A method for impurity removal and recycling of the extraction residual acid of by-products in wet-process purified phosphoric acid

Abstract

The present invention relates to the technical field of phosphorus chemical industry, and in particular to a method for removing impurities and recycling residual acid extracted from a by-product of wet-process purified phosphoric acid. The method comprises the following steps: continuously adding a stripping agent to the extracted residual acid to change the solubility of metal ion salts in the system, finally causing the metal cation salts to precipitate out of the system, and performing solid-liquid separation to obtain stripped slag and stripped acid. Since the stripping agent contains a large amount of sulfur element and cannot be directly used for the phosphoric acid back-end product, the stripped acid is returned to a phosphoric acid production device according to a wet-process phosphoric acid (concentrated sulfuric acid process) process to make the stripping agent (mainly SO4 2‑ ) reacts with phosphate concentrate to achieve the effect of removing acid and desulfurization, thereby recovering the phosphorus resources in the extracted residual acid and utilizing the phosphate concentrate to react with sulfate in the remover to recover the sulfur resources in the removed acid, reusing the phosphoric acid reaction system, and recycling the resources; the removal slag is neutralized with a weak alkaline salt to produce a compound fertilizer product, truly achieving a closed-loop process and efficiently utilizing and recycling phosphorus resources.

Description

Technical Field

[0001] The invention relates to the technical field of phosphorus chemical industry, in particular to a method for removing impurities and recycling residual acid extracted from a byproduct of wet-process purified phosphoric acid. Background Art

[0002] With the continuous breakthroughs in the purification technology of existing wet-process phosphoric acid, the production of purified phosphoric acid using low-grade phosphate rock has made new progress in recent years. The quality of the purified wet-process phosphoric acid is comparable to that of thermally produced phosphoric acid, while the production cost is lower. It has a tendency to replace thermal phosphoric acid in the industrial field. In the liquid-liquid solvent extraction process currently used to purify wet-process phosphoric acid, a by-product of the extraction residual acid is generated. - 、SO4 2- While the anion content is reduced, the metal cations in the wet-process phosphoric acid are enriched. These metal impurity ions are an important factor hindering the continued reuse of the extraction residual acid. The extraction residual acid is generally used to make fertilizers. However, when using the extraction residual acid to produce fertilizers, the content of impurity ions changes compared with ordinary wet-process phosphoric acid, resulting in a lower total nitrogen content in the fertilizer product or excessive moisture in the product. Therefore, finding a new process to digest these extraction residual acids has become an important factor affecting the continuous production of wet-process phosphoric acid purification equipment.

[0003] In view of this, the present application aims to provide a method for recycling the entire process of extracting residual acid, which is separated from the solid and liquid by removing impurities with a remover and then reacting with phosphate concentrate to recover the effective phosphorus resources in the extracting residual acid without producing other by-products, so as to better solve the problem that the extracting residual acid, a by-product of wet purification of phosphoric acid production, cannot be reused. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for removing impurities and recycling residual acid, a by-product of wet-process phosphoric acid purification. The method has a simple process, is easy to control, and has a high recycling rate. A sufficient amount of a stripping agent is added to the residual acid to change the solubility of a metal cation salt in the residual acid, so that the metal cation salt is precipitated out of the residual acid system. After solid-liquid separation, the metal cation salt leaves the residual acid system, thereby removing metal ion impurities from the residual acid. The stripping acid from which the metal impurities have been removed reacts with a mixed acid containing a high concentration of stripping agent according to a wet-process phosphoric acid production process with phosphate concentrate, and then enters a downstream phosphoric acid production system. This method achieves recycling of phosphorus resources and stripping agent resources without affecting phosphoric acid production and without requiring an external stripping acid-stripping agent device.

