A method of treating iron-containing spent acid

Abstract

This invention relates to the field of waste liquid recycling and proposes a method for treating iron-containing waste acid, comprising the following steps: S0, adding hydrogen peroxide to the iron-containing waste acid to oxidize ferrous ions in the waste acid to ferric ions, obtaining iron-containing waste acid; S1, using a composite extractant composed of sulfonated kerosene, acidic phosphate ester extractant, and sec-octylphenoxy-substituted acetic acid to extract the iron-containing waste acid, obtaining an iron-containing organic phase and an acid-containing aqueous phase; S2, after back-extraction with a back-extractant, obtaining a blank organic phase and an iron-containing aqueous phase; S3, the blank organic phase is regenerated and reused in step S1; the iron-containing aqueous phase is adjusted to pH 3.5-9 with the addition of alkali solution, and solid-liquid separation is performed to obtain solid ferric hydroxide. This technical solution solves the problems of low extraction efficiency and low purity of recovered iron products in related technologies for the extraction and treatment of iron-containing waste acid.

Description

Technical Field

[0001] This invention relates to the field of waste liquid recycling technology, specifically, to a method for treating iron-containing waste acid liquid. Background Technology

[0002] Iron-containing waste acid is a typical acidic waste liquid generated in industrial production such as metallurgy, chemical industry, and electroplating. This waste liquid contains a large amount of dissolved iron and free acid. Direct discharge will cause environmental problems such as water acidification, soil pollution, and heavy metal accumulation, while also resulting in a significant waste of acid and iron resources. Therefore, the resource-based treatment of iron-containing waste acid to achieve acid recovery and iron resource utilization is of great significance.

[0003] Currently, the main methods for treating iron-containing waste acid include neutralization, membrane separation, evaporation and concentration, and extraction. Among these, extraction has become one of the mainstream technologies for industrial treatment of iron-containing waste acid due to its advantages such as high treatment efficiency and high degree of process continuity. However, existing extraction processes still have some technical shortcomings in practical applications. For example, some iron-containing waste acid contains high concentrations of ferrous ions, which are difficult to extract efficiently by conventional extractants, directly affecting the iron extraction effect. At the same time, existing extraction processes often use a single extractant system, mostly employing a single acidic phosphate ester extractant, which has problems such as limited extraction capacity for iron ions, poor selectivity, and difficulty in back-extraction, resulting in low iron ion removal rates and low purity of the recovered iron product.

[0004] In summary, developing a high-efficiency and highly selective extraction process for treating iron-containing waste acid is an urgent problem to be solved in this field. Summary of the Invention

[0005] This invention proposes a method for treating iron-containing waste acid to solve or alleviate at least one of the above-mentioned problems.

[0006] The technical solution of the present invention is as follows: This invention proposes a method for treating iron-containing waste acid, comprising the following steps: S0. Add hydrogen peroxide to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thus obtaining the iron-containing waste acid solution. S1. Use a composite extractant consisting of sulfonated kerosene, acidic phosphate ester extractant and 2-octylphenoxy-substituted acetic acid to extract the waste acid liquid containing iron ions, and obtain an iron-containing organic phase and an acid-containing aqueous phase. S2. After the iron-containing organic phase is back-extracted by the back-extracting agent, a blank organic phase and an iron-containing aqueous phase are obtained. S3. The blank organic phase is regenerated and reused in step S1; the iron-containing aqueous phase is added to an alkaline solution to adjust the pH to 3.5-9, and solid-liquid separation is performed to obtain ferric hydroxide precipitate.

[0007] Preferably, the mass ratio of the sulfonated kerosene, the acidic phosphate extractant, and the 2-octylphenoxy-substituted acetic acid is 85:10:3~5.

[0008] Preferably, the acidic phosphate extractant includes 2-ethylhexyl phosphate-2-ethylhexyl ester and / or bis(2,4,4-trimethylpentyl)phosphonic acid.

[0009] Preferably, the acidic phosphate extractant is composed of 2-ethylhexyl phosphate-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphonic acid in a mass ratio of 1 to 3:1.

[0010] Preferably, in step S1, the extraction is countercurrent extraction, with 2 to 3 extraction stages, and the extraction time for each stage is 5 to 8 minutes.

