A method for washing chloride radicals from zirconium hydroxide filter cake

Abstract

A method for washing chloride ions from a zirconium hydroxide filter cake comprises the following steps: (1) adding the zirconium hydroxide slurry after neutralization and precipitation reaction to a vacuum filter, starting suction filtration, and removing mother liquor until the height difference between the mother liquor level and the filter cake surface is 10-20% of the filter cake thickness; (2) adding a washing liquid to the filter cake in the vacuum filter, wherein the washing liquid is ammonia water with a pH value of 9.5-10.5; removing the filtrate that has been exchanged with the filter cake by suction filtration until the height difference between the washing liquid level and the filter cake surface is 10-20% of the filter cake thickness; (3) sampling and detecting the chloride ion concentration of the filter cake after treatment in step (2); if the chloride ion concentration is equal to or lower than the control requirement value, proceeding to step (4); if the chloride ion concentration is higher than the control requirement value, returning to step (2); (4) continuing suction filtration to remove excess water in the filter cake until the filter cake meets the solid content control requirement. The present invention can quickly and effectively remove chloride ions from the zirconium hydroxide filter cake, is simple to operate, and helps reduce production costs.

Description

Technical Field

[0001] The invention relates to a method for washing a filter cake, in particular to a method for washing chloride radicals of a zirconium hydroxide filter cake. Background Art

[0002] The co-precipitation method is used to prepare zirconium hydroxide, which mainly uses zirconium oxychloride and ammonia water for neutralization precipitation reaction. The main reaction is: ZrOCl2 + 2NH4OH + nH2O = ZrO(OH)2∙nH2O↓ + 2NH4Cl. Therefore, the main impurity contained in the final zirconium hydroxide filter cake is Cl - Because Cl - The presence of salt bridges causes hard agglomerates between the colloid particles. If they are not removed, it will seriously affect the quality control of subsequent products.

[0003] At present, there are four common methods for washing chloride ions in zirconium hydroxide filter cakes: displacement washing, slurry washing, step-by-step dilution washing and centrifugal washing.

[0004] The displacement washing method is to wash the surface of the filter cake with a washing liquid, and then under the action of external force, the washing liquid passes through the filter cake for displacement and mass transfer to remove impurities in the filter cake.

[0005] Slurry washing, also known as re-slurry washing, refers to using fresh washing liquid to mechanically turn the filter cake into slurry for re-filtration. Generally, this process needs to be repeated several times until the washing requirements are met.

[0006] Step-by-step dilution washing means that when the filter cake is in a slurry state, after most of the mother liquor is removed during the concentration filtration, the slurry is then injected with new washing liquid for dilution, and then re-concentrated and diluted again. This operation is repeated until the filter cake meets the washing requirements.

[0007] The centrifugal washing method means that the filter cake formed after filtration is always filled with liquid layer, and fresh washing liquid is continuously added until the washing requirements are met.

[0008] All of the above washing methods are difficult to meet the requirements of both effectiveness and ease of operation. Among them, the equipment and operation used in the slurry washing method, the step-by-step dilution washing method and the centrifugal washing method are relatively complex. The displacement washing method is less effective and it is difficult to effectively remove chloride ions from the zirconium hydroxide filter cake. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for washing chloride ions from zirconium hydroxide filter cakes, which can quickly and effectively remove chloride ions from zirconium hydroxide filter cakes and is simple to operate. The technical solution adopted is as follows:

[0010] A method for washing chloride radicals from a zirconium hydroxide filter cake, characterized in that it comprises the following steps in sequence:

[0011] (1) Add the zirconium hydroxide slurry after the neutralization precipitation reaction into a vacuum filter, start the filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is 10-20% of the filter cake thickness;

[0012] (2) Add washing liquid to the filter cake in the above vacuum filter. The washing liquid is ammonia water with a pH value of 9.5-10.5. The mass ratio of filter cake to washing liquid is 1:(2.2-2.5). During and after the addition of washing liquid, continue to filter and remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is 10-20% of the filter cake thickness.

