A system and method for drying acid residue

Abstract

The application provides a kind of extraction acid residue drying system and method, method specifically includes the following steps: step 1: extraction acid residue sampling analysis, and measure the content of each component in extraction acid residue;Step 2: according to the content of each component in extraction acid residue measured in step 1 extraction acid residue phosphoric acid content result adds ammonium bicarbonate and fully mixes stirring;Step 3: after fully mixing stirring, make extraction acid residue and ammonium bicarbonate fully react, completely neutralize the phosphoric acid in extraction acid residue after again through the primary crusher is broken into diameter less than 100mm after in reaction site spreads and is aired dry;Step 4: after the moisture of the dry residue obtained by airing is reduced to less than 5%, it is broken again, and finer particles are obtained;Step 5: dry residue is screened.The application uses ammonium bicarbonate as a drying agent to dry the extraction acid residue, which can realize batch utilization of the extraction acid residue.

Description

Technical Field

[0001] This invention relates to the field of wet purification of phosphoric acid technology, specifically to a system and method for drying residual acid residue. Background Technology

[0002] Raffinate residue is the solid residue left after physical pressing of raffinate, a byproduct of phosphoric acid purification. Currently, it is sent to a phosphogypsum stockpile after being re-slurried from the pond water. Over a long period of enrichment, the amount of oxidized compounds in the stockpile water continuously increases, affecting phosphoric acid production and purification extraction rates. The separated raffinate residue contains 20%-25% phosphorus pentoxide, which is not effectively utilized, resulting in a waste of phosphorus resources. The free phosphoric acid and oxidized compounds in the residue also cause a decline in the quality of phosphogypsum, making its disposal more difficult. Therefore, it is urgent to find a disposal route for raffinate residue. The raffinate residue after filter pressing also contains a significant amount of free acid and metal oxides, causing caking and preventing it from being directly added to the production of phosphate compound fertilizers to be carried away by the phosphate compound fertilizer products.

[0003] Extraction residue, a product of phosphoric acid purification technology, is similar to phosphogypsum. However, it contains significantly higher levels of phosphorus and metal oxides, as well as organic solvents, resulting in higher viscosity, caking, and more moisture-laden free acid, making direct drying impossible. Traditionally, quicklime is mixed with the extraction residue for fermentation. After adjusting the pH, low-end fertilizers like superphosphate are produced, but these have low value. Furthermore, the reaction between quicklime and phosphoric acid produces calcium hydrogen phosphate precipitate (GaO + H3PO4 = GaHPO4 + H2O), reducing phosphoric acid activity and fertilizer effectiveness. The mixing and dispersion of extraction residue and quicklime is uneven; the quicklime absorbs water and dries, forming slaked lime, which then reacts with the free acid in the extraction residue, resulting in a long and slow reaction process. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for drying residual acid residue, which uses ammonium bicarbonate as a drying agent to dry the residual acid residue, enabling the batch utilization of the residual acid residue.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for drying raffinate residue specifically includes the following steps:

[0007] Step 1: Take samples of the residual acid residue for analysis and measure the content of each component in the residual acid residue;

[0008] Step 2: Based on the content of each component in the residual acid residue measured in Step 1, add ammonium bicarbonate and mix thoroughly.

[0009] Step 3: After thorough mixing and stirring, allow the residual acid residue and ammonium bicarbonate to fully react and completely neutralize the phosphoric acid in the residual acid residue. Then, use a crusher to initially crush it into particles with a diameter of less than 100 mm and spread it out on the reaction site for drying.

[0010] Step 4: After the moisture content of the dried slag obtained by sun-drying is reduced to below 5%, it is crushed again to obtain finer particles;

[0011] Step 5: Screen the dried slag. Particles smaller than 2mm are qualified particles, while those larger than 2mm are returned to Step 4 for further crushing.

[0012] Furthermore, in some preferred embodiments, in step 2, ammonium bicarbonate is added to the raffinate residue at a ratio of 1:1-1.2 to the phosphoric acid content and the mixture is stirred thoroughly.

[0013] In this invention, ammonium bicarbonate is used instead of quicklime as a drying agent, which can improve the reaction rate and quickly complete the neutralization reaction, neutralizing the free acid in the residual acid residue. The product is monoammonium phosphate, which is an easily soluble acidic fertilizer, consistent with the product category of existing phosphate compound fertilizer equipment, and convenient for later use.

