Method for removing impurities phosphorus, chromium and silicon in sodium vanadium solution

Abstract

The invention relates to the field of vanadium and chromium separation, and particularly discloses a method for removing impurities phosphorus, chromium and silicon in a sodium modified vanadium solution, which comprises the following steps: S100, adjusting the pH value of the sodium modified vanadium solution to enable the pH value of a solution system to be 8.0-9.0 at room temperature to obtain a pretreated sodium modified vanadium solution; s200, heating the pretreated sodium vanadium solution, sequentially adding a reducing agent and a polyelectrolyte into the solution while stirring, and carrying out phosphorus and chromium removal reaction while stirring; s300, after the removal reaction of phosphorus and chromium is carried out for a period of time, adding a silicon removal agent, and carrying out a removal reaction of silicon; and S400, after the silicon removal reaction is finished, standing sedimentation and solid-liquid separation are carried out, impurity-removed slag is washed with water and then merged into the filtrate, and purified vanadium liquid is obtained. According to the method, firstly, glucose is adopted to selectively reduce hexavalent chromium into trivalent chromium under the weakly alkaline condition, pentavalent vanadium is not reduced, the trivalent chromium forms chromium phosphate and chromium hydroxide precipitates in a weakly alkaline solution, and meanwhile, the chromium removal efficiency is improved in a polyelectrolyte coagulation mode.

Description

Technical Field

[0001] The invention belongs to the technical field of extracting vanadium oxide from vanadium slag, and particularly relates to a method for removing impurities phosphorus, chromium and silicon from sodium vanadium solution. Background Art

[0002] Among the existing vanadium slag vanadium extraction processes, the following have been industrialized: sodium roasting-water leaching, calcium roasting-acid leaching, and sub-molten salt techniques. The sodium roasting-water leaching process accounts for 70% of the industry's total production capacity. During the sodium roasting process, due to the similar physicochemical properties of vanadium and chromium, the low-valent vanadium in the vanadium slag is converted into water-soluble sodium vanadate, while some chromium is converted into sodium chromate. Furthermore, some sodium phosphate, sodium silicate, and other substances are generated. Consequently, during the water leaching process of the sodium roasted clinker, some phosphorus, chromium, and silicon enter the vanadium solution, becoming major impurities in the sodium roasting solution. In the subsequent acidic ammonium salt precipitation process, phosphorus forms a stable complex with vanadium, H7[P(V2O5)6], affecting the vanadium precipitation rate and product quality. Therefore, aluminum sulfate or calcium chloride is commonly used for dephosphorization before vanadium precipitation. After phosphorus removal, the sodium vanadium solution contains certain concentrations of chromium and silicon. These two impurities have little impact on the acidic ammonium salt vanadium precipitation process. Using sodium vanadium solution containing a certain range of chromium and silicon concentrations for acidic ammonium salt vanadium precipitation can produce vanadium oxide products that meet general quality requirements. However, high-end applications such as high-purity vanadium compounds, vanadium-based catalysts, and all-vanadium redox flow batteries require higher levels of silicon and chromium impurities in vanadium oxide. Therefore, to maximize the value of vanadium resources, it is necessary to simultaneously remove the impurities phosphorus, chromium, and silicon from the sodium vanadium solution before vanadium precipitation.

[0003] At present, the separation and removal of phosphorus, chromium and silicon in sodium vanadium solution mostly adopts the step-by-step impurity removal method, and there are also reports on the technology of co-removal of phosphorus and silicon, and co-removal of chromium and silicon.

