Coordination extraction method for extracting vanadium in high-acidity vanadium-containing solution

Abstract

The invention relates to a coordination extraction method for extracting vanadium in a high-acidity vanadium-containing solution. According to the technical scheme, the method comprises the following steps: mixing octyl hydroxamic acid and a high-acidity vanadium-containing solution according to the ratio of the amount of substance of vanadium to the amount of substance of octyl hydroxamic acid in the high-acidity vanadium-containing solution of 1: (0.5-4) to obtain an extraction stock solution; and then, according to the volume ratio of the organic extraction agent to the extraction stock solution being 1: (1-5), the organic extraction agent and the extraction stock solution are subjected to a positive extraction mixed reaction, phase splitting is conducted, and the vanadium-containing loaded organic phase and raffinate are obtained. Mixing oxalic acid and a sulfuric acid solution according to the ratio of the amount of substance of the oxalic acid to the amount of substance of the sulfuric acid solution being 1: (1-5) to obtain a stripping agent; and according to the volume ratio of the stripping agent to the vanadium-containing loaded organic phase being 1: (1-10), the stripping agent and the vanadium-containing loaded organic phase are subjected to a stripping mixed reaction, phase splitting is conducted, and vanadium-rich liquid and a lean organic phase are obtained. According to the method, the P204 extraction process has a wider extraction pH range, generation of neutralization slag can be reduced, the extraction stage number is short, and the extraction agent consumption is small.

Description

Technical Field

[0001] The invention belongs to the technical field of complex extraction for extracting vanadium from vanadium-containing solutions, and specifically relates to a complex extraction method for extracting vanadium from vanadium-containing solutions with high acidity. Background Art

[0002] Vanadium-containing minerals are leached with strong acids to obtain vanadium-containing solutions, which are usually characterized by high acidity and many impurities. Solvent extraction is widely used in the separation and recovery of metal ions, especially P204 extraction technology, which is one of the most common separation methods used in wet vanadium extraction. It has the advantages of low cost, high extraction efficiency, and good selectivity. P204 combines with vanadium in the solution through cation exchange reaction, so the pH value of the solution is the main factor affecting the vanadium extraction effect. At present, the P204 extraction of vanadium has a long series, and the optimal pH value is between 1.8 and 2.2. In the process of adjusting the pH, the alkali consumption is large, and a large amount of neutralization slag will be produced, which is not conducive to cleaning and environmental protection.

[0003] The patented technology of "A process for extracting vanadium from extraction" (CN 107245586A) uses sodium hydroxide to saponify P204, and uses the saponified P204 to extract vanadium from the acid leaching solution. This method improves the single-stage extraction rate of P204 and increases the vanadium-iron separation effect. However, the extraction pH range of this method is 1.5 to 2.2, which is narrow, and the pH still needs to be adjusted, resulting in the production of neutralization slag.

[0004] The patented technology of "A method for preparing vanadium pentoxide from vanadium shale extract solution cleanly and without ammonium" (CN 115505760 B) uses di(2-ethylhexyl) phosphate (P204 for short) to purify and enrich the vanadium shale extract solution, performs countercurrent extraction for 3 to 6 stages at 25 to 40°C to obtain a loaded organic phase, and then mixes the loaded organic phase with the stripping solution, performs countercurrent stripping for 3 to 7 stages at 30 to 50°C to obtain a vanadium-rich solution. Although this method successfully achieves efficient enrichment of vanadium, the number of extraction stages is too long.

[0005] The patented technology of "A method for extracting vanadium from a vanadium-containing solution" (CN 109306404A) uses vanadium slag or vanadium shale produced by smelting vanadium-titanium magnetite to directly extract vanadium from the leaching solution obtained by leaching with sulfuric acid. It first uses an amine extractant to extract and separate sulfuric acid, and then adsorbs and reduces the H in the vanadium-containing solution. + To achieve the purpose of adjusting the pH of the extraction solution, and then use a phosphorus extractant to extract the vanadium in the vanadium-containing solution. Although this method does not require the addition of alkali to adjust the pH value and does not produce neutralization slag, different types of extractants are used in the extraction process, and amine extractants cannot be recycled, resulting in a large amount of extractant consumption.

