Silicon dioxide grafting settling agent based on plant polysaccharide as well as preparation method and application of silicon dioxide grafting settling agent

Abstract

The invention discloses a silicon dioxide grafted settling agent based on plant polysaccharide, which takes plant polysaccharide as a skeleton and is prepared from acid-washed silicon dioxide and a plant polysaccharide aqueous solution, and the raw materials are simple, easy to obtain, environment-friendly, biodegradable and renewable. The invention also discloses a plant polysaccharide-based silicon dioxide grafted settling agent as a raffinate acid settling agent, which can be used for settling raffinate acid at 70-80 DEG C, has high settling efficiency, can adsorb a large amount of settling slag to obtain clarified phosphoric acid, has high phosphorus content in products except the settling slag, and promotes the recovery of phosphorus in the raffinate acid.

Description

Technical Field

[0001] This invention belongs to the technical field of residual acid sedimentation agents, specifically relating to silica-grafted sedimentation agents based on plant polysaccharides, their preparation methods, and applications. Background Technology

[0002] Wet-process phosphoric acid purification technologies include ion exchange, electrodialysis, chemical precipitation, solvent precipitation, cooling crystallization, solvent extraction, adsorption, oxidation, and membrane separation. Among these, solvent extraction is currently widely used in the industrial production of wet-process phosphoric acid. However, the production of high-purity phosphoric acid through solvent extraction inevitably produces a byproduct called raffinate. Raffinate is the raffinate phase left after solvent extraction of wet-process phosphoric acid. Its main components are phosphoric acid that was not extracted into the organic phase, various impurity ions concentrated in the raffinate phase, and various insoluble solid impurities.

[0003] The P2O5 content in the residual acid is almost the same as that of wet-process phosphoric acid, but its metal ion content (based on its corresponding oxide) is higher than that of Fe. 3 + Al 3+ Mg 2+ Both the solid content and the total solid content are higher than those of wet-process phosphoric acid. In general, residual acid is an unavoidable byproduct of current solvent extraction methods, and it is produced in large quantities, has high P2O5 content, and has significant utilization value. The high content of metal cations increases the viscosity of residual acid, and the high solid content makes it prone to scaling and clogging of pipelines. These characteristics severely limit the direct application of residual acid.

[0004] Adding a flocculant to the residual acid purification process can accelerate the settling speed of impurities and improve the clarity of the residual acid product. To a certain extent, this can solve the problem of poor quality concentrated phosphoric acid caused by low-grade phosphate rock, thus optimizing the residual acid production process. Sedimentation, as an important method for pollutant purification, is one of the most widely used and economical treatment technologies. The key to achieving high efficiency in sedimentation lies in adding a high-performance flocculant. Flocculants are substances that, through a series of chemical or physical reactions, can cause the solid phase in a solution to form flocs, thereby removing unnecessary impurities and accelerating the purification process. There are many types of flocculants, which are classified into three main categories based on their chemical composition: inorganic, organic, and microbial. According to their molecular size, they can be classified as high-molecular-weight or low-molecular-weight flocculants. Based on the nature of the charge carried by the functional groups after dissociation in water and the type of the functional groups themselves, they can be classified as cationic, anionic, nonionic, or amphoteric flocculants.

[0005] Traditional raffinate sedimentation technologies mainly include natural sedimentation, inorganic flocculant sedimentation, or organic polymeric flocculant sedimentation. Natural sedimentation is limited to coarse solid particles, relying on the particles' own gravity as the driving force. This results in a slow sedimentation rate and requires a large storage tank, occupying significant space and increasing the difficulty of subsequent processing. Inorganic flocculants require large quantities of flocculants, have low processing efficiency, are highly susceptible to pH fluctuations, and introduce excess impurity ions during sedimentation. Organic polymeric flocculant sedimentation involves adding organic flocculants such as polyacrylamide or carboxymethyl cellulose to the raffinate to accelerate the sedimentation of solid impurities. This increases production costs. Furthermore, the high viscosity of the raffinate makes it difficult for the flocculant to adsorb large amounts of sludge particles onto the surface. The loose sludge particles adsorbed on the surface lead to excessively high bottom liquid levels, making it difficult to obtain clarified phosphoric acid. In summary, traditional technologies fail to achieve rapid sedimentation of raffinate and hinder its subsequent processing.

