A method for preparing a fluorine-containing compound by treating a fluorine-containing waste water with a metal hydroxide

Abstract

The application discloses a method for preparing fluorine-containing compounds by treating fluorine-containing wastewater with metal hydroxide, and belongs to the technical field of fluorine-containing wastewater resource treatment. First, amorphous metal hydroxide is put into low-concentration fluorine-containing wastewater after high-concentration section treatment, and an adsorption reaction is carried out under acidic conditions; then, the system is adjusted to alkaline to carry out precipitation, and a fluorine-rich intermediate product is obtained by filtration; then, the intermediate product is crushed after heat treatment at 150-300 DEG C for 5-8 h, and is put into high-concentration fluorine-containing wastewater as a secondary adsorption material to carry out adsorption-precipitation reaction again under the same conditions; and fluorine-containing compounds are obtained after solid-liquid separation, washing and drying. The application adopts a two-step adsorption-precipitation process with concentration inversion, realizes step-by-step enrichment and directional conversion of fluorine resources in wastewater, and prepares fluorine-containing compounds such as cryolite, sodium fluorozirconate and sodium hexafluoroferrate, and has the advantages of high defluorination efficiency, high resource utilization degree, simple process flow and wide application range.

Description

Technical Field

[0001] This invention pertains to methods for treating fluoride-containing wastewater, and particularly relates to a method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides. Background Technology

[0002] Fluorides are widely present in wastewater discharged from industries such as integrated circuit manufacturing, photovoltaics, and electrolytic aluminum. For example, in integrated circuit manufacturing, processes such as etching, developing and rinsing, and chemical mechanical polishing generate large amounts of high-concentration fluoride-containing wastewater. This type of wastewater is typically characterized by complex water composition and large fluctuations in fluoride ion concentration. Currently, the demand for the treatment of fluoride-containing industrial wastewater in China continues to grow, but the relevant technologies for treating industrial wastewater fluorides and simultaneously recovering high-purity, high-value-added fluoride resources are still immature.

[0003] With the continuous expansion of the fluorine-related industry, my country's demand for fluorite (CaF2), a basic raw material for fluorine chemicals, has been steadily increasing. However, for a long time, my country's fluorite reserves have been far below the world average. Given that fluorine resources are mostly non-renewable, the need to recover fluorine from fluorine-containing industrial wastewater is becoming increasingly urgent. Therefore, developing efficient, low-cost, and highly resource-recovery defluorination technologies is of great significance for the long-term healthy and stable development of the fluorine-related industry.

[0004] Currently, the main technologies for treating fluoride-containing wastewater include chemical precipitation, coagulation, adsorption, ion exchange, and induced crystallization. Among these, metal hydroxides have a strong affinity for fluoride ions, and fluoride removal technology based on metal hydroxide-based adsorbents can achieve highly efficient removal of fluoride ions. Furthermore, a high-concentration fluoride-containing desorbed solution can be obtained through the regeneration process of the adsorbent, achieving a cyclical deep treatment of fluoride ion adsorption and desorption.

[0005] In recent years, the resource utilization of fluoride-containing wastewater has gradually gained attention. Fluorine-containing metal compounds, including cryolite, sodium fluorozirconate, and sodium hexafluoroferrate, have become important directions for fluoride resource recovery due to their high industrial application value. Simultaneous recovery of fluoride resources during defluorination can not only reduce hazardous waste production but also achieve the recovery and high-value conversion of fluoride resources. However, existing recovery processes generally suffer from low fluoride recovery rates, low product purity, complex processes, high energy consumption, and a disconnect between adsorption and resource recovery processes. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides, so as to improve the purity and recovery rate of fluoride-containing compounds.

[0007] Technical solution: A method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides, comprising the following steps:

[0008] (1) Amorphous metal hydroxide particles were added to low-concentration fluoride wastewater with a fluoride concentration of 0.03-0.05 mol / L after high-concentration adsorption. Acid was added to adjust the pH of the adsorption reaction to 3-6, and the reaction was carried out at room temperature for 1-5 h. Alkali was added to adjust the pH of the precipitation reaction to 6-9, and the reaction was carried out for 1-2 h. The intermediate product was obtained by filtration.

