Treatment method of phosphogypsum

Abstract

The invention discloses a phosphogypsum treatment method, and belongs to the technical field of phosphorus chemical industry. The method comprises the following steps: S1, collecting cooling wastewater generated in preparation of sulfuric acid from pyrite, and adding quick lime or slaked lime to adjust the pH value to 7.2-7.5; s2, washing the phosphogypsum with water; s3, mixing the cooling wastewater subjected to pH adjustment with the phosphogypsum subjected to water washing according to a mass ratio of (5-8): 1, stirring for 30-45 minutes, standing for 45-120 minutes, and separating supernate; s4, adding water into the sediment after the supernate is separated, repulping until the solid content is 23-28%, and carrying out solid-liquid separation to obtain treated phosphogypsum; wherein the cooling wastewater comes from a slag cooler and a cylinder humidifier; waste water obtained after washing in the step S2, supernate obtained in the step S3 and liquid obtained after solid-liquid separation in the step S4 are used as ardealite backwater. The cooling wastewater of sulfuric acid prepared from pyrite is treated by phosphogypsum, soluble phosphorus of the phosphogypsum is washed out, and the arsenic content and the iron content of the wastewater are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphorus chemical industry, and particularly relates to a method for processing phosphogypsum. Background Art

[0002] The preparation process of phosphoric acid is as follows: phosphoric acid is obtained by reacting phosphate slurry with concentrated sulfuric acid, and phosphogypsum and phosphogypsum return water are produced as byproducts, and the phosphogypsum return water is recycled; the amount of phosphogypsum produced is very large and usually cannot be treated, and is generally buried or piled up. Concentrated sulfuric acid can be obtained from pyrite through roasting, purification, conversion and absorption sections, etc. For details, please refer to the description of the patent with application number CN201410478737.4. The roasting section will produce a large amount of wastewater, and the wastewater in the roasting section is mainly the wastewater discharged during the cooling and humidification process of the hot slag.

[0003] For example, the patent with application number CN201110179254.0 discloses an integrated enhanced pelletizing process for hot slag waste heat and slag humidification. The hot slag discharged from the boiling furnace enters the slag cooler, and the heat exchange between water and hot slag is used inside the slag cooler to reduce the slag temperature to below 200°C. The slag is then transported to the slag intermediate bin, where the slag from the boiling furnace, waste heat boiler, and cyclone dust collector are combined. The combined slag comes out of the slag intermediate bin and enters the cylindrical humidifier for humidification with water and further cooling. After humidification to a water content of 14-17% by weight, it is transported to the slag material bin to further make the slag surface evenly moistened with water, thereby improving its balling properties.

[0004] The wastewater from the slag cooler and the drum humidifier has the following characteristics: 1. It has a high temperature, 2. It is weakly acidic, 3. It contains a lot of particulate matter, and 4. It contains high arsenic and iron content. The wastewater usually needs to be cooled and settled before being sent to the factory's sewage treatment plant for treatment. Summary of the invention In order to solve the above problems, the embodiment of the present invention provides a method for treating phosphogypsum, which uses phosphogypsum to treat the cooling wastewater of sulfuric acid produced from pyrite, washes out the soluble phosphorus in the phosphogypsum (fluorine is also washed out, but the extent is lower than that of phosphorus), and reduces the arsenic content and iron content of the wastewater (both of which affect the quality of phosphoric acid preparation). The technical solution is as follows: See also Figure 1 The embodiment of the present invention provides a method for treating phosphogypsum, the method comprising: S1: Collect cooling wastewater from sulfuric acid production from pyrite, add quicklime or slaked lime to adjust the pH value to 7.2-7.5 (first adjust to allow iron ions to react with alkali to obtain iron salts with flocculation effect; experiments show that the effect is better than adding quicklime or slaked lime in step S3).

[0005] S2: Wash the phosphogypsum. The conditions for washing the phosphogypsum are: mix the phosphogypsum and water in a mass ratio of 1:3-4, stir for 20-35 minutes, and then separate the solid and liquid. Washing can wash away the soluble impurities on the phosphogypsum and reduce the possibility of interaction with cooling wastewater.

[0006] S3: Mix the cooled wastewater after adjusting pH and cooling (cooling to 40-55℃, high temperature can slightly improve the extraction effect of soluble phosphorus, but it will significantly increase the F content of the wastewater) with the washed phosphogypsum in a mass ratio of 5-8:1 (experiments have shown that increasing the amount of water can slightly improve the effect, but it can significantly increase the water consumption, which is not cost-effective), stir for 30-45 minutes, let it stand for 45-120 minutes, and separate the supernatant.

[0007] S4: After separating the supernatant, water is added to the sediment to re-slurry until the solid content is 23-28%, and the solid-liquid separation is performed to obtain the treated phosphogypsum (processed according to the conventional processing flow, buried, piled or sent to a special solid waste treatment manufacturer, etc.).

[0008] Among them, the cooling waste water comes from the slag cooler and the cylindrical humidifier; the waste water after water washing in step S2, the supernatant in step S3 and the liquid from solid-liquid separation in step S4 are used as phosphogypsum return water.