[0004] Regarding phosphorus removal from sodium vanadium liquor, the patented "Phosphorus Removal and Purification Method for Vanadium-Containing Clinker Leachate" (CN 1506474 A) uses a certain weight ratio of crystallized aluminum chloride and calcium chloride to prepare a phosphorus removal purifier solution using industrial aqueous solution. This phosphorus removal purifier solution is then added to the vanadium-containing clinker leachate with a pH of 8.5-11.0 at a specific volume ratio. The solution is heated to 80±5°C and stirred for 15 minutes. A 3g / L neutral polyacrylamide solution is then added to the solution for flocculation and allowed to settle for clarification. The sedimentation underflow is then filtered through a plate and frame filter press, and the filtrate is incorporated into the upper layer of purified vanadium liquor. The underflow residue is washed and filtered to recover soluble vanadium. The patent "Method for Purifying Alkaline Vanadium Leachate" (CN 101709376 B) uses evaporated condensed water from vanadium precipitation wastewater to mix with part of acidic vanadium precipitation wastewater to obtain a leaching agent; uses the above leaching agent to leach sodium-roasted clinker to obtain an alkaline vanadium leachate; then uses magnesium nitrate to purify the alkaline vanadium leachate to obtain a purified clear solution; uses ammonium salt to precipitate vanadium in the purified clear solution to obtain vanadium products and vanadium precipitation wastewater, and partially reuses the wastewater in the mixing step.

[0005] In terms of chromium removal, that is, separation of vanadium and chromium, there are processes that use reduction dechromization or alkaline extraction to separate vanadium and chromium. For example, the patent "A method for separating vanadium and chromium in vanadium-chromium solution" (CN 117265268 A) first adds a reducing agent (one or more of sodium metabisulfite, sodium sulfite, and vanadyl sulfate) to the vanadium solution to convert the highly soluble hexavalent chromate anions into low-valent, easily precipitated Cr 3+ cations, and then add soluble Mn 2+ Chromium removal agent of salt, making Cr in vanadium-containing solution 3+Efficient precipitation achieves deep separation of chromium from vanadium solution. The patent "A Method for Separating and Recovering Vanadium Chromium from Vanadium Chromium Solution" (CN 105861829 B) describes adding a reducing agent selected from sodium sulfite, sodium metabisulfite, sodium thiosulfate, sodium bisulfite, sodium sulfide, sulfur dioxide, sulfur powder, hydrazine hydrate, methanol, ethanol, formaldehyde, acetaldehyde, glucose, sucrose, or starch to a vanadium chromium solution at a pH of 8-14 and a temperature of 20-100°C. This reduces pentavalent vanadium and hexavalent chromium to tetravalent vanadium and trivalent chromium under alkaline conditions. The trivalent chromium then forms an in-situ chromium hydroxide precipitate, which is filtered to obtain a chromium hydroxide filter cake and a vanadium-containing filtrate. The chromium hydroxide filter cake is used to prepare chromium trioxide, and the vanadium-containing filtrate is used to prepare hydrated vanadium dioxide, vanadyl sulfate, or vanadium pentoxide. The patent "A Method for Extracting and Separating Chromium from an Alkaline Vanadium-Chromium Solution" (CN 110629050 B) involves mixing an organic solution containing an ionic liquid extractant with an alkaline vanadium-chromium solution for extraction. This results in a system with two coexisting liquid layers: an upper chromium-containing organic phase and a lower vanadium-containing aqueous phase. The resulting chromium-containing organic phase is then mixed with a stripping agent solution and stripped to produce a lower chromium-containing aqueous phase and an upper organic phase. The upper organic phase is then recycled to separate the chromium. Compared to chemical precipitation, this extraction process is relatively costly.

[0006] In terms of removing impurity silicon, aluminum salts, calcium salts or magnesium salts are often used for separation and removal by chemical precipitation. For example, the patent "A method for desiliconization of alkaline vanadium solution" (CN 117737486 A) mixes alkaline vanadium solution and aluminate solution, then adjusts the pH value of the mixed solution, and obtains purified liquid and desiliconized slag through solid-liquid separation.

