Method for green vanadium precipitation and sodium-ammonium circulation of sodium-modified vanadium liquid

Abstract

The invention relates to a method for green vanadium precipitation and sodium-ammonium circulation of a sodium modified vanadium solution, and belongs to the technical field of hydrometallurgy. The method comprises the following steps: adding hydrochloric acid and ammonium chloride into the sodium vanadium solution, adjusting the pH value, carrying out heating reaction, and carrying out solid-liquid separation to obtain ammonium polyvanadate and vanadium precipitation wastewater; adding a reducing agent into the vanadium precipitation wastewater for reduction reaction; adding a polycarboxylic acid water reducer, adjusting the pH value with ammonia water, and carrying out solid-liquid separation to obtain purified wastewater and vanadium-chromium filter residues; introducing carbon dioxide gas into the purified wastewater until the purified wastewater is saturated, cooling, crystallizing, and carrying out solid-liquid separation to obtain sodium bicarbonate solid and crystallization mother liquor; and evaporating and concentrating the crystallization mother liquor until the concentration of ammonium chloride is 65-75g / L, then cooling and crystallizing at the temperature of-10-20 DEG C, and carrying out solid-liquid separation to obtain ammonium chloride solid and residual wastewater. According to the invention, high-efficiency and high-purity recovery of sodium and ammonium ions and closed circulation of the system are realized, and the problems of sodium and ammonium circulation and impurity accumulation in the traditional process are solved.

Description

TECHNICAL FIELD

[0001] The application relates to a method for green vanadium precipitation and sodium-ammonium circulation of sodiumized vanadium liquid, and belongs to the technical field of hydrometallurgy. BACKGROUND

[0002] Vanadium slag, stone coal, waste catalyst or petroleum residue containing vanadium is the main raw material for extracting vanadium. The most important existing process is sodiumization roasting-water leaching process. Sodiumization roasting uses sodium salt as an additive, and through high-temperature roasting, vanadium in the vanadium raw material is oxidized and converted into water-soluble sodium vanadate. After water leaching, vanadium is transferred into the liquid phase to obtain sodiumized vanadium liquid, which has the advantages of wide raw material adaptability, high vanadium recovery rate and the like.

[0003] At present, sodiumized vanadium liquid vanadium precipitation mainly adopts ammonium salt vanadium precipitation technology, such as ammonium sulfate vanadium precipitation, which has the advantages of high vanadium precipitation rate and good product quality, but introduces sulfate, produces a large amount of sodium sulfate and ammonium sulfate mixed salt which is difficult to economically and effectively separate, causing waste of sodium and ammonium resources and solid waste disposal problems, that is, the "sodium-ammonium circulation dilemma". Therefore, it is urgent to seek a new green vanadium precipitation process.

[0004] Patent CN202110425663 discloses a method for sodiumization roasting-water leaching purification liquid vanadium precipitation with hydrochloric acid. Hydrochloric acid is added to the purification liquid to adjust the pH value of the solution. Under heating and continuous stirring, the precipitate is separated out. After washing and heating, the product with a vanadium pentoxide content of 98.0%, 99.0% and 99.5% is obtained.

[0005] Patent CN202210241452 discloses a method for preparing ammonium metavanadate by sodiumization vanadium extraction combined with alkali production and low-cost utilization of vanadium slag. Vanadium slag and sodium carbonate are fully mixed in proportion, and sodiumization roasting and water leaching are carried out at 850-900 DEG C. After leaching and filtration, impurities such as phosphorus and silicon in the solution are removed by using calcium chloride and polyaluminum chloride in sequence. After filtration, the qualified liquid is obtained, then ammonium chloride is added for vanadium precipitation, and the precipitated ammonium metavanadate is purified and melted into vanadium tablets. The tail liquid of vanadium precipitation is adjusted in pH value by hydrochloric acid, then iron trichloride is added to remove vanadium, then ferrous chloride and sodium hydroxide are added to remove chromium, and then ammonium bicarbonate is added to precipitate sodium bicarbonate. After filtration, the filtrate is added with hydrochloric acid to remove carbonate, and then evaporated to supersaturation, and ammonium chloride crystals are precipitated by cooling.