[0006] Plant polysaccharides constitute a large proportion of natural polymeric flocculants. As natural polymeric flocculants, they are favored in various industries due to their environmentally friendly, biodegradable, and renewable properties. Therefore, developing a new, stable, and highly efficient flocculant is of great significance and has promising market prospects. Summary of the Invention

[0007] The purpose of this invention is to provide a silica-grafted flocculant based on plant polysaccharides as an inorganic-organic composite flocculant, in order to solve the technical problems in the prior art where flocculants are difficult to rapidly settle residual acid and difficult to recover phosphoric acid.

[0008] According to a first aspect of the present invention, a silica-grafted sedimentation agent based on plant polysaccharides is provided, which is prepared by reacting acid-washed silica with an aqueous solution of plant polysaccharides; the aqueous solution of plant polysaccharides is prepared by dispersing plant polysaccharides in deionized water, heating to 45-55°C, adding ammonium persulfate to the deionized water, and reacting to obtain the product; The plant polysaccharide is selected from at least one of carboxymethyl chitosan, sodium alginate, starch, and cellulose; the mass ratio of plant polysaccharide to ammonium persulfate is 1:0.06 to 1:0.10, and the mass ratio of acid-washed silica to ammonium persulfate is 1:0.05 to 1:0.09.

[0009] The silica-grafted flocculant based on plant polysaccharides of this invention is a silica-grafted composite, prepared by grafting and copolymerizing plant polysaccharides as the organic framework with silica. The plant polysaccharides contain a large number of hydroxyl groups, which, on the one hand, determines the flocculant's excellent water solubility; on the other hand, the hydroxyl groups can combine with the chemical components on the surface of solid particles in the raffinate, forming hydrogen bonds, thereby promoting the sedimentation of fine particles. Silica, on the one hand, acts as a carrier for the plant polysaccharides, forming a hybrid flocculant; on the other hand, silica's porous nature, high specific gravity, and large specific surface area facilitate the adsorption or high-speed sedimentation of low-specific-gravity, fine particles in the raffinate. The flocculant has a high specific gravity, low molecular weight, is easily dispersed, easily adsorbs fine particles, and is heat-resistant, enabling it to rapidly combine with fine particles in the system to be purified, thus achieving the sedimentation of the raffinate. Meanwhile, when the silica-grafted flocculant based on plant polysaccharides and polyacrylamide work together on the residual acid, the polyacrylamide can quickly adsorb the flocs formed by the sedimentation of the silica-grafted flocculant based on plant polysaccharides, enhance the net-catching effect, and achieve efficient sedimentation through synergistic effect.

[0010] In some embodiments, the silica particle size is 25-35 μm and the specific surface area is 1100-1300 m². 2 / kg. Preferably, the silica has a particle size of 30 μm and a specific surface area of ​​1100-1200 m². 2 / kg.

[0011] In some embodiments, silica can also be a byproduct of an anhydrous hydrogen fluoride unit, specifically silica produced as a byproduct of anhydrous hydrogen fluoride production via fluorosilicic acid recovery (see "TGZHG 037-2025 Silica Produced as a Byproduct of Anhydrous Hydrogen Fluoride Production via Fluorosilicic Acid Recovery"). It can be a byproduct obtained after pressure filtration and dehydration following the hydrolysis of fluorosilicic acid. Fluorosilicic acid hydrolysis is an important step in the production and recovery of wet-process phosphoric acid, and its byproduct silica has a most frequent particle size of 25-35 μm and a specific surface area of ​​1100-1200 m². 2 / kg, the volume average diameter D[4,3] can be 31.0 μm, the area average diameter D[3,2] can be 5.33 μm, and the volume median particle size D V (50) can be 6.35 μm. Silica has a porous surface, high specific gravity, and large specific surface area, which is conducive to adsorbing or carrying low specific gravity and fine particles in the residual acid. It can be used to prepare silica graft sedimentation agents based on plant polysaccharides, thereby realizing the recycling of silica.

[0012] In some embodiments, the acid-washed silica is prepared by mixing silica with a 1 mol / L hydrochloric acid solution or nitric acid solution, stirring for 20-40 min, washing, and drying.

[0013] In some embodiments, the mass ratio of silica to plant polysaccharides is 1:0.3 to 1:1.5.

[0014] According to a second aspect of the present invention, a method for preparing the above-mentioned silica-grafted sedimentation agent based on plant polysaccharides is provided, comprising the following steps: (1) Disperse plant polysaccharides in deionized water, heat to 45-55℃, add ammonium persulfate to the deionized water, and react for 1.5-2.5 h to obtain a low molecular weight aqueous solution; (2) Add the acid-washed silica to the low molecular weight aqueous solution at 700-900 rpm, add 10% ammonium persulfate solution to the low molecular weight aqueous solution under an inert gas atmosphere and at 45-55℃, and stir the reaction at 400-600 rpm for 5.5-7 h to obtain the product.

