A method for extracting iron and aluminum from wet-process phosphoric acid in steps

Abstract

The present invention relates to a method for extracting iron and aluminum in wet-process phosphoric acid in steps. The method comprises the following steps: firstly, mixing a first extraction system with wet-process phosphoric acid at a volume ratio of 1:(1-6) to perform a first extraction to obtain iron-removed phosphoric acid; then mixing a second extraction system with the iron-removed phosphoric acid in step (1) at a volume ratio of (1.2-6):1 to perform a second extraction to obtain iron-removed aluminum phosphoric acid; the first extraction system and the second extraction system each independently comprise an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus hydroxyl group; the method extracts iron and aluminum in the wet-process phosphoric acid in steps, and the iron ion extraction rate can be as high as more than 99%, and the aluminum ion extraction rate can be as high as more than 88%; the method facilitates subsequent separate recycling of iron and aluminum, thereby improving the resource utilization value of industrial wet-process phosphoric acid, and has a short process flow, low raw material cost, and is easy to industrialize.

Description

Technical Field

[0001] The present invention relates to the field of resource and environmental technology, and in particular to a method for extracting iron and aluminum from wet-process phosphoric acid in steps. Background Art

[0002] Phosphoric acid is a key product in the phosphorus chemical industry and a vital chemical raw material in industrial production. It can be used to produce chemical fertilizers, detergents, food and feed additives, and more. Wet-process phosphoric acid, due to its low cost and low energy consumption, has become the mainstream process for producing phosphoric acid from phosphate rock. However, wet-process phosphoric acid often contains various impurities, such as metal ions like iron and aluminum. These impurities not only affect product quality and hinder downstream applications, but can also damage production equipment and the environment. Therefore, it is crucial to analyze and treat impurities in wet-process phosphoric acid.

[0003] Currently, the main industrial methods for purifying wet-process phosphoric acid include crystallization, ion exchange, solvent precipitation, organic solvent extraction, concentration purification, and electrodialysis. Solvent extraction has become the mainstream method for purifying wet-process phosphoric acid due to its advantages, including excellent separation efficiency, low raw material consumption, and low energy consumption for impurity removal. Numerous studies have been conducted on impurity removal in wet-process phosphoric acid, but these efforts have focused on the efficient separation and selective recovery of iron and aluminum ions, impurity ions with very similar chemical properties.

[0004] For example, CN110116997A discloses a method for purifying and removing iron from wet-process phosphoric acid. This method first uses hydrogen peroxide to oxidize divalent ferrous ions in crude phosphoric acid to trivalent ferrous ions, and then uses tributyl phosphate and kerosene for multi-stage extraction and stripping to remove the impure iron ions. This method has a complex extraction process and high equipment requirements, and does not further remove aluminum ions with similar chemical properties to iron ions. Therefore, it fails to achieve efficient separation and recycling of impure aluminum ions in wet-process phosphoric acid.

[0005] CN101920946B discloses a method for reducing iron and aluminum ions in wet-process phosphoric acid. The method comprises first oxidizing the wet-process phosphoric acid with hydrogen peroxide, and then adding potassium oxalate and sodium carbonate to the oxidized wet-process phosphoric acid for chemical reaction treatment, thereby partially removing the iron and aluminum ions in the wet-process phosphoric acid. This method simultaneously removes the iron and aluminum ions in the wet-process phosphoric acid, but does not achieve efficient separation and recycling of the iron and aluminum ions. Furthermore, the maximum iron ion removal rate is only 70%.

[0006] Therefore, how to achieve efficient separation of iron ions and aluminum ions with similar chemical properties in wet-process phosphoric acid for selective recovery has become an urgent problem to be solved. Summary of the Invention

[0007] To solve the above technical problems, the method of the present invention first extracts iron from wet-process phosphoric acid at a lower O / A ratio, then adjusts the O / A ratio and further extracts aluminum at a larger O / A ratio. Iron and aluminum in wet-process phosphoric acid are extracted step by step, thereby achieving efficient separation and selective recovery of iron and aluminum in wet-process phosphoric acid, improving the comprehensive utilization of wet-process phosphoric acid, and having the advantages of simple process flow, low cost, no secondary pollution, and easy industrialization.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps, the method comprising the following steps:

[0010] (1) mixing the first extraction system and wet-process phosphoric acid in a volume ratio of 1:(1-6) to perform a first extraction to obtain iron-removing phosphoric acid;

[0011] (2) mixing the second extraction system and the iron-removing phosphoric acid described in step (1) at a volume ratio of (1.2-6):1 to perform a second extraction to obtain iron-removing aluminum phosphoric acid;

[0012] Wherein, the first extraction system and the second extraction system each independently comprise an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus hydroxyl group.

