A selective leaching system for dicyandiamide cake

Abstract

The utility model belongs to nitrogen carbon nitrogen (NCN) chemical industry solid by -product resource utilization equipment technical field, concretely relates to a kind of selective leaching system of dicyandiamide residue. Including acid leaching reaction system, it mainly includes dosing machine, acid leaching reactor and first solid-liquid separator connected in turn, acid leaching reactor is connected with ligand storage tank and acid liquor storage tank, the outlet of ligand storage tank is connected with ligand metering pump, the outlet of ligand metering pump is connected with the import of acid leaching reactor. The acid leaching reaction system of the application, by setting ligand metering pump and ligand storage tank, add organic complexing agent to reaction system, can adjust solution complexing balance, make calcium ion preferentially dissolve and reduce the dissolution degree of iron ion, improve calcium leaching rate, reduce iron leaching rate, the iron ion content in obtained leaching solution is lower, can reduce subsequent iron removal processing step.

Description

Technical Field

[0001] This utility model belongs to the technical field of equipment for the resource utilization of solid by-products in the nitrogen, carbon, and nitrogen (NCN) chemical industry, and specifically relates to a selective leaching system for dicyandiamide residue. Background Technology

[0002] In the production of dicyandiamide using calcium cyanamide as a raw material, a large amount of by-product slag rich in calcium phase and containing impurities such as iron and aluminum is generated. To achieve resource utilization, acid leaching is typically used to extract calcium salt products. Existing technologies mostly employ a simple, non-selective acid leaching process to recover calcium salts. However, as the pH value decreases, iron impurities (Fe2+) in the residue increase. 2+ / Fe 3+ Iron ions will dissolve in large quantities into the liquid phase simultaneously with calcium ions. High concentrations of iron impurities severely reduce the purity and whiteness of downstream calcium salt products, significantly increase subsequent purification costs, and lead to batch quality control issues, necessitating the addition of lengthy neutralization and precipitation processes to remove iron. Summary of the Invention

[0003] Based on this, this application provides a selective leaching system for dicyandiamide residue to solve the technical problem in the prior art where a large amount of iron impurities are leached out, reducing the purity and whiteness of downstream calcium salt products, increasing subsequent purification costs, and causing product batch quality to become out of control.

[0004] The technical solution of this application to solve the above-mentioned technical problems is as follows: A selective leaching system for dicyandiamide residue, characterized in that it comprises:

[0005] An acid leaching reaction system includes an acid leaching reactor and a ligand storage tank. The outlet of the ligand storage tank is connected to a ligand metering pump, and the outlet of the ligand metering pump is connected to the inlet of the acid leaching reactor. The inlet of the acid leaching reactor is also connected to a metering feeder and an acid storage tank. The metering feeder is used to transport slurry. The outlet of the acid storage tank is connected to an acid metering pump, and the outlet of the acid metering pump is connected to the inlet of the acid leaching reactor. The outlet of the acid leaching reactor is connected to a first solid-liquid separator.

[0006] Preferably, the selective leaching system for dicyandiamide residue further includes a slurry silo and a powder silo. The outlet of the powder silo is connected to the inlet of the slurry silo, and the outlet of the slurry silo is connected to the inlet of the quantitative feeder. The slurry silo is also equipped with a water injection pipe for adding water to the slurry silo to make slurry.

[0007] Preferably, in the selective leaching system for dicyandiamide residue described above, the acid leaching reaction system further includes a first pH sensor, which is inserted into the side wall of the acid leaching reactor and extends into its interior.

[0008] Preferably, in the selective leaching system for dicyandiamide residue described above, the acid leaching reactor is equipped with a mechanical stirring assembly.