[0005] The technical solution adopted in the present invention is:

[0006] A method for removing impurities and recycling residual acid extracted from a byproduct of wet purification of phosphoric acid comprises the following steps:

[0007] S1. Adding a metal-removing agent to the residual acid extracted from the wet-process purified phosphoric acid byproduct, wherein the residual acid is used as a matrix and the metal-removing agent is used as a daughter material. According to the reaction conditions, the metal-removing agent is continuously added to the residual acid to change the solubility of the metal salts to form a reaction slurry, and then solid-liquid separation is performed to obtain deslagging and deacidified residues;

[0008] S2, returning the deacidified acid and concentrated sulfuric acid to the phosphoric acid production system, so that the metal remover in the deacidified acid reacts with the phosphate concentrate to achieve deacidification and desulfurization, thereby obtaining wet-process phosphoric acid that meets the requirements of downstream phosphoric acid production;

[0009] S3. The removed slag is subjected to a neutralization reaction with a weak alkaline salt to produce a compound fertilizer product to achieve resource utilization.

[0010] Furthermore, in step S1, since the reaction between the metal remover and the extracted residual acid releases heat, a reaction stirring device and a control system need to be installed. During the reaction, the metal remover is slowly added under stirring conditions, and the flow rate of the metal remover added to the reactor is adjusted in time according to the reaction heat to control the reactor temperature at 80-100°C.

[0011] Furthermore, in step S1, when the metal removing agent and the extraction residue acid are mixed, the reaction is carried out in a plurality of reactors in sequence, and the plurality of reactors are connected via overflow pipes.

[0012] Furthermore, in step S1, the extracted residual acid is first sent to a buffer tank and then transported to the reactor via a delivery pump. Under stirring conditions, the metal removal agent is continuously added to the reactor through the delivery pipeline, and the reaction is continuously carried out at a temperature of 80-100°C for 5-8 hours to form a reaction slurry.

[0013] Furthermore, in step S1, a flow control valve is provided on the delivery pipeline for delivering the metal remover, and the delivery pipeline is connected to the reactor through an anti-corrosion mixing tee. The end of the anti-corrosion mixing tee that is not connected to the delivery pipeline and the reactor is provided with a remover buffer tank. During the reaction process, if the temperature of the reactor is stable, the metal remover enters the reactor through the anti-corrosion mixing tee. If the temperature of the reactor is high, the metal remover is temporarily stored in the remover buffer tank through the anti-corrosion mixing tee to control the remover flow according to the temperature of the reactor.

[0014] Furthermore, in step S1, the mass ratio of the metal removal agent to the extracted residual acid is 4:1.

[0015] Furthermore, in step S1, a centrifuge is used to separate the slurry into solid and liquid to obtain deslagging and deacidification.

[0016] Furthermore, in step S2, the deacidified acid is dripped back to the phosphoric acid production system through a pipeline, and the deacidifying agent reacts with the phosphate concentrate to generate product phosphoric acid and phosphogypsum.

[0017] Furthermore, in step S3, the weak base salt is any one of K2CO3, CaCO3 and Na2CO3.

[0018] Furthermore, in step S1, the metal removing agent is concentrated sulfuric acid or an acidic complex with a high sulfur content.

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

[0020] 1. The demetallization recycling method of the present application is simple in process operation, convenient and efficient. The metal removal agent used is concentrated sulfuric acid or an acidic compound with a high sulfuric acid content, which is simple and easy to obtain. The used concentrated sulfuric acid can also be used in subsequent processes. The SO4 in the metal removal agent 2- The recycling rate is high, which effectively reduces the processing cost;

[0021] 2. The present application changes the solubility of metal salts in the residual acid-metal-removing agent by adding a metal-removing agent to the residual acid extracted as a by-product of phosphoric acid production. When the metal salt reaches the solubility at a certain temperature, salting-out occurs. After that, solid-liquid separation is performed to obtain the removed slag and the removed acid. This allows for faster reaction separation, shortens the removal and purification time, and has a strong metal cation removal effect, greatly improving the removal efficiency of metal cations in the residual acid extracted.

[0022] 3. The present invention has a good removal effect on various metal ions after the residual acid extracted is treated with a remover. The removed acid will not affect the subsequent use of phosphoric acid downstream devices. In addition, the present invention will return the removed acid to the phosphoric acid production system, so that the remover in the removed acid reacts with the phosphate concentrate to achieve the effect of removing acid and desulfurization. The metal remover can continue to serve the phosphoric acid production, so as to reuse the remover in the removed acid, and convert the metal remover into raw material-product-raw material-product, thereby maximizing the value of resources.

