A coating agent for kiln-process phosphoric acid production and its preparation method

Abstract

This invention discloses a coating agent for kiln-process phosphoric acid production and its preparation method, belonging to the technical field of kiln-process phosphoric acid coating agents. The coating agent is composed of β-gypsum powder, coal powder, and residue from the kiln-process phosphoric acid reaction. First, each raw material is ground to below 75 micrometers. Then, β-gypsum powder and coal powder are mixed at a C:S mass ratio ≥4, and the residue from the kiln-process phosphoric acid reaction is added simultaneously, with the residue accounting for 70% to 80% of the total mass of the coating agent. The above materials are then uniformly mixed to complete the preparation of the coating agent for the kiln-process phosphoric acid production. When using, process water is added to coat the kiln-process phosphoric acid pellets. The coating agent of this invention can effectively prevent oxygen oxidation of the fixed carbon in the pellets and prevent the pellets from sticking together and forming rings.

Description

Technical Field

[0001] This invention relates to the field of encapsulating agents for kiln-process phosphoric acid, specifically to an encapsulating agent for kiln-process phosphoric acid and its preparation method. Background Technology

[0002] Phosphate rock is a strategic resource in my country. Conventional phosphate chemical processing suffers from problems such as low value of byproducts, environmental unfriendliness, and high energy consumption. For example, the sulfuric acid process has the problem of phosphogypsum storage, and the electric furnace process has the problem of high energy consumption. Non-molten kiln phosphoric acid processing technology is one of the most promising processes to solve the above problems.

[0003] The basic principle of the kiln process for phosphoric acid is as follows:

[0004] Ca 10 (PO4)6F2+15C+9SiO2=3P2(g)+15CO(g)+9CaSiO3+CaF2 (1-1)

[0005] 2P2(g) + 5O2(g) = P4O 10 (g) (1-2)

[0006] 2CO(g) + O2(g) = 2CO2(g) (1-3)

[0007] 0.5P4O 10 +3H₂O=2H₃PO₄ (1-4)

[0008] Fluorapatite first reacts with carbon at high temperature via a carbothermic reduction reaction to produce P2, CO, and other products (see (1-1)). This reaction is a strongly absorption reaction. Then, P2 and CO react with oxygen to produce P4O. 10 CO2, see (1-2) and (1-3), both of which are strongly exothermic reactions. Finally, P4O 10 It is absorbed by water and forms H3PO4.

[0009] The kiln-based phosphoric acid process allows for the simultaneous execution of steps (1-1), (1-2), and (1-3) within the same reactor (kiln), with reduction heat coupled with oxidation heat. Therefore, it features low acid consumption, low power consumption, and low unit energy consumption.

[0010] However, the kiln-process phosphoric acid production method suffers from low P yield and P4O due to the easy oxidation of the "reduction carbon". 10 The problem of backflow.

[0011] When reactions (1-1), (1-2), and (1-3) occur in the same kiln, if there is no clear interface between the "reduction reaction" and the "oxidation reaction," O2 may oxidize the "reduction carbon" in (1-1), leading to insufficient carbon (C) in (1-1). This, in turn, results in a low P2 escape rate and a low P recovery rate in (1-1). Simultaneously, due to the insufficient C in (1-1), the P4O generated in (1-2) may also be affected. 10 The reactants in (1-1) readily form calcium metaphosphate and calcium pyrophosphate, which is P4O 10 Backflow.

[0012] To address the aforementioned problems, the most effective method is to coat the reaction pellets (bulk) with a carbon-containing coating agent. This prevents or slows down the oxidation of the "reduction carbon" and P4O in (1-1). 10 The backflow is addressed. However, existing encapsulating agents have the following drawbacks: they contain alkali metals (sodium, potassium), contain silicon, and are costly. For example, CN 104211028 A proposes that the binder added to the inner and outer layers of the pellets can be one or more combinations of asphalt, sodium humate, ammonium humate, water glass, sulfite pulp waste liquor, syrup, and lignin sulfonate, with an addition amount of 0.2% to 15% (dry basis) of the added material's weight. For example, CN115159481A specifies that the binder is any one or more of sodium humate, bentonite, starch, and dextrin.

[0013] However, under the rigid conditions of the kiln-process phosphoric acid system, sodium and potassium are prone to stalactite reaction:

[0014] 2K2O(g) + P4O 10 (g) = 4KPO3 (1-5)

[0015] 2Na2O(g)+P4O10(g)=4NaPO3 (1-6)

[0016] 2KF(g) + SiF4(g) = K2SiF6 (1-7)

[0017] 2NaF(g)+SiF4(g)=Na2SiF6 (1-8)

[0018] KPO3, NaPO3, K2SiF6, Na2SiF6, and other substances mentioned above are high-melting-point and volatile materials in the kiln-process phosphoric acid system. They easily form soft fused rings in the reactant pellets, and in low-temperature zones, they deposit inside the pipes, clogging them and causing production interruptions.

