Regeneration method of molybdenum removal extraction agent for waste acid system

Abstract

The invention discloses a regeneration method of a molybdenum removal extraction agent for a waste acid system, and belongs to the technical field of extraction agent regeneration. The method comprises the following steps: adding 0.05-0.1 wt.% of polybasic carboxylate, organic phosphonate or hydroxy carboxylate complexing agent into a 5-8wt.% carbonate buffer system, mixing a water phase and an aging extraction agent according to a phase ratio O / A of 1: 1, reacting at 20-35 DEG C for 8-12 minutes, and separating an organic phase from a weak base phase. And washing the organic phase with 0.5-1.0 mol / L sulfuric acid according to a phase ratio O / A of 1: 1, separating, washing with water, and separating the organic phase from the water phase again. And dehydrating the organic phase until the water content is less than or equal to 150ppm, contacting the organic phase with a pre-equilibrium liquid containing sulfuric acid and / or sulfate according to a phase ratio O / A of 1: 1, so that the acid value of the organic phase is 0.10-0.35 mg KOH / g, and recovering the addition ratio of TBP.H2SO4 to 0.05-0.20 mol / mol. Adding 50-200ppm of hindered phenol antioxidant into the organic phase, filtering, and then sealing and aging at room temperature; the regenerated extraction agent has the advantages of low water content, stable acid value, improved interfacial tension, elimination of metal poisoning, good phase behavior, extraction capacity recovery degree of more than 90%, stable long-term cycle performance, and no generation of emulsification and third phase.

Description

Technical Field

[0001] This invention belongs to the field of extractant regeneration technology, specifically relating to a method for regenerating a molybdenum-removing extractant for a polluted acid system. Background Technology

[0002] The sulfuric acid waste produced during the copper smelting flue gas acidification process is generally characterized by high acidity, high sulfate content, high iron and aluminum impurity content, and low concentration of rare and dispersed metals (such as rhenium). In industrial treatment of this type of waste acid, to improve the recovery rate of valuable elements such as rhenium, a composite extraction system consisting of TBP (tributyl phosphate), D2EHPA (di(2-ethylhexyl)phosphate), fatty alcohol, and diluent is typically used to achieve effective removal of Mo(VI) and enrichment of rhenium.

[0003] However, during the extraction-back-extraction cycle, this type of composite extractant gradually ages, experiencing problems such as metal ion aggregation and poisoning in the organic phase, hydrolysis and degradation of TBP, polymerization or oxidation of D2EHPA, continuous increase in water content, and decrease in interfacial tension. These changes not only lead to a decrease in extraction capacity but also easily cause phase instability defects such as emulsification, sticky phase, and third phase formation, necessitating periodic regeneration of the extractant.

[0004] Existing technologies commonly employ regeneration methods involving alternating washing with strong acids and strong alkalis. For example, acid-base washing with oxalic acid, ammonia, or sodium carbonate is used to attempt to remove adsorbed metal ions, degradation products, or microparticles from the organic phase. However, under strong alkaline conditions, phosphate ester extractants are prone to saponification, leading to significant extractant loss, deteriorated phase behavior, and even organic phase disintegration, severely impacting regeneration efficiency.

[0005] Furthermore, existing extraction systems often use di(2-ethylhexyl)phosphoric acid (P204) or 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507) as acidic extractants. Currently, regeneration methods for phosphoric acid extractants such as P507 and P204 can remove metal poisoning substances through complexation precipitation. However, these methods are mostly applicable to organophosphonate extractants in vanadium, tungsten, and molybdenum systems, and are not suitable for TBP-D2EHPA-fatty alcohol complex systems. At the same time, these methods generally lack quantitative control over key parameters such as water content, acid value, and the addition structure of TBP·H2SO4, thus failing to restore the optimal interfacial state of the extractant.

