Method for removing soluble fluorine from phosphogypsum

Abstract

The application discloses a method for removing soluble fluorine in phosphogypsum, and belongs to the technical field of industrial solid waste treatment and disposal. The method for removing soluble fluorine in phosphogypsum comprises the following steps: S1, drying, grinding and screening phosphogypsum, and then storing the phosphogypsum in a sealed bag; S2, adjusting the pH of deionized water to obtain an acid washing solution; S3, mixing the phosphogypsum and the acid washing solution in a certain proportion to obtain a mixture; S4, placing the mixture in a shaking table to shake for 12 hours, then centrifuging and discarding the acid washing waste solution to obtain acid-washed phosphogypsum; and S5, repeating the steps S3 and S4 twice on the acid-washed phosphogypsum, and then drying the acid-washed phosphogypsum to obtain defluorinated phosphogypsum. The method can effectively remove fluorine in the phosphogypsum, and the content of fluorine in the phosphogypsum can be reduced from 0.10% to 0.02% through multiple batch experimental tests. The application has certain significance in realizing the harmlessness of the phosphogypsum and promoting the recycling and reuse of the phosphogypsum resources.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste treatment and disposal technology, specifically to a method for removing soluble fluoride from phosphogypsum. Background Technology

[0002] Phosphogypsum is an industrial byproduct of phosphoric acid production, generated from sulfuric acid and phosphate rock. Approximately 4.5-5.5 tons of phosphogypsum are produced for every ton of phosphoric acid produced. With the development of the agricultural fertilizer industry, the production of phosphogypsum has been continuously increasing.

[0003] The chemical composition of phosphogypsum is mainly calcium sulfate dihydrate, along with impurities such as fluorine, phosphorus, silicon, aluminum, and iron. Fluorine exists in both soluble and insoluble forms (mainly sodium fluoride and potassium fluoride) and insoluble forms (mainly calcium fluoride and aluminum fluoride), with soluble fluorine accounting for over 75% of the total. Leaching of soluble fluoride can pollute water bodies. When the concentration of fluoride ions in environmental water exceeds 1.0 mg / L, long-term ingestion can lead to fluorosis. Mild poisoning can cause dental fluorosis, skeletal fluorosis, and an increased probability of fractures and urolithiasis. Severe poisoning can cause endocrine, cardiac, and renal damage, and even loss of working ability.

[0004] Currently, phosphogypsum defluorination technologies mainly include physical, chemical, and biological methods:

[0005] Chemical methods: such as chemical precipitation, which involves adding precipitants such as calcium hydroxide, calcium oxide, or aluminum sulfate to form calcium fluoride or aluminum fluoride precipitates of fluoride ions. This method requires a large amount of reagents, and the resulting fine precipitates are similar in particle size to phosphogypsum, resulting in low solid-solid separation efficiency.

[0006] Biological method: using fluoride-tolerant plants / microorganisms to enrich and transform fluoride. This method has a long processing cycle and is easily limited by many factors such as temperature, humidity, and nutrients. The technology is not mature and has not yet been applied on a large scale.

[0007] In comparison, acid washing not only greatly improves the removal rate of fluoride from phosphogypsum, but also has the advantages of low cost, short process and simple operation, and has broad application prospects in removing soluble fluoride from phosphogypsum.

[0008] Currently, there are no publicly reported complete process routes for "fixed solid-liquid ratio - pH adjustment of pickling solution - multi-stage circulation". Summary of the Invention

[0009] This invention provides a method for removing soluble fluoride from phosphogypsum by adjusting the solid-liquid mass ratio and the pH value of the pickling solution under normal temperature and pressure conditions; the pickling solution preparation process is simple and the operating conditions are easy, which can achieve the purpose of reducing fluoride in phosphogypsum in a short time.

[0010] To achieve the above objectives, the present invention provides a method for removing soluble fluoride from phosphogypsum, comprising the following steps:

[0011] S1: Dry the phosphogypsum, grind and sieve it, then store it in a sealed bag while it is still dry.

[0012] S2: Adjust the pH of the deionized water to obtain the pickling solution;

[0013] S3: Mix phosphogypsum and pickling solution in a certain proportion to obtain a mixture;

[0014] S4: Place the mixture in a shaker and shake for 12 h. After shaking, centrifuge and discard the pickling waste liquid to obtain pickled phosphogypsum.

