A method for preparing potassium nitrate from potassium fluorosilicate

Abstract

The invention discloses a method for preparing potassium nitrate from potassium fluorosilicate, comprising: using potassium-containing nitric acid insolubles obtained by filtering after reacting Hanyuan potassium phosphate ore with nitric acid, nitric acid and fluorosilicic acid as raw materials for acidolysis reaction; mixing potassium fluorosilicate crystals precipitated after cooling the acid leaching solution I with nitric acid for pyrolysis and evaporating excess nitric acid to obtain potassium nitrate; pyrolysis-generated gas SiF4 and evaporated nitric acid are heated and absorbed by water to obtain a mixed solution of fluorosilicic acid, white carbon black and nitric acid; the obtained mixed absorption solution can be repeatedly used for acidolysis reaction. After separating potassium fluorosilicate, the remaining acid leaching solution II is rich in nitric acid and fluorosilicic acid, and most of the nitric acid and fluorosilicic acid can be recovered by evaporation and concentration, and the recovered acid can be recycled for acidolysis reaction. The method of the invention can not only obtain high-purity potassium nitrate with high potassium recovery rate, but also realize the recycling of fluorosilicic acid and nitric acid, reduce process costs, and realize harmless treatment of fluoride, solving the problem of utilization of potassium fluorosilicate.

Description

Technical Field

[0001] The invention belongs to the intersecting field of hydrometallurgy and chemical industry, and specifically relates to a method for preparing potassium nitrate from potassium fluorosilicate. Background Art

[0002] my country's soluble potassium resources are in short supply, accounting for only 1.74% of the world's proven potassium salt reserves. On the other hand, my country's insoluble potassium resources, mainly potassium feldspar, are very rich and widely distributed. Sichuan Hanyuan has 2 billion tons of phosphorus-potassium composite ore, which generally contains 10% to 20% P2O5 (collophane) and 3 to 7% K2O (potassium feldspar, containing insoluble potassium). However, it is precisely because of the coexistence of phosphorus and potassium that there is currently no mature Hanyuan phosphorus-potassium ore utilization process. For this reason, phosphorus-potassium ore has been regarded as a "dumb ore" and has not been mined and utilized for many years. Developing phosphorus-potassium ore resource utilization technology and realizing large-scale and engineering utilization of phosphorus-potassium ore are of great practical significance for revitalizing phosphorus-potassium ore resources.

[0003] The patent with publication number CN102001691A discloses a process for producing potassium nitrate by decomposing potassium feldspar at low temperature with fluorine-containing acid. Potassium fluorosilicate obtained by decomposing potassium feldspar is separated by alkaline hydrolysis with KOH at 60-100°C to obtain KF solution and SiO2. After the mass concentration of KF is increased to 30-40%, it can be reacted with Ca(NO3)2 to separate CaF2 and potassium nitrate products. The production process solves the technical problems of high energy consumption, low output and low recovery rate in the prior art. However, the process flow of this method is relatively long, and a large amount of fluorine-containing acid is used. The high temperature makes it easy for the fluorine-containing acid to volatilize and pollute the environment.

[0004] In view of the above defects, it is necessary to provide a potassium feldspar treatment method with a simpler process and less pollution. Summary of the invention

[0005] The technical problem solved by the present invention is to provide a method for preparing potassium nitrate from potassium fluorosilicate. The method can convert insoluble potassium feldspar into soluble potassium nitrate, solve the problem of environmental pollution caused by fluoride, and realize the recycling of the used fluorosilicic acid and nitric acid, greatly reduce the production cost, and realize the maximum resource utilization. The process flow is efficient and concise, expands the scope of potassium fluorosilicate treatment methods and potassium nitrate preparation, and utilizes the principle of low solubility of potassium fluorosilicate in cold water. The potassium fluorosilicate reacts with nitric acid to obtain soluble potassium nitrate, which has the advantages of being green, low-carbon and environmentally friendly and has great social and economic value.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing potassium nitrate from potassium fluorosilicate comprises the following steps:

[0008] S1: The potassium-containing nitric acid insolubles obtained by filtering the phosphate potassium ore after reacting with nitric acid are used as raw materials, nitric acid and fluosilicic acid are added for acid hydrolysis, and the obtained solid-liquid mixture is filtered and washed while hot to obtain acid leaching solution I and leaching residue. The reaction equation is as follows:

[0009] K2O·Al2O3·6SiO2+8HNO3+12H2SiF6=2KNO3+2Al(NO3)3+18SiF4↑+16H2O

[0010] S2: The above acid leaching solution I is allowed to stand and naturally cool and crystallize, so that potassium fluorosilicate is supersaturated and precipitated, and the acid leaching solution II and potassium fluorosilicate are obtained by filtration. The reaction equation is as follows:

[0011]

[0012] S3: Mix the potassium fluorosilicate crystals with nitric acid, heat and stir to perform a pyrolysis reaction, evaporate the excess nitric acid, distill the raw material until crystals appear, cool, and filter to obtain a potassium nitrate product. The reaction equation is as follows:

[0013] K2SiF6+2HNO3=2KNO3+H2SiF6

[0014] The H2SiF6 generated above decomposes into gaseous HF and SiF4 after heating, causing the reaction to continue to the right to generate potassium nitrate. The reaction equation is as follows:

[0015] H2SiF6=2HF↑+SiF4↑

[0016] S4: During the reaction process of S3, hot water is used to absorb the distilled nitric acid and the gas generated by the reaction, and the water absorption liquid is filtered to obtain white crystals. The filtered absorption liquid can be reused in the acid hydrolysis reaction process of step S1. The main components of the water absorption liquid are H2SiF6, HF and white SiO2 crystals, and the main components of the filtered absorption liquid are H2SiF6 and HF. The reaction equation of the hot water absorption process is as follows:

[0017] 3SiF4+4H2O=2H2SiF6+SiO2·2H2O

[0018] S5: The acid leaching solution II obtained in S2 is evaporated and concentrated to recover most of the nitric acid and fluorosilicic acid remaining from the acidolysis reaction. The recovered acid can be recycled for use in the acidolysis reaction.

[0019] S6: The mother liquor evaporated and concentrated in S5 is diluted and separated into a monovalent liquid and a high-valent liquid using a nanofiltration membrane. The monovalent liquid can be evaporated, concentrated, and frozen and crystallized to obtain potassium nitrate, while the high-valent liquid can be used for the subsequent preparation of aluminum nitrate.

[0020] Preferably in the present invention, the chemical composition of the potassium nitric acid insoluble matter includes: P2O 50-2.5wt%, K2O 6.0-12.0wt%, CaO 0-7.0wt%, MgO 0-2.0wt%, Al2O3 8.0-25.0wt%, Fe2O3 0-6.0wt%, SiO2 25.0-75.0wt%, and F 0-5.0wt%.

[0021] Preferably, in step S1, the amount of fluorosilicic acid added is 80-100% of the theoretical amount (molar amount) of fluorosilicic acid required for the reaction, the amount of nitric acid added is 150-250% of the theoretical amount (molar amount) of nitric acid required for the reaction, the concentration of fluorosilicic acid is 30-32%, the concentration of nitric acid is 40-60%, the reaction time is 4-8h, and the reaction temperature is 80-95°C.

[0022] In the acid hydrolysis reaction, the main component of potassium nitric acid insoluble matter is potassium feldspar, which has extremely stable chemical properties and is hardly decomposed by acid or alkali at room temperature and pressure. Fluorosilicic acid can destroy its chemical structure, and nitric acid can provide anions for generating metal salts. The above preferred parameters can destroy the structure of the insoluble potassium salt potassium feldspar and leach K and Al.

[0023] Preferably, in step S2, the acid leaching solution I is left to stand for 12 to 24 hours and cooled to a temperature of 10 to 30°C. A high temperature will cause other metal ions to enter the potassium fluorosilicate crystals, and a low temperature will result in a limited amount of potassium fluorosilicate crystals precipitated. Under this preferred embodiment, part of K can be separated from other metal ions (such as Al, Fe, etc.) to obtain potassium fluorosilicate crystals with higher purity.

[0024] Preferably, in step S3, the liquid-solid mass ratio of the nitric acid to the potassium fluorosilicate crystals is (10-20): 1, the nitric acid concentration is 40-60%, the reaction temperature is 70-90°C, the reaction time is 2-4h, and the reaction is cooled to a temperature of 0-30°C after completion. If insufficient nitric acid is added, potassium fluorosilicate cannot be completely decomposed, and excessive nitric acid is added, resulting in an increase in the cost of recovering nitric acid; an increase in the reaction temperature can promote the reaction to the right, but too high a temperature will accelerate the distillation rate of nitric acid, resulting in a decrease in the nitric acid content in the reaction solution. Under this preferred embodiment, the sparingly soluble potassium salt potassium fluorosilicate can be converted into a soluble potassium salt potassium nitrate.