[0006] Currently, in copper smelting waste acid systems, when using composite extractants for co-extraction, the extractants generally exhibit performance degradation with increasing cycles. This includes issues such as increased water content, decreased addition ratio, deteriorated interfacial behavior, and accumulated metal poisoning, severely impacting extraction efficiency and phase separation performance. Therefore, there is an urgent need for a regeneration method suitable for waste acid systems using a TBP+D2EHPA+fatty alcohol composite extractant, simultaneously achieving moisture control, addition ratio recovery, interfacial behavior adjustment, and metal poisoning elimination. This aims to address the overall performance degradation of such extractants after long-term recycling, enabling efficient recycling, reducing production costs, and minimizing hazardous waste generation. Summary of the Invention

[0007] To address the comprehensive aging problems of extractants in waste acid systems during long-term use, including metal poisoning, acidification imbalance, increased water content, decreased interfacial tension, and antioxidant consumption, a mild, efficient, low-loss, and repeatable extractant regeneration method is proposed. The goal is to restore the extractant's extraction capacity, interfacial stability, and long-term cycling performance, enabling it to once again meet the requirements for continuous industrial operation.

[0008] The objective of this invention is achieved as follows: the regeneration method of the polluted acid system using a molybdenum-removing extractant includes the following steps: Weak base complexation treatment: In a carbonate buffer system with a mass fraction of 5-8 wt.%, add any one of the complexing agents, such as polycarboxylate, organophosphonate, or hydroxycarboxylate, with a mass fraction of 0.05-0.1 wt.%, to form an aqueous phase. Mix this aqueous phase with the aging extractant at a ratio of O / A = 1:1 and react at room temperature for 8-12 min. After standing, separate the organic phase from the weak base phase. Washing and impurity removal: Wash the organic phase with 0.5-1.0 mol / L sulfuric acid according to the ratio O / A=1:1, let it stand and separate, then wash the organic phase with water, let it stand again and separate the organic phase from the aqueous phase; Addition ratio reconstruction: Dehydrate the organic phase to reduce the water content to ≤150ppm, then contact the organic phase with a pre-equilibration solution containing sulfuric acid and / or sulfate at a ratio of O / A=1:1, so that the acid value of the organic phase is stabilized at 0.10-0.35mg KOH / g, and the TBP·H2SO4 addition ratio is restored to 0.05-0.20mol / mol; Antioxidant fine-tuning: Add 50-200 ppm of hindered phenolic antioxidant to the organic phase, filter to remove impurities, and age in a sealed container at room temperature to complete the regeneration of the extractant.

[0009] Compared with the prior art, the technical solution described in this invention has the following advantages: 1. Removal of metal poisoning using a combined washing process involving a weak alkali and a complexing agent. This technical solution is the first to propose using a carbonate buffer system (NH4HCO3, (NH4)2CO3) and a complexing agent (polycarboxylate, organophosphonate, hydroxycarboxylate) to treat the aged TBP-D2EHPA-fatty alcohol system during the regeneration of the waste acid extractant. Through precise control of the pH range (7.5~8.5), the discomplexation of metal impurities is ensured, and Fe can be removed using the competitive coordination mechanism of the complexing agent without saponifying the extractant. 3+ Al 3+ Si 4+ The presence of poisoning ions is an advantage that the traditional strong alkali method does not possess.

[0010] 2. During dehydration, the water content of the organic phase must be strictly controlled to ≤150 ppm. This is a prerequisite for interfacial stability, addition ratio regulation, and anti-emulsification, because excessive water will occupy the coordination sites of the extractant, hindering its binding with sulfuric acid and metal ions. Dehydration using molecular sieves or membranes removes free water from the organic phase, thus fully exposing the active sites of the organic phase.

[0011] 3. Quantitative recalibration of the TBP·H2SO4 adduct ratio. The proposed technique utilizes a pre-equilibration solution containing sulfuric acid and / or sulfates to re-establish the solvation adduct (TBP·H2SO4) between TBP and H2SO4 under anhydrous or low-water-content conditions. The degree of TBP·H2SO4 adduct is controlled by maintaining an acid value of 0.10–0.35 mg KOH / g, restoring it to 0.05–0.20 mol / mol. This ensures that the extractant maintains stable extraction capacity and interfacial tension when reused.