[0009] (2) The intermediate product is calcined at 150-300℃ for 5-8h to obtain secondary adsorption material. After being crushed, it is added to high-concentration fluorine-containing wastewater with a fluorine concentration of 0.04 mol / L-0.06 mol / L and a sodium ion concentration greater than 0.02 mol / L. During the adsorption reaction, acid solution is added to adjust the pH of the reaction to 3-6, and the reaction is carried out at room temperature for 1-5h. During the precipitation reaction, alkaline solution is added to adjust the pH to 6-9, and the reaction is carried out for 1-2h. After filtration, washing and drying, fluorine-containing compounds are obtained.

[0010] Further, the amorphous metal hydroxide is amorphous aluminum hydroxide. In step (1), the solid-liquid ratio of the amorphous aluminum hydroxide is 0.8-1.2 g / L; and in the adsorption reaction, the pH is adjusted to 3-6 and the reaction time is 1-3 h; in the precipitation reaction, the pH is adjusted to 8-9.

[0011] Further, the amorphous metal hydroxide is amorphous zirconium hydroxide. In step (1), the solid-liquid ratio of the amorphous zirconium hydroxide is 0.9-1.3 g / L; and in the adsorption reaction, the pH is adjusted to 3-4.5 and the reaction time is 2-3 h; in the precipitation reaction, the pH is adjusted to 6-7 and the reaction time is 1-2 h.

[0012] Further, the amorphous metal hydroxide is amorphous iron hydroxide. In step (1), the solid-liquid ratio of the amorphous iron hydroxide is 1.5-2.5 g / L; and in the adsorption reaction, the pH is adjusted to 4-6 and the reaction time is 3-5 h; in the precipitation reaction, the pH is adjusted to 6-7 and the reaction time is 1-2 h.

[0013] Furthermore, in steps (1) and (2), the acid solution in the adsorption reaction is a 1-2 mol / L hydrochloric acid solution.

[0014] Furthermore, in steps (1) and (2), the alkaline solution in the precipitation reaction is a 1-2 mol / L sodium hydroxide solution.

[0015] Furthermore, the method for preparing the amorphous metal hydroxide includes the following steps:

[0016] (1) Prepare a soluble metal salt solution, add sodium hydroxide solution, carry out precipitation reaction, and filter to obtain metal hydroxide precursor;

[0017] (2) Dry the metal hydroxide precursor to constant weight to obtain amorphous metal hydroxide particles.

[0018] Furthermore, the soluble metal salt is one of aluminum salt, zirconium salt, and iron salt. In the precipitation reaction, the concentration of aluminum salt in the solution is 1.5-2.5 mol / L, the concentration of zirconium salt is 2.0-2.5 mol / L, and the concentration of iron salt is 0.8-1.2 mol / L; the concentration of sodium hydroxide in the precipitation reaction is 1.0-2.8 mol / L.

[0019] Furthermore, the metal hydroxide precursor is dried at a temperature of 60-80°C for 20-30 hours.

[0020] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the present invention uses the high adsorption activity of amorphous hydroxide materials to achieve efficient treatment of fluoride-containing wastewater, and the fluoride ion removal rate can reach more than 70%;

[0021] Through a two-step adsorption-precipitation process with inverted concentration, fluorine resources in wastewater are converted into valuable fluorine-containing compounds such as cryolite, sodium hexafluoroferrate, and sodium fluorozirconate, thus realizing the resource utilization of wastewater. Moreover, the amorphous metal hydroxide materials are inexpensive and have a simple preparation process, making them suitable for large-scale industrial applications. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0023] Figure 2 The XRD patterns are those of the amorphous hydroxides prepared in Examples 1-3 of this invention, specifically A, amorphous aluminum hydroxide, B, amorphous zirconium hydroxide, and C, amorphous iron hydroxide;

[0024] Figure 3 The XRD patterns of the fluorine-containing compounds prepared by the methods in Examples 1-3 of this invention are shown, specifically A. cryolite (Na3AlF6) and B. sodium fluorozirconate (Na5Zr2F6). 13 ) and sodium hexafluoroferrate (Na3FeF6). Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] It should be noted that all raw materials used in this invention are commercially available.