[0006] Patent CN202210632357 discloses a method for preparing sodium carbonate and co-producing ammonium sulfate by using sodium sulfate, which comprises the following steps: (1) mixing sodium sulfate, ammonium bicarbonate recovery liquid, ammonium bicarbonate solid or mixed gas of ammonia gas and carbon dioxide, and obtaining sodium bicarbonate and double decomposition mother liquor through double decomposition reaction; the obtained sodium bicarbonate is calcined to obtain sodium carbonate; (2) separating the double decomposition mother liquor through nanofiltration membrane to obtain ammonium bicarbonate recovery liquid and sulfate concentrate; (3) mixing complex salt, evaporation mother liquor and sulfate concentrate, and obtaining sodium sulfate and complex salt washing liquid through temperature rising crystallization; (4) cooling crystallization of the complex salt washing liquid to obtain complex salt and rich ammonium sulfate solution; (5) evaporation crystallization of the rich ammonium sulfate solution to obtain ammonium sulfate and evaporation mother liquor.

[0007] Patent CN202311790663 discloses a method for preparing high-purity sodium carbonate and ammonium chloride by using sodium chloride waste salt, which relates to the technical field of sodium chloride waste salt treatment. The method still adds sodium chloride for salting-out crystallization after obtaining sodium bicarbonate mother liquor through double decomposition reaction, and produces mixed crystals of sodium bicarbonate and ammonium chloride without adding other substances to decompose bicarbonate. The salting-out crystallization mother liquor is subjected to one-time cooling crystallization, and the ammonium chloride in the mixed crystals is dissolved by using the one-time cooling crystallization mother liquor. The method can prepare high-purity sodium carbonate and ammonium chloride, and the obtained products have high purity. The total alkali content of the sodium carbonate product is above 99.0%, meeting the requirements of GB / T 210-2022 for industrial sodium carbonate type II qualified products. The mass percentage of the ammonium chloride product is above 99%, meeting the requirements of GB / T 2946-2018 for industrial ammonium chloride qualified products.

[0008] The above technical process is long, and no effective solution is proposed for the deep removal and interference inhibition of high-concentration and multi-component impurities (such as V, Cr, Si, P, etc.) in vanadium precipitation wastewater, resulting in low purity of the recovered sodium bicarbonate and ammonium chloride products, which cannot be directly returned to the main process for circulation, and the circulation stability is poor, which makes industrial application difficult. Therefore, the existing technology lacks a short process and low-cost green vanadium precipitation process that can simultaneously realize high-purity vanadium pentoxide production, efficient and high-purity recovery of sodium and ammonium ions in vanadium precipitation wastewater, and long-term stable circulation of the entire system. SUMMARY

[0009] The purpose of the present application is to provide a method for green vanadium precipitation and sodium-ammonium circulation of sodium vanadate solution.

[0010] To achieve the purpose of the present application, the method comprises the following steps: A, vanadium precipitation: adding hydrochloric acid and ammonium chloride to the sodium vanadate solution, adjusting the pH to 1.6-2.2, heating at 80-100℃ for 30-120 minutes, and solid-liquid separation to obtain ammonium polyvanadate and vanadium precipitation wastewater; B, reduction: adding a reducing agent to the vanadium precipitation wastewater obtained in step A for reduction reaction; C. Deep impurity removal: Add polycarboxylate superplasticizer to the wastewater after reduction in step B. The amount added is 0.2% to 0.8% of the mass of the vanadium-precipitated wastewater. Then adjust the pH to 7 to 10 with ammonia water, and separate the solid and liquid to obtain purified wastewater and vanadium-chromium filter residue. D. Sodium recovery: Carbon dioxide gas is introduced into the purified wastewater obtained in step C until saturation, and then the water is cooled and crystallized at -10 to 20°C. Solid-liquid separation is performed to obtain sodium bicarbonate solid and crystallization mother liquor. E. Ammonium recovery: The crystallization mother liquor obtained in step D is evaporated and concentrated to an ammonium chloride concentration of 65-75 g / L, and then cooled and crystallized at -10-20℃. Solid-liquid separation is performed to obtain ammonium chloride solid and residual wastewater.

[0011] The solid-liquid separation can be achieved through filtration.