[0009] Preferably, the selective leaching system for dicyandiamide residue further includes a closed-circuit grinding and classification system, which includes a grinding host, an air classifier, a coarse powder return pipe, and a finished product collection device. The inlet of the grinding host is connected to the outlet of the powder silo, the outlet of the grinding host is connected to the inlet of the air classifier, the fine powder outlet of the air classifier is connected to the inlet of the finished product collection device, and the coarse powder outlet is connected to the inlet of the grinding host through the coarse powder return pipe. The outlet of the finished product collection device is connected to the inlet of the slurry silo.

[0010] Preferably, in the selective leaching system for dicyandiamide residue described above, the outlet of the finished product collection device is connected to the inlet of the heat conditioning rotary kiln.

[0011] Preferably, in the selective leaching system for dicyandiamide residue described above, the fine powder outlet of the air classifier is equipped with an online particle size monitor to detect the particle size of the powder discharged from the fine powder outlet.

[0012] Preferably, the selective leaching system for dicyandiamide residue further includes a pretreatment system, which includes a heat conditioning rotary kiln, a washing reaction tank, and a second solid-liquid separator. The inlet of the heat conditioning rotary kiln is connected to the outlet of the powder silo, the outlet of the heat conditioning rotary kiln is connected to the inlet of the washing reaction tank, the washing reaction tank is provided with a washing liquid feed pipe, the outlet of the washing reaction tank is connected to the inlet of the second solid-liquid separator, and the solid phase outlet of the second solid-liquid separator is connected to the inlet of the slurry silo.

[0013] Preferably, in the selective leaching system for dicyandiamide residue described above, the liquid phase outlet of the second solid-liquid separator is connected to the inlet of the washing reaction tank via a washing liquid recycling pipe, and a filter is provided on the washing liquid recycling pipe.

[0014] Preferably, in the selective leaching system for dicyandiamide residue described above, the liquid phase outlet of the first solid-liquid separator is connected to the inlet of the washing reaction tank via a leachate recycling pipe.

[0015] Compared with the prior art, this application has at least the following advantages:

[0016] This application discloses a selective leaching system for dicyandiamide residue, mainly comprising an acid leaching reaction system. In addition to an acid storage tank and an acid metering pump, the inlet of the acid leaching reactor in this system also includes a ligand storage tank and a ligand metering pump. By incorporating the ligand metering pump and ligand storage tank, the acid leaching reaction system of this application allows for the addition of an organic ligand to the reaction system, thereby adjusting the solution complexation balance, preferentially dissolving calcium ions and reducing the dissolution rate of iron ions. This increases the calcium leaching rate and decreases the iron leaching rate, resulting in a lower iron ion content in the leachate, which reduces the need for subsequent iron removal steps. Attached Figure Description

[0017] Figure 1 This is a system diagram of the selective leaching system for dicyandiamide residue in this application.

[0018] The diagram shows: acid leaching reaction system 100, acid leaching reactor 110, first pH sensor 111, mechanical stirring assembly 112, ligand storage tank 120, ligand metering pump 121, quantitative feeder 130, acid storage tank 140, acid metering pump 141, first solid-liquid separator 150, leachate collection pipe 160, leachate reuse pipe 161, slurry silo 200, water injection pipe 210, powder silo 300, pretreatment system 400, heat conditioning rotary kiln 410, thermocouple sensor 411, washing reaction tank 420, washing liquid inlet pipe 421, washing liquid reuse pipe 422, filter 423, second pH sensor 424, second solid-liquid separator 430, closed-circuit grinding and classification system 500, grinding host 510, air classifier 520, coarse powder return pipe 530, finished product collection device 540, and online particle size monitor 550. Detailed Implementation

[0019] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0020] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "top," "bottom," "end," "top," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for descriptive purposes only and is not intended to limit the scope of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Please refer to Figure 1 In one specific embodiment of this application, a selective leaching system for dicyandiamide residue includes: an acid leaching reaction system 100, which includes an acid leaching reactor 110 and a ligand storage tank 120. The outlet of the ligand storage tank 120 is connected to a ligand metering pump 121, and the outlet of the ligand metering pump 121 is connected to the inlet of the acid leaching reactor 110. The inlet of the acid leaching reactor 110 is also connected to a metering feeder 130 and an acid storage tank 140. The metering feeder 130 is used to transport slurry. The outlet of the acid storage tank 140 is connected to an acid metering pump 141, and the outlet of the acid metering pump 141 is connected to the inlet of the acid leaching reactor 110. The outlet of the acid leaching reactor 110 is connected to a first solid-liquid separator 150.

