A method for separating chromium from an alkaline low-chromium vanadium leach solution

Abstract

The application discloses a method for separating chromium from a low-chromium vanadium-containing leaching solution, and the specific steps are as follows: step 1: pretreating a vanadium-containing filter cake to prepare a slurry for standby; the VO(OH)2 content in the vanadium-containing filter cake is greater than or equal to 90 wt%; step 2: adding the slurry prepared in step 1 into an alkaline vanadium-containing leaching solution, adjusting the pH value of the solution to 8.5-10.5, and stirring and reacting at 80-100 DEG C for 60-120 min; wherein the molar ratio of vanadium V in the vanadium-containing filter cake to chromium Cr in the alkaline vanadium-containing leaching solution is n(V):n(Cr)=(4-10):1; step 3: after the reaction in step 2 is completed, standing and filtering to collect purified vanadium solution and chromium-removed residue; and step 4: using the purified vanadium solution for acid ammonium salt vanadium precipitation, collecting the upper liquid obtained after the acid ammonium salt vanadium precipitation, and performing reduction and neutralization to obtain a vanadium-containing filter cake, which is returned to step 1 for continuous use.

Description

Technical Field

[0001] This application relates to the field of hydrometallurgical technology of vanadium, specifically to a method for separating chromium from alkaline low-chromium vanadium-containing leachate. Background Technology

[0002] my country is rich in vanadium-titanium magnetite resources. Industrially, the "blast furnace ironmaking-converter vanadium extraction" process is widely used to obtain vanadium slag. Sodium vanadium extraction, with its mature technology and low cost, has become the industry mainstream, accounting for approximately 70% of production capacity. However, because vanadium and chromium are naturally occurring in vanadium-titanium magnetite and have extremely similar chemical properties, the vanadium-chromium separation coefficient is very low. The chromium content in sodium vanadium extraction solution can reach 1-5 g / L. During subsequent vanadium precipitation with weakly alkaline or acidic ammonium salts, chromium inevitably co-precipitates into ammonium metavanadate or ammonium polyvanadate, severely restricting the improvement of vanadium oxide product purity. In recent years, the all-vanadium redox flow battery industry has accelerated its development, placing stringent requirements on low-chromium vanadium oxide. Impurities in chromium not only reduce battery energy efficiency and system stability but also easily trigger side reactions and material aging. Relevant national standards clearly stipulate that the chromium content of high-quality vanadium electrolytes must not exceed 20 ppm, a level that current technologies struggle to consistently meet. Meanwhile, the upper layer of traditional acidic ammonium salt vanadium precipitation solution is actually a low-concentration vanadium-chromium solution. Current processes mostly use reduction neutralization-evaporation concentration, which is environmentally costly and makes it difficult to separate and recover the vanadium-chromium filter cake as a secondary resource, resulting in significant environmental and resource waste. Therefore, selectively removing chromium from sodium vanadium solution to obtain low-chromium vanadium solution is not only a key technology for preparing battery-grade vanadium oxide, but also a core problem that the industry urgently needs to solve.

[0003] To address the need for vanadium-chromium separation in alkaline vanadium solutions, various conventional reducing agent reduction precipitation processes have emerged in the industry. A related patented technology (CN105861829B) uses low-valent sulfur compounds such as sodium sulfite and sodium metabisulfite, as well as alcohols, aldehydes, and sugars, as reducing agents. Under specific pH and temperature conditions, pentavalent vanadium and hexavalent chromium in the solution are co-reduced to tetravalent vanadium and trivalent chromium, causing the trivalent chromium to precipitate as chromium hydroxide and be removed, while the tetravalent vanadium remains in the solution. Other processes (CN120964886A) use sodium sulfide or sodium hydrosulfide as chromium removal agents, achieving chromium removal through a reduction reaction. However, this type of process has unavoidable technical flaws. The reducing agent used lacks reactivity selectivity, and while reducing hexavalent chromium, it also reduces some pentavalent vanadium in the solution. The reduced vanadium precipitates into the slag phase along with chromium hydroxide, resulting in a direct loss of valuable vanadium. The tetravalent vanadium remaining in the solution requires an additional oxidation process to oxidize it to pentavalent vanadium during the subsequent preparation of vanadium oxide products, increasing reagent consumption, energy consumption, and production control, thus driving up overall production costs. When using sulfur-containing reducing agents such as sodium sulfide and sodium hydrosulfide, sulfur impurities are introduced into the system, affecting the purity of subsequent vanadium products and increasing the environmental pressure on wastewater treatment. Furthermore, this type of process does not achieve deep chromium removal at the vanadium precipitation stage, and the subsequent treatment of the vanadium precipitation supernatant will still produce a mixed vanadium-chromium filter cake, making secondary resource separation and recovery difficult and failing to solve the environmental disposal problem of vanadium-chromium filter cake at its source.

[0004] Of course, some companies in the industry also use a vanadium-chromium co-precipitation-step leaching process, using calcium chloride or barium chloride as precipitating agents (CN106987732B). This process first causes vanadium and chromium in the solution to co-precipitate, and then proceeds through stepwise steps of alkali leaching to extract vanadium and acid leaching to extract chromium, respectively, to prepare vanadium and chromium products. However, this process consumes a huge amount of acid and alkali reagents. After vanadium-chromium co-precipitation, two core processes, alkali leaching and acid leaching, are required, consuming large amounts of acid and alkali reagents throughout, significantly increasing raw material costs. The process is also lengthy, requiring multiple complex steps such as co-precipitation, multi-stage solid-liquid separation, alkali leaching to extract vanadium, and acid leaching to extract chromium. This results in numerous operational steps, a long production cycle, and low efficiency for large-scale production. Furthermore, during stepwise leaching, vanadium and chromium are prone to cross-dissolution, making complete separation impossible and severely limiting the purity of the final vanadium and chromium products. Multiple leaching and washing processes also generate large amounts of high-salinity wastewater, leading to high subsequent water treatment costs and significant environmental impact assessment pressures.

[0005] Existing technologies also include processes for separating chromium using ionic liquid extraction (CN110629050 B). These processes utilize ionic liquids composed of trihexyltetradecyl phosphorus chloride, tributyl phosphate, and diphenyl sulfone as extractants, mixed with an alkaline vanadium-chromium solution, to achieve selective separation of chromium through extraction. This process inevitably introduces phosphorus-containing impurities into the vanadium solution system, affecting the purity of subsequent vanadium oxide products and adding an extra burden to the phosphorus removal process during vanadium extraction. It may even prevent the product from meeting the requirements for high-purity vanadium in battery-grade applications. Furthermore, the ionic liquid extractant suffers from degradation and loss during recycling, requiring regular replenishment and regeneration, significantly increasing long-term operating costs. In addition, emulsification is prone to occur during extraction, and incomplete oil-water separation leads to vanadium entrainment losses. The resulting oily wastewater is difficult to treat, posing a significant environmental risk.

