CN105442047A - Method for extracting fluorine element from industrial gypsum - Google Patents

Abstract

The invention relates to the technical field of environmental protection and resource comprehensive utilization, in particular to a method for extracting fluorine element from industrial gypsum, which is a method for preparing gypsum whiskers and separating insoluble fluorosilicate at the same time by using the atmospheric pressure salt solution method of gypsum , to prepare gypsum whiskers with uniform size and good quality, and extract fluorine element at the same time. The invention opens up a new approach for purifying industrial gypsum and further obtaining fluorine element.

Description

A method for extracting fluorine element from industrial gypsum

technical field

The invention relates to the technical field of environmental protection and resource comprehensive utilization, in particular to a new method for purifying industrial gypsum and simultaneously extracting fluorine element from industrial gypsum.

Background technique

Industrial gypsum mainly includes phosphogypsum, fluorine gypsum and desulfurization gypsum. Phosphogypsum is a solid waste discharged from the production of phosphate fertilizer and phosphoric acid. The production of 1 ton of phosphoric acid produces about 4.5 to 5 tons of phosphogypsum. In recent years, with the development of the phosphate fertilizer industry, the discharge of phosphogypsum is also increasing. The annual discharge of phosphogypsum in my country exceeds 10 million tons, but its utilization rate is very low. Phosphogypsum occupies a large amount of land, pollutes the environment, and brings a great burden to production enterprises. The resource utilization of phosphogypsum has become a major issue in the phosphate fertilizer industry. key to sustainable development. Phosphogypsum is mainly composed of CaSO ₄ ·2H ₂ O and is an important renewable gypsum resource. Phosphogypsum contains impurities such as phosphorus and fluorine, and its structure is different from natural gypsum. Therefore, it must be pretreated before it can be used in the production of gypsum building materials. At present, a lot of research on the application of phosphogypsum has been carried out in China, and certain results have been obtained. Phosphogypsum has been reused in building materials, agriculture, chemical industry and other industries.

The main chemical components of phosphogypsum are CaO and SO ₃ , and it also contains impurities such as P ₂ O ₅ , F, Al ₂ O ₃ , Fe ₂ O ₃ , SiO ₂ , organic matter, and a small amount of elements such as uranium, radium, cadmium, lead, and copper. . Phosphogypsum mainly exists in four crystal forms: needle-like crystals, plate-like crystals, dense crystals, and polycrystalline nucleus crystals. Compared with natural gypsum, the performance of phosphogypsum cement is quite different, mainly manifested in long setting time and low strength. The chemical composition of phosphogypsum in different production enterprises and different batches is slightly different, which is mainly related to the control of phosphoric acid production process conditions and the variety of phosphate rock. Phosphoric acid production in my country is dominated by wet-process production. Sulfuric acid is used to decompose phosphate rock to generate extraction slurry, which is then filtered and washed to obtain phosphoric acid. Phosphogypsum is also produced during the filtering and washing process. Its reaction formula is:

Ca ₅ (PO ₄ )F+5H ₂ SO ₄ +10H ₂ O→3H ₃ PO ₄ +5CaSO ₄ 2H ₂ O+HF

In the phosphoric acid production process, some phosphate rocks are not decomposed, the washing and filtering process of phosphogypsum is not complete, and the additives added in the production process are the reasons why phosphogypsum contains various impurities such as phosphorus and fluorine. It is these impurities that affect the phosphogypsum. The performance of phosphogypsum prevents it from being directly applied to the production of gypsum building materials, which restricts the use of phosphogypsum. The fluorine in phosphogypsum comes from phosphate rock. When the phosphate rock is decomposed by sulfuric acid, ₂₀ % to 40% of the fluorine in the phosphate rock is mixed in the phosphogypsum. ₂ SiF ₆ exists in three forms. What affects the performance of phosphogypsum is soluble fluorine, which can accelerate coagulation, but when its content exceeds 0.3%, it will significantly reduce the strength of phosphogypsum. Soluble fluorine can be eliminated by a water washing process. The fluorine in phosphogypsum is also harmful to the environment. Studies have shown that the fluorine content in the leaching solution of newly produced phosphogypsum is higher than the maximum allowable value required by the national standard, which belongs to hazardous waste. After being stored in the yard for a period of time, part of the fluorine will be lost due to rainfall leaching, and part of the fluorine will form stable calcium fluoride with Ca ²⁺ in phosphogypsum, thereby reducing the soluble fluorine content in phosphogypsum. Phosphogypsum belongs to non-hazardous waste (an important content of the present invention is to recover the fluorine present in this part of phosphogypsum). The fluorine lost with rainfall leaching will seep into the water body around the stockyard, making the fluorine concentration in the water too high and causing environmental pollution.