[0015] This invention uses ammonium persulfate as a strong oxidizing agent, which decomposes under heating conditions to generate sulfate free radicals ( ): 2 These free radicals possess strong oxidizing properties, initiating the oxidation of plant polysaccharide molecules to yield a low-molecular-weight aqueous solution. Then, acid-washed silica is added to the low-molecular-weight aqueous solution, followed by the addition of ammonium persulfate solution. The resulting free radicals attack the hydroxyl groups (-OH) of the plant polysaccharide molecules, generating ketone groups (-C=O) or carboxylic acid groups (-COOH), forming active free radical sites (such as R0) on the molecular chain. This can trigger cross-linking or binding with SiO2. There are two ways in which plant polysaccharides bind with SiO2: one is that the hydroxyl groups (-Si-OH) on the surface of SiO2 bind with the carboxylic acid groups (-COOH) or hydroxyl groups of the plant polysaccharide through hydrogen bonds; the other is that ammonium persulfate oxidizes the plant polysaccharide to generate carboxylic acid groups, which then undergo esterification with the hydroxyl groups on the surface of SiO2.

[0016] In some embodiments, in step (1), the mass ratio of plant polysaccharide to ammonium persulfate is 1:0.06 to 1:0.10.

[0017] In some implementations, in step (1), each 1 gram of plant polysaccharide is dispersed in 40-60 mL of deionized water.

[0018] In some embodiments, in step (2), the volume ratio of ammonium persulfate solution to low molecular weight aqueous solution is 1:10 to 1:20.

[0019] In some implementations, the inert gas in step (2) is nitrogen.

[0020] According to a third aspect of the present invention, the application of the above-described silica-grafted precipitant based on plant polysaccharides in the preparation of raffinate precipitant is provided.

[0021] Specifically, silica-grafted sedimentation agents based on plant polysaccharides can be used alone for the sedimentation of residual raffinate, or in combination with acrylamide for the sedimentation of residual raffinate.

[0022] In some embodiments, for every 100 mL of residual raffinate, 0.5-0.8 mL of silica-grafted precipitant based on plant polysaccharides and 0.5-1 mL of acrylamide are used for sedimentation.

[0023] In some embodiments, when the silica-grafted precipitant based on plant polysaccharides is used as a precipitant for residual raffinate, the method of use is to preheat the residual raffinate at 70-80°C for ten minutes and then add the silica-grafted precipitant based on plant polysaccharides.

[0024] The beneficial effects of this invention are as follows: (1) The silica graft sedimentation agent based on plant polysaccharides of the present invention is obtained by grafting and copolymerizing plant polysaccharides with silica. The raw materials are simple, readily available, environmentally friendly, biodegradable and renewable.

[0025] (2) The silica-grafted precipitant based on plant polysaccharides of the present invention can be used as a precipitant for the precipitation of residual acid at 70-80℃. It has high precipitation efficiency, can adsorb a large amount of precipitate residue to obtain clear phosphoric acid, and has a high phosphorus content in the products other than precipitate residue, which promotes the recovery of phosphorus in residual acid. Attached Figure Description

[0026] Figure 1 This is the XRD pattern of SiO2 in this invention; Figure 2 This is a particle size diagram of SiO2 in this invention; Figure 3 (a) shows the dosage curve of SiO2-SA. Figure 3 (b) is the dosage curve of SiO2-CMCS; Figure 4 (a) shows the sedimentation effect of SiO2-SA at different dispersion times. Figure 4 (b) shows the sedimentation effect of SiO2-CMCS at different dispersion times; Figure 5 (a) shows the sedimentation effect of SiO2-SA at different temperatures. Figure 5 (b) shows the sedimentation effect of SiO2-CMCS at different temperatures; Figure 6 A comparison chart showing the sedimentation effects of different flocculants; Figure 7 (a) shows the sedimentation effect of 0.6 mL SiO2-carboxymethyl chitosan and 0.5 mL polyacrylamide; Figure 7(b) shows the sedimentation effect of 0.8 mL SiO2-sodium alginate and 0.5 mL polyacrylamide; Figure 7 (c) shows the sedimentation effect of 0.5 mL SiO2-cellulose and 0.5 mL polyacrylamide; Figure 7 (d) shows the sedimentation effect of 0.5 mL of polyacrylamide; Figure 8 XRD pattern of sediment obtained after SiO2-carboxymethyl chitosan treatment; Figure 9 The image shows the XRD pattern of the sediment obtained after SiO2-sodium alginate treatment. Figure 10 Working curve for phosphorus standard solution. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0028] I. Raw Materials and Reagents The SiO2 byproduct from the anhydrous hydrogen fluoride apparatus used in the experiment and the residual acid were both provided by Guizhou Phosphate Group. The residual acid used was in liquid form with a density of 1.717 g / mL. The main component of the residual acid was P2O5, with a content of 47.19%. The contents of water-insoluble matter and organic carbon were 6.70% and 0.019%, respectively.