[0006] The vanadium-chromium separation technology based on hydrolysis precipitation (see the literature "Separation of Vanadium and Chromium in Alkaline Solution and Preparation of its Products") uses an alkaline vanadium-chromium solution as raw material. Through hydrolysis precipitation, vanadium preferentially forms a vanadium-containing filter cake, achieving initial separation from chromium in the solution. The vanadium-containing filter cake and chromium-containing solution are then processed through multiple steps to prepare vanadium and chromium products. This technology has a lengthy process flow, requiring multiple precipitation, dissolution, separation, and calcination steps for both vanadium and chromium products. The operation is complex, the production cycle is long, and large-scale production efficiency is low. The entire process consumes large amounts of precipitants, acid-base reagents, and reducing agents. Furthermore, the multiple heating and calcination steps are extremely energy-intensive, significantly increasing overall production costs. During the hydrolysis precipitation process, some chromium co-precipitates with the vanadium into the filter cake. Subsequent vanadium removal processes in the chromium-containing solution are also unable to completely remove vanadium, failing to meet the requirements for preparing high-purity vanadium and chromium products. The multiple steps generate a variety of filter residues and large amounts of washing wastewater, resulting in high subsequent disposal costs and significant environmental pressure. The traditional vanadium precipitation supernatant reduction and neutralization-evaporation concentration process in the industry also has obvious shortcomings. The evaporation concentration process has extremely high energy consumption, and the reduction and neutralization process also requires a large amount of reagents, which greatly increases the operating cost of wastewater treatment. The vanadium-chromium mixed filter cake generated after treatment is a hazardous secondary solid waste. Deep separation of vanadium and chromium is difficult, the resource utilization efficiency is low, and long-term stockpiling poses serious environmental risks. At the same time, vanadium in the wastewater precipitates together with chromium, which cannot be efficiently recovered, resulting in the loss of valuable metal vanadium and reducing the overall vanadium yield of the process. Summary of the Invention

[0007] To address the aforementioned shortcomings, this application provides a method for separating chromium from alkaline low-chromium vanadium-containing leachate. This method solves the technical problems in the existing technology of vanadium-chromium separation from alkaline vanadium-containing leachate, such as high vanadium loss rate due to the lack of reactivity selectivity of the reducing agent, lengthy and cumbersome process, high reagent and energy costs, easy introduction of harmful impurities such as sulfur and phosphorus affecting the purity of vanadium products, inability to avoid the generation of vanadium-chromium mixed filter cake from the source, difficulty in environmentally friendly disposal of secondary solid waste, and difficulty in stably preparing high-purity low-chromium vanadium oxide products that meet the requirements of vanadium redox flow batteries.

[0008] This application provides a method for separating chromium from an alkaline, low-chromium vanadium-containing leaching solution, the specific steps of which are as follows:

[0009] Step 1: Pre-treat the vanadium-containing filter cake to prepare it into a slurry for later use; the VO(OH)2 content in the vanadium-containing filter cake is ≥90wt%;

[0010] Step 2: Add the slurry prepared in Step 1 to the alkaline vanadium-containing leachate, adjust its pH value to 8.5~10.5, and stir the reaction at 80~100 °C for 60~120 min; wherein, the molar ratio of vanadium V in the vanadium-containing filter cake to chromium Cr in the alkaline vanadium-containing leachate is n(V) : n(Cr) = (4~10) : 1;

[0011] Step 3: After the reaction in Step 2 is completed, let it stand and then filter to collect the purified vanadium solution and the chromium-removed slag.

[0012] Step 4: The purified vanadium solution is used for vanadium precipitation with acidic ammonium salts. The supernatant obtained after vanadium precipitation with acidic ammonium salts is collected and reduced-neutralized to obtain a vanadium-containing filter cake. This vanadium-containing filter cake is returned to Step 1 for continued use. The main component of the vanadium-containing filter cake is VO(OH)2, with a content ≥90wt%; the remainder consists of impurities, which will not affect the subsequent separation effect.

[0013] Preferably, in step 1, the preprocessing steps are as follows:

[0014] Mix dilute sulfuric acid with vanadium-containing filter cake, purge with air for 2-5 hours, and filter to obtain slurry for later use; wherein, the pH value of dilute sulfuric acid is 3.0-5.0, and the ratio of the mass of solid in vanadium-containing filter cake to (mass of liquid in vanadium-containing filter cake + mass of dilute sulfuric acid) is 1:(0.2-0.5).

[0015] Preferably, in step 2, the alkaline vanadium-containing leachate is a vanadium-containing solution obtained after sodium roasting, water leaching, and silicon and phosphorus removal from the vanadium-containing material; wherein, in the alkaline vanadium-containing leachate, the vanadium concentration is 15~50 g / L, the chromium concentration is 0.5~5 g / L, the sodium concentration is 10~40 g / L, the Si concentration is ≤0.01 g / L, the P concentration is ≤0.01 g / L, and the pH is 9.0~11.0.

[0016] Preferably, in step 2, sulfuric acid or NaOH is used to adjust the pH value.

[0017] Preferably, in step 4, the purified vanadium solution undergoes acidic ammonium salt precipitation of vanadium through the following steps:

[0018] Ammonium salt was added to control the pH of the purified vanadium solution at 1.8–2.2. The solution was heated to boiling and held at this temperature for at least 0.5 h, then the supernatant was collected. The ratio of m((NH4)2SO4) to m(V) was 1.4–2.0. The main components of the supernatant were: c(Cr) = 0.02–0.10 g / L, c(V) = 0.10–0.50 g / L, and c(NH4)2SO4 = 0.02–0.10 g / L. + The concentration of SO42-5 g / L is 5.00~10.00 g / L. 2- The concentrations of sodium (c) and sodium (cNa) range from 40.00 to 90.00 g / L, and the concentrations of sodium (cNa) range from 10.00 to 40.00 g / L.

[0019] Preferably, in step 4, the specific steps of the reduction-neutralization are as follows:

[0020] The collected supernatant was subjected to reduction-neutralization treatment. H2SO4 was used to control the pH of the reduction process at 1.0~3.0. The amount of reducing agent was calculated based on a molar ratio of n((reducing agent): n(V) = 2.0~4.0). The reduction was carried out by stirring at room temperature for 10~30 min. After the reduction was completed, alkali was added for neutralization, and the pH was controlled at 5.5~8.5. The mixture was stirred at room temperature for 30~60 min. The solid was then collected to obtain a vanadium-containing filter cake.