Fluorogypsum is a by-product of the production of hydrofluoric acid from fluorite and concentrated sulfuric acid. The production of 1 ton of hydrofluoric acid will produce 3.6 tons of anhydrous fluorogypsum. Among them, the content of CaSO ₄ is as high as more than 90%, which is a high-grade gypsum resource. What is even more rare is that the content of calcium fluoride is 1.2-4.0% (dry gypsum) and 2.7-6.8% (wet gypsum). If properly utilized, it will become one of the important sources of fluorine.

Calcium Sulfate Whisker (Calcium Sulfate Whisker, also known as calcium sulfate microfiber, international trade name ONODA-GPF) is a new type of inorganic material with high comprehensive performance. It is widely used in papermaking, precision parts molds, building material parts, cement mortar, polymer fillers, friction parts, etc.

The following patents are Chinese and foreign patent documents related to the preparation of modified calcium sulfate whiskers:

WO2009150037A1 discloses an organosilicon compound particle used as an additive to prepare hydrophobic gypsum, wherein the organosilicon compound is silane, siloxane and some silicon-containing compounds.

CN102337703A discloses a method for modifying the surface of gypsum whiskers using a titanate coupling agent. A certain amount of gypsum whisker suspension is heated to 60 ℃～90℃ for 10～30min.

CN102634847A discloses a method for modifying the surface of gypsum whiskers with quaternary ammonium salts. The calcium sulfate whiskers are first dried, and then calcium sulfate whiskers, polyquaternium salts, octadecylamine and absolute ethanol are mixed in a certain proportion The pH in the solution is adjusted to 6-9, and then filtered, and the filter residue is dried to obtain the modified calcium sulfate whisker.

CN1283548A, ZL200610051140.7, ZL200610051178.4 are Chinese patent documents related to the preparation of gypsum whiskers and the recovery of fluorine.

But there is no report about a kind of easy method and technique for extracting fluorine from phosphogypsum and fluorogypsum.

Contents of the invention

The object of the present invention is to provide a simple method and process for extracting fluorine from phosphogypsum and fluorogypsum.

The first aspect of the present invention provides a method for extracting fluorine from industrial gypsum, which is a method of preparing gypsum whiskers by using the normal pressure salt solution method of gypsum and simultaneously separating insoluble fluorosilicate, comprising the following steps:

(1) Ultrafine preparation of phosphogypsum or fluorogypsum particles: process phosphogypsum or fluorogypsum particles into ultrafine phosphogypsum or fluorogypsum particles with a particle size of about 1-20 μm by ball milling or jet milling (Part A);

(2) The ultrafine phosphogypsum or fluorogypsum particles (part A) prepared in step (1) are mixed and stirred by adding water, cosolvent, and crystal form regulator, and the pH is adjusted to 0.5-2.5 (preferably 0.5-1.5), and the 95～100℃ (preferably 95～98) reaction;

Described cosolvent is selected from sodium chloride, potassium chloride, sodium sulfate, one or more than two (preferably sodium chloride) in potassium sulfate; Described crystal form modifier is selected from tartaric acid, citric acid, apple A kind of (preferably sodium citrate) in acid, ethylenediaminetetraacetic acid and sodium salt thereof; The weight parts of described superfine phosphogypsum or fluorogypsum particles, water, cosolvent, crystal form modifier are respectively:

(3) Filter the reaction solution in step (2) to obtain calcium sulfate whisker mixed powder, ventilate and dry at 50-80°C; use a sieve or a grading device to classify the particles, and sieve out the aspect ratio of 1:1 to 3:1 Whisker particles (Part B), solid particles outside this size are combined to obtain a mixed powder rich in fluorosilicate, fluoride, silicate and other metal salts (Part C), using the existing extraction Fluorine technology extracts fluorine element from the above mixed powder.