[0013] Wherein, in step (1), the volume ratio of the first extraction system to the wet-process phosphoric acid is 1:(1-6), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5 or 1:6, etc.

[0014] The volume ratio of the second extraction system in step (2) to the iron-removing phosphoric acid in step (1) is (1.2-6):1, for example, it can be 1.2:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1 or 6:1, etc.

[0015] The invention extracts iron and aluminum in wet-process phosphoric acid in steps by adjusting the O / A ratio. First, the iron ions in the wet-process phosphoric acid are extracted at an O / A ratio of 1:(1-6) to obtain iron-removed phosphoric acid. Then, the aluminum ions in the iron-removed phosphoric acid are extracted at an O / A ratio of (1.2-6):1 to obtain iron-removed aluminophosphate. This solves the technical problem that iron ions and aluminum ions with similar properties in wet-process phosphoric acid are difficult to separate and separately recover, laying a foundation for subsequent high-quality utilization of iron-removed aluminophosphate. The method has a simple process flow, low cost, and is easy to industrialize.

[0016] It is worth noting that when the first extraction system and the second extraction system in the present invention extract iron ions and aluminum ions, there is a competition mechanism between the two ions. Iron ions have an advantage in the competition due to their stronger complexing ability. The extraction system is more inclined to react chemically with iron ions to form a stable complex, while the extraction of aluminum ions is relatively weak. This selectivity determines that under the same O / A ratio conditions, the iron extraction rate is higher, and a higher extraction efficiency can be achieved at a lower O / A ratio.

[0017] The present invention selects the first extraction system and the second extraction system to independently include an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus-hydroxyl group, and utilizes the phosphorus-oxygen double bond and the phosphorus-hydroxyl bond in the extractant to coordinate with iron ions and aluminum ions and form a stable complex. Due to the presence of the phosphorus-oxygen double bond, the extractant has a certain acidity, which enables the extractant to exchange with metal cations (such as iron ions and aluminum ions) in the aqueous phase. The stronger the acidity, the greater the ability to extract iron ions and aluminum ions. In addition, the oxygen atoms in the phosphorus-oxygen double bond have strong electrophilicity and can attract metal cations to form stable complexes, thereby achieving extraction; the hydrogen ions in the phosphorus-hydroxyl bond can form hydrogen bonds with water molecules or other oxygen-containing groups, which helps the extractant to disperse in the aqueous phase and contact with iron ions and aluminum ions. At the same time, the hydrogen ions exchange with anions in the aqueous phase, so that iron ions and aluminum ions are transferred from the aqueous phase to the organic phase, achieving extraction and separation.

[0018] It is worth emphasizing that the first extraction system and the second extraction system of the present invention may be the same or different, and are each independently selected from an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus-hydroxyl group.

[0019] Preferably, in step (1), the volume ratio of the first extraction system to wet-process phosphoric acid is 1:(1-3).

[0020] Preferably, the volume ratio of the second extraction system in step (2) to the iron-removing phosphoric acid in step (1) is (4-6):1.

[0021] It is worth noting that the present invention further preferably has a volume ratio of the first extraction system to the wet-process phosphoric acid in step (1) of 1: (1 to 3), and a volume ratio of the second extraction system to the iron-removing phosphoric acid in step (1) of step (2) of (4 to 6): 1, which further improves the efficient and selective step-by-step extraction of iron ions and aluminum ions in wet-process phosphoric acid; if the volume ratio of the first extraction system to the wet-process phosphoric acid in step (1) is too low, the extraction cost will increase and the iron ion extraction distribution ratio will decrease; if the volume ratio of the first extraction system to the wet-process phosphoric acid in step (1) is too high, the iron ions and aluminum ions in the wet-process phosphoric acid will be extracted simultaneously, resulting in the subsequent inability to achieve separate recovery and utilization of the iron ions and aluminum ions; if the volume ratio of the second extraction system to the iron-removing phosphoric acid in step (2) is too low, the aluminum ions in the iron-removing phosphoric acid will be insufficiently extracted, resulting in a decrease in the extraction rate of the aluminum ions; if the volume ratio of the second extraction system to the iron-removing phosphoric acid in step (1) is too high, the extraction rate of the aluminum ions is not significantly improved.