[0019] Therefore, the preparation of a class of low-cost encapsulating agents that do not contain (or have low content) alkali metals is of great significance for the kiln-process phosphoric acid. Summary of the Invention

[0020] To address the above shortcomings, this invention provides a low-cost encapsulating agent for kiln-process phosphoric acid production that contains no or low levels of alkali metals. This encapsulating agent simultaneously possesses the following properties: (1) preventing oxygen in kiln-process phosphoric acid from corroding the 'reduction carbon'; (2) preventing P4O... 10 (3) Does not contain (low content) alkali metals.

[0021] To achieve the above objectives, a coating agent for the kiln-process phosphoric acid production is prepared by mixing and compounding β-gypsum powder, coal powder, and the residue after the kiln-process phosphoric acid reaction. The β-gypsum powder meets the physical and mechanical properties specified in Table 2 of GB / T 9776-2022 "Building Gypsum" and is a common and inexpensive cementitious material.

[0022] As a preferred technical solution, the β-gypsum powder and coal powder are mixed in a ratio of C:S of ≥4.

[0023] As a further preferred option, the pulverized coal is either anthracite or coke, and the alkali metal content is less than 0.3%.

[0024] As a preferred technical solution, the mass of the residue after the kiln-process phosphoric acid reaction accounts for 70% to 80% of the total mass of the coating agent; the mass ratio of silicon to calcium in the pellets after the kiln-process phosphoric acid reaction is greater than 2.8.

[0025] As a preferred technical solution, the particle size of the residue after the reaction of β-gypsum powder, coal powder and kiln-processed phosphoric acid is ≤75 micrometers after grinding.

[0026] The present invention also provides a method for preparing the above-mentioned coating agent for the kiln-process phosphoric acid production, comprising the steps of:

[0027] 1) Grind β-gypsum powder, coal powder, and the residue after the kiln-process phosphoric acid reaction separately;

[0028] 3) Mix the above-ground β-gypsum powder with coal powder, and add the residue after the kiln-process phosphoric acid reaction.

[0029] 3) Mix the above materials evenly to obtain the coating agent for the kiln-process phosphoric acid.

[0030] As a preferred technical solution, the grinding in step 1) involves grinding the β-gypsum powder, coal powder, and the residue after the kiln-process phosphoric acid reaction to a particle size ≤75 micrometers.

[0031] As a preferred technical solution, in step 2), the pulverized β-gypsum powder and coal powder are mixed according to a C:S mass ratio ≥ 4.

[0032] As a further preferred option, the pulverized coal is either anthracite or coke, and the alkali metal content is less than 0.3%.

[0033] As a preferred technical solution, the mass of the residue after the kiln-process phosphoric acid reaction in step 2) accounts for 70% to 80% of the total mass of the coating agent; the material balls after the kiln-process phosphoric acid reaction satisfy the silicon-calcium mass ratio being greater than 2.8.

[0034] When used, adding a certain amount of water allows it to be used to coat phosphate pellets produced in kiln processes.

[0035] By adopting the above technical solution, a coating agent for kiln-process phosphoric acid production and its preparation method are disclosed. The coating agent is composed of β-gypsum powder, coal powder, and residue from the kiln-process phosphoric acid reaction. First, each raw material is ground to below 75 micrometers. Then, β-gypsum powder and coal powder are mixed at a C:S mass ratio ≥4. Simultaneously, residue from the kiln-process phosphoric acid reaction is added, with the residue accounting for 70% to 80% of the total mass of the coating agent. The coating agent for the kiln-process phosphoric acid production is prepared by uniformly mixing the above materials. When used, process water is added to coat the kiln-process phosphoric acid pellets. The coating agent of this invention can effectively prevent oxygen oxidation of the fixed carbon in the pellets and prevent the pellets from sticking together and forming rings.

[0036] Advantages of this invention:

[0037] The coating agent prepared in this invention for the kiln-process phosphoric acid production can effectively prevent oxygen in the kiln-process phosphoric acid production from corroding the "reduction carbon" and preventing P4O. 10 The backflow prevents pellet adhesion, ring formation, and blockage of the low-temperature exhaust pipe by being free of alkali metals. β-gypsum powder, used as a binder in the coating agent, is low-cost and exhibits rapid strength development. Coal powder reacts with oxygen to prevent further diffusion of oxygen into the pellets. Simultaneously, at high temperatures, the carbon in the coal powder and the CaSO4 in the β-gypsum powder react to form CaS. CaS can then directly react with oxygen to form CaSO4, which can be reintroduced into the coating agent along with the reacted pellet residue, reducing the amount of β-gypsum powder used and achieving recycling without environmental pollution. Detailed Implementation

[0038] This invention provides a coating agent for phosphate proto-embryos produced by the encapsulation kiln process and its preparation method.