[0025] Preferably, in step S4, the temperature of the absorption liquid is 45-65°C. Too high a temperature will cause the generated fluorosilicic acid to decompose, and too low a temperature will cause the reaction rate of SiF4 and water to decrease. Under this preferred embodiment, the SiF4 gas generated by the decomposition of the distilled nitric acid and fluorosilicic acid can be repeatedly used for acid decomposition of potassium feldspar after reaching a certain concentration, and white carbon black is produced as a by-product.

[0026] Preferably, in step S5, the acid leaching solution II obtained in S2 is heated to 70-90°C for vacuum evaporation and concentration, and the heating is stopped when solid begins to precipitate. The evaporated acid solution can be condensed to recover most of the nitric acid and fluorosilicic acid remaining in the acidolysis reaction. If the heating temperature is too high, the fluorosilicic acid remaining in the reaction will decompose, and if the temperature is too low, the distillation rate will decrease.

[0027] Preferably, in step S6, the mother liquor evaporated and concentrated in S5 is diluted to a total concentration of high-valent metal ions of 15 to 25 g / L, and a monovalent liquid mainly containing K is obtained by nanofiltration. + , while the high-valent solution mainly contains Al 3+ The monovalent liquid is evaporated and concentrated to a K concentration of 90-110 g / L, and potassium nitrate crystals can be obtained by freezing and crystallizing at -8-3°C for 1-2 hours.

[0028] The above technical solution provided by the present invention at least brings the following beneficial effects:

[0029] The method of the invention uses low-grade potassium phosphate ore, nitric acid and fluorosilicic acid as raw materials, cooperates with specific processing steps, specifically performs acid dissolution reaction under normal pressure conditions and separates potassium and other impurity metals through the properties of potassium fluorosilicate. The obtained potassium fluorosilicate is then reacted with nitric acid to obtain a potassium nitrate product with higher purity. The absorption liquid of the gas generated by the reaction can be recycled, and the potassium recovery rate is high.

[0030] The method of the present invention can prepare potassium nitrate with high purity, not only realizes the harmless treatment of fluoride, but also realizes the maximization of the product value utilization of potassium phosphate ore; a new process method for preparing potassium nitrate from potassium fluorosilicate is opened up, and SiF4 can be absorbed to obtain fluorosilicic acid at the same time, the original and auxiliary materials can be recycled, and the reaction is relatively simple without pressurizing equipment, which reduces the process cost. The materials used in the present invention are all common industrial products, easy to purchase, and cheap; the whole process is short, low in cost, wide in raw material source, low in energy consumption, easy to scale, and easy to realize industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a schematic flow diagram of a method for preparing potassium nitrate from potassium fluorosilicate. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below.

[0033] The analysis results of the components of the potassium nitric acid insoluble raw material obtained by filtering after the phosphate potassium ore used in the following examples reacted with nitric acid are shown in Table 1.

[0034] Table 1 Analysis results of various components of potassium acid insoluble matter

[0035]

[0036] Example 1

[0037] like Figure 1 As shown, a method for preparing potassium nitrate from potassium fluorosilicate specifically comprises the following steps:

[0038] S1: Using potassium nitric acid insoluble matter in potassium phosphate ore as raw material, adding 90% of the theoretical amount of fluorosilicic acid and 200% of the theoretical amount of nitric acid for acid hydrolysis, the concentration of fluorosilicic acid is 31%, the concentration of nitric acid is 60%, the reaction temperature is 85°C, the reaction time is 6h, and the obtained solid-liquid mixture is filtered and washed while hot to obtain acid leaching solution I and leaching residue;

[0039] S2: The acid leaching solution I is allowed to stand for 18 hours and naturally cooled to 20° C. for crystallization, and the acid leaching solution II and potassium fluorosilicate crystals are obtained by filtration;

[0040] S3: Mix the above 20g potassium fluorosilicate crystals with 400g 60wt% nitric acid, heat to 80°C, stir and react for 4h, distill off excess nitric acid until crystals appear and cool to 20°C, filter and obtain potassium nitrate product;

[0041] S4: During the reaction of S3, 60°C hot water is used to absorb the distilled nitric acid and the SiF4 gas generated by the reaction. The water absorption liquid is filtered to obtain white crystals (white carbon black), and the absorption liquid after filtration can be reused in the acid hydrolysis process.

