CN106977123A - A kind of citric acid for being used to remove impurity fluorine in ardealite adds water the process washed - Google Patents

Abstract

A process for removing impurity fluorine in phosphogypsum by washing with citric acid and water, comprising three steps of dissolving citric acid, washing with citric acid and washing with water, the preparation process of the process of washing with citric acid includes the following three steps: Steps: firstly, prepare different concentrations of citric acid aqueous solutions for later use; secondly, use the above-prepared citric acid solution to add water to wash the phosphogypsum; finally, use lime to neutralize the washing wastewater. function, transform impurities such as fluoride and phosphate in phosphogypsum into washable soluble substances, and then remove impurities through water washing process, so that after purification, reduce the fluoride content in the equipment and in the drying flue gas, and remove the fluorine The phosphogypsum of fluoride and phosphide can be used by the phosphogypsum acid co-production cement process. Due to the removal of fluoride, it will no longer cause corrosion to the equipment in the sulfuric acid and cement production process.

Description

A process of washing with citric acid and water for removing impurity fluorine in phosphogypsum

technical field

The invention relates to a method for removing impurity fluorine in phosphogypsum, and belongs to the technical field of industrial solid waste treatment and disposal.

Background technique

From the perspective of the ecological environment, phosphogypsum contains impurities such as fluorine, phosphorus, and silicon. Due to the accumulation of phosphogypsum, this part of the impurities is likely to pollute groundwater and damage the geological structure after being washed by rainwater. Therefore, in recent years, in the scientific treatment of phosphogypsum The exploration of its processing methods to meet the comprehensive utilization goals has attracted widespread attention from social research institutions. At present, specific pretreatment methods of phosphogypsum include water washing method, lime neutralization method, calcination method, etc., and these methods are widely used. Although these traditional treatment methods can meet the availability of phosphogypsum, there are still limitations in the comprehensive utilization, such as the washing method consumes a lot of water and the amount of phosphogypsum should not be too much, the calcination method has higher requirements for fuel, and the The degree of removal of impurities in phosphogypsum is small and so on. In summary, it is necessary to find a method that can effectively remove impurities in phosphogypsum, especially the impurity fluorine. Therefore, in order to solve the problem of high impurity fluorine content in phosphogypsum, it is urgent to find a process that can effectively remove impurity fluorine in phosphogypsum and make it meet the requirements of comprehensive utilization and environmental protection.

According to incomplete statistics, the annual production of phosphogypsum in the world is 2.12×10 ⁴ ~2.97×10 ⁴ t. In 2015, the stock of phosphogypsum in China has exceeded 3×10 ⁸ t. Phosphogypsum (PG) is a wet process phosphoric acid plant and The main solid waste of the phosphate fertilizer plant, the production of 1 ton of phosphoric acid produces about 4.5t~5t of phosphogypsum. The phosphogypsum is in powder form and its main component is CaSO ₄ 2H ₂ O. Compared with natural gypsum, phosphogypsum contains many impurities, such as Phosphorus, fluorine, silicon and organic matter, etc. Phosphorus impurities have the greatest impact on the comprehensive utilization characteristics of phosphogypsum. The acidic characteristics of phosphogypsum make it used as a soil amendment in North China, Northwest and Northeast China, but the resource utilization of this phosphogypsum cannot be used on a large scale. Fundamentally solve the utilization problem of phosphogypsum, and pretreatment of phosphogypsum by different methods can effectively improve its characteristics, so that it can be better utilized. Phosphorus in phosphogypsum has the greatest impact, followed by fluorine and organic matter. They will affect the strength, hydration rate and whiteness of phosphogypsum. Phosphogypsum also contains alkali metal salts, silicon, magnesium and radioactive elements such as uranium and radium. Phosphorus mainly exists in soluble salts such as phosphates and carbonates, which will cause phosphogypsum products to produce frost and pulverization when they meet water. Silicon mainly exists in the form of quartz and has little effect on the properties of phosphogypsum. Harmful impurities such as Fe ₂ O ₃ , Al ₂ O ₃ , and MgO can promote the hydration and hardening of cementing materials in the preparation of type II anhydrous gypsum, but their introduction into phosphogypsum will affect the shape of dihydrate gypsum crystals. appearance. And phosphogypsum contains radioactive elements that are difficult to separate, which will cause harm to the human body.

Phosphogypsum is the product of phosphoric acid produced by wet process. In recent years, domestic phosphogypsum has shown a rapid growth trend, especially in Yunnan, Guizhou, Hubei, Anhui, Sichuan, Shandong and other provinces with large phosphate mines. Comprehensive utilization of phosphogypsum On the one hand, the United States, Germany, Japan, Brazil, etc. have achieved success in this research. Although my country’s research on the comprehensive utilization of phosphogypsum started relatively late, it has developed rapidly. After years of development, especially the research institutes and enterprises Scientific and technological research, the application of phosphogypsum has made great progress in many fields. The comprehensive utilization of phosphogypsum is not only related to the economic and ecological interests of the phosphate fertilizer industry, but also related to the development of environmental protection and ecological construction, and is also in line with the economic development concept of circular economy and green development. By the end of 2015, the accumulation of phosphogypsum in China had exceeded 3×10 ⁸ t, but its utilization rate was low (about 10%).

