Method for producing ammonium dihydrogen phosphate by using phosphogypsum solid waste

Abstract

The application discloses a method for producing ammonium dihydrogen phosphate by using phosphogypsum solid waste. The method is characterized in that: firstly, a solution or solid of ammonium sulfate salt is prepared by using phosphogypsum and ammonium carbonate; then, phosphorite is mixed with the ammonium sulfate salt to perform a heating reaction, and a phosphorus-containing leaching solution and a phosphogypsum residue phase are obtained by water leaching; or, the phosphorite is added into a solution containing the ammonium sulfate salt to perform a heating reaction, and a phosphorus-containing leaching solution and a phosphogypsum residue phase are obtained by solid-liquid separation; the phosphorus-containing leaching solution is separated by cooling crystallization to obtain ammonium dihydrogen phosphate solid and a crystallization mother liquor, and the crystallization mother liquor is returned to be used for phosphorite decomposition reaction; the obtained phosphogypsum residue phase is reacted with ammonia water and carbon dioxide to obtain a calcium carbonate solid phase and an ammonium sulfate conversion solution, and the obtained ammonium sulfate conversion solution is returned to be used for phosphorite decomposition. The method effectively solves the problem of environmental pollution caused by phosphogypsum stacking, has low cost, and simultaneously produces high-value ammonium dihydrogen phosphate as a by-product, and provides a simple production process of ammonium dihydrogen phosphate.

Description

TECHNICAL FIELD

[0001] The application relates to a phosphogypsum solid waste treatment method, in particular to a method for producing ammonium dihydrogen phosphate by using phosphogypsum solid waste, and belongs to the field of phosphorus chemical industry. BACKGROUND

[0002] Phosphogypsum is a by-product produced in the process of wet-process phosphoric acid production. Although the main component of phosphogypsum is calcium sulfate, it also contains various impurities harmful to the environment. How to economically utilize phosphogypsum and make waste into treasure has become a worldwide problem. Since the industrialization of wet-process phosphoric acid, people have been researching the comprehensive utilization of phosphogypsum, including direct utilization of phosphogypsum after impurity removal and utilization of phosphogypsum after transformation by dissolution. At present, there are many phosphogypsum treatment technologies, but most of these technologies do not produce economic benefits after phosphogypsum treatment. At present, there are hundreds of millions of tons of phosphogypsum stored in the world. The environmental pollution caused by the storage of phosphogypsum has become a problem to be solved in the phosphorus chemical industry.

[0003] Ammonium dihydrogen phosphate, also known as monoammonium phosphate, is widely used as a fire retardant for wood, paper and fabric, and is also used in pharmaceuticals, food additives and ruminant feed additives. Ammonium dihydrogen phosphate is divided into food additive ammonium dihydrogen phosphate and industrial monoammonium phosphate. In addition to ammonium dihydrogen phosphate, industrial monoammonium phosphate also contains a large amount of other impurities. Only food additive ammonium dihydrogen phosphate can be used in the pharmaceutical, food processing and animal feed production industries. The production method of ammonium dihydrogen phosphate is mainly neutralization, that is, using ammonia or ammonium to neutralize phosphoric acid. The raw material phosphoric acid has two types, hot-process phosphoric acid and wet-process phosphoric acid. The production process of hot-process ammonium dihydrogen phosphate is as follows: first, hot-process phosphoric acid is obtained by burning yellow phosphorus in water; then, ammonia is introduced or ammonium bicarbonate is added to neutralize the phosphoric acid to a pH of 4.2-4.6; cooling and crystallization are performed; and filtration and drying are performed to obtain the ammonium dihydrogen phosphate product. The advantages of hot-process ammonium dihydrogen phosphate are mature process, less equipment investment and good product quality. The biggest defect is high energy consumption, high pollution and high production cost. The production process of wet-process ammonium dihydrogen phosphate is as follows: first, leaching is performed on the ore slurry by using sulfuric acid to prepare leaching phosphoric acid; then, the qualified phosphoric acid is neutralized by adding ammonia or ammonium bicarbonate to a pH of 4.2-4.6; cooling and crystallization are performed; and filtration and drying are performed to obtain the ammonium dihydrogen phosphate product. As can be seen, the production process of wet-process ammonium dihydrogen phosphate is long and complex, and the most critical point is that the purification technology of wet-process phosphoric acid is not mature at present. For this reason, some people also use ammonia to decompose high-purity phosphoric acid urea to prepare ammonium dihydrogen phosphate, but the raw material cost of high-purity phosphoric acid urea is also not low. In summary, the production technology of existing high-quality ammonium dihydrogen phosphate generally has the problem of high production cost.