[0023] 4. The removed slag in this application is mainly metal salts such as iron, magnesium, and aluminum. After solid-liquid separation, the removed slag is neutralized with a weak base salt to produce a compound fertilizer product, so as to achieve a closed-loop process, recycle all impurities, and realize efficient resource utilization and recovery of phosphorus resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the device used for the impurity removal and recycling reaction in an embodiment of the present invention;

[0025] Figure 2 Schematic diagram of the impurity removal and recycling process in an embodiment of the present invention;

[0026] Description of the accompanying symbols: reactor 1, overflow pipe 2, centrifuge 3, delivery pipeline 4, control valve 5, mixing tee 6. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present invention, the present invention will be described more fully below through examples, with preferred embodiments of the present invention provided below. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. Any other embodiments obtained by modifying or equivalently replacing the technical solution of the present invention without inventive results are within the scope of protection of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0029] The numerical values disclosed in the embodiments of the present invention are approximate values, not definite values. Where errors or experimental conditions permit, all values within the error range may be included without being limited to the specific numerical values disclosed in the embodiments of the present invention.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0031] like Figure 1-Figure 2 As shown, the method for removing impurities and recycling the residual acid extracted from the wet purification phosphoric acid byproduct provided in this embodiment includes the following steps:

[0032] S1. The residual acid extracted as a by-product of wet-process purified phosphoric acid production is first sent to a buffer tank, then pumped to a mixing tee 6 and slowly sent to reactor ①#. After the residual acid extracted has soaked the stirring paddle in the reaction tank, the stirring paddle is started; the concentrated sulfuric acid inlet valve is slowly opened, and a desorbent is slowly sent to the mixing tee 6. The flow rate of the desorbent is adjusted accordingly according to the flow rate of the residual acid extracted and the desorbent at a mass ratio of 1:4; the concentrated sulfuric acid enters reactor ①# and reacts continuously at a temperature of about 100°C for 8 hours. The reaction process must ensure that the concentrated sulfuric acid and the residual acid extracted are fully mixed. Then, the concentrated sulfuric acid overflows from reactor ①# and enters reactors ②#, ③#, and ④# in turn. The agitators of the corresponding reactors 1 are started in turn according to the liquid level. After the reaction time reaches 8 hours, the bottom valve of reactor ④# is slowly opened, and the reaction slurry is sent to centrifuge 3 at a small flow rate for solid-liquid separation to obtain deacidified and deslagging.

[0033] S2, wherein the removed acid is then returned to the phosphoric acid production system through a pipeline to undergo a desulfurization reaction with the phosphate concentrate, and the concentrated sulfuric acid reacts with the phosphate concentrate to produce phosphoric acid and phosphogypsum. After testing, all indicators of the phosphoric acid product meet the production requirements of phosphoric acid downstream products, thereby effectively achieving the recycling of the residual acid extracted as a by-product of wet-process phosphoric acid purification and recovering the phosphorus value in the residual acid;

[0034] S3. The removal slag is mainly composed of metal salts such as iron, magnesium, and aluminum. After the residual acid-removal agent mixed slurry is separated into solid and liquid, it is neutralized with weak alkaline salts (K2CO3, CaCO3, Na2CO3) to produce compound fertilizer products, so that the process is closed-loop, all impurities are eliminated, and phosphorus resources are efficiently recycled.

[0035] In the above embodiment, the residual acid extracted from the by-product of wet-process purified phosphoric acid is placed in the residual acid extraction reactor as the matrix, and the removal agent is added to the reactor in stages according to the reaction conditions as the sub-material.

[0036] Due to the nature of the remover, it reacts with the residual acid to release heat. Before the reaction, the reaction agitator and temperature control system are installed. During the reaction, the flow of the remover into the reactor is adjusted in time according to the reaction heat to control the reactor temperature at 80-100 ° C. As the remover is continuously added and fully mixed with the residual acid, the solubility of the metal salts in the residual acid changes, forming the residual acid removal reaction slurry. After the reaction is sufficient (measure the SO4 in the residual acid-removal agent mixed slurry), the reaction temperature is 80-100 ° C. 2- to judge whether the reaction has reached the end point) and obtain the deslagging and deacidification through solid-liquid separation.