[0012] In one specific embodiment, the amount of ammonium chloride added in step A is 0.8 to 1.5 times the molar amount of vanadium in the vanadium sodium solution.

[0013] In one specific embodiment, the vanadium sodium solution mentioned in step A is obtained by sodium roasting of vanadium slag, coal shale, waste catalyst or petroleum slag containing vanadium at 700-900°C, followed by water leaching.

[0014] In one specific embodiment, the chemical composition of the vanadium sodium solution satisfies the following: V 15~60g / L, Na 10~50g / L, Cr 0.5~25g / L, Si 0.1~2.0g / L, P 0.01~1.0g / L, Al 0.1~1.0g / L.

[0015] In one specific embodiment, the reducing agent in step B is iron powder or ferrous chloride.

[0016] In one specific embodiment, the amount of reducing agent added is 1.5 to 4.0 times the total molar amount of vanadium and chromium ions in the vanadium-precipitated wastewater.

[0017] In one specific embodiment, the volume concentration of carbon dioxide in step D is ≥80%.

[0018] In one specific embodiment, the sodium bicarbonate solid described in step D is dried to a moisture content of <5% and then returned to sodium roasting for recycling.

[0019] In one specific embodiment, the remaining wastewater from step E is returned to the water leaching recycling after sodium roasting.

[0020] In one specific embodiment, the CO2 and ammonia generated from the evaporation and concentration in step E are absorbed and returned to the purified wastewater in step D for recycling.

[0021] In one specific embodiment, the ammonium chloride solid described in step E is dried to a moisture content of <3% and then returned to step A for recycling.

[0022] Beneficial Effects: The technical solution provided by this invention achieves the following significant progress through the synergistic innovation of three core links: "hydrochloric acid-ammonium chloride vanadium precipitation system", "iron reduction + water-reducing agent synergistic impurity removal", and "CO2 direct carbonization-low temperature coupled crystallization": 1. It achieves efficient recovery and closed-loop recycling of sodium and ammonium ions, with near-zero wastewater discharge, effectively solving the sodium and ammonium recycling dilemma of traditional processes and supporting green vanadium precipitation.

[0023] 2. Good system cycle stability: The recovered sodium bicarbonate and ammonium chloride products have high purity (>97%) and can be directly reused. After multiple cycles, no significant accumulation of key impurity elements was observed in the system, demonstrating excellent long-term operational stability. This successfully solves the industry problem of "system failure caused by impurity accumulation during sodium ammonium recycling".

[0024] 3. Short-process, low-cost sodium ammonium recovery: Directly introducing CO2 gas into the purified wastewater and controlling the crystallization temperature between -10 and 20°C results in a shorter process, lower cost, and simpler operation compared to adding solid reagents such as ammonium bicarbonate. This specific temperature range is the optimized range for achieving highly selective crystallization and high yield of sodium bicarbonate; exceeding this range will lead to a decrease in product purity or economic benefits. Detailed Implementation

[0025] To achieve the objective of this invention, the method includes the following steps: A. Vanadium precipitation: Add hydrochloric acid and ammonium chloride to sodium vanadium solution, adjust the pH to 1.6-2.2, heat the reaction at 80-100℃ for 30-120 minutes, separate the solid and liquid, and obtain ammonium polyvanadate and vanadium precipitation wastewater; B. Reduction: Add a reducing agent to the vanadium-precipitated wastewater obtained in step A to carry out a reduction reaction; C. Deep impurity removal: Add polycarboxylate superplasticizer to the wastewater after reduction in step B. The amount added is 0.2% to 0.8% of the mass of the vanadium-precipitated wastewater. Then adjust the pH to 7 to 10 with ammonia water, and separate the solid and liquid to obtain purified wastewater and vanadium-chromium filter residue. D. Sodium recovery: Carbon dioxide gas is introduced into the purified wastewater obtained in step C until saturation, and then the water is cooled and crystallized at -10 to 20°C. Solid-liquid separation is performed to obtain sodium bicarbonate solid and crystallization mother liquor. E. Ammonium recovery: The crystallization mother liquor obtained in step D is evaporated and concentrated to an ammonium chloride concentration of 65-75 g / L, and then cooled and crystallized at -10-20℃. Solid-liquid separation is performed to obtain ammonium chloride solid and residual wastewater.