[0013] (3) sampling and testing the chloride concentration of the filter cake after treatment in step (2); if the chloride concentration is equal to or lower than the control requirement value, proceed to step (4); if the chloride concentration is higher than the control requirement value, return to step (2) and perform the next operation of adding washing liquid and filtering;

[0014] (4) Continue to filter and remove excess water from the filter cake until the filter cake meets the solid content control requirements.

[0015] In step (3), if the measured chloride concentration is equal to or lower than the required value, it is determined that the zirconium hydroxide filter cake meets the washing requirements.

[0016] In the above step (3), the method for sampling and detecting the chloride concentration of the filter cake after treatment in step (2) is as follows: when the filtration in step (2) approaches the end point, a sample is taken from the filtrate that has been exchanged with the filter cake, and the chloride concentration of the filtrate sample is detected; the chloride concentration of the filtrate sample can represent the chloride concentration of the filter cake after treatment in step (2).

[0017] In the above step (1), the chloride concentration of the filter cake obtained after removing the mother liquor is about 40,000-50,000 ppm.

[0018] The mass of the filter cake in step (2) can be determined as follows: a certain mass of zirconium hydroxide slurry from the same batch after neutralization and precipitation reaction is added to a vacuum filter, and the mother liquor is removed by filtration until the mother liquor in the filter cake is completely removed. The mass of the filter cake is then weighed, and the mass ratio of the filter cake to the zirconium hydroxide slurry is calculated. In subsequent production, the mass of the filter cake formed after vacuum filtration of a certain mass of zirconium hydroxide slurry can be calculated according to the mass ratio as the mass of the filter cake in step (2). For example, if 100g of zirconium hydroxide slurry is filtered through a vacuum filter and the mother liquor is completely removed, the mass of the filter cake obtained is 20g. Then, in subsequent production, when the chloride washing method of the present invention is used, if 200g of zirconium hydroxide slurry is added to the vacuum filter in step (1), the mass of the filter cake in step (2) can be determined to be 40g.

[0019] In step (2), the clean washing liquid on the upper layer of the filter cake is forced to pass through the filter cake for displacement and mass transfer by using the vacuum filtration pressure, so that the chloride ions contained in the filter cake are carried away by the washing liquid, thereby removing the chloride ions. Adding liquid while filtering can keep the washing liquid on the upper layer of the filter cake constantly replaced and diluted, so that the chloride ion content contained in the washing liquid on the upper layer of the filter cake is minimized, thereby maximizing the difference in chloride ion concentration between the filter cake and the washing liquid on the upper layer. In this way, the chloride ions in the filter cake can be carried away more quickly by the filtrate, thereby improving the washing effect.

[0020] In step (2), the height difference between the washing liquid level and the filter cake surface is set to 10-20% of the filter cake thickness. This is mainly to ensure that the filter cake surface is covered with a certain height of washing liquid during the washing process, thereby preventing the filter cake from cracking after the filtrate is drained. If the filter cake is partially cracked, the penetration resistance of the washing liquid at the crack will be relatively small, resulting in the washing liquid easily penetrating into the crack, and other areas of the filter cake will not be fully washed, resulting in unsatisfactory chloride removal effect.

[0021] In this system, chloride ions primarily exist as ammonium chloride. When washed with ammonia water of a certain concentration, the alkalinity of the ammonia water can form ammine compounds with the chloride ions in the ammonium chloride molecules, increasing their solubility. This increases the solubility of ammonium chloride in ammonia water, thereby promoting the removal of chloride ions from the filter cake. Experimental comparisons have shown that using ammonia water with a pH of 9.5-10.5 can effectively remove chloride ions while avoiding the cost pressure associated with excessively high ammonia concentrations.

