CN107827114B - Method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate - Google Patents
Method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate Download PDFInfo
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Abstract
The invention relates to the field of development and application of phosphorus chemical technology, and particularly discloses a method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate, wherein the wet-process phosphoric acid concentrated slag acid and process water are prepared in proportion and then added into a crystal rotating tank; adding the crystal transformation control agent and the crystal transformation auxiliary agent into a crystal transformation tank according to a proportion to perform a crystal transformation process of the semi-hydrated gypsum; the slurry after the crystallization is finished enters a suspension separator for settlement separation; filtering, purifying and filtering and washing slurry discharged from the bottom of the suspension separator to obtain dihydrate gypsum; and (3) filtering slurry discharged from the upper part of the suspension separator, purifying sodium fluosilicate, filtering and washing to obtain a product sodium fluosilicate, and directly returning the obtained filtrate to a phosphorite extraction tank or a dilute phosphoric acid storage tank. The invention realizes the recovery of phosphorus and the comprehensive utilization of waste residues in the wet-process phosphoric acid concentrated slag acid, improves the utilization value of the concentrated slag acid, and has the advantages of simple process, high phosphorus recovery rate, no waste residue and obvious economic benefit.
Description
A method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate.
Technical Field
The invention relates to the field of development and application of phosphorus chemical technology, in particular to a method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate.
Background
The wet phosphoric acid process mainly adopts a dihydrate method, phosphorus ore and sulfuric acid are subjected to extraction reaction to prepare 22-25% of dilute phosphoric acid, and then concentrated to obtain 40-45% of concentrated phosphoric acid. In the concentration process, as the water in the dilute phosphoric acid is evaporated, the concentration of the phosphoric acid is improved, so that impurities dissolved in the phosphoric acid are supersaturated and precipitated in a large amount, and concentrated phosphoric acid and slag acid are obtained through natural sedimentation separation. At present, the amount of the slag acid generated in the process of phosphoric acid concentration by a dihydrate wet method is about 10-15% of the yield of concentrated phosphoric acid. The main components of the slag acid are concentrated phosphoric acid, gypsum (mainly semi-hydrated gypsum), villiaumite, a small amount of phosphate and the like, and the solid content is 40-60 percentIn which liquid phase P is2O5The content is 40-45%; solid citric acid soluble P2O52-4% of CaO, 20-25% of SO328-36% of the total weight of the composition, 10-14% of Na2O and 22-32% of SiF 2-6.
In the concentration process of the dilute phosphoric acid, not only the dihydrate gypsum can be converted into the hemihydrate gypsum which is fine in crystal and carries a certain amount of intercrystalline phosphorus (citrate soluble phosphorus), but also villiaumite and phosphate which are fine in crystal form can be separated out, so that the solid phase sedimentation efficiency in the concentrated phosphoric acid is low, the yield of slag acid is high, the phosphoric acid loss is large, and the waste slag is difficult to treat.
The invention aims to recover phosphoric acid after treating the slag acid generated in the wet-process phosphoric acid concentration process by a simple process, obtain a crystal which is coarse and uniform in crystallization and easy to filter or settle and separate, and reduce intercrystalline phosphorus in the crystal. The recovered phosphoric acid can be used for producing fine phosphate with high added value, and the separated crystal can be directly sold as a product, so that the influence caused by directly returning the slag acid to a wet-process phosphoric acid production system is reduced, the device starting rate is improved, and the economic benefit of the slag acid is improved.
Disclosure of Invention
The invention aims to provide a method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate, and the method for treating the slag acid in the prior art comprises the following steps: the slag acid is directly returned to the coarse gypsum filtering system, so that the filtering cloth is easy to block, and the filtering system is paralyzed; the slag acid directly returns to the phosphorite extraction tank, and fluoride salt can be separated out when the temperature is slightly reduced in the conveying process, so that the conveying system is seriously blocked by scaling; a slag acid filtering system is independently arranged, but the viscosity of the slag acid is high, the solid phase crystal form is fine, and the filtering effect is poor; the slag acid is used as a raw material to produce other products such as chemical fertilizers, so that the utilization rate is low, impurities in the slag acid are all enriched in the fertilizer, and the slag acid is finally applied to the land to pollute the environment. The application aims to solve the problems in the prior art in the acid treatment process of the wet-process phosphoric acid concentrated slag.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate comprises the following steps:
step a: adding a crystal transformation agent into the mixture of the slag acid and the water to carry out a semi-hydrated gypsum crystal transformation process to obtain slurry A;
step b: carrying out sedimentation separation on the slurry A by using a suspension separator, wherein the slurry discharged from the bottom of the suspension separator is used as slurry B, and the slurry discharged from the top of the suspension separator is used as slurry C;
step c: filtering the slurry B, and performing gypsum purification on the obtained filter residue D to obtain dihydrate gypsum; returning the obtained filtrate to a phosphorite extraction tank or a dilute phosphoric acid storage tank;
step d: filtering the slurry C, and purifying the obtained filter residue E with sodium fluosilicate to obtain sodium fluosilicate; and returning the obtained filtrate to a phosphorite extraction tank or a dilute phosphoric acid storage tank.