[0027] Example 1

[0028] The high-concentration fluoride-containing wastewater used in Example 1 is fluoride-containing wastewater from a manufacturing enterprise in Nanjing, Jiangsu Province, after pre-process treatment. The specific composition is shown in Table 1 below.

[0029] Table 1. Composition of Fluoride-Containing Wastewater

[0030]

[0031] The amorphous metal hydroxide used in Example 1 was amorphous aluminum hydroxide, which was prepared by the following method:

[0032] (1) Add 400 ml of 1.2 mol / L sodium hydroxide solution to 150 ml of 1.8 mol / L aluminum chloride solution, precipitate and filter to obtain solid aluminum hydroxide;

[0033] (2) The solid aluminum hydroxide was dried at 65 °C for 20 h to constant weight, yielding 14.5 g of amorphous aluminum hydroxide material. The XRD pattern of the amorphous aluminum hydroxide is shown below. Figure 2 As shown in Figure A.

[0034] Methods for preparing fluoride-containing compounds by treating fluoride-containing wastewater with amorphous aluminum hydroxide, such as Figure 1 As shown, it includes the following steps:

[0035] (3) Take 10L of low-concentration fluoride wastewater (fluoride concentration is 0.037mol / L) after high-concentration adsorption, then add 1.0 g / L of amorphous aluminum hydroxide solid particles, adjust the pH of the system to 4.5 by adding 2 mol / L hydrochloric acid solution at room temperature, and perform the adsorption and defluorination reaction for 1h. Then add 2 mol / L sodium hydroxide solution until the pH of the system is 8, and carry out the precipitation reaction. After the reaction is completed for 1h, filter to obtain the intermediate product.

[0036] (4) The intermediate product was treated at 180℃ for 5 hours to obtain a secondary adsorbent material. After crushing, it was added to 10L of high-concentration (fluoride concentration of 0.051mol / L) fluoride-containing wastewater. At room temperature, a 2 mol / L hydrochloric acid solution was added to adjust the pH of the system to 4.5. The adsorption and fluoride removal reaction was carried out for 1 hour. Then, a 2 mol / L sodium hydroxide solution was added until the pH of the system reached 8 to carry out the precipitation reaction. After the reaction was carried out for 1 hour, the precipitate was filtered, washed, and dried at 60℃ for 25 hours to obtain cryolite (Na3AlF6). The XRD pattern of its fluoride is shown in the figure. Figure 3 As shown in Figure A.

[0037] Comparative Example 1

[0038] The fluoride-containing wastewater and amorphous hydroxide used in Comparative Example 1 are the same as those in Example 1. The difference is that the two-step adsorption-precipitation method with inverted concentration is not used in the comparative example. The specific steps are as follows:

[0039] (1) Take 10L of high concentration (fluorine concentration is 0.051mol / L), then add 1.0g / L of amorphous aluminum hydroxide solid particles, and adjust the pH of the system to 4.5 by adding hydrochloric acid solution with a concentration of 2 mol / L at room temperature. The fluorine adsorption reaction is carried out for 1h, and then sodium hydroxide solution with a concentration of 2 mol / L is added until the pH of the system is 8. The precipitation reaction is carried out. After the reaction is carried out for 1h, the intermediate product is obtained by filtration.

[0040] (2) After crushing the intermediate product, it was put into the low-concentration fluoride wastewater (fluoride concentration of 0.029 mol / L) after the 10L high-concentration stage treatment in step (1). At room temperature, a 2 mol / L hydrochloric acid solution was added to adjust the pH of the system to 4.5. The fluoride adsorption reaction was carried out for 1 h. Then, a 2 mol / L sodium hydroxide solution was added until the pH of the system was 8. The precipitation reaction was carried out. After the reaction was carried out for 1 h, the precipitate was filtered, washed and dried at 60 ℃ for 25 h to obtain cryolite (Na3AlF6).