[0029] The main reagents used in the experiment (all analytical grade) were: polyacrylamide (from Guizhou Phosphate Group); carboxymethyl chitosan (from Shanghai Maclean Biochemical Technology Co., Ltd.); sodium alginate, cellulose, starch, and ammonium persulfate (from Tianjin Fuchen Chemical Reagent Co., Ltd.); potassium persulfate solution (50 g / L); ascorbic acid solution (100 g / L); molybdate solution (26 g / L); phosphorus standard stock solution (50 μg / mL); phosphorus standard working solution (4 μg / mL); potassium dihydrogen phosphate; hydrochloric acid; and nitric acid. All experiments were conducted using deionized water.

[0030] It should be noted that the silica powder used in the embodiments and experiments of this invention can be SiO2 by-product of an anhydrous hydrogen fluoride plant, for example, derived from a concentrated sulfuric acid decomposition process using fluorosilicic acid, a by-product of wet-process phosphoric acid, as raw material. In this process, fluorosilicic acid (H2SiF6) reacts with concentrated sulfuric acid in a reactor to generate anhydrous hydrogen fluoride (HF) and silicon fluoride (SiF4). SiF4 is then absorbed by water / dilute fluorosilicic acid in an absorption tower and hydrolyzed to generate SiO2 precipitate (3SiF4 + 2H2O → 2H2SiF6 + SiO2↓). By-product silica is obtained through solid-liquid separation. A small number of plants use a thermal decomposition-hydrolysis route, which also generates SiO2 in the subsequent hydrolysis stage. The by-product SiO2 produced in this process is also the by-product SiO2 of the anhydrous hydrogen fluoride plant of this invention, and both are existing products obtained using existing technology.

[0031] The resulting SiO2 contains impurity ions including Fe, Mg, Al, and some dust, and is in a disordered state. The XRD pattern of the SiO2 used in Example 1 is shown below. Figure 1 As shown. From Figure 2 It can be seen that the most frequent particle size is approximately 30.5 μm, and the specific surface area is 1126 m². 2 / kg, the volume average diameter D[4,3] is 31.0 μm, the area average diameter D[3,2] is 5.33 μm, and the median volume diameter D V (50) is 6.35 μm.

[0032] The method for preparing acid-washed silica powder is as follows: Prepare a 1 mol / L hydrochloric acid or nitric acid solution, add silica powder and stir for 30 min, wash with deionized water, and then dry in an oven. The purpose of acid washing is mainly to remove the original impurity ions and dust from the silica powder. Each 1 g of silica can be mixed with 0.8-1 mL of a 1 mol / L hydrochloric acid or nitric acid solution for acid washing. In this invention, 3 g of anhydrous hydrogen fluoride byproduct SiO2 is added to 3 mL of a 1 mol / L hydrochloric acid solution and stirred for 30 min to obtain acid-washed silica.

[0033] Example 1 This embodiment provides a method for preparing a silica-grafted sedimentation agent based on plant polysaccharides, including the following steps: (1) Disperse 2g of sodium alginate in 100mL of deionized water, heat to about 50℃, add 0.16g of ammonium persulfate to the deionized water, react for 2h to obtain a low molecular weight aqueous solution.

[0034] (2) 2.4 g of acid-washed silica powder was added to a low-molecular-weight aqueous solution at 800 rpm. Nitrogen gas was introduced for 10 min to remove oxygen. The temperature was raised to 50 °C, and 5 mL of 10% ammonium persulfate solution was added. The mixture was stirred for 6 h under nitrogen and 500 rpm conditions. After vacuum drying at 60 °C, the product was obtained. The silica grafting sedimentation agent based on plant polysaccharides prepared in Example 1 is designated as SiO2-sodium alginate (SiO2-SA).

[0035] Example 2 This embodiment provides a method for preparing a silica-grafted sedimentation agent based on plant polysaccharides, including the following steps: (1) Take 2g of carboxymethyl chitosan and disperse it in 100mL of deionized water. Heat it to about 50℃ and add 0.16g of ammonium persulfate to the deionized water. React for 2 hours to obtain a low molecular weight aqueous solution.