[0007] Regarding the combined removal of phosphorus and silicon, the patent "A Method for Purifying and Removing Impurities from Vanadium Leaching Solution" (CN 102251113 A) uses a mixture of ammonium sulfate and magnesium sulfate to remove phosphorus from the vanadium leachate. The pH of the solution is then adjusted and aluminum sulfate is added to remove silicon. This method uses different purifiers to remove silicon and phosphorus in separate steps, resulting in a relatively lengthy process. The patent "A Method for Removing Silicon and Phosphorus from Sodium-Based Vanadium Extraction Leachate" (CN 102477493 B) uses soluble magnesium salts, ammonium salts, and soluble aluminum salts to synergistically remove silicon and phosphorus impurities. Aluminum salts offer high desiliconization efficiency and low vanadium loss.

[0008] Furthermore, regarding the co-removal of chromium and silicon from sodium vanadium solution, the patent "A Method for Selective Reduction of Chromium and Silicon in Sodium Vanadium Solution" (CN 118726770 A) involves adjusting the pH of the sodium vanadium solution to 10.5-11.5 at 60°C. A predetermined amount of sodium sulfide / sodium hydrosulfide is then added for a reduction reaction. At the end of the reaction, aluminum sulfate is added for silicon removal. Solid-liquid separation is then performed, and the solid phase is washed with water and added to the filtrate to produce a decontamination solution. The decontamination solution is then subjected to an oxidative purification treatment to produce a purified solution. This method utilizes the fact that, under specific concentration and pH conditions in the sodium solution, vanadium primarily exists as pyrovanadate, which has low oxidizability, stable properties, and is not easily reduced. Even if a small amount is reduced, the vanadium remains in the solution as vanadate, while the chromate is selectively reduced to form chromium hydroxide, completing the vanadium-chromium separation as a chromium hydroxide precipitate. The patent "A Method for Preparing Low-Silicon, Low-Chromium Vanadium Liquid" (CN 109136556 A) provides a method for preparing low-silicon, low-chromium vanadium liquid, comprising the following steps: Step 1: Leaching a vanadium-containing material with water or an acid solution, followed by filtration to obtain a vanadium-containing leachate; Step 2: Heating the vanadium-containing leachate to 60-80°C, adjusting the pH to 7.0-9.0, adding sodium metaaluminate to the solution at a molar ratio of 0.5-1.0:1 to the Si content of the vanadium-containing leachate, and filtering to obtain a low-silicon vanadium liquid; Step 3: Adjusting the pH of the low-silicon vanadium liquid to 7.0-9.0, adding sodium sulfite at a molar ratio of 0.4-1.0:1 to the Cr content of the vanadium-containing leachate, stirring, and filtering to obtain a low-silicon, low-chromium vanadium liquid. This method boasts high impurity removal efficiency, simple process operation, and broad application prospects. The patent "A method for the synergistic removal of silicon and chromium from vanadium solution by nickel ions to prepare high-purity vanadium pentoxide" (CN114480883 B) describes a method for the synergistic removal of silicon and chromium from vanadium solution by nickel ions. The method comprises: providing a vanadium-containing solution, adding acid to the vanadium-containing solution, adjusting the pH value to 6-9, adding a reducing agent to carry out a reduction reaction; adding alkali to the reduced vanadium solution, adjusting the pH value to 10.5-12, adding Ni 2+ The method of the present invention reduces the silicon, chromium, and nickel contents in the vanadium solution to below 5 ppm, achieving excellent impurity removal. The resulting high-purity vanadium pentoxide has a purity exceeding 99.99%, resulting in a high-purity product.

[0009] In summary, to remove the impurities phosphorus, chromium, and silicon from sodium vanadium solution, aluminum, calcium, or magnesium salts are commonly used for phosphorus removal. However, calcium and magnesium salts result in relatively high vanadium loss during use, and the chloride ions introduced place high demands on system equipment. Aluminum salts can simultaneously remove the impurities phosphorus and silicon, but also require precise control of the solution pH range. For chromium removal, reduction precipitation is often used. However, most reducing agents are sulfur-containing, which is not conducive to the subsequent recycling of sodium salts, making wastewater treatment technically difficult. Furthermore, partial reduction of vanadium occurs, requiring the subsequent oxidation step of low-valent vanadium. Desiliconization often uses aluminum salts, which offer low cost and high efficiency, but require high operational requirements and precise pH control to avoid the introduction of aluminum impurities. For the co-removal of phosphorus and silicon or chromium and silicon, two or more composite impurity removers are often used to achieve impurity purification. No relevant technology has been found to simultaneously remove the impurities phosphorus, chromium, and silicon.