[0042] S5: The acid leaching solution II obtained in S2 is heated to 90° C. and concentrated by vacuum evaporation. The heating is stopped when solid begins to precipitate, and the evaporated acid solution is recovered by condensation.

[0043] S6: The concentrated mother liquor in S5 is diluted to a total high-valent metal ion concentration of 20 g / L, and a monovalent liquid and a high-valent liquid are separated using a NF4040 nanofiltration membrane. The monovalent liquid is evaporated and concentrated to a K concentration of 100 g / L, and frozen and crystallized at -5°C for 1 hour to obtain potassium nitrate crystals.

[0044] In this embodiment, the leaching rate of K in S1 is 96.37%, and the leaching rate of Al is 97.85%; the output rate of potassium fluorosilicate in S2 is 69.52%. The purity of potassium nitrate obtained in S3 is 98.37%, and the potassium recovery rate is 97.21%; the output rate of SiO2 in S4 is 52.06%; the recovery rate of nitric acid in S5 is 98.36%, and the recovery rate of fluorosilicic acid is 91.67%; the purity of potassium nitrate in S6 is 95.89%; potassium nitrate is obtained from S3 and S6, and the total potassium recovery rate is 97.36%.

[0045] Example 2

[0046] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0047] In step S3, 20 g of potassium fluorosilicate crystals are mixed with 300 g of 60 wt% nitric acid, the reaction time is 4 h, the reaction temperature is 80° C., the excess nitric acid is distilled out until crystals appear and cooled to 20° C., and the potassium nitrate product is filtered;

[0048] In step S4, 60° C. hot water is used to absorb the distilled nitric acid and the SiF 4 gas generated by the reaction.

[0049] The purity of potassium nitrate obtained in S3 of this embodiment is 98.87%, and the potassium recovery rate is 98.74%; the nitric acid recovery rate in S4 is 90.22%, and the fluorine recovery rate is 96.93%.

[0050] Example 3

[0051] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0052] In step S3, 20 g of potassium fluorosilicate crystals are mixed with 400 g of 40 wt% nitric acid, the reaction time is 4 h, the reaction temperature is 80° C., the excess nitric acid is distilled out until crystals appear and cooled to 20° C., and the potassium nitrate product is filtered;

[0053] In step S4, 60° C. hot water is used to absorb the distilled nitric acid and the SiF 4 gas generated by the reaction.

[0054] The purity of potassium nitrate obtained in S3 of this embodiment is 99.03%, and the potassium recovery rate is 98.62%; the nitric acid recovery rate in S4 is 91.15%, and the fluorine recovery rate is 96.87%.

[0055] Comparative Example 1

[0056] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0057] In step S1, the potassium nitric acid insoluble matter of potassium phosphate ore is used as raw material, and only 200% of the theoretical amount of nitric acid is added for acid hydrolysis, and no fluosilicic acid is added. The reaction temperature is 85°C, the reaction time is 6h, and the obtained solid-liquid mixture is filtered and washed while hot to obtain acid leaching solution I and leaching residue;

[0058] In this comparative example S1, the leaching rate of K is 3.16%, and the leaching rate of Al is 3.63%, indicating that the leaching rate of K is significantly reduced without adding fluorosilicic acid.

[0059] Comparative Example 2

[0060] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0061] In step S2, the acid leaching solution I is allowed to stand for 18 hours and naturally cooled to 60° C. for crystallization, and the acid leaching solution II and potassium fluorosilicate crystals are obtained by filtration;

[0062] The yield of potassium fluorosilicate in Comparative Example S2 is 38.17%, indicating that the yield of potassium fluorosilicate is reduced due to the excessively high crystallization temperature.

[0063] Comparative Example 3

[0064] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0065] In step S3, the above 20g potassium fluorosilicate crystals are mixed with 400g 60wt% nitric acid, and then heated to 40°C and stirred to react for 4h, and the excess nitric acid is distilled out until crystals appear and cooled to 20°C, and filtered to obtain a potassium nitrate product;

[0066] In this comparative example S3, the purity of the obtained potassium nitrate was 33.92%, and the potassium recovery rate was 34.61%, which indicated that the potassium recovery rate was reduced due to the too low heating temperature.