[0022] Preferably, the content of iron ions in the wet-process phosphoric acid in step (1) is 0.10-0.50 wt%, calculated as a percentage by mass, for example, 0.10 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt% or 0.50 wt%, etc.

[0023] Preferably, the content of aluminum ions in the wet-process phosphoric acid in step (1) is 0.60 to 3.0 wt%, calculated as a percentage by mass, for example, 0.60 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt% or 3.0 wt%.

[0024] Preferably, the extractant containing a phosphorus-oxygen double bond comprises any one or a combination of at least two of trialkylphosphine oxide, tributyl phosphate, Cyanex 272, dimethylheptyl methylphosphonate or 2-ethylhexyldiphenyl phosphate, wherein typical but non-limiting combinations include a combination of trialkylphosphine oxide and tributyl phosphate, a combination of trialkylphosphine oxide and dimethylheptyl methylphosphonate, or a combination of Cyanex 272 and 2-ethylhexyldiphenyl phosphoric acid, etc.

[0025] Preferably, the extractant containing phosphorus hydroxyl groups comprises di(2-ethylhexyl) phosphate and / or 2-ethylhexyl phosphate 2-ethylhexyl ester. Preferably, the first extraction system in step (1) further comprises a first diluent.

[0026] Preferably, the volume ratio of the extractant to the first diluent in the first extraction system is 1:(1-4), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, etc., preferably 1:(1-2).

[0027] Preferably, the second extraction system in step (2) further includes a second diluent.

[0028] Preferably, the volume ratio of the extractant to the second diluent in the second extraction system is 1:(1-4), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, etc.

[0029] Preferably, the first diluent and the second diluent each independently include any one or a combination of at least two of kerosene, sulfonated kerosene, cyclohexane, xylene, n-heptane or ethyl acetate, wherein typical but non-limiting combinations include a combination of sulfonated kerosene and cyclohexane, a combination of kerosene and cyclohexane, or a combination of sulfonated kerosene and ethyl acetate.

[0030] Preferably, the temperature of the first extraction in step (1) is 20-50°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C.

[0031] Preferably, the first extraction time in step (1) is 5 to 30 minutes, for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0032] Preferably, the first extraction in step (1) is accompanied by a first stirring.

[0033] Preferably, the first stirring rate is 50-200 r / min, for example, 50 r / min, 80 r / min, 100 r / min, 120 r / min, 150 r / min, 180 r / min or 200 r / min, etc., preferably 100-180 r / min.

[0034] Preferably, the temperature of the second extraction in step (2) is 20-90°C, for example, it can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, etc., preferably 60-90°C.

[0035] The present invention further prefers that the temperature of the second extraction is 60-90° C., which is conducive to the extraction of aluminum ions in the iron-removing phosphate; if the temperature of the second extraction is too low, the aluminum ion extraction rate will decrease; if the temperature of the second extraction is too high, the extraction effect will not be significantly improved, but will result in higher energy consumption.

[0036] Preferably, the second extraction time in step (2) is 5 to 60 min, for example, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0037] Preferably, the second extraction process in step (2) is accompanied by a second stirring.

[0038] Preferably, the second stirring rate is 50-300 r / min, for example, 50 r / min, 100 r / min, 150 r / min, 200 r / min, 250 r / min or 300 r / min, etc., preferably 200-300 r / min.

[0039] The present invention further preferably has a second stirring rate of 200 to 300 r / min during the second extraction process, which is conducive to sufficient mixing of the second extraction system with the iron-removing phosphoric acid to improve the extraction effect of aluminum ions.

[0040] Preferably, the first extraction and the second extraction methods each independently include single-stage extraction and / or multi-stage extraction; preferably, the first extraction method is single-stage extraction; preferably, the second extraction method is multi-stage extraction.

[0041] Preferably, the number of extraction stages of the multi-stage extraction is 2 to 5, for example, it can be 2, 3, 4 or 5 stages.

[0042] The present invention further preferably comprises the step of single-stage extraction and multi-stage extraction, wherein the number of extraction stages is 2 to 5. This not only achieves efficient extraction of iron ions and aluminum ions from wet-process phosphoric acid, but also ensures low extraction energy consumption.

[0043] Preferably, after the first extraction in step (1), an iron-loaded extractant is obtained.