[0041] Comparative Example 2

[0042] The fluoride-containing wastewater and amorphous hydroxide used in Comparative Example 2 are the same as those in Example 1, except that the intermediate product is not subjected to high-temperature treatment in the comparative example; the specific steps are as follows:

[0043] (1) Take 10L of low-concentration fluoride wastewater (fluoride concentration is 0.046mol / L) after high-concentration adsorption, then add 1.0g / L of amorphous aluminum hydroxide solid particles, adjust the pH of the system to 4.5 by adding 2 mol / L hydrochloric acid solution at room temperature, and perform the adsorption and defluorination reaction for 1h. Then add 2 mol / L sodium hydroxide solution until the pH of the system is 8, and carry out the precipitation reaction. After the reaction is completed for 1h, filter to obtain the intermediate product.

[0044] (2) The intermediate product was crushed and put into 10L of high-concentration (fluoride concentration of 0.051mol / L) fluoride-containing wastewater. At room temperature, 2 mol / L hydrochloric acid solution was added to adjust the pH of the system to 4.5. The fluoride adsorption reaction was carried out for 1h. Then, 2 mol / L sodium hydroxide solution was added until the pH of the system was 8 to carry out the precipitation reaction. After the reaction was carried out for 1h, the precipitate was filtered, washed and dried at 60 ℃ for 25h to obtain cryolite (Na3AlF6).

[0045] Example 2

[0046] The high-concentration fluoride-containing wastewater used in Example 2 is fluoride-containing wastewater from a manufacturing enterprise in Hefei, Anhui Province, after being treated by the previous process. The specific composition is shown in Table 2 below.

[0047] Table 2 Composition of Fluoride-Containing Wastewater

[0048]

[0049] The amorphous metal hydroxide used in Example 2 was amorphous zirconium hydroxide, which was prepared by the following method:

[0050] (1) Add 400 ml of 2.6 mol / L sodium hydroxide solution to 100 ml of 2.2 mol / L zirconium chloride solution, precipitate and filter to obtain solid zirconium hydroxide;

[0051] (2) The solid zirconium hydroxide was dried at 60 °C for 25 h to constant weight, yielding 22 g of amorphous zirconium hydroxide material. The XRD pattern of the amorphous zirconium hydroxide is shown below. Figure 2 As shown in B.

[0052] A method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with amorphous zirconium hydroxide includes the following steps:

[0053] (3) Take 7L of low-concentration fluoride-containing wastewater (fluoride concentration is 0.040mol / L) after high-concentration adsorption, then add 1.10g / L of amorphous zirconium hydroxide solid particles, adjust the pH of the system to 3.8 by adding 1 mol / L hydrochloric acid solution at room temperature, and perform the adsorption and defluorination reaction for 2h. Then add 1 mol / L sodium hydroxide solution until the pH of the system is 7, and carry out the precipitation reaction. After the reaction is 1.5h, filter to obtain the intermediate product.

[0054] (4) The intermediate product was treated at 160℃ for 5 hours to obtain a secondary adsorbent material. After crushing, it was added to 7L of high-concentration (fluoride concentration of 0.052 mol / L) fluoride-containing wastewater. At room temperature, 1 mol / L hydrochloric acid solution was added to adjust the pH of the system to 3.8. The adsorption and fluoride removal reaction was carried out for 2 hours. Then, 1 mol / L sodium hydroxide solution was added until the pH of the system was 7 to carry out the precipitation reaction. After the reaction was carried out for 1 hour, the precipitate was filtered, washed, and dried at 60℃ for 25 hours to obtain sodium fluorozirconate (Na5Zr2F). 13 The XRD pattern of its fluoride is as follows: Figure 3 As shown in B.

