A method for removing metals from wet-process phosphoric acid and a method for synthesizing industrial-grade type II ammonium polyphosphate products

Abstract

The present invention relates to the technical field of ammonium polyphosphate synthesis, and specifically relates to a method for removing metals from wet-process phosphoric acid and a method for synthesizing industrial-grade type II ammonium polyphosphate products. The method for removing metals from wet-process phosphoric acid comprises the following steps: using a mixed extractant to extract and remove metal impurities in wet-process phosphoric acid, the mixed extractant comprising an extractant and a diluent with a volume ratio of 1 to 5:1, wherein the extractant is selected from one or more of bis(2-ethylhexyl) phosphate, tributyl phosphate, and n-butanol, and the diluent is selected from one or two of dodecane and xylene; after extraction is completed, standing for phase separation, and taking the aqueous phase to remove aluminum impurities using ammonium fluoride and fluorosilicic acid. Through the method for removing metals from wet-process phosphoric acid of the present invention, in combination with sulfate removal treatment, the pretreated wet-process phosphoric acid obtained can be prepared by the synthesis method of the present invention to obtain industrial-grade type II ammonium polyphosphate products with a higher degree of polymerization, and the flame retardant effect of the products is better.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonium polyphosphate synthesis, and specifically relates to a method for removing metals from wet-process phosphoric acid and a method for synthesizing industrial-grade type II ammonium polyphosphate products. Background Art

[0002] Ammonium polyphosphate (APP) is an efficient halogen-free phosphorus-based flame retardant, which has the characteristics of high nitrogen and phosphorus mass fractions, good flame retardant effect, high decomposition temperature, etc. It has dual functions of acid source and gas source in typical halogen-free intumescent flame retardants. In recent years, it has gradually become one of the research hotspots in the flame retardant field and has been widely used in many fields such as materials, coatings, flame retardant fire extinguishing agents, etc. As the basic material of intumescent flame retardants, ammonium polyphosphate is widely used in the flame retardant industry. With the development of the global flame retardant towards halogen-free, intumescent flame retardants mainly based on ammonium polyphosphate have increasingly become the focus of the industry, especially the demand for type II ammonium polyphosphate with high polymerization degree is becoming increasingly strong.

[0003] Traditional methods for synthesizing ammonium polyphosphate are condensation reactions using thermal phosphoric acid or phosphorus pentoxide and urea as raw materials. However, the production processes of thermal phosphoric acid and phosphorus pentoxide are often accompanied by high pollution and high energy consumption. Therefore, for the purpose of environmental protection and energy conservation and emission reduction, technicians have developed a method for synthesizing ammonium polyphosphate using wet-process phosphoric acid and urea as raw materials. However, metal impurities such as sulfate radicals, iron, magnesium, and aluminum in wet-process phosphoric acid will affect the polymerization degree of the synthesized ammonium polyphosphate, and it is difficult for the product to meet the standard requirements of industrial-grade type II ammonium polyphosphate. For this reason, it is necessary to pretreat wet-process phosphoric acid before synthesis to control the impurity content in the wet-process phosphoric acid raw material. Existing pretreatment processes usually use the method of adding phosphate ore slurry / calcium hydrogen phosphate to wet-process phosphoric acid for desulfurization. After desulfurization, pressure filtration is carried out, and then an extractant is used to remove metal impurities. Since a large amount of metal impurities and heteropolyacids will be adsorbed in the extractant during the extraction process, if the extraction ratio is not well controlled, there will be an emulsification phenomenon, and it is difficult to recover the extractant, resulting in an increase in extractant loss and a relatively high economic cost. Summary of the Invention

[0004] Aiming at the technical problems that the impurities in wet-process phosphoric acid affect the product polymerization degree before synthesizing ammonium polyphosphate with wet-process phosphoric acid and urea as raw materials, and the extractant is difficult to recover in the metal removal treatment of wet-process phosphoric acid, the present invention provides a method for removing metals from wet-process phosphoric acid and a method for synthesizing industrial-grade type II ammonium polyphosphate products.

[0005] In the first aspect, the present invention provides a method for removing metals from wet-process phosphoric acid, including the following steps:

[0006] The metal impurities in wet-process phosphoric acid, such as iron impurities, magnesium impurities, etc., are extracted and removed by using a mixed extractant. The mixed extractant includes an extractant and a diluent with a volume ratio of 1-5:1. The extractant is selected from one or more of bis(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or more of dodecane and xylene;

[0007] After the extraction is completed, it is left to stand for phase separation, and the aqueous phase is taken and aluminum impurities are removed by using ammonium fluoride and fluosilicic acid;

[0008] The oil phase is taken and an alkali solution is added. The volume ratio of the oil phase to the alkali solution is 10-15:1. After phase separation, an alkali-washed organic phase and an alkali washing solution are obtained. Then, demineralized water is added to the alkali-washed organic phase and phase separation is carried out to obtain a regenerated mixed extractant.

[0009] Further, the extraction phase ratio (O / A), that is, the volume ratio of the mixed extractant to the wet-process phosphoric acid is 3-7:1.

[0010] Further, the extraction temperature is 40-60 °C, the extraction time is 20-60 min. Stirring is carried out during extraction. The stirring method is preferably mechanical stirring, more preferably paddle stirring, and the stirring speed is 200-300 rpm.