[0011] Preferably, in step S1, during each extraction stage, the volume ratio of the composite extractant and the iron-containing waste acid solution is independently 1:1~2.

[0012] Preferably, in step S1, the temperature of each extraction stage is independently 25~40℃.

[0013] Preferably, the stripping agent comprises an acid solution.

[0014] Preferably, in step S2, the back-extraction is countercurrent back-extraction, with 2 to 3 back-extraction stages, and the back-extraction time for each stage is independent, ranging from 8 to 12 minutes.

[0015] Preferably, in step S2, during each stage of back-extraction, the volume ratio of the back-extracting agent to the iron-containing organic phase is independently 0.3~0.6:1.

[0016] The beneficial effects of this invention are as follows: This invention proposes a method for treating iron-containing waste acid. Firstly, addressing the problems of difficult direct and efficient extraction of ferrous ions and low purity of iron recovery products, this invention uses hydrogen peroxide as an oxidant. The oxidizing properties of hydrogen peroxide oxidize the high concentration of ferrous ions in the waste acid to ferric ions. Secondly, by using a composite extractant consisting of sulfonated kerosene, acidic phosphate ester extractants, and 2-octylphenoxy-substituted acetic acid, the extraction efficiency and the purity of the ferric hydroxide precipitate are improved. The reason for this is presumably that: sulfonated kerosene acts as a diluent, improving the flowability and phase separation properties of the organic phase, reducing emulsification and impurity entrainment; the acidic phosphate ester extractant provides the main chelating sites for ferric ions, ensuring extraction capacity and reaction rate; and 2-octylphenoxy-substituted acetic acid, as a synergistic extractant, increases the maximum loading capacity of the organic phase for ferric ions, while simultaneously inhibiting the co-extraction of impurities such as calcium, magnesium, and aluminum through steric hindrance and charge selectivity. The synergistic effect of these three components not only improves the ferric ion extraction efficiency but also significantly reduces the impurity content in the back-extraction solution, ultimately resulting in a significant increase in the purity of the obtained ferric hydroxide precipitate. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0018] A specific embodiment of the first aspect of the present invention provides a method for treating iron-containing waste acid liquid, comprising the following steps: S0. Add hydrogen peroxide to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thus obtaining the iron-containing waste acid solution. S1. Use a composite extractant consisting of sulfonated kerosene, acidic phosphate ester extractant and 2-octylphenoxy-substituted acetic acid to extract the waste acid liquid containing iron ions, and obtain an iron-containing organic phase and an acid-containing aqueous phase. S2. After the iron-containing organic phase is back-extracted by the back-extracting agent, a blank organic phase and an iron-containing aqueous phase are obtained. S3. The blank organic phase is regenerated and reused in step S1; the iron-containing aqueous phase is added to an alkaline solution to adjust the pH to 3.5-9, and solid-liquid separation is performed to obtain ferric hydroxide precipitate.

[0019] In this invention, the hydrogen peroxide is a 35% (w / w) aqueous solution of hydrogen peroxide, and the volume ratio of the iron-containing waste acid solution to the hydrogen peroxide is 100:0.6~0.7.

[0020] In one embodiment of the present invention, the mass ratio of sulfonated kerosene, acidic phosphate extractant, and 2-octylphenoxy-substituted acetic acid is 85:10:3~5.

[0021] In this invention, the mass ratio of sulfonated kerosene, acidic phosphate ester extractant, and 2-octylphenoxy-substituted acetic acid is 85:10:3~5. This mass ratio improves the extraction efficiency of the composite extractant while ensuring excellent back-extraction effect, thereby improving the purity of the ferric hydroxide precipitate. If the amount of 2-octylphenoxy-substituted acetic acid is too small, the synergistic extraction effect is insufficient, the extraction selectivity for iron ions decreases, and impurity ions such as calcium, magnesium, and aluminum are easily co-extracted into the organic phase, leading to a decrease in the purity of the ferric hydroxide product. If the amount of 2-octylphenoxy-substituted acetic acid is too high, the viscosity of the organic phase increases significantly, the phase separation rate during extraction and back-extraction slows down, and emulsification entrainment is prone to occur, resulting in increased organic phase loss.

