A method for comprehensive utilization of solid by-products of thermal-process phosphoric acid

Abstract

The present invention discloses a method for comprehensive utilization of solid by-products of thermal phosphoric acid, which relates to the technical field of by-product reuse in phosphoric acid production. The solid by-products of thermal phosphoric acid are crushed to below 75 um, and the crushed solid by-products of thermal phosphoric acid are added into wet-process phosphoric acid to desulfurize the wet-process phosphoric acid; the desulfurized wet-process phosphoric acid is filtered and washed to obtain desulfurized slag, and the desulfurized slag is ground and then added to the thermal phosphoric acid batching for pelletizing, which is used in the production of thermal phosphoric acid. By using the solid by-products of thermal phosphoric acid as the raw material for reducing sulfate radicals, calcium silicate in the solid by-products reacts with excessive sulfuric acid in the wet-process phosphoric acid to form calcium sulfate precipitation, so as to achieve the purpose of reducing the sulfate radical content in the wet-process phosphoric acid, and at the same time, a large amount of solid by-products of thermal phosphoric acid are consumed; at the same time, the solid desulfurized slag generated in the desulfurization process is effectively utilized, and the desulfurized slag is used in the production of molten thermal phosphoric acid to further recover phosphorus, and at the same time, calcium silicate is utilized to reduce the batching cost of thermal phosphoric acid.

Description

Technical Field

[0001] The present invention relates to the technical field of by - product reuse in phosphoric acid production, and specifically relates to a method for comprehensive utilization of solid by - products of thermal phosphoric acid. Background Technique

[0002] Thermal phosphoric acid mainly includes conventional molten - state electric - furnace phosphoric acid and non - molten - state kiln phosphoric acid. Therefore, there are mainly two types of solid by - products of thermal phosphoric acid. One type is the solid by - products of conventional molten electric - furnace phosphoric acid. The main components of such solid by - products are wollastonite, cuspidine, meta - wollastonite, rankinite, etc., with the main component being calcium silicate, and at the same time containing a small amount of elements such as aluminum, iron, magnesium, phosphorus, fluorine, etc. The other type is non - molten - state kiln phosphoric acid. The main components of such solid by - products are quartz and wollastonite, followed by feldspar, apatite, phosphoferrite, etc. The main components of the two types of solid by - products are calcium - and silicon - containing substances, and the main difference is that the content of SiO2 in the solid by - products of non - molten - state kiln phosphoric acid is higher.

[0003] The by - products of molten - state thermal phosphoric acid are mainly applied to cement - related cementitious materials, concrete, etc. Such applications are the largest digestion of the by - products of molten - state thermal phosphoric acid. The advantage is high later strength, and the disadvantage is that if there is no other ingredient (such as an activator), the early setting rate is slow and the strength development is slow. In addition, it is also used to prepare white carbon black, glass - ceramics, etc., but due to reasons such as complex processes and generation of other by - products, its relative usage is less. For non - molten - state thermal phosphoric acid by - products, the silicon content is relatively high, and the uses are relatively few, mostly used for producing ceramsite, which wastes silicon resources to a certain extent.

[0004] The phosphoric acid production process relative to thermal phosphoric acid is the wet - process phosphoric acid process. In such a phosphoric acid production method, sulfuric acid is mostly used to react with phosphate rock to produce phosphoric acid. In the wet - process phosphoric acid production process, in order to improve the P2O5 recovery rate and promote the growth of gypsum crystals to improve the liquid - solid (i.e., phosphoric acid and gypsum) separation strength, it is necessary to add an excessive amount of sulfuric acid. However, the excessive sulfuric acid will affect the subsequent purification of phosphoric acid and also affect the purity of subsequent phosphate products. Therefore, it is necessary to reduce the content of sulfate radicals in wet - process phosphoric acid in advance, that is, desulfurization.

[0005] The desulfurization technologies in wet - process phosphoric acid mainly include chemical precipitation method, solvent extraction method, ion - exchange method, etc. Considering the cost and removal efficiency, generally the chemical precipitation method is mainly used, that is, adding a calcium salt or barium salt to wet - process phosphoric acid to form a sulfate precipitate, and achieving the purpose of removing SO4 2- by filtration. The calcium - salt removal method mainly uses phosphate rock slurry, calcium carbonate, lime milk, calcium hydrogen phosphate, etc.; the barium - salt removal method mainly includes barium carbonate and barium hydroxide, etc. The currently used calcium salts and barium salts have relatively high costs and single functions.