[0036] (2) Take 2.4g of acid-washed silica powder, add it to a low molecular weight aqueous solution at 800 rpm, purge with nitrogen for 10 min to remove oxygen, heat to 50℃, add 5mL of 10% ammonium persulfate solution, and stir the reaction for 6 h while maintaining nitrogen and 500 rpm. Dry under vacuum at 60℃ to obtain the final product. The silica grafting sedimentation agent based on plant polysaccharides prepared in Example 1 is denoted as SiO2-carboxymethyl chitosan (SiO2-CMCS).

[0037] Example 3 This embodiment provides a method for preparing a silica-grafted sedimentation agent based on plant polysaccharides, including the following steps: (1) Take 2g of cellulose and disperse it in 100mL of deionized water. Heat it to about 50℃, add 0.16g of ammonium persulfate to the deionized water, and react for 2h to obtain a low molecular weight aqueous solution.

[0038] (2) Take 2.4 g of acid-washed silica powder, add it to a low molecular weight aqueous solution at 800 rpm, purge with nitrogen for 10 min to remove oxygen, heat to 50℃, add 5 mL of 10% ammonium persulfate solution, and stir the reaction for 6 h while maintaining nitrogen and 500 rpm. Dry under vacuum at 60℃ to obtain the final product. The silica grafting sedimentation agent based on plant polysaccharides prepared in Example 1 is denoted as SiO2-cellulose (SiO2-EC).

[0039] Example 4 This embodiment provides a method for preparing a silica-grafted sedimentation agent based on plant polysaccharides, including the following steps: (1) Disperse 2g of starch in 100mL of deionized water, heat to about 50℃, add 0.16g of ammonium persulfate to the deionized water, react for 2h to obtain a low molecular weight aqueous solution.

[0040] (2) Take 2.4g of acid-washed silica powder, add a low molecular weight aqueous solution at 800 rpm, purge with nitrogen for 10 min to remove oxygen, heat to 50℃, add 5mL of 10% ammonium persulfate solution, and stir the reaction for 6 h while maintaining nitrogen and 500 rpm. Dry under vacuum at 60℃ to obtain the product. The silica grafting sedimentation agent based on plant polysaccharides prepared in Example 1 is denoted as SiO2-starch (SiO2-ST).

[0041] Experimental Example 1 The silica-grafted settling agents based on plant polysaccharides prepared in Examples 1 and 2 were subjected to indoor settling experiments to provide a reference for the settling of residual acid and the recovery and utilization of phosphorus resources in the settling residue.

[0042] Working curve for phosphorus standard solution: Take 0, 0.5, 1, 3, 5, 10, and 15 mL of phosphate standard solution into 50 mL colorimetric tubes, respectively, and dilute with water to 25 mL. Take 25 mL of the above-diluted sample solutions into 50 mL colorimetric tubes, add 4 mL of 50 g / L potassium persulfate solution to the sample and phosphorus standard solution, seal the glass stopper with a small piece of cloth and thread, place in a pressure cooker and heat. After the pressure reaches the set value, keep for 30 min and then stop heating. After cooling, dilute with water to 50 mL. Add 1 mL of 100 g / L ascorbic acid solution and 2 mL of 26 g / L molybdate solution to each digestion solution and mix thoroughly. After color development at room temperature for 15 min, measure the absorbance at 700 nm wavelength with water as a reference to plot the standard curve.

[0043] Sedimentation experiments were conducted in a graduated cylinder, and the sedimentation effect was determined by the volume of the supernatant and the volume of the precipitate during the sedimentation process. The residual raffinate used in the experiment was preheated at 70℃ for ten minutes, removed, stirred evenly, and 100 mL of the residual raffinate was accurately measured and poured into the graduated cylinder. Then, 0.5 mL of polyacrylamide flocculant (PAM) was added and dispersed for 60 seconds to ensure uniformity. Next, the prepared silica-grafted sedimentating agent based on plant polysaccharides was added, dispersed again, and placed in a water bath for natural sedimentation at a constant temperature. The height of the clarified layer was recorded at regular intervals. Following the above steps, the optimal parameters for using the sedimentating agent were determined by changing the temperature, the amount of sedimentating agent, and the dispersion time.

[0044] 1. Testing Method The composition and crystal structure of the sediment were analyzed and tested using an X-ray diffractometer. The scanning range was set to 5~90° and the scanning rate was 5° / min.

