Novel process for preparing NPK compound fertilizer by using phosphogypsum and potassium feldspar
Technical Field
The invention relates to the field of inorganic chemical industry, in particular to a novel process for preparing an NPK compound fertilizer by using phosphogypsum and potassium feldspar.
Background
The phosphogypsum is solid waste discharged in the wet-process phosphoric acid production, and 4-5 t of phosphogypsum is generated every 1t of phosphoric acid production. The main component of the phosphogypsum is CaSO4 ·2H2And O, the pH value is 1.5-4.5, the phosphogypsum is acidic, and the phosphogypsum usually contains undecomposed phosphorite, phosphoric acid, calcium fluoride, iron-aluminum oxide, acid insoluble substances, organic substances and other impurities which are not washed clean and is slightly soluble in water. With the rapid development of the phosphate fertilizer industry in China, the discharge amount of the phosphogypsum is in a greatly increasing trend year by year. The discharge of the phosphogypsum not only pollutes the environment, but also occupies a large amount of land, enterprises also need to invest a large amount of slag yard construction capital and operation management cost, the comprehensive utilization of the phosphogypsum is listed as a resource key project by the nation, the comprehensive utilization and harmless treatment of the phosphogypsum are well done to become an important task of the phosphorus chemical industry, and the method has important significance for saving natural resources, protecting the ecological environment, building a conservation-oriented society, developing the recycling economy and realizing the sustainable development of the industry. Currently, phosphorus chemical industry enterprises in China face double pressure of resources and environment, and sustainable development is seriously challenged; the industrial chain is not perfect, the product structure is not rich, and the added value of the product is low. At present, an effective technology is lacked for high-value utilization of phosphogypsum, and reasonable connection of upstream and downstream industries is realized.
The phosphate fertilizer and the potash fertilizer are used as nutrient element fertilizers of crops and play an extremely important role in the life metabolic process of the crops. In China, the yield of potash fertilizer and compound fertilizerAnd the dosage is insufficient, the proportion of nitrogen, phosphorus and potassium in the applied fertilizer is seriously imbalanced, and the phenomena of more nitrogen, less phosphorus and potassium deficiency are serious. The extraction of potassium mainly comes from soluble sylvite deposits, but China is seriously poor and the distribution is very uneven. According to statistics, the storage capacity of the water-soluble potassium salt in the world of 2012 is converted into K2The O accounts for 95.52 hundred million tons, the Chinese accounts for 2.1 hundred million tons, accounts for about 2.2 percent of the total storage capacity of the world, is mainly distributed in the Qinghai Kerr salt lake and the Xinjiang Apocynum venetum salt lake, and is inconvenient to develop and utilize. The water-insoluble potassium-containing ore beds in China are abundant, the reserves exceed 200 hundred million tons, and the potassium feldspar is mostly distributed in middle and eastern agriculture developed areas in the form of potassium feldspar. At present, the demand of potassium is large in China, the domestic market gap is huge, and a large amount of potassium fertilizer is imported every year. If the non-soluble potassium resource with huge reserves, such as potassium feldspar, can be changed into soluble potassium, the method has great significance. Therefore, how to develop the non-soluble potassium phosphate feldspar efficiently and economically is a difficult task for modern chemical engineering technologists.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a novel process for preparing an NPK compound fertilizer by using phosphogypsum and potassium feldspar.
The purpose of the invention is realized by the following technical scheme:
a new process for preparing NPK compound fertilizer by using phosphogypsum and potassium feldspar comprises the following steps:
(1) acid leaching: mixing the ground phosphogypsum, potassium feldspar and hydrochloric acid, blending, carrying out leaching reaction at 50-100 ℃, and carrying out solid-liquid separation after 2-10 hours to obtain leaching residue and leaching liquid.
(2) And (3) circulating acid leaching: and (3) supplementing acid to the leachate obtained in the step (1), then recycling the next batch of minerals, and after repeating the step (1) for a plurality of times, carrying out solid-liquid separation to obtain filter residue and P, K-enriched filtrate.
