Method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace particle water-soluble fertilizer from phosphate tailings

Abstract

The invention relates to the technical field of tailing treatment, in particular to a method for producing low-magnesium phosphate concentrate and a high-magnesium medium-trace particle water-soluble fertilizer from phosphate tailings. The invention provides a method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace particle water-soluble fertilizer from phosphate tailings, which comprises the following steps: calcining the phosphate tailings to obtain calcined tailings; the calcined tailings are subjected to leaching treatment, and leaching feed liquid is obtained; the leaching material liquid is neutralized, and neutralized material liquid is obtained; filtering the neutralized feed liquid to obtain low-magnesium phosphate concentrate and calcium-magnesium filtrate; and carrying out concentration treatment and granulation treatment on the calcium-magnesium filtrate to obtain the high-magnesium medium-trace particle water-soluble fertilizer. According to the method for producing the low-magnesium phosphate concentrate and the high-magnesium medium-trace particle water-soluble fertilizer from the phosphate tailings, the phosphate tailings are subjected to calcination treatment, leaching treatment and neutralization treatment, the low-magnesium phosphate concentrate and the high-magnesium medium-trace particle water-soluble fertilizer are obtained, the method is simple in process, rapid treatment of the phosphate tailings can be achieved, and the yield of the phosphate tailings is improved. The efficient resource utilization of the phosphate tailings is successfully realized.

Description

Technical Field

[0001] The invention relates to the technical field of tailings treatment, in particular to a method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings. Background Art

[0002] Tailings refer to waste that fails to reach the required grade or cannot be further recycled after crushing, grinding, and sorting during ore mining and processing. In the phosphate industry, phosphate tailings usually refer to slag with a low P2O5 mass fraction discharged after physical beneficiation (such as flotation). These phosphate tailings not only contain a certain amount of phosphorus, but are also rich in other elements such as calcium, magnesium, iron, aluminum, silicon, etc.

[0003] At present, the treatment methods of phosphate tailings are: piling them up in tailings ponds, which takes up a lot of land resources and poses environmental pollution risks. Heavy metals and other elements in phosphate tailings may pollute soil and water sources. At the same time, the safety risks of phosphate tailings ponds cannot be ignored. Once an accident such as a dam breach occurs, it will cause great harm to the surrounding environment and residents.

[0004] Alternatively, the phosphate tailings can be directly filled into the well for backfill treatment. However, the phosphate tailings still contain certain phosphorus and other metal elements, which will cause serious waste of resources.

[0005] To this end, the present application provides a method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings. Summary of the invention

[0006] The method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings described in the present application obtains low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer by calcining, leaching and neutralizing the phosphate tailings. The method has a simple process, can realize rapid processing of phosphate tailings, and successfully realizes efficient resource utilization of phosphate tailings.

[0007] The technical solution adopted by this application to solve its technical problem is:

[0008] In a first aspect, the present application provides a method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings, comprising the following steps:

[0009] Calcining the phosphate tailings to obtain calcined tailings;

[0010] The calcined tailings are subjected to leaching treatment to obtain a leaching solution;

[0011] The leached liquid is subjected to a neutralization treatment to obtain a neutralized liquid;

[0012] The neutralized liquid is filtered to obtain low-magnesium phosphate concentrate and calcium-magnesium filtrate;

[0013] The calcium and magnesium filtrate is concentrated and granulated to obtain a high-magnesium medium-trace granular water-soluble fertilizer.

[0014] In one or more technical solutions, the calcination treatment is calcination at 700-950° C. for 1-2 hours.

[0015] In one or more technical solutions, the leaching treatment is to use acid solution to leach the calcined tailings at 15-60°C, and the pH of the leaching solution is maintained at 1.0-1.5 during the leaching treatment.

[0016] In one or more technical solutions, the acid solution is a nitric acid solution.

[0017] In one or more technical solutions, a neutralization treatment is performed after the leaching treatment is completed, wherein calcium hydroxide is added to the leaching solution to obtain a neutralized solution; during the neutralization treatment, the pH of the neutralized solution is 6.0-7.0.

[0018] In one or more technical solutions, the mass content of P2O5 in the phosphate tailings is ≤12%, and the mass content of MgO is ≥10%.

[0019] In one or more technical solutions, the low-magnesium phosphate concentrate has a P2O5 mass content of ≥18% and a MgO mass content of <2%.