[0015] S5: Repeat steps S3 and S4 twice with the acid-washed phosphogypsum and then dry it to obtain defluorinated phosphogypsum.

[0016] S6: Add calcium oxide to the pickling waste liquid to obtain a waste liquid mixture;

[0017] S7: Place the waste liquid mixture in a shaker and shake for 24 hours. After shaking, let it stand and filter to obtain purified waste liquid.

[0018] S8: Adjust the pH of the purified waste liquid to neutral.

[0019] Preferably, the sieve used in step S1 is 100 mesh (0.15 mm).

[0020] Preferably, the pickling solution in step S2 is prepared by adjusting the pH of deionized water to 4 ± 0.05 with 1 mol / L hydrochloric acid or sodium hydroxide.

[0021] Preferably, the mass ratio of phosphogypsum to pickling solution in step S3 is 1:10.

[0022] Preferably, the shaking temperature in step S4 is set to 25 ℃ and the rotation speed is set to 180 rpm.

[0023] Preferably, the centrifuge speed in step S4 is set to 3000 rpm, and the centrifugation time is 4 min.

[0024] Preferably, the oven temperature in step S5 is set to 60 °C.

[0025] Preferably, the amount of calcium oxide added in step S6 is 2.5% of the mass of the pickling waste liquid.

[0026] Preferably, the shaking temperature in step S7 is set to 25 ℃ and the rotation speed is set to 180 rpm.

[0027] Preferably, the pH of the purified waste liquid in step S8 is adjusted to neutral by using 1 mol / L hydrochloric acid or sodium hydroxide.

[0028] Compared with the prior art, this invention patent has the following beneficial effects:

[0029] 1. The pickling solution of the present invention is prepared by mixing conventional acid, alkali and deionized water, which is inexpensive; the entire pickling process is carried out at room temperature and pressure, without the need for special or precision equipment, the process is simple and highly controllable, and can achieve efficient removal of fluoride from phosphogypsum.

[0030] 2. The total fluorine mass fraction of phosphogypsum treated by this invention is reduced to 0.02%, the pH value increases, and the acidity risk is eliminated, providing an environmentally safe prerequisite for its subsequent use in building materials.

[0031] 3. This invention neutralizes the pickling waste liquid with acid and alkali, causing the fluoride in the solution to precipitate as calcium fluoride. The fluoride in the waste liquid can be removed by filtration, effectively avoiding environmental pollution caused by the discharge of pickling waste liquid. Attached Figure Description

[0032] Figure 1 a represents the leaching of fluorine under acidic conditions;

[0033] Figure 1 b represents the leaching of fluorine under neutral and alkaline conditions;

[0034] Figure 2 a represents the leaching of fluorine at different solid-liquid ratios when pH=3;

[0035] Figure 2 b represents the leaching of fluorine at different solid-liquid ratios when pH=4;

[0036] Figure 2 c represents the leaching of fluorine at different solid-liquid ratios when pH=5;

[0037] Figure 3 This refers to the change in fluoride content during cyclic pickling;

[0038] Figure 4 The concentration of fluoride in the supernatant after adding 0.1% to 2.5% calcium oxide to the pickling solution;

[0039] Figure 5 The pH value of the supernatant after cyclic pickling;