(3) Purifying the filtrate: and (3) sequentially removing calcium from the filtrate obtained in the step (2) by using sulfuric acid, and neutralizing with ammonia water to remove impurities such as aluminum, iron, magnesium and the like to obtain a refined filtrate.
(4) Preparing an NPK compound fertilizer; and (4) supplementing phosphorus to the filtrate obtained in the step (3), and then carrying out evaporation concentration to prepare the low (no) chlorine high-concentration NPK compound fertilizer.
P in the phosphogypsum2O55-20wt% of the total weight of the composition, and 0.5-5 wt% of the total weight of the composition.
K in the potassium feldspar2The content of O is 7-15 wt%.
The concentration of the hydrochloric acid used in the step (1) is 10-37%, and the dosage is 2: 1-6: 1 of liquid-solid ratio (hydrochloric acid volume (mL): phosphogypsum + potassium feldspar (g)).
The recycling time of the pickle liquor in the step (2) is 2-8 times, preferably 3-5 times.
The calcium sulfate removal conditions in the step (3) are as follows: according to n (Ca)2+): n(SO4 2-) =1: (0.8-1.2) adding 50-98% sulfuric acid solution at the reaction temperature of 30-90 ℃, the stirring speed of 400-1000 rpm and the reaction time of 0.5-3 h.
And (3) adjusting the pH value of the solution by using an ammonia water solution to perform fractional precipitation and impurity removal, slowly adjusting the pH value to 3.5, precipitating and removing iron, precipitating and removing aluminum when the pH value is 6.5, and precipitating and removing magnesium when the pH value is 9.
The phosphorus supplement agent in the step (4) is one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate, and the addition amount of the phosphorus supplement agent is N + P in the obtained low-chlorine high-concentration NPK compound fertilizer or chlorine-free high-concentration NPK compound fertilizer2O5+K2The proportion of O is more than or equal to 40 percent (mass).
The principle of the invention is as follows: since potassium feldspar has a stable structure and does not generally react with other acids except hydrofluoric acid, hydrofluoric acid or fluoride salt (such as calcium fluoride) and other acids (such as sulfuric acid, phosphoric acid and hydrochloric acid) are required to be added in the process of decomposing the potassium feldspar by acid. The method utilizes the reaction of hydrochloric acid and fluorine in the phosphogypsum to generate hydrogen fluoride to decompose potassium feldspar in the phosphorus and potassium associated ore, and fluorosilicate formed by the reaction further participates in the decomposition of the potassium feldspar in the phosphorus and potassium associated ore. Assuming that the fluorine in phosphogypsum exists in the form of fluoride MF2 and the leaching agent is hydrochloric acid, the main chemical reactions involved include:
MF2 + 2HCl =MCl2 + 2HF↑ (1)
12HF + KAlSi3O8 + 4HCl = KCl + AlCl3 + 3SiF4 ↑ + 8H2O (2)
4HF + SiO2 =SiF4 ↑+2H2O (3)
2HF + SiF4 = H2SiF6 (4)
3SiF4 + 2H2O = 2H2SiF6 + SiO2↓(5)
H2SiF6 =2HF↑+ SiF4 ↑ (6)
compared with the prior art, the invention has the advantages that:
(1) the method can decompose the potassium feldspar by utilizing the fluorine in the phosphogypsum without additionally adding fluorine resources, has low decomposition temperature, and can recycle the acid and the fluorine in the system.
(2) The lixiviant hydrochloric acid used in the invention has wide sources, is an industrial byproduct, and solves the problem of the outlet of the byproduct hydrochloric acid.
(3) The process of the invention does not relate to high temperature and high pressure, and a plurality of production devices can refer to inorganic chemical industries such as wet-process phosphoric acid, soda chemical industry and the like, so the process of the invention is easy to implement.
(4) It can be used for treating potassium feldspar, and can also be used for treating various potassium-containing ores such as clay and nepheline.
Drawings
FIG. 1 is a schematic process flow diagram of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples, but the present invention is not limited thereto.
