Method for preparing calcium magnesium phosphate fertilizer from phosphogypsum and phosphate tailings

Abstract

The invention discloses a method for preparing a calcium magnesium phosphate fertilizer from ardealite and phosphate tailings, which comprises the following steps: fully mixing ardealite and rice hull ash for reaction, adding sodium carbonate for mixing, adding water for dissolving, fully reacting, filtering to obtain calcium carbonate solid, preheating calcium carbonate at 300-400 DEG C, continuously heating, and reacting with silica at high temperature to generate calcium silicate; the method comprises the following steps: carrying out acidolysis reaction on phosphate tailings and hydrochloric acid, after the reaction is completed, filtering to remove insoluble substances so as to obtain an acidolysis solution, adjusting the pH value, and filtering again to obtain a phosphate solid; and drying the obtained calcium silicate and phosphate to finally prepare the powdery calcium magnesium phosphate meeting the standard. According to the invention, the industrial by-product phosphogypsum, phosphate tailings and other resources are utilized, the product prepared under the catalytic action of the novel metal nanomaterial has high uniformity and dispersity, the standard of the powdery calcium magnesium phosphate fertilizer can be reached without further grinding, and meanwhile, the harmful components such as soluble fluorine in the phosphogypsum are effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of tailings treatment and fertilizers, and in particular relates to a method for preparing calcium magnesium phosphate fertilizer by utilizing phosphogypsum and phosphate tailings. Background Art

[0002] Phosphogypsum is a byproduct of phosphorus chemical industry. Its main component is calcium sulfate dihydrate (CaSO4·2H2O). It contains a large amount of calcium resources. At the same time, harmful impurities such as soluble fluorine in phosphogypsum damage the environment. Phosphate tailings are also waste. Phosphate flotation tailings contain a large amount of calcium, magnesium and phosphorus resources, but these resources have not been fully utilized. Long-term accumulation not only wastes resources, but also causes environmental pollution. Traditional calcium magnesium phosphate fertilizer production relies on ore resources, with high costs and high resource consumption. Coal gangue and rice husk ash are also wastes, and they are difficult to handle in large quantities. They contain elements such as magnesium and aluminum, and alkali metal ions can react with soluble fluorine to form insoluble substances. The present invention uses phosphogypsum to extract calcium sources, uses phosphate tailings as calcium, magnesium and phosphorus sources, and uses coal gangue and rice husk ash to remove harmful impurities such as soluble fluorine in phosphogypsum, thereby providing an environmentally friendly and efficient method for producing calcium magnesium phosphate fertilizer.

[0003] CN101747090B discloses a method for preparing calcium magnesium phosphate fertilizer by using phosphorus flotation tailings blast furnace method, but this method requires high-temperature melting at more than 1350°C, with high process cost and great operation difficulty; CN110642646A discloses a method for preparing calcium magnesium phosphate fertilizer by mixing phosphorus-containing waste liquid and waste residue as phosphorus-containing raw materials with calcium and magnesium-containing alkaline materials, but this method may require complex equipment during high-temperature reaction and cooling, and the operation process is relatively cumbersome and the cost is high. Summary of the invention

[0004] In order to solve the above problems, the present invention aims to provide a method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings, which makes full use of phosphogypsum, a byproduct of phosphorus chemical industry, as a calcium source, and realizes the secondary utilization of waste through the calcium, phosphorus and magnesium resources in the tailings, and effectively converts phosphogypsum and phosphate tailings into high value-added calcium magnesium phosphate fertilizer. At the same time, a mixture of coal gangue and rice husk ash is used to remove some soluble fluorine and other harmful impurities. Through this innovation, the environmental protection problems of phosphogypsum accumulation and tailings disposal are solved, and waste resources are realized. Through the key reaction steps of phosphogypsum dissolution, new catalyst catalysis, high temperature reaction, acid hydrolysis and neutralization of phosphate tailings, the composite reaction of phosphogypsum and phosphate tailings is realized, the cost is reduced, and the environmental protection and operability of the process are improved.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings, the method comprising the following steps:

[0007] S1 Raw material preparation

[0008] First, the mass fraction of the raw materials: 5-10% of rice husk ash-coal gangue mixture, 60-70% of phosphogypsum, 20-30% of phosphate tailings, and 2-7% of metal oxide composite nanomaterials;