[0021] Preferably, in step 4, the upper liquid is reduced by a reducing agent; the reducing agent is selected from sodium sulfite, sodium metabisulfite or sodium thiosulfate.

[0022] Preferably, in step 4, the neutralization is carried out by one of sodium hydroxide, sodium carbonate, or ammonia.

[0023] Preferably, in step 4, the pH during the precipitation and collection of the vanadium-containing filter cake is 5.5 to 8.5.

[0024] Preferably, the chromium-removed slag obtained in step 3 is used to prepare Cr2O3.

[0025] Compared with the prior art, this application has the following beneficial effects:

[0026] 1. This application addresses the core problem of existing alkaline vanadium-chromium separation technology in vanadium-containing leaching solutions. Through process coupling and innovative selection of reducing agents, it achieves highly efficient and selective separation of vanadium and chromium, forming a closed-loop vanadium extraction process system. This application achieves highly selective reduction of hexavalent chromium, fundamentally reducing vanadium loss and significantly improving the comprehensive utilization rate of vanadium resources. In conventional reducing agent precipitation technologies used in the prior art, reducing agents such as sodium sulfite, sodium sulfide, alcohols, and sugars lack reaction selectivity. While reducing hexavalent chromium, they inevitably reduce pentavalent vanadium in the system simultaneously, causing vanadium to be lost through co-precipitation with the chromium slag. An additional oxidation process for tetravalent vanadium is required to complete subsequent vanadium extraction. Based on the difference in redox potential between vanadium and chromium redox couples under alkaline conditions, this application uses VO(OH)2 as the core reducing agent. It has selective reduction capability only for hexavalent chromium and will not reduce pentavalent vanadium in the system, thus fundamentally avoiding the loss of valuable metals caused by vanadium entering the chromium slag due to co-reduction. At the same time, the tetravalent vanadium in the reducing agent is oxidized to pentavalent vanadium after reducing hexavalent chromium and re-enters the vanadium-containing solution system, realizing the closed-loop recovery of vanadium in the vanadium precipitation supernatant. Compared with the existing technology, it not only eliminates the process loss of vanadium, but also recovers vanadium resources in wastewater, significantly improving the overall vanadium yield.

[0027] 2. This application eliminates the generation of mixed vanadium-chromium hazardous waste at the source, significantly reducing environmental disposal costs and risks. Existing technologies do not consider deep chromium removal before vanadium precipitation, inevitably leading to the generation of mixed vanadium-chromium filter cakes during subsequent treatment of the acidic ammonium salt vanadium precipitation supernatant. These filter cakes are hazardous solid wastes, difficult to separate deeply from vanadium, have low resource utilization efficiency, and pose serious environmental risks with long-term storage and disposal. Furthermore, processes such as vanadium-chromium co-precipitation and stepwise leaching generate large amounts of high-salt wastewater and waste residue, resulting in high environmental disposal costs. This application achieves deep chromium removal before ammonium salt vanadium precipitation, enriching chromium in a single chromium hydroxide filter cake. The subsequent vanadium precipitation supernatant contains only a low concentration of vanadium, which, after reduction precipitation, yields only a single vanadium-containing filter cake for direct recycling. This completely avoids the generation of mixed vanadium-chromium filter cakes, eliminating the industry problem of secondary hazardous waste separation at the source, significantly reducing environmental costs for wastewater treatment and solid waste disposal, and mitigating the environmental risks associated with hazardous waste storage.

[0028] 3. The method described in this application introduces no harmful foreign impurities throughout the entire process, ensuring the preparation of high-purity vanadium oxide products and consistently meeting the stringent requirements for battery-grade vanadium products. Existing technologies using sulfur-containing reducing agents introduce sulfur impurities into the system, while ionic liquid extraction and separation processes inevitably introduce phosphorus impurities. These impurities not only affect the purity of the final vanadium oxide product but also require additional impurity removal steps, increasing the process burden. Furthermore, they are difficult to reliably meet the national standard requirement that the chromium content of vanadium electrolyte for vanadium redox flow batteries should not exceed 20 ppm. The reducing agent used in this application originates from the reduction product of the vanadium precipitation supernatant in the vanadium extraction process itself, with VO(OH)2 as its core component. The products of the reduction reaction are only pentavalent vanadium and chromium hydroxide precipitates, without introducing any harmful foreign impurities such as sulfur or phosphorus into the system. No additional impurity removal steps are required, and the purified vanadium solution after chromium removal can directly enter the subsequent acidic ammonium salt precipitation process, enabling the stable preparation of low-chromium, high-purity vanadium oxide products, fully meeting the high-quality vanadium raw material requirements of the vanadium redox flow battery industry.

[0029] 4. The process flow of the method described in this application is greatly simplified, and the consumption of reagents and production energy is significantly reduced, giving it a cost advantage for large-scale production. Existing vanadium-chromium separation technologies generally suffer from lengthy process flows: conventional reduction methods require an additional vanadium oxidation step; vanadium-chromium co-precipitation-stepwise leaching processes require multiple precipitation, solid-liquid separation, alkaline leaching, and acid leaching steps; hydrolysis precipitation of vanadium requires separate multi-step production lines for vanadium and chromium; and extraction processes require supporting steps such as extractant regeneration and oil-water separation. All of these suffer from long production cycles, numerous operating steps, and low efficiency in large-scale production, and require the consumption of large amounts of purchased reagents, acid and alkali reagents, and energy. This application deeply couples the vanadium recovery process of the vanadium precipitation supernatant with the upstream alkaline vanadium solution chromium removal process, forming a closed-loop process system. This eliminates the need for additional complex processes and removes the cumbersome steps of secondary oxidation of vanadium, multiple acid-base leaching, and extractant regeneration in existing technologies, significantly shortening the production cycle and improving production efficiency. At the same time, the reducing agent is a by-product of the process, eliminating the need to purchase large quantities of reducing agents or consume large amounts of acid-base reagents for stepwise leaching. This significantly reduces the consumption of raw materials and reagents, as well as the energy consumption of heating and evaporation, thereby greatly reducing overall production costs and making it more suitable for the needs of large-scale industrial production.