[0022] In one embodiment of the present invention, the acidic phosphate extractant includes one or more of 2-ethylhexyl phosphate-2-ethylhexyl ester, bis-(2,4,4-trimethylpentyl)phosphonic acid, bis(2,4,4-trimethylpentyl)monothiophosphonic acid, bis(2,4,4-trimethylpentyl)dithiophosphonic acid, di(2-ethylhexyl)phosphonic acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, and di-n-butylphosphonic acid. The acidic phosphate extractant is preferably 2-ethylhexyl phosphate-2-ethylhexyl ester and / or bis(2,4,4-trimethylpentyl)phosphonic acid, and most preferably 2-ethylhexyl phosphate-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphonic acid in a mass ratio of 1 to 3:1.

[0023] In this invention, by further combining the acidic phosphate ester extractant, preferably 2-ethylhexyl phosphate-2-ethylhexyl ester, bis(2,4,4-trimethylpentyl)phosphonic acid, and sec-octylphenoxy-substituted acetic acid, the extraction efficiency and the purity of the ferric hydroxide precipitate are further improved. 2-ethylhexyl phosphate-2-ethylhexyl ester is a strong acid with a large extraction capacity and fast kinetics, ensuring efficient and rapid capture of iron ions. Bis(2,4,4-trimethylpentyl)phosphonic acid is a weak acid but has excellent selectivity for iron ions, effectively suppressing the co-extraction of divalent impurity metal ions. Furthermore, this compound phosphate ester system can form hydrogen bonds with sec-octylphenoxy-substituted acetic acid, constructing a stable synergistic extraction system, significantly improving the extraction capacity for iron ions, and further enhancing the chelation and coordination ability for iron ions.

[0024] In one embodiment of the present invention, in step S1, the extraction is countercurrent extraction, the number of extraction stages is 2 to 3, and the extraction time for each stage is 5 to 8 minutes independently.

[0025] In one embodiment of the present invention, in step S1, during each extraction stage, the volume ratio of the composite extractant and the iron-containing waste acid liquid is independently 1:1~2.

[0026] In this invention, in step S1, the extraction is countercurrent extraction with 2-3 extraction stages. During each extraction stage, the volume ratio of the composite extractant to the iron-containing waste acid is independently 1:1-2. Countercurrent extraction allows the composite extractant to fully contact the iron-containing waste acid, significantly improving the extraction efficiency of iron ions. Secondly, the 2-3 extraction stages ensure the removal rate of iron ions while avoiding the complexity and increased cost associated with too many stages, balancing efficiency and economy. Furthermore, controlling the volume ratio to 1:1-2 for each stage maximizes the extraction efficiency of the composite extractant.

[0027] In one embodiment of the invention, the stripping agent comprises an acid solution.

[0028] In this invention, the acid solution undergoes ion exchange with iron ions loaded in the organic phase through a high concentration of hydrogen ions, disrupting the extractant structure formed by the iron ions and the extractant. This allows the iron ions to desorb from the organic phase and enter the aqueous phase, achieving the regeneration of the organic phase and the recovery of iron. The acid solution can be at least one of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid, and its concentration is 1~3 mol / L, which can be any value among 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, and 3 mol / L.

[0029] In one embodiment of the present invention, in step S1, the temperature of each extraction stage is independently 25~40°C, for example, any value among 25°C, 30°C, 35°C, and 40°C.

[0030] In one embodiment of the present invention, in step S2, the temperature of each stage of back-extraction is independently 20~35°C, for example, it can be any value among 20°C, 25°C, 30°C and 35°C.

[0031] In one embodiment of the present invention, in step S2, during each stage of back-extraction, the volume ratio of the back-extracting agent to the iron-containing organic phase is 0.3 to 0.6:1, for example, it can be any value among 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, and 0.6:1.

[0032] In this invention, the regeneration of the blank organic phase specifically includes: the blank organic phase is washed with water and then allowed to stand for phase separation to obtain the regenerated organic phase; wherein, the number of water washing stages is 3 to 4, the temperature of each water washing stage is 30 to 50°C, and the time of each water washing stage is 10 to 15 minutes.

[0033] In this invention, water washing can remove residual inorganic acid radicals, entrained trace metal ions, and water-soluble impurities from the blank organic phase, preventing the accumulation of impurities during the cycle and ensuring the stable extraction performance of the extractant. At the same time, it improves the phase separation state of the organic phase, reduces the tendency to emulsify, extends the service life of the composite extractant, and ensures that it can still maintain a high iron extraction efficiency after multiple cycles.