In the invention, the slag acid contains liquid phase P2O5Solid phase P2O5、CaO、Na2The content of O is 10-14%, and SiF 2-6, in order to improve the utilization rate of concentrated phosphoric acid in the slag acid and realize comprehensive utilization of waste slag without generating wastes, dihydrate gypsum and sodium fluosilicate are produced through slag acid crystal transformation, waste slag separation and purification, and the additional value of the dihydrate gypsum and the sodium fluosilicate is improved.
Preferably, the mass ratio of the slag acid to the water in the mixture is 1:0.5 to 1.5.
Preferably, the crystal transformation agent comprises a crystal transformation control agent and a crystal transformation auxiliary agent.
Under the optimized addition proportion of the process water, a crystal transformation control agent and a crystal transformation auxiliary agent are added, and the crystal transformation process can be realized under a mild condition.
Preferably, the crystal transformation control agent is one or more of concentrated sulfuric acid accounting for 1.5-5.5% of the mass of the slag acid, calcium sulfate dihydrate accounting for 1-2% of the mass of the slag acid or fluosilicic acid accounting for 8-12% of the mass of the slag acid.
In the crystal transformation process, sulfuric acid and calcium sulfate dihydrate are used as crystal transformation control agents of the semi-hydrated gypsum, sulfuric acid is added to adjust the concentration of sulfur trioxide in a liquid phase, the dissolution of the dihydrate gypsum is inhibited, and the dissolved dihydrate gypsum and Ca in the liquid phase are mixed2+Combining to generate dihydrate gypsum; adding a small amount of sulfur dihydrateThe calcium carbonate is used as a crystal seed, and the crystal transformation of the hemihydrate gypsum into dihydrate gypsum with large grain diameter is promoted under the action of the crystal transformation auxiliary agent, and the crystal-substituted phosphorus in the hemihydrate gypsum is released, so that the phosphorus content of the dihydrate gypsum is reduced. The fluosilicic acid is used as a crystal transformation control agent to inhibit the dissolution of sodium fluosilicate in the slurry, and the content of sodium oxide in the returned filtrate is reduced.
Preferably, the crystal transformation auxiliary agent is one or more of diammonium phosphate, triethanolamine dodecylbenzene sulfonate, sodium ethoxylated alkyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate, and accounts for 0.005-0.01% of the mass of the slag acid.
Preferably, the crystal transformation temperature of the semi-hydrated gypsum crystal transformation process in the step a is 55-65 ℃, the stirring linear speed is 0.6-0.9 m/s, and the crystal transformation time is 90-120 min.
In the crystal transformation process, the reaction temperature, the stirring speed and the reaction time need to be controlled, and under the control condition of the invention, the dihydrate gypsum is good in crystallization and easy to separate.
Preferably, the feed inlet of the suspension separator is positioned in the middle of the guide shell, the bottom of the suspension separator is conical or circular, the stirring paddle is of a double-layer downward pressing type, and the discharge port at the top adopts overflow discharge.
Preferably, the stirring linear speed during the sedimentation separation is 0.5-0.7 m/s, and the retention time is 120-150 min.
Preferably, the gypsum purification is to purify the filter residue D and water according to a mass ratio of 1: 1-2, adding one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or fluosilicic acid to adjust the pH value of the materials to 3-7, and purifying at 60-90 ℃ for 30-60 min.
The method adopts a flotation separator to carry out solid-liquid separation on the crystal-transferring slurry, because the dihydrate gypsum is coarse in crystallization in the crystal-transferring process, after filter residue obtained by filtering the slurry discharged from the upper part after passing through the suspension separator is mixed with water, the pH value of the gypsum slurry is adjusted to 3-7 by adopting one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and fluosilicic acid, the sodium fluosilicate impurity in the gypsum slurry is removed by purification, and the dihydrate gypsum can be obtained by filtering and washing, and the product purity can reach the special grade standard of natural gypsum.