[0040] Figure 6 This is a flowchart of the method of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0042] The following is combined Figures 1-5 The method for reducing fluoride in phosphogypsum according to the present invention includes the following steps: (1) crushing and sieving phosphogypsum; (2) acid washing of phosphogypsum; and (3) treatment of acid washing waste liquid. Specifically, the method includes the following steps: S1: drying phosphogypsum, grinding and sieving it, and then storing it in a sealed bag for drying; S2: adjusting the pH of deionized water to obtain acid washing solution; S3: mixing phosphogypsum and acid washing solution in proportion to obtain a mixture; S4: placing the mixture in a shaker and shaking it for 12 h, then centrifuging and discarding the acid washing waste liquid to obtain acid-washed phosphogypsum; S5: repeating steps S3 and S4 twice with the acid-washed phosphogypsum and then drying it to obtain defluorinated phosphogypsum; S6: adding calcium oxide to the acid washing waste liquid to obtain a waste liquid mixture; S7: placing the waste liquid mixture in a shaker and shaking it for 24 h, then letting it stand and filtering it to obtain purified waste liquid; S8: adjusting the pH of the purified waste liquid to neutral. In step S1, the phosphogypsum is sieved through a 100-mesh sieve (0.15 mm). In step S2, the pH meter is calibrated using standard solutions with pH values ​​of 4.01, 6.86, and 9.18. Then, the pH of the deionized water is adjusted to 4 ± 0.05 using 1 mol / L hydrochloric acid or sodium hydroxide. In step S3, phosphogypsum and pickling solution are mixed at a mass ratio of 1:10. In step S4, the shaking incubator temperature is set to 25 °C and the rotation speed is set to 180 rpm. In step S4, the centrifuge speed is set to 3000 rpm for 4 minutes, and the supernatant is discarded after centrifugation. In step S5, the defluorinated phosphogypsum is dried in an oven at 60 °C until constant weight. In step S6, the added calcium oxide mass is 2.5% of the pickling waste liquid mass. In step S7, the shaking incubator temperature is set to 25 °C and the rotation speed is set to 180 rpm. In step S8, the pH of the purified waste liquid is adjusted to neutral using 1 mol / L hydrochloric acid or sodium hydroxide.

[0043] Furthermore, specific methods include the following embodiments:

[0044] Example 1: Selection of pH for pickling solution

[0045] (1) Pretreatment of phosphogypsum materials:

[0046] First, dry the phosphogypsum at 60 ℃, grind it using an agate mortar and pestle, then pass it through a 100-mesh (0.15 mm) sieve and store it in a sealed bag to dry.

[0047] (2) Prepare pickling solution:

[0048] First, calibrate the pH meter using standard solutions with pH values ​​of 4.01, 6.86, and 9.18. Then, adjust the pH of the deionized water to 3, 4, 5, 6, 7, 8, 9, 10, and 11, respectively, using 1 mol / L hydrochloric acid and sodium hydroxide.

[0049] (3) Leaching removal of fluoride from phosphogypsum:

[0050] Phosphogypsum and pickling solution were mixed at a mass ratio of 1:10 and shaken in a shaker at 25 ℃ and 180 rpm for 168 h. The supernatant was collected at 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 120 h, and 168 h to determine the fluoride content. The fluoride content in the supernatant is shown in the figure. Figure 1 .

[0051] As shown in the figure, phosphogypsum reaches fluoride leaching equilibrium within 12 hours; the fluoride leaching amount is the highest at pH=4. Therefore, this method selects deionized water with pH=4 as the acid washing medium, and the single leaching time is set to 12 hours.

[0052] Example 2: Selection of solid-liquid ratio during pickling

[0053] (1) Pretreatment of phosphogypsum materials:

[0054] First, dry the phosphogypsum at 60 ℃, grind it using an agate mortar and pestle, then pass it through a 100-mesh (0.15 mm) sieve and store it in a sealed bag to dry.

[0055] (2) Prepare pickling solution:

[0056] First, calibrate the pH meter using standard solutions with pH values ​​of 4.01, 6.86, and 9.18. Then, adjust the pH of the deionized water to 3 ± 0.05 using 1 mol / L hydrochloric acid and sodium hydroxide.

[0057] (3) Leaching removal of fluoride from phosphogypsum:

[0058] Phosphogypsum and pickling solution were mixed at mass ratios of 1:10, 1:50, and 1:100, respectively, and shaken in a shaker at 25 ℃ and 180 rpm for 168 h. The supernatant was collected at 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h, 120 h, and 168 h to determine the fluoride content. (See attached table for fluoride content determination of the supernatant). Figure 2 a.

[0059] Example 3: Selection of solid-liquid ratio during pickling

[0060] The selection of the solid-liquid ratio during pickling is basically the same as in Example 2, except that the pH in step (2) is adjusted to 4 ± 0.05, and the fluoride content of the supernatant is measured as shown in the figure. Figure 2 b.

[0061] Example 4: Selection of solid-liquid ratio during pickling

[0062] The selection of the solid-liquid ratio during pickling is basically the same as in Example 2, except that the pH in step (2) is adjusted to 5 ± 0.05, and the fluoride content of the supernatant is measured as shown in the figure. Figure 2 c.

