A method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery

Abstract

The present invention belongs to the technical field of vanadium battery energy storage, and discloses a method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery. The sulfuric acid stripping solution is maintained in a stirred state, sodium chlorate is first added to oxidize ferrous iron, then soda ash is added to adjust the pH value, and finally anhydrous calcium sulfate is added. After stirring, filtration is carried out to obtain a purified sulfuric acid stripping solution. In the present invention, sodium chlorate is used as an oxidant to oxidize ferrous iron, and then soda ash is used to adjust the pH, and anhydrous calcium sulfate is added for coprecipitation, which can efficiently remove iron impurities in the sulfuric acid stripping solution. The purified sulfuric acid stripping solution is subsequently subjected to conventional extraction process operations, and qualified electrolytes for vanadium redox flow batteries can be produced by a short process.

Description

Technical Field

[0001] The present invention belongs to the technical field of vanadium battery energy storage, and particularly relates to a method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte of a vanadium redox flow battery. Background Art

[0002] Vanadium-bearing stone coal is produced by a fully wet process for vanadium extraction. The leaching solution has a high impurity content and a low vanadium content. The separation and enrichment of vanadium mainly adopt P204+TBP+sulfonated kerosene extraction separation and enrichment, and dilute sulfuric acid stripping. When using this sulfuric acid stripping solution to produce the electrolyte of a vanadium redox flow battery by a short process, the pH value of the sulfuric acid stripping solution is adjusted to 2-2.5, and then P204 is used to extract vanadium from the stripping solution. Vanadium is stripped cyclically with a sulfuric acid solution of a certain concentration, and finally, after degreasing and preparation, a qualified electrolyte for a vanadium redox flow battery is produced.

[0003] The above process has the following problems: Since P204 has a high extraction rate for iron, iron also enters the stripping solution during dilute sulfuric acid stripping. When producing the electrolyte of a vanadium battery by a short process, iron enters the stripping solution again when vanadium is stripped with sulfuric acid, resulting in an excessive iron content in the electrolyte of the vanadium redox flow battery and unqualified product quality. If a conventional oxidant is used to oxidize and remove iron and then the pH value is adjusted to 2-2.5, due to the small amount and fine particles of the newly formed iron hydroxide, it is extremely difficult to coagulate and settle in production, and it is extremely difficult to filter in production, resulting in an unsmooth process and inability to produce; when calcium powder is used for neutralization and alkali adjustment, although the problem of difficult filtration can be solved, due to the large amount of calcium powder added, a large amount of wet slag will be generated, and a large amount of vanadium is entrained in the wet slag, resulting in an increase in the vanadium return amount and the complication of the process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte of a vanadium redox flow battery in view of the deficiencies of the prior art. Sodium chlorate is used as an oxidant to oxidize ferrous ions, and then soda ash is used to adjust the pH, and anhydrous calcium sulfate is added for coprecipitation, which can efficiently remove iron impurities. After the purified sulfuric acid stripping solution is subjected to a conventional extraction process operation, a qualified electrolyte for a vanadium redox flow battery can be produced by a short process.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte of a vanadium redox flow battery, including the following steps:

[0006] Maintain the sulfuric acid stripping solution in a stirred state, first add sodium chlorate to oxidize ferrous ions, then add soda ash to adjust the pH value, and finally add anhydrous calcium sulfate. After stirring, filter to obtain the purified sulfuric acid stripping solution.

[0007] In the above solution, the sulfuric acid stripping solution is a stripping solution obtained by extracting vanadium from a stone coal acid leaching solution with an organic phase of P204+TBP+sulfonated kerosene and stripping vanadium with sulfuric acid. Its ferrous ion content is 0.5-3 g / L, and the total iron content is 0.5-5 g / L.

[0008] In the above solution, the stirring rate is 45 - 60 r / min.

[0009] In the above solution, the following reaction occurs after sodium chlorate is added to the sulfuric acid stripping solution:

[0010] NaClO 3 +6FeSO 4 +3H 2 SO 4 =NaCl + 3Fe 2 (SO4) 3 +3H 2 O

[0011] Fe 2 (SO4) 3 +6H 2 O = 2Fe(OH) 3 ↓ + 3H 2 SO 4

[0012] In the above solution, the molar ratio of sodium chlorate to ferrous iron in the sulfuric acid stripping solution is (0.16 - 0.2):1.

[0013] In the above solution, after adding sodium chlorate, stir and react for 1 - 2 h and then add soda ash.

[0014] In the above solution, the soda ash is used to adjust the pH value to 2 - 2.5.

[0015] In the above solution, after adding soda ash, when there are no obvious bubbles on the liquid surface, continue to stir for 30 - 60 min and then add anhydrous calcium sulfate.

[0016] In the above solution, the addition amount of anhydrous calcium sulfate is 10 - 50 kg / m 3 .

[0017] Preferably, the addition amount of anhydrous calcium sulfate is 20 kg / m 3 .

[0018] In the above solution, after adding anhydrous calcium sulfate, stir for 30 - 60 min and then filter.

[0019] In the above solution, the total iron content in the purified sulfuric acid stripping solution is ≤ 10 mg / L.