[0006] Patent CN106115643B uses boiler waste residue to remove sulfate radicals in high-concentration wet-process phosphoric acid. To prepare feed-grade calcium dihydrogen phosphate, sodium carbonate and activated silica are added to remove excessive fluorine. The remaining residue after defluorination is added to the fertilizer finished product in the form of a filter cake. If the precipitate after desulfurization enters the defluorination process directly without separation, it will affect the defluorination effect. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for comprehensive utilization of solid by-products of thermal phosphoric acid, so as to solve the problem that the calcium and silicon contents in the existing solid by-products of thermal phosphoric acid are high but the utilization rate is relatively low.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions: A method for comprehensive utilization of solid by-products of thermal phosphoric acid, characterized in that the steps are as follows:

[0009] S1. Crush the solid by-products of thermal phosphoric acid to 50-75um; The reaction rate of fine-particle materials is high and the reaction completion degree is high, but if the particle size is too fine, agglomeration is likely to occur in subsequent reactions, affecting the reaction and filtration rates.

[0010] S2. Add the crushed solid by-products of thermal phosphoric acid to wet-process phosphoric acid to desulfurize the wet-process phosphoric acid.

[0011] S3. Filter and separate the desulfurized wet-process phosphoric acid to obtain desulfurized slag. A plate-and-frame filter press can be used to press and separate the desulfurized slag in the wet-process phosphoric acid.

[0012] S4. Add the above desulfurized slag to the thermal phosphoric acid feedstock and mix it in a planetary wheel mill. After mixing, the feedstock enters a disk granulator to form pellets, and the pellets are dried and used for the production of thermal phosphoric acid.

[0013] A further technical solution is that in step S2, the mass ratio of calcium oxide in the solid by-products of thermal phosphoric acid to the mass of calcium sulfate in the wet-process phosphoric acid is 0.58-1.71, the desulfurization reaction temperature is 40-80°C, the reaction time is 0.5-3h, and the stirring rate is 80-120rpm.

[0014] A further technical solution is that in step S4, the ground desulfurized slag is used for the molten-state thermal phosphoric acid feedstock, and the SiO2 / CaO in the feedstock system is controlled to be 0.75-0.85, the reaction temperature is 1300-1500°C, and the reaction time is 0.5-3h.

[0015] A further technical solution is that in step S4, the ground desulfurized slag is used for the non-molten-state thermal phosphoric acid feedstock, and the SiO2 / CaO in the feedstock system is controlled to be 2.5-3.0, the reaction temperature is 1300-1400°C, and the reaction time is 0.5-3h.

[0016] A further technical solution is that the SO3 content in the thermal process phosphoric acid batching is 7.5% - 12.5%.

[0017] A further technical solution is that the SiO2 content in the solid by - product of the thermal process phosphoric acid is 40.5% - 69%, and the CaO content is 48.5% - 23%.

[0018] A further technical solution is that the P2O5 content in the wet - process phosphoric acid is 25% - 40%, and the SO4 2- content is 2% - 2.6%.

[0019] Reaction mechanism:

[0020] The present invention uses the solid by - product of thermal process phosphoric acid as the raw material for reducing sulfate. Calcium silicate in the solid by - product reacts with the excessive sulfuric acid in the wet - process phosphoric acid to form calcium sulfate precipitate, so as to reduce the sulfate content in the wet - process phosphoric acid, that is

[0021] CaSiO3 + H2SO4 + H2O = CaSO4·2H2O↓+SiO2·H2O↓ (1)

[0022] The solid by - product is a high - temperature quenching product, and the contained silicon dioxide has high activity. The hydrated silicon dioxide generated after desulfurization also has high activity. It can react with hydrofluoric acid and fluorosilicic acid in the wet - process phosphoric acid to promote the escape of fluorine in the wet - process phosphoric acid, reduce the fluorine content in the wet - process phosphoric acid, and replace part of the role of active silicon dioxide.