In the step (2), 25% by mass of acid is added to adjust the pH value, and the reaction time is 1 to 4 hours (preferably 2 hours).

The part B is calcium sulfate whisker with an aspect ratio of 1:1-3:1, which can be used for other applications of high-strength gypsum and calcium sulfate whisker.

The mixed powder in part C is a mixed powder rich in fluorosilicate, fluorine salt, silicate and other metal salts. Using the existing mature technology for extracting fluorine, it is possible to further extract fluorine from this part of the powder Extract fluorine. The described existing mature technology of extracting fluorine comprises: 1) direct method (Swiss Bass company BASSAG); 2) indirect method: sodium hydroxide (potassium) intermediate method; 3) indirect method: ammonium fluoride salt method ( liquid ammonia). (Reference: Gong Changsheng, "Modern Phosphorus Chemical Technology and Application", Chemical Industry Press, Beijing: 2013pp532-543.)

The invention uses phosphogypsum and fluorogypsum as raw materials to prepare gypsum whiskers with uniform size and good quality by adopting normal pressure salt solution method. Gypsum also follows the "dissolution-recrystallization" reaction mechanism in salt solution, that is, dihydrate gypsum dissolves calcium ions and sulfate ions in salt solution, because the solubility of hemihydrate gypsum in salt solution is higher than that of dihydrate gypsum and The solubility of gypsum hydrate is low, which leads to the recrystallization of calcium ions and sulfate ions to form hemihydrate gypsum crystals. The impurities in the gypsum escape from the gypsum crystals with the dissolution of the gypsum, which has a beneficial effect on the purification of the crystal structure of the gypsum. The present invention considers the factors affecting the crystal structure of impurities when selecting the crystal form regulator, and also considers the dosage of the crystal form regulator and the effect on the crystal of gypsum while removing impurities. The invention uses organic acids such as citric acid as crystal form regulators to prepare gypsum whiskers with uniform size and high quality, which opens up a new way for purifying industrial gypsum and further obtaining fluorine element.

detailed description

The specific implementation modes provided by the present invention will be described in detail below in conjunction with the examples.

Example 1

Add 288mL of water and 72g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 60g of phosphogypsum, adjust the pH of the salt solution to ₂ with dilute _H2SO4 and NaOH solution, and finally Add 5mL of aqueous solution containing 0.36g of sodium citrate, adjust the reaction temperature to 95°C, and carry out the reaction at the set stirring speed for 2 hours, cool, filter quickly, wash with hot deionized water, and dry , using a vibrating sieve to screen out whisker particles of 5-20 μm. Solid particles outside this size combine to form a fluorosilicate-rich fraction. The obtained calcium sulfate whiskers were uniform in size, and the particle size distribution was shown in Table 1 below.

Example 2

Add 288mL of water and 72g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 60g of fluorogypsum, adjust the pH of the salt solution to 2.5 with dilute _H2SO4 and _NaOH solution, and finally Add 5mL of aqueous solution containing 0.50g of sodium citrate, adjust the reaction temperature to 99°C, carry out the reaction at the set stirring speed for 2 hours, cool down, filter quickly, wash with hot deionized water, and dry , Use a vibrating sieve to screen out whisker particles of 5-60 μm. Solid particles outside this size combine to form a fluorosilicate-rich, fluoride-salt component. The obtained calcium sulfate whiskers were uniform in size, and the particle size distribution was shown in Table 1 below.