[0026] The solid-liquid separation can be achieved through filtration.

[0027] In one specific embodiment, the amount of ammonium chloride added in step A is 0.8 to 1.5 times the molar amount of vanadium in the vanadium sodium solution.

[0028] In one specific embodiment, the vanadium sodium solution mentioned in step A is obtained by sodium roasting of vanadium slag, coal shale, waste catalyst or petroleum slag containing vanadium at 700-900°C, followed by water leaching.

[0029] In one specific embodiment, the chemical composition of the vanadium sodium solution satisfies the following: V 15~60g / L, Na 10~50g / L, Cr 0.5~25g / L, Si 0.1~2.0g / L, P 0.01~1.0g / L, Al 0.1~1.0g / L.

[0030] In one specific embodiment, the reducing agent in step B is iron powder or ferrous chloride.

[0031] In one specific embodiment, the amount of reducing agent added is 1.5 to 4.0 times the total molar amount of vanadium and chromium ions in the vanadium-precipitated wastewater.

[0032] In one specific embodiment, the volume concentration of carbon dioxide in step D is ≥80%.

[0033] In one specific embodiment, the sodium bicarbonate solid described in step D is dried to a moisture content of <5% and then returned to sodium roasting for recycling.

[0034] In one specific embodiment, the remaining wastewater from step E is returned to the water leaching recycling after sodium roasting.

[0035] In one specific embodiment, the CO2 and ammonia generated from the evaporation and concentration in step E are absorbed and returned to the purified wastewater in step D for recycling.

[0036] In one specific embodiment, the ammonium chloride solid described in step E is dried to a moisture content of <3% and then returned to step A for recycling.

[0037] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0038] The vanadium sodium solution involved in this embodiment is obtained by calcining vanadium slag and sodium bicarbonate (or sodium carbonate) at 850°C for 2 hours with a Na / V molar ratio of 0.8~1.2, followed by water leaching. Its chemical composition is as follows: V 15~60g / L, Na 10~50g / L, Cr 0.5~25g / L, Si 0.1~2.0g / L, P 0.01~1.0g / L, Al 0.1~1.0g / L.

[0039] Example 1

[0040] Take 2L of vanadium sodium solution with a vanadium concentration of 15g / L, add 47g of ammonium chloride while stirring, then add hydrochloric acid to adjust the pH of the solution to 2.0, heat the solution to 90℃ and keep it at that temperature for 60min. After vanadium precipitation, age for 30min (aging can make the precipitated crystals grow more completely and have larger particle size, thereby improving filtration efficiency and reducing impurities entrained in the product). Filter to obtain ammonium polyvanadate and vanadium precipitation wastewater. Dry the ammonium polyvanadate at 100℃ for 5h, and then calcine it at 520℃ for 2h to obtain V2O5 product with a V2O5 content of 99.2%. The impurity elements meet the requirements of YBT5304-2017 standard 99 grade vanadium powder. The vanadium concentration in the vanadium precipitation wastewater is 0.1g / L and chromium concentration is 2.5g / L. Add 22.4g of reduced iron powder, stir to reduce vanadium and chromium, then add 10g of polycarboxylate superplasticizer, and finally adjust the pH to 9.0 with ammonia water. Filter to obtain vanadium-chromium filter residue and purified wastewater.

[0041] CO2 gas (CO2 concentration > 80%) is introduced into the purified wastewater until saturation. The solution is then cooled to 5°C, crystallized, and filtered to obtain sodium bicarbonate. This sodium bicarbonate product is dried at 100°C for 4 hours with a purity > 98%, meeting the requirements for return to roasting. The remaining ammonium chloride solution is heated and evaporated to an ammonium chloride concentration of 70 g / L. The solution is then cooled to 5°C, crystallized, and filtered to obtain ammonium chloride. This ammonium chloride product is dried at 80°C for 6 hours with a purity > 98%, meeting the requirements for utilization in the vanadium precipitation process. The wastewater after recovering sodium bicarbonate and ammonium chloride is returned to the leaching process for recycling.