[0034] In this invention, the alkaline solution can be one or more combinations of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, and ammonia solution, preferably an aqueous sodium hydroxide solution. The concentration of the aqueous sodium hydroxide solution is 10wt% to 32wt%, for example, it can be any value among 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, and 32wt%.

[0035] The present invention will now be described in detail with reference to preferred embodiments and comparative examples. The preferred embodiments of the invention described below can be modified in various ways, and therefore the scope of the invention should not be construed as limited to the preferred embodiments described in detail below. Preferred embodiments are provided to help those skilled in the art to more readily understand the invention.

[0036] In the following examples and comparative examples, the ferrous ion concentration in the iron-containing waste acid solution was 5.62 g / L, and the acid concentration (calculated as H2SO4) was 11.26 g / L.

[0037] Example 1 A method for treating iron-containing waste acid includes the following steps: S0. Add a 35% hydrogen peroxide aqueous solution to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thereby obtaining an iron-containing waste acid solution. The volume ratio of the iron-containing waste acid solution to the hydrogen peroxide aqueous solution is 100:0.6. S1. A composite extractant (composed of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester and sec-octylphenoxy-substituted acetic acid in a mass ratio of 85:10:2) is used to extract the waste acid liquid containing iron ions, resulting in an iron-containing organic phase and an acid-containing aqueous phase. The extraction process is a two-stage countercurrent extraction, with each stage at a temperature of 25°C and a time of 8 min. The volume ratio of the composite extractant to the waste acid liquid containing iron ions is 1:1. S2. After the iron-containing organic phase is back-extracted with a back-extracting agent (dilute sulfuric acid with a concentration of 2 mol / L), a blank organic phase and an iron-containing aqueous phase are obtained. The back-extraction process is a two-stage countercurrent back-extraction, with a back-extraction temperature of 35℃ and a back-extraction time of 8 min per stage. The volume ratio of the back-extracting agent to the iron-containing organic phase is 0.3:1. S3. The blank organic phase is washed with water and allowed to stand for phase separation to obtain a regenerated organic phase, which is then reused in step S1. An alkaline solution (22wt% sodium hydroxide aqueous solution) is added to the iron-containing aqueous phase to adjust the pH to 3.5, and solid-liquid separation is performed to obtain ferric hydroxide precipitate. The water washing process consists of 3 stages, with each stage at a temperature of 30℃ and a washing time of 15 minutes.

[0038] Example 2 A method for treating iron-containing waste acid includes the following steps: S0. Add a 35% hydrogen peroxide aqueous solution to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thereby obtaining an iron-containing waste acid solution. The volume ratio of the iron-containing waste acid solution to the hydrogen peroxide aqueous solution is 100:0.7. S1. A composite extractant (composed of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester and sec-octylphenoxy-substituted acetic acid in a mass ratio of 85:10:2) is used to extract the waste acid liquid containing iron ions, resulting in an iron-containing organic phase and an acid-containing aqueous phase. The extraction process is a two-stage countercurrent extraction, with each stage at a temperature of 40°C and a time of 5 min. The volume ratio of the composite extractant to the waste acid liquid containing iron ions is 1:2. S2. After the iron-containing organic phase is back-extracted with a back-extracting agent (dilute sulfuric acid with a concentration of 2 mol / L), a blank organic phase and an iron-containing aqueous phase are obtained. The back-extraction process is a two-stage countercurrent back-extraction, with a back-extraction temperature of 35℃ and a back-extraction time of 12 min per stage. The volume ratio of the back-extracting agent to the iron-containing organic phase is 0.6:1. S3. The blank organic phase is washed with water and allowed to stand for phase separation to obtain a regenerated organic phase, which is then reused in step S1. An alkaline solution (22wt% sodium hydroxide aqueous solution) is added to the iron-containing aqueous phase to adjust the pH to 9, and solid-liquid separation is performed to obtain ferric hydroxide precipitate. The water washing process consists of 4 stages, with each stage at a temperature of 50℃ and a washing time of 10 min.