[0030] 5. The method described in this application has high chromium removal efficiency, strong process adaptability and operational stability, and is easy to promote and apply industrially. Under optimized process conditions, the chromium removal rate can reach over 98.5%, with a maximum of 99.15%. It can stably reduce the chromium content in alkaline vanadium-containing leachate to below 0.1 g / L, and as low as 0.02 g / L, laying a solid foundation for the subsequent preparation of high-purity vanadium products. At the same time, the process parameter window of this application is wide, with strong adaptability to fluctuations in vanadium and chromium concentrations in the raw material solution. It can be directly connected to the existing mainstream sodium vanadium extraction production line without large-scale modification of the existing main production process. It has strong process compatibility and is easy to promote and apply industrially. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method for separating chromium from alkaline low-chromium vanadium-containing leaching solution described in this application. Detailed Implementation

[0032] This application will clearly and completely describe the technical solutions in the embodiments of this application with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0033] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0034] I. A method for separating chromium from alkaline low-chromium vanadium-containing leachate

[0035] This application addresses the common industry challenge of efficient vanadium-chromium separation in alkaline vanadium-containing leaching solutions during the mainstream sodium vanadium extraction process. Vanadium and chromium are naturally occurring in vanadium-titanium magnetite and have highly similar chemical properties, resulting in an extremely low vanadium-chromium separation coefficient in alkaline sodium vanadium extraction solutions. Existing technologies suffer from the following problems: First, conventional reducing agents such as sodium sulfite, sodium sulfide, and aldolose lack potentioselectivity for the reduction of hexavalent chromium and pentavalent vanadium in alkaline systems, inevitably leading to the simultaneous reduction of pentavalent vanadium. This causes vanadium to be lost through co-precipitation with the chromium slag, necessitating an additional tetravalent vanadium oxidation step, thus lengthening the process and increasing production costs. Second, sulfur-containing reducing agents introduce sulfur impurities into the system, while ionic liquid extraction processes introduce phosphorus impurities. These impurities not only directly affect… The purity of vanadium oxide products requires additional impurity removal processes, which cannot meet the stringent requirements for high-purity vanadium products used in vanadium redox flow batteries. Thirdly, existing processes do not consider deep chromium removal before ammonium salt precipitation, which inevitably leads to the generation of hazardous vanadium-chromium mixed solid waste during subsequent vanadium precipitation supernatant treatment. This type of solid waste is difficult to separate from vanadium and chromium in the second stage, has high environmental disposal costs, and cannot achieve a closed-loop recycling of vanadium resources. Resource utilization and environmental protection requirements cannot be balanced. Fourthly, the existing process parameter window is narrow, and its adaptability to fluctuations in the concentration of vanadium and chromium in the raw material solution is poor. The chromium removal rate is difficult to consistently exceed 98%, and the chromium content in the vanadium solution cannot be stably reduced to below 0.1 g / L, making it difficult to adapt to the needs of large-scale industrial production and the preparation of high-end vanadium products.

[0036] To address the aforementioned core issues, this application proposes a redesign of the vanadium and chromium separation process. In this regard, this application finds that prior art CN105567964A discloses a method for selectively reducing and separating vanadium and chromium from a vanadium-chromium solution. This method uses compounds of V(IV) and / or V(III) and their solutions as reducing agents. Under strongly acidic conditions of pH 0.1~3.5, Cr(VI) in the solution is selectively reduced to Cr(III). Vanadium is then separated by precipitation of polyvanadate / ammonium polyvanadate under acidic conditions, and finally, chromium is recovered from the vanadium-precipitated solution. However, after in-depth research on this scheme, this application found that the core reaction system of the scheme is strictly limited to the strongly acidic range. The thermodynamic basis of its selective reduction is the redox potential difference between dichromate and vanadate ions under strongly acidic conditions, which can only be adapted to acidic vanadium-chromium solution systems. For the alkaline vanadium-containing leachate produced by the mainstream sodium vanadium extraction process, which accounts for more than 70% of the domestic vanadium industry capacity, this scheme requires a large amount of strong acid to adjust the pH of the system from 9.0~11.0 to below 3.5. The subsequent vanadium precipitation and chromium precipitation processes require a large amount of alkali to adjust the pH, resulting in extremely high acid and alkali consumption and a significant increase in industrial application costs. More importantly, the scheme adopts a process logic of reduction first and then vanadium precipitation. The reduced Cr(III) remains in the liquid phase, which cannot solve the problem of insufficient purity of vanadium products caused by chromium co-precipitation in the acidic ammonium salt vanadium precipitation process in the sodium vanadium extraction process, nor can it prevent the generation of mixed hazardous waste of vanadium and chromium during the treatment of vanadium precipitation wastewater from the source. Therefore, this application abandons the above-mentioned approach and starts with the alkaline vanadium-containing leachate produced by the mainstream sodium vanadium extraction process, thereby discovering the occurrence forms and redox couple characteristics of vanadium and chromium in the alkaline system:

[0037] Under alkaline conditions, chromium mainly exists as CrO4. 2- The form exists, and the corresponding half-reaction is as follows:

[0038] CrO4 2- + 4H2O + 3e - ⇌ Cr(OH)3↓ + 5OH - Its redox potential is E θ (CrO4 2- / Cr(OH)3)≈1.25-0.099pH;

[0039] At the same time, vanadium is mainly in the form of VO2(OH)2 - The form exists, and the corresponding half-reaction is as follows:

[0040] VO2(OH)2 - + H2O + e - ⇌ VO(OH)2↓+ 2OH - Its redox potential is E θ (VO2(OH)2 - / VO(OH)2)≈0.2-0.059pH.

[0041] This application, through systematic calculations of the potentials of two redox couples within the pH range of 7.0 to 11.0, discovered that E in this alkaline range... θ (VO2(OH)2 - / VO(OH)2) was consistently significantly lower than E θ (CrO4 2- / Cr(OH)3), which means that VO(OH)2 in this system has the ability to reduce CrO4. 2- The thermodynamic feasibility of the reaction is demonstrated, and since VO(OH)₂ itself is a reduction product of pentavalent vanadium, it will not reduce the pentavalent vanadium in the system, fundamentally solving the problem of selectivity of the reducing agent and completely avoiding the technical problem of co-reduction of pentavalent vanadium. Furthermore, this application calculates the Gibbs free energy of the overall reaction, verifying the thermodynamic feasibility of CrO₄. 2- The reduction precipitation reaction with VO(OH)2 has a negative ΔG value in the range of 0~100 °C, theoretically the reaction can proceed spontaneously, and the reduction products are only Cr(OH)3 precipitate and pentavalent vanadium. The former can be directly removed by solid-liquid separation, and the latter can be reintroduced into the vanadium-containing solution system without causing vanadium loss, and vanadium can be recycled. Based on this, this application unexpectedly discovered that the upper layer liquid produced by acidic ammonium salt precipitation of vanadium in the sodium vanadium extraction process itself contains a low concentration of pentavalent vanadium. After reduction-neutralization precipitation, a vanadium-containing filter cake with VO(OH)2 as the main component can be prepared. This provides a closed-loop source of reducing agent within the process, eliminating the need to purchase reducing agent externally and preventing the introduction of any foreign impurities into the system. At the same time, it can also solve the industry problem of vanadium recovery from the upper layer liquid of vanadium precipitation, avoiding the generation of vanadium-chromium mixed filter cake from the source, forming an integrated solution of "selective reduction chromium removal - closed-loop recycling of vanadium resources - no impurity introduction - hazardous waste source reduction".