[0037] Table 1 below shows the changes in the components of the extracted residual acid during the impurity removal process in the above embodiment (wherein: the removal rate is calculated by converting the removed acid to the same phosphorus content as the original acid of the extracted acid and then calculating the metal ion removal rate):

[0038]

[0039]

[0040] As can be seen from the above table, the impurity removal and recycling method in this embodiment has a removal effect on various metal ions. The removed acid contains phosphoric acid with a concentration of about 8% and sulfuric acid with a concentration of about 90%. The removed acid is dripped back into the phosphoric acid production system, and the concentrated sulfuric acid reacts with the phosphate concentrate to achieve the effect of removing acid and desulfurization. The removed acid after removal will not affect the subsequent use of phosphoric acid downstream equipment.

[0041] Table 2 below shows the pH and ion content of the decontaminated slag produced during the decontamination process in the above embodiment, as well as the corresponding changes after neutralization with a weak base salt. The other components in the decontaminated slag are some unknown impurities. After the decontaminated slag is mixed with a weak base salt, the other components are components introduced into the weak base salt. If potassium salt is used to neutralize the decontaminated slag, the other components after neutralization are mainly K2SO4 and KHSO4.

[0042]

[0043] As shown in the table above, neutralization of the deslagging with weak alkaline salt not only can neutralize the residual acid solution therein to make the deslagging solid, but also reduces the pH of the deslagging, making the deslagging after neutralization more widely used.

[0044] Table 3 below shows the changes in various indicators during the desulfurization reaction between the deacidification and back-trickling phosphoric acid production system and the phosphate concentrate in the above embodiment:

[0045]

[0046]

[0047] As shown in the table above, the removed acid is trickled back into phosphoric acid production and reacts with phosphate concentrate for desulfurization. The various indicators of the generated phosphoric acid meet the requirements of downstream phosphoric acid production, and the trace amount of concentrated sulfuric acid as a removal agent will not affect downstream use.

[0048] Specifically, the impurity removal and recycling method provided in this embodiment, on the one hand, achieves good removal of metal cations in the residual acid, a by-product of wet-process purified phosphoric acid, among which the removal effect of magnesium ions is the best, and the removal effect of other metal cations is also relatively good; on the other hand, without affecting the reaction effect, the four reactors are connected to continuously feed and react, thereby increasing the total reaction volume of the constant-volume reactor and improving the reaction efficiency; on the other hand, after the residual acid, a by-product of wet-process purified phosphoric acid production, is subjected to the removal of metal cations by concentrated sulfuric acid as a removal agent, the obtained removed acid meets the requirements. Various indicators of the return acid in phosphoric acid production do not affect the subsequent production of phosphoric acid, and the resource recycling rate is high. Fourthly, the concentrated sulfuric acid used as the removal agent in the deacidification can be dripped back into the phosphoric acid production system, thereby realizing the recycling and recovery of the concentrated sulfuric acid used as the removal agent in the deacidification, thereby maximizing resource utilization. Fifthly, the concentrated sulfuric acid used as the cation removal agent in this embodiment enters the reactor together with the extracted residual acid through a mixing tee and a reactor overflow pipe in an overflow connection manner, thereby greatly increasing the safety of the concentrated sulfuric acid reaction and avoiding corrosion caused by direct contact of the concentrated sulfuric acid with the reactor wall, thereby increasing the durability of the reaction device.

