A filter aid for decomposing phosphorite acidolysis liquid with nitric acid and a filtering method

Abstract

This invention relates to the field of filter aids, specifically to a filter aid and filtration method for acid hydrolysis of phosphate rock using nitric acid. The filter aid is a magnetic carbon filter aid, and its preparation includes the following steps: coarse coal gasification slag is thoroughly mixed with an electrolyte solution containing calcium ions and then ground in a ball mill; the mixture is then transferred to a tubular reactor; the reaction product is then immersed in a solution of alginic acid and amino acid iron, ultrasonically vibrated, and centrifuged to obtain a solid product; the solid product is then further processed in the tubular reactor. During filtration, humic acid is first added to the acid hydrolysis solution, stirred, and allowed to settle for initial pressure filtration to obtain initial filter cake and initial filtrate; then, the magnetic carbon filter aid is added to the initial filtrate, stirred, and allowed to settle for secondary pressure filtration. The filter aid provided by this invention can improve the filtration efficiency of the acid hydrolysis solution, and the filter cake from the initial pressure filtration can be used to produce organic-inorganic mixed fertilizer, purifying the environment; it also lays a foundation for improving the quality of subsequent gypsum.

Description

Technical Field

[0001] This invention relates to the field of filter aids, and more specifically to a filter aid and filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution. Background Technology

[0002] Currently, 77% of my country's phosphate rock production is used for processing into phosphate fertilizer. Phosphate rock processing can be divided into thermal and wet processes. The wet process involves decomposing phosphate rock powder with inorganic acids to separate crude phosphoric acid, which is then purified to obtain phosphoric acid products. This process primarily uses sulfuric acid to decompose phosphate rock. This method has low production costs and mature technology, and has long been the dominant method in phosphoric acid production. However, sulfuric acid decomposition of phosphate rock produces large amounts of phosphogypsum. When stored, phosphogypsum not only occupies a large amount of land, but the water-soluble fluorine and phosphorus pentoxide it contains can leach out with rainwater, producing acidic wastewater and causing serious environmental pollution. It also wastes valuable sulfur resources. Currently, various methods for decomposing phosphate rock with nitric acid have been developed abroad. Based on different treatment methods for calcium resources, the main methods that have been industrialized domestically and internationally include: the freezing method, the nitric acid-sulfuric acid or sulfate method, and the nitric acid-phosphoric acid method.

[0003] The acid hydrolysis solution from phosphate rock decomposed by nitric acid contains organic suspended matter and acid-insoluble matter. The acid-insoluble matter mainly includes silica sand, undecomposed minerals, insoluble phosphates, insoluble fluorides, and magnetically insoluble matter. Without treatment, the separation efficiency during solid-liquid separation of the acid hydrolysis solution is extremely low, which cannot meet the needs of industrial production. Moreover, it will be trapped in gypsum during the subsequent decalcification process, which will not only affect the size of dihydrate gypsum crystals and hinder filtration and washing, but also lead to increased nutrient loss and make it difficult to reprocess and utilize gypsum, which is not in line with the circular economy.

[0004] In the application "A process for producing high-concentration nitrate phosphate fertilizer" (application number: 200910009223.3), the acid hydrolysate was treated by sedimentation of acid-insoluble matter. However, there were still fine acid-insoluble matter and organic suspended matter in the solution. Moreover, the sedimentation method required a long time and was not very effective. Summary of the Invention

[0005] To address the technical problems of poor removal efficiency and long removal time of fine acid-insoluble matter and organic suspended matter in the sedimentation treatment of acid hydrolysate produced by nitric acid decomposition of phosphate rock, this invention provides a filter aid and filtration method for acid hydrolysate produced by nitric acid decomposition of phosphate rock.

[0006] In a first aspect, the present invention provides a filter aid for nitric acid decomposition of phosphate rock acid hydrolysis solution. The filter aid is a magnetic carbon filter aid, and the preparation method of the magnetic carbon filter aid includes the following steps:

[0007] (1) Mix the coarse coal gasification residue with an electrolyte solution containing calcium ions at a solid-liquid ratio of 1g:6-8ml and then grind it in a plasma ball mill.

[0008] (2) Transfer the ball-milled product to a tube reactor, heat it to 200-500℃, and react it for 1-3 hours under a steam atmosphere;

[0009] (3) The reaction product obtained in the tubular reactor in step (2) is immersed in a solution of alginate and amino acid iron at a solid-liquid ratio of 1g:10-20ml, ultrasonically vibrated for 1-3h, and then centrifuged to obtain the solid product.

[0010] (4) Place the solid product in a tubular reactor and heat and dry it at a temperature of 300-600℃ for 1-2 hours.

[0011] Furthermore, in step (1), the excitation voltage of the ball mill is 5-10KV, the rotation speed is 500-1000r / min, and the grinding time is 1-1.5h.

