Phosphoric acid production process

Abstract

The invention discloses a phosphoric acid production process which comprises the following steps: S1, mixing phosphoric acid and phosphorite in a reactor for reaction, and filtering and washing reaction liquid to obtain monocalcium phosphate filtrate; s2, the monocalcium phosphate filtrate enters a bipolar membrane electrodialyzer, the bipolar membrane electrodialyzer is formed by sequentially arranging a cation exchange membrane, an anion exchange membrane and a bipolar membrane, and an acid chamber, a salt chamber and an alkali chamber are formed respectively; the monocalcium phosphate is converted into phosphoric acid and calcium hydroxide under the action of the electrodialyzer. According to the method, phosphoric acid with relatively high purity can be directly prepared, and phosphogypsum is not generated. Compared with the traditional wet-process phosphoric acid, the produced solid waste amount is sharply reduced and is about one tenth to one twentieth of that of the traditional wet-process phosphoric acid, and the phosphoric acid is rich in silicon, magnesium, iron and the like and can be used as a fertilizer additive.

Description

Technical Field

[0001] The invention relates to a phosphoric acid production process and belongs to the technical field of phosphoric acid production. Background Art

[0002] Phosphoric acid is a basic chemical raw material widely used in the production of fertilizers and phosphates. There are two industrial methods for producing phosphoric acid. One is the thermal process, which involves burning yellow phosphorus in excess air and then hydrating it. While this process can produce high-purity phosphoric acid, it requires converting phosphate rock into yellow phosphorus, resulting in high energy consumption and significant pollution. The other is the wet process, which involves decomposing natural phosphate rock using sulfuric acid, nitric acid, or hydrochloric acid. Wet process phosphoric acid has mild reaction conditions, and the process using sulfuric acid as the raw material is the most basic method for wet process phosphoric acid production. The products of sulfuric acid decomposition of phosphate rock are phosphoric acid and calcium sulfate. Calcium sulfate exists in the acid hydrolysis slurry as crystals and has low solubility. Phosphoric acid can be separated from the acid hydrolysis slurry by vacuum filtration, a simple method that facilitates large-scale industrial production. However, wet process phosphoric acid production produces approximately 4.5 to 5 tons of phosphogypsum as a by-product for every ton of phosphoric acid produced. This phosphogypsum contains unwashed phosphoric acid and fluoride, making it difficult to handle and utilize in large quantities. Summary of the Invention

[0003] Based on the above, the present invention provides a phosphoric acid production process, which can not only produce phosphoric acid with high purity, but also significantly reduce the generation of solid waste, thereby achieving green and environmentally friendly phosphoric acid production.

[0004] The technical solution of the present invention is: a phosphoric acid production process, comprising: S1 reaction: Phosphoric acid and phosphate rock are mixed and reacted in a reactor, and the reaction solution is filtered and washed to obtain calcium dihydrogen phosphate filtrate; the specific reaction is as follows: Ca5F(PO4)3+ 7H3PO4=5 Ca(H2PO4)2+HF↑ S2 separation: the calcium dihydrogen phosphate filtrate enters a bipolar membrane electrodialyzer, wherein the bipolar membrane electrodialyzer is composed of a bipolar membrane, a cation exchange membrane, an anion exchange membrane and a bipolar membrane arranged in sequence, forming an acid chamber, a salt chamber and an alkali chamber respectively; Wherein, the calcium dihydrogen phosphate filtrate flows into the salt chamber, and the anion H2PO4 — The phosphoric acid solution is generated in the acid chamber through the anion exchange membrane. After a part of the phosphoric acid solution reaches a predetermined concentration, it returns to the reactor to decompose the phosphate rock, and a part of the phosphoric acid solution is used as the product. 2+ The calcium hydroxide solution is generated in the alkaline chamber through the cation exchange membrane; the dilute calcium dihydrogen phosphate solution in the salt chamber after the dialysis treatment is returned to the reaction solution in step S1 for re-filtration and washing.

[0005] Preferably, in step S1, the phosphate rock is phosphate rock powder or phosphate rock slurry.

[0006] Preferably, in step S1, the phosphoric acid is 1-90 parts by mass and the phosphate rock is 1-50 parts by mass; and the reaction is carried out at 0-200° C. for more than 5 minutes.

[0007] Preferably, in step S1, the fluorine-containing gas generated by the reaction is absorbed by water to produce fluorosilicic acid.