[0045] The P2O5 content in the residual acid and sediment was measured using an ultraviolet spectrophotometer, and the phosphorus resource recovery rate in the sediment was calculated. The specific operating steps are as follows: Sample preparation: Take approximately 1g of the supernatant acid after sedimentation and the sludge acid from centrifugation and washing several times into an Erlenmeyer flask. Add 15mL of hydrochloric acid and 5mL of nitric acid, cover with a watch glass, heat to boiling for 15 minutes, remove the watch glass and continue boiling for 3 minutes to expel nitrogen dioxide gas, cool and make up to 250 mL. Dilute to the appropriate concentration using a pipette.

[0046] A fixed addition of 0.5 mL of polyacrylamide flocculant was used; the dispersion time after adding the plant polysaccharide-based silica grafted flocculant was 20, 40, 60, and 80 s; the water bath temperature was 30–90 °C; and the dosage of the plant polysaccharide-based silica grafted flocculant was 0.2, 0.4, 0.6, 0.8, and 1 mL. The dosage, dispersion time, and water bath temperature of the plant polysaccharide-based silica grafted flocculant were then varied.

[0047] 2. Results and Discussion (1) Effect of dosage on sedimentation effect The amount of flocculant used is an important factor affecting the sedimentation effect of residual raffinate. On the one hand, insufficient dosage will result in insufficient charge of the flocculant, thus the adsorption and trapping effect will be insufficient and the sedimentation effect will be poor. Residual raffinate will produce sediment flocs, but the upper layer will be relatively turbid and the sedimentation will be slow. On the other hand, excessive dosage will result in waste and increase the viscosity of residual raffinate, which will be detrimental to sedimentation. Therefore, confirming the dosage is an important parameter for the use of flocculant.

[0048] The effect of the dosage of plant polysaccharide-based silica-grafted sedimentation agent on sedimentation effect is as follows: Figure 3 As shown. Figure 3 (a) shows the dosage curve of SiO2-SA. Figure 3 (b) shows the dosage curve of SiO2-CMCS. As can be seen from the figure, the sedimentation effect of the silica-grafted sedimentation agent based on plant polysaccharides is better with the increase of sedimentation time. Among them, when the dosage of SiO2-SA is 0.8 mL, the sedimentation effect is the best when it is added together with polyacrylamide flocculant and residual acid; when the dosage of SiO2-CMCS is 0.6 mL, the sedimentation effect is the best when it is added together with polyacrylamide flocculant and residual acid.

[0049] (2) Effect of dispersion time on sedimentation effect The effect of varying dispersion time on the sedimentation of residual acid was studied using a silica-grafted flocculant based on plant polysaccharides and a polyacrylamide flocculant. The results are as follows: Figure 4 As shown. Figure 4 (a) shows the sedimentation effect of SiO2-SA at different dispersion times. Figure 4(b) shows the sedimentation effect of SiO2-CMCS at different dispersion times. Figure 4 It can be seen that the optimal dispersion time for both SiO2-SA and SiO2-CMCS is 60s. After 60s, the settling rate decreases with the extension of time. This is because the longer dispersion time breaks up the formed flocs, reducing the settling speed and effect.

[0050] (3) Effect of temperature on sedimentation The water bath temperature was modified to 30~90℃, and the effect of temperature on the sedimentation effect was as follows: Figure 5 As shown. Figure 5 (a) shows the sedimentation effect of SiO2-SA at different temperatures. Figure 5 (b) shows the sedimentation effect of SiO2-CMCS at different temperatures. From Figure 5 It can be seen that the higher the water bath temperature, the better the sedimentation effect of SiO2-SA and SiO2-CMCS. When the temperature reaches 90℃, the synergistic use of the two sedimentation agents and polyacrylamide still has a very good sedimentation effect, indicating that the two sedimentation agents can be used in systems with higher temperatures. The system temperature in the production process of raffinate is usually 70~80℃. Therefore, silica-grafted sedimentation agents based on plant polysaccharides have broad application prospects in the sedimentation of raffinate.