[0012] Furthermore, the specific surface area of ​​the magnetic carbon filter aid is 300-500 m². 2 / g, with a pore size of 20-100 micrometers.

[0013] Secondly, the present invention provides a filtration method for acid hydrolysate obtained from phosphate rock decomposition by nitric acid. The acid hydrolysate obtained from phosphate rock decomposition by nitric acid is subjected to pressure filtration in two steps. First, humic acid is added to the acid hydrolysate, stirred until uniformly mixed, and then allowed to settle. This is followed by initial pressure filtration to obtain primary filter residue and primary filtrate. Then, the aforementioned magnetic carbon filter aid is added to the primary filtrate, stirred until uniformly mixed, and then allowed to settle. This is followed by secondary pressure filtration to obtain secondary filter residue and secondary filtrate.

[0014] Furthermore, the humic acid is brown humic acid and / or black humic acid, which are insoluble in acid.

[0015] Furthermore, the primary filter residue is used to produce organic-inorganic mixed fertilizer.

[0016] Furthermore, it also includes a regeneration step for the magnetic carbon filter aid, in which the secondary filter residue is calcined at 500-600℃ for 0.5-1h, and the resulting magnetic carbon filter aid is used again for secondary pressure filtration of the acid hydrolysate.

[0017] Furthermore, the amount of magnetic carbon filter aid added is 5%-10% of the weight of the acid hydrolysate.

[0018] Furthermore, a frame filter press is used for primary and secondary filtration.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The filter aid provided by the present invention can improve the filtration efficiency of acid hydrolysate. The filter cake after adding the filter aid has larger and more varied particles, resulting in better filtration.

[0021] (2) The filter cake obtained from the first pressing can be used to produce organic-inorganic mixed fertilizer, which can improve fertilizer efficiency, meet the nutritional needs of different crops, protect and purify the environment, and improve economic benefits.

[0022] (3) The present invention uses magnetic carbon filter aid for secondary pressure filtration, which can further absorb the remaining organic floating matter and acid insoluble matter in the acid hydrolysate of the first pressure filtration. In particular, it has a good adsorption effect on magnetic insoluble matter, which lays a good foundation for improving the quality of gypsum after subsequent decalcification. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only 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.

[0024] The magnetic carbon filter aid used in the following examples has a specific surface area of ​​350 m². 2 / g, with a pore size of 70 micrometers, is prepared as follows:

[0025] (1) The coarse coal gasification residue and the electrolyte solution containing calcium ions were thoroughly mixed at a solid-liquid ratio of 1g:8ml and then added to a plasma ball mill for grinding. The excitation voltage of the ball mill was 8KV, the rotation speed was 700r / min, and the grinding time was 1h.

[0026] (2) Transfer the ball-milled product to a tube reactor, heat it to 450°C, and react it for 2 hours under a steam atmosphere.

[0027] (3) The reaction product obtained in the tubular reactor in step (2) was immersed in a solution of 4 mol / L alginate and 5 mol / L amino acid iron at a solid-liquid ratio of 1 g: 13 ml, with a volume ratio of 1:0.6. After ultrasonic oscillation for 2 h, the solid product was obtained by centrifugation.

[0028] (4) The solid product is placed in a tubular reactor for heating and drying at 500°C for 1 hour.

[0029] The suspended solids (organic suspended matter, acid-insoluble matter) content in the acid hydrolysate used in the following examples and comparative examples is 10 g / L.

[0030] Example 1

[0031] 100 kg of acid hydrolysate obtained from the decomposition of phosphate rock with nitric acid was subjected to pressure filtration. First, 3 kg of humic acid was added, stirred for 5 minutes, and then allowed to settle. Then, a frame filter press was used to complete the primary filtration, obtaining primary filter residue and primary filtrate. Next, 5 kg of magnetic carbon filter aid was added to the primary filtrate, stirred for 10 minutes, and then allowed to settle. Then, a frame filter press was used to complete the secondary filtration, obtaining secondary filter residue and secondary filtrate. The primary filter residue can be used to produce organic-inorganic mixed fertilizer. The obtained secondary filter residue is regenerated by roasting at 500℃ for 1 hour, with nitrogen gas introduced during roasting.

[0032] Comparative Example 1

[0033] Take 100 kg of the acid hydrolysate obtained by nitric acid decomposition of phosphate rock, the same as in Example 1, and perform pressure filtration. Before pressure filtration, do not add humic acid or magnetic carbon filter aid. Directly use sedimentation method to wait for organic floating matter and acid insoluble matter to settle before pressure filtration.