Example 1
(1) Acid leaching: 60g of ground phosphogypsum, 20g of potassium feldspar and 320mL of hydrochloric acid solution (the mass concentration is 22.5%) are mixed and proportioned. And (3) carrying out leaching reaction on the prepared feed liquid at 90 ℃, and carrying out solid-liquid separation after 4 hours to obtain leaching residues and leaching liquid.
(2) And (3) circulating acid leaching: and (3) supplementing acid to the leachate obtained in the step (1) and then recycling the next batch of minerals according to the addition amount of hydrochloric acid and the liquid-solid ratio in the step (1), and carrying out solid-liquid separation after repeating the step (1) for 3 times to obtain filter residue and the filtrate enriched with P, K.
(3) Purifying the filtrate: the filtrate obtained in the step (2) is processed according to the formula of n (Ca)2+): n(SO4 2-) Adding a sulfuric acid solution with the mass concentration of 85% in a ratio of 1:1, carrying out calcium removal reaction at 50 ℃ under the stirring condition of 500 revolutions per minute, and carrying out solid-liquid separation after 2 hours of reaction. Adding ammonia water into the obtained filtrate to slowly adjust the pH value to 3.5 to generate white precipitate, continuously adding ammonia water into the filtrate after filtration and separation to adjust the pH value to 6.5 to generate white precipitate, adding ammonia water into the filtrate after filtration and separation again to adjust the pH value to 9 to generate white precipitate, and performing filtration and separation to obtain filter residue and purified filtrate.
(4) Preparing an NPK compound fertilizer: adding 3g of ammonium dihydrogen phosphate serving as a phosphorus supplement agent into the purified filtrate obtained in the step (3), then performing evaporation concentration at 100 ℃ until the solid content in the filtrate is more than 500g/L, preparing the NPK compound fertilizer, and detecting N, P in the compound fertilizer2O5、K2The contents of O and Cl are respectively 16.8%, 35.1%, 5.9% and 9.4%, which meet the national standard and belong to low-chlorine high-concentration NPK compound fertilizer.
Example 2
(1) Acid leaching: and mixing 50g of ground phosphogypsum, 30g of potassium feldspar and 160mL of hydrochloric acid solution (the mass concentration is 37 percent). And (3) carrying out leaching reaction on the prepared feed liquid at 70 ℃, and carrying out solid-liquid separation after 6 hours to obtain leaching residues and leaching liquid.
(2) And (3) circulating acid leaching: and (3) supplementing acid to the leachate obtained in the step (1) and then recycling the next batch of minerals according to the addition amount of hydrochloric acid and the liquid-solid ratio in the step (1), and carrying out solid-liquid separation after repeating the step (1) for 5 times to obtain filter residue and the filtrate enriched with P, K.
(3) Purification of the filtrate: the filtrate obtained in the step (2) is processed according to the formula of n (Ca)2+): n(SO4 2-) Adding a 65% sulfuric acid solution in a ratio of 1:1.2, carrying out calcium removal reaction at 30 ℃ under the stirring condition of 800 revolutions per minute, and carrying out solid-liquid separation after reaction for 0.5 h. Adding ammonia water into the obtained filtrate to slowly adjust the pH value to 3.5 to generate white precipitate, continuously adding ammonia water into the filtrate after filtration and separation to adjust the pH value to 6.5 to generate white precipitate, adding ammonia water into the filtrate after filtration and separation again to adjust the pH value to 9 to generate white precipitate, and performing filtration and separation to obtain filter residue and purified filtrate.
(4) Preparing an NPK compound fertilizer: adding 5g of phosphoric acid serving as a phosphorus supplement agent into the purified filtrate obtained in the step (3), and then performing evaporation concentration at 100 ℃ until the solid content in the filtrate is more than 500g/L to prepare the NPK compound fertilizer, wherein detection shows that N, P in the compound fertilizer2O5、K2The contents of O and Cl are respectively 19.8%, 30.4%, 3.9% and 12.4%, which meet the national standard and belong to low-chlorine high-concentration NPK compound fertilizer.