[0023] Simple acid leaching can dissolve calcium, but it also dissolves more than 20% of iron, leading to a significant increase in subsequent purification costs. The acid leaching reaction system 100 of this application has a ligand storage tank 120 connected to the inlet of the acid leaching reactor 110. The ligand storage tank 120 stores organic ligands (e.g., citrate, acetate, or lactate). The organic ligands are fed into the acid leaching reactor 110 via a ligand metering pump 121, preferably a variable frequency metering pump, which can adjust the amount of ligand added according to the amount of reactants. The organic ligands are added during the acid leaching process, and these ligands can selectively stabilize calcium. 2+ without complexing Fe 2+ / Fe 3+ This avoids iron impurities (Fe). 2+ / Fe 3+ Simultaneously, calcium ions dissolve in large quantities into the liquid phase to improve the selective leaching of calcium ions and reduce the leaching degree of iron impurities. The acid solution required for the acid leaching reaction (e.g., acetic acid, hydrochloric acid) is stored in acid solution storage tank 140 and transported to acid leaching reactor 110 by acid solution metering pump 141 to react with the dicyandiamide slurry. During operation, the dicyandiamide slurry is transported to acid leaching reactor 110 by metering feeder 130, while acid solution metering pump 141 transports acid solution from acid solution storage tank 140 to acid leaching reactor 110, and ligand metering pump 121 transports organic ligand from ligand storage tank 120 to acid leaching reactor 110 for acid leaching reaction.

[0024] The acid leaching reaction system 100 of this application, by setting up a ligand metering pump 121 and a ligand storage tank 120, adds an organic ligand to the reaction system, which can adjust the complexation balance of the solution, so that calcium ions are preferentially dissolved and the degree of iron ion dissolution is reduced, thereby increasing the calcium leaching rate and reducing the iron dissolution rate. The resulting leachate has a low iron ion content, which can reduce the number of subsequent iron removal steps.

[0025] Since the main raw material for the reaction is dicyandiamide residue slurry, the dicyandiamide residue needs to be slurried first and then stored in the slurry silo 200. Therefore, the selective leaching system also includes a slurry silo 200 and a powder silo 300. The outlet of the powder silo 300 is connected to the inlet of the slurry silo 200, and the outlet of the slurry silo 200 is connected to the inlet of the quantitative feeder 130. The slurry silo 200 is also equipped with a water injection pipe 210 for adding water to the slurry silo 200 for slurry preparation. The dicyandiamide residue is stored in the powder silo 300. During production, the dicyandiamide residue in the powder silo 300 is added to the slurry silo 200, and water is added to the slurry silo 200 through the water injection pipe 210. After stirring evenly, a dicyandiamide residue slurry is obtained. Then, the obtained dicyandiamide residue slurry is conveyed from the slurry silo 200 to the quantitative feeder 130, and then to the acid leaching reactor 110. The dicyandiamide residue slurry is quite viscous, so the quantitative feeder 130 can be selected as a suitable device for conveying viscous materials, such as a screw conveyor or screw pump. The first solid-liquid separator 150 can be a filter press or centrifuge. The liquid outlet of the first solid-liquid separator 150 is also equipped with a leachate collection pipe 160. The slurry after the acid leaching reaction is transported to the first solid-liquid separator 150 for solid-liquid separation, yielding a calcium-containing leachate and iron-rich tailings. The calcium-containing leachate is discharged and collected through the leachate collection pipe 160, while the iron-rich tailings are discharged from the solid outlet of the first solid-liquid separator 150.