[0008] Preferably, the calcium hydroxide solution in the alkali chamber is drawn out and carbon dioxide is introduced to produce calcium carbonate.

[0009] Preferably, the calcium hydroxide solution in the alkali chamber is drawn out and sulfuric acid is introduced to produce calcium sulfate.

[0010] The present invention has the following beneficial effects: It can directly produce high-purity phosphoric acid without generating phosphogypsum. Compared with traditional wet-process phosphoric acid, the amount of solid waste generated is significantly reduced to approximately one-tenth to one-twentieth. Furthermore, the product, rich in silicon, magnesium, and iron, can be used as a fertilizer additive.

[0011] Specifically, the present invention first uses phosphoric acid to directly react with phosphate rock to produce monocalcium phosphate, rather than difficult-to-handle phosphogypsum, thereby avoiding the problem of using sulfuric acid to decompose phosphate rock in traditional wet-process phosphoric acid production and producing a large amount of phosphogypsum; wherein the monocalcium phosphate is separated into phosphoric acid and calcium hydroxide through a bipolar membrane electrodialyzer. This process does not require the addition of other chemical reagents, avoiding the introduction of new impurities, while ensuring that phosphoric acid and calcium hydroxide can be generated and collected in different chambers, avoiding mutual interference. At the same time, the electrodialysis process can produce phosphoric acid with higher purity, solving the problem of low purity of traditional wet-process phosphoric acid. In addition, part of the generated phosphoric acid is returned to the reactor for decomposition of phosphate rock, forming a closed circulation system, improving the utilization rate of phosphorus and reducing raw material consumption. In addition, the fluorine-containing gas generated by the reaction is absorbed by water to generate hydrofluoric acid or fluorosilicic acid; the calcium hydroxide generated in the alkali chamber is converted into valuable calcium carbonate or calcium sulfate products by reacting with carbon dioxide or sulfuric acid, realizing the resource utilization of by-products and further reducing the generation of waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a process flow chart for phosphoric acid production; Figure 2 This is the working diagram of the bipolar membrane electrodialysis unit. DETAILED DESCRIPTION

[0013] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0014] Example 1: 1) Add 10 parts phosphate rock powder and 90 parts 25% phosphoric acid to a reactor and mix thoroughly. Incubate at 30°C for at least 60 minutes, filter and wash, and absorb the gas into water to produce hydrofluoric acid. 2) The filtrate is passed through a bipolar membrane electrodialyzer, where it converts calcium dihydrogen phosphate into phosphoric acid and calcium hydroxide solutions. The phosphoric acid in the acid chamber is partially returned to the reactor to decompose the phosphate rock, while the remaining portion is used as the product. The calcium hydroxide solution in the alkali chamber is withdrawn and reacted with carbon dioxide, then enters a sedimentation tank. The supernatant is returned to the alkali chamber, and the calcium carbonate at the bottom is periodically scraped off and dried to produce the calcium carbonate product. Testing indicates a final phosphoric acid yield of 95.2%.

[0015] Example 2: 1) Add 20 parts phosphate rock, 1 part silica, and 79 parts 30% phosphoric acid to a reactor and mix thoroughly. Incubate at 80°C for at least 30 minutes, filter, and wash. The gas is absorbed by water to produce fluorosilicic acid. 2) The filtrate is passed through a bipolar membrane electrodialyzer, where calcium dihydrogen phosphate is converted into phosphoric acid and calcium hydroxide. The phosphoric acid in the acid chamber evaporates and concentrates to 30%, after which part is returned to the reactor to decompose the phosphate rock, and part is used as the product. The calcium hydroxide solution in the alkali chamber is drawn into a buffer tank, where it reacts with 98% sulfuric acid and then enters a sedimentation tank. The supernatant is returned to the alkali chamber, and the calcium sulfate at the bottom is periodically scraped and dried to produce the calcium sulfate product. Testing indicates a final phosphoric acid yield of 96.8%.

[0016] Example 3: 1) Add 30 parts of 30% phosphate slurry containing water and 70 parts of 35% phosphoric acid to the reactor and mix thoroughly under stirring. React at 60°C for more than 60 minutes, filter and wash, and absorb the gas into water to obtain fluorosilicic acid. 2) The filtrate is passed through a bipolar membrane electrodialyzer, where calcium dihydrogen phosphate is converted into phosphoric acid and calcium hydroxide. The phosphoric acid in the acid chamber evaporates and concentrates to 35%, after which a portion is returned to the reactor to decompose the phosphate rock, and a portion is used as the product. The calcium hydroxide solution in the alkali chamber is withdrawn and reacted with carbon dioxide, then passed into a sedimentation tank. The supernatant is returned to the alkali chamber, and the calcium carbonate at the bottom is periodically scraped and dried to produce the calcium carbonate product. Testing indicates a final phosphoric acid yield of 95.8%.