[0011] Further, ammonium fluoride and fluosilicic acid are added to the aqueous phase to remove aluminum impurities. The addition amounts of ammonium fluoride and fluosilicic acid are 1-2 times the theoretical addition amounts. The reaction formula for removing aluminum impurities by ammonium fluoride and fluosilicic acid is 6NH4F + H2SiF6 + 2Al 3+ + 6Na + + 2H2O = 2Na3AlF6↓ + SiO2↓ + 6NH4 + + 6H + , before removing aluminum impurities, first the aluminum content in the aqueous phase is measured, and then the theoretical addition amounts of ammonium fluoride and fluosilicic acid can be calculated according to this reaction formula.

[0012] Further, the alkali solution is a 5wt%-20wt% sodium hydroxide solution.

[0013] Further, the volume ratio of the alkali-washed organic phase to the demineralized water is 1-5:1.

[0014] In a second aspect, the present invention provides a method for synthesizing an industrial-grade type II ammonium polyphosphate product, using the above-mentioned wet-process phosphoric acid metal removal method to pretreat the wet-process phosphoric acid raw material. That is, the present invention provides an application of the above-mentioned wet-process phosphoric acid metal removal method in the synthesis of an industrial-grade type II ammonium polyphosphate product. The wet-process phosphoric acid raw material mentioned in the present invention refers to the wet-process phosphoric acid used as the raw material for the industrial-grade type II ammonium polyphosphate product.

[0015] Further, the synthesis method includes the following steps:

[0016] (1) Desulfurization of wet-process phosphoric acid:

[0017] Add a desulfurizing agent to the wet-process phosphoric acid raw material. The desulfurizing agent is selected from one or two of phosphate rock slurry and calcium hydrogen phosphate. After stirring, let it stand still to obtain clarified desulfurized wet-process phosphoric acid;

[0018] (2) Demetallization of wet-process phosphoric acid:

[0019] Mix the desulfurized wet-process phosphoric acid in step (1) with a mixed extractant. The volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3 - 7:1. Extract while stirring, control the extraction temperature at 40 - 60 °C, the extraction time at 20 - 60 min, and the stirring speed at 200 - 300 rpm. After extraction, let it stand still for phase separation;

[0020] Take the aqueous phase, add fluosilicic acid and ammonium fluoride. The addition amounts of ammonium fluoride and fluosilicic acid are 1 - 2 times the theoretical addition amounts to obtain pretreated wet-process phosphoric acid;

[0021] Take the oil phase, add an alkali solution for cleaning. The volume ratio of the oil phase to the alkali solution is 10 - 15:1. After cleaning 1 - 3 times, perform phase separation to obtain the alkali-washed organic phase and the alkali washing solution. Add demineralized water to the alkali-washed organic phase. The volume ratio of the alkali-washed organic phase to the demineralized water is 1 - 5:1. After cleaning 1 - 3 times, perform phase separation to obtain the regenerated mixed extractant;

[0022] (3) Mix the pretreated wet-process phosphoric acid and urea in a reaction kettle at a molar ratio of 1:1.8 - 3.2, pre-polymerize at 100 - 130 °C for 10 - 30 min, use a vacuum pump to extract the gas generated during the pre-polymerization process, maintain the pressure in the reaction kettle ≤ 0.09 MPa, then raise the temperature to 200 - 250 °C, and continue to react for 60 - 180 min. The white solid obtained is ammonium polyphosphate.

[0023] Further, in step (1), the addition amount of the desulfurizing agent is 1 - 2 times the theoretical addition amount. The theoretical addition amount is determined according to the minimum amount of the desulfurizing agent capable of removing all sulfur impurities in the wet-process phosphoric acid. The desulfurization principles of phosphate rock slurry and calcium hydrogen phosphate are respectively: Ca3(PO4)2 + 3H2SO4 = 3CaSO4↓ + 2H3PO4, 2CaHPO4 + H2SO4 = CaSO4↓ + Ca(H2PO4)2.

[0024] Further, after step (2), detect the contents of sulfate radical and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid. After meeting the requirements, proceed to step (3).

[0025] Further, the content of phosphorus pentoxide in the wet-process phosphoric acid raw material in step (1) is 20 wt% - 25 wt%;

[0026] Before step (2) of demetallization, the wet-process phosphoric acid after desulfurization is concentrated to a phosphorus pentoxide content of 36.2 wt% - 50.7 wt%.

[0027] Before step (3) of mixing with urea, the pretreated wet-process phosphoric acid is concentrated to a phosphorus pentoxide content of ≥ 61.5 wt%.

[0028] Furthermore, the gas (containing ammonia gas) generated during the prepolymerization process in step (3) is sent to a tail gas scrubbing tower for treatment to obtain by-product ammonia water. The ammonia water can be used for self-use or sold externally, increasing the economic benefits of this synthesis method.

[0029] Furthermore, it also includes step (4): After the white solid prepared in step (3) is cooled, it is crushed and packaged to obtain a type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard. The type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard mentioned in the present invention refers to an ammonium polyphosphate product that meets the index requirements of the type II product specified in the HG / T 2770-2020 industrial ammonium polyphosphate standard. The specific index requirements are shown in Table 1 below.

[0030] Table 1 Index requirements for type II products of HG / T 2770-2020 industrial ammonium polyphosphate

[0031]

[0032] The beneficial effects of the present invention are as follows:

[0033] The wet-process phosphoric acid demetallization method provided by the present invention can effectively remove metal impurities such as iron, magnesium, and aluminum in the raw materials. The mixed extractant used overcomes the deficiencies of existing extractants, such as high viscosity, poor fluidity, and difficult phase separation when used directly. It has the effects of easy separation, easy regeneration, and recyclability, greatly reducing the production cost, reducing the discharge of wastewater containing the extractant, and being more environmentally friendly and economical.