[0051] (4) Comparison of Settlement Effects The dispersion time was set to 60 s and the water bath temperature to 70 ℃. The sedimentation effect of different flocculants combined with polyacrylamide flocculants was studied compared with the use of polyacrylamide alone. The results are as follows: Figure 6 and Figure 7 As shown. Figure 6 This is a comparison chart of the sedimentation effects of different flocculants. Figure 7 (a) shows the sedimentation effect of 0.6 mL SiO2-carboxymethyl chitosan and 0.5 mL polyacrylamide; Figure 7 (b) shows the sedimentation effect of 0.8 mL SiO2-sodium alginate and 0.5 mL polyacrylamide; Figure 7 (c) shows the sedimentation effect of 0.5 mL SiO2-cellulose and 0.5 mL polyacrylamide; Figure 7 (d) shows the sedimentation effect of 0.5 mL of polyacrylamide. From Figure 6 and Figure 7 It can be seen that the combined use of different settling agents and polyacrylamide flocculants has a significantly better settling effect on residual acid than the use of polyacrylamide flocculant alone.

[0052] The settling rates of different flocculants are shown in Table 1. As can be seen from Table 1, when the settling time is 30 min, the settling rate and compression ratio (the ratio of the volume of the clear liquid to the volume of the sludge) of the two flocculants used in combination are better than those of polyacrylamide alone.

[0053] Table 1. Settling rates of different flocculants

[0054] Experiment Example 2 In this experiment, XRD analysis was performed on the sediment obtained by treating residual raffinate with 0.6 mL SiO2-carboxymethyl chitosan and 0.5 mL polyacrylamide for 30 min in Experiment Example 1, and on the sediment obtained by treating residual raffinate with 0.8 mL SiO2-sodium alginate and 0.5 mL polyacrylamide for 30 min in Experiment Example 1.

[0055] The XRD pattern of the sediment obtained after treatment with SiO2-carboxymethyl chitosan and polyacrylamide is shown in the figure. Figure 8 As shown, its main components include the following: C2H4K2N4O4, Ca6(H2O)6Fe9O6(PO4)9(H2O)3, Fe2(SO4)3(H2O)9, CuFe2(SO4)4(H2O)6, (H3O)(Al3(H2PO4)6(HPO4)2)(H2O)4, (Ca2(H2O)2)(Mn3O2(PO4)3)(H2O), Mg2(B6O7(OH)6)2(H2O)9, C 15 H 11 NO2, (Fe 0.84 Al 0.16 3KH 14 (PO4)8 4H2O, Al3KH 14 (PO4)8 4H2O, Fe3K(NH4)H 14 (PO4)8 4H2O, C6H 14 CdN2O4 3H2O, C6H 18 Br2CoO3, C 16 H40I6N2Sn, C 12 H 10 N2O2, KFeH 14 (PO4)8 4H2O.

[0056] The XRD pattern of the sediment obtained after treatment with SiO2-sodium alginate and polyacrylamide is shown in the figure. Figure 9 As shown, its main components include the following: Mn2(Al4Si5O)18 ), Na3Fe(PO4)(CO3), (Na,K)(Na,Ca)(Mg,Fe,Ti)5Si8O 22 (OH,F)2, (Fe,Ca,Mg,Mn,Na)7(Si,Al)8O 22 (OH) 1.9 Mg2Si5Al4O 18 、KFeH 14 (PO4)8 4H2O, (Mg 0.30 Fe 0.70 )2Na 0.05 (Al4Si5O 18 (H2O) 0.66 Na₂Ca(Fe,Mg)₄FeSi₇AlO 22 (F,OH)2,Na2Ca(Mg,Fe)4Al(Si7Al)O 22 (OH)2, Mg 0.34 Fe 1.66 Al4Si5O 18 , Ca6(Si2O7)(OH)6, (Ca2(H2O)2)(Mn3O2(PO4)3)(H2O), Ca6(H2O)6(Fe9O6(PO4)9)(H2O)3.

[0057] from Figure 8 and Figure 9 It can be seen that the composition of the sediment obtained by treating residual acid with different silica-grafted sedimentation agents based on plant polysaccharides and polyacrylamide is different. The sediment is rich in metal elements and has certain application potential in the production of fertilizer and feed grade phosphates, metal recovery, or as an industrial raw material.

[0058] Experimental Example 3 In this experiment, the sediment obtained from treating raffinate with 0.6 mL of SiO2-carboxymethyl chitosan and 0.5 mL of polyacrylamide for 30 min, and the sediment obtained from treating raffinate with 0.8 mL of SiO2-sodium alginate and 0.5 mL of polyacrylamide for 30 min, were washed three times with 20 mL of water respectively, and then centrifuged at 8000 rpm for 30 min to obtain supernatant after different washing cycles. The absorbance of the supernatant acid after sedimentation and the supernatant after different washing cycles were measured using a UV spectrophotometer, and their P2O5 content was calculated.