[0022] The present invention utilizes a vacuum filter as displacement washing equipment and ammonia with a pH of 9.5-10.5 as a special washing liquid. This combination achieves the goal of rapidly and effectively removing chloride impurities from zirconium hydroxide filter cakes. Not only does the present invention utilize simple washing equipment and require minimal investment, but the washing liquid is also inexpensive and requires minimal usage. The entire washing process eliminates the need for multiple unloading, making operation simple and helpful in reducing production costs. Furthermore, the present invention rapidly and effectively removes chloride impurities, helping to ensure the quality of the zirconium hydroxide product. DETAILED DESCRIPTION

[0023] The zirconium hydroxide slurry used in all the following examples and comparative examples after neutralization and precipitation was the same type of slurry. After precipitation and removal of the mother liquor, the original filter cake had a chloride content of approximately 45,000 ppm. After vacuum filtration and removal of the mother liquor, 100 g of the zirconium hydroxide slurry was filtered to obtain a filter cake weighing 22 g.

[0024] Example 1

[0025] In this embodiment, the chloride washing method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0026] (1) Add 200 g of the zirconium hydroxide slurry after the neutralization precipitation reaction into a vacuum filter, start the filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is about 0.5 cm (about 15% of the filter cake thickness);

[0027] (2) Add 110 g of washing liquid (mass ratio of filter cake to washing liquid is 1:2.5) to the filter cake in the above vacuum filter. The washing liquid is ammonia water with a pH value of 10.0. During and after the addition of the washing liquid, continue to filter to remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is about 0.5 cm (about 15% of the filter cake thickness).

[0028] (3) sampling and testing the chloride concentration of the filter cake after treatment in step (2); if the chloride concentration is equal to or lower than the control requirement value, proceed to step (4); if the chloride concentration is higher than the control requirement value, return to step (2) and perform the next operation of adding washing liquid and filtering;

[0029] (4) Continue to filter and remove excess water from the filter cake until the filter cake meets the solid content control requirements.

[0030] In the above step (3), the method for sampling and detecting the chloride concentration of the filter cake after treatment in step (2) is as follows: when the filtration in step (2) approaches the end point, a sample is taken from the filtrate that has been exchanged with the filter cake, and the chloride concentration of the filtrate sample is detected; the chloride concentration of the filtrate sample can represent the chloride concentration of the filter cake after treatment in step (2).

[0031] In this embodiment, step (2) of adding the washing solution and filtering was performed three times, and the pH value and amount of the washing solution added were consistent in the three operations. The chloride concentration measured after the first addition of the washing solution and filtering was 5400 ppm, and the chloride concentration measured after the second addition of the washing solution and filtering was 495 ppm.

[0032] The chloride concentration of the zirconium hydroxide filter cake finally obtained was 40 ppm and the solid content was 40.05%.

[0033] Example 2

[0034] In this embodiment, the chloride washing method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0035] (1) Add 150 kg of zirconium hydroxide slurry after neutralization and precipitation reaction into a vacuum filter, start filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is about 5 cm (about 15% of the filter cake thickness);

[0036] (2) Add 80 kg of washing liquid (the mass ratio of filter cake to washing liquid is 1:2.42) to the filter cake in the above vacuum filter. The washing liquid is ammonia water with a pH value of 10.0. During and after the addition of the washing liquid, continue to filter and remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is about 5 cm (about 15% of the filter cake thickness).

[0037] (3) sampling and testing the chloride concentration of the filter cake after treatment in step (2); if the chloride concentration is equal to or lower than the control requirement value, proceed to step (4); if the chloride concentration is higher than the control requirement value, return to step (2) and perform the next operation of adding washing liquid and filtering;

[0038] (4) Continue to filter and remove excess water from the filter cake until the filter cake meets the solid content control requirements.

[0039] In the above step (3), the method for sampling and detecting the chloride concentration of the filter cake after treatment in step (2) is as follows: when the filtration in step (2) approaches the end point, a sample is taken from the filtrate that has been exchanged with the filter cake, and the chloride concentration of the filtrate sample is detected; the chloride concentration of the filtrate sample can represent the chloride concentration of the filter cake after treatment in step (2).

[0040] In this embodiment, step (2) of adding the washing solution and filtering was performed three times, and the pH value and amount of the washing solution added were consistent in the three operations. The chloride concentration measured after the first addition of the washing solution and filtering was 8100 ppm, and the chloride concentration measured after the second addition of the washing solution and filtering was 760 ppm.