[0006] In summary, the existing P204 extraction process has technical defects such as narrow extraction pH range, generation of neutralization residue, long extraction stages and high consumption of extraction agent. Summary of the invention

[0007] The present invention aims to overcome the existing technical defects and aims to provide a coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution, which method can enable the P204 extractant to achieve extraction within a wider pH range, can reduce the generation of neutralization slag, has a short extraction stage and low extraction agent consumption.

[0008] To achieve the above object, the specific steps of the technical solution adopted by the present invention are:

[0009] The steps of the coordination extraction method are:

[0010] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of vanadium substance in the high-acidity vanadium-containing solution to octyl hydroxamic acid at 1:0.5-4 to obtain an extraction stock solution; then, subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of organic extractant to the extraction stock solution at 1:1-5, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0011] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:1 to 5 to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:1 to 10 to obtain a vanadium-rich solution and a lean organic phase.

[0012] The pH value of the high-acidity vanadium-containing solution is 0.4-1.0.

[0013] In the organic extractant, the phosphonic acid extractant P204 accounts for 10-30% of the total volume, the phase regulator accounts for 1-5% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is one of TBP and octanol.

[0014] The positive extraction mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

[0015] The concentration of the sulfuric acid solution is 1-4 mol / L.

[0016] The stripping mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

[0017] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0018] The washing detergent is sulfuric acid with a volume fraction of 10 to 50%, and the washing time is 15 to 45 minutes.

[0019] Due to the adoption of the above technical solution, the present invention has the following positive effects compared with the prior art:

[0020] 1. The present invention uses a high-acidity vanadium-containing solution as an extraction raw material, and there is no need to neutralize the high-acidity vanadium-containing solution. Octyl hydroxamic acid enhances the extraction and binding ability of P204 to vanadium, so that P204 can efficiently extract vanadium under a wider pH environment, reducing the use of alkaline agents such as sodium hydroxide and calcium hydroxide used to adjust the pH value, avoiding the generation of neutralization slag and the loss of vanadium generated in the process, which is beneficial to environmental protection and makes the extraction process cleaner and more environmentally friendly.

[0021] 2. The present invention only needs to add octyl hydroxamic acid during the extraction process, so that the P204 extractant can directly extract the vanadium in the high-acid vanadium-containing solution. When pH < 1.0, the vanadium in the high-acid vanadium-containing solution is mainly in the form of VO 2+ In the solution, octyl hydroxamic acid reacts with VO 2+ The double coordination with P204 makes the hydroxamic group have a stronger binding ability to vanadium in the high-acidity vanadium-containing solution than the P-OH in P204. During the extraction process, octyl isohydroxamic acid combines with the vanadium in the high-acidity vanadium-containing solution and P204, which improves the single-stage extraction rate of P204 in a high-acidity environment and significantly shortens the number of extraction stages.

[0022] 3. The present invention uses a mixed solution of sulfuric acid and oxalic acid for stripping. Oxalate ions react with VO 2+ The coordination capacity is much greater than that of the extracted organic phase, which allows vanadium to be separated from the organic phase and improves the stripping rate of vanadium. + With VO 2+ Ions are exchanged, and the organic phase is regenerated during stripping, so that it can be used for extraction recycling, thus reducing the consumption of the extractant.

[0023] The invention is tested: after 2-3 levels of forward extraction, the forward extraction rate is greater than 99%, and the 3-level back extraction rate is 90.17-98.37%.