[0042] Based on the above findings, this application has specifically designed a fully coupled technical solution for the separation of chromium from alkaline vanadium-containing leaching solutions, the specific steps of which are as follows:

[0043] Step 1: Pre-treat the vanadium-containing filter cake to prepare it into a slurry for later use; the VO(OH)2 content in the vanadium-containing filter cake is ≥90wt%;

[0044] Step 2: Add the slurry prepared in Step 1 to the alkaline vanadium-containing leachate, adjust its pH value to 8.5~10.5, and stir the reaction at 80~100 °C for 60~120 min; wherein, the molar ratio of vanadium V in the vanadium-containing filter cake to chromium Cr in the alkaline vanadium-containing leachate is n(V) : n(Cr) = (4~10) : 1;

[0045] Step 3: After the reaction in Step 2 is completed, let it stand and then filter to collect the purified vanadium solution and the chromium-removed slag.

[0046] Step 4: The purified vanadium solution is used for vanadium precipitation with acidic ammonium salt. The supernatant obtained after vanadium precipitation with acidic ammonium salt is collected and reduced and neutralized to obtain a vanadium-containing filter cake. The vanadium-containing filter cake is returned to Step 1 for continued use.

[0047] First, this application designs a self-production and pretreatment process for the reducing agent. For the low-concentration vanadium in the upper layer of the acidic ammonium salt vanadium precipitation solution, a vanadium-containing filter cake with VO(OH)2 as the main component is prepared through a reduction-neutralization precipitation process. Simultaneously, a pretreatment step of slurrying with dilute sulfuric acid through air is used to convert the small amount of trivalent vanadium in the filter cake into VO(OH)2, ensuring that the effective component content of the reducing agent is ≥90%, guaranteeing the stability and efficiency of the reduction reaction, and solving the problem of fluctuating dechromium removal efficiency caused by insufficient effective component of the reducing agent. Second, this application designs a core process for selective reduction dechromium removal. For the alkaline vanadium-containing leaching solution after desilication and phosphorus removal, the pH of the reaction system is precisely controlled at 8.5~10.5 and the reaction temperature at 80~100 °C. The pretreated vanadium-containing filter cake is added according to a ratio of n(V):n(Cr) = 4.0~10.0. Stirring and slurrying ensure that the reducing agent is fully dispersed in the system. Utilizing the exclusive selective reduction capability of VO(OH)2 for hexavalent chromium, CrO4 is reduced... 2- The vanadium is reduced to trivalent chromium and forms chromium hydroxide precipitate in situ. VO(OH)2 itself is oxidized to pentavalent vanadium and re-enters the vanadium-containing solution system. This achieves deep removal of chromium and fundamentally eliminates vanadium loss during the process. Furthermore, this application also designs a solid-liquid separation and closed-loop circulation process. After the reduction reaction is completed, purified vanadium solution and chromium hydroxide filter cake are obtained through static sedimentation, filtration, and washing. The purified vanadium solution can be directly fed into the subsequent acidic ammonium salt precipitation process, and the chromium hydroxide filter cake can be directly used for calcination to prepare chromium trioxide, realizing the resource utilization of chromium. The upper layer liquid produced in the vanadium precipitation process is again reduced and neutralized to precipitate vanadium-containing filter cake, which is returned to the front-end pretreatment and recycled as a reducing agent, forming a closed-loop circulation system that completely avoids the generation of hazardous mixed vanadium and chromium waste and maximizes the recovery of vanadium resources. Finally, addressing the issue of fluctuating raw material composition in industrial production, this application optimizes key process parameters such as reducing agent ratio, reaction pH, temperature, and stirring time, forming a wide-window parameter control system. This ensures that the process is highly adaptable to raw material solutions with vanadium concentrations of 15~50 g / L and chromium concentrations of 0.5~5 g / L, and can be directly connected to mainstream domestic sodium vanadium extraction production lines without requiring large-scale modifications to the main process, significantly reducing the difficulty of industrialization.

[0048] The method described in this application has achieved unexpected technical effects after practical application: First, it breaks the inherent perception that "chromium removal inevitably involves vanadium loss," achieving a near-zero vanadium loss rate while simultaneously increasing the vanadium resource recovery rate. In existing conventional reduction processes, even optimized solutions generally result in vanadium loss rates exceeding 3%, requiring an additional oxidation process to recover the reduced vanadium. In this application, VO(OH)2 selectively reduces only hexavalent chromium, completely eliminating pentavalent vanadium in the system, fundamentally eliminating vanadium co-reduction losses. Simultaneously, the reducing agent itself is oxidized to pentavalent vanadium and enters the vanadium solution system, further recovering vanadium resources from the upper vanadium layer. The overall vanadium recovery rate is increased by more than 2% compared to existing mainstream processes, achieving simultaneous completion of the chromium removal process and vanadium recovery. Second, it solves the long-standing technical problem of "the inability to simultaneously address deep chromium removal and impurity introduction," achieving ultra-deep chromium removal without impurity introduction. Existing technologies, such as reduction, extraction, and precipitation methods, either inevitably introduce harmful impurities like sulfur and phosphorus, or fail to achieve sufficient chromium removal depth, making it impossible to stably reduce the chromium content in vanadium solutions to below 0.1 g / L. In contrast, the reducing agent used in this application is VO(OH)2, produced in-process. The reduction reaction products are only chromium hydroxide precipitate and pentavalent vanadium, without introducing any external harmful impurities or requiring additional impurity removal steps. Under optimized process conditions, the chromium removal rate can reach up to 99.15%, stably reducing the chromium content in alkaline vanadium-containing leachate to below 0.02 g / L. This lays a solid foundation for the subsequent preparation of battery-grade high-purity vanadium electrolytes with a chromium content ≤20 ppm, fully meeting the stringent requirements of the vanadium redox flow battery industry for high-end vanadium raw materials. Thirdly, this application achieves a dual breakthrough in environmental protection and cost reduction for vanadium extraction processes, completely eliminating the generation of hazardous mixed vanadium-chromium waste from the source. Existing technologies have consistently failed to prevent the generation of mixed vanadium-chromium hazardous waste during the treatment of vanadium precipitation supernatant. The disposal cost of this type of hazardous waste is extremely high, and secondary separation of vanadium and chromium is difficult. Furthermore, existing processes generally suffer from high reagent consumption and energy consumption. This application, however, couples the front-end chromium removal process with vanadium recovery from the vanadium precipitation supernatant, allowing chromium to be enriched and separated at the front end as a single chromium hydroxide filter cake. Subsequently, the vanadium precipitation supernatant only produces a single vanadium-containing filter cake, which is directly recycled, completely avoiding the generation of mixed vanadium-chromium filter cakes and solving the industry problem of hazardous waste disposal at its source. Simultaneously, the reducing agent does not need to be purchased externally, eliminating the consumption of large quantities of externally purchased reducing agents, acid-base reagents, and extractants in existing processes, as well as the energy consumption of evaporation concentration, multiple leaching processes, and extractant regeneration. The overall production cost of this process is reduced by more than 15% compared to existing mainstream processes, achieving simultaneous improvement in environmental and economic benefits. Fourth, it breaks through the bottleneck of the difficulty in large-scale promotion of high-end vanadium-chromium separation processes, with process adaptability and operational stability far exceeding existing technologies.Existing high-end vanadium-chromium separation processes generally suffer from narrow parameter windows, sensitivity to fluctuations in raw material composition, and complex operating procedures, making them difficult to integrate with existing industrial sodium vanadium extraction production lines. In contrast, this solution offers a wide process parameter control window, exhibits strong adaptability to fluctuations in vanadium and chromium concentrations in the feed solution, has a simple operating procedure, and operates stably. It does not require large-scale modifications to existing sodium vanadium extraction production lines; only the addition of a chromium removal reaction unit is needed for industrial integration. The difficulty of industrialization is extremely low, making it highly valuable for industrial promotion.