[0026] During the acid leaching reaction, commonly used industrial acids (such as acetic acid and hydrochloric acid) are used to regulate the pH of the slurry in the acid leaching reactor 110 between 1.5 and 4.0. To monitor the pH in the reactor in real time and adjust the acid dosage, the acid leaching reaction system 100 preferably also includes a first pH sensor 111. The first pH sensor 111 is inserted into the side wall of the acid leaching reactor 110 and extends into its interior. The first pH sensor 111 is electrically connected to the acid metering pump 141. The pH signal detected by the first pH sensor 111 can guide the adjustment of the stroke or speed of the acid metering pump 141 (preferably a variable frequency metering pump, such as a variable frequency diaphragm metering pump) to avoid excessive dissociation of the iron phase due to local over-acidity.

[0027] Furthermore, a mechanical stirring assembly 112 is installed inside the acid leaching reactor 110, and a heating jacket is provided around the outer wall of the acid leaching reactor 110. The temperature of the acid leaching reaction is usually between 20℃ and 80℃. Therefore, by providing a heating jacket around the outer wall of the acid leaching reactor 110, the reactants inside the acid leaching reactor 110 can be heated as needed. At the same time, the stirring by the mechanical stirring assembly 112 inside the acid leaching reactor 110 can make the reaction more uniform and efficient.

[0028] Specifically, the working process of the above-mentioned acid leaching reaction system 100 is as follows: Dicyandiamide residue in powder silo 300 is added to slurry silo 200, and water is added to slurry silo 200 through water injection pipe 210. After stirring evenly, dicyandiamide residue slurry is obtained. Dicyandiamide residue slurry is fed from slurry silo 200 to quantitative feeder 130. Quantitative feeder 130 delivers dicyandiamide residue slurry to acid leaching reactor 110 according to preset feed flow rate / feed amount. Acid leaching reactor 110 starts mechanical stirring and heating. At the same time, acid metering pump 141 delivers acid from acid storage tank 140 to acid leaching reactor 110, and ligand metering pump 121 delivers organic ligand from ligand storage tank 120 to acid leaching reactor 110 for selective leaching. During this process, the first pH sensor 111 monitors the pH value of the slurry in the acid leaching reactor 110 in real time to guide the adjustment of the stroke or speed of the acid metering pump 141, so that the pH value of the slurry in the acid leaching reactor 110 is maintained at a preset value. The slurry after the acid leaching reaction is transported to the first solid-liquid separator 150 for solid-liquid separation to obtain calcium-containing leachate and iron-rich tailings.

[0029] The acid leaching reaction system 100 of this application, by setting up a ligand metering pump 121 and a ligand storage tank 120, adds an organic complexing agent to the reaction system, which can adjust the solution complexation balance, preferentially dissolve calcium ions and reduce the dissolution of iron ions, thereby increasing the calcium leaching rate and reducing the iron leaching rate. The resulting leachate has a low iron ion content, which can reduce the number of subsequent iron removal steps. Through the electrical interlock between the online first pH sensor 111 and the acid metering pump 141, the process control requirements are directly converted into the physical response of the equipment, improving the stability of the batch quality of the leachate. The acid leaching reactor 110 is simultaneously connected to the acid metering pump 141 and the acid storage tank 140, and the ligand metering pump 121 and the ligand storage tank 120, forming a unique dual-liquid path addition structure, which provides better hardware mixing conditions for the complexing ligand to inhibit iron dissolution. The various devices are sequentially connected through closed pipelines and pumping equipment, and the equipment structure is compact, effectively avoiding splashing and volatilization caused by disordered feeding, and improving the working environment of the production workshop.