Preferably, the sodium fluosilicate is purified by mixing the filter residue E and water according to a mass ratio of 1: 1-4, adding a purifying agent which accounts for 0.1-1% of the mass of the filter residue E, and purifying at 60-90 ℃ for 30-60 min, wherein the purifying agent is one or more of ammonium chloride, ammonium sulfate, monoammonium phosphate, diammonium phosphate, ammonium acetate or ammonium bicarbonate.
And (2) carrying out solid-liquid separation on the crystal-converted slurry by adopting a flotation separator, wherein sodium fluosilicate crystal particles are fine, filtering the slurry discharged from the upper part after passing through the suspension separator to obtain filter residue, mixing the filter residue with water, adding one or more of ammonium chloride, ammonium sulfate, monoammonium phosphate, diammonium phosphate, ammonium acetate and ammonium bicarbonate, purifying and removing gypsum impurities in the filter residue, and filtering and washing to obtain the qualified product standard sodium fluosilicate.
Compared with the prior art, the invention has the beneficial effects of at least one of the following:
(1) the invention provides a novel method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and comprehensively utilizing waste residues, which not only recovers the phosphoric acid in the slag acid to produce a phosphorus product with a high added value, but also co-produces dihydrate gypsum and sodium fluosilicate, breaks through the prior art that the slag acid is used for producing a fertilizer with a low added value, and harmful impurities in the slag acid are applied to soil along with the fertilizer to pollute the nature.
(2) The method can be used for recovering phosphorus resources in the slag acid and simultaneously producing the dihydrate gypsum and the sodium fluosilicate, can convert the hemihydrate gypsum into coarse dihydrate gypsum crystals by mainly controlling the gypsum crystal conversion process in the slag acid, and can convert citrate soluble intercrystalline phosphorus in the gypsum into water soluble phosphorus, thereby achieving the purpose of improving the phosphorus recovery rate in the slag acid.
(3) After crystal transformation, the crystal particles of solid matters in the slag acid are large, and the filtering performance of the slurry is improved. The purity and whiteness of the purified dihydrate gypsum far exceed the primary standard of phosphogypsum, and the purified dihydrate gypsum can be used as a raw material for producing building gypsum; the purity of the sodium fluosilicate can also reach the standard of qualified products, and the sodium fluosilicate can be sold as a product, thereby improving the economic benefit.
(4) The process provided by the invention mainly comprises crystal transformation, separation and purification to obtain the product, and has the advantages of short flow, simple equipment requirement and low investment and operation cost.
(5) The invention realizes the high-efficiency utilization of the acid in the phosphoric acid concentrated slag by the wet process of the dihydrate method, improves the added value of the acid, has obvious economic benefit, can return the filtrate to a system for cyclic utilization, does not generate waste slag and waste gas, and realizes clean production.
Drawings
FIG. 1 is a flow chart of the method for recovering phosphorus from wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1:
the raw material wet-process phosphoric acid concentrated slag acid used in the present example comprises the following components:
the wet-process phosphoric acid concentrated slag acid and water with the indexes are prepared according to the mass ratio of 1:0.5 and added into a crystal conversion tank. Then concentrated sulfuric acid with the slag acid content of 1.5%, calcium sulfate dihydrate with the slag acid content of 1%, fluosilicic acid with the slag acid content of 8% and diammonium phosphate with the slag acid content of 0.005% are added, the crystal transformation temperature is 55 ℃, the stirring linear speed is 0.7m/s, and the crystal transformation time is 120 minutes. After the crystal transformation is finished, the materials enter a suspension separator, the stirring linear speed is 0.5m/s, and the material retention time is 120 minutes. Filtering and separating filter residue obtained by slurry discharged from the bottom of the suspension separator and water according to the weight ratio of 1:1, regulating the pH value of the gypsum slurry to 3 by adopting sulfuric acid, purifying at 90 ℃ for 60 minutes, filtering and washing to obtain the dihydrate gypsum product. Filtering and separating filter residue obtained by slurry discharged from the upper part of the suspension separator and water according to the weight ratio of 1:1, adding ammonium chloride accounting for 0.1 percent of the mass of filter residue, purifying at the temperature of 60 ℃ for 60 minutes, filtering and washing to obtain the product fluorineSodium silicate. Dihydrate Gypsum has a purity of 98.6%, P2O5The content is 0.09%; the purity of the sodium fluosilicate is 97.4 percent; the phosphorus yield was 99.85%.