[0042] Example 2

[0043] Take 2L of vanadium sodium solution with a vanadium concentration of 60g / L, add 128g of ammonium chloride while stirring, then add hydrochloric acid to adjust the pH of the solution to 1.6, heat the solution to 100℃ and keep it at that temperature for 90min. After vanadium precipitation, age for 30min, filter to obtain ammonium polyvanadate and vanadium precipitation wastewater. Dry the ammonium polyvanadate at 100℃ for 3h, then calcine it at 550℃ for 1h to obtain V2O5 product with a V2O5 content of 99.1%, and the impurity elements meet the requirements of YBT5304-2017 standard 99 grade vanadium powder. The vanadium concentration in the vanadium precipitation wastewater is 0.2g / L and chromium concentration is 5.0g / L. Add 101g of ferrous chloride, stir to reduce vanadium and chromium, then add 16g of polycarboxylate superplasticizer, and finally adjust the pH to 8.0 with ammonia water, filter to obtain vanadium-chromium filter residue and purified wastewater.

[0044] CO2 gas (CO2 concentration > 90%) is introduced into the purified wastewater until saturation. The solution is then cooled to 0°C, crystallized, and filtered to obtain sodium bicarbonate. This sodium bicarbonate product is dried at 90°C for 6 hours, with a purity > 98%, meeting the requirements for return to roasting. The remaining ammonium chloride solution is heated and evaporated to an ammonium chloride concentration of 75 g / L. The solution is then cooled to 20°C, crystallized, and filtered to obtain ammonium chloride. This ammonium chloride product is dried at 100°C for 2 hours, with a purity > 97%, meeting the requirements for use in the vanadium precipitation process. The wastewater after recovering sodium bicarbonate and ammonium chloride is returned to the leaching process for recycling.

[0045] Example 3

[0046] Take 2L of vanadium sodium solution with a vanadium concentration of 40g / L, add 55g of ammonium chloride (1.7mol) while stirring, then add hydrochloric acid to adjust the pH of the solution to 1.8, heat the solution to 95℃ and keep it at that temperature for 120min. After vanadium precipitation, age for 30min, filter to obtain ammonium polyvanadate and vanadium precipitation wastewater. Dry the ammonium polyvanadate at 95℃ for 4h, then calcine it at 500℃ for 2h to obtain V2O5 product with a V2O5 content of 99.4%, and the impurity elements meet the requirements of YBT5304-2017 standard 99 grade vanadium powder. The vanadium concentration in the vanadium precipitation wastewater is 0.15g / L and chromium concentration is 25.0g / L. Add 492g of ferrous chloride, stir to reduce vanadium and chromium, then add 13g of polycarboxylate superplasticizer, and finally adjust the pH to 10.0 with ammonia water, filter to obtain vanadium-chromium filter residue and purified wastewater.

[0047] CO2 gas (CO2 concentration > 98%) is introduced into the purified wastewater until saturation. The solution is then cooled to 0°C, crystallized, and filtered to obtain sodium bicarbonate. This sodium bicarbonate product is dried at 95°C for 4 hours with a purity > 98%, meeting the requirements for return to roasting. The remaining ammonium chloride solution is heated and evaporated to an ammonium chloride concentration of 65 g / L. The solution is then cooled to 0°C, crystallized, and filtered to obtain ammonium chloride. This ammonium chloride product is dried at 95°C for 6 hours with a purity > 98%, meeting the requirements for utilization in the vanadium precipitation process. The wastewater after recovering sodium bicarbonate and ammonium chloride is returned to the leaching process for recycling.