[0030] In another specific embodiment of this application, the selective leaching system for dicyandiamide residue further includes a closed-circuit grinding and classification system 500. The closed-circuit grinding and classification system 500 includes a grinding host 510, an air classifier 520, a coarse powder return pipe 530, and a finished product collection device 540. The inlet of the grinding host 510 is connected to the outlet of the powder silo 300, the outlet of the grinding host 510 is connected to the inlet of the air classifier 520, the fine powder outlet of the air classifier 520 is connected to the inlet of the finished product collection device 540, the coarse powder outlet is connected to one end of the coarse powder return pipe 530, and the other end of the coarse powder return pipe 530 is connected to the inlet of the grinding host 510. The outlet of the finished product collection device 540 is connected to the inlet of the slurry silo 200.

[0031] Before acid leaching dicyandiamide residue, it can be mechanically ground. However, if the particle size is too coarse, the calcium-containing phase is insufficiently exposed, severely limiting calcium leaching. Conversely, if the particle size is too fine (over-grinding), the iron-bearing phase coating is easily destroyed, increasing the dissolution of iron impurities in the strongly acidic system and raising subsequent iron removal and purification costs. Therefore, it is necessary to control the particle size of the dicyandiamide residue within a suitable range, for example, the particle size D of the ground dicyandiamide residue. 90 ≤75µm. To achieve this, this application employs a closed-circuit grinding and classification system 500. Mechanical grinding is carried out in a grinding host 510, which is preferably a continuous ball mill or a vertical roller mill. The dicyandiamide residue in the powder silo 300 is fed into the grinding host 510 for grinding. The ground dicyandiamide residue enters the inlet (also called the raw material inlet) of the air classifier 520 for classification. The air classifier 520 in this application is preferably driven by a variable frequency motor. The classified fine powder is sent to the finished product collection device 540 through the fine powder outlet. The finished product collection device 540 is preferably a cyclone collector or a pulse bag filter. The fine powder in the finished product collection device 540 is sent to the slurry silo 200 for slurry preparation to obtain dicyandiamide residue slurry for the next acid leaching process. The coarse powder classified by the air classifier 520 is discharged from the coarse powder outlet at the lower end of the air classifier 520, and then connected in reverse to the feed end of the grinding host 510 through the coarse powder return pipe 530, and enters the grinding host 510 for further grinding.

[0032] Furthermore, the fine powder outlet of the air classifier 520 is equipped with an online particle size monitor 550 for detecting the particle size of the powder discharged from the fine powder outlet. The online particle size monitor 550 is located on the fine powder conveying pipeline in front of the fine powder outlet of the air classifier 520 and the inlet of the finished product collection device 540. The online particle size monitor 550 is electrically connected to the variable frequency motor at the top of the air classifier 520, forming a hardware automatic feedback adjustment closed loop.

[0033] Specifically, the working process of the closed-circuit grinding and grading system 500 is as follows: Dicyandiamide residue in the powder silo 300 is fed into the grinding host 510 for grinding. The ground dicyandiamide residue enters the inlet of the air classifier 520 for grading. The graded fine powder is then sent to the finished product collection device 540 through the fine powder outlet. Unqualified coarse particles after grading by the air classifier 520 are discharged from the coarse powder outlet at the lower end of the air classifier 520, and then reversed through the coarse powder return pipe 530 to the feed end of the grinding host 510, entering the grinding host 510 for further grinding. The online particle size analyzer 550 monitors the particle size of the fine powder in real time to guide the adjustment of the grading parameters of the air classifier 520, ensuring that the particle size of the fine powder is controlled within the set particle size range. The fine powder collected by the finished product collection device 540 has two transmission paths: First, the fine powder is transported to the pretreatment system 400 (see below) for pretreatment, that is, it is sent to the heat conditioning rotary kiln 410 for heat conditioning and washing pretreatment, and then sent to the slurry bin 200 for pulping to obtain dicyandiamide residue slurry for the next acid leaching process; Second, the fine powder is not pretreated and is directly sent to the slurry bin 200 for pulping to obtain dicyandiamide residue slurry for the next acid leaching process.