[0020] In one or more technical solutions, the mass content of MgO in the high-magnesium trace granular water-soluble fertilizer is greater than 4%.

[0021] In one or more technical solutions, the calcium magnesium filtrate is concentrated to obtain a granulation slurry, and the specific gravity of the granulation slurry is ≥1.75g / cm 3 , the mass content of Mg in the granulation slurry is ≥4.0%.

[0022] In one or more technical solutions, the calcined tailings are subjected to ball milling to obtain tailings slurry, and then the tailings slurry is subjected to leaching treatment; the solid content in the tailings slurry is ≤50%.

[0023] In a second aspect, the present application provides a high-magnesium medium-trace granular water-soluble fertilizer, including a high-magnesium medium-trace granular water-soluble fertilizer prepared by the method described in the first aspect.

[0024] The beneficial effects of this application are:

[0025] The method described in the present application can obtain a low-magnesium phosphate concentrate with zero organic matter and a magnesium content reduced to below 0.8%. The phosphorus loss rate is low during the preparation of the phosphate tailings into the low-magnesium phosphate concentrate, and a high-magnesium medium-trace granular water-soluble fertilizer can also be prepared. The method described in the present application can successfully achieve efficient resource utilization of phosphate tailings by reusing the phosphate tailings, turning waste into treasure without generating new waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0027] Figure 1 The present invention is a process flow chart of the method for producing low-magnesium phosphate concentrate and high-magnesium trace granular water-soluble fertilizer from phosphate tailings described in this application. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0029] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0030] In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0031] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0032] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0033] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0034] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0035] The present application provides a method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings, comprising the following steps:

[0036] Calcining the phosphate tailings to obtain calcined tailings;

[0037] The calcined tailings are subjected to leaching treatment to obtain a leaching solution;

[0038] The leached liquid is subjected to a neutralization treatment to obtain a neutralized liquid;

[0039] The neutralized liquid is filtered to obtain low-magnesium phosphate concentrate and calcium-magnesium filtrate;

[0040] The calcium and magnesium filtrate is concentrated and granulated to obtain a high-magnesium medium-trace granular water-soluble fertilizer.

[0041] Specifically, the method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings comprises the following steps:

[0042] S1. Calcination treatment

[0043] The phosphate tailings are calcined at 700-950° C. for 1-2 hours to obtain calcined tailings;

[0044] S2. Make slurry

[0045] The calcined tailings are ball-milled to prepare tailings slurry with a solid content of ≤50%;

[0046] Among them: the ball milling pulping is wet ball milling, and the particle fineness of the tailings slurry is ≤0.25mm.

[0047] S3. Leaching treatment

[0048] Adding acid solution to tailings slurry at 15-60°C to obtain leaching solution, maintaining the pH of the leaching solution at 1.0-1.5 for 1-2 hours;

[0049] S4. Neutralization

[0050] After the leaching treatment is completed, calcium hydroxide is added to the leaching solution at 15-60°C to obtain a neutralized solution, and the pH of the neutralized solution is maintained at 6.0-7.0 for 1-2 hours;

[0051] S5. Filtering

[0052] After the neutralization treatment is completed, the neutralized liquid is filtered to obtain low-magnesium phosphate concentrate and calcium-magnesium filtrate.

[0053] S6. Preparation of water-soluble fertilizer

[0054] The calcium and magnesium filtrate is concentrated and granulated to obtain a high-magnesium medium-trace granular water-soluble fertilizer.

[0055] Current research on the treatment of phosphate tailings has found that if the phosphate tailings are directly leached with acid, a large number of bubbles will be generated when the phosphate tailings react with the acid, such as nitric acid, causing the leaching equipment to easily "bubble" and overflow the liquid, posing safety and environmental risks.

[0056] After careful analysis, the inventor found that the reasons for the bubbling are as follows:

[0057] 1. Reaction of carbonate and nitric acid:

[0058] Phosphate tailings contain carbonates such as calcium carbonate and magnesium carbonate. When these carbonates react with nitric acid, carbon dioxide gas (CO2) is generated. The specific chemical reaction equation is:

[0059] CaCO3+2HNO3=Ca(NO3)2+H2O+2CO2↑

[0060] MgCO3+2HNO3=Mg(NO3)2+H2O+2CO2↑

[0061] These reactions are exothermic and the CO2 gas produced will be released rapidly, forming bubbles.