[0014] In this invention, the residual acid is quantitatively analyzed to determine the content of each component. Then, ammonium bicarbonate is added according to the calculated amount to ensure that all free acid in the residual acid residue is neutralized into monoammonium phosphate. The gas generated during neutralization promotes the expansion and loosening of the residual acid residue, reducing its viscosity. The neutralized residue is then turned over and naturally dried to reduce moisture content and further improve its dispersibility. The dried residual acid residue is then crushed and screened. Qualified fine particles can be used directly, while coarse particles undergo further drying, crushing, and screening. The qualified residual acid residue is then sent to the production unit for use. This achieves the effective utilization of phosphorus pentoxide in the residual acid residue.

[0015] Furthermore, in some preferred embodiments, in step 2, ammonium bicarbonate is used to neutralize the free acid in the raffinate residue, so that the phosphoric acid in the residue is neutralized into monoammonium phosphate. The carbon dioxide released in the reaction is used to promote the expansion and loosening of the raffinate residue. After neutralization, the raffinate residue no longer contains acid.

[0016] Furthermore, in some preferred embodiments, in step 3, the moisture in the residue is evaporated using ambient temperature.

[0017] This invention also discloses a raffinate residue drying system, which includes a feeding device, a stirring device, a drying device, a crushing device, and a screening device. The feeding device is used for feeding the raffinate residue, the stirring device is used for fully stirring the mixed raffinate residue and ammonium bicarbonate, the drying device is used for drying the stirred raffinate residue and ammonium bicarbonate, the crushing device is used for crushing the dried material, and the screening device is used for screening the crushed material. A return material mechanism is provided between the screening device and the crushing device, which is used to send the large particles screened out to the crushing device for further crushing.

[0018] Furthermore, in some preferred embodiments, the feeding device includes a feeding funnel and a screw feeder. The feeding funnel is connected to the screw feeder. The feeding funnel is used to mix the residual acid residue and ammonium bicarbonate. The screw feeder is used to mix the mixed residual acid residue and ammonium bicarbonate again and then send them to the stirring device for stirring reaction.

[0019] Furthermore, in some preferred embodiments, the diameter of the discharge end of the screw feeder gradually decreases.

[0020] Furthermore, in some preferred embodiments, the discharge end of the screw feeder is located at the end of the cylinder of the screw feeder, and a plurality of discharge holes are provided at the end. The first rotating shaft of the screw feeder extends out of the end of the cylinder and is connected to a cutting unit.

[0021] Furthermore, in some preferred embodiments, the cutting unit includes mounting screws and a cutter, the mounting screws being used to fix the cutter to the end of the first rotating shaft after connection with the first rotating shaft.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention uses ammonium bicarbonate instead of quicklime as a drying agent, which can improve the reaction rate and quickly complete the neutralization reaction, neutralizing the free acid in the residual acid residue. The product is monoammonium phosphate, which is an easily soluble acidic fertilizer, consistent with the existing phosphate compound fertilizer product category, and convenient for later use. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the overall principle of the present invention.

[0026] Figure 2This is a schematic diagram of the overall structure of the feeding device of the present invention.

[0027] Figure 3 For the present invention Figure 2 A magnified view of a portion of point A in the middle.

[0028] Figure 4 For the present invention Figure 2 A magnified view of a portion of point B in the middle.

[0029] Figure label:

[0030] 101 Feeding hopper, 102 Screw feeder, 103 Discharge hole, 104 Cutting unit, 105 Mounting screw, 106 Cutter, 107 Discharge port, 108 First rotating shaft, 109 Rotating shaft, 110 First drive unit, 111 Fixed cutter, 112 Rotating cutter, 113 First hopper, 114 Rotating shaft, 115 First spiral blade, 116 Second spiral blade, 117 Mounting plate, 118 First motor, 119 Fixing box, 120 Second motor, 121 Transmission mechanism, 122 Enclosure plate. Detailed Implementation

[0031] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0032] In the description of the embodiments of the present invention, it should be understood that the terms "length", "vertical", "horizontal", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In this embodiment of the invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment of the invention according to the specific circumstances.

[0035] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] The following disclosure provides many different implementations or examples for carrying out different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0037] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0038] Example 1

[0039] This embodiment discloses a method for drying raffinate residue, which specifically includes the following steps:

[0040] Step 1: Take samples of the residual acid residue for analysis and measure the content of each component in the residual acid residue; the residual acid residue mainly contains 20-25% phosphorus pentoxide, about 15% metal cations such as iron, magnesium, and aluminum, and the rest is mostly phosphogypsum.

[0041] Step 2: Based on the content of each component in the residual acid residue measured in Step 1, add ammonium bicarbonate and mix thoroughly.