[0034] The closed-circuit grinding and grading system 500 of this application, through the electrical interlock between the online particle size monitor 550 and the air classifier 520, converts the particle size requirement into the physical response of the equipment, thereby improving the stability of the output particle size; unqualified coarse particles are automatically returned to the grinding host 510 for re-grinding, which helps to improve the continuity of grinding process and the stability of particle size control; the various devices are connected by a closed pipeline and operate under negative pressure, which can reduce dust escape and improve the working environment of the production workshop.

[0035] In another specific embodiment of this application, the selective leaching system for dicyandiamide residue further includes a pretreatment system 400. The pretreatment system 400 includes a heat conditioning rotary kiln 410, a washing reaction tank 420, and a second solid-liquid separator 430. The inlet of the heat conditioning rotary kiln 410 is connected to the outlet of the powder silo 300, and the outlet of the heat conditioning rotary kiln 410 is connected to the inlet of the washing reaction tank 420. The washing reaction tank 420 is provided with a washing liquid feed pipe 421, and the outlet of the washing reaction tank 420 is connected to the inlet of the second solid-liquid separator 430. The solid phase outlet of the second solid-liquid separator 430 is connected to the inlet of the slurry silo 200.

[0036] Alternatively, the ground dicyandiamide residue, i.e., fine powder, can be pretreated, i.e., heat conditioning and washing. Then, the outlet of the finished product collection device 540 is connected to the inlet of the heat conditioning rotary kiln 410. After heat conditioning, the fine powder is sent to the slurry bin 200 through the solid phase outlet of the second solid-liquid separator 430 in the pretreatment system 400.

[0037] Before acid leaching, dicyandiamide slag can be pretreated, primarily through heat conditioning and washing. Heat conditioning removes the water of crystallization from the iron phase, while washing removes the iron film from the slag surface. Heat conditioning is mainly carried out in a heat conditioning rotary kiln 410. The dicyandiamide slag is fed into the heat conditioning rotary kiln 410, whose inner wall is fixedly equipped with internal spiral baffles along the material feeding direction. These baffles promote material agitation and forward movement, ensuring a uniform heat residence time (typically 0.5–2.0 hours), allowing the dicyandiamide slag to be uniformly heated to a preset temperature (typically 200–400°C). In some preferred embodiments, several thermocouple sensors 411 are sequentially arranged axially within the kiln body of the heat conditioning rotary kiln 410. These thermocouple sensors 411 can detect the temperature inside the kiln in real time and guide the heating temperature of the heat conditioning rotary kiln 410, ensuring that the kiln remains at the preset temperature. The dicyandiamide residue, after being heat-conditioned in the rotary kiln 410, is sent to the washing reaction tank 420 for washing treatment (usually a weakly acidic wash, lasting 5-15 minutes). The washing reaction tank 420 is equipped with a washing liquid inlet pipe 421, through which washing liquid is introduced into the washing reaction tank 420. A mechanical stirring assembly 112 is installed inside the washing reaction tank 420 to enhance the mixing of the material and the washing liquid. Preferably, the washing reaction tank 420 is also equipped with a second pH sensor 424, which is inserted into the side wall of the washing reaction tank 420 and extends into its interior. The second pH sensor 424 is used to detect the pH value within the washing reaction tank 420, enabling real-time monitoring of the washing liquid pH and helping to improve the stability of the washing process.

[0038] The solid-liquid mixture in the washing reaction tank 420 is then fed into the second solid-liquid separator 430 for solid-liquid separation, yielding washing waste liquid and pretreated dicyandiamide residue. The second solid-liquid separator 430 can be a filter press or a centrifuge, etc. The pretreated dicyandiamide residue is then transported to the slurry silo 200 for slurry preparation through the solid phase outlet of the second solid-liquid separator 430, and then sent to the acid leaching reaction system 100 for acid leaching reaction.