[0049] In some embodiments of this application, the preprocessing steps in step 1 are as follows:

[0050] The vanadium-containing filter cake is mixed with dilute sulfuric acid and aerated for 2-5 hours. The resulting slurry is then filtered and reserved for use. The pH of the dilute sulfuric acid is 3.0-5.0, and the ratio of the mass of solids in the vanadium-containing filter cake to (the mass of liquid in the vanadium-containing filter cake + the mass of dilute sulfuric acid) is 1:(0.2-0.5). The pretreatment raw material is the vanadium-containing filter cake obtained by reduction and neutralization of the vanadium precipitation supernatant. In addition to the target effective component VO(OH)2, excessive reduction may also generate non-reducible trivalent vanadium V(III). Oxidation using dilute sulfuric acid in a weakly acidic environment, combined with the introduction of air (oxygen), can directionally oxidize inactive V(III) to tetravalent vanadium, generating VO(OH)2, thus increasing the VO(OH)2 content in the filter cake to a certain extent. Simultaneously, using dilute sulfuric acid instead of hydrochloric acid, nitric acid, or other acids avoids the introduction of new impurities such as chloride and nitrate ions, ensuring complete compatibility with the main process's sulfate system and eliminating the risk of additional impurities. The vanadium-containing filter cake particles obtained from neutralization and precipitation are extremely fine and prone to agglomeration. Direct addition would result in clumping, significantly reducing the contact area with hexavalent chromium in the solution, leading to incomplete reduction and a low chromium removal rate. Stirring for 2-5 hours, combined with air aeration and shearing, can thoroughly disperse the agglomerated filter cake particles, preparing a uniform and highly dispersed slurry. This ensures that VO(OH)2 can react with CrO4 after subsequent addition to the main system. 2- Sufficient contact ensures complete and stable reduction reaction, guaranteeing batch-to-batch consistency in chromium removal efficiency.

[0051] In some embodiments of this application, in step 2, the alkaline vanadium-containing leachate is a vanadium-containing solution obtained after sodium roasting-water leaching-desilicon and dephosphorization of vanadium-containing materials; wherein, in the alkaline vanadium-containing leachate, the vanadium concentration is 15~50 g / L, the chromium concentration is 0.5~5 g / L, the sodium concentration is 10~40 g / L, the Si concentration is ≤0.01 g / L, the P concentration is ≤0.01 g / L, and the pH is 9.0~11.0.

[0052] In some embodiments of this application, in step 4, the purified vanadium solution is subjected to conventional acidic ammonium salt precipitation using existing technology to obtain ammonium polyvanadate, thus completing the recovery of vanadium. Simultaneously, the prepared ammonium polyvanadate can be used to prepare high-purity vanadium oxide products, meeting the requirements of the all-vanadium redox flow battery industry for high-end vanadium raw materials. The specific steps are as follows: ammonium salt is added to the purified vanadium solution, the pH value of the purified vanadium solution is controlled at 1.8~2.2 using sulfuric acid, and after heating to boiling and maintaining the temperature for at least 0.5 h, the upper layer is collected; wherein, m((NH4)2SO4): m(V) = 1.4~2.0. The main components of the obtained upper layer are: c(Cr) = 0.02~0.10 g / L, c(V) = 0.10~0.50 g / L, and c(NH4)2SO4 = 0.02~0.10 g / L. + The concentration of SO42-5 g / L is 5.00~10.00 g / L. 2- The concentrations of sodium (c) and sodium (cNa) range from 40.00 to 90.00 g / L, and the concentrations of sodium (cNa) range from 10.00 to 40.00 g / L.

[0053] In some embodiments of this application, in step 4, after the purified vanadium solution is precipitated with acidic ammonium salt, the collected supernatant is subjected to reduction-neutralization treatment, and the collected solid is a vanadium-containing filter cake, which is directly returned to step 1 for reuse. This operation also allows the vanadium-containing filter cake to be reused. The specific steps of the reduction-neutralization are as follows: the collected supernatant is subjected to reduction-neutralization treatment, and H2SO4 is used to control the pH of the reduction process to 1.0~3.0. The amount of reducing agent is calculated as a molar ratio of n((reducing agent): n(V) = 2.0~4.0), and the reduction is carried out by stirring at room temperature for 10~30 min; after the reduction is completed, alkali is added for neutralization, and the pH is controlled to 5.5~8.5. The mixture is stirred at room temperature for 30~60 min, and then the solid is collected to obtain a vanadium-containing filter cake.

[0054] In some embodiments of this application, in step 4, the upper liquid is reduced by a reducing agent; the reducing agent is selected from sodium sulfite, sodium metabisulfite, or sodium thiosulfate.

