out in the slurry mixed coating slurry for 1-3 minutes and then removed; The blast drying is carried out at a temperature of 120°C for 3-8 hours; The calcination is carried out at 300° C.-500° C. for 2-4 h.

9. The preparation method according to any one of claims 6 to 8, characterized in that In step 3: The stirring and dipping time is 5-10 min; The forced air drying is carried out at 100°C for 1-3 hours; The re-immersing in the precursor solution lasts for 5-10 minutes; The second forced air drying is carried out at 120°C for 1-3 hours; The calcination is carried out at 300° C.-500° C. for 2-4 h.

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