[0039] As mentioned above, the acid leaching reaction produces calcium-containing leachate. To avoid waste, this calcium-containing leachate can be reused. Therefore, in the selective leaching system for dicyandiamide residue described above, the liquid phase outlet of the first solid-liquid separator 150 is connected to the inlet of the washing reaction tank 420 via a leachate reuse pipe 161. The calcium-containing leachate separated by the first solid-liquid separator 150 is transported to the washing reaction tank 420 through the leachate reuse pipe 161 to be used as washing liquid to wash the heat-conditioned dicyandiamide residue. This reduces the amount of fresh washing liquid, minimizes waste, and saves costs.

[0040] Directly discarding the washing wastewater would lead to significant water and chemical reagent consumption. Therefore, in the selective leaching system for dicyandiamide residue described above, the liquid phase outlet of the second solid-liquid separator 430 is connected to the inlet of the washing reaction tank 420 via a washing liquid recycling pipe 422, which is equipped with a filter 423. The washing wastewater separated by the second solid-liquid separator 430 is transported to the washing reaction tank 420 through the washing liquid recycling pipe 422 and recycled again as washing liquid, reducing waste. The filter 423 on the washing liquid recycling pipe 422 can filter and remove impurities from the washing wastewater, reducing the risk of pipe and equipment blockage.

[0041] Specifically, the pretreatment system 400 operates as follows: The dicyandiamide residue in the powder silo 300 is fed into a heat-conditioning rotary kiln 410, where it is heated to a preset temperature. The residue is agitated and moved forward by the spiral baffles inside the kiln, ensuring uniform heating and maintaining a preset heat residence time. The heat-conditioned residue is then fed into a washing reaction tank 420, where washing liquid is fed through a washing liquid inlet pipe 421 to wash the residue. The resulting solid-liquid mixture is then fed into a second solid-liquid separator 430 for solid-liquid separation, yielding washing waste liquid and pretreated dicyandiamide residue. The pretreated residue is then transported through the solid phase outlet of the second solid-liquid separator 430 to a slurry silo 200 for pulping, and then sent to an acid leaching reaction system 100 for acid leaching. The washing waste liquid is discharged to the washing liquid recycling pipe 422 through the liquid phase outlet of the second solid-liquid separator 430 and then transported to the washing reaction tank 420 to be recycled as washing liquid.

[0042] The pretreatment system 400 of this application combines heat conditioning and washing. Heat conditioning can remove the crystal water of the iron phase, which helps to reduce the activity of iron phase minerals in the subsequent acid leaching process. The subsequent chemical washing is a weak acid chemical washing, which helps to remove the surface adhesion layer and some soluble iron components formed during heat treatment, and can improve the calcium phase leaching conditions in the subsequent acid leaching. By connecting the liquid phase outlet of the second solid-liquid separator 430 to the inlet of the washing reaction tank 420 through the washing liquid recycling pipe 422, the washing liquid can be recycled and reused, and the consumption of washing liquid can be reduced. By setting a filter device in the recycling pipeline, fine particles in the circulating liquid can be removed, reducing the risk of pipeline and equipment blockage. By connecting the liquid phase outlet of the first solid-liquid separator 150 to the inlet of the washing reaction tank 420 through the leaching liquid recycling pipe 161, the calcium-containing leaching liquid can be recycled and reused, reducing fresh detergent, reducing waste, and saving costs.

[0043] The dicyandiamide residue in the powder silo 300 also has the following transport paths: First, the dicyandiamide residue in the powder silo 300 is directly added to the slurry silo 200 for pulping, and then transported to the quantitative feeder 130 in the acid leaching reaction system 100 for acid leaching reaction; Second, the dicyandiamide residue in the powder silo 300 is transported from the pretreatment system 400 to the heat conditioning rotary kiln 410 in the pretreatment system 400 for heat conditioning and then washing, and finally added to the slurry silo 200 for pulping, and then transported to the quantitative feeder 130 in the acid leaching reaction system 100 for acid leaching reaction; Third, the dicyandiamide residue in the powder silo 300 is transported to the closed-circuit grinding and classification system 500, that is, sent to the grinding host 510 for grinding and then air classification, and the classified fine powder is sent to the finished product collection device 540. The fine powder in the finished product collection device 540 can be pretreated and then pulped for acid leaching reaction, or it can be directly pulped for acid leaching reaction, as described above.