[0017] Example 4: 1) Add 20 parts of phosphate rock and 80 parts of 80% phosphoric acid to a reactor and mix thoroughly. Incubate at 90°C for at least 30 minutes, filter and wash, and absorb the gas into water to obtain fluorosilicic acid. 2) The filtrate is passed through a bipolar membrane electrodialyzer, where calcium dihydrogen phosphate is converted into phosphoric acid and calcium hydroxide. The phosphoric acid in the acid chamber is concentrated by evaporation to a concentration of 80%, after which part is returned to the reactor to decompose the phosphate rock, and part is used as the product. The calcium hydroxide solution in the alkali chamber is withdrawn and reacted with carbon dioxide, then passed into a sedimentation tank. The supernatant is returned to the alkali chamber, and the calcium carbonate at the bottom is periodically scraped and dried to produce the calcium carbonate product. Testing indicates a final phosphoric acid yield of 96.4%.

[0018] As can be seen, over 95% of the phosphorus in the phosphate rock is transferred to the phosphoric acid product, with less than 5% carried away by the slag. Compared with traditional wet-process phosphoric acid production, solid waste is reduced by over 90%, and fluorine is recovered as fluorosilicic acid, eliminating the problem of phosphogypsum accumulation. Furthermore, experiments have shown that the presence of a small amount of fluoride ions or fluorosilicate ions in the phosphoric acid after passing through the bipolar membrane does not affect the return of the phosphoric acid to the reactor to decompose the phosphate rock. The phosphoric acid produced by this method contains almost no other cations such as calcium, iron, aluminum, and magnesium after passing through the bipolar membrane, making it more advantageous for the production of food-grade phosphoric acid. The direct preparation of high-concentration phosphoric acid after passing through the bipolar membrane is limited by osmotic pressure, and evaporation and concentration are required to obtain high-concentration phosphoric acid.

[0019] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A phosphoric acid production process, characterized in that: include: S1 reaction: phosphoric acid and phosphate rock are mixed and reacted in a reactor, and the reaction solution is filtered and washed to obtain calcium dihydrogen phosphate filtrate; S2 separation: passing the calcium dihydrogen phosphate filtrate into a bipolar membrane electrodialyzer, wherein the bipolar membrane electrodialyzer is composed of a bipolar membrane, a cation exchange membrane, an anion exchange membrane and a bipolar membrane arranged in sequence to form an acid chamber, a salt chamber and an alkali chamber respectively; Wherein, the calcium dihydrogen phosphate filtrate flows into the salt chamber, and the anion H2PO4 — The phosphoric acid solution is generated in the acid chamber through the anion exchange membrane. After a part of the phosphoric acid solution reaches a predetermined concentration, it returns to the reactor to decompose the phosphate rock, and a part of the phosphoric acid solution is used as the product. 2+ The calcium hydroxide solution is generated in the alkaline chamber through the cation exchange membrane; the dilute calcium dihydrogen phosphate solution in the salt chamber after the dialysis treatment is returned to the reaction solution in step S1 for re-filtration and washing.

2. The phosphoric acid production process according to claim 1, characterized in that: In step S1, the phosphate rock is phosphate rock powder or phosphate rock slurry.

3. The phosphoric acid production process according to claim 2, characterized in that: In step S1, the amount of phosphoric acid is 1-90 parts by mass, and the amount of phosphate rock is 1-50 parts by mass; and the reaction is carried out at 0-200° C. for more than 5 minutes.

4. The phosphoric acid production process according to claim 1, characterized in that: In step S1, the fluorine-containing gas generated by the reaction is absorbed by water to produce fluorosilicic acid.

5. The phosphoric acid production process according to claim 1, characterized in that: The calcium hydroxide solution in the alkali chamber is drawn out and carbon dioxide is introduced to produce calcium carbonate.

6. The phosphoric acid production process according to claim 1, characterized in that: The calcium hydroxide solution in the alkali chamber is drawn out and sulfuric acid is introduced to produce calcium sulfate.

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