Method for selective leaching of dicyandiamide residues
By using organic ligands and pretreatment methods in the acid leaching reaction of dicyandiamide residue, the purity and cost problems caused by iron impurity leaching were solved, achieving efficient and selective leaching of calcium ions and reducing iron leaching rate and operating costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGXIA JIAFENG CHEMICALS CO LTD
- Filing Date
- 2026-05-20
- Publication Date
- 2026-06-19
AI Technical Summary
The acid leaching process of dicyandiamide residue in the existing technology leads to the leaching of a large amount of iron impurities, which reduces the purity and whiteness of calcium salt products, increases operating costs, and generates secondary hazardous solid waste.
Organic ligands such as citrates, acetates, or lactates are used to adjust the complexation equilibrium of the solution during the acid leaching reaction, selectively dissolving calcium ions and reducing iron ion dissolution. This is combined with mechanical grinding and pretreatment such as heat conditioning and chemical washing to improve the calcium phase leaching effect.
Achieving a calcium leaching rate of ≥90% and an iron leaching rate of ≤10% reduces the need for subsequent iron removal treatment, and decreases alkali consumption and operating costs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of resource utilization technology of by-products in nitrogen, carbon, and nitrogen (NCN) chemical industry, and specifically relates to a selective leaching method for dicyandiamide residue. Background Technology
[0002] Dicyandiamide (DCDA) is a fundamental chemical in the nitrogen, carbon, and nitrogen chemical industries, widely used in pharmaceuticals, coatings, fine chemicals, and new materials. In the dicyandiamide production route using calcium cyanamide (calcium aminocyanide) as a raw material, a large amount of industrial by-product solid residue, namely dicyandiamide residue, is inevitably generated. The main components of this residue are calcium compounds (such as calcium carbonate, calcium hydroxide, and calcium oxide), along with impurity minerals such as iron, aluminum, silicon, and unreacted carbon.
[0003] Existing technologies mostly employ simple, non-selective acid leaching processes to recover calcium salts. However, as the pH value decreases, iron impurities (Fe) 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, necessitating a lengthy neutralization and precipitation process to remove iron. This not only consumes large amounts of alkali and increases operating costs but also generates secondary hazardous waste. Summary of the Invention
[0004] Based on this, this application provides a selective leaching method for dicyandiamide residue to solve the technical problems of excessive leaching of iron impurities, increased operating costs, and generation of secondary hazardous solid waste in the prior art.
[0005] The technical solution to the above-mentioned technical problems in this application is as follows:
[0006] A selective leaching method for dicyandiamide residue includes adding an organic complexing agent to a dicyandiamide residue slurry for an acid leaching reaction, wherein the organic complexing agent includes at least one of citrate, acetate, or lactate; the amount of the organic complexing agent added is 0.1% to 2.0% of the dry basis mass of the dicyandiamide residue slurry.
[0007] Preferably, in the above-mentioned selective leaching method for dicyandiamide residue, the amount of organic ligand added is 0.3% to 0.5% of the dry basis mass of the dicyandiamide residue slurry.
[0008] Preferably, in the selective leaching method for dicyandiamide residue described above, the organic ligand includes at least one of citrate, acetate, or lactate.
[0009] Preferably, in the above-mentioned selective leaching method for dicyandiamide residue, the acid leaching reaction specifically comprises:
[0010] Add an acidic leaching agent and an organic complexing agent to the slurry, maintain the pH of the system between 1.5 and 4.0, and react at 20 to 80°C for 15 to 120 minutes.
[0011] Preferably, in the above-mentioned selective leaching method for dicyandiamide residue, the reaction temperature is 50-70°C and the reaction time is 45-70 minutes.
[0012] Preferably, in the above-mentioned selective leaching method for dicyandiamide residue, the acidic leaching agent includes any one of hydrochloric acid, nitric acid, or sulfuric acid.
[0013] Preferably, in the above selective leaching method for dicyandiamide residue, the dicyandiamide residue slurry is prepared by mixing dicyandiamide residue and water at a mass ratio of 1:3 to 1:10 to form a slurry.