Sulfuric acid is an important basic chemical raw material, which can be widely used in chemical fertilizer, smelting, gunpowder, petrochemical, agricultural (medical) medicine, military industry and other industries. The raw materials for the traditional production of sulfuric acid are sulfur and pyrite, which account for 70% of the total sulfuric acid production. China is a country with poor sulfur resources. Every year, it needs to rely on imported sulfur to meet the demand. In 2008, the imported sulfur was 1500t; cement is a social construction Important building materials, used in civil engineering, hydraulic, national defense and other projects. The main raw material for cement production is limestone. The production also consumes a lot of fuel and electricity, and emits a lot of CO ₂ and dust.

Every year in the production of sulfuric acid and cement, China needs to import sulfur and mine a large amount of mineral resources. This behavior will not only occupy foreign exchange and quickly consume my country's mineral resources, but also cause serious pollution to our environment. Circular economy is the theme of the development of the times, but my country's demand for sulfuric acid and cement is increasing year by year, and the problem of phosphogypsum stacking needs to be solved urgently. The use of phosphogypsum to produce acid and co-produce cement not only solves the demand for sulfur resources and cement, but also avoids mining and environmental pollution. This will serve multiple purposes. This will be an effective way for the comprehensive utilization of phosphogypsum in the future.

The advantage of co-production of cement from gypsum with sulfuric _acid is that it uses gypsum as raw material and decomposes it into SO2 and CaO. CaO and the prepared auxiliary materials are directly calcined into cement clinker after decomposition, and then ground together with the mixed materials. into cement products, other impurities in gypsum are added to clinker, and SO ₂ -containing gas is produced into sulfuric acid. One raw material can produce two kinds of products, which will expand the benefits. At the same time, there will be no solid waste and waste water discharge. It can also replace traditional raw materials for sulfuric acid and cement production, which not only reduces mining, but also reduces environmental pollution during production. However, phosphorus The fluorine content in gypsum is large, especially when it passes through the flue gas of the drying section, the fluoride content is relatively large, and the degree of corrosion to equipment is relatively high.

The chemical components of phosphogypsum from different origins are slightly different. The phosphogypsum samples from Weng'an, Guizhou, Hefei, Anhui, and Kunming, Yunnan were all brought back to the laboratory with sealing materials, and the reference standards GB/T5484-2000, GB/T23456 -2009, GC/T2073-2011 conducted research and analysis on phosphogypsum samples, dried the samples at 120°C for 2 hours, cooled to room temperature, and measured the chemical components of phosphogypsum from different origins, as shown in Table 1.

Table 1 Contents of chemical components of phosphogypsum from different origins place of origin state CaO SO ₃ SiO ₂ P ₂ O ₅ ^F- Al ₂ O _{3 Fe2O3 _} MgO other Guizhou powdery 30.54 42.84 2.773 0.74 0.45 0.613 0.111 0.30 21.633 Anhui powdery 32.16 44.37 4.28 2.62 0.23 0.35 0.13 0.29 15.57 Yunnan powdery 31.94 45.38 14.52 0.94 0.12 1.66 0.15 0.17 5.12

At present, the existing processes using phosphogypsum require pretreatment of phosphogypsum. In the process of phosphogypsum acid production and co-production of cement in this plant, phosphogypsum is dried by high-temperature flue gas, and fluorine impurities are decomposed into fluoride and exist in the In the drying flue gas, the fluoride is acidic, which causes the equipment to be corroded, so some researchers have studied the removal of fluoride in the flue gas of phosphogypsum acid production by means of equipment.

Wang Yanjun introduced in the published patent "a dilute acid defluorination device for sulfuric acid flue gas purification from phosphogypsum" (CN205821060U) that by connecting the defluorination reactor at the rear end of the dilute sulfuric acid storage tank to be treated, at the same time, at the entrance of the defluorination reactor Set up the fluoride removal agent pipe, pass the dilute sulfuric acid to be treated and the fluoride removal agent into the fluoride removal reactor at the same time, and complete the fluoride removal process in the fluoride removal reactor. The defluorination reactor has a small volume and a small footprint, and does not need other power stirring devices. Under the action of pressure, the defluorination agent and dilute acid are fully and homogeneously reacted by the action of compressed air, which improves the reaction speed and saves reaction time. In order to improve the removal efficiency of fluorine, an air flotation settler, an automatic backwash surface filter and a plate and frame filter press are arranged in sequence at the back end of the defluorination reactor to further purify the filtrate after defluorination, so as to achieve the purpose of purification at one time , This device is simple in structure and easy to operate. However, using equipment to remove fluorine from flue gas in the process of making sulfuric acid from phosphogypsum is not the fundamental solution to solve the high fluorine content of phosphogypsum flue gas. At the same time, it is difficult to clean the device. Once a failure occurs, it will cause serious fluorine leakage problems, which poses safety and environmental problems. Pollution hazard.