[0004] For the production of industrial monoammonium phosphate, the phosphorus chemical industry enterprises basically use the production process of phosphorite sulfuric acid decomposition, decomposition liquid desulfurization, ammonia neutralization, slurry filtration impurity removal, filtrate concentration, crystallization, liquid-solid separation, drying and packaging. The decomposition liquid is purified to remove solid suspensions, SO3 and other impurities, and then reacts with ammonia to produce a slurry with a relative density of 1.2-1.24 and a pH of 3.9-4.2. The impurities precipitated are removed by filtration to obtain refined liquid with a relative density of 1.18-1.2. The refined liquid is concentrated by evaporation to obtain concentrated liquid with a relative density of 1.38-1.4. After cooling crystallization, solid-liquid separation, fluidized drying, cooling and packaging, the industrial monoammonium phosphate product is obtained. The solution obtained by phosphorite sulfuric acid decomposition is usually crude phosphoric acid with P2O5 of 22-25 w%, which contains solid phase, Fe, Al, Mg, Ca, SO3, F, SiO2, K, Na and other impurities. The crude phosphoric acid is desulfurized by using calcium carbonate, sodium carbonate, barium carbonate and other purifying agents, which will bring Ca 2﹢ , Na ﹢ ions, affecting the crystal content and shape. If ore slurry is used as a desulfurizer, the desulfurization cannot be too deep, and 5-12 g / L of SO3 must be left in the liquid after desulfurization, otherwise too much Ca 2﹢ ion will be brought in, affecting the crystal shape and causing equipment and pipeline scaling. Therefore, the decomposition liquid ore slurry needs to be desulfurized again with a purifying agent after desulfurization. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for clean production of ammonium dihydrogen phosphate by using phosphogypsum solid waste. The method is simple, low in cost, green and environmentally friendly, and can effectively solve the problem of low phosphogypsum solid waste treatment efficiency.

[0006] In order to achieve the above technical purpose, the present application provides a method for clean production of ammonium dihydrogen phosphate by using phosphogypsum solid waste. The method is to mix and heat phosphorite and ammonium sulfate salt for decomposition reaction I, and the obtained decomposition solid product is leached with water to obtain a phosphorus-containing leaching liquid and a phosphogypsum residue phase; or mix and heat phosphorite and a solution containing ammonium sulfate salt for decomposition reaction II, and solid-liquid separation to obtain a phosphorus-containing leaching liquid and a phosphogypsum residue phase; the phosphorus-containing leaching liquid is separated by cooling crystallization to obtain ammonium dihydrogen phosphate solid and crystallization mother liquor, and the crystallization mother liquor is returned to the phosphorite decomposition reaction; the phosphogypsum residue phase is converted by reaction with ammonia and carbon dioxide to obtain calcium carbonate solid phase and ammonium sulfate conversion liquid, and the ammonium sulfate conversion liquid is returned to the phosphorite decomposition reaction.

[0007] As a preferred scheme, the ammonium sulfate salt includes ammonium sulfate and / or ammonium bisulfate.

[0008] As a preferred solution, the carbon dioxide is replaced by ammonium bicarbonate.

[0009] As a preferred solution, the crystallization mother liquor is used to configure a solution containing ammonium sulfate salt.

[0010] As a preferred solution, the ammonium sulfate conversion solution is used to configure a solution containing ammonium sulfate salt, or ammonium sulfate is obtained by concentration crystallization. The ammonium sulfate obtained by concentration crystallization can be directly used for the decomposition reaction of phosphorite.