Example 3

Add 240mL of water and 60g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 50g of phosphogypsum, adjust the pH of the salt solution to 1.5 with dilute _H2SO4 and _NaOH solution, and finally Add 5 mL of an aqueous solution containing 0.55 g of sodium citrate, adjust the reaction temperature to 100°C, and carry out the reaction at the set stirring speed for 2.5 hours, cool down, filter quickly, wash with hot deionized water, and dry , Use a vibrating sieve to screen out whisker particles of 5-60 μm. Solid particles outside this size combine to form a fluorosilicate-rich fraction. The obtained calcium sulfate whiskers were uniform in size, and the particle size distribution was shown in Table 1 below.

Example 4

Add 240mL of water and 55g of sodium chloride into a 500mL three-necked flask with a thermometer, then weigh a certain amount of phosphogypsum 60g, adjust the pH of the salt solution to ₂ with dilute _H2SO4 and NaOH solution, and finally Add 5mL of aqueous solution containing 0.20g of sodium citrate, adjust the reaction temperature to 95°C, and carry out the reaction at the set stirring speed for 2 hours, cool down, filter quickly, wash with hot deionized water, and dry , to obtain calcium sulfate whiskers with a length of 10-50 μm and an aspect ratio of 10:1 and sieve them out with a standard vibrating sieve. Solid particles outside this size combine to form a fluorosilicate-rich fraction. The obtained calcium sulfate whiskers were uniform in size, and the particle size distribution was shown in Table 1 below.

Example 5

Add 240mL of water and 55g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 70g of fluorine gypsum, adjust the pH of the salt solution to 2.5 with dilute _H2SO4 and _NaOH solution, and finally Add 5mL of aqueous solution containing 0.25g of sodium citrate, adjust the reaction temperature to 99°C, and carry out the reaction at the set stirring speed for 2 hours, cool down, quickly filter with suction, wash with hot deionized water, and dry , to obtain calcium sulfate whiskers with a length of 5-60 μm and an aspect ratio of 10:1 and sieve them with a standard vibrating sieve. Solid particles outside this size combine to form a fluorosilicate-rich, fluoride-salt component. The obtained calcium sulfate whiskers were uniform in size, and the particle size distribution was shown in Table 1 below.

Table 1. Particle Size Distribution % by Laser Particle Size Analyzer

Table 2. F content and recovery of F before and after treatment

Note: The content in this table does not include SO ₂ , crystal water, and other trace metal elements. F element refers to fluorine-containing silicate, fluorine element in fluorine salt.

It can be seen from Table 1 and Table 2 that the particle size distribution of the gypsum crystals prepared in Examples 1-5 is relatively concentrated in the range of 5-50 μm, and the recovery rate of F element is relatively high.

The present invention considers the influence of impurities on the crystal structure when selecting the crystal modifier, and also takes into account the amount of the crystal modifier and the effect on the crystal of gypsum while removing impurities. The present invention uses organic acids such as citric acid as the crystal-transforming agent, thereby preparing gypsum whiskers with uniform size and high quality. The following is a comparative test about the crystal-transforming agent (crystal form regulator):

Comparative example 1

Add 288mL of water and 72g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 60g of phosphogypsum, adjust the pH of the salt solution to ₂ with dilute _H2SO4 and NaOH solution, and finally Add 5 mL of aqueous solution containing 0.36 g of malonic acid, adjust the reaction temperature to 95°C, and carry out the reaction at the set stirring speed for 2 hours, cool down, quickly filter with suction, wash with hot deionized water, and dry , Use a standard sieve to screen out 5-20μm whisker particles. Solid particles outside this size combine to form a fluorosilicate-rich fraction. The obtained calcium sulfate whiskers are irregular in size, and the particle size distribution is shown in Table 3; the recovery rate of F is 43%.