[0044] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A system for selective leaching of dicyandiamide cake, characterized by, include: An acid leaching reaction system includes an acid leaching reactor and a ligand storage tank. The outlet of the ligand storage tank is connected to a ligand metering pump, and the outlet of the ligand metering pump is connected to the inlet of the acid leaching reactor. The inlet of the acid leaching reactor is also connected to a metering feeder and an acid storage tank. The metering feeder is used to transport slurry. The outlet of the acid storage tank is connected to an acid metering pump, and the outlet of the acid metering pump is connected to the inlet of the acid leaching reactor. The outlet of the acid leaching reactor is connected to a first solid-liquid separator.

2. The selective leaching system for dicyandiamide residue as described in claim 1, characterized in that, It also includes a slurry silo and a powder silo. The outlet of the powder silo is connected to the inlet of the slurry silo, and the outlet of the slurry silo is connected to the inlet of the quantitative feeder. The slurry silo is also equipped with a water injection pipe for adding water to the slurry silo to make slurry.

3. The selective leaching system for dicyandiamide residue as described in claim 1, characterized in that, The acid leaching reaction system also includes a first pH sensor, which is inserted into the side wall of the acid leaching reactor and extends into its interior.

4. The selective leaching system for dicyandiamide residue as described in claim 1, characterized in that, The acid leaching reactor is equipped with a mechanical stirring assembly.

5. The selective leaching system for dicyandiamide residue as described in claim 2, characterized in that, It also includes a closed-circuit grinding and grading system, which includes a grinding host, an air classifier, a coarse powder return pipe, and a finished product collection device; the inlet of the grinding host is connected to the outlet of the powder silo, the outlet of the grinding host is connected to the inlet of the air classifier, the fine powder outlet of the air classifier is connected to the inlet of the finished product collection device, and the coarse powder outlet is connected to the inlet of the grinding host through the coarse powder return pipe; the outlet of the finished product collection device is connected to the inlet of the slurry silo.

6. The selective leaching system for dicyandiamide residue as described in claim 5, characterized in that, The air classifier is equipped with an online particle size monitor at the fine powder outlet to detect the particle size of the powder discharged from the fine powder outlet.

7. The selective leaching system for dicyandiamide residue as described in claim 5, characterized in that, It also includes a pretreatment system, which comprises a heat conditioning rotary kiln, a washing reaction tank, and a second solid-liquid separator. The inlet of the heat conditioning rotary kiln is connected to the outlet of the powder silo, the outlet of the heat conditioning rotary kiln is connected to the inlet of the washing reaction tank, the washing reaction tank is provided with a washing liquid feed pipe, the outlet of the washing reaction tank is connected to the inlet of the second solid-liquid separator, and the solid phase outlet of the second solid-liquid separator is connected to the inlet of the slurry silo.

8. The selective leaching system for dicyandiamide residue as described in claim 7, characterized in that, The outlet of the finished product collection device is connected to the inlet of the heat conditioning rotary kiln.

9. The selective leaching system for dicyandiamide residue as described in claim 7, characterized in that, The liquid phase outlet of the second solid-liquid separator is connected to the inlet of the washing reaction tank through a washing liquid recycling pipe, and a filter is installed on the washing liquid recycling pipe.

10. The selective leaching system for dicyandiamide residue as described in claim 7, characterized in that, The liquid phase outlet of the first solid-liquid separator is connected to the inlet of the washing reaction tank through a leachate recycling pipe.

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