[0010] Therefore, the existing process technology for removing impurities such as phosphorus, chromium and silicon from sodium vanadium solution still needs to be optimized and upgraded. Summary of the Invention

[0011] In response to the shortcomings of the existing technology, the main purpose of the present invention is to provide a method for removing phosphorus, chromium and silicon impurities from sodium vanadium solution. The sodium vanadium solution obtained by the sodium roasting-water leaching process of vanadium slag is used as raw material (pH=10.0~12.0). To solve the problem of separating and removing the impurities phosphorus, chromium and silicon in the alkaline solution, glucose is first used to selectively reduce hexavalent chromium to trivalent chromium under weakly alkaline conditions. Pentavalent vanadium is not reduced, and trivalent chromium forms chromium phosphate and chromium hydroxide precipitates in the weakly alkaline solution. At the same time, the chromium removal efficiency is improved by polyelectrolyte coagulation.

[0012] In order to solve at least one of the above technical problems, the present invention adopts the following technical solutions: According to the present invention, a method for removing impurities such as phosphorus, chromium and silicon from sodium vanadium solution is provided, comprising the following steps: S100, adjusting the pH value of the sodium vanadium solution so that the pH value of the solution system at room temperature is 8.0-9.0, thereby obtaining a pretreated sodium vanadium solution; S200, heating the pretreated sodium vanadium solution, sequentially adding a reducing agent and a polyelectrolyte to the solution while stirring, and performing a phosphorus and chromium removal reaction under stirring; S300, after the phosphorus and chromium removal reaction has been carried out for a period of time, adding a silicon removal agent to perform a silicon removal reaction, wherein the phosphorus and chromium removal reaction and the silicon removal reaction constitute the entire impurity removal reaction; S400, after the silicon removal reaction is completed, allowing the solution to settle, performing solid-liquid separation, washing the impurity removal residue with water, and then combining it with the filtrate to obtain a purified vanadium solution.

[0013] According to one embodiment of the present invention, in step S100, CO2 gas is introduced into the sodium vanadium solution to adjust the pH value of the solution.

[0014] According to one embodiment of the present invention, in step S200, the temperature of the phosphorus and chromium removal reaction is controlled to be 85-95°C.

[0015] According to one embodiment of the present invention, the molar ratio of the reducing agent to Cr in the sodium vanadium solution is (0.3-0.5):1.

[0016] According to one embodiment of the present invention, in step S200, the reducing agent is anhydrous glucose; and the polyelectrolyte is a sulfur-free polymer.

[0017] According to one embodiment of the present invention, the sulfur-free polymer is one of sodium polyacrylate and sodium polymethacrylate.

[0018] According to one embodiment of the present invention, the polyelectrolyte is sodium polyacrylate with a molecular weight of 1000-3000; in step S200, the mass ratio of the reducing agent to sodium polyacrylate is (10-20):1.

[0019] According to one embodiment of the present invention, the entire impurity removal reaction is maintained for 30 to 60 minutes; in step S300, the silicon remover is added 10 to 20 minutes before the end of the entire impurity removal reaction.

[0020] According to one embodiment of the present invention, in step S300, the molar ratio of the silicon remover to Si in the sodium vanadium solution is (0.2-0.4):1; the silicon remover is sodium metaaluminate.

[0021] According to one embodiment of the present invention, in step S400, the static sedimentation time is controlled to be 120-240 minutes.