[0023] SiO2 + 4HF = SiF4↑+2H2O (2)

[0024] SiO2 + 2H2SiF6 = 3SiF4↑+2H2O (3)

[0025] After the reaction of active calcium oxide and silicon dioxide in the solid by - product, a lap - shaped stacked structure is formed, which can accelerate the precipitation of solids in the wet - process phosphoric acid, improve the liquid - solid separation strength, increase the washing efficiency, and reduce the phosphorus content in the precipitate.

[0026] Furthermore, the solid desulfurization slag generated in the desulfurization process is effectively utilized: The solid obtained after filtration in the desulfurization process contains a large amount of calcium sulfate, substances with low reaction activity containing SiO2 and CaO and a small amount of P2O5, which can be used for the production of molten thermal process phosphoric acid, further recovering phosphorus, and at the same time using calcium silicate to reduce the cost of thermal process phosphoric acid batching.

[0027] According to the differences between molten thermal process phosphoric acid and non - molten thermal phosphoric acid, the amount of solid precipitate added is also different. The basic principle of thermal process phosphoric acid is as follows:

[0028] Ca 10(PO4)6F2 + 15C + 9zSiO2 = 3P2(g) + 15CO(g) + 9[CaO·(SiO2) z + CaF2 (4)

[0029] In the above formula, Ca 10 (PO4)6F2 - fluorapatite, is the effective component of phosphate rock; z is a ratio parameter, and its value range is 0 to 1. CaO·(SiO2) z - calcium silicate salt, the composition changes with z, and can be CaSiO3, Ca3Si2O7, Ca2SiO4, Ca3SiO5, CaO, etc.

[0030] For molten thermal phosphoric acid, to ensure it is in a molten state at 1300°C to improve the electric furnace efficiency, the SiO2 / CaO ratio is usually between 0.75 and 0.85, and the reaction products are mostly CaSiO3, Ca3Si2O7, Ca2SiO4, etc.; for non-molten thermal phosphoric acid, to ensure it does not soften at 1300°C and has a fast enough reaction rate, the SiO2 / CaO ratio is between 2.5 and 3.0, and the reaction products are mostly CaSiO3.

[0031] It was found in the experiment that when adding desulfurized slag to balance the silicon-calcium ratio to ensure the characteristics of the thermal phosphoric acid batching at high temperature and ensure that the content of SO3 in the system is between 7.5% and 12.5%, the phosphorus escape rate in the reaction system increases by 3.0% to 5.2%.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. By using the solid by-product of thermal phosphoric acid as the raw material to reduce sulfate, calcium silicate in the solid by-product reacts with the excessive sulfuric acid in wet-process phosphoric acid to form calcium sulfate precipitate, so as to achieve the purpose of reducing the sulfate content in wet-process phosphoric acid, and at the same time consume a large amount of solid by-products of thermal phosphoric acid.

[0034] 2. Utilizing the characteristic that the silicon dioxide contained in the solid by-product has relatively high activity, hydrated silicon dioxide with relatively high activity is obtained, which promotes the escape of fluorine in wet-process phosphoric acid, reduces the fluorine content in wet-process phosphoric acid, and reduces the dosage of defluorination reagent for wet-process phosphoric acid.

[0035] 3. After the reactive calcium oxide and silicon dioxide in the solid by-product react, a porous skeleton structure is formed, which can accelerate the precipitation of solids in wet-process phosphoric acid, improve the liquid-solid separation strength, increase the washing efficiency, and reduce the phosphorus content in the precipitate.

[0036] 4. Effectively utilize the solid desulfurized slag generated in the desulfurization process, use the desulfurized slag for the production of molten thermal phosphoric acid, further recover phosphorus, and at the same time utilize silicon and calcium to reduce the batching cost of thermal phosphoric acid. Description of the Drawings

[0037] Figure 1 This is the process flow chart of the present invention.

[0038] Figure 2 This is the desulfurization rate curve graph at different times in Example 1 of the present invention.

[0039] Figure 3 This is the desulfurization rate curve graph at different times in Example 2 of the present invention.

[0040] Figure 4 This is the desulfurization rate curve graph at different times in Example 3 of the present invention.

[0041] Figure 5 This is the desulfurization rate curve graph at different times in Example 4 of the present invention.

[0042] Figure 6 This is the desulfurization rate curve graph at different times in Example 5 of the present invention.