[0041] The chloride concentration of the zirconium hydroxide filter cake finally obtained was 60 ppm and the solid content was 37.98%.

[0042] 1. Repeatability test

[0043] In addition to the above examples, the applicant also conducted a stability test on the same type of zirconium hydroxide filter cake using the same method as in Examples 1 and 2 to verify the feasibility of the washing method of the present invention. The conditions and results of the repeatability test are shown in Table 1 below.

[0044] Table 1

[0045] Test No. Slurry quality Single washing liquid dosage pH value of washing liquid ammonia Washing times Chloride results (ppm) Solid content (%) 1# 198g 105g 9.5 3 55 39.63% 2# 205g 110g 10.2 3 65 40.95% 3# 145kg 80kg 9.5 3 65 37.65% 4# 148kg 80kg 10.5 3 60 37.76%

[0046] It can be seen from the test results in Table 1 that the chloride and solid content results of different batches of zirconium hydroxide filter cakes have good repeatability, indicating that the process of the present invention has good stability.

[0047] 2. Comparative Test

[0048] During the research process of this invention, the applicant has tried various other washing methods, such as ultrasonic washing, slurry washing, pure water washing, etc., but the effect of chloride washing on zirconium hydroxide filter cake is not ideal. Some comparative experiments and test results are as follows:

[0049] Comparative Example 1

[0050] In this comparative example, the chloride washing test method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0051] (1) Pour 200 g of the zirconium hydroxide slurry after the neutralization precipitation reaction into a suction filtration container, remove the mother liquor, and obtain a zirconium hydroxide filter cake;

[0052] (2) Add all the above zirconium hydroxide filter cakes into a container, then add 110 g of ammonia water with a pH value of 10.0 as the first washing liquid, stir it evenly by hand, and then put it into an ultrasonicator. After ultrasonication for 25 minutes, pour all the slurry into a suction filtration container, remove the filtrate, and obtain the zirconium hydroxide filter cake;

[0053] (3) Repeat step (2) twice, adding ammonia water of the same quality and specification as the second and third washing liquids, respectively. The resulting zirconium hydroxide filter cake has a chloride concentration of 1583 ppm and a solid content of 25%.

[0054] By adopting the method of Comparative Example 1, the water content of the zirconium hydroxide filter cake will increase significantly during the washing process, and the mass of the zirconium hydroxide filter cake will increase.

[0055] Comparative Example 2

[0056] In this comparative example, the chloride washing test method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0057] (1) Pour 200 g of the zirconium hydroxide slurry after the neutralization precipitation reaction into a suction filtration container, remove the mother liquor, and obtain a zirconium hydroxide filter cake;

[0058] (2) Add all the above zirconium hydroxide filter cakes into a container, and then add 110g of ammonia water with a pH value of 10.0 as the first washing liquid. After stirring at room temperature for 25 minutes using a mechanical stirring paddle, pour all the slurry into a suction filtration container, remove the filtrate, and obtain the zirconium hydroxide filter cake;

[0059] (3) Repeat step (2) twice, adding ammonia water of the same mass and specification as the second washing liquid and the third washing liquid respectively; the chloride concentration of the zirconium hydroxide filter cake finally obtained is 1069 ppm and the solid content is 31.02%.

[0060] By adopting the method of Comparative Example 2, the water content of the zirconium hydroxide filter cake will increase significantly during the washing process, and the mass of the zirconium hydroxide filter cake will increase.

[0061] Comparative Example 3

[0062] In this comparative example, the chloride washing test method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0063] (1) Add 200 g of the zirconium hydroxide slurry after the neutralization precipitation reaction into a vacuum filter, start the filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is about 0.5 cm;

[0064] (2) Add 110 g of washing liquid (pure water) to the filter cake in the vacuum filter. Continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is approximately 0.5 cm.