[0055] In some embodiments of this application, in step 4, the neutralization is carried out by neutralization using one of sodium hydroxide, sodium carbonate, or ammonia.

[0056] In some embodiments of this application, the chromium-removing slag obtained in step 3 is used to prepare Cr2O3. Specifically, Cr2O3 is prepared by calcination.

[0057] II. Examples and Comparative Examples

[0058] The following examples and comparative examples all use the alkaline vanadium-containing leaching solution shown in Table 1.

[0059] Table 1. Composition of alkaline vanadium-containing leachate (g / L)

[0060]

[0061] Example 1

[0062] Add the vanadium-containing filter cake to a dilute sulfuric acid aqueous solution with a pH of 3.0. The liquid-to-solid ratio of the solution to the vanadium-containing filter cake (wet basis, water content 30%) is 0.4:1. Pulverize with air for 4 hours, then filter and set aside for use.

[0063] Example 2

[0064] The vanadium-containing filter cake prepared in Example 4 was added to a dilute sulfuric acid aqueous solution with a pH of 4.0. The liquid-to-solid ratio of the solution to the vanadium-containing filter cake was 0.2:1. The mixture was aerated and pulped for 2 hours, then filtered and set aside for use.

[0065] Example 3

[0066] The vanadium-containing filter cake prepared in Example 5 was added to a dilute sulfuric acid aqueous solution with a pH of 5.0 at a liquid-to-solid ratio of 0.5:1. The mixture was then aerated and pulped for 5 hours, and filtered for later use.

[0067] Example 4

[0068] Take 200 mL of the alkaline vanadium-containing leachate from Table 1, add 15.43 g of the vanadium-containing filter cake treated in Example 1 (moisture content 28.5%, VO(OH)2 content 91.2%), n(V): n(Cr) = 10.0 (n(V) refers only to the V content of the vanadium-containing filter cake), and disperse by slurrying; add sulfuric acid to adjust the pH of the solution to 10.5, and stir the reaction in a 90 °C water bath for 60 min; after the reaction is complete, filter and wash the slurry to obtain 210 mL of purified vanadium solution, the Cr content in the purified solution is 0.03 g / L, and the chromium removal rate is 98.78%.

[0069] The supernatant after vanadium precipitation in the purified vanadium solution was reduced with sodium metabisulfite and neutralized with sodium hydroxide. The pH of the precipitate was controlled to be 5.5 to obtain a vanadium-containing filter cake with a VO(OH)2 content of 91.5% and a water content of 26.4%. This filter cake was returned to the front-end chromium removal process.

[0070] Example 5

[0071] Take 500 mL of the alkaline vanadium-containing leachate from Table 1, add 14.94 g of the vanadium-containing filter cake treated in Example 2 (moisture content 26.4%, VO(OH)2 content 91.5%), n(V): n(Cr) = 4.0 (n(V) refers only to the V content of the vanadium-containing filter cake), and disperse by slurry; add sulfuric acid to adjust the pH of the solution to 9.5, and stir the reaction in an 80 °C water bath for 120 min; after the reaction is complete, filter and wash the slurry to obtain 520 mL of purified vanadium solution, the Cr content in the purified solution is 0.03 g / L, and the chromium removal rate is 98.80%.

[0072] The supernatant after vanadium precipitation in the purified vanadium solution was reduced with sodium metabisulfite and neutralized with sodium hydroxide. The pH of the precipitate was controlled to 7.0 to obtain a vanadium-containing filter cake with a VO(OH)2 content of 91.1% and a water content of 27.3%. This filter cake was returned to the front-end chromium removal process.

[0073] Example 6

[0074] Measure 1000 mL of the alkaline vanadium-containing leachate from Table 1, add 53.17 g of the vanadium-containing filter cake treated in Example 3 (moisture content 27.3%, VO(OH)2 content 91.1%), n(V): n(Cr) = 7.0 (n(V) refers only to the V content of the vanadium-containing filter cake), and disperse by slurry; add sulfuric acid to adjust the pH of the solution to 8.5, and stir the reaction in a 100 °C water bath for 90 min; after the reaction is complete, filter and wash the slurry to obtain 1100 mL of purified vanadium solution, the Cr content in the purified solution is 0.02 g / L, and the chromium removal rate is 99.15%.

[0075] The supernatant after vanadium precipitation in the purified vanadium solution was reduced with sodium metabisulfite and neutralized with sodium hydroxide. The pH of the precipitate was controlled to be 8.5 to obtain a vanadium-containing filter cake with a VO(OH)2 content of 90.8% and a water content of 25.4%. The filter cake was returned to the front-end chromium removal process.

[0076] Comparative Example 1

[0077] Chromium removal was performed using Na₂S. 400 mL of the alkaline vanadium-containing leaching solution from Table 1 was measured, and sulfuric acid was added to adjust the pH to 9.0. Then, 7.77 g of Na₂S (sodium sulfide to chromium molar ratio of 5:1) was added, and the mixture was stirred in a 60 °C water bath for 90 min. After the reaction was complete, the slurry was filtered and washed to obtain 450 mL of purified vanadium solution. The purified solution contained 0.04 g / L of Cr and 40.04 g / L of V, with a chromium removal rate of 98.26% and a vanadium loss rate of 7.54%.

[0078] Comparative Example 2

[0079] Chromium removal was performed using NaHS. 600 mL of the alkaline vanadium-containing leaching solution from Table 1 was measured, and sulfuric acid was added to adjust the pH to 8.5. Then, 8.37 g of NaHS (sodium hydrosulfide to chromium molar ratio of 5:1) was added, and the mixture was stirred in a 90 °C water bath for 60 min. After the reaction was complete, the slurry was filtered and washed to obtain 680 mL of purified vanadium solution. The purified solution contained 0.08 g / L of Cr and 40.25 g / L of V, with a chromium removal rate of 96.45% and a vanadium loss rate of 6.37%.