[0009] S2. reacting phosphogypsum (main component CaSO4·2H2O) with a mixture of rice husk ash and coal gangue in an aqueous solution reactor, then adding sodium carbonate (Na2CO3) to the mixture, heating and continuously stirring the mixture to allow the reactants to be fully mixed and react chemically, and filtering to obtain solid calcium carbonate;

[0010] In S2, the mass ratio of the mixture of rice husk ash and coal gangue: phosphogypsum: sodium carbonate is 0.1:1:(1-1.2), and the liquid-to-solid ratio of the solution is 1:(10-15), and the temperature is controlled at 40-60°C for 2-3 hours. In the step S1, the mass ratio of coal gangue and rice husk ash in the mixture of coal gangue and rice husk ash is 30:70, and the SiO2 in the mixture is 70%, and the Al2O3 is 30%. The soluble fluorine in the phosphogypsum reacts with the aluminum in the rice husk ash-coal gangue to form insoluble fluoride, and the main component of the phosphogypsum, calcium sulfate, forms a more insoluble calcium carbonate precipitate in the solution;

[0011] 3F - +Al 3+ →AlF3

[0012] CaSO4+CO3 2- →CaCO3+SO4 2- ;

[0013] The calcium carbonate solid obtained in S3.S2 is preheated at 300-500°C, AlF3 reacts with water vapor to generate hydrogen fluoride gas, which is absorbed by sodium hydroxide solution, and reacts with silica (mainly SiO2) under high temperature conditions under the action of metal oxide type composite nanomaterial (CuFe2O4@MgO2), and fully reacts in an electric furnace to generate calcium silicate;

[0014] The aluminum fluoride impurities in the calcium carbonate in S3 react with water vapor at 300-500°C to generate hydrogen fluoride gas that overflows, and the gas is absorbed by sodium hydroxide solution;

[0015] 2AlF3+3H2O→Al2O3+6HF↑;

[0016] CuFe2O4 and MgO2 in the metal oxide type composite nanomaterial (CuFe2O4@MgO2) in S3 are metal oxides, and the active sites on their surfaces can adsorb reactant molecules and promote the reaction. At the same time, the metal oxide type composite nanomaterial also has an unexpected effect, which enables the calcium silicate product to form a uniform powder.

[0017] The mass ratio of calcium carbonate to silica in S3 is 1:0.3-0.5, and they react completely at 1000-1300℃ to form calcium silicate and carbon dioxide gas; calcium carbonate decomposes under heat to form CaO and CO2, and the main component of silica is SiO2, and CaO reacts with SiO2 to form calcium silicate;

[0018] CaCO3→CaO+CO2↑;

[0019] CaO+SiO2→CaSiO3;

[0020] S4. Add the phosphate tailings to the reactor and add hydrochloric acid to react, maintain the reaction temperature at 20-35°C, adjust the pH to 1-2, and the liquid-solid ratio to 15-25:1. Stir the reaction for 2 hours to allow the calcium, magnesium and phosphate minerals in the phosphate tailings to react completely;

[0021] The phosphate tailings in S3 are mixed with hydrochloric acid; magnesium oxide (MgO) or magnesium carbonate (MgCO3) in the phosphate tailings in S3 dissolves under the action of acid to generate soluble magnesium ions; apatite dissolves under the action of acid to generate soluble calcium ions and dihydrogen phosphate ions:

[0022] CaMg(CO3)2+4H + =Ca2 + +Mg 2+ +2CO2+2H2O;

[0023] Ca5F(PO4)+6H + =5Ca 2+ +3H2PO4 - +F - ;

[0024] S5. After the reaction is complete, filtering is performed to obtain insoluble matter and acid hydrolyzate; CaO is added to the acid hydrolyzate to adjust the pH to 7-8, and metal oxide type composite nanomaterials (CuFe2O4@MgO2) are added to achieve uniform particle size, and precipitate begins to be generated, and solid-liquid separation is performed to collect the precipitate and supernatant; the precipitate is mainly composed of phosphate, containing soluble calcium, magnesium and phosphorus, and the generated phosphate has good dispersibility and is in powder form;

[0025] 10Ca 2+ +6H2PO4+2H2O=Ca10 (PO4)6(OH)2+14H + ;

[0026] Ca 2+ +H2PO4 - +2H2O=CaHPO4·2H2O+H + ;

[0027] 3Ca 2+ +2H2PO4=Ca3(PO4)2+4H + ;

[0028] 8Ca 2+ +6H2PO4+5H2O=Ca8H2(PO4)6·5H2O+10H + ;