[0011] The present application makes full use of phosphogypsum through the recycling of ammonium sulfate, and the reaction process principle involved is as follows:

[0012] Ca5F(PO4)3 + 5(NH4)2SO4 + 5 n H2O =Δ= 3NH4H2PO4 + 5CaSO4· n H2O + HF↑ +7NH3↑ (1)

[0013] Ca5F(PO4)3 + 5(NH4)2SO4 + 5 n H2O + a H3PO4 =Δ= (3+ a )NH4H2PO4 + 5CaSO4· n H2O+ HF↑ + (7- a )NH3↑,0 < a ≤ 5 (2)

[0014] Ca5F(PO4)3 + (5- b )(NH4)2SO4 + 5 n H2O + b H2SO4 =Δ= 3NH4H2PO4 + 5CaSO4· n H2O+ HF↑ + (2×(5- b )-3)NH3↑,0 < b ≤ 3 (3)

[0015] CaSO4· n H2O + CO2 + 2NH3 = CaCO3 + (NH4)2SO4 + ( n -1)H2O (4)

[0016] (NH4)2SO4 =Δ= NH4HSO4 + NH3↑ (5)

[0017] Ca5F(PO4)3 + 5(NH4HSO4 + 5 n H2O =Δ= 3NH4H2PO4 + 5CaSO4· n H2O + HF↑+ 2 NH3↑ (6)

[0018] Wherein, the gas containing NH3 and HF generated in the process of decomposition of phosphate rock, after step-by-step condensation, ammonium fluoride crystals and ammonia gas or ammonia water can be obtained. In addition, the production of ammonia can also significantly reduce the corrosion of HF gas on the equipment, and further simplify the configuration of the phosphate rock decomposition equipment and the post-processing process of phosphogypsum, and improve the recovery rate of phosphorus and fluorine.

[0019] From the above reaction principle, it can be seen that the ammonium sulfate salt is not only a decomposition agent of phosphate rock in the process, but also a purifying agent of phosphogypsum and a salting-out agent for ammonium dihydrogen phosphate crystallization. In the solution containing ammonium sulfate salt, the addition of phosphate rock powder and heating and stirring can not only promote the decomposition of apatite and directly convert it into ammonium dihydrogen phosphate, but also prevent the entrainment and precipitation of calcium dihydrogen phosphate during the formation of calcium sulfate, and also reduce the solubility of ammonium dihydrogen phosphate in the decomposition solution, so as to facilitate its separation and recovery. In addition, the ammonia generated by the decomposition of ammonium sulfate can increase the pH of the solution, which is helpful for the precipitation and precipitation of impurities such as Fe and Al:

[0020] Fe 3+ + NH4H2PO4 + 2NH3 = 3NH4 + + FePO4↓ (7)

[0021] Al 3+ + NH4H2PO4 + 2NH3 = 3NH4 + + AlPO4↓ (8)

[0022] The ammonium sulfate or ammonium bisulfate used in the present application can be purchased or produced by comprehensive utilization of phosphogypsum in the process itself.

[0023] As a preferred scheme, the molar ratio of Ca element in the phosphate rock to S element in the ammonium sulfate is 1:1-3.

[0024] As a preferred scheme, the conditions of the decomposition reaction I are that the temperature is 150-420℃, and the time is 1-3h.

[0025] As a preferred scheme, the particle size of the phosphate rock is ≤297μm.

[0026] As a preferred scheme, the solid-liquid ratio of the phosphate rock to the solution containing ammonium sulfate salt is 1g:1-6mL.

[0027] As a preferred solution, the concentration of the ammonium sulfate salt in the solution containing the ammonium sulfate salt is 100-800 g / L.

[0028] As a preferred solution, the solution containing the ammonium sulfate salt further comprises phosphoric acid and / or sulfuric acid, the molar amount of the phosphoric acid is not more than the ammonium sulfate salt, and the molar amount of the sulfuric acid is not more than 1.5 times the molar amount of the ammonium sulfate salt.

[0029] As a preferred solution, the conditions of the decomposition reaction II are as follows: the temperature is 95-195℃, and the time is 0.5-2.5 h.

[0030] As a preferred solution, the phosphorus-containing leaching solution is subjected to purification and impurity removal treatment by crystallization to remove fluorine and adjust pH, and then is subjected to cooling crystallization treatment.