[0012] 4. Using sulfates to enhance the stability of pre-coordination. The preferred method in this approach is to add 0.1~1.0 mol / L sodium sulfate (Na₂SO₄) to the pre-coordination system, which dissociates into SO₄²⁻ upon dissolution in water. 2- It can react with H in the solution + Combine to form HSO4 - Alternatively, H2SO4 molecules can be used to maintain sulfate concentration, provide TBP coordination, stabilize interfacial charge, reduce the third phase, and ensure the accuracy of addition ratio reconstruction.

[0013] 5. The aforementioned technical solution is the first to utilize an interfacial stability reconstruction technique combining antioxidant supplementation, fine filtration, and aging. Adding 50–200 ppm of a hindered phenolic antioxidant (e.g., BHT) can provide hydrogen atoms to alkoxy or peroxy radicals, blocking the chain reaction and inhibiting the formation of gels and polymer particles. Fine filtration with a 5 μm filter removes micromolecular particles / polymers, followed by aging at 25–35°C for 2–4 hours, allowing the antioxidant, undenatured extractant, and diluent to reform a uniform molecular arrangement in the organic phase. This combined treatment restores interfacial tension and improves long-term stability.

[0014] In summary, the technical solution described in this invention can significantly restore the physicochemical properties and extraction performance of the extractant. The regenerated extractant exhibits reduced water content, stable acid value, increased interfacial tension, elimination of metal poisoning, and good phase behavior. The extraction capacity recovery rate can reach over 90%, and it maintains stable long-term cycling performance without emulsification or the formation of a third phase. Compared with traditional strong alkali regeneration methods, the technical solution described in this invention results in extremely low extractant loss, minimal environmental impact, and a significantly extended extractant lifespan. Detailed Implementation

[0015] The present invention will be further described below, but this is not intended to limit the invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the scope of protection of the present invention.

[0016] The regeneration method for the waste acid system using a molybdenum-removing extractant according to the present invention includes the following steps: Weak base complexation treatment: In a carbonate buffer system with a mass fraction of 5-8 wt.%, add 0.05-0.1 wt.% of any one of the following complexing agents: polycarboxylate, organophosphonate, or hydroxycarboxylate, to form an aqueous phase. Mix this aqueous phase with the aged extractant at a ratio of O / A = 1:1 and react at room temperature for 8-12 minutes. After standing, separate the organic phase from the weak base phase. Wash with a combination of weak base and complexing agent to remove the Fe accumulated in the aged extractant. 3+ Al 3+ Si 4+ Impurity ions enter the aqueous phase in the form of complexes. This step avoids D2EHPA saponification initiated by strong bases and effectively removes metal poisoning sites.

[0017] Washing and impurity removal: The organic phase is washed with 0.5–1.0 mol / L sulfuric acid at a ratio of O / A = 1:1. After standing and separation, the organic phase is washed with water, and then separated from the aqueous phase after standing again. Acid washing removes residual carbonate, ammonium salts, and complexing agents to prevent them from affecting subsequent acidification control; then it is washed with water to bring the system to a stable pretreatment state.

[0018] Addition ratio reconstruction: The organic phase was dehydrated to reduce the water content to ≤150 ppm, and then contacted with a pre-equilibration solution containing sulfuric acid and / or sulfate at a ratio O / A = 1:1 to stabilize the acid value of the organic phase at 0.10–0.35 mg KOH / g, restoring the TBP·H₂SO₄ addition ratio to 0.05–0.20 mol / mol. By controlling the water content and reconstructing the TBP·H₂SO₄ addition ratio, the extraction capacity and interfacial stability of the extractant were effectively restored.

[0019] Antioxidant fine-tuning: Add 50–200 ppm of hindered phenolic antioxidant to the organic phase, filter to remove impurities, and age in a sealed environment at room temperature to complete the regeneration of the extractant. Through antioxidant replenishment and fine filtration, gel and polymer particles are removed; aging treatment allows the components to be redistributed uniformly in the organic phase.

[0020] In the weak base complexation process, the carbonate buffer system is an ammonium bicarbonate and / or ammonium carbonate solution. The complexing agent is any one of citrate, polyphosphonate, and tartrate. The temperature of the complexation reaction is 20-35°C. The pH value of the reaction system is pH 7.5-8.5.