Example 3
(1) Acid leaching: 40g of ground phosphogypsum, 40g of potassium feldspar and 160mL of hydrochloric acid solution (the mass concentration is 10%) are mixed and proportioned. And (3) carrying out leaching reaction on the prepared feed liquid at 100 ℃, and carrying out solid-liquid separation after 2 hours to obtain leaching residues and leaching liquid.
(2) And (3) circulating acid leaching: and (3) supplementing acid to the leachate obtained in the step (1) and then recycling the next batch of minerals according to the addition amount of hydrochloric acid and the liquid-solid ratio in the step (1), and carrying out solid-liquid separation after repeating the step (1) for 2 times to obtain filter residue and the filtrate enriched with P, K.
(3) Purifying the filtrate: the filtrate obtained in the step (2) is processed according to the formula of n (Ca)2+): n(SO4 2-) Adding 50% sulfuric acid solution at a ratio of 1:0.8, performing calcium removal reaction at 60 ℃ under a stirring condition of 400 r/min, and performing solid-liquid separation after 3h of reaction. Adding ammonia water into the filtrate to slowly adjust pH to 3.5 to generate white precipitate, filtering, adding ammonia water into the filtrate to adjust pH to 6.5 to generate white precipitate, filtering, adding ammonia water into the filtrate to adjust pH to 9 to generate white precipitate, filtering, separating to obtain filter residue and purifyingAnd (4) liquid.
(4) Preparing an NPK compound fertilizer: adding 5g of phosphoric acid serving as a phosphorus supplement agent into the purified filtrate obtained in the step (3), and then performing evaporation concentration at 100 ℃ until the solid content in the filtrate is more than 500g/L to prepare the NPK compound fertilizer, wherein detection shows that N, P in the compound fertilizer2O5、K2The contents of O and Cl are respectively 23.4%, 33.4%, 4.9% and 10.5%, which meet the national standard and belong to low-chlorine high-concentration NPK compound fertilizer.
Example 4
(1) Acid leaching: and mixing 30g of ground phosphogypsum, 50g of potassium feldspar and 480mL of hydrochloric acid solution (the mass concentration is 25 percent). And (3) carrying out leaching reaction on the prepared feed liquid at 50 ℃, and carrying out solid-liquid separation after 10 hours to obtain leaching residues and leaching liquid.
(2) Leaching liquor is circularly leached: and (3) supplementing acid to the leachate obtained in the step (1) and then recycling the next batch of minerals according to the addition amount of hydrochloric acid and the liquid-solid ratio in the step (1), and carrying out solid-liquid separation after repeating the step (1) for 8 times to obtain filter residue and the filtrate enriched with P, K.
(3) Purifying the filtrate: the filtrate obtained in the step (2) is processed according to the formula of n (Ca)2+): n(SO4 2-) Adding a sulfuric acid solution with the mass concentration of 98% in a ratio of 1:1, carrying out calcium removal reaction at 90 ℃ under the stirring condition of 1000 revolutions per minute, and carrying out solid-liquid separation after 2 hours of reaction. Adding ammonia water into the obtained filtrate to slowly adjust the pH value to 3.5 to generate white precipitate, continuously adding ammonia water into the filtrate after filtration and separation to adjust the pH value to 6.5 to generate white precipitate, adding ammonia water into the filtrate after filtration and separation again to adjust the pH value to 9 to generate white precipitate, and performing filtration and separation to obtain filter residue and purified filtrate.
(4) Preparing an NPK compound fertilizer: adding 8g of diammonium hydrogen phosphate serving as a phosphorus supplement agent into the purified filtrate obtained in the step (3), then performing evaporation concentration at 100 ℃ until the solid content in the filtrate is more than 500g/L, preparing the NPK compound fertilizer, and detecting N, P in the compound fertilizer2O5、K2The contents of O and Cl are respectively 15.4%, 26.4%, 2.9% and 7.5%, which meet the national standard and belong to low-chlorine high-concentration NPK compound fertilizer.