[0039] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. The physicochemical properties of β-gypsum powder, anthracite, coke, and the residue after the kiln reaction in the embodiments are shown in Tables 1 to 5.

[0040] Table 1 Physical and mechanical properties of β-gypsum powder

[0041]

[0042] Table 2. Main chemical composition (%) of β-gypsum powder

[0043] <![CDATA[CaSO4·1 / 2H2O]]> <![CDATA[CaSO4·2H2O]]> <![CDATA[P2O5]]> F <![CDATA[Na2O]]> MgO Cl SiO2 86.32 3.67 1.62 0.14 0.42 2.00 2.34 2.15

[0044] Table 3. Main chemical composition of anthracite (%)

[0045] Fixed carbon S Ash Volatile components Moisture alkali metals 74.07 0.62 10.89 8.42 4.34 0.12

[0046] Table 4. Main chemical composition of coke (%)

[0047] Fixed carbon S Ash Volatile components Moisture alkali metals 79.96 0.57 12.2 1.29 4.05 0.06

[0048] Table 5. Main chemical composition (%) of the residue after phosphoric acid reaction in the kiln process

[0049] <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> MgO <![CDATA[P2O5]]> <![CDATA[SO3]]> F 68.22 17.73 3.52 3.55 1.42 1.59 1.81 1.29

[0050] Example 1

[0051] First, take β-gypsum powder, anthracite, and the residue from the kiln-process phosphoric acid reaction and grind them to a fineness of less than or equal to 75 micrometers. Then, take 100g of β-gypsum powder, 41g of anthracite powder, and 329g of the kiln-process phosphoric acid reaction residue and mix them evenly. Control the C:S (material mass ratio) in the mixture to be 4, and the kiln-process phosphoric acid reaction residue to account for 70%.

[0052] In use, the kiln-processed phosphate pellets are placed in a granulator, and the aforementioned coating agent and process water are added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C and subsequently solidified at 900°C under oxygen-free conditions. The solidified pellets are then subjected to a 720-hour continuous test in a rotary kiln at 1300°C and an oxygen concentration of 0.1%. The pellets did not stick together, form rings, or clog the pipes, and the P2O5 conversion rate was 86.56%.

[0053] Example 2

[0054] First, β-gypsum powder, anthracite, and the residue from the kiln-process phosphoric acid reaction are ground to a fineness of 75 micrometers or less. Then, 100g of β-gypsum powder, 41g of anthracite powder, and 564g of the kiln-process phosphoric acid reaction residue are mixed evenly, and the C:S (material mass ratio) in the mixture is controlled to be 4, with the kiln-process phosphoric acid reaction residue accounting for 80%.

[0055] In use, the kiln-processed phosphate pellets are placed in a granulation tank, the aforementioned coating agent is added, and a certain amount of process water is added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C and subsequently solidified at 900°C under oxygen-free conditions. After solidification, the pellets are subjected to a 720-hour continuous test at 1320°C with an oxygen concentration of 0.1%. The pellets do not stick together, do not form rings, and the pipes do not become clogged; the P2O5 conversion rate is 92.45%.

[0056] Example 3

[0057] First, take β-gypsum powder, anthracite, and the residue from the kiln-process phosphoric acid reaction and grind them to a fineness of less than or equal to 75 micrometers. Then, take 100g of β-gypsum powder, 51g of anthracite powder, and 453g of the kiln-process phosphoric acid reaction residue and mix them evenly. Control the C:S (material mass ratio) in the mixture to be 5, and the kiln-process phosphoric acid reaction residue to account for 75%.

[0058] In use, the kiln-processed phosphate pellets are placed in a granulation tank, the aforementioned coating agent is added, and a certain amount of process water is added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C and subsequently solidified at 900°C under oxygen-free conditions. After solidification, the pellets are subjected to a continuous 720-hour test at 1320°C with an oxygen concentration of 0.1%. The pellets do not stick together, do not form rings, and the pipes do not become clogged; the P2O5 conversion rate is 93.56%.

[0059] Example 4

[0060] First, β-gypsum powder, coke, and the residue from the kiln-process phosphoric acid reaction are ground to a fineness of 75 micrometers or less. Then, 100g of β-gypsum powder, 38g of coke, and 552g of the kiln-process phosphoric acid reaction residue are mixed evenly, and the C:S (material mass ratio) in the mixture is controlled to be 4, with the kiln-process phosphoric acid reaction residue accounting for 80%.