[0034] Through this wet-process phosphoric acid demetallization method and in combination with the treatment of removing sulfate ions, the pretreated wet-process phosphoric acid obtained can, compared with the traditional wet-process phosphoric acid that directly reacts without pretreatment, obtain an industrial-grade type II ammonium polyphosphate product with a higher degree of polymerization. The average degree of polymerization reaches 80 - 120, so the flame retardant effect of the product is also better.

[0035] The synthesis of the industrial-grade type II ammonium polyphosphate product of the present invention adopts two-step operations of prepolymerization and polymerization, using urea as the reaction raw material, which not only acts as a nitrogen source but also functions as a condensing agent. Therefore, there is no need to additionally introduce ammonia gas. Compared with the traditional reaction kettle synthesis method, it avoids the increase in the pressure inside the reaction kettle caused by introducing ammonia gas. Instead, a negative pressure form is adopted, effectively reducing the explosion risk of the reaction kettle and increasing the safety factor of production operations. Description of the Drawings

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 is a flow chart of the synthesis method of the industrial grade type II ammonium polyphosphate product provided by the present invention. Specific embodiments

[0038] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] A method for removing metals from wet-process phosphoric acid includes the following steps:

[0040] (1) Using a mixed extractant to extract and remove metal impurities in wet-process phosphoric acid, such as iron impurities, magnesium impurities, etc. The volume ratio of the mixed extractant to wet-process phosphoric acid is 3 - 7:1. The mixed extractant includes an extractant and a diluent with a volume ratio of 1 - 5:1. The extractant is selected from one or more of bis(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or two of dodecane and xylene;

[0041] While using a stirring paddle to stir, perform extraction. Control the stirring speed at 200 - 300 rpm, the extraction temperature at 40 - 60 °C, and the extraction time at 20 - 60 min;

[0042] (2) After extraction, let it stand for phase separation, take the aqueous phase, detect the remaining aluminum content in the aqueous phase, calculate the theoretical addition amounts of fluorosilicic acid and ammonium fluoride according to the detection results, and add ammonium fluoride and fluorosilicic acid according to 1 - 2 times of the theoretical addition amounts to remove aluminum impurities;

[0043] (3) Take the organic phase and add an alkali solution. The alkali solution is a 5wt% - 20wt% sodium hydroxide solution. The volume ratio of the organic phase to the alkali solution is 10 - 15:1. After phase separation, obtain an alkali-washed organic phase and an alkali washing solution. Then add desalted water with a volume ratio of 1 - 5:1 to the alkali-washed organic phase and perform phase separation to obtain a regenerated mixed extractant.

[0044] A method for synthesizing an industrial grade type II ammonium polyphosphate product, such as Figure 1As shown, it includes the following steps:

[0045] (1) Desulfurization of wet-process phosphoric acid:

[0046] Using wet-process phosphoric acid with a phosphorus pentoxide content of 20wt% - 25wt% as the raw material, detecting the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material. First, calculate the theoretical addition amount of the desulfurizer according to the sulfate content. The desulfurizer is selected from one or two of phosphate slurry and calcium hydrogen phosphate. Add the desulfurizer to the wet-process phosphoric acid raw material at 1 - 2 times the theoretical addition amount, stir and then stand still to obtain clarified desulfurized wet-process phosphoric acid;

[0047] (2) Demetallization of wet-process phosphoric acid:

[0048] Concentrate the desulfurized wet-process phosphoric acid in step (1) to a phosphorus pentoxide content of 36.2wt% - 50.7wt%, and then mix it with a mixed extractant. The volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3 - 7:1. The mixed extractant includes an extractant and a diluent with a volume ratio of 1 - 5:1. The extractant is selected from one or several of bis(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or two of dodecane and xylene;

[0049] Perform extraction while stirring with a stirring paddle, control the stirring speed at 200 - 300 rpm, the extraction temperature at 40 - 60°C, and the extraction time at 20 - 60 min. After extraction, stand still to separate phases;

[0050] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, calculate the theoretical addition amounts of fluorosilicic acid and ammonium fluoride according to the detection results, and add ammonium fluoride and fluorosilicic acid at 1 - 2 times the theoretical addition amounts to remove aluminum impurities to obtain pretreated wet-process phosphoric acid;

[0051] Take the organic phase, add an alkali solution for cleaning. The alkali solution is a 5wt% - 20wt% sodium hydroxide solution, and the volume ratio of the organic phase to the alkali solution is 10 - 15:1. After cleaning 1 - 3 times, separate phases to obtain the alkali-washed organic phase and the alkali washing solution. Add demineralized water to the alkali-washed organic phase, and the volume ratio of the alkali-washed organic phase to the demineralized water is 1 - 5:1. After cleaning 1 - 3 times and separating phases, the regenerated mixed extractant is obtained;

[0052] (3)Detect the contents of sulfate radical, iron, magnesium, aluminum and other impurities in the pretreated wet-process phosphoric acid. Concentrate the qualified pretreated wet-process phosphoric acid to a phosphorus pentoxide content of ≥61.5 wt%, and then mix it with urea in a reaction kettle at a molar ratio of 1:1.8 - 3.2. Pre-polymerize at 100 - 130 °C for 10 - 30 min. Use a vacuum pump to extract the gas generated during the pre-polymerization process and send it to the tail gas scrubber for treatment to obtain the by-product ammonia water. During the pre-polymerization process, maintain the pressure in the reaction kettle ≤0.09 MPa, then raise the temperature to 200 - 250 °C and continue to react for 60 - 180 min. The white solid obtained is ammonium polyphosphate;