[0031] As a preferred solution, the purification and impurity removal treatment process is as follows: the phosphorus-containing leaching solution is mixed with a potassium salt or a sodium salt according to a molar ratio of Si element / K (Na) element in the phosphorus-containing leaching solution of 1:2-3, and is subjected to crystallization to remove fluorine at-25-85℃ for 1-8 h, to obtain potassium fluosilicate or sodium fluosilicate crystals and a fluorine removal solution through solid-liquid separation; the fluorine removal solution is adjusted to a pH of 4.5-5.5 by ammonia or ammonium bicarbonate, and is subjected to solid-liquid separation to obtain a purified phosphorus-containing solution and a purification residue phase.

[0032] As a preferred solution, the potassium salt comprises at least one of potassium chloride, potassium carbonate, potassium bicarbonate, potassium phosphate, dipotassium phosphate, and monopotassium phosphate.

[0033] As a preferred solution, the sodium salt comprises at least one of sodium chloride, sodium carbonate, sodium bicarbonate, sodium phosphate, disodium phosphate, and monosodium phosphate.

[0034] As a preferred solution, the purified phosphorus-containing solution is adjusted to a pH of 2.5-4.6 by phosphoric acid and / or sulfuric acid, and then is subjected to cooling crystallization to separate ammonium phosphate solid and a crystallization mother liquor; or the purified phosphorus-containing solution is supplemented with ammonium sulfate and adjusted to a (NH4)2SO4 concentration of 70-700 g / L, and then is subjected to cooling crystallization to separate ammonium phosphate solid and a crystallization mother liquor. The crystallization mother liquor is returned to be used for the decomposition reaction of the phosphate rock.

[0035] As a preferred solution, the purification residue phase is mixed with a sulfuric acid-containing solution according to a solid-liquid ratio of 1 g:1-10 mL, and is subjected to solid-liquid separation to obtain a treatment solution and a treatment residue, the treatment solution is returned to be used for preparation of the sulfuric acid-containing solution or for the decomposition reaction of the phosphate rock, and the treatment residue is subjected to recycling and comprehensive utilization. The concentration of sulfuric acid in the sulfuric acid-containing solution is ≥1500 g / L. In this process, the phosphates of Fe, Al, etc. in the solution system are converted into anhydrous sulfate salt precipitates.

[0036] As a preferred scheme, the ammonium dihydrogen phosphate solid is purified by washing or recrystallization with a saturated ammonium dihydrogen phosphate solution to obtain refined ammonium dihydrogen phosphate. GB25569- 2010 The refined ammonium dihydrogen phosphate meets the quality standard of the specified food additive ammonium dihydrogen phosphate.

[0037] As a preferred scheme, the purification process is that the ammonium dihydrogen phosphate solid is added into a saturated ammonium dihydrogen phosphate solution for stirring and washing or recrystallization, the pH of the solution is adjusted to 2.5-4.6, and solid-liquid separation is performed to obtain refined ammonium dihydrogen phosphate and a post-refining solution; the post-refining solution is returned for preparation of the saturated ammonium dihydrogen phosphate solution.

[0038] As a preferred scheme, when the content of the impurities including Ca and F in the post-refining solution is ≤ the upper limit of the national quality standard of the ammonium dihydrogen phosphate product, ammonium sulfate is added into the post-refining solution, the concentration of ammonium sulfate in the solution is adjusted to 250-500 g / L, and solid-liquid separation is performed to obtain ammonium dihydrogen phosphate solid and a salting-out mother liquor; the salting-out mother liquor is returned for the decomposition reaction of the phosphate rock.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] (1) The ammonium sulfate salt obtained by comprehensive utilization of the phosphogypsum produced in the process itself is used as a decomposition agent of the phosphate rock, which promotes the direct conversion of the phosphate rock into ammonium dihydrogen phosphate, effectively solves the problems of environmental pollution and low utilization rate of the phosphogypsum, and at the same time, the high-value ammonium dihydrogen phosphate product is prepared, a simplified production process of ammonium dihydrogen phosphate is provided, and the maximum utilization of resources is realized.

[0041] (2) The method is simple, low in cost, green and environment-friendly, does not produce secondary pollution, and is suitable for industrial scale production. DETAILED DESCRIPTION

[0042] The present application will be further described below in combination with examples, and the following examples are intended to illustrate the present application rather than further limit the present application.