[0009] Specifically, solid-liquid separation is performed by filter pressing (steps S2 and S4).

[0010] Preferably, in step S3, after stirring for 30-40 minutes, the mixture is allowed to stand for 60-90 minutes.

[0011] The technical solution provided by the embodiment of the present invention has the following beneficial effects: (1) Treat the cooling wastewater from the production of sulfuric acid from pyrite, and use the treated wastewater as phosphogypsum return water to reduce the amount of wastewater treated and discharged.

[0012] (2) It can reduce the arsenic content (removal rate greater than 60%) and iron content (removal rate greater than 85%) in cooling wastewater, reducing the impact on phosphoric acid production; it can increase the pH value of wastewater (can be increased by about 0.4-0.5), which is beneficial to the use of phosphogypsum return water.

[0013] (3) Further extraction of soluble phosphorus from phosphogypsum is achieved by cooling the wastewater. Water washing can only extract a portion of the soluble phosphorus. Increasing the water washing time, water washing amount and water washing times has basically no further effect on the extraction of soluble phosphorus.

[0014] (4) Although alkaline solution can increase the extraction of soluble phosphorus, the extraction effect is not as good as that of this patent, and the extraction effect of F is better than that of this patent; high F content is not conducive to the use of phosphogypsum return water.

[0015] (5) The washed and re-pulped phosphogypsum slurry has good solid-liquid separation, which improves the processing speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the method for processing phosphogypsum provided by the present invention. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0018] Example 1 Embodiment 1 provides a method for treating phosphogypsum, the method comprising: S1: Collect the cooling wastewater from the production of sulfuric acid from pyrite, and add quicklime to adjust the pH value to 7.4.

[0019] S2: washing the phosphogypsum. The conditions for washing the phosphogypsum are: mixing the phosphogypsum with water in a mass ratio of 1:4, stirring for 30 minutes, and then separating the solid and the liquid.

[0020] S3: The cooling wastewater after pH adjustment and cooling (cooling to 50°C and achieving reaction at the same time) is mixed with the washed phosphogypsum in a mass ratio of 6:1, stirred for 32 minutes, allowed to stand for 60 minutes, and the supernatant was separated.

[0021] S4: After separating the supernatant, water is added to the sediment to re-slurry until the solid content is 25%, and the solid-liquid separation is performed to obtain the treated phosphogypsum.

[0022] Among them, the cooling wastewater comes from the slag cooler and the cylinder humidifier; the parameters of the cooling wastewater are shown in Table 1: Table 1

[0023] The wastewater after water washing in step S2, the supernatant in step S3 and the liquid after solid-liquid separation in step S4 are used as phosphogypsum return water; the parameters of the liquid after water washing in step S2, the supernatant in step S3 and the liquid after solid-liquid separation in step S4 (the mass is about 1.8 times the mass of cooling wastewater) are shown in Table 2: Table 2

[0024] Among them, the parameters of phosphogypsum in each step are shown in Table 3: Table 3

[0025] As can be seen from Table 3, the extraction effect of soluble phosphorus is not good only by water washing. The repulping process can only slightly improve the extraction effect of soluble phosphorus. The recovery rates of soluble phosphorus and fluorine in this patent are both around 50%.

[0026] From Tables 1 and 2, we can get Table 4: Table 4

[0027] As can be seen from Table 4, the method of this patent can significantly reduce the concentrations of arsenic and iron ions in the treated wastewater.

[0028] Example 2 Embodiment 2 provides a method for treating phosphogypsum, the method comprising: S1: Collect the cooling wastewater from the production of sulfuric acid from pyrite, and add slaked lime to adjust the pH value to 7.5.

[0029] S2: washing the phosphogypsum. The conditions for washing the phosphogypsum are: mixing the phosphogypsum with water in a mass ratio of 1:3.6, stirring for 35 minutes, and then separating the solid and the liquid.

[0030] S3: Mix the cooling wastewater after pH adjustment and cooling (cooling to 50°C) with the washed phosphogypsum in a mass ratio of 7:1, stir for 35 minutes, let stand for 75 minutes, and separate the supernatant.

[0031] S4: After separating the supernatant, water is added to the sediment to re-slurry until the solid content is 24%, and the solid-liquid separation is performed to obtain the treated phosphogypsum.

[0032] Comparative Example 1 Only water washing was performed, and the water washing process was carried out according to Example 1, and the number of water washings was twice. The results are shown in Table 5: Table 5

[0033] It can be seen from Table 5 that the effect of water washing is average, and increasing the number of water washings does not improve the effect.

[0034] Comparative Example 2 Only water washing, the water washing process is carried out according to Example 1, and alkali washing is carried out after water washing (quicklime is added to adjust the pH value to about 8, the amount is adjusted according to the needs, and the alkali washing process is carried out according to the prior art). The results are shown in Table 6: Table 6

[0035] It can be seen from Table 6 that adding alkaline washing can further improve the effect on the basis of water washing, but the effect is not as good as that of this patent, and a large amount of fluorine will be washed out, which will significantly increase the fluorine content in the wastewater.