[0053] (4)After the white solid prepared in step (3) is cooled, it is crushed and packaged to obtain a type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0054] Example 1

[0055] (1)Desulfurization of wet-process phosphoric acid:

[0056] Using wet-process phosphoric acid with a phosphorus pentoxide content of 21 wt% as the raw material, detect the contents of sulfate radical, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material (as shown in Table 2). Use a pump to transport the wet-process phosphoric acid raw material to the desulfurization tank, calculate the theoretical addition amount of the desulfurizing agent phosphate rock slurry required according to the sulfate radical content, add the phosphate rock slurry to remove the sulfate radical, add the phosphate rock slurry at 1.4 times the theoretical addition amount, stir with a stirring paddle for 50 min, the stirring speed is 180 r / min, then let it stand for 150 min. After the desulfurization reaction is completed, filter press the material to obtain clarified desulfurized wet-process phosphoric acid;

[0057] (2)Demetallization of wet-process phosphoric acid:

[0058] Send the desulfurized wet-process phosphoric acid in step (1) to concentrator ① to concentrate it to a phosphorus pentoxide content of 43.5 wt%, and then transport it to the extraction reactor. Use bis(2-ethylhexyl) phosphate (D2EHPA) and dodecane with a volume ratio of 3:1 as the mixed extractant. The volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 5:1. Stir while extracting with a stirring paddle, control the stirring speed at 200 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. After standing for 60 min, separate the phases to obtain the extraction organic phase and the aqueous phase;

[0059] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, and then transport the aqueous phase to the refining kettle with a pump. Calculate the theoretical addition amounts of fluorosilicic acid and ammonium fluoride according to the detection results, add ammonium fluoride and fluorosilicic acid at 1.5 times the theoretical addition amounts to further remove the metal impurity aluminum and obtain the pretreated wet-process phosphoric acid;

[0060] Pump the oil phase into the caustic washing kettle, add a 5wt% sodium hydroxide solution to wash the oil phase. The volume ratio of the washing oil phase to the caustic solution is 15:1. After washing twice, separate the phases to obtain the caustic-washed organic phase and the caustic washing solution. Add demineralized water to the caustic-washed organic phase. The volume ratio of the caustic-washed organic phase to the demineralized water is 4:1. After washing twice and separating the phases, the regenerated mixed extractant is obtained.

[0061] (3)Detect the contents of sulfate, iron, magnesium, aluminum and other impurities in the pretreated wet-process phosphoric acid (as shown in Table 3). Transport the qualified pretreated wet-process phosphoric acid to the concentration kettle ② for concentration until the phosphorus pentoxide content reaches 61.5wt%. At the same time, weigh the urea and put it into the prepolymerization reaction kettle. According to the molar ratio of pretreated wet-process phosphoric acid to urea of 1:1.8, use a stirring paddle to mix the two to obtain a transparent and clear liquid. Let the mixed solution carry out prepolymerization in the prepolymerization reaction kettle. Raise the temperature in the prepolymerization reaction kettle to 124°C and react for 25 minutes. During the prepolymerization process, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to maintain the pressure in the reaction kettle at 0.085 MPa. Send the extracted ammonia-containing gas to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water. Subsequently, transport the material after the prepolymerization is completed to the polymerization and curing reaction kettle and continue to raise the temperature to 230°C for polymerization and curing. React for 140 minutes to obtain a white solid, which is ammonium polyphosphate.

[0062] (4)Wait for the white solid prepared in step (3) to cool, send it to the crushing system through the conveying system, crush and package it. Detect the prepared ammonium polyphosphate product according to the test method recorded in the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0063] Example 2

[0064] (1)Desulfurization of wet-process phosphoric acid:

[0065] Use wet-process phosphoric acid with a phosphorus pentoxide content of 24wt% as the raw material. Detect the contents of sulfate, iron, magnesium, aluminum and other impurities in the wet-process phosphoric acid raw material (as shown in Table 2). Pump the wet-process phosphoric acid raw material into the desulfurization tank, calculate the theoretical addition amount of the desulfurizing agent phosphate rock slurry required according to the sulfate content, add the phosphate rock slurry to remove sulfate, add the phosphate rock slurry at 1.5 times the theoretical addition amount, stir with a stirring paddle for 45 minutes, and the stirring speed is 150 r / min. Then let it stand for 180 minutes. After the desulfurization reaction is completed, filter the material under pressure to obtain clear desulfurized wet-process phosphoric acid.

[0066] (2)Demetalization of wet-process phosphoric acid:

[0067] The desulfurized wet-process phosphoric acid from step (1) is sent to concentrator kettle ① for concentration until the phosphorus pentoxide content reaches 47.1 wt%, and then it is transported to the extraction reactor. Di(2-ethylhexyl) phosphoric acid (D2EHPA) and xylene with a volume ratio of 4:1 are used as the mixed extractant. The volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 6:1. Extraction is carried out while stirring with a paddle, controlling the stirring speed at 230 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. After standing for 70 min, phase separation is performed to obtain the extraction organic phase and the aqueous phase;

[0068] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, and then pump the aqueous phase into the refining kettle. Calculate the theoretical addition amounts of fluosilicic acid and ammonium fluoride according to the detection results, and add ammonium fluoride and fluosilicic acid at 1.5 times the theoretical addition amounts to further remove the metal impurity aluminum, obtaining the pretreated wet-process phosphoric acid;