[0014] Preferably, in the above-mentioned selective leaching method for dicyandiamide residue, before the acid leaching reaction, the dicyandiamide residue is further subjected to mechanical grinding, wherein the particle size D of the ground dicyandiamide residue is... 90 ≤75µm.
[0015] Preferably, the selective leaching method for dicyandiamide residue described above further includes pretreatment of the dicyandiamide residue before the acid leaching reaction, the pretreatment including:
[0016] Heat conditioning: Heat the dicyandiamide residue to 200–400°C and calcine for 0.5–2.0 hours, then cool.
[0017] Wash the heat-conditioned dicyandiamide residue with the calcium-containing leachate produced by the acid leaching reaction for 5-15 minutes, then drain.
[0018] Compared with the prior art, this application has at least the following advantages:
[0019] This invention discloses a selective leaching method and system for dicyandiamide residue. The method includes adding an organic complexing agent to the dicyandiamide residue slurry for an acid leaching reaction. The organic complexing agent includes at least one of citrate, acetate, or lactate; the organic complexing agent accounts for 0.1% to 2.0% of the dry weight of the dicyandiamide residue slurry. The addition of the organic complexing agent can adjust the solution complexation equilibrium, preferentially dissolving calcium ions and reducing the dissolution of iron ions. Using this method, a calcium leaching rate ≥90% and an iron dissolution rate ≤10% can be achieved, resulting in a low iron ion content in the leachate, thus reducing the need for subsequent iron removal steps. Detailed Implementation
[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. The technical solutions of this invention will be further described below in conjunction with the embodiments of this invention, and this invention is not limited to the specific implementation methods described below.
[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] In one specific embodiment of this application, a selective leaching method for dicyandiamide residue includes a process of adding an organic complexing agent to the dicyandiamide residue slurry for an acid leaching reaction, wherein the organic complexing agent includes at least one of citrate, acetate, or lactate; the amount of the organic complexing agent added is 0.1% to 2.0% of the dry basis mass of the dicyandiamide residue slurry.
[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. This application incorporates an organic ligand (also known as a complexing agent) during the acid leaching process. This organic ligand 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. Introducing a carboxyl-containing organic ligand improves the selective leaching of calcium ions and reduces the leaching of iron impurities. The product of the acid leaching reaction is a mixture of calcium-containing leachate and iron-rich tailings. After the reaction, the product is separated into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings. The leaching rates of calcium and iron can be calculated by detecting the calcium and iron content in the leachate. Experiments show that when any one of the organic ligands, citrate, acetate, or lactate, is added during the acid leaching process, the calcium leaching rate is increased and the iron leaching rate is significantly reduced compared to the blank sample without the addition of an organic ligand. Sodium citrate shows the best effect. Preferably, the amount of the organic ligand added is 0.3% to 0.5% of the dry basis mass of the dicyandiamide slurry (i.e., the dry mass of dicyandiamide slurry).
[0024] Since the acid leaching reaction uses dicyandiamide residue slurry as the reactant, it is necessary to prepare the slurry before the acid leaching reaction. The dicyandiamide residue slurry is prepared by mixing dicyandiamide residue and water at a mass ratio of 1:3 to 1:10 to form a slurry.
[0025] In a preferred embodiment, the "acid leaching reaction" specifically refers to:
[0026] An acidic leaching agent and an organic ligand are added to the slurry, maintaining the pH of the system between 1.5 and 4.0, and the reaction is carried out at 20–80°C for 15–120 minutes. A pH of 1.5–4.0 allows CaCO3 and Ca3(PO4)2 to dissolve rapidly, while the iron-containing silicate phase remains passivated. Further, the acidic leaching agent includes any one of hydrochloric acid, nitric acid, or sulfuric acid. Further, the reaction temperature is 50–70°C, and the reaction time is 45–70 minutes.
[0027] In a preferred embodiment, prior to the acid leaching reaction, the dicyandiamide residue is further subjected to mechanical grinding, wherein the particle size D of the ground dicyandiamide residue is... 90 ≤75µm.
[0028] Mechanical grinding is carried out in a ball mill. When the particle size is too coarse, the calcium-containing phase is insufficiently exposed, and calcium leaching is severely limited. Conversely, when the particle size is too fine, resulting in "over-grinding," the coating of the iron-containing ore phase is easily destroyed, which can increase the dissolution of iron impurities in the strongly acidic system, leading to higher costs for subsequent iron removal and purification. Therefore, grinding is performed until 90% of the particles pass through a 75µm sieve, preferably D. 90 The size is 50–75 μm, and further reduced to 50–60 μm.