[0024] Therefore, the present invention enables the P204 extraction process to have a wider extraction pH range, can reduce the generation of neutralization residues, has a short extraction stage and low extraction agent consumption. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments, but is not intended to limit its protection scope:

[0026] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method of this specific embodiment is:

[0027] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of vanadium substance in the high-acidity vanadium-containing solution to octyl hydroxamic acid at 1:0.5-4 to obtain an extraction stock solution; then, subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of organic extractant to the extraction stock solution at 1:1-5, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0028] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:1 to 5 to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:1 to 10 to obtain a vanadium-rich solution and a lean organic phase.

[0029] The pH value of the high-acidity vanadium-containing solution is 0.4-1.0.

[0030] In the organic extractant, the phosphonic acid extractant P204 accounts for 10-30% of the total volume, the phase regulator accounts for 1-5% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is one of TBP and octanol,

[0031] The positive extraction mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

[0032] The concentration of the sulfuric acid solution is 1-4 mol / L.

[0033] The stripping mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

[0034] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0035] The washing detergent is sulfuric acid with a volume fraction of 10 to 50%, and the washing time is 15 to 45 minutes.

[0036] Example 1

[0037] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method described in this embodiment is:

[0038] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of 1:0.5 between the amount of vanadium in the high-acidity vanadium-containing solution and the amount of octyl hydroxamic acid to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of 1:1 between the organic extractant and the extraction stock solution, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0039] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:1 between the amount of oxalic acid and the amount of sulfuric acid solution to obtain a stripping agent; subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:1 between the stripping agent and the vanadium-loaded organic phase, and separate the phases to obtain a vanadium-rich liquid and a lean organic phase.

[0040] The pH value of the high-acidity vanadium-containing solution is 1.0.

[0041] In the organic extractant, the phosphonic acid extractant P204 accounts for 10% of the total volume, the phase regulator accounts for 1% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is TBP.

[0042] The positive extraction mixed reaction is stirred for 10 minutes at a temperature of 50° C. and a rotation speed of 300 r / min.

[0043] The concentration of the sulfuric acid solution is 1 mol / L.

[0044] The stripping mixed reaction was stirred for 10 minutes at a temperature of 25° C. and a rotation speed of 300 r / min.

[0045] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0046] The washing detergent is 10% sulfuric acid by volume, and the washing time is 45 minutes.

[0047] The present embodiment was tested: after three-stage forward extraction, the three-stage forward extraction rate was 99.02%, and the three-stage reverse extraction rate was 98.37%.

[0048] Example 2

[0049] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method described in this embodiment is:

[0050] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of 1:1 between the amount of vanadium in the high-acidity vanadium-containing solution and the amount of octyl hydroxamic acid to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a forward extraction mixing reaction at a volume ratio of 1:2 between the organic extractant and the extraction stock solution, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0051] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:2 between the amount of oxalic acid and the amount of sulfuric acid solution to obtain a stripping agent; subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:3 between the stripping agent and the vanadium-loaded organic phase, and separate the phases to obtain a vanadium-rich liquid and a lean organic phase.

[0052] The pH value of the high-acidity vanadium-containing solution is 0.9.

[0053] In the organic extractant, the phosphonic acid extractant P204 accounts for 15% of the total volume, the phase regulator accounts for 2% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is 2-octanol.

[0054] The positive extraction mixed reaction is stirred for 15 minutes at a temperature of 40° C. and a rotation speed of 350 r / min.

[0055] The concentration of the sulfuric acid solution is 1.5 mol / L.

[0056] The stripping mixed reaction was stirred for 15 minutes at a temperature of 30° C. and a rotation speed of 350 r / min.

[0057] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0058] The washing detergent is sulfuric acid with a volume fraction of 20%, and the washing time is 30 minutes.

[0059] The present embodiment was tested: after three-stage forward extraction, the three-stage forward extraction rate was 99.25%, and the three-stage reverse extraction rate was 96.54%.

[0060] Example 3

[0061] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method described in this embodiment is:

[0062] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of 1:2 between the amount of vanadium in the high-acidity vanadium-containing solution and the amount of octyl hydroxamic acid to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of 1:3 between the organic extractant and the extraction stock solution, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0063] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:3 between the amount of oxalic acid and the amount of sulfuric acid solution to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:5 between the stripping agent and the vanadium-loaded organic phase, and separate the phases to obtain a vanadium-rich liquid and a lean organic phase.