[0069] Pump the oil phase into the caustic washing kettle, add a 10 wt% sodium hydroxide solution for washing. The volume ratio of the washing oil phase to the caustic solution is 10:1. After washing twice, phase separation is performed to obtain the caustic washing organic phase and the caustic washing solution. Add deionized water to the caustic washing organic phase. The volume ratio of the caustic washing organic phase to the deionized water is 5:1. After washing twice, phase separation is carried out to obtain the regenerated mixed extractant;

[0070] (3) Detect the contents of sulfate radicals and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid (as shown in Table 3). Transport the qualified pretreated wet-process phosphoric acid to concentrator kettle ② for concentration until the phosphorus pentoxide content reaches 65.2 wt%. At the same time, weigh urea and put it into the prepolymerization reaction kettle. According to the molar ratio of the pretreated wet-process phosphoric acid to urea of 1:2, use a paddle to mix the two to obtain a transparent and clear liquid. Let the mixed solution carry out prepolymerization in the prepolymerization reaction kettle. Raise the temperature in the prepolymerization reaction kettle to 124 °C and react for 30 min. During the prepolymerization process, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to maintain the pressure in the reaction kettle at 0.075 MPa. The extracted ammonia-containing gas is sent to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water. Subsequently, transport the material after the end of prepolymerization to the polymerization and curing reaction kettle and continue to raise the temperature to 230 °C for polymerization and curing. React for 160 min to obtain a white solid, which is ammonium polyphosphate;

[0071] (4) Wait for the white solid prepared in step (3) to cool, send it to the crushing system through the conveying system, crush and package it, and detect the prepared ammonium polyphosphate product according to the test method recorded in the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0072] Example 3

[0073] (1) Desulfurization of wet-process phosphoric acid:

[0074] Using wet-process phosphoric acid with a phosphorus pentoxide content of 25 wt% as the raw material, the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material were detected (as shown in Table 2). The wet-process phosphoric acid raw material was pumped into a desulfurization tank, and the theoretical addition amount of the desulfurizing agent phosphorite slurry was calculated based on the sulfate content, and the phosphorite slurry was added to remove sulfate. The phosphorite slurry was added at 1.2 times the theoretical addition amount, and stirred with a stirring paddle for 60 min at a stirring speed of 150 r / min, then left to stand for 180 min. After the desulfurization reaction ended, the material was pressure-filtered to obtain clarified desulfurized wet-process phosphoric acid;

[0075] (2) Demetallization of wet-process phosphoric acid:

[0076] The desulfurized wet-process phosphoric acid from step (1) was sent to a concentration kettle ① for concentration to a phosphorus pentoxide content of 48.2 wt%, and then sent to an extraction reactor. Tributyl phosphate (TBP) and dodecane with a volume ratio of 4:1 were used as the mixed extractant, and the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid was 5:1. Extraction was carried out while stirring with a stirring paddle, controlling the stirring speed at 230 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. After standing for 45 min, phase separation was carried out to obtain an extraction organic phase and an aqueous phase;

[0077] The aqueous phase was taken, the remaining aluminum content in the aqueous phase was detected, and then the aqueous phase was pumped into a refining kettle. The theoretical addition amounts of fluosilicic acid and ammonium fluoride were calculated based on the detection results, and ammonium fluoride and fluosilicic acid were added at 1.7 times the theoretical addition amount to further remove the metal impurity aluminum to obtain pretreated wet-process phosphoric acid;

[0078] The oil phase was pumped into an alkali washing kettle, and a 5 wt% sodium hydroxide solution was added for washing. The volume ratio of the washing oil phase to the alkali solution was 13:1. After washing three times, phase separation was carried out to obtain an alkali-washed organic phase and an alkali washing solution. Demineralized water was added to the alkali-washed organic phase, and the volume ratio of the alkali-washed organic phase to the demineralized water was 5:1. After washing three times, phase separation was carried out to obtain a regenerated mixed extractant;

[0079] (3)Detect the contents of sulfate radical, iron, magnesium, aluminum and other impurities in the pretreated wet-process phosphoric acid (as shown in Table 3). Transfer the qualified pretreated wet-process phosphoric acid to concentrator kettle ② for concentration until the phosphorus pentoxide content reaches 68.8 wt%. At the same time, weigh urea and put it into the prepolymerization reactor. According to the molar ratio of pretreated wet-process phosphoric acid to urea of 1:1.8, use a stirring paddle to mix the two to obtain a transparent and clear liquid. Let the mixed solution carry out prepolymerization in the prepolymerization reactor. Raise the temperature in the prepolymerization reactor to 128 °C and react for 30 min. During the prepolymerization process, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to keep the pressure in the reactor at 0.085 MPa. The extracted ammonia-containing gas is sent to the tail gas scrubbing tower for treatment to obtain by-product ammonia water. Subsequently, transfer the material after the end of prepolymerization to the polymerization and curing reactor and continue to raise the temperature to 250 °C for polymerization and curing. React for 140 min to obtain a white solid, which is ammonium polyphosphate;

[0080] (4)Wait for the white solid prepared in step (3) to cool, send it to the crushing system through the conveying system, crush and package it. Detect the prepared ammonium polyphosphate product according to the test method recorded in the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0081] Comparative Example 1

[0082] (1)Desulfurization of wet-process phosphoric acid:

[0083] Use the same wet-process phosphoric acid raw material as in Example 3, pump it into the desulfurization tank, calculate the theoretical amount of phosphate rock slurry added to remove sulfate radical according to the detection data, add phosphate rock slurry to remove sulfate radical, and the addition amount of phosphate rock slurry is 1.2 times the theoretical amount. Stir with a stirring paddle for 60 min at a stirring speed of 150 r / min, then let it stand for 180 min. After the desulfurization reaction is completed, filter the material under pressure to obtain clear desulfurized wet-process phosphoric acid;