[0039] Example 3 A method for treating iron-containing waste acid includes the following steps: S0. Add a 35% hydrogen peroxide aqueous solution to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thereby obtaining an iron-containing waste acid solution. The volume ratio of the iron-containing waste acid solution to the hydrogen peroxide aqueous solution is 100:0.65. S1. A composite extractant (composed of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester and sec-octylphenoxy-substituted acetic acid in a mass ratio of 85:10:2) is used to extract the waste acid liquid containing iron ions, resulting in an iron-containing organic phase and an acid-containing aqueous phase. The extraction process is a two-stage countercurrent extraction, with each stage at a temperature of 35°C and a time of 6 min. The volume ratio of the composite extractant to the waste acid liquid containing iron ions is 1:1.5. S2. After the iron-containing organic phase is back-extracted with a back-extracting agent (dilute sulfuric acid with a concentration of 2 mol / L), a blank organic phase and an iron-containing aqueous phase are obtained. The back-extraction process is a two-stage countercurrent back-extraction, with a back-extraction temperature of 35℃ and a back-extraction time of 10 min per stage. The volume ratio of the back-extracting agent to the iron-containing organic phase is 0.4:1. S3. The blank organic phase is washed with water and allowed to stand for phase separation to obtain a regenerated organic phase, which is then reused in step S1. An alkaline solution (22wt% sodium hydroxide aqueous solution) is added to the iron-containing aqueous phase to adjust the pH to 7, and solid-liquid separation is performed to obtain ferric hydroxide precipitate. The water washing process consists of 3 stages, with each stage at a temperature of 40℃ and a washing time of 12 minutes.

[0040] Example 4 In this embodiment, except that the mass ratio of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester and 2-octylphenoxy-substituted acetic acid is 85:10:3, everything else is the same as in Example 1.

[0041] Example 5 In this embodiment, except that the mass ratio of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester, and 2-octylphenoxy-substituted acetic acid is 85:10:5, everything else is the same as in Example 1.

[0042] Example 6 In this embodiment, except that the mass ratio of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester, and 2-octylphenoxy-substituted acetic acid is 85:10:7, everything else is the same as in Example 1.

[0043] Example 7 In this embodiment, the only difference from Example 5 is that 2-ethylhexyl phosphate-2-ethylhexyl ester is replaced with an equal amount of bis(2,4,4-trimethylpentyl)phosphonic acid.

[0044] Example 8 In this embodiment, the only difference from Example 5 is that 2-ethylhexyl phosphate-2-ethylhexyl ester is replaced with 2-ethylhexyl phosphate-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphonic acid in a mass ratio of 1:1.

[0045] Example 9 In this embodiment, the only difference from Example 5 is that 2-ethylhexyl phosphate-2-ethylhexyl ester is replaced with 2-ethylhexyl phosphate-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphonic acid in a mass ratio of 1:2.

[0046] Comparative Example 1 In this comparative example, except that octylphenoxy-substituted acetic acid was not added to the composite extractant, everything else was the same as in Example 1.

[0047] Comparative Example 2 In this comparative example, except that 2-ethylhexyl phosphate-2-ethylhexyl ester was not added to the composite extractant, everything else was the same as in Example 1.

[0048] Experimental Example 1 The ferrous ion removal rate of the ferrous ion-containing waste acid solutions obtained in Examples 1-3 was tested. Ferrous ion removal rate = (ferrous ion concentration in iron-containing waste acid solution - ferrous ion concentration in iron-containing waste acid solution) / ferrous ion concentration in iron-containing waste acid solution × 100%; The test results are shown in Table 1 below.

[0049] Table 1. Results of ferrous ion removal rate test

[0050] As can be seen from the data in Table 1, after the iron-containing waste acid liquid was treated with a 35% hydrogen peroxide aqueous solution, almost all the ferrous ions were oxidized to ferric ions, and the removal rate of ferrous ions could reach more than 98%, which meets the process requirements for subsequent solvent extraction of ferric ions.

[0051] Experimental Example 2 The iron ions (Fe) in the acid-containing aqueous phases obtained in Examples 1-9 and Comparative Examples 1-2 3+ The concentration and ferric hydroxide precipitate were tested as follows: The test results are shown in Table 2 below.