[0080] As can be seen from the examples and comparative examples:

[0081] (1) All embodiments achieved stable and ultra-deep chromium removal, with chromium removal rates consistently above 98.78%, reaching a maximum of 99.15%; they were able to stably reduce the chromium concentration in the raw material solution from 2.59 g / L to below 0.03 g / L, with a minimum reduction to 0.02 g / L. The process achieved ultra-deep chromium removal in an alkaline system, fully meeting the pre-processing requirements for subsequent battery-grade high-purity vanadium products. All examples maintained excellent chromium removal performance across a wide parameter range with no significant performance fluctuations, demonstrating the process's strong adaptability to raw material composition fluctuations and production parameter adjustments, and its stability for large-scale continuous production. The vanadium-containing filter cake obtained after reduction-neutralization treatment of the vanadium precipitation supernatant had a stable VO(OH)2 content of 90.8%~91.5%, fully meeting the reducing agent quality requirements of the front-end chromium removal process. It can be directly returned to the pretreatment stage for recycling, eliminating the need for externally purchased reducing agents and forming a closed-loop process system. No vanadium loss occurred in any of the examples. While completing vanadium product preparation through vanadium precipitation, the remaining vanadium element remained in the system. The reducing agent VO(OH)2 selectively reduced hexavalent chromium but not pentavalent vanadium in the system, and was itself oxidized to pentavalent vanadium and re-entered the vanadium solution system, fundamentally avoiding the problem of vanadium co-precipitation with chromium slag.

[0082] (2) The two comparative examples using the mainstream sulfur-containing reducing agent of the prior art had an optimal chromium removal rate of only 98.26%, which is lower than the chromium removal level of all embodiments of this application; the chromium removal rate of the NaHS reduction group was only 96.45%, which could not achieve deep removal of chromium, and the technical effect of the examples was significantly different; at the same time, there was also a serious loss of valuable metal vanadium. The vanadium loss rate of Comparative Example 1 (Na2S reduction) was as high as 7.54%, and the vanadium loss rate of Comparative Example 2 (NaHS reduction) was 6.37%, which directly verified that the conventional reducing agent of the prior art has no reaction selectivity. While reducing hexavalent chromium, it will simultaneously reduce pentavalent vanadium in the system, resulting in a large loss of vanadium.

[0083] (3) The direct comparison between the example with no vanadium loss and the comparative example with over 6% vanadium loss fully demonstrates the exclusive reduction selectivity of VO(OH)2 reducing agent for hexavalent chromium in an alkaline system, completely avoiding the reduction of pentavalent vanadium in the system and thus completely preventing the loss of vanadium due to co-reduction into the chromium slag; at the same time, the reducing agent itself is oxidized to pentavalent vanadium and enters the vanadium liquid system, additionally recovering vanadium resources in the upper layer of vanadium precipitation, and realizing the improvement of the overall vanadium yield; at the same time, it also proves that this application can achieve ultra-deep chromium removal, and can stably meet the stringent requirements of high-purity vanadium products for vanadium redox flow batteries. The example with a maximum chromium removal rate of 99.15% and the result of stably reducing the chromium concentration to below 0.02 g / L, compared with the comparative example with a maximum chromium removal rate of only 98.26%, fully verifies the deep removal capability of this application, and lays the foundation for the subsequent preparation of chromium content ≤20 The ppm battery-grade vanadium electrolyte lays the foundation and solves the technical problem that existing technologies cannot stably meet national standards for high-end vanadium products. In the example, the reducing agent is a vanadium-containing filter cake produced in-process, and the reduction products are only pentavalent vanadium and chromium hydroxide precipitates, without any foreign impurities such as sulfur or phosphorus. Compared with the impurity introduction defects of the sulfur-containing reducing agent in the comparative example, it proves that this application does not require an additional impurity removal process. At the same time, it eliminates the cumbersome steps of secondary oxidation of vanadium, multiple acid and alkali leaching, and extractant regeneration in the prior art, which greatly shortens the production cycle and reduces the process complexity and production control costs. In the example, chromium is enriched and separated in the form of a single chromium hydroxide filter cake at the front end of vanadium precipitation, and the subsequent vanadium precipitation supernatant only produces The single vanadium-containing filter cake is recycled, completely avoiding the generation of hazardous solid waste containing vanadium and chromium, thus solving the problem of secondary separation and disposal of hazardous waste at the source. At the same time, the reducing agent does not need to be purchased externally. Compared with the comparative example, which requires a large amount of externally purchased reducing agents, this application can significantly reduce the consumption of raw materials and agents and the cost of environmental disposal, achieving simultaneous improvement in environmental protection and efficiency. The examples maintain excellent chromium removal effect within a wide parameter window, verifying the strong adaptability of the process to fluctuations in the concentration of raw vanadium and chromium. It can be directly connected to the mainstream sodium vanadium extraction production line, which accounts for 70% of the domestic production capacity, without the need for large-scale modification of the main production process. The difficulty of industrialization is low, and it has extremely high industrial promotion and application value.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of this application without departing from the spirit and scope of this technical solution should be covered within the scope of the claims of this application.

Claims

1. A method for separating chromium from an alkaline, low-chromium, vanadium-containing leaching solution, characterized in that, The specific steps are as follows: Step 1: Pre-treat the vanadium-containing filter cake to prepare it into a slurry for later use; the VO(OH)2 content in the vanadium-containing filter cake is ≥90wt%; Step 2: Add the slurry prepared in Step 1 to the alkaline vanadium-containing leachate, adjust its pH value to 8.5~10.5, and stir the reaction at 80~100 °C for 60~120 min; wherein, the molar ratio of vanadium V in the vanadium-containing filter cake to chromium Cr in the alkaline vanadium-containing leachate is n(V) : n(Cr) = (4~10) : 1; Step 3: After the reaction in Step 2 is completed, let it stand and then filter to collect the purified vanadium solution and the chromium-removed slag. Step 4: The purified vanadium solution is used for vanadium precipitation with acidic ammonium salt. The supernatant obtained after vanadium precipitation with acidic ammonium salt is collected and reduced and neutralized to obtain a vanadium-containing filter cake. The vanadium-containing filter cake is returned to Step 1 for continued use.

2. The method according to claim 1, characterized in that, In step 1, the preprocessing steps are as follows: Mix dilute sulfuric acid with vanadium-containing filter cake, purge with air for 2-5 hours, and filter to obtain slurry for later use; wherein, the pH value of dilute sulfuric acid is 3.0-5.0, and the ratio of the mass of solid in vanadium-containing filter cake to (mass of liquid in vanadium-containing filter cake + mass of dilute sulfuric acid) is 1:(0.2-0.5).

3. The method according to claim 1, characterized in that, In step 2, the alkaline vanadium-containing leachate is a vanadium-containing solution obtained after the vanadium-containing material has undergone sodium roasting, water leaching, and desiliconization and dephosphorization.

4. The method according to claim 1, characterized in that, In step 2, the pH value is adjusted using H2SO4 or NaOH.

5. The method according to claim 1, characterized in that, In step 4, when collecting the vanadium-containing filter cake, the neutralization pH value is controlled between 5.5 and 8.

5.

6. The method according to claim 1, characterized in that, The chromium-removed slag obtained in step 3 is used to prepare Cr2O3.

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