[0084] (2)Demetallization of wet-process phosphoric acid:

[0085] Transfer the desulfurized wet-process phosphoric acid in step (1) to concentrator kettle ① for concentration until the phosphorus pentoxide content reaches 48.2 wt%. Then transfer it to the extraction reactor. Use tributyl phosphate (TBP) as the extractant. The volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1. Stir while extracting with a stirring paddle, control the stirring speed at 230 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. Phase separation occurs only after standing for 15 h to obtain an extraction organic phase and an aqueous phase;

[0086] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, then pump the aqueous phase into the refining kettle, calculate the theoretical addition amounts of fluosilicic acid and ammonium fluoride according to the detection results, and add ammonium fluoride and fluosilicic acid at 1.7 times the theoretical addition amounts to further remove the metal impurity aluminum, obtaining pretreated wet-process phosphoric acid;

[0087] Pump the oil phase into the caustic washing kettle, add a 5wt% sodium hydroxide solution to wash the oil phase. The volume ratio of the washing oil phase to the caustic liquor is 13:1. After washing three times, separate the phases to obtain the caustic-washed organic phase and the caustic washing liquor. Add demineralized water to the caustic-washed organic phase. The volume ratio of the caustic-washed organic phase to the demineralized water is 5:1. After washing three times and separating the phases, the regenerated mixed extractant is obtained;

[0088] (3) Detect the contents of sulfate radical and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid (as shown in Table 3). Pump the pretreated wet-process phosphoric acid that meets the requirements into the concentration kettle ② and concentrate it to a phosphorus pentoxide content of 68.8wt%. Then pump it into the prepolymerization reaction kettle. At the same time, weigh the urea and put it into the prepolymerization reaction kettle. According to the molar ratio of the pretreated wet-process phosphoric acid to urea of 1:1.8, use a stirring paddle to mix the two to obtain a transparent and clear liquid. Let the mixed solution carry out prepolymerization in the prepolymerization reaction kettle. Raise the temperature in the prepolymerization reaction kettle to 128°C and react for 30 minutes. During the prepolymerization process, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to maintain the pressure in the reaction kettle at 0.085 MPa. Send the extracted ammonia-containing gas to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water. Subsequently, convey the material after the prepolymerization is completed to the polymerization and curing reaction kettle and continue to raise the temperature to 250°C for polymerization and curing, and react for 140 minutes to obtain a white solid;

[0089] (4) Wait for the white solid prepared in step (3) to cool, send it to the crushing system through the conveying system, crush and package it, and detect the prepared ammonium polyphosphate product according to the test method recorded in the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0090] Comparative Example 2

[0091] (1) Desulfurization of wet-process phosphoric acid:

[0092] Use the same wet-process phosphoric acid raw material as in Example 3, pump it into the desulfurization tank, calculate the theoretical amount of phosphate rock slurry added to remove sulfate radical according to the detection data, add phosphate rock slurry to remove sulfate radical, and the addition amount of phosphate rock slurry is 1.2 times the theoretical amount. Stir with a stirring paddle for 60 minutes at a stirring speed of 150 r / min, then let it stand for 180 minutes. After the desulfurization reaction is completed, filter the material under pressure to obtain clear desulfurized wet-process phosphoric acid;

[0093] (2) Demetallization of wet-process phosphoric acid:

[0094] The desulfurized wet-process phosphoric acid from step (1) is sent to concentrator ① for concentration until the phosphorus pentoxide content reaches 48.2 wt%, and then it is transported to the extraction reactor. Tributyl phosphate (TBP) and kerosene with a volume ratio of 4:1 are used as the mixed extractant, and the volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1. Extraction is carried out while stirring with a paddle, controlling the stirring speed at 230 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. After standing for 90 min, phase separation is performed to obtain the extracted organic phase and the aqueous phase;

[0095] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, and then pump the aqueous phase into the refining kettle. Calculate the theoretical addition amounts of fluorosilicic acid and ammonium fluoride according to the detection results, and add ammonium fluoride and fluorosilicic acid at 1.7 times the theoretical addition amounts to further remove the metal impurity aluminum to obtain the pretreated wet-process phosphoric acid;

[0096] Pump the oil phase into the caustic washing kettle, add a 5 wt% sodium hydroxide solution for washing. The volume ratio of the washing oil phase to the caustic liquor is 13:1. After washing three times, phase separation is carried out to obtain the caustic-washed organic phase and the caustic washing liquor. Add deionized water to the caustic-washed organic phase, and the volume ratio of the caustic-washed organic phase to the deionized water is 5:1. After washing three times, phase separation is carried out to obtain the regenerated mixed extractant;

[0097] (3) Detect the contents of sulfate radicals and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid (as shown in Table 3). Transport the qualified pretreated wet-process phosphoric acid to concentrator ② for concentration until the phosphorus pentoxide content reaches 68.8 wt%, and then pump it into the pre-polymerization reaction kettle. At the same time, weigh urea and put it into the pre-polymerization reaction kettle. According to the molar ratio of the pretreated wet-process phosphoric acid to urea of 1:1.8, use a paddle to mix the two to obtain a transparent and clear liquid. Let the mixed solution carry out pre-polymerization in the pre-polymerization reaction kettle. Raise the temperature in the pre-polymerization reaction kettle to 128 °C and react for 30 min. During the pre-polymerization process, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to maintain the pressure in the reaction kettle at 0.085 MPa. The extracted ammonia-containing gas is sent to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water. Subsequently, transport the material after the pre-polymerization is completed to the polymerization and curing reaction kettle and continue to raise the temperature to 250 °C for polymerization and curing, and react for 140 min to obtain a white solid;

[0098] (4) Wait for the white solid prepared in step (3) to cool, send it to the crushing system through the conveying system, crush and package it, and detect the prepared ammonium polyphosphate product according to the test method recorded in the HG / T 2770-2020 industrial ammonium polyphosphate standard. The results are shown in Table 4.