[0029] 3Mg 2+ +2H2PO4+8H2O=Mg3(PO4)2·8H2O+4H + ;

[0030] Mg 2+ +2H2PO4+4H2O=Mg(H2PO4)2·4H2O;

[0031] Mg 2+ +H2PO4+3H2O=MgHPO4·3H2O+H + ;

[0032] S6. Dry the calcium silicate obtained in S3 and the phosphate precipitate obtained in S5 to a moisture content of ≤0.5% to obtain a final powdered calcium magnesium phosphate fertilizer product, which can meet the fineness and nutrient requirements of powdered calcium magnesium phosphate fertilizer type III without grinding.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] Through reasonable raw material ratio and optimized reaction conditions, harmful impurities such as soluble fluorine in phosphogypsum are effectively removed. Under the action of new catalyst, the product has good uniform dispersion. Soluble phosphorus is the nutrient component of calcium magnesium phosphate fertilizer. High-quality calcium magnesium phosphate fertilizer is produced through phosphogypsum and phosphate tailings, meeting the nutritional standards required for plant growth. DETAILED DESCRIPTION

[0035] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0036] Example 1

[0037] Preparation of calcium magnesium phosphate fertilizer using Yidu Xingfa gypsum slag and phosphate tailings:

[0038] Raw materials and their main components

[0039] Table 1 Main components of gypsum slag %

[0040] <![CDATA[SO2]]> CaO <![CDATA[SiO2]]> <![CDATA[P2O5]]> Soluble F 39.46 34.09 2.94 1.48 2.54

[0041] Table 2 Main components of phosphorus tailings %

[0042] CaO MgO <![CDATA[P2O5]]> <![CDATA[SiO2]]> 34.91 12.50 10.07 2.66

[0043] Implementation process:

[0044] S1, solid raw materials: rice husk ash-coal gangue mixture (5%); phosphogypsum (mass fraction 65%), phosphate tailings (mass fraction 24%) and metal oxide type composite nanomaterials (CuFe2O4@MgO2) (mass fractions in the two steps are 4% and 2% respectively);

[0045] S2, dissolving the rice husk ash-coal gangue mixture and phosphogypsum in water in a reactor to fully react, then mixing with sodium carbonate (phosphogypsum and sodium carbonate mass ratio is 1:0.7), dissolving in water (liquid-solid ratio is 15:1), controlling the temperature at 40-60°C to react for 2-3 hours to generate and filter to obtain calcium carbonate solid;

[0046] S3, preheating calcium carbonate at 400°C until no gas is generated, and then reacting with silica (mass ratio of 1:1.2) at 1250°C for 30 minutes under the catalytic action of metal oxide type composite nanomaterial (CuFe2O4@MgO2) to form powdered calcium silicate;

[0047] S4, mixing the phosphate tailings with hydrochloric acid for acid hydrolysis, adjusting the pH to 1, and the liquid-solid ratio to 25:1. After the reaction is complete, filtering to remove insoluble matter;

[0048] S5, adding CaO to the acid hydrolyzate obtained in S3 to adjust the pH to 7.5, adding metal oxide type composite nanomaterial (CuFe2O4@MgO2), and filtering again to obtain powdery phosphate solid;

[0049] S6. Drying the calcium silicate powder obtained in S1 and the phosphate powder obtained in S5 without grinding to finally obtain powdered calcium magnesium phosphate fertilizer that meets the standards.

[0050] Table 3 Nutrient composition of calcium magnesium phosphate fertilizer obtained in Example 1

[0051] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 28.3 24.32 5.86 13.21 0.078 0.5 85.1

[0052] Example 2

[0053] Calcium magnesium phosphate fertilizer was prepared using gypsum slag and phosphate tailings from Yidu Xingfa.

[0054] Raw materials and their ingredients

[0055] Table 4 Main elements of gypsum slag %

[0056] <![CDATA[SO2]]> CaO <![CDATA[SiO2]]> <![CDATA[P2O5]]> Soluble F 39.46 34.09 2.94 1.48 2.54

[0057] Table 5 Main elements of phosphorus flotation tailings %

[0058] CaO MgO <![CDATA[P2O5]]> <![CDATA[SiO2]]> 34.31 12.50 10.07 2.66

[0059] Implementation process

[0060] S1. Solid raw materials: rice husk ash-coal gangue mixture (mass fraction 5%), phosphogypsum (mass fraction 60%), phosphate tailings (mass fraction 30%) and metal oxide composite nanomaterials (CuFe2O4@MgO2) in two steps (mass fraction 3% and 2%)