[0065] (3) Add 110 g of washing liquid (pure water) to the filter cake in the vacuum filter again; continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is about 0.5 cm;

[0066] (4) Add 110 g of washing liquid (pure water) to the filter cake in the vacuum filter for the third time; continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake;

[0067] (5) Continue to filter until all excess water in the filter cake is completely removed.

[0068] The chloride concentration of the zirconium hydroxide filter cake finally obtained was 1980 ppm and the solid content was 40.05%.

[0069] Comparative Example 4

[0070] In this comparative example, the chloride washing test method of the zirconium hydroxide filter cake comprises the following steps in sequence:

[0071] (1) Add 200 g of the zirconium hydroxide slurry after the neutralization precipitation reaction into a vacuum filter, start the filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is about 0.5 cm;

[0072] (2) Add 110 g of washing liquid, which is ammonia water with a pH value of 8.3, to the filter cake in the above vacuum filter; continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is about 0.5 cm;

[0073] (3) Add 110 g of washing liquid to the filter cake in the vacuum filter again. The washing liquid is ammonia water with a pH value of 8.3. Continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is about 0.5 cm.

[0074] (4) Add 110 g of washing liquid to the filter cake in the vacuum filter for the third time. The washing liquid is ammonia water with a pH value of 8.3. Continue to filter during and after the addition of the washing liquid to remove the filtrate that has exchanged with the filter cake.

[0075] (5) Continue to filter until all excess water in the filter cake is completely removed.

[0076] The chloride concentration of the zirconium hydroxide filter cake finally obtained was 585 ppm and the solid content was 37.17%.

[0077] As can be seen, the vacuum filtration washing method employed in the present invention, using ammonia water with a pH of 9.5-10.5 as the washing liquid, produces a significantly lower chloride content in the resulting zirconium hydroxide filter cake compared to the four methods of ultrasonic washing, reslurry washing, and using only pure water or low-pH (approximately pH 8-9) ammonia water as the washing liquid, given the same number of washes and the same amount of washing liquid. This demonstrates that the washing method of the present invention is the most effective in removing chloride from the zirconium hydroxide filter cake, and the entire process does not require multiple unloading, resulting in a simple and convenient operation. Therefore, the present invention is a simple and effective method for washing chloride from zirconium hydroxide filter cake.

Claims

1. A method for washing chloride radicals from zirconium hydroxide filter cakes, characterized in that The steps are as follows: (1) Add the zirconium hydroxide slurry after the neutralization precipitation reaction into a vacuum filter, start the filtration, and remove the mother liquor until the height difference between the mother liquor level and the filter cake surface is 10-20% of the filter cake thickness; (2) Add washing liquid to the filter cake in the above vacuum filter. The washing liquid is ammonia water with a pH value of 9.5-10.

5. The mass ratio of filter cake to washing liquid is 1:(2.2-2.5). During and after the addition of washing liquid, continue to filter and remove the filtrate that has exchanged with the filter cake until the height difference between the washing liquid level and the filter cake surface is 10-20% of the filter cake thickness. (3) sampling and testing the chloride concentration of the filter cake after treatment in step (2); if the chloride concentration is equal to or lower than the control requirement value, proceed to step (4); if the chloride concentration is higher than the control requirement value, return to step (2) and perform the next operation of adding washing liquid and filtering; (4) Continue to filter and remove excess water from the filter cake until the filter cake meets the solid content control requirements.

2. The method for washing the zirconium hydroxide filter cake with chloride according to claim 1, wherein: In step (3), the method for sampling and detecting the chloride concentration of the filter cake after treatment in step (2) is as follows: when the filtration in step (2) approaches the end point, a sample is taken from the filtrate that has been exchanged with the filter cake, and the chloride concentration of the filtrate sample is detected; the chloride concentration of the filtrate sample can represent the chloride concentration of the filter cake after treatment in step (2).

3. The method for washing the zirconium hydroxide filter cake with chloride according to claim 1, wherein: In step (1), the chloride concentration of the filter cake obtained after removing the mother liquor is 40,000-50,000 ppm.