[0043] Figure 7 This is the scanning electron microscope image of the desulfurization slag Detailed implementation manners

[0044] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the invention in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] Example 1

[0046] Crush and grind the solid by-product of conventional molten-state electric furnace method phosphoric acid to 75um, and detect its chemical composition, as shown in Table 1

[0047] Table 1 Chemical composition of the solid by-product of conventional molten-state electric furnace method phosphoric acid

[0048] Composition <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> MgO <![CDATA[P2O5]]> Content (%) 40.56 48.73 0.71 2.58 1.85 1.65

[0049] The chemical composition of wet-process phosphoric acid is shown in Table 2,

[0050] Table 2 Chemical composition of wet-process phosphoric acid

[0051] Composition <![CDATA[P2O5]]> <![CDATA[SO4 2- > CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> MgO Content (%) 25.13 2.18 0.17 0.68 0.83 0.63

[0052] Weigh 2.58 kg of the solid product of conventional molten-state electric furnace method phosphoric acid crushed and ground to 75um (the composition is as shown in Table 1). Add it to 100.00 kg of wet-process phosphoric acid (the composition is as shown in Table 2). The ratio R of the mass of calcium oxide in the solid by-product of thermal-process phosphoric acid to the mass of calcium sulfate in wet-process phosphoric acid is 0.58, the reaction temperature is 40°C, and the reaction time is controlled at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 h respectively. The desulfurization rate at different times is shown inFigure 2 。

[0053] From Figure 2 It can be seen that as time increases, the desulfurization rate increases, from 18.20% to 34.68%. At the same time, it is found in the experiment that after reacting for 3 h, about 1 kg of defluorinating agent can be added less in the subsequent treatment of 100.00 kg of phosphoric acid defluorination process, and the deposition time is reduced by 0.1 h.

[0054] After completing the desulfurization process under the optimal conditions (40 °C, R = 0.58, 3 h), the reaction precipitate is added to the hot-process phosphoric acid batching after filtration and washing, and then enters the planetary wheel mill for mixing. After mixing, the batching enters the disk granulation to make balls. After the balls are dried, they are used for the production of hot-process phosphoric acid. Control SiO2 / CaO (mass ratio) = 0.75, the percentage content of SO3 is 7.5%, the reaction temperature is 1500 °C, the reaction time is 0.5 h, and the phosphorus escape rate is 95.3%. Comparing with the phosphorus escape rate of molten phosphorus without desulfurization slag under this condition, it is 92.3%. The reason for the increase in the phosphorus escape rate may be that S and Fe are easier to form iron sulfide compounds relative to P and Fe, reducing the formation of iron phosphate compounds.

[0055] Example 2

[0056] Weigh 5.10 kg of the conventional molten-state electric furnace method phosphoric acid solid product crushed and ground to 75 μm (the composition is shown in Table 1), and add it to 100.00 kg of wet-process phosphoric acid (the composition is shown in Table 2). The ratio R of the mass of calcium oxide in the hot-process phosphoric acid solid by-product to the mass of calcium sulfate in the wet-process phosphoric acid is 1.14, the reaction temperature is 60 °C, the rotation speed is 80 rpm, and the reaction time is controlled at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h respectively. The desulfurization rates at different times are shown in Figure 3 。

[0057] From Figure 3 It can be seen that as time increases, the desulfurization rate increases, from 54.60% to 81.84%. At the same time, it is found in the experiment that after reacting for 3 h, about 1.2 kg of defluorinating agent can be added less in the subsequent treatment of 100.00 kg of phosphoric acid defluorination process, and the deposition time is reduced by 0.3 h.

[0058] After completing the desulfurization process under the optimal conditions (60 °C, R = 1.14, 3 h), the reaction precipitate is filtered, washed, ground and then added to the molten hot-process phosphoric acid batching, control SiO2 / CaO (mass ratio) = 0.85, the percentage content of SO3 is 7.5%, the reaction temperature is 1300 °C, the reaction time is 3 h, and the phosphorus escape rate is 92.6%. Comparing with the phosphorus escape rate of molten phosphorus without desulfurization slag under this condition, it is 89.2%.