[0099] Comparative Example 3

[0100] (1) Desulfurization of wet-process phosphoric acid:

[0101] Using the same wet-process phosphoric acid raw material as in Example 3, it is pumped into the desulfurization tank. According to the detection data, the theoretical amount of phosphate rock slurry added to remove sulfate is calculated, and the phosphate rock slurry is added to remove sulfate. The addition amount of the phosphate rock slurry is 1.2 times the theoretical amount. It is stirred with a stirring paddle for 60 min, and the stirring speed is 150 r / min. Then it is allowed to stand for 180 min. After the desulfurization reaction is completed, the material is pressure-filtered to obtain clarified desulfurized wet-process phosphoric acid;

[0102] (2)Demetallization of wet-process phosphoric acid:

[0103] The desulfurized wet-process phosphoric acid from step (1) is sent to concentrator ① for concentration until the phosphorus pentoxide content reaches 48.2 wt%. Then it is transported to the extraction reactor. Using tributyl phosphate (TBP) and dodecane with a volume ratio of 4:1 as the mixed extractant, the volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1. Extraction is carried out while stirring with a stirring paddle, controlling the stirring speed at 230 rpm, the extraction temperature at 50 °C, and the extraction time at 30 min. After standing for 45 min, phase separation is carried out to obtain the extracted organic phase and the aqueous phase;

[0104] Take the aqueous phase, detect the remaining aluminum content in the aqueous phase, and then pump the aqueous phase into the refining kettle. According to the detection results, calculate the theoretical addition amounts of fluosilicic acid and ammonium fluoride, and add ammonium fluoride and fluosilicic acid at 1.7 times the theoretical addition amounts to further remove the metal impurity aluminum to obtain pretreated wet-process phosphoric acid;

[0105] Pump the oil phase into the caustic washing kettle, add a 5 wt% sodium hydroxide solution for washing. The volume ratio of the washing oil phase to the caustic solution is 13:1. After washing three times, phase separation is carried out to obtain the caustic-washed organic phase and the caustic washing solution. Add deionized water to the caustic-washed organic phase. The volume ratio of the caustic-washed organic phase to the deionized water is 5:1. After washing three times, phase separation is carried out to obtain the regenerated mixed extractant;

[0106] (3)Detect the contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid (as shown in Table 3). Transport the qualified pretreated wet-process phosphoric acid to concentrator ② for concentration until the phosphorus pentoxide content reaches 68.8 wt%. Then pump it into the polymerization and curing reaction kettle. At the same time, weigh the urea. According to the molar ratio of the pretreated wet-process phosphoric acid to urea of 1:1.8, use a stirring paddle to mix the two to obtain a transparent and clarified liquid. Raise the temperature in the polymerization and curing reaction kettle to 250 °C and react for 170 min. During the reaction, a large amount of bubbles will be generated due to the formation of ammonia gas. Use a vacuum pump to extract the ammonia-containing gas to maintain the pressure in the reaction kettle at 0.085 MPa. The extracted ammonia-containing gas is sent to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water. After the reaction, a white solid is obtained;

[0107] (4) After the white solid prepared in step (3) is cooled, it is sent to the pulverizing system through the conveying system, pulverized and packaged, and the prepared ammonium polyphosphate product is detected according to the test method described in the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0108] Table 2 Detection Results of Impurities in Wet-Process Phosphoric Acid Raw Materials for Each Example and Comparative Example

[0109]

[0110] Table 3 Detection Results of Impurities in Pretreated Wet-Process Phosphoric Acid for Each Example and Comparative Example

[0111]

[0112] Table 4 Performance Indexes of Industrial Grade II Ammonium Polyphosphate Products for Each Example and Comparative Example

[0113]

[0114] As can be seen from Table 4, the removal effect of impurities such as iron, magnesium, aluminum, and sodium in the wet-process phosphoric acid pretreated by the wet-process phosphoric acid demetallization method of the present invention is good, and the treatment efficiency is high; the industrial grade II ammonium polyphosphate products prepared by the synthesis method of the present invention all meet the requirements of the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard.

[0115] In Comparative Example 1, only TBP was used as the extractant in the extraction step, and no diluent was added. Other conditions were the same as those in Example 3. The finally produced ammonium polyphosphate did not meet the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The reason is that it is extremely difficult to phase-separate after the extraction reaction in step (2). The organic phase and the aqueous phase were separated only after standing for 15 hours. A large amount of TBP was carried by the phosphoric acid in the separated aqueous phase. As a result, when reacting with urea subsequently, phosphoric acid and urea could only polycondense into short-chain ammonium polyphosphate and could not condense from short-chain ammonium polyphosphate to long-chain ammonium polyphosphate. Therefore, the degree of polymerization of the ammonium polyphosphate produced in Comparative Example 1 was low and could not meet the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard.