[0061] S2, dissolving the rice husk ash-coal gangue mixture and phosphogypsum in water in a reactor to fully react, then mixing with sodium carbonate (phosphogypsum and sodium carbonate mass ratio is 1:0.7), dissolving in water (liquid-solid ratio is 15:1), controlling the temperature at 40-60°C to react for 2-3 hours to generate and filter to obtain calcium carbonate solid;

[0062] S3, preheating calcium carbonate at 400°C until no gas is generated, adding metal oxide type composite nanomaterial (CuFe2O4@MgO2), and then reacting with silica (mass ratio of 1:1.2) at 1250°C for 30 minutes to form powdered calcium silicate;

[0063] S4, subjecting the phosphate tailings to an acid hydrolysis reaction with hydrochloric acid, adjusting the pH to 1, and the liquid-solid ratio to 25:1, and filtering to remove insoluble matter after the reaction is complete;

[0064] S5, adding CaO to the acid hydrolyzate obtained in S3 to adjust the pH to 7.5, adding metal oxide type composite nanomaterial (CuFe2O4@MgO2), and filtering again to obtain powdery phosphate solid;

[0065] S6. Drying the calcium silicate obtained in S1 and the powdered calcium phosphate and powdered magnesium phosphate obtained in S5, without grinding, to finally obtain powdered calcium magnesium phosphate fertilizer that meets the standards.

[0066] Table 6 Nutritional composition of calcium magnesium phosphate fertilizer obtained in Example 2

[0067] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 29.51 24.06 5.61 12.95 0.080 0.5 84.2

[0068] Example 3

[0069] Based on Example 1, in step S2, sodium carbonate is not added but potassium carbonate is added, and the nutritional components of the calcium magnesium phosphate fertilizer finally obtained are as follows:

[0070] Table 7 Nutrient composition of calcium magnesium phosphate fertilizer obtained in Comparative Example 1

[0071] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 24.63 19.32 6.01 14.31 0.088 0.5 82

[0072] By comparing Example 1 with Example 3, it can be seen that after sodium carbonate is replaced by potassium carbonate in step 2, the content of the main nutrients CaO and soluble silicon is reduced. Since the difference in chemical properties between potassium carbonate and sodium carbonate affects the conditions of the reaction system, the degree of reaction between potassium carbonate and phosphogypsum is low, and less calcium is recovered in the phosphogypsum, resulting in changes in the stability or activity of the nutrients, which in turn affects their retention rate.

[0073] Example 4

[0074] Based on Example 1, in step S3, instead of adding silica, mica is added, and the nutritional components of the obtained calcium magnesium phosphate fertilizer are as follows:

[0075] Table 8 Nutrient composition of calcium magnesium phosphate fertilizer obtained in Comparative Example 2

[0076] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 26.63 18.32 8.26 12.35 0.089 0.5 82

[0077] Based on Example 1, replacing the silica in step S3 with mica will result in a significant reduction in the soluble silicon content. This is attributed to the differences in chemical composition, physical properties and reactivity between silica and mica. The silicon dioxide content in mica is relatively low, which reduces the source of soluble silicon in the reaction system when mica is used as a raw material, resulting in a reduction in the soluble silicon content of the final product.

[0078] Comparative Example 1

[0079] Based on Example 1, in step S2, the rice husk ash-coal gangue mixture (mass fraction 5%) is not added, and the nutritional components of the calcium magnesium phosphate fertilizer finally obtained are as follows:

[0080] Table 7 Nutrient composition of calcium magnesium phosphate fertilizer obtained in Comparative Example 1

[0081] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 27.96 22.32 6.01 14.31 0.158 0.5 84.1

[0082] By comparing Example 1 with Comparative Example 1, it is found that the decrease in the soluble fluorine content in the system is significantly reduced without the addition of the rice husk ash-coal gangue mixture. This shows that the introduction of the rice husk ash-coal gangue mixture plays a key role in effectively reducing the soluble fluorine content. At the same time, by comparing the nutritional data of the two groups of experiments, we found that the content of the main nutrients remained basically unchanged, which further shows that the addition of the rice husk ash-coal gangue mixture improves the fluorine content index while not adversely affecting the overall nutritional structure, thereby verifying the effectiveness and safety of the mixture in specific applications.