[0063] Depend on Figure 2 It can be seen that when the solid-liquid mass ratio of phosphogypsum to deionized water is 1:10, the fluorine leaching amount is significantly higher than that at 1:50 and 1:100. Therefore, this method determines a solid-liquid mass ratio of 1:10 as the pickling condition.

[0064] Example 5: A method for removing soluble fluoride from phosphogypsum

[0065] (1) Pretreatment of phosphogypsum materials:

[0066] First, dry the phosphogypsum at 60 ℃, grind it using an agate mortar and pestle, then pass it through a 100-mesh (0.15 mm) sieve and store it in a sealed bag to dry.

[0067] (2) Prepare pickling solution:

[0068] First, calibrate the pH meter using standard solutions with pH values ​​of 4.01, 6.86, and 9.18. Then, adjust the pH of the deionized water to 4 ± 0.05 using 1 mol / L hydrochloric acid and sodium hydroxide.

[0069] (3) Leaching removal of fluoride from phosphogypsum:

[0070] Phosphogypsum and pickling solution were mixed at a mass ratio of 1:10 and shaken in a shaker at 25 ℃ and 180 rpm for 12 h. The supernatant was collected at 2 h, 4 h, 8 h, and 12 h to determine the fluoride content. The fluoride content in the supernatant is shown in the figure below. Figure 3 The pH of the supernatant was measured after each reaction. The pH measurement results are shown in [the table below]. Figure 5 Then, centrifuge at 3000 rpm for 4 minutes. After centrifugation, discard the acid washing waste liquid and repeat the above steps twice to obtain defluorinated phosphogypsum. Dry the defluorinated phosphogypsum in a 60 ℃ forced-air drying oven until constant weight. The fluorine content in the original phosphogypsum and defluorinated phosphogypsum is shown in Table 1.

[0071] As shown in Table 1, after cyclic acid washing, the fluorine content in phosphogypsum decreased by 746.7 mg / kg.

[0072] Depend on Figure 3 It can be seen that the fluoride concentration of the pickling solution in the first pickling is as high as 61.43 mg / L, the fluoride concentration of the pickling solution in the second pickling is reduced to 18.57 mg / L, the fluoride concentration of the pickling solution in the third pickling is 2.08 mg / L, and the fluoride concentration of the pickling solution in the fourth pickling is reduced to 0.98 mg / L, which is lower than the value specified in GB3838-2002 Surface Water Environmental Quality Standard. Therefore, this method adopts three-cycle water washing.

[0073] Figure 5 It can be seen that after cyclic acid washing, the pH of the supernatant gradually increases and the acidity decreases.

[0074] Example 6: Purification of pickling waste liquid

[0075] (1) Mixing of pickling waste liquid

[0076] Collect the pickling waste liquid from the three pickling processes and mix it thoroughly in a beaker.

[0077] (2) Purification of pickling waste liquid

[0078] Add 2.5% (w / w) calcium oxide to the pickling waste liquid, shake in a shaker for 24 hours, let stand, and filter to obtain purified waste liquid. The fluoride content in the purified waste liquid is shown in the figure. Figure 4 Adjust the pH of the solution to neutral using 1 mol / L hydrochloric acid and sodium hydroxide before discharging.

[0079] As shown in the figure, after combining the three pickling waste liquids, calcium oxide was added at a concentration of 0.1%-2.5% of the pickling waste liquid mass. When the calcium oxide dosage was 2.5%, the fluoride removal rate in the supernatant was the highest, and the residual fluoride concentration was reduced to the lowest.

[0080] Example 7: Determination of total fluoride content and soluble fluoride content

[0081] (1) Preparation of hydrochloric acid (1+1):

[0082] Add 1 volume of concentrated hydrochloric acid to 1 volume of deionized water and cool to room temperature to prepare hydrochloric acid (1+1).

[0083] (2) Sample preparation for total fluoride content determination:

[0084] According to the method for determination of phosphorus and fluorine in phosphogypsum (JC / T2073-2011), weigh 1 g of dried phosphogypsum and place it in a 100 mL beaker. Add 10 mL of deionized water to disperse it, then add 12 mL of hydrochloric acid (1+1). Heat to a gentle boil and maintain for 1-2 min. Dilute with deionized water to about 50 mL and add to a 250 mL volumetric flask. After cooling, make up to volume.