[0055] Example 3

[0056] The high-concentration fluoride-containing wastewater used in Example 3 is fluoride-containing wastewater from a manufacturing enterprise in Yancheng, Jiangsu Province, after being treated by the previous process. The specific composition is shown in Table 3 below.

[0057] Table 3 Composition of Fluoride-Containing Wastewater

[0058]

[0059] The amorphous metal hydroxide used in Example 3 was amorphous iron hydroxide, which was prepared by the following method:

[0060] (1) Add 400 ml of 1.6 mol / L sodium hydroxide solution to 200 ml of 1 mol / L ferric chloride solution, precipitate and filter to obtain solid ferric hydroxide;

[0061] (2) The solid ferric hydroxide was dried at 60 °C for 25 h to constant weight, yielding 17.3 g of amorphous ferric hydroxide material. The XRD pattern of the amorphous ferric hydroxide is shown below. Figure 2 As shown in C.

[0062] A method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with amorphous ferric hydroxide includes the following steps:

[0063] (3) Take 10L of low-concentration fluoride-containing wastewater (fluoride concentration is 0.041mol / L) after high-concentration adsorption, then add 1.5g / L of amorphous iron hydroxide solid particles, adjust the pH of the system to 5.5 by adding 2 mol / L hydrochloric acid solution at room temperature, and perform the adsorption and defluorination reaction for 5h. Then add 2 mol / L sodium hydroxide solution until the pH of the system is 7, and carry out the precipitation reaction. After the reaction is 1.5h, filter to obtain the intermediate product.

[0064] (4) The intermediate product was treated at 160℃ for 8 hours to obtain a secondary adsorbent material. After crushing, it was added to 10L of high-concentration (fluoride concentration of 0.051mol / L) fluoride-containing wastewater. At room temperature, a 2 mol / L hydrochloric acid solution was added to adjust the pH of the system to 5.5. The adsorption and fluoride removal reaction was carried out for 5 hours. Then, a 2 mol / L sodium hydroxide solution was added until the pH of the system was 7 to carry out the precipitation reaction. After the reaction was carried out for 1 hour, the precipitate was filtered, washed, and dried at 60℃ for 25 hours to obtain sodium hexafluoroferrate (Na3FeF6). The XRD pattern of its fluoride is shown in the figure. Figure 3 As shown in C.

[0065] The fluoride concentrations of the low-concentration fluoride-containing wastewater in step (3) and the high-concentration fluoride-containing wastewater in step (4) of Examples 1-3 were detected, and the fluoride removal efficiency was calculated as (fluoride concentration of high-concentration fluoride-containing wastewater - fluoride concentration of low-concentration fluoride-containing wastewater after treatment) / fluoride concentration of high-concentration fluoride-containing wastewater, as shown in Table 4.

[0066] Table 4. Fluorine concentration and defluorination efficiency of low-concentration and high-concentration fluoride wastewater after treatment.

[0067]

[0068] The elemental content and purity of the fluorine-containing compounds obtained in Examples 1-3 were tested, as shown in Table 5.

[0069] Table 5. Elemental content and purity of fluorine-containing compounds

[0070]

[0071] Depend on Figure 2-3 It can be seen that, through the method of preparing fluoride-containing compounds by treating fluoride-containing wastewater with amorphous aluminum hydroxide according to the present invention, the final products of different hydroxides are cryolite (Na3AlF6) and sodium fluorozirconate (Na5Zr2F6). 13 ) and sodium hexafluoroferrate (Na3FeF6); to achieve the defluorination of fluorine while preparing fluorine-containing compounds, thus realizing the conversion of fluorine resources.

[0072] Furthermore, as shown in Table 4-5, the fluoride removal efficiency of this method is much higher than that of Comparative Example 1. The conventional high-concentration to low-concentration adsorption process not only reduces the fluoride removal efficiency but also results in lower product purity and a decrease in metal recovery rate.