[0064] The pH value of the high-acidity vanadium-containing solution is 0.7.

[0065] In the organic extractant, the phosphonic acid extractant P204 accounts for 20% of the total volume, the phase regulator accounts for 3% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is TBP.

[0066] The positive extraction mixed reaction is stirred for 20 minutes at a temperature of 35° C. and a rotation speed of 400 r / min.

[0067] The concentration of the sulfuric acid solution is 2.0 mol / L.

[0068] The stripping mixed reaction was stirred for 20 minutes at a temperature of 35° C. and a rotation speed of 400 r / min.

[0069] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0070] The washing detergent is 30% sulfuric acid by volume, and the washing time is 25 minutes.

[0071] The present embodiment was tested: after three-stage forward extraction, the three-stage forward extraction rate was 99.69%, and the three-stage reverse extraction rate was 92.76%.

[0072] Example 4

[0073] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method described in this embodiment is:

[0074] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of vanadium substance in the high-acidity vanadium-containing solution to octyl hydroxamic acid at 1:3 to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of organic extractant to the extraction stock solution at 1:4, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0075] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:4 to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:8 to phase separation to obtain a vanadium-rich liquid and a lean organic phase.

[0076] The pH value of the high-acidity vanadium-containing solution is 0.6.

[0077] In the organic extractant, the phosphonic acid extractant P204 accounts for 25% of the total volume, the phase regulator accounts for 4% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is 2-octanol.

[0078] The positive extraction mixed reaction is stirred for 25 minutes at a temperature of 30° C. and a rotation speed of 500 r / min.

[0079] The concentration of the sulfuric acid solution is 3.0 mol / L.

[0080] The stripping mixed reaction was stirred for 25 minutes at a temperature of 40° C. and a rotation speed of 500 r / min.

[0081] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0082] The washing detergent is 40% sulfuric acid by volume, and the washing time is 20 minutes.

[0083] This embodiment was tested: after 2-stage forward extraction, the 2-stage forward extraction rate was 99.19%, and the 3-stage back extraction rate was 91.85%.

[0084] Example 5

[0085] A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution. The coordination extraction method described in this embodiment is:

[0086] Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of vanadium substance in the high-acidity vanadium-containing solution to octyl hydroxamic acid at 1:4 to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a forward extraction mixing reaction at a volume ratio of organic extractant to the extraction stock solution at 1:5, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate.

[0087] Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:5 between the amount of oxalic acid and the amount of sulfuric acid solution to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:10 between the stripping agent and the vanadium-loaded organic phase, and separate the phases to obtain a vanadium-rich liquid and a lean organic phase.

[0088] The pH value of the high-acidity vanadium-containing solution is 0.4.

[0089] In the organic extractant, the phosphonic acid extractant P204 accounts for 30% of the total volume, the phase regulator accounts for 5% of the total volume, and the rest is No. 260 solvent oil; the phase regulator is TBP.

[0090] The positive extraction mixed reaction is stirred for 30 minutes at a temperature of 25° C. and a rotation speed of 600 r / min.

[0091] The concentration of the sulfuric acid solution is 4 mol / L.

[0092] The stripping mixed reaction is stirred for 30 minutes at a temperature of 50° C. and a rotation speed of 600 r / min.

[0093] The lean organic phase is washed and recycled as the organic extractant in step 1.

[0094] The washing detergent is 50% sulfuric acid by volume, and the washing time is 15 minutes.

[0095] The present embodiment was tested: after three-stage forward extraction, the second-stage forward extraction rate was 99.11%, and the third-stage reverse extraction rate was 90.17%.