[0062] 2. Oxidation reaction of organic matter

[0063] Phosphate tailings also contain a certain amount of organic matter. Nitric acid has strong oxidizing properties and can react with organic matter to produce carbon dioxide and water, while releasing heat. A certain amount of CO2 gas is also produced in this process.

[0064] In order to eliminate the bubbling phenomenon, the method described in the present application is to calcine the phosphate tailings at a temperature of 700-950°C. At this temperature, the organic matter in the phosphate tailings is basically oxidized, while carbonates such as calcium carbonate and magnesium carbonate are partially or mostly decomposed into corresponding oxides. Then, during the leaching process, when reacting with the acid solution, the generation of bubbles is greatly reduced, and the bubbling phenomenon will not occur.

[0065] In order to better contact the calcined phosphate tailings with acid solution and dissolve beneficial elements such as calcium and magnesium ions in the phosphate tailings, the present application ball-mills the calcined phosphate tailings to obtain tailings slurry with a solid content of ≤50%.

[0066] Specifically, in the leaching treatment, a nitric acid solution with a mass content of 17-20% is added to the tailings slurry with a solid content of ≤50% to obtain a leaching solution. During the leaching treatment: the temperature is maintained at 10-60°C, the pH of the leaching solution is controlled to be 1.0-1.5, and the pH is maintained for 1-2h.

[0067] During the leaching process, most of the magnesium and calcium in the phosphate tailings are dissolved, thereby reducing the magnesium and calcium content in the phosphate tailings and dissolving the elements in the phosphate tailings that are beneficial to the soil; however, under the condition of pH = 1.0-1.5, part of the phosphorus element in the phosphate tailings is dissolved, resulting in a decrease in the phosphorus content in the phosphate tailings. In order to increase the phosphorus content in the phosphate tailings and improve the grade (P content) of the phosphate tailings and reduce the loss of phosphorus, calcium hydroxide is added for neutralization after the leaching process is completed. Under the condition of pH = 6.0-7.0 of the neutralization liquid, the phosphoric acid in the leaching liquid reacts to form calcium hydrogen phosphate, which adheres to the phosphate tailings and is then filtered to obtain a low-magnesium phosphate concentrate and a neutralization filtrate containing a higher content of magnesium ions.

[0068] Specifically, in the present application, the phosphate tailings are phosphate tailings produced in a physical beneficiation process or phosphate tailings in other beneficiation processes; in the physical beneficiation process, the phosphate tailings discharged after a primary reverse flotation have a P2O5 mass fraction ≤12% and a MgO mass fraction ≥10%, while the phosphate tailings discharged after a secondary reverse flotation have a P2O5 mass fraction ≤10% and a MgO mass fraction ≥15%. Both types of phosphate tailings can be calcined at 700-950°C for 1-2h to obtain the calcined tailings described in the present application.

[0069] Specifically, in the present application, the prepared low-magnesium phosphate concentrate has a P2O5 mass content ≥18% and a MgO mass content <2%, and the low-magnesium phosphate concentrate can be used as a raw material for corresponding phosphorus chemical processing.

[0070] Specifically, in the present application, the prepared high-magnesium trace granular water-soluble fertilizer has a Mg mass content of >4%, and can be used as a water-soluble fertilizer for crops.

[0071] The following is an explanation with reference to specific preparation examples, embodiments and comparative examples.

[0072] The raw materials used in the following implementation cases can be purchased from the market, or they can be obtained by self-preparation.

[0073] The following preparation examples, embodiments and comparative examples were carried out using the phosphate tailings (diameter ≤ 0.5 mm) in Table 1 below;

[0074] Table 1

[0075] Chemical composition <![CDATA[N 总 %]]> <![CDATA[P2O5%]]> CaO% MgO% <![CDATA[Fe2O3%]]> <![CDATA[Al2O3%]]> <![CDATA[SiO2%]]> Loss on ignition% F％ content 0.21 10.71 34.6 12.61 1.15 0.69 7.78 23.96 1.69

[0076] Example 1

[0077] The method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings comprises the following steps:

[0078] S1. Calcination treatment

[0079] 300 g of phosphate tailings were calcined at 700° C. for 2 h to obtain calcined tailings;

[0080] S2. Make slurry

[0081] 210 g of calcined tailings were taken and ball-milled to prepare tailings slurry with a solid content of 50%;

[0082] S3. Leaching treatment

[0083] A nitric acid solution with a mass content of 17% is added to the tailings slurry at 15°C to obtain a leaching solution, and the pH of the leaching solution is maintained at 1.0-1.5 for 1 hour.