[0042] Step 3: After thorough mixing and stirring, allow the residual acid residue and ammonium bicarbonate to fully react and completely neutralize the phosphoric acid in the residual acid residue. Then, use a crusher to initially crush it into particles with a diameter of less than 100 mm and spread it out on the reaction site for drying.

[0043] Step 4: After the moisture content of the dried slag obtained by sun-drying is reduced to below 5%, it is crushed again to obtain finer particles;

[0044] Step 5: Screen the dried slag. Particles smaller than 2mm are qualified particles, while those larger than 2mm are returned to Step 4 for further crushing.

[0045] Furthermore, in practical application, in step 2, ammonium bicarbonate is added to the raffinate residue at a phosphoric acid content of 1:1-1.2 and thoroughly mixed. In practical application, a ratio of 1:1.1 is preferred to ensure complete reaction and reduce the residual amount of ammonium bicarbonate.

[0046] In step 2, ammonium bicarbonate is used to neutralize the free acid in the raffinate residue, so that the phosphoric acid in the residue is neutralized into monoammonium phosphate. The carbon dioxide released in the reaction is used to promote the expansion and loosening of the raffinate residue. After neutralization, the raffinate residue no longer contains acid.

[0047] Furthermore, in step 3, the moisture in the residue is evaporated using the ambient temperature. In actual use, a drying device can also be used to achieve the purpose of rapid drying.

[0048] See Figures 1-4 In addition, the present invention also discloses a raffinate residue drying system, which includes a feeding device, a stirring device, a drying device, a crushing device, and a screening device. The feeding device is used for feeding the raffinate residue, the stirring device is used for fully stirring the mixed raffinate residue and ammonium bicarbonate, the drying device is used for drying the stirred raffinate residue and ammonium bicarbonate, the crushing device is used for crushing the dried material, and the screening device is used for screening the crushed material. A return material mechanism is provided between the screening device and the crushing device. The return material mechanism is used to send the large particles screened out to the crushing device for further crushing.

[0049] In practical applications, since the residual acid residue is formed by physical plate and frame extrusion, the residual phosphoric acid content is about 20%. Due to the presence of phosphoric acid, the residual acid residue is usually a paste-like or blocky semi-solid material. When mixing the residual acid residue with ammonium bicarbonate, strong stirring is required. When the residual acid residue and ammonium bicarbonate are placed directly in a stirring device, it is difficult to mix the paste-like or blocky semi-solid residual acid residue with ammonium bicarbonate, and strong stirring for a long time is required to achieve effective mixing.

[0050] Therefore, in practical applications, the residual acid residue and ammonium bicarbonate need to be mixed before stirring to reduce subsequent stirring time while ensuring the mixing effect.

[0051] The structure of the feeding device is improved as follows:

[0052] The feeding device includes a feeding hopper 101 and a screw feeder 102. The feeding hopper 101 is connected to the screw feeder 102. The feeding hopper 101 is used to mix the residual acid residue and ammonium bicarbonate. The screw feeder 102 is used to mix the mixed residual acid residue and ammonium bicarbonate again and send them to the stirring device for stirring reaction.

[0053] In practical applications, the residual acid residue and ammonium bicarbonate are mixed in the feeding hopper 101, and automated feeding is achieved through a screw conveyor. The residual acid residue and ammonium bicarbonate are initially mixed in the screw conveyor; since carbon dioxide gas is generated after the residual acid residue and ammonium bicarbonate are mixed, an exhaust port can be installed on the screw conveyor as needed.

[0054] The diameter of the discharge end of the screw feeder 102 gradually decreases. The discharge end of the screw feeder 102 is located at the end of the cylinder of the screw feeder 102, and several discharge holes 103 are provided at the end. The first rotating shaft 108 of the screw feeder 102 extends out of the end of the cylinder and is connected to the cutting unit 104.

[0055] As the diameter of the discharge end gradually decreases, the residual acid residue has undergone a preliminary mixing reaction in the screw feeder. When the mixed material passes through the discharge port 107, the material is cut and dispersed by the cutting unit 104, so that the mixed residual acid residue and ammonium bicarbonate can enter the mixing device in a dispersed state.

[0056] The cutting unit 104 includes mounting screws 105 and a cutter 106. The mounting screws 105 are used to connect to the first rotating shaft 108 and fix the cutter 106 to the end of the first rotating shaft 108. The mounting screws 105 are used to install the cutter 106, and the rotating shaft 109 is used to drive the cutter 106, so that the cutter 106 cuts and breaks up the mixture.