[0022] By adopting the above technical solution, the present invention has at least one of the following advantages compared to the prior art: (1) The impurity removal process is simple and feasible, with low investment cost and easy implementation; (2) The amount of reducing agent used is small and the cost is low; (3) The phosphorus, chromium and silicon co-removal process does not introduce sulfur-containing by-products, which is conducive to the subsequent recovery and recycling of sodium salts; (4) The removal efficiency of phosphorus, chromium and silicon is high, achieving deep purification of vanadium liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 Schematic diagram of the steps of a method for removing phosphorus, chromium and silicon impurities from sodium vanadium solution according to one embodiment of the present invention; Figure 2 Flowchart of a method for removing phosphorus, chromium and silicon impurities from sodium vanadium solution according to one embodiment of the present invention; Figure 3 This is a trend diagram of the oxidation-reduction potential (ORP) values ​​of glucose (GLC) and chromium and vanadium ions changing with pH. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0026] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in the present invention, it is readily apparent to those skilled in the art that various modifications are feasible without departing substantially from the teachings of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, variations, and deletions may be made to the design, operating conditions, and parameters of the following exemplary embodiments.

[0027] This method uses sodium-containing vanadium liquid (pH 10.0-12.0) obtained through a sodium-containing roasting and water leaching process of vanadium slag as raw material. To address the separation and removal of phosphorus, chromium, and silicon impurities in alkaline solutions, glucose is first used under weakly alkaline conditions to selectively reduce hexavalent chromium to trivalent chromium, while pentavalent vanadium is not reduced. The trivalent chromium precipitates as chromium phosphate and chromium hydroxide in the weakly alkaline solution. Simultaneously, polyelectrolyte coagulation is used to improve chromium removal efficiency. Later in the reaction, aluminum salt is added to the solution for synergistic silicon removal, achieving a one-step removal of phosphorus, chromium, and silicon impurities from the solution, achieving deep purification of the vanadium liquid. The entire vanadium liquid purification process is a one-step process, simple to operate, and eliminates the introduction of sulfur-containing byproducts. The vanadium-containing filtrate can be used to recover vanadium resources by precipitating ammonium metavanadate with ammonium bicarbonate. The vanadium precipitation wastewater can be separated and crystallized to produce sodium carbonate, enabling sodium salt recycling. This simplifies wastewater treatment processes and reduces treatment costs.

[0028] Specific as Figure 1 As shown, the method for removing phosphorus, chromium and silicon impurities from sodium vanadium solution according to one embodiment of the present invention generally includes the following steps: S100, adjusting the pH value of the sodium vanadium solution so that the pH value of the solution system at room temperature is 8.0-9.0, thereby obtaining a pretreated sodium vanadium solution; S200, heating the pretreated sodium vanadium solution, adding a reducing agent and a polyelectrolyte to the solution in sequence while stirring, and performing a phosphorus and chromium removal reaction under stirring; S300, after the phosphorus and chromium removal reactions have been carried out for a period of time, a silicon removal agent is added to carry out a silicon removal reaction, wherein the phosphorus and chromium removal reactions and the silicon removal reactions constitute the entire impurity removal reaction; S400, after the silicon removal reaction is completed, the mixture is allowed to settle and solid-liquid separated, and the impurity-removed residue is washed with water and then added to the filtrate to obtain a purified vanadium solution.