[0052] Table 2 Test Results

[0053] The iron ion concentration in the acidic aqueous phase obtained in Comparative Examples 1-2 was higher than that in Examples 1-9, and the purity of the iron hydroxide precipitate was lower than that in Examples 1-9. This indicates that by using a compound extractant consisting of sulfonated kerosene, acidic phosphate ester extractant, and 2-octylphenoxy-substituted acetic acid, the extraction efficiency and the purity of the iron hydroxide precipitate can be improved.

[0054] Examples 4 and 5, by limiting the mass ratio of sulfonated kerosene, acidic phosphate extractant, and sec-octylphenoxy-substituted acetic acid to 85:10:3-5, yielded an acidic aqueous phase with a lower iron ion concentration than in Examples 1 and 6, and a higher purity of ferric hydroxide precipitate than in Examples 1 and 6. This indicates that when the mass ratio of sulfonated kerosene, acidic phosphate extractant, and sec-octylphenoxy-substituted acetic acid is 85:10:3-5, the extraction efficiency and the purity of the ferric hydroxide precipitate can be further improved.

[0055] Examples 8 and 9, using a compound of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester, bis(2,4,4-trimethylpentyl)phosphonic acid, and sec-octylphenoxy-substituted acetic acid, yielded an acidic aqueous phase with a lower iron ion concentration than in Examples 5 and 7, and a higher purity of iron hydroxide precipitate than in Examples 5 and 7. This indicates that the extraction efficiency and the purity of iron hydroxide precipitate can be further improved by using a compound of sulfonated kerosene, 2-ethylhexyl phosphate-2-ethylhexyl ester, bis(2,4,4-trimethylpentyl)phosphonic acid, and sec-octylphenoxy-substituted acetic acid.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating iron-containing waste acid, characterized in that, Includes the following steps: S0. Add hydrogen peroxide to the iron-containing waste acid solution to oxidize the ferrous ions in the waste acid solution to ferric ions, thus obtaining the iron-containing waste acid solution. S1. Use a composite extractant consisting of sulfonated kerosene, acidic phosphate ester extractant and 2-octylphenoxy-substituted acetic acid to extract the waste acid liquid containing iron ions, and obtain an iron-containing organic phase and an acid-containing aqueous phase. S2. After the iron-containing organic phase is back-extracted by the back-extracting agent, a blank organic phase and an iron-containing aqueous phase are obtained. S3. The blank organic phase is regenerated and reused in step S1; the iron-containing aqueous phase is added to an alkaline solution to adjust the pH to 3.5-9, and solid-liquid separation is performed to obtain ferric hydroxide precipitate.

2. The method for treating iron-containing waste acid according to claim 1, characterized in that, The mass ratio of the sulfonated kerosene, acidic phosphate extractant, and 2-octylphenoxy-substituted acetic acid is 85:10:3~5.

3. The method for treating iron-containing waste acid according to claim 2, characterized in that, The acidic phosphate extractant includes 2-ethylhexyl phosphate-2-ethylhexyl ester and / or bis(2,4,4-trimethylpentyl)phosphonic acid.

4. The method for treating iron-containing waste acid according to claim 3, characterized in that, The acidic phosphate extractant is composed of 2-ethylhexyl phosphate-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphonic acid in a mass ratio of 1 to 3:

1.

5. The method for treating iron-containing waste acid according to claim 1, characterized in that, In step S1, the extraction is countercurrent extraction, with 2 to 3 extraction stages, and each stage has an independent extraction time of 5 to 8 minutes.

6. The method for treating iron-containing waste acid according to claim 5, characterized in that, In step S1, during each extraction stage, the volume ratio of the composite extractant and the iron-containing waste acid solution is independently 1:1~2.

7. The method for treating iron-containing waste acid according to claim 6, characterized in that, In step S1, the extraction temperature for each stage is independently 25~40℃.

8. The method for treating iron-containing waste acid according to claim 1, characterized in that, The stripping agent includes an acid solution.

9. A method for treating iron-containing waste acid according to claim 1, characterized in that, In step S2, the back-extraction is countercurrent back-extraction, with 2 to 3 back-extraction stages, and the back-extraction time for each stage is independent, ranging from 8 to 12 minutes.

10. A method for treating iron-containing waste acid according to claim 9, characterized in that, In step S2, during each stage of back-extraction, the volume ratio of the back-extracting agent to the iron-containing organic phase is independently 0.3~0.6:1.

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