[0029] The grinding process specifically includes: (1) Feeding: Dicyandiamide residue is fed into the grinding host at a uniform speed through a quantitative feeding device; (2) Grinding: Mechanical crushing is performed in the grinding host; (3) Grading: The ground material enters the grading equipment with the airflow for dynamic screening; (4) Recirculation: Unqualified coarse particles generated during grading are automatically returned to the grinding host for re-grinding through the coarse powder recirculation pipeline; (5) Collection and control: Qualified fine powder is discharged with the airflow, monitored in real time by an online particle size monitor, and collected by a finished product collection device. The system automatically adjusts the grading parameters according to the particle size feedback to ensure that the output material is strictly locked within a specific target particle size window.
[0030] In a preferred embodiment, prior to the acid leaching reaction, the process further includes pretreatment of the dicyandiamide residue, the pretreatment comprising:
[0031] Heat conditioning: Heat the dicyandiamide residue to 200–400°C and calcine for 0.5–2.0 hours, then cool.
[0032] Wash the heat-conditioned dicyandiamide residue with the calcium-containing leachate produced by the acid leaching reaction for 5-15 minutes, then drain.
[0033] The pretreatment combines heat conditioning with short-term chemical washing. Heat conditioning removes the water of crystallization from the iron phase, helping to reduce the activity of the iron phase minerals in the subsequent acid leaching process. The subsequent chemical washing is a weakly acidic chemical washing, preferably with the system pH controlled between 3.5 and 4.5, which helps to remove the surface deposits and some soluble iron components formed during heat treatment, thereby improving the leaching conditions of the calcium phase in the subsequent acid leaching. Because the pH of the washing system is controlled by the washing solution, it is preferred that the pH of the washing solution is between 2 and 5. It is worth noting that during the initial startup of the system (first batch), there is no calcium-containing leachate (the product of the subsequent acid leaching reaction stage) available for reuse, and pure water with acid must be used for washing. In order not to introduce new impurity ions into the reaction system, the acid used must be consistent with the acidic leaching agent used in the subsequent step S40. In the initial stage of the system's first operation or when there is no calcium-containing leachate to be reused as washing liquid, the washing liquid is a dilute acid solution in which water is adjusted to the target pH using the acidic leaching agent (hydrochloric acid, nitric acid, or sulfuric acid) corresponding to the acid leaching reaction stage, or the corresponding acidic leaching agent is dynamically added dropwise during the washing of pure water to maintain the system pH. After the system is operating normally and calcium-containing leachate is generated, the calcium-containing leachate generated in the acid leaching section is reused as washing liquid to reduce the amount of acid and water used.
[0034] The synergistic effect of heat conditioning and chemical washing helps to reduce the leaching degree of the iron phase in the subsequent acid leaching process; the synergistic pretreatment can improve the leaching effect of the calcium phase in the subsequent acid leaching of dicyandiamide residue. Reusing the calcium-containing leachate generated in the acid leaching section as a washing liquid can significantly reduce the amount of acid and water used, reduce waste, and save costs.
[0035] It is worth noting that the process temperature and process time involved in the above embodiments are all temperatures or times used in the experiment. Any reasonable adjustments made by those skilled in the art based on the process temperature and process time provided by the present invention, within the error range, should be included within the protection scope of the present invention.
[0036] The technical solution and effects of the present invention will be further illustrated below through specific embodiments.
[0037] 1. Experimental Materials and Methods
[0038] 1.1 Experimental Materials
[0039] The dicyandiamide residue was prepared by the applicant. Analysis showed that the total calcium (calculated as Ca) and total iron (calculated as Fe) of the original residue on a dry basis were 38.5 wt%.
[0040] All other reagents are commercially available products and can be used directly without further purification.
[0041] 1.2 Experimental Methods
[0042] Determine Ca²⁺ and total Fe by ICP-OES according to ISO 11885; determine pH according to GB / T 9724-2007.