[0057] Furthermore, in practical use, since the residual acid residue added to the feeding hopper 101 is in solid block form, its premixing effect in the screw feeder is limited. Therefore, in practical use, a crushing mechanism is provided in the feeding hopper 101. The crushing mechanism includes a rotating shaft 109, a first drive unit 110, a fixed cutter 111, and a rotating cutter 112. The fixed cutter 111 is located in the feeding hopper 101, and the rotating cutter 112 is located on the rotating shaft 109. The rotating shaft 109 is rotatably mounted on the feeding hopper 101. The first drive unit 110 is mounted on the feeding hopper 101 and connected to the rotating shaft 109. The fixed cutter 111 and the rotating cutter 112 are arranged alternately.

[0058] In use, the fixed cutter 111 and the rotating cutter 112 are used to initially crush and cut the residual acid residue, so as to improve the subsequent mixing effect.

[0059] Furthermore, in actual use, the rotating shaft 109 is a hollow shaft, with a rotating shaft 114 inside the rotating shaft 109, a first funnel 113 connected to the rotating shaft, a first spiral blade 115 on the rotating shaft 114, and a second spiral blade 116 on the outer wall of the rotating shaft 109.

[0060] The upper end of the rotating shaft is provided with a mounting plate 117, which is fixedly connected to the feeding hopper 101. The mounting plate 117 is provided with a first motor 118 connected to the rotating shaft.

[0061] A fixed box 119 is provided on the feeding hopper 101. The rotating shaft 109 passes through the fixed box 119 and is rotatably connected to the fixed box 119. The first drive unit 110 includes a second motor 120 and a transmission mechanism 121. The second motor 120 drives the rotating shaft 109 to rotate through the transmission mechanism 121.

[0062] In practical use, this allows for accurate control of the mixing ratio of residual acid residue and ammonium bicarbonate. Two independent feeding mechanisms are formed in the feeding hopper 101, and the mixture enters the screw feeder after mixing, thus achieving the proportional mixing of residual acid residue and ammonium bicarbonate.

[0063] In use, the first drive motor drives the rotating shaft to rotate, thereby realizing the quantitative feeding of ammonium bicarbonate; at the same time, the first drive unit 110 drives the rotating shaft 109 to rotate, thereby realizing the quantitative feeding of the crushed raffinate residue. Since the rotating shaft 109 will rotate in actual use, the rotation speed of the rotating shaft 109 is different from that of the rotating shaft to ensure normal feeding.

[0064] Furthermore, in practical use, a sealing plate 122 is provided at the lower end of the rotating shaft 109, and the rotating shaft is rotatably mounted on the sealing plate 122. Several discharge ports 107 are provided on the side of the rotating shaft 109 near the sealing plate 122. This arrangement enables side discharge, allowing ammonium bicarbonate to be mixed with the residual acid residue after side discharge. This achieves quantitative mixing of the residual acid residue and ammonium bicarbonate, initial mixing, further mixing under the action of the feeding device, and further crushing under the action of the cutting unit 104, resulting in smaller volumes and more dispersed states of the residual acid residue and ammonium bicarbonate entering the mixing device, facilitating a thorough neutralization reaction.

[0065] In practical applications, the gas produced during neutralization promotes the expansion and loosening of the raffinate residue, reducing its viscosity. After mixing, drying reduces the moisture content of the residue, further improving its dispersibility. The dried raffinate residue is then crushed and screened; qualified fine particles can be used directly, while coarse particles undergo further drying, crushing, and screening. The dried and qualified raffinate residue is then sent to the production unit for use.

[0066] In existing technologies, lime is mixed with raffinate residue and then the pH of the raffinate residue is adjusted to produce low-end fertilizers such as superphosphate. The product value is low, and the reaction of quicklime with phosphoric acid will produce calcium hydrogen phosphate precipitate, with the chemical reaction equation GaO + H3PO4 = GaHPO4 + H2O, which reduces the activity of phosphoric acid and reduces fertilizer efficiency.

[0067] In this invention, ammonium bicarbonate is mixed with the residual acid residue for reaction, neutralizing the phosphoric acid in the residue before drying and dehydration. The dried residue is then finely crushed and metered before being added to the phosphate compound fertilizer product, forming a high-end phosphate compound fertilizer product and increasing the value of the residual acid residue. Phosphorus in the residual acid residue is recovered and utilized, while the abundant calcium, magnesium, iron, and other elements enriched in the residue provide more comprehensive nutrition for plants, improving the application effect of the phosphate compound fertilizer product.

[0068] More importantly, in this invention, the drying path prevents phosphorus pentoxide from forming citrate-soluble phosphorus, thus reducing its activity.