[0049] The recycling method provided by the present application continuously adds a stripping agent to the residual acid to change the solubility of the metal ion salt in the system, and finally makes the metal cation salt precipitate out of the system, and obtains the stripping slag and stripping acid through solid-liquid separation; since the stripping agent contains a large amount of sulfur element and cannot be directly used for the phosphoric acid back-end product, the stripping acid after solid-liquid separation is returned to the phosphoric acid production device according to the wet phosphoric acid (concentrated sulfuric acid method) process, so that the stripping agent (mainly SO4 2- ) reacts with phosphate concentrate to achieve the effect of deacidification and desulfurization, thereby recovering the phosphorus resources in the extracted residual acid and recovering the sulfur resources in the deacidification by utilizing the reaction of phosphate concentrate with sulfate in the deacidification agent, and reusing the phosphoric acid reaction system to recycle the resources; the deacidification slag is reacted with a weak alkaline salt to produce a compound fertilizer product, truly achieving a closed-loop process and efficiently utilizing and recovering phosphorus resources. The process is simple and easy to control, with a high recycling rate, and the recycling of phosphorus resources and deacidification agent resources is achieved without affecting the production of phosphoric acid and without the need for additional deacidification equipment.

[0050] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for removing impurities and recycling residual acid extracted from wet-process purified phosphoric acid by-products, characterized in that: The steps include: S1. Adding a metal-removing agent to the residual acid extracted from the wet-process purified phosphoric acid byproduct, wherein the residual acid is used as a matrix and the metal-removing agent is used as a daughter material. According to the reaction conditions, the metal-removing agent is continuously added to the residual acid to change the solubility of the metal salts to form a reaction slurry, and then solid-liquid separation is performed to obtain deslagging and deacidified residues; When the metal remover and the extraction residue acid are mixed, the reaction is carried out in multiple reactors in sequence, and the multiple reactors are connected by overflow pipes; First, the extracted residual acid is sent to the buffer tank, and then transported to the reactor through the delivery pump. Under stirring conditions, the metal removal agent is continuously added to the reactor through the delivery pipeline, and the reaction is continuously carried out at a temperature of 80-100°C for 5-8 hours to form a reaction slurry; The mass ratio of metal remover to residual acid is 4:1; S2, returning the deacidified acid and concentrated sulfuric acid to the phosphoric acid production system, so that the metal remover in the deacidified acid reacts with the phosphate concentrate to achieve deacidification and desulfurization, thereby obtaining wet-process phosphoric acid that meets the requirements of downstream phosphoric acid production; S3, neutralizing the removed slag with a weak alkaline salt to produce a compound fertilizer product to achieve resource utilization; In step S1, a flow control valve is provided on the delivery pipeline for delivering the metal remover, and the delivery pipeline is connected to the reactor through an anti-corrosion mixing tee. The end of the anti-corrosion mixing tee that is not connected to the delivery pipeline and the reactor is provided with a remover buffer tank. During the reaction process, if the temperature of the reactor is stable, the metal remover enters the reactor through the anti-corrosion mixing tee. If the temperature of the reactor is high, the metal remover is temporarily stored in the remover buffer tank through the anti-corrosion mixing tee to control the remover flow according to the temperature of the reactor. The metal remover is concentrated sulfuric acid or an acidic complex with a high sulfur content.

2. The method for removing impurities and recycling residual acid extracted from wet-process purified phosphoric acid byproducts according to claim 1, characterized in that: In step S1, since the reaction between the metal remover and the extracted residual acid releases heat, a reaction stirring device and a control system need to be installed. During the reaction, the metal remover is slowly added under stirring conditions, and the flow rate of the metal remover added to the reactor is adjusted in time according to the reaction heat to control the reactor temperature at 80-100°C.

3. The method for removing impurities and recycling residual acid extracted from wet-process purified phosphoric acid byproducts according to claim 1, characterized in that: In step S1, a centrifuge is used to separate the slurry into solid and liquid to obtain deslagging and deacidification.

4. The method for removing impurities and recycling residual acid extracted from wet-process purified phosphoric acid byproducts according to claim 1, characterized in that: In step S2, the deacidified product is dripped back to the phosphoric acid production system through a pipeline, and the deacidifying agent reacts with the phosphate concentrate to generate phosphoric acid and phosphogypsum products.

5. The method for removing impurities and recycling residual acid extracted from wet-process purified phosphoric acid byproducts according to claim 1, characterized in that: In step S3, the weak base salt is any one of K2Co3, CaCo3 and Na2Co3.

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