Some researchers choose to pre-treat phosphogypsum before it enters the drying section. The main methods include washing phosphogypsum to remove fluorine and other impurities, acid leaching to remove fluorine impurities in phosphogypsum, and citric acid to dissolve and remove impurities. At the same time, the pickling method to remove phosphogypsum is to first use sulfuric acid solution to pickle the phosphogypsum, then filter and wash to neutrality, and the pickling solution is returned to the wet phosphoric acid process to decompose phosphate rock, and the washing waste can be passed through The acid cycle is used for leaching and removing impurities of phosphogypsum, which can avoid secondary pollution to the environment during the process. Kong Xia, Li Huping, etc. published the journal "Studies on the Removal of Impurity Fluorine in Phosphorus Gypsum by Sulfuric Acid Leaching Method" (Chemical Engineering, 2012, 40 (8): 65-68), pointing out that the research found that after hot leaching of sulfuric acid solution The removal rate of fluorine in the phosphogypsum can reach 84.5%, and the mass fraction of fluorine can be reduced to 0.0350%. The ideal optimized experimental conditions are as follows: the leaching temperature is set at 88°C, the leaching time is 45min, the mass of sulfuric acid The fraction is 30%, and the solid content is 0.43g/mL. The whiteness of the phosphogypsum treated by this method is improved, and the utilization rate of the phosphogypsum is greatly expanded. The method is simple and effective, and will not cause secondary pollution. Wang Hong et al. introduced a water washing and filtering process to control the concentration of free phosphoric acid in phosphogypsum in the journal "Water Washing and Filtration Process of Phosphogypsum" (Guizhou Chemical Industry, 2013, 38 (2): 42-43). Within the scope, it is used as a raw material for the production of ammonium sulfate, which not only solves the pollution problem of phosphogypsum stacking, but also plays a role in promoting economy through recycling, and plays a positive role in promoting the progress and development of China's phosphorus chemical industry. In the journal "Phosphogypsum Purification and Washing Test and Technology" (Phosphate and Compound Fertilizer, 2007, 22 (5): 66-67), Hu Chengjun used the washing treatment method to remove impurities in phosphogypsum, so that phosphogypsum can be widely used in paper production of building materials such as gypsum boards, gypsum blocks, etc., but these studies are to remove phosphorus, soluble phosphorus and soluble fluorine in phosphogypsum by washing, and cannot remove insoluble fluorine such as CaF ₂ , Na ₂ SiF ₆ , NaF, etc., and at the same time The washing waste liquid needs to be treated, otherwise it will cause secondary pollution. The Soviet Institute of Fertilizer, Pest Control and Sterilization Science proposed a method for removing fluorine, that is, heat-treating phosphogypsum at 300°C for 30 minutes, with an acidity pH of 1.8~2.2, and a humidity higher than 20%, it can remove 85~ 95% fluorine, but the waste liquid obtained by the above method is strongly acidic, and improper treatment will pollute the environment.

In recent years, we have disclosed a preparation method and application of an adsorbent for treating zinc-containing wastewater. The method is to modify the phosphogypsum by using aluminum sulfate modification technology after pretreatment with sodium chloride to obtain Aluminum-based modified phosphogypsum adsorbent, Al ³⁺ enters the interlayer of phosphogypsum through ion exchange reaction, and makes the interlayer open to increase the interlayer distance and pore size, the microporous structure of the adsorbent is further increased, thereby improving the phosphorus The porosity and specific surface area of gypsum have good adsorption performance, and the further processed phosphogypsum has a high adsorption capacity, making it an excellent adsorption material for removing zinc ions (CN201410690082.7), hydroxyapatite (HA) has a strong adsorption effect on F- ^, but the adsorption of HA synthesized by common methods is poor. We report a new method for the synthesis of nano- to micro-sized hydroxyapatite (HA), which can effectively Improve the adsorption efficiency of HA filter to F ^– ( Environmental Science & Technology , 2014, 48 (10): 5798), after that, some improvements were made to the treatment of phosphogypsum waste residue in cement plants, and the direct carbonation of phosphogypsum made it in Carbonation products obtained during the calcium cycle can be used for _CO2 capture and the use of spent CaO-based sorbents to manufacture cement clinker, while _CO2 derived from cement plant flue gas can directly convert calcium sulfate in phosphogypsum Therefore, this method can not only recycle phosphogypsum waste residue, but also reduce CO ₂ emissions from cement plants ( Energy & Fuels , 2016, 30 (2)). For the recovery of phosphogypsum, we use high-sulfur gypsum Coal was used as the reducing agent. The decomposition process of phosphogypsum in nitrogen atmosphere under different atmospheric conditions was characterized by means of thermogravimetric analysis, differential thermal analysis, scanning electron microscopy, and X-ray diffraction. The main product was calcium sulfoaluminate ( Industrial & Engineering Chemistry Research , 2010, 49 (8):3597-3602), in the "wet process phosphoric acid method" fertilizer production, phosphogypsum is a waste by-product, but phosphogypsum is very useful in other fields, so Its recovery is particularly important. We reported a method for the decomposition and recovery of phosphogypsum, in which the reducing agent is CO, the additive is calcium chloride, the decomposition temperature is 790 °C, and the main product is calcium sulfoaluminate. The reducing agent used in this method is CO, which is a toxic gas and is easy to cause harm to the human body ( Industrial & Engineering Chemistry Research , 2012, 51 (19):6680–6685). The global demand for rare earth elements is increasing rapidly, and phosphoric acid production The by-product of phosphogypsum is considered to be one of the sources of rare earth elements, and we report that the addition of calcium sulfate anhydrite seeds to the leach solution inhibits the degradation of calcium sulfate in the leach solution And reduce the calcium concentration, and the leaching efficiency of rare earth is related to the solubility of phosphogypsum, that is, the decrease of its concentration can increase the leaching amount of rare earth elements ( Industrial & Engineering Chemistry Research , 2016, 55 , 12309-12316).