[0036] Comparative Example 3 Step S2 was not performed (i.e., water washing was not performed), and the other processes were consistent with Example 1. The results are shown in Table 7: Table 7

[0037] It can be seen from Tables 5 and 7 that although water washing is not effective, it is necessary. The applicant speculates that the composition of phosphogypsum is complex and the acidity is low (water washing can remove some impurities and reduce acidity), and the composition of cooling wastewater is complex, and direct mixing will produce unpredictable reactions.

[0038] Comparative Example 4 In step S1, the pH value was not adjusted (i.e., quicklime was not added) and the pH value was adjusted to 8.5 by adding quicklime. The other processes were consistent with Example 1. The results are shown in Table 8: Table 8

[0039] It can be seen from Table 8 that in step S1, the pH value has a good effect only within a specific range.

[0040] Comparative Example 5 In step S1, quicklime was not added, but in step S3, quicklime equal to that in Example 1 was added, and the other processes were consistent with those in Example 1. The results are shown in Table 9: Table 9

[0041] It can be seen from Table 9 that, compared with Comparative Example 5, adding quicklime to the cooling wastewater in advance has a better effect.

[0042] Comparative Example 6 In step S3, instead of using cooling wastewater, tap water + quicklime was used, and the pH value was adjusted to 7.4; the other processes were consistent with Example 1. The results are shown in Table 10: Table 10

[0043] It can be seen from Table 6 and Table 10 that the effect of directly using lime water in step S3 is not good.

[0044] Comparative Example 7 Step S3 is not performed, and the other processes are consistent with Example 1. The results are shown in Table 11: Table 11

[0045] It can be seen from Table 11 that in step S3, although cooling the wastewater will increase the extraction effect of fluorine, the extraction effect of soluble P is obviously better than that of fluorine, which is beneficial to the use of phosphogypsum return water.

[0046] Comparative Example 8 Step S4 is not performed, and the other processes are consistent with Example 1. The results are shown in Table 12: Table 12

[0047] It can be seen from Table 12 that reslurry can further improve the extraction effect of soluble phosphorus and significantly increase the filtration speed.

[0048] Comparative Example 9 The steps are as follows: not performing step S4; using tap water + quicklime, adjusting the pH value to 7.4; using tap water + quicklime, adjusting the pH value to 7.4, and not performing step S4. The other processes are consistent with those in Example 1. The results are shown in Table 13: Table 13

[0049] It can be seen from Table 13 that the use of cooling wastewater will significantly increase the difficulty of filtration and require re-slurrying.

[0050] Comparative Example 10 The solid-water ratio of step S2 was adjusted, and the other processes were consistent with Example 1. The results are shown in Table 14: Table 14

[0051] It can be seen from Table 14 that increasing the amount of water can improve the effect, but after the water is increased to a certain level, the improvement in the effect is minimal.

[0052] Comparative Example 11 The solid-water ratio in step S3 was adjusted, and the other processes were consistent with Example 1. The results are shown in Table 15: Table 15

[0053] It can be seen from Table 15 that increasing the amount of water can improve the effect, but after the water is increased to a certain level, the improvement in the effect is minimal.

[0054] Comparative Example 12 The temperature of the cooling water in step S3 was adjusted, and the other processes were consistent with Example 1. The results are shown in Table 16: Table 16

[0055] It can be seen from Table 16 that at room temperature, the effect will be reduced; high temperature can slightly improve the effect, but the improvement of F is more significant, which is more unfavorable to the use of phosphogypsum return water.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating phosphogypsum, characterized in that: The method comprises: S1: Collect the cooling wastewater from the production of sulfuric acid from pyrite, and add quicklime or slaked lime to adjust the pH value to 7.2-7.5; S2: washing the phosphogypsum with water; S3: Mix the pH-adjusted cooling wastewater and the washed phosphogypsum in a mass ratio of 5-8:1, stir for 30-45 minutes, let stand for 45-120 minutes, and separate the supernatant; S4: adding water to the sediment after separation of the supernatant to re-slurry to a solid content of 23-28%, and separating the solid and liquid to obtain the treated phosphogypsum; The cooling wastewater comes from a slag cooler and a cylindrical humidifier; the wastewater after water washing in step S2, the supernatant in step S3 and the liquid after solid-liquid separation in step S4 are used as phosphogypsum return water.

2. The method for treating phosphogypsum according to claim 1, characterized in that: The conditions for washing phosphogypsum are: mixing phosphogypsum and water in a mass ratio of 1:3-4, stirring, and then separating the solid and liquid.

3. The method for treating phosphogypsum according to claim 2, characterized in that: The time for washing and stirring phosphogypsum is 20-35 minutes.

4. The method for treating phosphogypsum according to claim 2, characterized in that: The solid-liquid separation is carried out by filter pressing.

5. The method for treating phosphogypsum according to claim 1, characterized in that: In step S3, the cooling wastewater is cooled to 40-55°C.

6. The method for treating phosphogypsum according to claim 1, characterized in that: In step S3, after stirring for 30-40 minutes, the mixture is allowed to stand for 60-90 minutes.

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