[0067] Comparative Example 4

[0068] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0069] In step S4, during the reaction process of S3, 20°C hot water is used to absorb the distilled nitric acid and the SiF4 gas generated by the reaction. The water absorption liquid is filtered to obtain white crystals (white carbon black), and the absorption liquid after filtration can be reused in the acid hydrolysis process.

[0070] In this comparative example S4, the SiO2 yield is 33.40%, which indicates that the SiO2 yield is reduced due to the low absorption water temperature.

[0071] Comparative Example 5

[0072] A method for preparing potassium nitrate from potassium fluorosilicate is implemented according to the method described in Example 1, except that:

[0073] In step S3, the above 20g potassium fluorosilicate crystals are mixed with 50g 60wt% nitric acid, and then heated to 90°C and stirred to react for 4h, and the excess nitric acid is distilled out until crystals appear and cooled to 20°C, and filtered to obtain a potassium nitrate product;

[0074] In this comparative example S3, the purity of the obtained potassium nitrate was 23.93%, and the potassium recovery rate was 24.66%, indicating that the amount of nitric acid added was too small, resulting in a decrease in the purity and recovery rate of potassium nitrate.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing potassium nitrate from potassium fluorosilicate, It is characterized in that It consists of the following steps: S1: using potassium nitric acid insolubles obtained by filtering after reacting potassium phosphate ore with nitric acid as raw materials, adding nitric acid and fluosilicic acid for acid hydrolysis, filtering and washing the obtained solid-liquid mixture while hot, and obtaining acid leaching solution I and leaching residue; In step S1, the amount of fluorosilicic acid added is 80-100% of the theoretical amount of fluorosilicic acid required for the reaction, the amount of nitric acid added is 150-250% of the theoretical amount of nitric acid required for the reaction, the concentration of fluorosilicic acid is 30-32%, the concentration of nitric acid is 40-60%, the reaction time is 4-8h, and the reaction temperature is 80-95°C; S2: allowing the acid leaching solution I to stand and naturally cool and crystallize, and filtering to obtain the acid leaching solution II and potassium fluorosilicate crystals; In step S2, the acid leaching solution I is left to stand for 12 to 24 hours and cooled to a temperature of 10 to 30°C; S3: mixing the potassium fluorosilicate crystals with nitric acid, heating and stirring to perform a pyrolysis reaction, while evaporating excess nitric acid, distilling the raw material until crystals appear, cooling, and filtering to obtain a potassium nitrate product; In step S3, the liquid-solid mass ratio of the nitric acid to the potassium fluorosilicate crystals is (10-20):1, the nitric acid concentration is 40-60%, the reaction temperature is 70-90° C., the reaction time is 2-4 hours, and the reaction is cooled to a temperature of 0-30° C. after completion of the reaction; S4: During the reaction process of S3, hot water is used to absorb the distilled nitric acid and the gas generated by the pyrolysis reaction, and the water absorption liquid is filtered to obtain white crystals, and the filtered absorption liquid is reused in the acid hydrolysis process of S1; S5: evaporating and concentrating the acid leaching solution II obtained in S2, recovering most of the nitric acid and fluorosilicic acid remaining from the acidolysis reaction, and recycling the recovered acid for the acidolysis reaction; S6: The mother liquor evaporated and concentrated in S5 is diluted and separated into monovalent liquid and high-valent liquid using a nanofiltration membrane, wherein the monovalent liquid contains K + The monovalent liquid is evaporated, concentrated, and frozen to obtain potassium nitrate, while the high-valent liquid contains Al 3+ , the high-valent liquid is used for the subsequent preparation of aluminum nitrate.

2. The method according to claim 1, It is characterized in that In step S4, the hot water temperature is 45-65°C.

3. The method according to claim 1, It is characterized in that In step S5, the acid leaching solution II obtained in S2 is heated to 70-90° C. and concentrated by negative pressure evaporation. The heating is stopped when solid begins to precipitate. The evaporated acid solution is condensed to recover most of the nitric acid and fluorosilicic acid remaining in the acidolysis reaction.

4. The method according to claim 1, It is characterized in that In step S6, the mother liquor evaporated and concentrated in S5 is diluted to a total high-valent metal ion concentration of 15 to 25 g / L, the monovalent liquid is evaporated and concentrated to a K concentration of 90 to 110 g / L, and frozen crystallized at -8 to -3°C for 1 to 2 hours to obtain potassium nitrate crystals.

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