[0085] (3) Sample preparation for determining soluble fluoride content

[0086] Weigh 5 g of dried phosphogypsum into a 50 mL beaker, add 50 mL of deionized water, and shake in a shaker at 25 ℃ and 180 rpm for 12 h.

[0087] (4) Preparation of TISAB buffer

[0088] According to GB / T 15555.11-1995 Determination of Fluorides in Solid Waste by Ion Selective Electrode Method, 500 mL of deionized water is measured into a 1 L beaker, 57 mL of glacial acetic acid, 58 g of sodium chloride and 4 g of cyclohexanediaminetetraacetic acid are added, and after stirring to dissolve, 125 mL of 6 mol / L sodium hydroxide is slowly added to bring the pH to between 5.0 and 5.5 to prepare TISAB buffer.

[0089] (5) Fluorine concentration determination

[0090] Take 10 mL of sample and 10 mL of TISAB buffer in a volumetric flask, add deionized water to bring the volume to 50 mL, pour into a polypropylene beaker, place the rotor, fluoride ion selective electrode and reference electrode in the beaker, stop the rotor after 5 min, and count after the reading stabilizes.

[0091] In summary, the pickling solution used in this invention is simple, and the solution used to adjust the pH of the pickling solution is common and readily available. The pickling method is simple and easy to operate, requiring no complex instruments or equipment, thus achieving efficient treatment. In this invention, fluorine is leached in ionic form, which is easily separated from the solid form of phosphogypsum, resulting in more thorough fluorine removal. The phosphogypsum cleaned by this invention ultimately contains only 0.02% fluorine, achieving a fluorine removal rate of 90%, and the acidity is slightly reduced, thus reducing harm to the natural environment and facilitating subsequent utilization.

[0092] Table 1: Fluorine content in phosphogypsum before and after acid washing

[0093]

[0094] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art based on the technical solution and concept of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for removing soluble fluoride from phosphogypsum, comprising the following steps: S1: Dry the phosphogypsum, grind and sieve it, then store it in a sealed bag while it is still dry. S2: Adjust the pH of the deionized water to obtain the pickling solution; S3: Mix phosphogypsum and pickling solution in a certain proportion to obtain a mixture; S4: Place the mixture in a shaker and shake for 12 h. After shaking, centrifuge and discard the pickling waste liquid to obtain pickled phosphogypsum. S5: Repeat steps S3 and S4 twice with the acid-washed phosphogypsum and then dry it to obtain defluorinated phosphogypsum. S6: Add calcium oxide to the pickling waste liquid to obtain a waste liquid mixture; S7: Place the waste liquid mixture in a shaker and shake for 24 hours. After shaking, let it stand and filter to obtain purified waste liquid. S8: Adjust the pH of the purified waste liquid to neutral.

2. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S1, the phosphogypsum is sieved through a 100-mesh sieve (0.15 mm).

3. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In S2, the pH meter is first calibrated using standard solutions with pH values ​​of 4.01, 6.86, and 9.

18. Then, the pH of the deionized water is adjusted to 4 ± 0.05 using 1 mol / L hydrochloric acid or sodium hydroxide.

4. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S3, phosphogypsum and pickling solution are mixed at a mass ratio of 1:

10.

5. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S4, the temperature of the shaker is set to 25 ℃ and the rotation speed is set to 180 rpm.

6. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S4, the centrifuge speed is set to 3000 rpm, centrifuged for 4 minutes, and the supernatant is poured out after centrifugation.

7. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S5, the defluorinated phosphogypsum is placed in an oven at 60 °C and dried to constant weight.

8. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S6, the mass of calcium oxide added is 2.5% of the mass of the pickling waste liquid.

9. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S7, the temperature of the shaker is set to 25 ℃ and the rotation speed is set to 180 rpm.

10. The method for removing soluble fluoride from phosphogypsum according to claim 1, characterized in that, In step S8, the pH of the purified waste liquid is adjusted to neutral using 1 mol / L hydrochloric acid or sodium hydroxide.

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