[0029] Combine Figure 2 As shown, in step S100, a certain volume of sodium vanadium solution can be pumped into the impurity removal tank, CO2 gas is introduced, and the pH value of the solution is adjusted to 8.0-9.0. In the pH range of 8.0-9.0, the vanadium in the sodium vanadium solution is mostly in the form of HV2O7 3- Chromium exists in the form of CrO4 2- Form exists. Combined Figure 3 The trend of the oxidation-reduction potential (ORP) value of chromium and vanadium ions with pH is shown in the graph. Under this condition, CrO4 2- The redox potential (ORP-Cr) of the Cr(OH)3 precipitate is always higher than that of HV2O7. 3- Reduction to HV2O5 - The oxidation-reduction potential (ORP-V) of the product. For the specific reduction reaction formula, please refer to Formula 1 and Formula 2: HV2O7 3- +4H + +2e HV2O5 - +2H2O φ =0.991-0.11832pH+0.02958lg(a(HV2O7 3- ) / a(HV2O5 - )) (Formula 1) CrO4 2- +5H + +3e Cr(OH)3↓+H2O φ =1.23+0.0197lga(CrO4 2- )-0.0985pH(Formula 2) In an embodiment of the present invention, step S200 can heat the vanadium solution to 85-95°C by steam, add glucose (0.3-0.5):1 times the stoichiometric ratio of hexavalent chromium and sodium polyacrylate (1 / 20-1 / 10 of the mass of glucose) under stirring, and stir and keep warm for reaction. Figure 3 The results of the ORP-GLC test of glucose solution (0.1 mol / L, 25°C) at different pH values ​​show that the ORP value of glucose is between E θ (CrO4 2- / Cr(OH)3) and E θ (HV2O7 - / HV2O5 3- ), indicating that within the pH range of 8.0-9.0, using glucose as a reducing agent can achieve selective reduction of hexavalent chromium in the sodium vanadium solution, while leaving pentavalent vanadium unreduced, while simultaneously forming a chromium hydroxide precipitate to remove chromium. Furthermore, at a pH of 8.0-9.0, phosphate in the solution can also react with trivalent chromium to form a chromium phosphate precipitate, thereby contributing to dephosphorization. Furthermore, considering the colloidal nature of trivalent chromium (positively charged), the introduction of sodium polyacrylate (an electrolyte with a negative charge) during the reduction and chromium removal process can better achieve colloidal coagulation, thereby achieving higher chromium removal efficiency. Aluminum salts are highly effective in removing silicon. To control the introduction of aluminum impurities, the present invention adds sodium metaaluminate as a silicon removal agent within the pH range of 8.0-9.0. It is worth noting that since the precipitates generated during the impurity removal process, such as chromium phosphate, chromium hydroxide, aluminum silicate, and aluminum hydroxide, are all colloidal and have different charges, a certain degree of coprecipitation occurs, thereby reducing the amount of impurity removal agent used and achieving deep purification of the sodium vanadium solution.

[0030] In embodiments of the present invention, the entire impurity removal reaction can last for 30-60 minutes. Preferably, in step S300, sodium metaaluminate at a stoichiometric ratio of (0.2-0.4) times the Si content of the original sodium vanadium solution can be added 10-20 minutes before the end of the entire impurity removal reaction to remove silicon. Subsequently, the silicon removal reaction is controlled to continue for 10-20 minutes, completing the entire impurity removal reaction.

[0031] After the entire impurity removal reaction is completed, heating and stirring are stopped. In step S400, the reaction slurry is allowed to settle for 120-240 minutes, and plate-frame filter pressing and washing are performed to obtain purified vanadium liquid. The purified vanadium-containing filtrate is subjected to a process of direct precipitation of ammonium metavanadate using ammonium carbonate to obtain ammonium metavanadate, and the vanadium precipitation wastewater is separated and crystallized to produce sodium carbonate. The ammonia generated during the evaporation process is absorbed by dilute sulfuric acid to achieve ammonia reuse, and the sodium carbonate is returned to the roasting process for recycling. The crystallized liquid is returned to the leaching process. The ammonium carbonate can be ammonium carbonate or ammonium bicarbonate.

[0032] The following is a specific embodiment of the method for removing phosphorus, chromium and silicon impurities from sodium vanadium solution according to the present invention and its specific process parameters.

[0033] Examples 1-3 all used solutions with chemical compositions as shown in Table 1 (pH = 10.2 / 25°C) to remove phosphorus, chromium, and silicon impurities: Table 1 Composition of sodium vanadium solution (g•L) -1

[0034] Example 1: Take 500 ml of the sodium solution of the composition shown in Table 1, and introduce CO2 to adjust its pH to 8.0 / 25°C to obtain the pretreated vanadium solution; heat the pretreated vanadium solution in a water bath to 85°C, add 1.70 g of glucose (n(C6H 12 O6) / n(Cr)=0.5), 0.17g sodium polyacrylate (1 / 10 of the mass of glucose), maintain the water bath temperature, and stir to react for 40min; continue to add 0.36g sodium aluminate (n(NaAlO2) / n(Si)=0.4), and stir to react for 20min; after the reaction is completed, let it stand and settle for 120min, filter and wash the slurry to obtain 550ml of purified vanadium solution.