[0020] In the above solution, after the purified sulfuric acid stripping solution reduces pentavalent vanadium with sodium sulfite, it is extracted and stripped again according to the conventional extraction process, and the total iron content in the electrolyte for the all-vanadium redox flow battery produced is ≤ 30 mg / L.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] In the present invention, sodium chlorate is first used as an oxidant to oxidize ferrous iron, then soda ash is used to adjust the pH value, and then anhydrous calcium sulfate is added for coprecipitation and filtration. Anhydrous calcium sulfate is a neutral inorganic compound that hardly reacts chemically with the chemical components in the sulfuric acid stripping solution. Anhydrous calcium sulfate is converted into calcium sulfate dihydrate in an aqueous solution, and the volume expansion can entrain the newly formed iron hydroxide colloid for coprecipitation, thus enabling efficient filtration to obtain a purified sulfuric acid stripping solution. Through subsequent conventional extraction process operations, qualified electrolytes for all-vanadium redox flow batteries can be produced in a short process, greatly reducing the production cost of electrolytes for all-vanadium redox flow batteries. Specific Embodiments

[0023] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0024] Example 1

[0025] An acid leaching solution produced by a fully wet vanadium extraction process is extracted with P204 + TBP + sulfonated kerosene and stripped with dilute sulfuric acid. The vanadium content in the sulfuric acid stripping solution is 85 g / L, the sulfuric acid concentration is 4.6%, the ferrous iron content is 0.5 g / L, and the total iron content is 0.7 g / L. This sulfuric acid stripping solution is neutralized with soda ash to adjust the pH value to 2.5, and then the P204 extraction method is used again to produce an electrolyte for a vanadium battery. The iron content in the product exceeds the standard, and the total iron content is as high as 180 mg / L (GB / T37204-2018 requires ≤50 mg / L).

[0026] Keep the sulfuric acid stripping solution under stirring at a stirring rate of 45 r / min. First, add sodium chlorate. The molar ratio of sodium chlorate to ferrous iron in the sulfuric acid stripping solution is 0.2:1. After reacting for 1 h, then add soda ash to adjust the pH value to 2.5. When there are no obvious bubbles on the liquid surface, continue stirring for 30 min, and then add 3 anhydrous calcium sulfate at 20 kg / m. After stirring for 30 min, filter to obtain a purified sulfuric acid stripping solution with a total iron content of 8 mg / L.

[0027] After the purified sulfuric acid stripping solution reduces pentavalent vanadium with sodium sulfite, according to the conventional extraction process operation, extract vanadium again with P204 + TBP + sulfonated kerosene, strip vanadium with dilute sulfuric acid again to obtain a sulfuric acid stripping solution again. After degreasing and formulation, the total iron content in the electrolyte for the all-vanadium redox flow battery produced is 25 mg / L, meeting the quality standard of GB / T37204-2018.

[0028] Example 2

[0029] The acid leaching solution produced by the vanadium extraction process with sulfuric acid is extracted with P204 + TBP + sulfonated kerosene and then back-extracted with sulfuric acid. The sulfuric acid back-extraction solution contains 60 g / L of vanadium, 4% sulfuric acid concentration, 2.1 g / L of ferrous iron content, and 2.5 g / L of total iron content.

[0030] Keep the sulfuric acid back-extraction solution in a stirred state at a stirring rate of 60 r / min. First, add sodium chlorate. The molar ratio of sodium chlorate to ferrous iron in the sulfuric acid back-extraction solution is 0.16:1. After reacting for 2 h, then add soda ash to adjust the pH value to 2. When there are no obvious bubbles on the liquid surface, continue stirring for 60 min, and then add 3 anhydrous calcium sulfate per 30 kg / m. Stir for 60 min and then filter to obtain the purified sulfuric acid back-extraction solution with a total iron content of 10 mg / L.

[0031] After the purified sulfuric acid back-extraction solution reduces pentavalent vanadium with sodium sulfite, operate according to the conventional extraction process. Extract vanadium again with P204 + TBP + sulfonated kerosene, back-extract vanadium with dilute sulfuric acid again to obtain the sulfuric acid back-extraction solution again. After degreasing and formulation, the total iron content in the electrolyte for all-vanadium redox flow batteries produced is 30 mg / L, meeting the quality standard of GB / T 37204-2018.

[0032] The above embodiments are merely examples clearly described and not limitations on the implementation methods. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here, and the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery, characterized in that, It includes the following steps: maintaining the sulfuric acid stripping solution under stirring, first adding sodium chlorate to oxidize ferrous ions, with the molar ratio of sodium chlorate to ferrous ions in the sulfuric acid stripping solution being (0.16 - 0.2):1, then adding soda ash to adjust the pH value to 2 - 2.5, and finally adding anhydrous calcium sulfate, with the addition amount of anhydrous calcium sulfate being 10 - 50 kg / m 3 , filtering after stirring to obtain the purified sulfuric acid stripping solution; the sulfuric acid stripping solution is a stripping solution obtained by extracting vanadium from a stone coal acid leaching solution with an organic phase of P204 + TBP + sulfonated kerosene and then stripping vanadium with sulfuric acid. The total iron content before purification is 0.5 - 5 g / L, and the total iron content after purification is ≤ 10 mg / L.

2. The method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, the content of ferrous ions in the sulfuric acid stripping solution is 0.5 - 3 g / L.

3. The method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, the stirring rate in the stirring state is 45 - 60 r / min.

4. The method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, after adding anhydrous calcium sulfate, stir for 30 - 60 min and then filter.

5. The method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, after adding sodium chlorate, stir and react for 1 - 2 h, then add soda ash. After adding soda ash, when there are no obvious bubbles on the liquid surface, continue to stir for 30 - 60 min and then add anhydrous calcium sulfate.

6. The method for purifying and removing impurities from a sulfuric acid stripping solution for preparing an electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, after the purified sulfuric acid stripping solution reduces pentavalent vanadium with sodium sulfite, it is extracted and stripped again according to the conventional extraction process, and the total iron content in the electrolyte for the vanadium redox flow battery produced is ≤ 30 mg / L.