[0073] Although Comparative Example 2 uses a concentration inversion method to adsorb and generate fluorine compounds, the high-temperature treatment of the intermediate product is omitted, resulting in insufficient activity of the intermediate product. This makes it difficult to process more fluoride ions in the subsequent adsorption process, leading to a decrease in defluorination efficiency and low purity of the final product.

[0074] Therefore, by using the concentration inversion method of the present invention and high temperature to activate the intermediate product, the defluorination efficiency can be improved, while also increasing the purity and recovery rate of fluorine-containing compounds.

[0075] In addition to the above embodiments, it should be noted that the method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to the present invention and the defined parameter range can achieve the technical effects claimed by the present invention. Therefore, no further examples will be provided to support this claim.

Claims

1. A method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides, characterized in that, (1) Amorphous metal hydroxide particles were added to low-concentration fluoride wastewater with a fluoride concentration of 0.03-0.05 mol / L after high-concentration adsorption. Acid was added to adjust the pH of the adsorption reaction to 3-6, and the reaction was carried out at room temperature for 1-5 hours. Alkali was added to adjust the pH of the precipitation reaction to 6-9, and the reaction was carried out for 1-2 hours. The intermediate product was obtained by filtration. (2) The intermediate product is calcined at 150-300℃ for 5-8h to obtain secondary adsorption material. After crushing, it is added to high-concentration fluorine-containing wastewater with a fluorine concentration of 0.04 mol / L-0.06 mol / L and a sodium ion concentration greater than 0.02 mol / L. In the adsorption reaction, acid solution is added to adjust the pH of the reaction to 3-6, and the reaction is carried out at room temperature for 1-5h. In the precipitation reaction, alkaline solution is added to adjust the pH to 6-9, and the reaction is carried out for 1-2h. After filtration, washing and drying, fluorine-containing compounds are obtained.

2. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, The amorphous metal hydroxide is amorphous aluminum hydroxide. In step (1), the solid-liquid ratio of the amorphous aluminum hydroxide is 0.8-1.2 g / L; and the pH of the adsorption reaction is controlled at 3-6 and the reaction time is 1-3 h; the pH of the precipitation reaction is controlled at 8-9.

3. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, The amorphous metal hydroxide is amorphous zirconium hydroxide. In step (1), the solid-liquid ratio of the amorphous zirconium hydroxide is 0.9-1.3 g / L; and the pH of the adsorption reaction is controlled at 3-4.5 and the reaction time is 2-3 h; the pH of the precipitation reaction is controlled at 6-7.

4. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, The amorphous metal hydroxide is amorphous iron hydroxide. In step (1), the solid-liquid ratio of the amorphous iron hydroxide is 1.5-2.5 g / L; and the pH of the adsorption reaction is adjusted to 4-6, and the reaction time is 3-5 h; the pH of the precipitation reaction is adjusted to 6-7.

5. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, In steps (1) and (2), the acid solution in the adsorption reaction is a 1-2 mol / L hydrochloric acid solution.

6. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, In steps (1) and (2), the alkaline solution in the precipitation reaction is a 1-2 mol / L sodium hydroxide solution.

7. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 1, characterized in that, The method for preparing the amorphous metal hydroxide includes the following steps: (1) Prepare a soluble metal salt solution, add sodium hydroxide solution, carry out precipitation reaction, and filter to obtain metal hydroxide precursor; (2) Dry the metal hydroxide precursor to constant weight to obtain amorphous metal hydroxide particles.

8. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 7, characterized in that, The soluble metal salt is one of aluminum salt, zirconium salt, and iron salt. In the precipitation reaction, the concentration of aluminum salt in the solution is 1.5-2.5 mol / L, the concentration of zirconium salt is 2.0-2.5 mol / L, and the concentration of iron salt is 0.8-1.2 mol / L; the concentration of sodium hydroxide in the precipitation reaction is 1.0-2.8 mol / L.

9. The method for preparing fluoride-containing compounds by treating fluoride-containing wastewater with metal hydroxides according to claim 7, characterized in that, The metal hydroxide precursor is dried at a temperature of 60-80℃ for 20-30 hours.

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