[0021] In the washing and impurity removal process, the total number of washing cycles is ≥2, including ≥1 sulfuric acid washing and ≥1 pure water washing. The washing time is ≥5 minutes. After water washing, the acid value of the organic phase decreases to ≤0.20 mg KOH / g.

[0022] In the addition ratio reconstruction process, the dehydration is performed using molecular sieve dehydration or membrane dehydration. The pre-equilibration solution contains 0.8~1.0 mol / L H2SO4 and / or 0.1~1.0 mol / L Na2SO4. The number of contact cycles is ≥1, with each cycle involving shaking and mixing for 10 min.

[0023] In the antioxidant fine-tuning process, the hindered phenolic antioxidant is 2,6-di-tert-butyl-4-methylphenol. The filtration uses a 5μm filter cartridge. The aging temperature is 25~35℃, and the time is 2~4 hours.

[0024] Example 1

[0025] --Regeneration methods for extractants in typical waste acid systems A 1.0L sample of the aged extractant from the waste acid extraction process was taken. Analysis revealed that the extractant contained 1050ppm of water, had an acid value of 0.62mg KOH / g, and contained 135mg / L of Fe and 92mg / L of Al, respectively.

[0026] Metal poisoning was removed using a weak base complexation treatment. Specifically, 0.1 wt.% sodium citrate was added to an 8 wt.% (NH₄)₂CO₃ solution to provide mild complexing ability. This aqueous phase was then mixed with an aged extractant at a ratio of O / A = 1:1. The mixture was stirred at 30°C for 8 min, allowed to stand for 3 min, and then the organic phase was separated from the weak base phase. Analysis of the treated organic phase showed that the Fe content decreased to 8 mg / L and the Al content decreased to 5 mg / L, indicating a significant improvement in metal poisoning. No significant emulsification was observed.

[0027] Alkaline residues were removed by washing with a weak acid and water. Specifically, the treated organic phase was washed twice with 0.8 mol / L sulfuric acid at a ratio of O / A = 1:1, with stirring for 5 min each time. After washing, the phases were allowed to stand for separation. No gelation or sticky phase occurred during the weak acid washing process. To thoroughly remove ammonium salts, carbonate ions, and weak acid residues, the organic phase was washed once more with water, with stirring for 5 min. After standing again, the organic phase was separated from the aqueous phase. After washing, the acid value of the organic phase decreased to 0.18 mg KOH / g, reaching the standard state for subsequent addition control.

[0028] The effective extraction structure was restored through dehydration and addition ratio reconstruction. Specifically, the organic phase was dehydrated using a 3A molecular sieve at 35℃ for 6 hours. Coulometric analysis (KF) showed a water content reduction to 120 ppm. The dehydrated organic phase was then contacted twice with a pre-equilibration solution containing 0.8 mol / L H₂SO₄ and 0.3 mol / L Na₂SO₄ at a ratio of O / A = 1:1, with each contact lasting 10 min of shaking. After these two pre-equilibration operations, the acid value of the organic phase stabilized at 0.22 mg KOH / g, restoring the TBP·H₂SO₄ addition ratio to 0.13 mol / mol. Both the polarity and interfacial tension of the extractant were restored.

[0029] The antioxidant fine-tuning and aging restoration of interfacial behavior were specifically carried out as follows: 100 ppm of the hindered phenolic antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT) was added to the treated organic phase, and the mixture was precisely filtered using a 5 μm diatomaceous earth filter to remove micro-molecular particles and polymer particles. The filtered organic phase was then placed in a sealed container and aged at 30°C for 2 hours to allow the system to regain its thermodynamic stability.

[0030] Evaluation of Regeneration Effect After treatment by the method described in this invention, the key physicochemical properties of the aged extractant were significantly improved: its water content decreased from 1050 ppm before regeneration to 130 ppm, its acid value stabilized from 0.62 mg KOH / g to 0.22 mg KOH / g, its interfacial phase separation time was significantly shortened from 128 s to 42 s, metal impurities were basically removed, and no emulsification, sticky phase, or third phase was observed during the entire regeneration process. The distribution ratio of Mo to the regenerated extractant, D(Mo), increased to 0.87, the extraction capacity recovery exceeded 92%, and the interfacial tension and stability were comparable to those of the fresh extractant. This indicates that the four-step regeneration process of this invention can effectively restore the extraction performance and long-term operational stability of the TBP–D2EHPA–fatty alcohol system.