[0084] S4. Neutralization

[0085] After the leaching treatment is completed, calcium hydroxide is added to the leaching solution at 15°C to obtain a neutralized solution, and the pH of the neutralized solution is maintained at 6.0-7.5 for 2 hours.

[0086] S5. Filtering

[0087] After the neutralization treatment is completed, the neutralized liquid is filtered to obtain a coarse ore, and the coarse ore is pulped or rinsed, and then dried to obtain a low-magnesium phosphate concentrate;

[0088] collecting the filtrate, the pulping filtrate or the rinsing liquid to obtain a calcium-magnesium filtrate;

[0089] S6. Concentration and granulation

[0090] The calcium magnesium filtrate is concentrated at 151-155°C to obtain a granulation slurry, and the specific gravity of the granulation slurry is controlled at 1.78-1.82 g / cm 3 The granulation slurry is granulated under the following granulation conditions to obtain a high-magnesium medium-trace granular water-soluble fertilizer;

[0091] Granulation conditions: temperature controlled at 100-105°C, 20% return material, return material temperature of 45°C, spraying pressure controlled at 0.2-0.6MPa, and device air pressure controlled at 0.3-0.8MPa.

[0092] Example 2

[0093] The method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings comprises the following steps:

[0094] S1. Calcination treatment

[0095] 300 g of phosphate tailings were calcined at 950° C. for 1 h to obtain calcined tailings;

[0096] S2. Make slurry

[0097] 210 g of calcined tailings were taken and ball-milled to prepare tailings slurry with a solid content of 48%;

[0098] S3. Leaching treatment

[0099] A nitric acid solution with a mass content of 20% is added to the tailings slurry at 60° C. to obtain a leaching solution, and the pH of the leaching solution is maintained at 1.0-1.5 for 2 hours.

[0100] S4. Neutralization

[0101] After the leaching treatment is completed, calcium hydroxide is added to the leaching solution at 60° C. to obtain a neutralized solution, and the pH of the neutralized solution is maintained at 6.5-7.0 for 1 hour.

[0102] S5. Filtering

[0103] After the neutralization treatment is completed, the neutralized liquid is filtered to obtain a coarse ore, and the coarse ore is pulped or rinsed, and then dried to obtain a low-magnesium phosphate concentrate;

[0104] collecting the filtrate, the pulping filtrate or the rinsing liquid to obtain a calcium-magnesium filtrate;

[0105] S6. Concentration and granulation

[0106] The calcium magnesium filtrate is concentrated at 160-165°C to obtain a granulation slurry, and the specific gravity of the granulation slurry is controlled at 1.78-1.82 g / cm 3 The granulation slurry is granulated under the following granulation conditions to obtain a high-magnesium medium-trace granular water-soluble fertilizer;

[0107] Granulation conditions: temperature controlled at 110-115°C, 20% return material, return material temperature of 49°C, spraying pressure controlled at 0.2-0.6MPa, and device air pressure controlled at 0.3-0.8MPa.

[0108] Example 3

[0109] The method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings comprises the following steps:

[0110] S1. Calcination treatment

[0111] 300 g of phosphate tailings were calcined at 800° C. for 1.5 h to obtain calcined tailings;

[0112] S2. Make slurry

[0113] 210 g of calcined tailings were taken and ball-milled to prepare tailings slurry with a solid content of 47%;

[0114] S3. Leaching treatment

[0115] A nitric acid solution with a mass content of 18% is added to the tailings slurry at 45° C. to obtain a leaching solution, and the pH of the leaching solution is maintained at 1.0-1.5 for 1.5 hours.

[0116] S4. Neutralization

[0117] After the leaching treatment is completed, calcium hydroxide is added to the leaching solution at 45°C to obtain a neutralized solution, and the pH of the neutralized solution is maintained at 6.5-7.0 for 1.5 hours.