[0043] Example 1

[0044] Take 500g of phosphate rock powder with P2O5 content of 32.58% and CaO content of 50.26% in -350 mesh, grind and mix with ammonium sulfate according to Ca / S molar ratio of 1:1.9, put into a muffle furnace at 320℃ for 1.5h, add water to the obtained calcined sand according to solid-liquid ratio of 1g:4mL, heat to 95℃, stir and leach, filter while hot to obtain filter residue (phosphogypsum) and filtrate. Cool the filtrate to crystallize, filter to obtain coarse crystalline material and its crystallization mother liquor, recrystallize the coarse crystalline material with saturated ammonium dihydrogen phosphate solution, dry the obtained recrystallized material to obtain ammonium dihydrogen phosphate with purity of 99.6% meeting the quality requirements of food additives specified in GB25569-2010. Wash the obtained phosphogypsum, add ammonia water, pass CO2 and maintain the pH of the solution at ≥7.5 with ammonia, stir at room temperature for 1h, filter to obtain transformation residue and transformation liquid. Evaporate and concentrate the transformation liquid to crystallize, filter to obtain ammonium sulfate crystals 516.3g; dry the transformation residue and take sample analysis, which contains Ca: 35.81%, S: 1.37%, P: 0.67%, F: 0.09%.

[0045] Example 2

[0046] Take 250g of phosphate rock powder with P2O5 content of 29.76% and CaO content of 48.37% in -100 mesh, add the crystallization mother liquor obtained in Example 1, and add ammonium sulfate obtained in Example 1 according to Ca / S molar ratio of 1:1.1, while adding 25mL of phosphoric acid (85%), heat and stir, and the slurry boils (107~135℃) for 2h, the steam generated in the reaction is stepwise condensed to obtain ammonium fluoride crystals and ammonia water. Filter the filtrate and phosphogypsum while hot after the reaction is completed, wash and dry the phosphogypsum to take sample analysis, which contains Ca: 22.13%, S: 16.06%, P: 0.81%, F: 0.11%; first add potassium carbonate to the filtrate according to Si / K molar ratio of 1:1.2, crystallize while hot to remove fluorine, then add ammonia to adjust the pH to 5.4 to purify and remove impurities, and then solid-liquid separation to obtain purified liquid and purification residue, then add phosphoric acid to the purified liquid to adjust the pH to 4.5, cool and crystallize, filter to obtain coarse crystalline material and its crystallization mother liquor, recrystallize the obtained coarse crystalline material with the recrystallization solution used in Example 1, and dry the obtained recrystallized material to obtain ammonium dihydrogen phosphate with purity of 99.7% meeting the quality requirements of food additives specified in GB25569-2010. Wash the obtained phosphogypsum, add ammonia water, and add ammonium bicarbonate according to Ca / C molar ratio of 1:1.2 at room temperature to stir and transform, filter to obtain transformation residue and transformation liquid. Evaporate and concentrate the transformation liquid to crystallize to obtain ammonium sulfate crystals.

[0047] Example 3

[0048] Take 250g of phosphate rock powder with P2O5 content of 30.61% and CaO content of 49.15%, add 250mL of water, and add ammonium bisulfate produced by pyrolysis of ammonium sulfate according to the Ca / S molar ratio of 1:2.5, heat and stir, and boil the slurry for 1h, then filter while hot to obtain filtrate and phosphogypsum. Wash and dry the phosphogypsum, and analyze the sample, which contains Ca: 22.89%, S: 16.87%, P: 0.76%, and F: 0.13%; cool and crystallize the filtrate, filter to obtain monoammonium phosphate crystals and their crystallization mother liquor, and dry the obtained monoammonium phosphate crystals, of which the total nutrient content (N+P2O5) is 72.51%, meeting the quality requirements of monoammonium phosphate fertilizer specified in GB10205-2009. Add ammonia water to the obtained phosphogypsum after washing, and transform it into a transformation liquid containing ammonium sulfate by stirring under CO2 for standby use. The monoammonium phosphate is impure diammonium phosphate used as a chemical fertilizer.