[0059] After digesting and developing color in a 4 μg / mL phosphorus standard solution, the absorbance was measured to plot a working curve. Figure 10As shown in the figure. The absorbance of the supernatant acid obtained from sedimentation with different flocculants and the supernatant after different washing and centrifugation cycles were substituted into the above curves. The phosphorus content of the supernatant acid obtained from sedimentation with the two flocculants and the supernatant after different washing cycles are shown in Tables 2 and 3. In Table 3, the P recovery rate is the ratio of the P2O5 content of the sediment obtained after washing with water to the P2O5 content of the sediment before washing.

[0060] As shown in Table 2, the phosphorus content of the supernatant acid obtained after sedimentation by both flocculants is above 50%. The resulting sediment is viscous, and some residual acid is not completely obtained. The sediment is directly centrifuged to obtain the supernatant acid and the solid residue. At this point, the percentage of supernatant acid (clear liquid) to the sediment before centrifugation (clear liquid percentage) reaches 70%, and the phosphorus content (P2O5 content) is about 45%.

[0061] Table 3 shows the phosphorus content in the sedimentation liquid obtained after one washing and the sedimentation liquid obtained after two washings. The phosphorus content in the sedimentation liquid obtained after one washing is above 25%, and the phosphorus recovery rate of both sedimentation liquids after one washing is above 50%. The phosphorus content in the sedimentation liquid obtained after two washings is around 12%, and the phosphorus recovery rate of the sedimentation liquid obtained after two washings is around 25%. These results indicate that the phosphorus content in the sedimentation residue obtained after treating residual acid with a silica-grafted sedimentation agent based on plant polysaccharides is reduced after washing, indicating a high phosphorus resource recovery rate in the obtained sedimentation liquid.

[0062] Table 2. Acidity and phosphorus content of the supernatant and sedimentation liquid after sedimentation with different flocculants

[0063] Table 3. Phosphorus content of the first and second wash liquors of sediment obtained with different settling agents

[0064] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A silica-grafted sedimentation agent based on plant polysaccharides, characterized in that, It is prepared from acid-washed silica and an aqueous solution of plant polysaccharides; the aqueous solution of plant polysaccharides is prepared by the following method: plant polysaccharides are dispersed in deionized water, heated to 45-55℃, and ammonium persulfate is added to the deionized water, and the reaction is carried out to obtain the product; The plant polysaccharide is selected from at least one of carboxymethyl chitosan, sodium alginate, starch, and cellulose; the mass ratio of the plant polysaccharide to the ammonium persulfate is 1:0.06 to 1:0.10, and the mass ratio of the acid-washed silica to the ammonium persulfate is 1:0.05 to 1:0.

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2. The silica-grafted sedimentation agent based on plant polysaccharides according to claim 1, characterized in that, Silica has a particle size of 25-35 μm and a specific surface area of ​​1100-1300 m². 2 / kg.

3. The silica-grafted sedimentation agent based on plant polysaccharides according to claim 1, characterized in that, Acid-washed silica is prepared by mixing silica with 1 mol / L hydrochloric acid solution or nitric acid solution and stirring for 20-40 min, then washing and drying.

4. The silica-grafted sedimentation agent based on plant polysaccharides according to any one of claims 1 to 3, characterized in that, The silicon dioxide is silicon dioxide produced as a byproduct of anhydrous hydrogen fluoride recovery from fluorosilicic acid.

5. The method for preparing the silica-grafted sedimentation agent based on plant polysaccharides according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Disperse plant polysaccharides in deionized water, heat to 45-55℃, add ammonium persulfate to the deionized water, and react for 1.5-2.5 h to obtain a low molecular weight aqueous solution; (2) Add the acid-washed silica to the low molecular weight aqueous solution at 700-900 rpm, add 10% ammonium persulfate solution to the low molecular weight aqueous solution under an inert gas atmosphere and at 45-55℃, and stir the reaction at 400-600 rpm for 5.5-7 h to obtain the product.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of plant polysaccharide to ammonium persulfate is 1:0.06 to 1:0.

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7. The preparation method according to claim 5, characterized in that, The mass ratio of pickled silica to ammonium persulfate is 1:0.05 to 1:0.

09.

8. The preparation method according to claim 5, characterized in that, In step (2), the volume ratio of ammonium persulfate solution to low molecular weight aqueous solution is 1:10 to 1:

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9. The preparation method according to claim 5, characterized in that, In step (2), the inert gas is nitrogen.

10. The application of the silica-grafted precipitant based on plant polysaccharides according to any one of claims 1 to 4 in the preparation of raffinate precipitant.

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