[0043] 1.2.1 Formula for calculating calcium dissolution rate
[0044]
[0045] Where: η Ca Calcium dissolution rate (%)
[0046] C Ca Calcium concentration in leachate (g / L)
[0047] V: Total volume of filtrate after leaching (L)
[0048] m0: Dry weight of dicyandiamide residue (g)
[0049] w Ca,total : Mass fraction of calcium in raw material residue (%, calculated as Ca)
[0050] 1.2.2 Formula for calculating iron dissolution rate
[0051]
[0052] Where: η Fe Iron leaching rate (%)
[0053] C Fe Iron concentration in leachate (g / L)
[0054] V: Total volume of filtrate after leaching (L)
[0055] m0: Dry weight of dicyandiamide residue (g)
[0056] w Fe,total The mass fraction of iron in the raw slag (%), expressed as Fe.
[0057] 2. Blank example
[0058] Take 100g of unprocessed and untreated dicyandiamide residue, add 500g of water to make a slurry, and then slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0059] 3. Example 1 (only an organic ligand was added to the acid leaching system, without any other treatment)
[0060] Take 100g of unprocessed and untreated dicyandiamide residue, add 500g of water to make a slurry, and then slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5. At the same time, add 0.5g of organic complexing agent (see Table 1) and react for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0061] The calcium and iron content in the leachate was measured, and their dissolution rates were calculated. The results are shown in the table below:
[0062] Table 1 Experimental results of different organic ligands
[0063]
[0064] The experimental results show that, in the blank example without an organic ligand, the calcium leaching rate was less than 90%, while the iron dissolution rate was as high as 42.3%, resulting in an extremely high iron content in the leachate due to the large amount of iron impurities dissolved. In Examples 1 to 3, organic ligands were added during the acid leaching reaction stage, achieving calcium leaching rates exceeding 90% and keeping the iron dissolution rate below 10%. All three ligands achieved high calcium leaching rates and low iron dissolution rates, with sodium citrate in Example 1 showing the best results. With the addition of organic ligands during the acid leaching reaction stage, the Fe concentration in the leachate was <50 mg / L, requiring only minimal polishing treatment in the downstream process.
[0065] 3. Example 2 (only the dicyandiamide residue was ground; no other treatment was performed)
[0066] Take 100g of untreated dicyandiamide residue, grind it according to the particle size shown in Table 2, add 500g of water to make a slurry, and then slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0067] The calcium and iron content in the leachate was measured, and their dissolution rates were calculated. The results are shown in the table below:
[0068] Table 2 Experimental results for different grinding particle sizes
[0069]
[0070] As can be seen from the table above, the appropriate particle size of the dicyandiamide residue has a significant impact on the calcium leaching rate and the iron dissolution rate. Example 4: When D... 90 When the particle size is 150 μm, the dicyandiamide residue particles are too coarse. The presence of a large number of coarse particles leads to insufficient calcium exposure, preventing complete leaching, and the iron dissolution rate is also relatively high; in Experimental Example 5, when D 90 At a concentration of 100 μm, calcium release was incomplete, and the iron dissolution rate remained high; in Experiments 6 to 8, when D... 90Calcium dissolves efficiently at a particle size of 75 to 50 μm, while iron dissolution is also controlled within a low range; in Experimental Example 9, the refining process involved milling (D... 90 When the iron ore phase structure is at 40 μm, the iron ore phase structure is destroyed, causing the iron leaching rate to rebound to 10%.
[0071] 4. Example 3
[0072] 4.1 Experimental Example 10 (Only the dicyandiamide residue was heat-conditioned; no other treatment was performed)
[0073] Take 100g of unground and untreated dicyandiamide residue and feed it into a rotary kiln. Roast it at 300℃ for 1 hour and then cool it. Add 500g of water to the cooled dicyandiamide residue and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 and react for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0074] 4.2 Experimental Example 11 (Only the dicyandiamide residue was washed; no other treatment was performed)
[0075] Take 100g of unprocessed and untreated dicyandiamide residue and send it into the washing reactor. Use washing liquid (calcium-containing leachate generated during the acid leaching reaction stage is reused as washing liquid) to control the pH of the system at 4 for 10 minutes. After solid-liquid separation and draining, pretreated dicyandiamide residue and washing liquid are obtained.