After literature research, three methods for removing fluorine impurities in phosphogypsum were compared from the aspects of fluoride removal effect, environmental pollution, economic cost, and technical difficulty. The method is used to pretreat phosphogypsum to achieve the purpose of removing fluorine impurities in phosphogypsum. Citric acid is widely used in food, chemical, and pharmaceutical industries. The food industry is mainly used as a sour agent and preservative. The chemical industry uses citric acid as a complexing agent and buffer solution. The pharmaceutical industry mainly uses citric acid as citrate ions. , It can form a soluble complex with calcium ions that is difficult to dissociate, thus reducing the concentration of calcium ions in the blood and hindering blood coagulation. It is a good anticoagulant in vitro. Citric acid reacts with various impurities in phosphogypsum to generate a large amount of water-soluble components, and the reaction equation with fluoride is:

2C ₆ H ₈ O ₇ +3NaF→Na ₃ (C ₆ H ₅ O ₇ ) ₂ +3HF

4C ₆ H ₈ O ₇ +3Na ₂ SiF ₆ →2Na ₃ (C ₆ H ₅ O ₇ ) ₂ +H ₃ SiF ₆

2C ₆ H ₈ O ₇ +2Na ₃ AlF ₆ →2Na ₃ (C ₆ H ₅ O ₇ ) ₂ +H ₃ AlF ₆

2C ₆ H ₈ O ₇ +3Na ₂ FeF ₆ →2Na ₃ (C ₆ H ₅ O ₇ ) ₂ +H ₃ FeF ₆

2C ₆ H ₈ O ₇ +3CaF ₂ →Ca ₃ (C ₆ H ₅ O ₇ ) ₂ +6HF

The reaction equation with phosphate is:

2C ₆ H ₈ O ₇ +3Ca(H ₂ PO ₄ ) ₂ ·H ₂ O→Ca ₃ (C ₆ H ₅ O ₇ ) ₂ +2H ₃ PO ₄

2C ₆ H ₈ O ₇ +3CaHPO ₄ 2H ₂ O→Ca ₃ (C ₆ H ₅ O ₇ ) ₂ +2H ₃ PO ₄ +2H ₂ O

2C ₆ H ₈ O ₇ +Ca ₃ (PO ₄ ) ₂ →Ca ₃ (C ₆ H ₅ O ₇ ) ₂ +2H ₃ PO ₄

From the above reaction between citric acid and phosphogypsum, it can be seen that citric acid can react with phosphate and fluoride in phosphogypsum to form easily soluble substances that can be washed with water, and the effect of removing impurities can be achieved by washing with water.

In the present invention, we report a method of purifying phosphogypsum with citric acid as a dissolving agent, combined with water washing to remove impurity fluorine in phosphogypsum.

In recent years, the comprehensive utilization of solid waste phosphogypsum has aroused the interest of experts and scholars from all walks of life. Liao Qiushi, Qin Mingwu et al. (Journal of Hubei Three Gorges Vocational and Technical College, 2015, (1): 98-100) introduced the processes of sulfuric acid production and phosphogypsum production Advantages and disadvantages and the current situation of comprehensive utilization of phosphogypsum. In 2013, Li Jisheng and others disclosed the preparation method of the invention patent (CN201310475824.X) "Washing and purification method of phosphogypsum". It adopts the following steps: put the phosphogypsum into the water, wash it with water, remove the fine soluble impurities, and then enter the stepped pool for graded washing. The stepped pool is divided into 2-5 levels to remove the fine insoluble impurities in the phosphogypsum. Then carry out wet sieve filtration to remove large particles of quartz and unreacted impurities in the phosphogypsum, and finally neutralize with lime to remove the residual acid in the phosphogypsum. In 2015, Cao Zhiqiang and others disclosed the use method of the invention patent (CN201520404286.X) "a device for removing organic matter in phosphogypsum". This method mainly describes a device for removing organic matter in phosphogypsum. The organic matter in the phosphogypsum slurry is brought to the ring-shaped overflow tank on the upper part of the separation cone tank by the air flotation gravity method to overflow and collect the organic matter in the separation cone tank. After the slurry is cleaned by the cleaning device, it is collected at the discharge port. In 2016, Merka et al. disclosed the preparation method of the invention patent (WO2016186527) "Method for complex treatment of phosphogypsum". It uses the following steps: after reacting phosphogypsum with sulfuric acid solution, the resulting mixture is separated into a liquid and a sediment, the sediment mainly contains calcium sulfate, the sediment is reacted with ammonia and _CO2 to form ammonium sulfate and calcium carbonate, filtered After drying, the resulting precipitated calcium carbonate is dissolved in nitric acid, and the resulting mixture is separated to obtain a nitrate solution and a fluoride precipitate and a silicate precipitate. In 2017, Konstantin Kovler et al. disclosed the preparation method of the invention patent (US20170022070) "System and methods for removing impurities from phosphogypsum and manufacturing gypsumbinders and products". It adopts the following steps: react phosphogypsum with chloride solution in an acidic environment to obtain phosphogypsum precipitates, dehydrate and filter, and use electrochemical and zeolite adsorption to remove impurities contained in the phosphogypsum. In 2017, Eогатырева Елена Владимировна and others disclosed the preparation method of the invention patent (RU0002607862) "Method of extracting rare-earth metals and producing gypsum plaster from anhydrate". The method mainly describes a method for obtaining rare earth metals and phosphogypsum building gypsum from the waste residue of apatite acid production and sulfuric acid production.

Although the above methods have many advantages, some of the methods involved in the methods are difficult to operate in practice, and the treatment of fluorine content is not thorough enough, the pertinence is poor, and the problem cannot be fundamentally solved. Pretreatment, and the fluorine contained in phosphogypsum and insoluble fluorine are highly targeted, and the removal rate is high, and the subsequent washing wastewater can be recycled after treatment.