[0031] Example 2

[0032] Extractant regeneration in high-impurity acidic environments 1.0L of aging extractant from the high-impurity acid section of a smelter was taken, and the Fe content was found to be 210mg / L and the Al content was 130mg / L.

[0033] Weak base complexation treatment: 0.05 wt.% polyphosphonate was added to a 6 wt.% (NH₄)₂CO₃ solution to form an aqueous phase. This aqueous phase was mixed with the aging extractant at a ratio of O / A = 1:1, and the mixture was stirred at 35°C for 10 min. After standing for 3 min, the organic phase and the weak base phase were separated. Analysis of the treated organic phase showed that the Fe and Al contents decreased to 12 mg / L and 9 mg / L, respectively.

[0034] Washing and impurity removal: Take the organic phase after the above treatment and wash it twice with 1.0 mol / L sulfuric acid at a ratio of O / A=1:1 to remove residual alkaline substances and complexing agents. Stir for 5 min each time, let it stand and separate, then wash the organic phase once with water, stir for 5 min, let it stand again and separate the organic phase from the aqueous phase. After washing with water, the acid value of the organic phase drops to 0.20 mg KOH / g, which meets the standard state for subsequent addition and control.

[0035] Addition ratio reconstruction: The organic phase was dehydrated using a hydrophobic membrane, reducing its water content from 860 ppm to 90 ppm. Then, at a ratio O / A = 1:1, the dehydrated organic phase was contacted once with a pre-equilibration solution containing 1.0 mol / L H₂SO₄ and 0.5 mol / L Na₂SO₄, and agitated for 10 min. After this pre-equilibration process, the acid value of the organic phase was stabilized at 0.16 mg KOH / g, restoring the TBP·H₂SO₄ addition ratio to 0.10 mol / mol. Both the polarity of the extractant and the interfacial tension were restored.

[0036] Antioxidant fine-tuning: Add 150 ppm of 2,6-di-tert-butyl-4-methylphenol to the above-treated organic phase and perform precision filtration using a 5 μm diatomaceous earth filter. Place the filtered organic phase in a sealed container and age it at 28°C for 3 hours to allow the system to return to a thermodynamically stable state.

[0037] Evaluation of Regeneration Effect After treatment by the method described in this invention, the key physicochemical properties of the aged extractant are significantly improved: the D(Mo) recovery rate reaches 101%, the interfacial tension increases by 65%, and there is no third phase at all, making it suitable for high impurity conditions.

[0038] Example 3

[0039] Extractant regeneration under low-temperature operating conditions A 1.0L sample of the aged extractant from the waste acid extraction process was taken, and the Fe content was found to be 102mg / L and the Al content was 77mg / L.

[0040] Weak base complexation treatment: 0.1 wt.% sodium tartrate was added to a 5 wt.% NH4HCO3 solution to form an aqueous phase. This aqueous phase was mixed with the aging extractant at a ratio of O / A = 1:1 and reacted at 20℃ for 12 min. After standing for 3 min, the organic phase and the weak base phase were separated. Analysis of the treated organic phase showed that the Fe and Al contents decreased from 102 mg / L and 77 mg / L to 6 mg / L and 4 mg / L, respectively.

[0041] Washing and impurity removal: Take the organic phase after the above treatment, wash the organic phase twice with 0.5 mol / L sulfuric acid at a ratio of O / A=1:1, stirring for 5 min each time. After standing and separation, wash the organic phase once with water, stirring for 5 min. After standing again, separate the organic phase from the aqueous phase. After washing with water, the acid value of the organic phase drops to 0.17 mg KOH / g, reaching the standard state for subsequent addition and control.

[0042] Addition ratio reconstruction: The organic phase was dehydrated at 20℃ for 8 h using 3A molecular sieves, reducing its water content from 780 ppm to 110 ppm. Then, the dehydrated organic phase was contacted twice with a pre-equilibration solution containing 0.8 mol / L H₂SO₄ at a ratio of O / A = 1:1, with each contact lasting 10 min of shaking. After these two pre-equilibration operations, the acid value of the organic phase stabilized at 0.21 mg KOH / g, restoring the TBP·H₂SO₄ addition ratio to 0.12 mol / mol. Both the polarity of the extractant and the interfacial tension were restored.