Comparative example 2

Add 288mL of water and 72g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 60g of fluorogypsum, adjust the pH of the salt solution to 2.5 with dilute _H2SO4 and _NaOH solution, and finally Add 5 mL of aqueous solution containing 0.5 g of glutaric acid, adjust the reaction temperature to 99°C, and carry out the reaction at the set stirring speed for 2 hours, cool down, quickly filter with suction, wash with hot deionized water, and dry , Use a standard sieve to screen out 5-20μm whisker particles. Solid particles outside this size combine to form a fluorosilicate-rich, fluoride-salt component. The obtained calcium sulfate whiskers are irregular in size, the particle size distribution is shown in Table 3, and the F recovery rate is 38%.

Comparative example 3

Add 240mL of water and 60g of sodium chloride into a 500mL three-neck flask with a thermometer, then weigh a certain amount of 50g of phosphogypsum, adjust the pH of the salt solution to 1.5 with dilute _H2SO4 and _NaOH solution, and finally Add 5 mL of aqueous solution containing 0.55 g of oxalic acid, adjust the reaction temperature to 100°C, and carry out the reaction at the set stirring speed for 2.5 hours, cool down, filter quickly, wash with hot deionized water, dry, and use Standard sieve whisker particles of 5-40μm. Solid particles outside this size combine to form a fluorosilicate-rich fraction. The obtained calcium sulfate whiskers are irregular in size, and the particle size distribution is shown in Table 3; the recovery rate of F is 36%.

Table 3. Particle size distribution % by laser particle size analyzer

Table 4. F content and recovery of F before and after treatment

It can be seen from Table 3 and Table 4 that the particle size distribution of the gypsum crystals prepared in Comparative Examples 1-3 is relatively dispersed, and the recovery rate of F element is low.

The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the described embodiments, and those skilled in the art can also make various equivalents without violating the spirit of the present invention. These equivalent modifications or replacements are all included within the scope defined by the claims of the present application.

Claims (5)

1. from industrial gypsum, extract a method for fluorine element, it is characterized in that, be the method adopting the normal pressure salt solustion mehtod of gypsum to prepare crystal whisker of gypsum, the simultaneously silicofluoride of separatin non-soluble, comprise the steps:

(1) super-refinement prepares phosphogypsum or fluorgypsum particle: the ultra-fine phosphogypsum or the fluorgypsum particle that by ball milling or comminution by gas stream, phosphogypsum or fluorgypsum are processed into particle diameter about 1 ~ 20 μm;

(2) ultra-fine phosphogypsum step (1) prepared or fluorgypsum particle, add water, solubility promoter, crystal structure adjusting agent mix and blend, regulates pH to be 0.5 ~ 2.5, in 95 ~ 100 DEG C of reactions;

Described solubility promoter is selected from sodium-chlor, Repone K, sodium sulfate, one or more in potassium sulfate; Described crystal structure adjusting agent is selected from the one in tartrate, citric acid, oxysuccinic acid, edta and its sodium salt; The weight part of described ultra-fine phosphogypsum or fluorgypsum particle, water, solubility promoter, crystal structure adjusting agent is respectively:

(3) by the reaction solution of step (2), filter and obtain calcium sulfate crystal whiskers mixed powder, 50-80 DEG C of air seasoning; Screen cloth or sorting equipment is utilized to carry out gradation, sift out the whisker particle of length-to-diameter ratio 1:1 ~ 3:1, solid particulate merging beyond this size obtains being rich in silicofluoride, villiaumite, the mixed powder of silicate and other metallic salts, utilize the technology of existing extraction fluorine, from above-mentioned mixed powder, extract fluorine element.

2. the method extracting fluorine element from industrial gypsum according to claim 1, is characterized in that, adds the acid for adjusting pH value of mass percent 25% in described step (2).

3. the method extracting fluorine element from industrial gypsum according to claim 1, is characterized in that, the reaction times in described step (2) is 1 ~ 4 hour.

4. the method extracting fluorine element from industrial gypsum according to claim 1, is characterized in that, described solubility promoter is sodium-chlor.

5. the method extracting fluorine element from industrial gypsum according to claim 1, is characterized in that, described crystal structure adjusting agent is Trisodium Citrate.