Contents of the invention

Purpose of the invention: Aiming at the deficiencies of the current prior art, the present invention utilizes the difference in solubility of impurity components in phosphogypsum by citric acid to realize the conversion of impurities such as fluoride in phosphogypsum into soluble water-washable impurities, and combined with water-washing Methods, a process for removing fluorine impurities in phosphogypsum by washing with citric acid and water was designed. In this method, by comparing the removal rate of impurity fluorine in phosphogypsum by dissolving with different concentrations of citric acid and washing with water, an effective method for pretreatment of phosphogypsum to make it meet the process standard of phosphogypsum acid production co-production cement is found.

The technical proposal of the present invention is: a process method for removing impurity fluorine in phosphogypsum by adding citric acid and water washing, including three processes of citric acid dissolution, citric acid washing and water washing. It is characterized in that: the citric acid solution can chemically react with impurities in phosphogypsum, so that impurities such as fluoride and phosphate in phosphogypsum can be converted into water-washable and easily soluble substances, and then impurities can be removed by water washing process, so that after purification The phosphogypsum can be better utilized by the phosphogypsum acid production co-production cement process, thereby reducing the fluoride content in the drying flue gas, and does not affect the sulfuric acid and cement production process at the same time, the preparation of the process method of adding citric acid and water washing The process consists of three steps:

1.1 The first step is to prepare different concentrations of citric acid solutions: accurately weigh 3.00g, 4.00g, 5.00g, 6.00g and 7.00g of citric acid with an electronic balance with an accuracy of 1%, and the proportioning mass concentration is 3 %, 4%, 5%, 6% and 7% citric acid aqueous solution for later use, then measure 10mL from the above-mentioned prepared citric acid aqueous solution and place it in a 150mL beaker, add 90mL deionized water each, and dilute it to The citric acid aqueous solution that mass concentration is 0.3%, 0.4%, 0.5%, 0.6% and 0.7% is standby;

1.2 The second step is to wash the phosphogypsum with citric acid and water: use an electronic balance with an accuracy of 1% to weigh six samples of phosphogypsum raw materials of 9.00g~9.60g, and place them in glassware with the same scale and size. , and then take 10mL of 3%, 4%, 5%, 6% and 7% citric acid aqueous solution into the phosphogypsum sample, stir mechanically for 15~25min until dissolved, the dissolved mixture is filtered through the filter device, and the filtrate is pipetted To the collection tank for collection, the filtered filter residue was ultrasonically dispersed and washed with citric acid aqueous solutions with a mass concentration of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% for 6-10 minutes, and centrifuged in a centrifuge at a speed of 3000-4000rpm 8~12min, then add pure water to ultrasonically disperse and wash and rotate and centrifuge twice, the purified phosphogypsum samples 1 ^# , 2 ^# , 3 ^# , 4 ^# , 5 ^# obtained after centrifugation, and then the purified phosphogypsum samples are passed through Dry in an electric heating constant temperature blast drying oven at 85°C for 12 hours to obtain the finished product;

1.3 The third step is lime neutralization and treatment of washing wastewater: add lime water with a mass concentration of 0.3~0.5% into the waste liquid collection tank, stir for 8~12 minutes to obtain a uniform slurry, and use a pH meter to measure the pH of the slurry value, and add lime water with a mass concentration of 85-95% to adjust the pH value of the slurry to 7; finally add alum solution, stir in the wastewater treatment tank for 10-15 minutes, and then let it stand for stratification to obtain the pH value of the upper layer 7. Neutralize the water and the insoluble sediment in the lower layer.

As a further improvement to the prior art, the method of using citric acid plus water to wash phosphogypsum to achieve the effect of fluoride removal does not add other acid-base additives except citric acid in the process of phosphogypsum defluoridation. The said phosphogypsum is the solid waste produced by the wet method of the phosphoric acid plant. The said phosphogypsum removal of fluoride is the relative removal rate relative to the fluorine content of untreated phosphogypsum. The citric acid is washed with water to remove the fluorine impurities in the phosphogypsum, and the process operation is simple, the economic cost is reasonable, and the production cycle is short. Said phosphogypsum raw material is rich in sources, low in cost and easy to obtain. The defluoridated phosphogypsum is used as a raw material for the co-production of cement with phosphogypsum acid, which can reduce the fluoride in the flue gas generated by the phosphogypsum in the drying section and avoid equipment erosion, which has certain environmental protection significance.

Compared with the beneficial effects of the prior art:

In recent years, the comprehensive utilization of solid waste phosphogypsum has aroused the interest of experts and scholars from all walks of life. Liao Qiushi, Qin Mingwu et al. (Journal of Hubei Three Gorges Vocational and Technical College, 2015, (1): 98-100) introduced the processes of sulfuric acid production and phosphogypsum production Advantages and disadvantages and the current situation of comprehensive utilization of phosphogypsum. In 2013, Li Jisheng and others disclosed the preparation method of the invention patent (CN201310475824.X) "Washing and purification method of phosphogypsum". It adopts the following steps: put the phosphogypsum into the water, wash it with water, remove the fine soluble impurities, and then enter the stepped pool for graded washing. The stepped pool is divided into 2-5 levels to remove the fine insoluble impurities in the phosphogypsum. Then carry out wet sieve filtration to remove large particles of quartz and unreacted impurities in the phosphogypsum, and finally neutralize with lime to remove the residual acid in the phosphogypsum. In 2015, Cao Zhiqiang and others disclosed the preparation method of the invention patent (CN201520404286.X) "a device for removing organic matter in phosphogypsum". This method mainly describes a device for removing organic matter in phosphogypsum. The organic matter in the phosphogypsum slurry is brought to the ring-shaped overflow tank on the upper part of the separation cone tank by the air flotation gravity method to overflow and collect the organic matter in the separation cone tank. After the slurry is cleaned by the cleaning device, it is collected at the discharge port. In 2016, Merka et al. disclosed the preparation method of the invention patent (WO2016186527) "Method for complex treatment of phosphogypsum". It uses the following steps: after reacting phosphogypsum with sulfuric acid solution, the resulting mixture is separated into a liquid and a sediment, the sediment mainly contains calcium sulfate, the sediment is reacted with ammonia and _CO2 to form ammonium sulfate and calcium carbonate, filtered After drying, the resulting precipitated calcium carbonate is dissolved in nitric acid, and the resulting mixture is separated to obtain a nitrate solution and a fluoride precipitate and a silicate precipitate. In 2017, Konstantin Kovler et al. disclosed the preparation method of the invention patent (US20170022070) "System and methods for removing impurities from phosphogypsum and manufacturing gypsum binders and products". It adopts the following steps: react phosphogypsum with chloride solution in an acidic environment to obtain phosphogypsum precipitates, dehydrate and filter, and use electrochemical and zeolite adsorption to remove impurities contained in the phosphogypsum. In 2017, Eогатырева Елена Владимировна and others disclosed the preparation method of the invention patent (RU0002607862) "Method of extracting rare-earth metals and producing gypsum plaster from anhydrate". The method mainly describes a method for obtaining rare earth metals and phosphogypsum building gypsum from the waste residue of apatite acid production and sulfuric acid production.

Although the above methods have many advantages, some of the methods involved in the methods are difficult to operate in practice, and the treatment of fluorine content is not thorough enough, the pertinence is poor, and the problem cannot be fundamentally solved. Pretreatment, and the fluorine contained in phosphogypsum and insoluble fluorine are highly targeted, and the removal rate is high, and the subsequent washing wastewater can be recycled after treatment.

The present invention first prepares citric acid solutions with different concentrations: accurately weigh 3.00g, 4.00g, 5.00g, 6.00g and 7.00g of citric acid respectively with an electronic balance with an accuracy of 1%, and the proportioning mass concentration is 3% respectively , 4%, 5%, 6% and 7% citric acid aqueous solutions for later use, then measure 10mL from the above prepared citric acid aqueous solution and place them in 150mL beakers, add 90mL deionized water each, and dilute it to mass Concentration is the citric acid aqueous solution of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% standby;

The second is to wash the phosphogypsum with citric acid and water: use an electronic balance with an accuracy of 1% to weigh six samples of phosphogypsum raw materials of 9.00g~9.60g, place them in glassware with the same scale and size, and then weigh them separately. Take 10mL of 3%, 4%, 5%, 6% and 7% citric acid aqueous solution and add it to the phosphogypsum sample, stir mechanically for 15~25min until dissolved, the dissolved mixture is filtered through the filter device, and the filtrate is moved to the collection tank Collect, use citric acid aqueous solution with mass concentration of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% to ultrasonically disperse and wash the filtered filter residue for 6~10min, and centrifuge at 3000~4000rpm in a centrifuge for 8~12min , and then add pure water to ultrasonically disperse and wash and rotate and centrifuge twice. After centrifugation, the purified phosphogypsum samples 1 ^# , 2 ^# , 3 ^# , 4 ^# , 5 ^# are subjected to a temperature of 85 ° C. Dry in an electric heating constant temperature blast drying oven for 12 hours to obtain the finished product;

Finally, lime is neutralized to treat washing wastewater: lime water with a mass concentration of 0.3-0.5% is added to the waste liquid collection tank, stirred for 8-12 minutes to obtain a uniform slurry, and the pH value of the slurry is measured with a pH meter, and Add lime water with a mass concentration of 85-95% to adjust the pH value of the slurry to 7; finally add alum solution, stir in the wastewater treatment tank for 10-15 minutes, and then let it stand for stratification to obtain a medium with a pH value of 7 in the upper layer. and water and insoluble precipitates in the lower layer.

In summary, a process of washing with citric acid for removing impurity fluorine in phosphogypsum has the following advantages:

One: The wet-process phosphoric acid solid waste phosphogypsum is treated with citric acid plus water washing, which can significantly remove the fluorine impurities in the phosphogypsum.

Second: the main components of the phosphogypsum after washing with citric acid and water have not changed, which does not affect the process of producing acid and co-producing cement from phosphogypsum.

Third: Phosphogypsum is the main solid waste of wet-process phosphoric acid, and its production volume and accumulation are increasing year by year. Due to the large amount of impurities, it is easy to cause environmental pollution. The pretreated phosphogypsum as a raw material is more in line with the characteristics of comprehensive utilization , has a certain environmental significance.

Fourth: the citric acid plus water washing waste liquid is collected and treated with alum and lime neutralization method, and the obtained neutral water can be used for process recycling.

Fifth: Compared with other phosphogypsum defluorination methods, it has the characteristics of simple operation, low investment cost, easy implementation and good fluorine impurity removal effect.

Sixth: After treatment, phosphogypsum is used as raw material in the process of phosphogypsum acid production and co-production of cement. Due to the reduction of fluorine content, the content of fluoride in the drying flue gas is relatively reduced, and the problem of equipment erosion is effectively solved.