Claims

1. A method for clean production of ammonium dihydrogen phosphate by using phosphogypsum solid waste, characterized in that: The phosphate ore is mixed with an ammonium sulfate salt and heated to perform a decomposition reaction, and the obtained decomposition solid product is subjected to water leaching to obtain a phosphorus-containing leaching solution and a phosphogypsum residue phase; the phosphorus-containing leaching solution is subjected to cooling crystallization to separate ammonium dihydrogen phosphate solid and a crystallization mother liquor, and the crystallization mother liquor is returned to the phosphate ore decomposition reaction; the phosphogypsum residue phase is converted by reaction with ammonia and carbon dioxide to obtain a calcium carbonate solid phase and an ammonium sulfate conversion liquid, and the ammonium sulfate conversion liquid is returned to the phosphate ore decomposition reaction. ​ The molar ratio of Ca in the phosphate ore to S in the ammonium sulfate salt is 1:1-3. The decomposition reaction is performed at a temperature of 150-420°C for 1-3 hours.

2. The method for clean production of ammonium dihydrogen phosphate by phosphogypsum solid waste according to claim 1, characterized in that: The phosphorus-containing leaching solution is subjected to fluorine removal by crystallization and impurity removal by pH adjustment, and then is subjected to cooling crystallization.

3. The method for clean production of ammonium dihydrogen phosphate by phosphogypsum solid waste according to claim 2, characterized in that: The purification and impurity removal process is as follows: the phosphorus-containing leaching solution is mixed with a potassium salt or a sodium salt at a molar ratio of Si / K or Na in the phosphorus-containing leaching solution of 1:2-3, and is subjected to fluorine removal by crystallization at -25-85°C for 1-8 hours to obtain potassium fluorosilicate or sodium fluorosilicate crystals and a fluorine removal solution; the fluorine removal solution is adjusted to a pH of 4.5-5.5 by adding ammonia or ammonium bicarbonate, and is subjected to solid-liquid separation to obtain a purified phosphorus-containing solution and a purification residue phase.

4. The method according to claim 3, characterized in that: The potassium salt includes at least one of potassium chloride, potassium carbonate, potassium bicarbonate, potassium phosphate, dipotassium phosphate, and monopotassium phosphate. The sodium salt includes at least one of sodium chloride, sodium carbonate, sodium bicarbonate, sodium phosphate, disodium phosphate, and monosodium phosphate.

5. The method for cleaning production of ammonium dihydrogen phosphate by using phosphogypsum solid waste according to claim 3 or 4, characterized in that: The purification residue phase is mixed with a sulfuric acid-containing solution at a solid-liquid ratio of 1g:1-10mL, and is subjected to solid-liquid separation to obtain a treatment solution and a treatment residue, wherein the treatment solution is returned to preparation of the sulfuric acid-containing solution or to the phosphate ore decomposition reaction, and the treatment residue is subjected to recycling and comprehensive utilization.

6. The method for clean production of ammonium dihydrogen phosphate by phosphogypsum solid waste according to claim 1, characterized in that: The ammonium dihydrogen phosphate solid is washed with a saturated ammonium dihydrogen phosphate solution or is subjected to recrystallization to obtain refined ammonium dihydrogen phosphate.

7. The method for clean production of ammonium dihydrogen phosphate by phosphogypsum solid waste according to claim 6, characterized in that: The purification process is as follows: the ammonium dihydrogen phosphate solid is added to a saturated ammonium dihydrogen phosphate solution and is subjected to stirring washing or recrystallization, and the pH of the solution is adjusted to 2.5-4.6, and then the solution is subjected to solid-liquid separation to obtain refined ammonium dihydrogen phosphate and a post-refinement solution; the post-refinement solution is returned to preparation of the saturated ammonium dihydrogen phosphate solution.

8. The method for cleaning production of ammonium dihydrogen phosphate by phosphogypsum solid waste according to claim 7, characterized in that: When the impurity content of Ca and F in the post-refinement solution is ≤the upper limit of the national quality standard GB25569-2010 for ammonium dihydrogen phosphate products, ammonium sulfate salt is added to the post-refinement solution, and the concentration of the ammonium sulfate salt in the solution is adjusted to 250-500g / L, and then the solution is subjected to solid-liquid separation to obtain ammonium dihydrogen phosphate solid and a salting-out mother liquor; the salting-out mother liquor is returned to the phosphate ore decomposition reaction.