[0059] Example 3

[0060] Weigh 7.65 kg of the solid product of conventional molten electric furnace process phosphoric acid crushed and ground to 75 μm (the composition is shown in Table 1), add it to 100.00 kg of wet-process phosphoric acid (the composition is shown in Table 2). The ratio R of the mass of calcium oxide in the solid by-product of thermal process phosphoric acid to the mass of calcium sulfate in wet-process phosphoric acid is 1.71. The reaction temperature is 60 °C, the rotation speed is 120 rpm, and the reaction time is controlled at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h respectively. The desulfurization rates at different times are shown in Figure 4 .

[0061] From Figure 4 It can be seen that as the time increases, the desulfurization rate increases, and the desulfurization rate increases from 60.06% to 87.39%. At the same time, it is found in the experiment that after reacting for 3 h, about 1.5 kg less defluorinating agent is added in the subsequent defluorination process of 100.00 kg of phosphoric acid, and the deposition time is reduced by 0.3 h.

[0062] After completing the desulfurization process under the optimal conditions (40 °C, R = 1.71, 3 h), the reaction precipitate is filtered, washed, and ground, and then added to the molten thermal process phosphoric acid batching. Control SiO2 / CaO (mass ratio) = 0.75, the percentage content of SO3 is 12.5%, the reaction temperature is 1400 °C, the reaction time is 2 h, and the phosphorus evolution rate is 94.4%. Comparing with the phosphorus evolution rate of molten phosphorus without desulfurization slag under this condition, it is 91.3%.

[0063] Example 4

[0064] Crush and grind the solid by-product of conventional molten electric furnace process phosphoric acid to 75 μm, (the composition is shown in Table 1), and the chemical composition of wet-process phosphoric acid is shown in Table 3.

[0065] Table 3 Chemical composition of wet-process phosphoric acid

[0066]

[0067]

[0068] Weigh 6.05 kg of the solid product of conventional molten electric furnace process phosphoric acid crushed and ground to 75 μm (the composition is shown in Table 1), add it to 100.00 kg of wet-process phosphoric acid (the composition is shown in Table 3). The ratio R of the mass of calcium oxide in the solid by-product of thermal process phosphoric acid to the mass of calcium sulfate in wet-process phosphoric acid is 1.14. The reaction temperature is 80 °C, the rotation speed is 80 rpm, and the reaction time is controlled at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h respectively. The desulfurization rates at different times are shown in Figure 5 .

[0069] From Figure 5It can be seen that with the increase of time, the desulfurization rate increases, from 74.62% to 95.71%. At the same time, it is found in the experiment that after 3 hours of reaction, about 1.8 kg of defluorinating agent can be added less during the subsequent defluorination process of 100.00 kg of phosphoric acid, and the deposition time is reduced by 0.5 h.

[0070] After completing the desulfurization process under the optimal conditions (80 °C, R = 1.14, 3 h), the reaction precipitate is filtered, washed, and ground, and then added to the non-molten thermal phosphoric acid batching. Control SiO2 / CaO (mass ratio) = 2.5, the SO3 percentage content is 12.5%, the reaction temperature is 1300 °C, and the reaction time is 0.5 h. The phosphorus escape rate is 89.7%. Compared with the phosphorus escape rate of molten phosphorus without desulfurization slag under this condition, it is 84.5%. Under the condition of non-molten thermal phosphoric acid, in addition to the competition between S and P to form compounds with iron, the reason for the increase in the phosphorus escape rate after adding desulfurization slag may also be related to the addition of desulfurization slag increasing the local liquid phase and accelerating the phosphorus escape rate.

[0071] Example 5

[0072] The solid by-products of non-molten kiln-process phosphoric acid are crushed and ground to 75 μm, and their chemical compositions are detected, as shown in Table 4. The chemical compositions of wet-process phosphoric acid are shown in Table 2.

[0073] Table 4 Chemical Compositions of Solid By-Products of Non-Molten Kiln-Process Phosphoric Acid

[0074] Composition <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> MgO <![CDATA[P2O5]]> Content (%) 69.17 23.11 2.56 2.38 0.45 2.80

[0075] Weigh 8.3 kg of the solid product of non-molten kiln-process phosphoric acid crushed and ground to 75 μm (the composition is shown in Table 4), and add it to 100.00 kg of wet-process phosphoric acid (the composition is shown in Table 3). The mass ratio R of calcium oxide in the solid by-product of thermal phosphoric acid to calcium sulfate in wet-process phosphoric acid is 0.88. The reaction temperature is 80 °C, the rotation speed is 120 rpm, and the reaction time is controlled at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h respectively. The desulfurization rates at different times are shown in Figure 6 .