Seventh: The chemical composition content (m%) of phosphogypsum after washing with different concentrations of citric acid and water, the effect of 5% and 0.5% citric acid aqueous solution combined with water washing is the best (P ₂ O ₅ , F ^-mass in 3# sample score is the smallest), as shown in Table 2.

Table 2 Chemical composition content of phosphogypsum after washing with different concentrations of citric acid and water (m%)* sample CaO SO ₃ SiO ₂ P ₂ O ₅ ^F- Al ₂ O _{3 Fe2O3 _} MgO other 1 ^# 29.760 38.563 2.068 0.274 0.120 0.482 0.129 0.140 28.564 2 ^# 30.240 40.985 1.461 0.280 0.070 0.427 0.086 0.118 26.333 3 ^# 30.130 41.427 2.546 0.220 0.039 0.466 0.104 0.173 24.890 4 ^# 29.290 40.132 1.862 0.250 0.043 0.425 0.103 0.210 27.685 5 ^# 29.666 39.976 2.545 0.230 0.044 0.436 0.166 0.232 26.708

*: X-ray fluorescence analyzer was used to analyze the chemical composition of the purified sample.

Description of drawings

Fig. 1 is the XRD pattern of phosphogypsum before (A) and after (B) treatment of citric acid plus water washing used in the present invention.

Fig. 2 is the SEM image of the phosphogypsum before the citric acid plus water washing treatment used in the present invention.

Fig. 3 is an SEM image of phosphogypsum at different magnifications after washing with citric acid and water used in the present invention.

Further explain the specific embodiment according to the accompanying drawings

Fig. 1 is the XRD spectrum of phosphogypsum before (A) and after (B) treatment of the citric acid plus water washing treatment adopted in the present invention, and the illustration shows the spectrum characteristics of phosphogypsum under X-ray. According to the comparison of phosphogypsum treated with water washing with different concentrations of citric acid, the method of combining citric acid dissolution with a mass concentration of 5% and washing with citric acid with a mass concentration of 0.5% is selected. Figure A is the raw material of phosphogypsum before treatment. According to the XRD diagram, according to the Jade software, the main components of phosphogypsum are CaSO ₄ 2H ₂ O and SiO ₂ , and their PDF card numbers are 33-0311 and 44-0696 respectively. At the same time, there are diffuse peaks of different sizes in the background, which contain A small amount of P ₂ O ₅ has a PDF card number 23-1301. Figure B is the XRD pattern of the treated phosphogypsum raw material. According to Jade software analysis, the main component CaSO ₄ ·2H ₂ O has not changed, but the purified sample contains a small amount of CaPO ₃ (OH) · 2H ₂ O.

Fig. 2 is the SEM image of the phosphogypsum used in the present invention before washing with citric acid and water, showing the shape and impurities of the phosphogypsum crystals before treatment. The figure shows that the phosphogypsum particles are in the shape of a regular parallelogram plate, and a large number of fine impurity particles are densely attached to the surface of a single particle. According to the scanning electron microscope image, it can be seen that phosphogypsum is mainly gray in color, and the overall phosphogypsum presents a relatively regular parallelogram plate structure. Wait.

Fig. 3 is the SEM figure of phosphogypsum under different magnifications after the citric acid and water washing treatment adopted in the present invention, Fig. A is that the raw material of phosphogypsum is dissolved in citric acid aqueous solution, and washed with citric acid aqueous solution after dilution, and finally passes through two Compared with the phosphogypsum sample before purification, the impurities of the phosphogypsum sample obtained after the first water washing are obviously removed at a magnification of 450 times, and the whole is clean, and the phosphogypsum has a parallelogram structure as a whole. Figure B is the phosphogypsum raw material dissolved in citric acid aqueous solution, washed with citric acid aqueous solution after dilution, and finally washed twice with water. The phosphogypsum whisker diagram is viewed at a magnification of 2200 times, and the impurities are removed. The whiskers have distinct layers and clear outlines, indicating that the purified phosphogypsum has removed certain impurities such as Ca(H ₂ PO ₄ ) ₂ , CaHPO ₄ , Ca ₃ (PO ₄ ) ₂ and organic matter.

Specific embodiments: a process method of citric acid plus water washing for removing impurity fluorine in phosphogypsum, including three processes of citric acid dissolution, citric acid washing and water washing. It is characterized in that: the citric acid solution can chemically react with impurities in phosphogypsum, so that impurities such as fluoride and phosphate in phosphogypsum can be converted into water-washable and easily soluble substances, and then impurities can be removed by water washing process, so that after purification The phosphogypsum can be better utilized by the phosphogypsum acid co-production cement process, thereby reducing the fluoride content in the drying flue gas without affecting the sulfuric acid and cement production process. The preparation process of the present invention includes the following steps:

The first step is to prepare different concentrations of citric acid solutions: accurately weigh 3.00g, 4.00g, 5.00g, 6.00g and 7.00g of citric acid with an electronic balance with an accuracy of 1%, respectively, and the proportioning mass concentration is 3%. , 4%, 5%, 6% and 7% citric acid aqueous solutions for later use, then measure 10mL from the above prepared citric acid aqueous solution and place them in 150mL beakers, add 90mL deionized water each, and dilute it to mass Concentration is the citric acid aqueous solution of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% standby;