[0035] The purified liquid contains c(P)=0.005g / L, c(Cr)=0.004g / L, c(Si)=0.009g / L, c(Al)=0.010g / L, c(V)=20.61g / L, c(V 4+ )<0.1g / L. According to the calculation, the removal rates of impurities P, Cr, and Si (liquid basis) are 91.67%, 99.78%, and 98.39% respectively, and the V loss is 1.52%.

[0036] Example 2: Take 1000 ml of the sodium solution of the composition shown in Table 1, and introduce CO2 to adjust its pH to 8.5 / 25°C to obtain the pretreated vanadium solution; heat the pretreated vanadium solution in a water bath to 90°C, add 2.71 g of glucose (n(C6H 12 O6) / n(Cr)=0.4), 0.18g sodium polyacrylate (1 / 15 of the mass of glucose), maintain the water bath temperature, and stir to react for 30min; continue to add 0.54g sodium aluminate (n(NaAlO2) / n(Si)=0.3), and stir to react for 15min; after the reaction is completed, let it stand and settle for 180min, filter and wash the slurry to obtain 1150ml of purified vanadium solution.

[0037] The purified liquid contains c(P)=0.003g / L, c(Cr)=0.005g / L, c(Si)=0.008g / L, c(Al)=0.009g / L, c(V)=19.55g / L, c(V 4+ )<0.1g / L. According to the calculation, the removal rates of impurities P, Cr, and Si (liquid basis) are 94.77%, 99.71%, and 98.51% respectively, and the V loss is 2.33%.

[0038] Example 3: Take 2000 ml of the sodium solution of the composition shown in Table 1, and add CO2 to adjust its pH to 9.0 / 25°C to obtain the pretreated vanadium solution; heat the pretreated vanadium solution in a water bath to 95°C, add 4.07 g of glucose (n(C6H12 O6) / n(Cr)=0.3), 0.20g sodium polyacrylate (1 / 20 of the mass of glucose), maintain the water bath temperature, and stir to react for 20min; continue to add 0.72g sodium aluminate (n(NaAlO2) / n(Si)=0.2), and stir to react for 10min; after the reaction is completed, let it stand and settle for 240min, filter and wash the slurry to obtain 2280ml of purified vanadium solution.

[0039] The obtained purified liquid contains c(P)=0.004g / L, c(Cr)=0.006g / L, c(Si)=0.007g / L, c(Al)=0.008g / L, c(V)=19.76g / L, c(V 4+ )<0.1g / L. According to the calculation, the removal rates of impurities P, Cr, and Si (liquid basis) are 93.09%, 99.65%, and 98.70% respectively, and the V loss is 2.14%.

[0040] Example 4 Take 2000 ml of the sodium solution of the composition shown in Table 1, and add CO2 to adjust its pH to 9.0 / 25°C to obtain the pretreated vanadium solution; heat the pretreated vanadium solution in a water bath to 95°C, add 4.07 g of glucose (n(C6H 12 O6) / n(Cr)=0.3), 0.21g sodium polymethacrylate (1 / 20 of the mass of glucose), maintain the water bath temperature, and stir to react for 20min; continue to add 0.72g sodium aluminate (n(NaAlO2) / n(Si)=0.2), and stir to react for 10min; after the reaction is completed, let it stand and settle for 240min, filter and wash the slurry to obtain 2265ml of purified vanadium solution.