[0083] Comparative Example 2

[0084] Based on Example 1, the metal oxide type composite nanomaterial (CuFe2O4@MgO2) is eliminated in step S3 and step 5, and the nutritional components of the calcium magnesium phosphate fertilizer finally obtained are as follows:

[0085] Table 8 Nutrient composition of calcium magnesium phosphate fertilizer obtained in Comparative Example 2

[0086] Ca <![CDATA[SiO2]]> MgO <![CDATA[P2O5]]> Soluble F Moisture ≥0.25mm 24.72 18.32 8.26 12.35 0.089 0.5 76.6

[0087] By comparing and analyzing Example 1 and Comparative Example 1, it is found that without adding the metal oxide type composite nano material (CuFe2O4@MgO2) catalyst, the main nutrients of the reaction system or product are significantly reduced. This shows that the metal oxide type composite nano material (CuFe2O4@MgO2) catalyst promotes the reaction. At the same time, the fineness of the product has also decreased, which means that the particle size distribution of the product may become more uneven, or the overall particle size has increased. This finding shows that the metal oxide type composite nano material (CuFe2O4@MgO2) catalyst has a significant effect in improving product quality, maintaining nutrients, and improving product uniformity. Therefore, the addition of the catalyst is crucial to improving overall product performance and quality.

[0088] The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

Claims

1. A method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings, wherein the mass fraction of the raw materials is as follows: 5-10% of rice husk ash-coal gangue mixture, 60-70% of phosphogypsum, 20-30% of phosphate tailings, and 2-7% of CuFe2O4@MgO2, characterized in that: The method comprises the following steps: S1. Grind the coal gangue and rice husk ash into powder, mix and react with the phosphogypsum aqueous solution, add sodium carbonate and stir to generate calcium carbonate precipitation, and filter to obtain calcium carbonate solid after the reaction is complete; S2, preheating calcium carbonate, and then reacting with silica under the catalytic action of CuFe2O4@MgO2 at high temperature to form calcium silicate; S3, adding the phosphate tailings into a reactor, adding hydrochloric acid to perform an acidolysis reaction to fully dissolve the phosphate tailings; performing solid-liquid separation on the mixture after the acidolysis reaction to remove acid-insoluble substances to obtain an acidolysis solution rich in calcium ions, magnesium ions and phosphate ions; S4. Add CaO to the obtained acid solution for neutralization reaction, and add CuFe2O4@MgO2 catalyst at the same time. At this time, a precipitate is generated in the acid solution, mainly a phosphate precipitate, and at this time, the phosphate has good uniform dispersion and is in powder form; S5. Dry the phosphate obtained after neutralization, and add the calcium silicate obtained in S1 and mix thoroughly to obtain the final powdered calcium magnesium phosphate fertilizer.

2. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In the step S1, the mass ratio of the rice husk ash-coal gangue mixture: phosphogypsum: sodium carbonate is 0.1:1:(1-1.2); when water is added for dissolution, the solid-liquid ratio is 1:(10-15); In the step S1, the mass ratio of the coal gangue and the rice husk ash in the mixture of the coal gangue and the rice husk ash is (25-30):70, and the mass ratio of SiO2 and Al2O3 in the mixture is (60-70):(20-30).

3. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In the step S2, the obtained calcium carbonate is preheated at 300-500°C for a period of time, and the generated gas substances are absorbed by sodium hydroxide solution. After no gas is generated, calcium silicate is generated with silica at 1000-1300°C under the catalytic action of CuFe2O4@MgO2; The amount of CuFe2O4@MgO2 used in step S2 accounts for 1-4% of the mass fraction of the raw materials.

4. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In step S3, the phosphate tailings are mixed with hydrochloric acid, the pH is adjusted to 1-1.5, and the liquid-to-solid ratio is 1:(20-25).

5. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In step S3, the acid hydrolysis time is 2-4 hours to ensure the full dissolution of the minerals containing calcium, magnesium and phosphorus.

6. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In the step S4, the pH is adjusted to 7-8 during the neutralization reaction, and the reaction temperature is maintained at 20-30° C. to promote the precipitation of phosphate; the amount of the metal oxide composite nanomaterial (CuFe2O4@MgO2) used in the step S4 accounts for 1-3% of the mass fraction of the raw materials.

7. The method for preparing calcium magnesium phosphate fertilizer using phosphogypsum and phosphate tailings according to claim 1, characterized in that: In step S5, the moisture content of the dried product is controlled at ≤0.5%, and the particles with a particle size of ≥0.25 mm account for more than 80% of the final product.