[0048] Example 4

[0049] Cyclic stability verification

[0050] The sodium bicarbonate, ammonium chloride, and wastewater recovered in Example 1 were all used for the treatment of the next batch of new materials (i.e., the recovered sodium bicarbonate was used to calcine the new vanadium slag with sodium chloride, and the vanadium chloride solution obtained after water leaching was used to precipitate vanadium and undergo subsequent treatment with the recovered ammonium chloride and wastewater. In each cycle, the carbon-containing substances generated in the evaporation and concentration step were...). Both the ammonia vapor and water vapor are absorbed by water or dilute ammonia solution and then recycled back to the purified wastewater from sodium recovery. This cycle is repeated 5 times, and the purity of the V2O5 product, the purity of sodium bicarbonate and ammonium chloride, and the concentration changes of key impurity elements such as Cr, P, and Si in the system are monitored in each cycle. The results are shown in Table 1 below. Even after 5 complete cycles, the purity of the V2O5 product is still higher than 98.5%, and the purity of sodium bicarbonate and ammonium chloride remains above 97%. Although the concentration of key impurity elements in the system increases slightly, there is no significant accumulation, and the concentration level is far below the critical value affecting process stability and product purity. This indicates that the synergistic process of "iron reduction + water-reducing agent impurity removal" and "CO2 crystallization recovery" of this invention can effectively control the system impurity level, has good long-term operational stability and industrial application feasibility, and successfully solves the industry problem of "impurity accumulation leading to system failure during sodium ammonium recycling" in vanadium liquid treatment.

[0051] Table 1 Results of Cyclic Stability Experiment in Example 4

[0052] Comparative Example 1

[0053] Take 2L of the same sodium vanadium solution (high chromium content) as in Example 3, and precipitate vanadium according to the steps of this invention to obtain vanadium-precipitated wastewater. In the wastewater treatment stage, only iron powder (or ferrous chloride) is added for reduction, and then the pH is adjusted to 10.0 with ammonia water; no polycarboxylate superplasticizer is added. Subsequent steps are the same as in Example 3, including filtration and C-flushing. Crystallization, evaporation crystallization, etc. Reduction and neutralization with ammonia water are performed without adding polycarboxylate superplasticizer. Subsequent steps are the same as in Example 3, including filtration and C2000 filtration. Crystallization, evaporative crystallization, etc. The vanadium-chromium filter residue obtained after filtration has a water content as high as 65%, making it difficult to press filter, and the filtrate is turbid; the residual Cr concentration in the purified wastewater is still 1.2 g / L, far exceeding the limits of the embodiments of this invention (<0.05 g / L); the Cr impurity content in the sodium bicarbonate product obtained from subsequent crystallization exceeds the standard (>0.1%), making it unsuitable for direct return to roasting; a large amount of co-precipitated impurities appear during the ammonium chloride crystallization process, and the product purity is only about 92%, which cannot meet the requirements for vanadium precipitation and reuse. Omitting the water-reducing agent leads to a significant decrease in impurity removal efficiency and high impurity residue, seriously affecting the purity and recycling feasibility of the subsequent sodium ammonium recovery product, indicating that "water-reducing agent + iron reduction + ammonia water neutralization" is a synergistic effect, and none of them can be omitted.

[0054] Comparative Example 2

[0055] Take 2L of the purified wastewater, the same as in Example 2. Do not introduce C. Instead of using a gas, solid ammonium bicarbonate (or a concentrated solution) was added to saturation in an attempt to precipitate sodium bicarbonate. The temperature was controlled in the same manner as in Example 2. Subsequent steps were the same, including evaporating and crystallizing ammonium chloride. The resulting sodium bicarbonate crystallization rate was low (<60%), and the crystal particles were fine and difficult to filter; the product contained a large amount of NH4. + Its purity is only about 90%, making it unsuitable for direct sodium roasting; the mother liquor contains CO3. 2- High residual CO2 levels lead to the generation of a large amount of CO2 bubbles during the subsequent ammonium chloride crystallization process, resulting in low evaporation efficiency and an ammonium chloride product purity of only about 94%. The overall process cost is high, and the introduction of an additional ammonia source disrupts the system's ammonia balance. Using ammonium bicarbonate to replace CO2 not only complicates the process and increases costs, but also fails to meet the product purity requirements for recycling. This further highlights the simplicity, economy, and product purity advantages of the "direct CO2 + low-temperature crystallization" process of this invention.