[0034] Example 2

[0035] Take 100 kg of the acid hydrolysate obtained from the nitric acid decomposition of phosphate rock, the same as in Example 1, and perform pressure filtration. First, add 5 kg of black humic acid, stir for 5 min, and let stand for sedimentation. Then, use a frame filter press to complete the primary filtration, obtaining primary filter residue and primary filtrate. Next, add 10 kg of magnetic carbon filter aid to the primary filtrate, stir for 10 min, and let stand for sedimentation. Then, use a frame filter press to complete the secondary filtration, obtaining secondary filter residue and secondary filtrate. The primary filter residue can be used to produce organic-inorganic mixed fertilizer, and the obtained secondary filter residue can be regenerated by roasting at 500℃ for 1 h, with nitrogen gas introduced during roasting.

[0036] Comparative Example 2

[0037] Take 100 kg of the acid hydrolysate obtained by nitric acid decomposition of phosphate rock as in Example 1 and perform pressure filtration. First, add 5 kg of black humic acid, stir for 5 minutes and let stand for sedimentation. Then, use a frame filter press to complete the pressure filtration and obtain filter residue and filtrate.

[0038] The pressure filtration data for Examples 1-2 and Comparative Examples 1-2 are shown in Table 1:

[0039] Table 1: Filtration data of the examples and comparative examples

[0040]

[0041] As shown in Table 1, the filtration speed with the addition of humic acid and magnetic carbon filter aid is 15 times faster than that without humic acid and magnetic carbon filter aid. Comparing Example 2, Example 1, and Comparative Example 2, the filtration efficiency with the addition of magnetic carbon filter aid is better than that without it, based on the comparison of the filtrate mass and the content of suspended solids in the secondary filtrate after removing fine acid-insoluble matter and organic suspended matter.

[0042] Example 3

[0043] The acid hydrolysate was filtered using the magnetic carbon filter aid regenerated in Example 1. After filtration, it was regenerated again for reuse. The filtration and regeneration methods were the same as in Example 1, and the process was repeated four times. The total filtration time, secondary filtrate mass, and suspended solids content were measured for each filtration. The results are shown in Table 2.

[0044] Table 2: Filtration data of regenerated magnetic carbon filter aid

[0045] Number of regenerations Total filtration time (min) Suspended solids content (mg / L) 1 30 65.1 2 32 65.9 3 33 67.0 4 35 70.0 5 40 98

[0046] The data analysis in Table 2 shows that the magnetic carbon filter aid still has a good filtration effect after being regenerated 5 times. The suspended solids content of the final filtrate is below 100 mg / L, and the suspended solids removal rate is over 99%.

[0047] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for filtering a solution of phosphate rock hydrolysate decomposed by nitric acid, characterized in that, The acid hydrolysate obtained from the phosphate rock decomposition with nitric acid is filtered in two steps. First, humic acid is added to the acid hydrolysate, and after stirring until it is evenly mixed, it is allowed to stand and settle. Then, the first filter is filtered to obtain the first filter residue and the first filtrate. Then, magnetic carbon filter aid with a specific surface area of ​​300-500 m² is added to the initial filtrate. 2 / g, with a pore size of 20-70 micrometers; after stirring until uniformly mixed, allow to settle and perform secondary pressure filtration to obtain secondary filter residue and secondary filtrate; it also includes a regeneration step of magnetic carbon filter aid, in which the secondary filter residue is calcined at 500-600℃ for 0.5-1h, and the obtained magnetic carbon filter aid is used again for secondary pressure filtration of acid hydrolysate. The preparation of magnetic carbon filter aid includes the following steps: (1) Mix the coarse coal gasification residue with an electrolyte solution containing calcium ions at a solid-liquid ratio of 1g:6-8ml and then grind it in a plasma ball mill. (2) Transfer the ball-milled product to a tube reactor, heat it to 200-500℃, and react it for 1-3 hours under a steam atmosphere; (3) The reaction product obtained in the tubular reactor in step (2) is immersed in a solution of alginate and amino acid iron at a solid-liquid ratio of 1g:10-20ml, and then centrifuged after ultrasonic oscillation for 1-3h to obtain a solid product. (4) Place the solid product in a tubular reactor and heat and dry it at a temperature of 300-600℃ for 1-2 hours.

2. The filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution as described in claim 1, characterized in that, Humic acid is brown humic acid and / or black humic acid, which are insoluble in acid.

3. The filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution as described in claim 1, characterized in that, The primary filter residue is used to produce organic-inorganic mixed fertilizer.

4. The filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution as described in claim 1, characterized in that, The amount of magnetic carbon filter aid added is 5%-10% of the weight of the acid hydrolysate.

5. The filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution as described in claim 1, characterized in that, A frame filter press is used for primary and secondary filtration.

6. The filtration method for nitric acid decomposition of phosphate rock acid hydrolysis solution as described in claim 1, characterized in that, In step (1), the excitation voltage of the plasma ball mill is 5-10KV, the rotation speed is 500-1000r / min, and the grinding time is 1-1.5h.

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