[0043] Antioxidant fine-tuning: Add 80 ppm of 2,6-di-tert-butyl-4-methylphenol to the above-treated organic phase and perform precision filtration using a 5 μm diatomaceous earth filter. Place the filtered organic phase in a sealed container and age it at 25°C for 3 hours to allow the system to return to a thermodynamically stable state.

[0044] Evaluation of Regeneration Effect The regenerated extractant maintains stable phase behavior at both low and normal temperatures, making it suitable for winter operation.

[0045] Example 4

[0046] —Comparative example of no weak base complexation treatment and addition ratio reconstruction To illustrate the necessity of process 1 and step 3, the aged extractant was only washed with 1.0 mol / L H2SO4 twice, for 5 min each time, and aged without weak base complexation treatment or addition ratio reconstruction.

[0047] The regeneration results are as follows: The water content was 960 ppm, which is still too high; the acid value was 0.45 mg KOH / g, which is not within the reasonable range; the phase separation time was 95 s, which is significantly slowed down; the D(Mo) recovery rate was only 58%; and slight emulsification and sticky interface were observed. These results indicate that without the weak base complexation depoisoning step (step 1) and the addition ratio reconstruction step (step 3) in the technical solution of this invention, the extractant cannot be restored to a stable state suitable for industrial use.

Claims

1. A method for regenerating a polluted acid system using a molybdenum-removing extractant, characterized in that, The process includes the following steps: Weak base complexation treatment: In a carbonate buffer system with a mass fraction of 5-8 wt.%, add any one of the complexing agents, such as polycarboxylate, organophosphonate, or hydroxycarboxylate, with a mass fraction of 0.05-0.1 wt.%, to form an aqueous phase. Mix this aqueous phase with the aging extractant at a ratio of O / A = 1:1 and react at room temperature for 8-12 min. After standing, separate the organic phase from the weak base phase. Washing and impurity removal: Wash the organic phase with 0.5-1.0 mol / L sulfuric acid according to the ratio O / A=1:1, let it stand and separate, then wash the organic phase with water, let it stand again and separate the organic phase from the aqueous phase; Addition ratio reconstruction: Dehydrate the organic phase to reduce the water content to ≤150ppm, then contact the organic phase with a pre-equilibration solution containing sulfuric acid and / or sulfate at a ratio of O / A=1:1, so that the acid value of the organic phase is stabilized at 0.10-0.35mg KOH / g, and the TBP·H2SO4 addition ratio is restored to 0.05-0.20mol / mol; Antioxidant fine-tuning: Add 50-200 ppm of hindered phenolic antioxidant to the organic phase, filter to remove impurities, and age in a sealed container at room temperature to complete the regeneration of the extractant.

2. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the weak base complexation process, the carbonate buffer system is an ammonium bicarbonate and / or ammonium carbonate solution.

3. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the weak base complexation process, the complexing agent is any one of citrate, polyphosphonate, and tartrate.

4. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the washing and impurity removal process, the total number of washing cycles is ≥2, including ≥1 sulfuric acid washing and ≥1 pure water washing.

5. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, During the washing and impurity removal process, the acid value of the organic phase is reduced to ≤0.20mg KOH / g.

6. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the addition ratio reconstruction process, the dehydration is performed using molecular sieve dehydration or membrane dehydration.

7. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the addition ratio reconstruction process, the pre-equilibration solution contains 0.8~1.0 mol / L H2SO4 and / or 0.1~1.0 mol / L Na2SO4.

8. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the addition ratio reconstruction process, the number of contact times is ≥1, and each time the mixing lasts for 10 minutes.

9. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the antioxidant fine-tuning process, the hindered phenolic antioxidant is 2,6-di-tert-butyl-4-methylphenol.

10. The regeneration method for the waste acid system using the molybdenum-removing extractant according to claim 1, characterized in that, In the antioxidant fine-tuning process, the aging temperature is 25~35℃ and the time is 2~4h.