[0076] From Figure 6 It can be seen that with the increase of time, the desulfurization rate increases, from 70.24% to 92.14%. At the same time, it is found in the experiment that after 3 hours of reaction, about 2.5 kg of defluorinating agent can be added less during the subsequent defluorination process of 100.00 kg of phosphoric acid, and the deposition time is reduced by 0.5 h.

[0077] After the desulfurization process is completed under the optimal conditions (80 °C, R = 0.88, 3 h), the reaction precipitate is filtered, washed, and ground, and then added to the non-molten thermal phosphoric acid formulation. Control SiO2 / CaO (mass ratio) = 3.0, the SO3 percentage content is 10.5%, the reaction temperature is 1400 °C, the reaction time is 1 h, and the phosphorus escape rate is 93.4%. Compared with the phosphorus escape rate of molten phosphorus without desulfurized slag under these conditions, it is 90.0%. The reaction precipitate after desulfurization is desulfurized slag, and its electron micrograph is as Figure 7 shown, which is a lap flake stacking structure, can accelerate the precipitation of solids in wet-process phosphoric acid, improve the liquid-solid separation intensity, increase the washing efficiency, and reduce the phosphorus content in the precipitate.

[0078] Although the present invention has been described herein with reference to a number of illustrative embodiments of the invention, it should be understood that those skilled in the art can devise many other modifications and embodiments that will fall within the scope of the disclosure of this application. More specifically, within the scope of the disclosure of this application, the drawings, and the claims, various deformations and improvements can be made to the component parts or the layout. In addition to the deformations and improvements to the component parts or the layout, other uses will also be apparent to those skilled in the art.

Claims

1. A method for comprehensive utilization of solid by-products of thermal phosphoric acid, characterized in that The steps are as follows: S1. Crush the solid by-product of thermal phosphoric acid to 50 - 75 μm; S2. Add the crushed solid by-product of thermal phosphoric acid into wet-process phosphoric acid to desulfurize the wet-process phosphoric acid; S3. Filter and wash the desulfurized wet-process phosphoric acid to obtain desulfurized slag; S4. Add the above-mentioned desulfurized slag into the thermal phosphoric acid feedstock and mix it in a planetary wheel mill. After mixing, the feedstock enters a disk granulator to form pellets. After drying the pellets, they are used for the production of thermal phosphoric acid; In step S2, the mass ratio of calcium oxide in the solid by-product of thermal phosphoric acid to the mass of calcium sulfate in wet-process phosphoric acid is 0.58 - 1.71, the desulfurization reaction temperature is 40 - 80 °C, and the reaction time is 0.5 - 3 h; the SiO₂ content in the solid by-product of thermal phosphoric acid is 40.5% - 69%, and the CaO content is 48.5% - 23%.

2. The method for comprehensive utilization of solid by-products of thermal process phosphoric acid according to claim 1, wherein: In step S4, the ground desulfurized slag is used for the feedstock of molten thermal phosphoric acid, and the SiO₂ / CaO in the feedstock system is controlled to be 0.75 - 0.85, the reaction temperature is 1300 - 1500 °C, and the reaction time is 0.5 - 3 h.

3. The method for comprehensive utilization of solid by-products of thermal-process phosphoric acid according to claim 1, wherein: In step S4, the ground desulfurized slag is used for the feedstock of non-molten thermal phosphoric acid, and the SiO₂ / CaO in the feedstock system is controlled to be 2.5 - 3.0, the reaction temperature is 1300 - 1400 °C, and the reaction time is 0.5 - 3 h.

4. A method for comprehensive utilization of solid by-products of thermal-process phosphoric acid according to claim 2 or 3, characterized in that: The SO₃ content in the thermal phosphoric acid feedstock is 7.5% - 12.5%.

5. A method for comprehensive utilization of solid by-products of thermal process phosphoric acid according to claim 1, characterized in that: The P2O5 content in the wet-process phosphoric acid is 25% to 40%, and the SO4 2- content is 2% to 2.6%.

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