[0076] Add 500g of water to the pretreated dicyandiamide residue and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 and react for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0077] 4.3 Experimental Example 12 (The dicyandiamide residue was pretreated by heat conditioning and washing only, without any other treatment)
[0078] Take 100g of untreated dicyandiamide residue and feed it into a rotary kiln. Roast it at 300℃ for 1 hour and then cool it. Feed the heat-treated dicyandiamide residue into a washing reactor. Use a washing liquid (calcium-containing leaching liquid generated in the acid leaching reaction stage is reused as washing liquid) to control the pH of the system at 4 and wash for 10 minutes. Separate the solid and liquid, drain it, and obtain the pretreated dicyandiamide residue and washing liquid.
[0079] Add 500g of water to the pretreated dicyandiamide residue and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 and react for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0080] The calcium and iron content in the leachate was measured, and their dissolution rates were calculated. The results are shown in the table below:
[0081] Table 3 Experimental results of different pretreatments
[0082]
[0083] As can be seen from the table above, compared with the blank example, although heat conditioning alone in Example 10 can reduce the iron leaching rate, it leads to a decrease in the calcium leaching rate; although chemical washing alone in Example 11 can improve the surface condition of the material, its effect on reducing the iron leaching rate is limited. In contrast, the combined heat conditioning and washing pretreatment method in Example 12 can simultaneously exhibit a higher calcium leaching rate and a lower iron leaching rate during the subsequent acid leaching process, indicating that it has a better pretreatment effect and is suitable for industrial implementation.
[0084] 5. Example 4 (only the dicyandiamide residue was pretreated by grinding, heat conditioning and washing, without any other treatment)
[0085] Take 100g of untreated dicyandiamide residue and mechanically grind it to D. 90 The sample was 50 μm thick and fed into a rotary kiln. It was calcined at 300°C for 1 hour and then cooled. The heat-treated dicyandiamide residue was then fed into a washing reactor. The pH of the system was controlled at 4 using a washing liquid (calcium-containing leaching solution generated during the acid leaching reaction stage was reused as the washing liquid). The residue was washed for 10 minutes, and the solid and liquid were separated and drained to obtain the pretreated dicyandiamide residue and the washing liquid.
[0086] Add 500g of water to the pretreated dicyandiamide residue and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5 and react for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0087] The calcium and iron content in the leachate was measured, and their dissolution rates were calculated. The results are as follows:
[0088] Calcium leaching rate: 96.5%, iron leaching rate: 5.8%, leachate: Fe content 25 mg / L.
[0089] The experimental data shows that, with the combined effect of grinding and pretreatment, the calcium leaching rate was further improved compared to grinding alone and pretreatment alone, while the iron dissolution rate was further reduced, but it was still higher than the iron dissolution rate in Experiment 1.
[0090] 6. Example 5 (Grinding dicyandiamide residue and adding an organic complexing agent to the acid leaching system)
[0091] Take 100g of untreated dicyandiamide residue and mechanically grind it to D. 90The sample was 50 μm thick, then 500 g of water was added to make a slurry. Then, 70% hydrochloric acid was slowly added dropwise at 60 °C to maintain the pH at 2.5, and 0.5 g of sodium citrate was added at the same time. The reaction was carried out for 60 minutes. The reaction product was separated into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0092] 7. Example 6 (Pretreatment of dicyandiamide residue by heat conditioning and washing, and addition of organic complexing agent to acid leaching system)
[0093] Take 100g of untreated dicyandiamide residue and feed it into a rotary kiln. Roast it at 300℃ for 1 hour and then cool it. Feed the heat-treated dicyandiamide residue into a washing reactor. Use a washing liquid (calcium-containing leaching liquid generated in the acid leaching reaction stage is reused as washing liquid) to control the pH of the system at 4 and wash for 10 minutes. Separate the solid and liquid, drain it, and obtain the pretreated dicyandiamide residue and washing liquid.