Example 2
The raw material wet-process phosphoric acid concentrated slag acid used in the present example comprises the following components:
the wet-process phosphoric acid concentrated slag acid and water with the indexes are prepared according to the mass ratio of 1:1 and added into a crystal conversion tank. Then concentrated sulfuric acid with the slag acid content of 3%, calcium sulfate dihydrate with the slag acid content of 2%, fluosilicic acid with the slag acid content of 12%, ethoxylated sodium alkyl sulfate with the slag acid content of 0.005% and fatty alcohol-polyoxyethylene ether sodium sulfate with the slag acid content of 0.01% are added, the crystal transformation temperature is 60 ℃, the stirring linear speed is 0.8m/s, and the crystal transformation time is 110 minutes. After the crystal transformation is finished, the materials enter a suspension separator, the stirring linear speed is 0.6m/s, and the material retention time is 140 minutes. Filtering and separating filter residue obtained by slurry discharged from the bottom of the suspension separator and water according to the weight ratio of 1:1.2, regulating the pH value of the gypsum slurry to be 4 by adopting hydrochloric acid, purifying at 70 ℃ for 35 minutes, filtering and washing to obtain the dihydrate gypsum product. Filtering and separating filter residue obtained by slurry discharged from the upper part of the suspension separator and water according to the weight ratio of 1: 2, mixing, adding ammonium sulfate accounting for 1 percent of the mass of the filter residue and monoammonium phosphate accounting for 0.5 percent of the mass of the filter residue, purifying at the temperature of 80 ℃ for 50 minutes, and filtering and washing to obtain the product sodium fluosilicate. Dihydrate Gypsum has a purity of 98.1%, P2O5The content is 0.07 percent; the purity of the sodium fluosilicate is 97.3 percent; the phosphorus yield was 99.88%.
Example 3
The raw material wet-process phosphoric acid concentrated slag acid used in the present example comprises the following components:
the wet-process phosphoric acid concentrated slag acid and water with the indexes are prepared according to the mass ratio of 1:1.2 and added into a crystal conversion tank. Then concentrated sulfuric acid with 4 percent of slag acid content, calcium sulfate dihydrate with 1.5 percent of slag acid content, diammonium phosphate with 0.01 percent of slag acid content and dodecyl benzene sulfonic acid with 0.01 percent of slag acid content are addedAnd (3) triethanolamine is subjected to acid crystallization, wherein the crystal transformation temperature is 55 ℃, the stirring linear speed is 0.8m/s, and the crystal transformation time is 100 minutes. After the crystal transformation is finished, the materials enter a suspension separator, the stirring linear speed is 0.6m/s, and the material retention time is 130 minutes. Filtering and separating filter residue obtained by slurry discharged from the bottom of the suspension separator and water according to the weight ratio of 1: 1.6, adopting nitric acid to adjust the pH value of the gypsum slurry to 5, purifying at 85 ℃ for 45 minutes, filtering and washing to obtain the dihydrate gypsum product. Filtering and separating filter residue obtained by slurry discharged from the upper part of the suspension separator and water according to the weight ratio of 1: 3, adding diammonium phosphate accounting for 1 percent of the mass of the filter residue and ammonium bicarbonate accounting for 0.05 percent of the mass of the filter residue, purifying at 40 ℃ for 60 minutes, and filtering and washing to obtain the product sodium fluosilicate. Dihydrate Gypsum has a purity of 98.5%, P2O5The content is 0.11%; the purity of the sodium fluosilicate is 97.9 percent; the phosphorus yield was 99.82%.
Example 4
The raw material wet-process phosphoric acid concentrated slag acid used in the present example comprises the following components:
the wet-process phosphoric acid concentrated slag acid and water with the indexes are prepared according to the mass ratio of 1:1.5 and added into a crystal conversion tank. Then concentrated sulfuric acid with the slag acid content of 5.5 percent, triethanolamine dodecyl benzene sulfonate with the slag acid content of 0.01 percent, ethoxylated sodium alkyl sulfate with the slag acid content of 0.01 percent and sodium fatty alcohol-polyoxyethylene ether sulfate with the slag acid content of 0.01 percent are added, the crystal transformation temperature is 65 ℃, the stirring linear velocity is 0.9m/s, and the crystal transformation time is 90 minutes. After the crystal transformation is finished, the materials enter a suspension separator, the stirring linear speed is 0.7m/s, and the material retention time is 150 minutes. Filtering and separating filter residue obtained by slurry discharged from the bottom of the suspension separator and water according to the weight ratio of 1: 2, mixing, adopting phosphoric acid to adjust the pH value of the gypsum slurry to be 6, purifying at 60 ℃ for 30 minutes, filtering and washing to obtain the dihydrate gypsum product. Filtering and separating filter residue obtained by slurry discharged from the upper part of the suspension separator and water according to the weight ratio of 1: 4, mixing, adding ammonium acetate accounting for 0.5 percent of the mass of the filter residue and ammonium bicarbonate accounting for 0.5 percent of the mass of the filter residue, and purifying at the temperature of 90 ℃ for 30 minutes. Filtering and washing to obtain the product sodium fluosilicate. Dihydrate Gypsum has a purity of 98.5%, P2O5The content is 0.1%; the purity of the sodium fluosilicate is 98.2 percent; the phosphorus yield was 99.83%.