[0096] Compared with the prior art, this specific implementation has the following positive effects:

[0097] 1. This specific implementation method uses a high-acidity vanadium-containing solution as an extraction raw material, and there is no need to neutralize the high-acidity vanadium-containing solution. Octyl hydroxamic acid enhances the extraction and binding ability of P204 to vanadium, so that P204 can efficiently extract vanadium under a wider pH environment, reducing the use of alkaline agents such as sodium hydroxide and calcium hydroxide used to adjust the pH value, avoiding the generation of neutralization slag and the loss of vanadium generated in the process, which is beneficial to environmental protection and makes the extraction process cleaner and more environmentally friendly.

[0098] 2. This specific implementation method only needs to add octyl hydroxamic acid during the extraction process, so that the P204 extractant can directly extract the vanadium in the high-acidity vanadium-containing solution. When pH < 1.0, the vanadium in the high-acidity vanadium-containing solution is mainly in the form of VO 2+ In the solution, octyl hydroxamic acid reacts with VO 2+ The double coordination with P204 makes the hydroxamic group have a stronger binding ability to vanadium in the high-acidity vanadium-containing solution than the P-OH in P204. During the extraction process, octyl isohydroxamic acid combines with the vanadium in the high-acidity vanadium-containing solution and P204, which improves the single-stage extraction rate of P204 in a high-acidity environment and significantly shortens the number of extraction stages.

[0099] 3. This specific embodiment uses a mixed solution of sulfuric acid and oxalic acid for stripping. Oxalate ions react with VO 2+ The coordination capacity is much greater than that of the extracted organic phase, which allows vanadium to be separated from the organic phase and improves the stripping rate of vanadium. + With VO 2+ Ions are exchanged, and the organic phase is regenerated during stripping, so that it can be used for extraction recycling, thus reducing the consumption of the extractant.

[0100] The present specific implementation method has been tested: after 2-3 levels of forward extraction, the forward extraction rate is greater than 99%, and the 3-level reverse extraction rate is 90.17-98.37%.

[0101] Therefore, this specific embodiment enables the P204 extraction process to have a wider extraction pH range, can reduce the generation of neutralization residues, has a short extraction stage and low extraction agent consumption.

Claims

1. A coordination extraction method for extracting vanadium from a high-acidity vanadium-containing solution, characterized in that: The steps of the coordination extraction method are: Step 1: mixing the octyl hydroxamic acid and the high-acidity vanadium-containing solution at a ratio of 1:0.5-4 of the amount of vanadium in the high-acidity vanadium-containing solution to the amount of octyl hydroxamic acid to obtain an extraction stock solution; then subjecting the organic extractant and the extraction stock solution to a positive extraction mixing reaction at a volume ratio of 1:1-5 of the organic extractant to the extraction stock solution, and performing phase separation to obtain a vanadium-loaded organic phase and a raffinate; Step 2: Mix the oxalic acid and the sulfuric acid solution at a ratio of 1:1 to 5 to obtain a stripping agent; and subject the stripping agent and the vanadium-loaded organic phase to a stripping mixed reaction at a volume ratio of 1:1 to 10 to obtain a vanadium-rich solution and a lean organic phase.

2. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: The pH value of the high-acidity vanadium-containing solution is 0.4-1.

0.

3. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: In the organic extractant, the phosphonic acid extractant P204 accounts for 10-30% of the total volume, the phase regulator accounts for 1-5% of the total volume, and the rest is No. 260 solvent oil; The phase regulator is one of TBP and octanol.

4. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: The positive extraction mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

5. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: The concentration of the sulfuric acid solution is 1-4 mol / L.

6. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: The stripping mixed reaction is stirred for 10 to 30 minutes at a temperature of 25 to 50° C. and a rotation speed of 300 to 600 r / min.

7. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 1, characterized in that: The lean organic phase is washed and recycled as the organic extractant in step 1.

8. The method for extracting vanadium from a vanadium-containing solution with high acidity according to claim 7, characterized in that: The washing detergent is sulfuric acid with a volume fraction of 10 to 50%, and the washing time is 15 to 45 minutes.