[0116] In Comparative Example 2, kerosene was used as the diluent, but the finally produced ammonium polyphosphate did not meet the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. Compared with xylene and methane, kerosene has better fluidity and better synergy with the extractant. Therefore, using kerosene as the diluent will result in higher impurity ion content in the pretreated wet-process phosphoric acid, and the higher impurity ions cause the quality of the finally produced ammonium polyphosphate to not meet the HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard.

[0117] The method of comparative example 3 does not perform prepolymerization, and the other conditions are consistent with those of example 3, and the ammonium polyphosphate finally generated does not meet the HG / T 2770-2020 industrial ammonium polyphosphate standard. The present invention uses urea as both a nitrogen source and a condensing agent in the reaction process. The condensation effect can only be exerted at 100-130°C to cause the ammonium polyphosphate to undergo a chain extension reaction. When the temperature is directly raised to 250°C, the urea has no time to react and is almost completely decomposed or condensed, resulting in very little urea in the material, which inhibits the chain extension reaction of the ammonium polyphosphate, resulting in most of the short-chain ammonium polyphosphate in comparative example 3, which cannot meet the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0118] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for removing metals from wet-process phosphoric acid, characterized in that, It includes the following steps: Use a mixed extractant to extract and remove metal impurities in wet-process phosphoric acid. The mixed extractant includes an extractant and a diluent with a volume ratio of 1 - 5:

1. The extractant is selected from one or more of bis(2-ethylhexyl) phosphate, tributyl phosphate, and n-butanol, and the diluent is selected from one or two of dodecane and xylene; After extraction, let it stand for phase separation. Take the aqueous phase and use ammonium fluoride and fluosilicic acid to remove aluminum impurities; Take the organic phase and add lye. The volume ratio of the organic phase to the lye is 10 - 15:

1. After phase separation, obtain the alkali-washed organic phase and the alkali washing solution. Then add demineralized water to the alkali-washed organic phase and perform phase separation to obtain the regenerated mixed extractant.

2. The wet-process phosphoric acid de-metallization method according to claim 1, wherein The volume ratio of the mixed extractant to the wet-process phosphoric acid is 3 - 7:

1.

3. The wet-process phosphoric acid de-metallization method according to claim 1, wherein The extraction temperature is 40 - 60 °C, the extraction time is 20 - 60 min, and stirring is carried out during extraction.

4. The wet-process phosphoric acid de-metallization method according to claim 1, characterized in that, Add ammonium fluoride and fluosilicic acid to the aqueous phase to remove aluminum impurities. The addition amounts of ammonium fluoride and fluosilicic acid are 1 - 2 times the theoretical addition amounts.

5. The wet-process phosphoric acid de-metallization method according to claim 1, characterized in that, The volume ratio of the alkali-washed organic phase to the demineralized water is 1 - 5:

1.

6. A synthesis method of an industrial grade type II ammonium polyphosphate product, characterized in that, It includes the following steps: (1) Desulfurization of wet-process phosphoric acid: Add a desulfurizing agent to the wet-process phosphoric acid raw material. The desulfurizing agent is selected from one or two of phosphate rock slurry and calcium hydrogen phosphate. After stirring and standing, obtain clarified desulfurized wet-process phosphoric acid; (2) Demetallization of wet-process phosphoric acid: Mix the desulfurized wet-process phosphoric acid in step (1) with a mixed extractant. The volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3 - 7:

1. Extract while stirring, control the extraction temperature at 40 - 60 °C, the extraction time at 20 - 60 min, and the stirring speed at 200 - 300 rpm. After extraction, let it stand for phase separation; Take the aqueous phase and add fluosilicic acid and ammonium fluoride. The addition amounts of ammonium fluoride and fluosilicic acid are 1 - 2 times the theoretical addition amounts to obtain pretreated wet-process phosphoric acid; Take the organic phase and wash it with lye. The volume ratio of the organic phase to the lye is 10 - 15:

1. After washing 1 - 3 times, perform phase separation to obtain the alkali-washed organic phase and the alkali washing solution. Add demineralized water to the alkali-washed organic phase. The volume ratio of the alkali-washed organic phase to the demineralized water is 1 - 5:

1. After washing 1 - 3 times, perform phase separation to obtain the regenerated mixed extractant; (3) Mix the pretreated wet-process phosphoric acid and urea in a reaction kettle according to a molar ratio of 1:1.8 - 3.2, pre-polymerize at 100 - 130 °C for 10 - 30 min, use a vacuum pump to extract the gas generated during the pre-polymerization process, maintain the pressure in the reaction kettle ≤ 0.09 MPa, then raise the temperature to 200 - 250 °C, and continue to react for 60 - 180 min. The white solid obtained is ammonium polyphosphate.

7. The synthesis method according to claim 6, wherein It also includes step (4): After the white solid prepared in step (3) cools, pulverize and package it to obtain a type II product that meets the HG / T 2770 - 2020 industrial ammonium polyphosphate standard.

8. The synthesis method according to claim 6, characterized in that, The content of phosphorus pentoxide in the wet-process phosphoric acid raw material in step (1) is 20 wt% - 25 wt%; Before demetallization in step (2), concentrate the desulfurized wet-process phosphoric acid to a phosphorus pentoxide content of 36.2 wt% - 50.7 wt%; Before mixing with urea in step (3), concentrate the pretreated wet-process phosphoric acid to a phosphorus pentoxide content ≥ 61.5 wt%.

9. The synthesis method according to claim 6, characterized in that, The gas generated during the pre-polymerization process in step (3) is sent to the tail gas scrubbing tower for treatment to obtain the by-product ammonia water.

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