The second step is to wash the phosphogypsum with citric acid and water: use an electronic balance with an accuracy of 1% to weigh six samples of phosphogypsum raw materials of 9.00g~9.60g, and place them in glassware with the same scale and size. Then take 10mL of 3%, 4%, 5%, 6% and 7% citric acid aqueous solution into the phosphogypsum sample, stir mechanically for 15~25min until dissolved, the dissolved mixture is filtered through the filter device, and the filtrate is transferred to Collect in the collection tank, use citric acid aqueous solution with mass concentration of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% to ultrasonically disperse and wash the filtered filter residue for 6~10min, and centrifuge at 3000~4000rpm in a centrifuge for 8 ~12min, then add pure water for ultrasonic dispersion washing and spin centrifugation twice, the purified phosphogypsum samples 1 ^# , 2 ^# , 3 ^# , 4 ^# , 5 ^# after centrifugation, and then pass the purified phosphogypsum samples through 85 ℃ for 12 hours in an electric heating constant temperature blast drying oven to obtain the finished product;

The third step is lime neutralization to treat washing wastewater: add lime water with a mass concentration of 0.3-0.5% into the waste liquid collection tank, stir for 8-12 minutes to obtain a uniform slurry, and measure the pH value of the slurry with a pH meter , and add lime water with a mass concentration of 85-95% to adjust the pH value of the slurry to 7; finally add alum solution, stir in the wastewater treatment tank for 10-15 minutes, and then let it stand for stratification to obtain a pH value of 7 in the upper layer. The neutralized water and the insoluble sediment in the lower layer.

Claims (7)

1. A process of washing with citric acid for removing impurity fluorine in phosphogypsum, comprising three processes of citric acid dissolution, citric acid washing and water washing, characterized in that: the citric acid solution can be mixed with impurities in phosphogypsum Chemical action occurs to convert impurities such as fluoride and phosphate in phosphogypsum into water-washable soluble substances, and then remove impurities through water washing process, so that the purified phosphogypsum can be better produced by phosphogypsum acid production cement process utilization, thereby reducing the fluoride content in the drying flue gas, and does not affect the sulfuric acid and cement production process at the same time, the preparation process of the described citric acid plus water washing process includes the following three steps: 1.1 Prepare different concentrations of citric acid solutions: use an electronic balance with an accuracy of 1% to accurately weigh 3.00g, 4.00g, 5.00g, 6.00g and 7.00g of citric acid respectively, and the proportioning mass concentration is 3% and 4% respectively , 5%, 6% and 7% citric acid aqueous solutions for later use, then measure 10mL from the above prepared citric acid aqueous solution and place them in 150mL beakers, add 90mL deionized water each, and dilute it to a mass concentration of 0.3 %, 0.4%, 0.5%, 0.6% and 0.7% citric acid aqueous solution for subsequent use; 1.2 Washing phosphogypsum with citric acid and water: Weigh six samples of phosphogypsum raw materials of 9.00g~9.60g with an electronic balance with an accuracy of 1%, put them in glassware with the same scale and size, and then take them separately. 10mL of 3%, 4%, 5%, 6% and 7% citric acid aqueous solution was added to the phosphogypsum sample, stirred mechanically for 15-25min until dissolved, the dissolved mixture was filtered through a filter device, and the filtrate was transferred to a collection tank for collection , with mass concentrations of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% citric acid aqueous solution, the filtered filter residue was ultrasonically dispersed and washed for 6-10 minutes, and centrifuged at 3000-4000rpm in a centrifuge for 8-12 minutes, Then add pure water to ultrasonically disperse and wash and rotate and centrifuge twice. After centrifugation, the purified phosphogypsum samples 1 ^# , 2 ^# , 3 ^# , 4 ^# , 5 ^# are then subjected to electric heating at 85 ° C. Dry in a constant temperature blast drying oven for 12 hours to obtain the finished product; 1.3 Lime neutralization treatment of washing wastewater: add lime water with a mass concentration of 0.3-0.5% into the waste liquid collection tank, stir for 8-12 minutes to obtain a uniform slurry, measure the pH value of the slurry with a pH meter, and add The lime water with a mass concentration of 85-95% adjusts the pH value of the slurry to 7; finally, add alum solution, stir in the wastewater treatment tank for 10-15 minutes, and then stand for stratification to obtain a neutralized slurry with a pH value of 7 in the upper layer. Water and insoluble sediment in the lower layer. 2. A process of washing with citric acid for removing impurity fluorine in phosphogypsum according to claim 1, characterized in that: said fluorine removal for impurity is fluorine in phosphogypsum. 3. A process of washing with citric acid for removing impurity fluorine in phosphogypsum according to claim 1, characterized in that: said phosphogypsum is the main solid waste produced by wet-process phosphoric acid. 4. A kind of citric acid washing process for removing impurity fluorine in phosphogypsum according to claim 1, is characterized in that: described mass concentration is 3%, 4%, 5%, 6% and 7% citric acid aqueous solution is prepared by mixing water and citric acid. 5. A process of washing with citric acid for removing impurity fluorine in phosphogypsum according to claim 1, characterized in that: the diluted mass concentration is 0.3%, 0.4%, 0.5%, 0.6% % and 0.7% citric acid aqueous solution for pickling process. 6. A kind of citric acid washing process for removing impurity fluorine in phosphogypsum according to claim 1 is characterized in that: the mass concentration of alum added in the described lime neutralization treatment washing wastewater is 50 %, and accounts for one-tenth of the washing water. 7. A kind of citric acid washing process for removing impurity fluorine in phosphogypsum according to claim 1, characterized in that: said lime neutralizes and treats the neutralized water with pH 7 in the upper stratum in the washing wastewater It can be used as washing water again, and the insoluble matter in the lower layer is mainly CaF ₂ .