Although the invention has been described herein with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More specifically, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, other uses will also be apparent to those skilled in the art.
Claims (7)
1. A method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate is characterized by comprising the following steps: the method comprises the following steps:
step a: adding a crystal transformation agent into the mixture of the slag acid and the water to carry out a semi-hydrated gypsum crystal transformation process to obtain slurry A;
step b: carrying out sedimentation separation on the slurry A by using a suspension separator, wherein the slurry discharged from the bottom of the suspension separator is used as slurry B, and the slurry discharged from the top of the suspension separator is used as slurry C;
step c: filtering the slurry B, and performing gypsum purification on the obtained filter residue D to obtain dihydrate gypsum; returning the obtained filtrate to a phosphorite extraction tank or a dilute phosphoric acid storage tank;
step d: filtering the slurry C, and purifying the obtained filter residue E with sodium fluosilicate to obtain sodium fluosilicate; returning the obtained filtrate to a phosphorite extraction tank or a dilute phosphoric acid storage tank;
the crystal transformation agent comprises a crystal transformation control agent and a crystal transformation auxiliary agent: the crystal transition control agent is one or more of concentrated sulfuric acid accounting for 1.5-5.5% of the mass of the slag acid, calcium sulfate dihydrate accounting for 1-2% of the mass of the slag acid or fluosilicic acid accounting for 8-12% of the mass of the slag acid; the crystal transformation auxiliary agent is one or more of diammonium phosphate, triethanolamine dodecylbenzene sulfonate and ethoxylated sodium alkyl sulfate, and accounts for 0.005-0.01% of the mass of the slag acid.
2. The method for recovering phosphorus and coproducing dihydrate gypsum and sodium fluosilicate in wet-process phosphoric acid concentrated slag acid as claimed in claim 1, wherein the mass ratio of the slag acid to the water in the mixture is 1:0.5 to 1.5.
3. The method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate according to claim 1, characterized in that the crystal transformation temperature of the hemihydrate gypsum in the crystal transformation process is 55-65 ℃, the stirring linear speed is 0.7-0.9 m/s, and the crystal transformation time is 90-120 min.
4. The method for recovering phosphorus and coproducing dihydrate gypsum and sodium fluosilicate in wet-process phosphoric acid concentrated slag acid according to claim 1, wherein a feed inlet of the suspension separator is positioned in the middle of a guide shell, the bottom of the suspension separator is conical or circular, a stirring paddle is in a double-layer downward pressing type, and a discharge port at the top adopts overflow discharge.
5. The method for recovering phosphorus and coproducing dihydrate gypsum and sodium fluosilicate in wet-process phosphoric acid concentrated slag acid according to claim 1, wherein the stirring linear speed during settling separation is 0.5-0.7 m/s, and the retention time is 120-150 min.
6. The method for recovering phosphorus and coproducing dihydrate gypsum and sodium fluosilicate in wet-process phosphoric acid concentrated slag acid according to claim 1, wherein the gypsum purification is to purify the filter residue D and water according to a mass ratio of 1: 1-2, adding one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or fluosilicic acid to adjust the pH value of the materials to 3-7, and purifying at 60-90 ℃ for 30-60 min.
7. The method for recovering phosphorus in wet-process phosphoric acid concentrated slag acid and co-producing dihydrate gypsum and sodium fluosilicate according to claim 1, wherein the sodium fluosilicate is purified by mixing the filter residue E and water according to a mass ratio of 1: 1-4, adding a purifying agent which accounts for 0.1-1% of the mass of the filter residue E, and purifying at 60-90 ℃ for 30-60 min, wherein the purifying agent is one or more of ammonium chloride, ammonium sulfate, monoammonium phosphate, diammonium phosphate, ammonium acetate or ammonium bicarbonate.
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