[0118] S5. Filtering

[0119] After the neutralization treatment is completed, the neutralized liquid is filtered to obtain a coarse ore, and the coarse ore is pulped or rinsed, and then dried to obtain a low-magnesium phosphate concentrate;

[0120] collecting the filtrate, the pulping filtrate or the rinsing liquid to obtain a calcium-magnesium filtrate;

[0121] S6. Concentration and granulation

[0122] The calcium magnesium filtrate is concentrated at 155-160°C to obtain a granulation slurry, and the specific gravity of the granulation slurry is controlled at 1.78-1.82 g / cm 3 The granulation slurry is granulated under the following granulation conditions to obtain a high-magnesium medium-trace granular water-soluble fertilizer;

[0123] Granulation conditions: temperature controlled at 105-110°C, 20% return material, return material temperature of 47°C, spraying pressure controlled at 0.2-0.6MPa, and device air pressure controlled at 0.3-0.8MPa.

[0124] Comparative Example 1

[0125] The method for treating phosphate tailings comprises the following steps:

[0126] S1. Make slurry

[0127] 300 g of phosphate tailings were ball-milled to prepare tailings slurry with a solid content of 50%;

[0128] The remaining conditions are the same as those in Example 1.

[0129] Comparative Example 2

[0130] The method for treating phosphate tailings comprises the following steps:

[0131] In step S3, a nitric acid solution with a mass content of 45% is added, and the amount of the nitric acid solution added is consistent with that in Example 1, and at this time, the pH of the leaching solution is less than 1.0;

[0132] The remaining conditions are the same as those in Example 1.

[0133] Comparative Example 3

[0134] The method for treating phosphate tailings comprises the following steps:

[0135] S1. Calcination treatment

[0136] 300 g of phosphate tailings were calcined at 700° C. for 2 h to obtain calcined tailings;

[0137] S2. Make slurry

[0138] 210 g of calcined tailings were taken and ball-milled to prepare tailings slurry with a solid content of 50%;

[0139] S3. Leaching treatment

[0140] A nitric acid solution with a mass content of 17% is added to the tailings slurry at 15°C to obtain a leaching solution, and the pH of the leaching solution is maintained at 1.0-1.5 for 1 hour.

[0141] S4. Filtering

[0142] After the leaching treatment is completed, the leached liquid is filtered to obtain a coarse ore, and the coarse ore is pulped or rinsed, and then dried to obtain a low-magnesium phosphate concentrate;

[0143] collecting the filtrate, the pulping filtrate or the rinsing liquid to obtain a calcium-magnesium filtrate;

[0144] S5. Concentration and granulation

[0145] The calcium magnesium filtrate is concentrated at 151-155°C to obtain a granulation slurry, and the specific gravity of the granulation slurry is controlled at 1.78-1.82 g / cm 3 The granulation slurry is granulated under the following granulation conditions to obtain a high-magnesium medium-trace granular water-soluble fertilizer;

[0146] Granulation conditions: temperature controlled at 100-105°C, 20% return material, return material temperature of 45°C, spraying pressure controlled at 0.2-0.6MPa, and device air pressure controlled at 0.3-0.8MPa.

[0147] Comparative Example 4

[0148] The method for treating phosphate tailings comprises the following steps:

[0149] In step S5, the specific gravity of the granulation slurry is controlled at 1.95-2.0 g / cm 3 , the other conditions are the same as those in Example 1.

[0150] Comparative Example 5

[0151] The method for treating phosphate tailings comprises the following steps:

[0152] In step S5, the specific gravity of the granulation slurry is controlled at 1.45-1.50 g / cm 3 , the other conditions are the same as those in Example 1.

[0153] The phosphate concentrates, granulation slurries, and granular water-soluble fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are summarized in Table 1 below;

[0154] Among them, the chemical element content is detected by ICP-OES (inductively coupled plasma emission spectrometer); the H2O content is accurately measured by Karl Fischer water determination;

[0155] The stability of granular water-soluble fertilizer was determined by placing the sample at a temperature of 30°C and a humidity of 45% for 20 days to observe whether there was any agglomeration. The particle strength of granular water-soluble fertilizer was determined by selecting 100 undamaged particles and measuring them using a particle strength tester. The average value was taken to obtain the particle strength.

[0156] Table 1

[0157]

[0158] From Table 1, we can see that:

[0159] In Example 1, the weight of the phosphate concentrate is 118 g, the total N content is 0.12%, the P2O5 content is 24.9%, the CaO content is 29.47%, and the MgO content is 0.65%;

[0160] Example 2 Phosphate concentrate weight 119g, total N content 0.07%, P2O5 content 25.1%, CaO content 29.34%, MgO content 0.59%;

[0161] The weight of the phosphate concentrate of Example 3 is 117g, the total N content is 0.08%, the P2O5 content is 25.5%, the CaO content is 30.15%, and the MgO content is 0.76%. It can be seen that Examples 1-3 all successfully prepared low-magnesium phosphate concentrates, in which the P2O5 content was greatly increased to more than 24%, and the MgO content was reduced to less than 0.8%, meeting the standards of low-magnesium phosphate concentrates (P2O5 mass content ≥18%, MgO mass content <2%).