[0069] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for drying residual acid residue, characterized in that: The raffinate residue drying system includes a feeding device, a stirring device, a drying device, a crushing device, and a screening device. The feeding device is used to feed the raffinate residue and ammonium bicarbonate. The stirring device is used to fully stir the mixed raffinate residue and ammonium bicarbonate. The drying device is used to dry the stirred raffinate residue and ammonium bicarbonate. The crushing device is used to crush the dried material. The screening device is used to screen the crushed material. A return material mechanism is set between the screening device and the crushing device. The return material mechanism is used to send the large particles screened out to the crushing device for further crushing. The feeding device includes a feeding hopper and a screw feeder, with the feeding hopper connected to the screw feeder. A crushing mechanism is installed in the feeding hopper, which includes a rotating shaft, a first drive unit, a fixed cutter, and a rotating cutter. The fixed cutter is installed in the feeding hopper, and the rotating cutter is installed on the rotating shaft. The rotating shaft is rotatably mounted on the feeding hopper, and the first drive unit is installed on the feeding hopper and connected to the rotating shaft. The fixed cutter and the rotating cutter are arranged alternately. The rotating shaft is a hollow shaft with a rotating shaft inside. A first funnel is connected to the rotating shaft, a first spiral blade is provided on the rotating shaft, and a second spiral blade is provided on the outer wall of the rotating shaft. A mounting plate is rotatably provided at the upper end of the rotating shaft, and the mounting plate is fixedly connected to the feeding funnel. A first motor connected to the rotating shaft is provided on the mounting plate. A fixed box is provided on the feeding hopper, and the rotating shaft passes through the fixed box and is rotatably connected to the fixed box. The first drive unit includes a second motor and a transmission mechanism. The second motor drives the rotating shaft to rotate through the transmission mechanism. It can accurately control the mixing ratio of the raffinate residue and ammonium bicarbonate. Two independent feeding mechanisms are formed in the feeding hopper, and after mixing, they enter the screw feeder, realizing the proportional mixing of the raffinate residue and ammonium bicarbonate. A sealing plate is provided at the lower end of the rotating shaft, and the rotating shaft is rotatably mounted on the sealing plate. Several discharge ports are provided on the side of the rotating shaft near the sealing plate.

2. The raffinate residue drying system according to claim 1, characterized in that: The diameter of the discharge end of the screw feeder gradually decreases.

3. The raffinate residue drying system according to claim 1, characterized in that: The discharge end of the screw feeder is located at the end of the cylinder of the screw feeder, and several discharge holes are provided at the end. The first rotating shaft of the screw feeder extends out of the end of the cylinder and is connected to the cutting unit.

4. The raffinate residue drying system according to claim 3, characterized in that: The cutting unit includes mounting screws and a cutter. The mounting screws are used to fix the cutter to the end of the first rotating shaft after being connected to it.

5. A method for drying residual acid residue, employing the residual acid residue drying system described in any one of claims 1-4, characterized in that, Specifically, the steps include the following: Step 1: Take samples of the residual acid residue for analysis and measure the content of each component in the residual acid residue; Step 2: Based on the content of each component in the residual acid residue measured in Step 1, add ammonium bicarbonate and mix thoroughly. Step 3: After thorough mixing and stirring, allow the residual acid residue and ammonium bicarbonate to fully react and completely neutralize the phosphoric acid in the residual acid residue. Then, use a crusher to initially crush it into particles with a diameter of less than 100 mm and spread it out on the reaction site for drying. Step 4: After the moisture content of the dried slag obtained by sun-drying is reduced to below 5%, it is crushed again to obtain finer particles; Step 5: Screen the dried slag. Particles smaller than 2mm are qualified particles, while those larger than 2mm are returned to Step 4 for further crushing.

6. A method for drying residual acid residue according to claim 5, characterized in that: In step 2, ammonium bicarbonate is added to the residual acid residue at a ratio of 1:1-1.2 to the phosphoric acid content and the mixture is stirred thoroughly.

7. A method for drying residual acid residue according to claim 5, characterized in that: In step 2, ammonium bicarbonate is used to neutralize the free acid in the raffinate residue, so that the phosphoric acid in the residue is neutralized into monoammonium phosphate. The carbon dioxide released in the reaction is used to promote the expansion and loosening of the raffinate residue. After neutralization, the raffinate residue no longer contains acid.

8. A method for drying residual acid residue according to claim 5, characterized in that: In step 3, the ambient temperature is used to evaporate the moisture in the residue.

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