[0094] Add 500g of water to the pretreated dicyandiamide residue and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5, and add 0.5g of sodium citrate at the same time. React for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0095] 8. Example 7 (Pretreatment of dicyandiamide residue by grinding, heat conditioning and washing, and addition of organic complexing agent to acid leaching system)
[0096] Take 100g of untreated dicyandiamide residue and mechanically grind it to D. 90 The sample was 50 μm thick and fed into a rotary kiln. It was calcined at 300°C for 1 hour and then cooled. The heat-treated dicyandiamide residue was then fed into a washing reactor. The pH of the system was controlled at 4 using a washing liquid (calcium-containing leaching solution generated during the acid leaching reaction stage was reused as the washing liquid). The residue was washed for 10 minutes, and the solid and liquid were separated and drained to obtain the pretreated dicyandiamide residue and the washing liquid.
[0097] Add 500g of water to the pretreated dicyandiamide and slurry it. Then, slowly add 70% hydrochloric acid at 60℃ to maintain the pH at 2.5, and add 0.5g of sodium citrate at the same time. React for 60 minutes. Separate the reaction product into solid and liquid components to obtain calcium-containing leachate and iron-rich tailings.
[0098] The calcium and iron content in the leachate was measured, and their dissolution rates were calculated. The results are as follows:
[0099] Table 4 Experimental results of different treatment methods
[0100]
[0101] Please refer to the table above. In Example 5, the dicyandiamide slag was first ground, and an organic complexing agent was added during the acid leaching reaction. Compared with grinding alone (Experimental Example 8), the calcium leaching rate increased by 1% and the iron dissolution rate decreased by 4.5%. In Example 6, the dicyandiamide slag was first pretreated, and an organic complexing agent was added during the acid leaching reaction. Compared with pretreatment alone (Experimental Example 12), the calcium leaching rate increased by 1.2% and the iron dissolution rate decreased by 5%. In Example 7, the dicyandiamide slag was ground and then subjected to heat conditioning and washing pretreatment, and an organic complexing agent was added to the acid leaching system. Compared with Example 4, the calcium leaching rate increased by 2% and the iron dissolution rate decreased by 4%. Compared with Experimental Example 1, the calcium leaching rate increased by 4.3% and the iron dissolution rate decreased by 2.3%.
[0102] 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 method for selective leaching of dicyandiamide residue, characterized in that, The process includes adding an organic complexing agent to a dicyandiamide slurry for acid leaching, wherein the organic complexing agent includes at least one of citrate, acetate, or lactate; the amount of the organic complexing agent added is 0.1% to 2.0% of the dry basis mass of the dicyandiamide slurry.
2. The selective leaching method for dicyandiamide residue as described in claim 1, characterized in that, The amount of the organic ligand added is 0.3% to 0.5% of the dry basis mass of the dicyandiamide slurry.
3. The selective leaching method for dicyandiamide residue as described in claim 1, characterized in that, The acid leaching reaction is specifically as follows: Add an acidic leaching agent and an organic complexing agent to the slurry, maintain the pH of the system between 1.5 and 4.0, and react at 20 to 80°C for 15 to 120 minutes.
4. The selective leaching method for dicyandiamide residue as described in claim 3, characterized in that, The reaction temperature is 50–70℃, and the reaction time is 45–70 minutes.
5. The selective leaching method for dicyandiamide residue as described in claim 3, characterized in that, The acidic leaching agent includes any one of hydrochloric acid, nitric acid, or sulfuric acid.
6. The selective leaching method for dicyandiamide residue as described in claim 1, characterized in that, The dicyandiamide residue slurry is prepared by mixing dicyandiamide residue and water at a mass ratio of 1:3 to 1:10 to form a slurry.
7. The selective leaching method for dicyandiamide residue as described in claim 6, characterized in that, Before the acid leaching reaction, the dicyandiamide residue is mechanically ground, and the particle size D of the ground dicyandiamide residue is... 90 ≤75µm.
8. The selective leaching method for dicyandiamide residue as described in claim 6, characterized in that, Prior to the acid leaching reaction, the dicyandiamide residue is further subjected to pretreatment, the pretreatment including: Heat conditioning: Heat the dicyandiamide residue to 200–400°C and calcine for 0.5–2.0 hours, then cool. Wash the heat-conditioned dicyandiamide residue with the calcium-containing leachate produced by the acid leaching reaction for 5-15 minutes, then drain.