[0041] The purified liquid contains c(P)=0.005g / L, c(Cr)=0.003g / L, c(Si)=0.006g / L, c(Al)=0.005g / L, c(V)=19.82g / L, c(V 4+ )<0.1g / L. According to the calculation, the removal rates of impurities P, Cr, and Si (liquid basis) are 91.42%, 99.83%, and 98.90% respectively, and the V loss is 2.49%.

[0042] By adopting the above technical solution, according to the method of the present invention for removing phosphorus, chromium and silicon impurities from sodium vanadium solution, based on the differences in the ionic forms and oxidation-reduction potential (ORP) of vanadium and chromium in aqueous solution within a specific pH range, glucose is used as an alkaline reducing agent to first selectively reduce hexavalent chromium to trivalent chromium, while pentavalent vanadium is not reduced. Trivalent chromium and phosphate form a co-precipitation of chromium phosphate and chromium hydroxide in a weakly alkaline solution, and efficient chromium removal is achieved under the coagulation action of a polyelectrolyte. In the later stage of the reaction, sodium metaaluminate is used to collaboratively remove silicon from the solution, thereby achieving a one-step removal of the impurities phosphorus, chromium and silicon in the solution, thereby achieving the purpose of deep purification of the vanadium solution.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. If the present invention is modified or replaced with equivalents without departing from the spirit and scope of the present invention, they should be included in the scope of protection of the claims of the present invention.

[0044] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the disclosure of the embodiments of the present invention is limited to these examples. Within the spirit of the embodiments of the present invention, the technical features of the above embodiments or different embodiments may be combined, and there are many other variations of different aspects of the above embodiments of the present invention, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention shall be included within the scope of protection of the embodiments of the present invention.

Claims

1. A method for removing impurities such as phosphorus, chromium and silicon from sodium vanadium solution, characterized in that: The following steps are involved: S100, adjusting the pH value of the sodium vanadium solution so that the pH value of the solution system at room temperature is 8.0-9.0, thereby obtaining a pretreated sodium vanadium solution; S200, heating the pretreated sodium vanadium solution, adding a reducing agent and a polyelectrolyte to the solution in sequence while stirring, and performing a phosphorus and chromium removal reaction under stirring; S300, after the phosphorus and chromium removal reaction proceeds for a period of time, adding a silicon removal agent to perform a silicon removal reaction, wherein the phosphorus and chromium removal reaction and the silicon removal reaction constitute the entire impurity removal reaction; S400, after the silicon removal reaction is completed, the mixture is allowed to settle and solid-liquid separated, and the impurity-removed residue is washed with water and then added to the filtrate to obtain a purified vanadium solution.

2. The method according to claim 1, characterized in that In step S100, CO2 gas is introduced into the sodium vanadium solution to adjust the pH value of the solution.

3. The method according to claim 1, characterized in that In step S200, the temperature of the phosphorus and chromium removal reaction is controlled to be 85-95°C.

4. The method according to claim 1, wherein In step S200, the molar ratio of the reducing agent to Cr in the sodium vanadium solution is (0.3-0.5):

1.

5. The method according to claim 1, wherein In step S200, The reducing agent is anhydrous glucose; The polyelectrolyte is a sulfur-free polymer.

6. The method according to claim 5, characterized in that The sulfur-free polymer is one of sodium polyacrylate and sodium polymethacrylate.

7. The method according to claim 6, characterized in that The polyelectrolyte is sodium polyacrylate with a molecular weight of 1000-3000; In step S200, the mass ratio of the reducing agent to sodium polyacrylate is (10-20):

1.

8. The method according to claim 1, characterized in that The entire impurity removal reaction is maintained for 30 to 60 minutes; In step S300, the time for adding the silicon remover is 10 to 20 minutes before the end of the entire impurity removal reaction.

9. The method according to claim 8, characterized in that In step S300, The molar ratio of the silicon remover to Si in the sodium vanadium solution is (0.2-0.4):1; The silicon remover is sodium metaaluminate.

10. The method according to claim 1, characterized in that In step S400, the static sedimentation time is controlled to be 120-240 minutes.

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