[0162] Granulation slurry: Example 1 Granulation slurry N total content 9.62%, P2O5 content 1.64%, CaO content 13.45%, Mg content 5.17%, specific gravity content 1.78g / cm 3 The corresponding data of Example 2 are: total N content 9.55%, P2O5 content 1.58%, CaO content 13.27%, Mg content 4.65%, specific gravity 1.82g / cm 3 Example 3 has a total N content of 9.01%, a P2O5 content of 1.47%, a CaO content of 12.94%, a Mg content of 4.12%, and a specific gravity of 1.79 g / cm 3 This indicates that the granulation slurry contains a certain amount of nutrients, and the specific gravity meets the requirements for preparing high-magnesium trace granular water-soluble fertilizer (specific gravity ≥ 1.75 g / cm 3 , magnesium mass content ≥4.0%).

[0163] Granular water-soluble fertilizer: Example 1 granular water-soluble fertilizer has a Mg content of 5.4%, a granule strength of 47.8N, and stability is shown by no moisture absorption and no agglomeration; Example 2 has a Mg content of 4.9%, a granule strength of 47.1N, and also no moisture absorption and no agglomeration; Example 3 has a Mg content of 4.2%, a granule strength of 48.3N, and also has good stability. It shows that the prepared high-magnesium medium-trace granular water-soluble fertilizer has a suitable magnesium content and good physical properties.

[0164] Comparative Example 1: The subsequent steps were carried out directly without calcination. Compared with Example 1, the MgO content in the phosphate concentrate increased significantly and the P2O5 content decreased. This is because the calcium carbonate, magnesium carbonate and organic matter in the phosphate tailings reacted with nitric acid during the acid leaching process without calcination to produce a large amount of CO2 gas, which increased the risk of "bubbling" and affected the dissolution and conversion of elements such as phosphorus and magnesium, resulting in a decrease in the quality of the phosphate concentrate, and the stability of the granular water-soluble fertilizer also deteriorated, with a slight moisture absorption phenomenon.

[0165] Comparative Example 2: A nitric acid solution with a mass content of 45% and a pH value of less than 1.0 was used during leaching. Compared with Example 1, the P2O5 content in the phosphate concentrate was greatly reduced. This is because the excessively low pH value caused excessive dissolution and loss of phosphorus, which destroyed the overall component balance of the phosphate concentrate. However, the other properties of the granulated slurry and granular water-soluble fertilizer were relatively less affected, and they still remained non-hygroscopic and non-caking.

[0166] Comparative Example 3: Lack of neutralization treatment step. Compared with Example 1, the MgO content in the phosphate concentrate is reduced but not as significant as in Example 1, and the granular water-soluble fertilizer absorbs moisture and agglomerates. Because the neutralization treatment can make the phosphoric acid in the leaching liquid react to generate calcium hydrogen phosphate, which adheres to the phosphate tailings to increase the phosphorus content and improve the product stability, the lack of this step cannot effectively achieve these effects, resulting in poor product performance.

[0167] Comparative Example 4: The specific gravity of the granulation slurry is controlled at 1.95-2.0 g / cm 3 , compared with Example 1 (1.78 g / cm 3 ), the Mg content in the granulation slurry increased, the particle strength of the granular water-soluble fertilizer decreased significantly, and the stability became worse. This shows that the higher specific gravity changes the nutrient distribution and particle forming process, affects the magnesium content and particle strength, and has a significant negative impact on stability.

[0168] Comparative Example 5: The specific gravity of the granulation slurry is controlled at 1.45-1.50 g / cm 3 Compared with Example 1, the Mg content in the granulation slurry is reduced, the particle strength of the granular water-soluble fertilizer is reduced, and the stability is deteriorated and a slight moisture absorption phenomenon occurs. This shows that too low a specific gravity may lead to the loss of nutrients and poor particle formation, thereby affecting product performance.