[0056] Comparative Example 3

[0057] Take 2L of the purified wastewater, the same as in Example 2. Introduce CO2 gas until saturated, and control the temperature at -15~-11℃. Subsequent steps are the same: evaporate and crystallize ammonium chloride. The sodium bicarbonate crystallization rate is slightly improved, but the crystals contain a large amount of ammonium chloride, reducing the purity to approximately 95%. The solution viscosity increases at low temperatures, making filtration difficult and significantly increasing equipment energy consumption. Na+ appears during the ammonium chloride crystallization process. + Co-crystallization occurred, resulting in a product purity of only about 96%. Although exceeding the temperature range described in this invention can improve sodium recovery, it sacrifices product purity and process economy, proving that "-10 ~ 20℃" is the optimal range that balances recovery rate, purity, and energy consumption.

[0058] Comparative Example 4

[0059] The vanadium-precipitated wastewater from Example 1 of this invention was treated using the combined alkali production process described in CN202210241452, and directly passed through C... Low-temperature crystallization was controlled. Residual impurities such as Cr, Si, and P in the wastewater severely interfered with the crystallization process, resulting in excessive impurity content in the sodium bicarbonate product (P > 0.05%, Si > 0.1%). The accumulation of impurities in the crystallization mother liquor led to an ammonium chloride product purity of only about 90%, rendering it unusable. The system became saturated with impurities after the second cycle and could not continue operating. This indicates that the existing combined alkali production method is not directly applicable to vanadium-precipitated wastewater with complex compositions.

Claims

1. A method for green vanadium precipitation and sodium-ammonium cycle of sodium vanadate solution, characterized in that, The method comprises the following steps: A. Vanadium precipitation: adding hydrochloric acid and ammonium chloride to the sodium vanadate solution, adjusting the pH to 1.6-2.2, heating at 80-100°C for 30-120 minutes, and solid-liquid separation to obtain ammonium polyvanadate and vanadium precipitation wastewater; B. Reduction: adding a reducing agent to the vanadium precipitation wastewater obtained in step A for reduction reaction; C. Deep impurity removal: adding a polycarboxylic acid water reducer to the wastewater after reduction in step B, the amount of which is 0.2%-0.8% of the mass of the vanadium precipitation wastewater, then adjusting the pH to 7-10 with ammonia water, and solid-liquid separation to obtain purified wastewater and vanadium-chromium filter residue; D. Sodium recovery: passing carbon dioxide gas into the purified wastewater obtained in step C until saturation, then performing cooling crystallization at -10-20°C, and solid-liquid separation to obtain sodium bicarbonate solid and crystallization mother liquor; E. Ammonium recovery: evaporating and concentrating the crystallization mother liquor obtained in step D to a concentration of 65-75 g / L of ammonium chloride, then cooling and crystallizing at -10-20°C, and solid-liquid separation to obtain ammonium chloride solid and residual wastewater.

2. The method for green vanadium precipitation and sodium-ammonium recycling of sodium vanadate solution according to claim 1, characterized in that: The amount of ammonium chloride added in step A is 0.8-1.5 times the molar amount of vanadium in the sodium vanadate solution.

3. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The sodium vanadate solution in step A is obtained by sodium roasting of vanadium-containing materials such as vanadium slag, stone coal, waste catalyst or petroleum residue at 700-900°C, followed by water leaching.

4. The method for green vanadium precipitation and sodium ammonium circulation of sodium vanadate solution according to claim 3, characterized in that, The chemical composition of the sodium vanadate solution meets the requirements of V 15-60 g / L, Na 10-50 g / L, Cr 0.5-25 g / L, Si 0.1-2.0 g / L, P 0.01-1.0 g / L, and Al 0.1-1.0 g / L.

5. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The reducing agent in step B is iron powder or ferrous chloride.

6. The method for green vanadium precipitation and sodium ammonium circulation of sodium vanadate solution according to claim 5, characterized in that, The amount of the reducing agent added is 1.5-4.0 times the total molar amount of vanadium and chromium ions in the vanadium precipitation wastewater.

7. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The sodium bicarbonate solid in step D is dried to a moisture content of <5% and then recycled for sodium roasting.

8. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The residual wastewater in step E is recycled for water leaching after sodium roasting.

9. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The CO2 and ammonia gas generated during evaporation and concentration in step E are absorbed and then recycled to the purified wastewater in step D.

10. The method for green vanadium precipitation and sodium ammonium circulation according to claim 1 or 2, characterized in that, The ammonium chloride solid in step E is dried to a moisture content of <3% and then recycled to step A.

Images