[0061] In use, the kiln-processed phosphate pellets are placed in a granulation tank, the aforementioned coating agent is added, and a certain amount of process water is added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C and subsequently solidified at 900°C under oxygen-free conditions. After solidification, the pellets are subjected to a continuous 720-hour test at 1320°C with an oxygen concentration of 0.1%. The pellets do not stick together, do not form rings, and the pipes do not become clogged; the P2O5 conversion rate is 93.79%.

[0062] Example 5

[0063] First, β-gypsum powder, coke, and the residue from the kiln-process phosphoric acid reaction are ground to a fineness of 75 micrometers or less. Then, 100g of β-gypsum powder, 38g of coke, and 322g of the kiln-process phosphoric acid reaction residue are mixed evenly, with the C:S (mass ratio) in the mixture controlled at 4 and the kiln-process phosphoric acid reaction residue accounting for 70%.

[0064] In use, the kiln-processed phosphate pellets are placed in a granulation tank, the aforementioned coating agent is added, and a certain amount of process water is added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C and subsequently solidified at 900°C under oxygen-free conditions. After solidification, the pellets are subjected to a continuous 720-hour test at 1320°C with an oxygen concentration of 0.1%. The pellets do not stick together, do not form rings, and the pipes do not become clogged; the P2O5 conversion rate is 93.79%.

[0065] Example 6

[0066] First, β-gypsum powder, coke, and the residue from the kiln-process phosphoric acid reaction are ground to a fineness of 75 micrometers or less. Then, 100g of β-gypsum powder, 38g of coke, and 322g of the kiln-process phosphoric acid reaction residue are mixed evenly, with the C:S (mass ratio) in the mixture controlled at 4 and the kiln-process phosphoric acid reaction residue accounting for 70%.

[0067] In use, the kiln-processed phosphate pellets are placed in a granulation tank, the aforementioned coating agent is added, and a certain amount of process water is added to achieve a coating thickness of 0.2 cm. The coated pellets are then dried at 120°C. After drying, the pellets are subjected to a 720-hour continuous test at 1320°C with an oxygen concentration of 0.1%. The pellets do not stick together, do not form rings, and the pipes do not become clogged, with a P2O5 conversion rate of 91.21%.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A coating agent for a kiln-process phosphoric acid production process, characterized in that: The coating agent is a mixture of β-gypsum powder, coal powder, and the residue from the kiln-process phosphoric acid reaction. The mass of the residue from the kiln-process phosphoric acid reaction accounts for 70% to 80% of the total mass of the coating agent. The β-gypsum powder and coal powder are mixed in a ratio of C:S mass of ≥4. The coal powder is either anthracite or coke, and the alkali metal content is less than 0.3%. The residue from the kiln-process phosphoric acid reaction satisfies a silicon-calcium mass ratio greater than 2.

8.

2. The coating agent for the kiln-process phosphoric acid production as described in claim 1, characterized in that: The residue from the reaction of β-gypsum powder, coal powder, and kiln-processed phosphoric acid has a particle size ≤75 micrometers after grinding.

3. A method for preparing a coating agent for the kiln-process phosphoric acid production as described in claim 1 or 2, characterized in that... Including the following steps: 1) Grind β-gypsum powder, coal powder, and the residue from the kiln-process phosphoric acid reaction separately; 2) Mix the above-ground β-gypsum powder with coal powder, and add the residue from the kiln-process phosphoric acid reaction. 3) Mix the above materials evenly to obtain the coating agent for the kiln-process phosphoric acid.

4. The method for preparing a coating agent for the kiln-process phosphoric acid production according to claim 3, characterized in that: The grinding in step 1) involves grinding the β-gypsum powder, coal powder, and the residue after the kiln-process phosphoric acid reaction to a particle size ≤ 75 micrometers.

5. The method for preparing a coating agent for the kiln-process phosphoric acid production according to claim 3, characterized in that: In step 2), the pulverized β-gypsum powder and coal powder are mixed according to a C:S mass ratio of ≥4.

6. The method for preparing a coating agent for the kiln-process phosphoric acid production according to claim 3, characterized in that: The pulverized coal is either anthracite or coke, and the alkali metal content is less than 0.3%.

7. The method for preparing a coating agent for the kiln-process phosphoric acid production according to claim 3, characterized in that: In step 2), the residue after the kiln-process phosphoric acid reaction accounts for 70% to 80% of the total mass of the coating agent; the residue after the kiln-process phosphoric acid reaction satisfies a silicon-to-calcium mass ratio greater than 2.8.

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