[0169] Therefore, in the present application, the phosphate tailings are calcined at 700-950°C for 1-2h, and the organic matter therein is basically oxidized, reducing the possibility of carbon dioxide bubbles generated by the reaction of organic matter with acid during the subsequent leaching process, avoiding the "bubbling" phenomenon, and at the same time partially or mostly decomposing carbonates such as calcium carbonate and magnesium carbonate into corresponding oxides. This makes it easier to dissolve elements such as magnesium and calcium during leaching, and reduces the MgO content in the phosphate concentrate. For example, in Comparative Example 1, which is directly treated without calcination, the MgO content in the phosphate concentrate is as high as 2.5%, while in Examples 1-3, it is all below 0.8%, which fully reflects the key role of calcination in reducing the magnesium content.

[0170] The leaching treatment is carried out at 15-60°C, and the tailings slurry (solid content ≤ 50%) is leached with a 17-20% nitric acid solution, and the pH of the leaching solution is maintained at 1.0-1.5, so that most of the magnesium and calcium in the phosphate tailings are dissolved, but this process will cause some phosphorus elements to dissolve and reduce the phosphorus content. The subsequent neutralization treatment adds calcium hydroxide at 15-60°C to make the neutralization solution pH = 6.0-7.0. At this time, the phosphoric acid in the leaching solution reacts to form calcium hydrogen phosphate and adheres to the phosphate tailings, thereby increasing the P2O5 content in the phosphate concentrate. The pH of the leaching solution of Comparative Example 2 is less than 1.0, resulting in a P2O5 content of only 16.5% in the phosphate concentrate, which is much lower than that of the embodiment, indicating that appropriate leaching and neutralization conditions are crucial to the regulation of the composition of the phosphate concentrate.

[0171] Effect of granulation treatment: The calcium and magnesium filtrate is concentrated to obtain granulation slurry, and the specific gravity of the granulation slurry is controlled to be ≥1.75g / cm 3 The water-soluble fertilizer is made into granules under specific granulation conditions (such as temperature, return material, pressure, etc.), which ensures the nutritional content and physical properties of the water-soluble fertilizer. 3 ), Comparative Example 5 has a low specific gravity (1.45-1.50 g / cm 3 ), the performance of its granular water-soluble fertilizer is not as good as that of the embodiment, highlighting the importance of suitable granulation process parameters.

[0172] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing low-magnesium phosphate concentrate and high-magnesium medium-trace granular water-soluble fertilizer from phosphate tailings, characterized in that: The following steps are involved: Calcining the phosphate tailings to obtain calcined tailings; The calcined tailings are subjected to leaching treatment to obtain a leaching solution; The leached liquid is subjected to a neutralization treatment to obtain a neutralized liquid; The neutralized liquid is filtered to obtain low-magnesium phosphate concentrate and calcium-magnesium filtrate; The calcium and magnesium filtrate is concentrated and granulated to obtain a high-magnesium medium-trace granular water-soluble fertilizer.

2. The method according to claim 1, characterized in that The calcination treatment is performed at 700-950° C. for 1-2 hours.

3. The method according to claim 1, characterized in that The leaching treatment is to use acid solution to leach the calcined tailings at 15-60° C., and the pH of the leaching solution is maintained at 1.0-1.5 during the leaching treatment.

4. The method according to claim 3, characterized in that The acid solution is a nitric acid solution.

5. The method according to claim 1, characterized in that After the leaching treatment is completed, a neutralization treatment is performed, wherein calcium hydroxide is added to the leaching solution to obtain a neutralized solution; during the neutralization treatment, the pH of the neutralized solution is 6.0-7.

0.

6. The method according to claim 1, characterized in that The mass content of P2O5 in the phosphate tailings is ≤12%, and the mass content of MgO is ≥10%.

7. The method according to claim 1, characterized in that The mass content of P2O5 in the low-magnesium phosphate concentrate is ≥18%, and the mass content of MgO is <2%.

8. The method according to claim 1, characterized in that The calcium magnesium filtrate is concentrated to obtain a granulation slurry, wherein the specific gravity of the granulation slurry is ≥1.75g / cm 3 , the mass content of Mg in the granulation slurry is ≥4.0%.

9. The method according to claim 1, characterized in that: The calcined tailings are subjected to ball milling to obtain tailings slurry, and then the tailings slurry is subjected to leaching treatment; the solid content in the tailings slurry is ≤50%.

10. High-magnesium trace granular water-soluble fertilizer, characterized in that: The invention comprises a high-magnesium medium-trace granular water-soluble fertilizer prepared by the method according to any one of claims 1 to 9.

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