[0044] Preferably, after the second extraction in step (2), an aluminum-loaded extractant is obtained.

[0045] As a further preferred technical solution of the present invention, refer to Figure 1 The process flow shown in FIG. 1 includes the following steps:

[0046] (1) mixing the first extraction system and wet-process phosphoric acid in a volume ratio of 1:(1-6), performing a first extraction for 5-30 minutes at 20-50° C. and a first stirring rate of 50-200 r / min to obtain iron-removing phosphoric acid and an iron-loaded extractant;

[0047] (2) mixing the second extraction system with the iron-removing phosphoric acid in step (1) at a volume ratio of (1.2-6):1, performing a second extraction for 5-60 minutes at 20-90° C. and a second stirring rate of 50-300 r / min to obtain iron-removing aluminum phosphoric acid; wherein the iron ion content in the wet-process phosphoric acid in step (1) is 0.10-0.50 wt%, and the aluminum ion content is 0.60-3.0 wt%; the first extraction and the second extraction are each independently a single-stage extraction and / or a multi-stage extraction, and the number of stages of the multi-stage extraction is 2-5;

[0048] The first extraction system and the second extraction system each independently include an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus hydroxyl group; the first extraction system also includes a first diluent; the volume ratio of the extractant to the first diluent in the first extraction system is 1:(1 to 4); the second extraction system also includes a second diluent; the volume ratio of the extractant to the second diluent in the second extraction system is 1:(1 to 4).

[0049] Optionally, the iron-loaded extractant in step (1) and the aluminum-loaded extractant in step (2) are subjected to back extraction, separation and purification steps to further prepare an iron product or an aluminum product; the iron-removed aluminum phosphate is further purified to prepare a phosphorus product.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects:

[0051] (1) The present invention provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. By selecting a specific O / A ratio, the iron ions and aluminum ions in the wet-process phosphoric acid are extracted efficiently in steps, so that the iron ions and aluminum ions in the wet-process phosphoric acid can be separately recovered and the high-quality utilization of the wet-process phosphoric acid can be achieved. The method has a simple process flow, low cost, and is easy to industrialize.

[0052] (2) The method for extracting iron and aluminum from wet-process phosphoric acid in a step-by-step manner provided by the present invention further improves the extraction rate of iron ions and aluminum ions from wet-process phosphoric acid by further optimizing the process parameters such as the O / A ratio, extraction temperature, extraction time, extraction stage, and stirring rate of the first extraction and the second extraction. The extraction rate of iron ions can be as high as over 99%, and the extraction rate of aluminum ions can be as high as over 88%. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The present invention provides a process flow chart of the method for extracting iron and aluminum from wet-process phosphoric acid in steps. DETAILED DESCRIPTION

[0054] The technical solution of the present invention will be further described below by way of specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention, which shall be subject to the claims.

[0055] The wet-process phosphoric acid used in the following examples and comparative examples was obtained from Yichang Xingfa Chemical Co., Ltd. and included the components shown in Table 1 and the balance water.

[0056] Table 1

[0057] Components Fe Al Mg Si <![CDATA[P2O5]]> Content / wt% 0.205 0.838 0.644 0.118 35.573

[0058] 1. Implementation

[0059] Example 1

[0060] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps, the method comprising the following steps:

[0061] (1) mixing a first extraction system and wet-process phosphoric acid at a volume ratio of 1:1, performing a first extraction for 25 minutes at 30° C. and a first stirring rate of 150 r / min to obtain iron-removing phosphoric acid and an iron-loaded extractant; the first extraction is a single-stage extraction;

[0062] (2) mixing the second extraction system with the iron-removing phosphoric acid described in step (1) at a volume ratio of 5:1, performing a second extraction for 50 minutes at 70° C. and a second stirring rate of 250 r / min to obtain an iron-removing aluminum phosphoric acid and an aluminum-loaded extractant; the second extraction is a multi-stage extraction with 5 extraction stages;

[0063] Wherein, the first extraction system is composed of dimethylheptyl methylphosphonate extractant and sulfonated kerosene diluent in a volume ratio of 1:1;

[0064] The second extraction system is consistent with the first extraction system.

[0065] Example 2

[0066] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps, the method comprising the following steps:

[0067] (1) mixing the first extraction system and wet-process phosphoric acid at a volume ratio of 1:1.5, performing a first extraction for 25 minutes at 30° C. and a first stirring rate of 150 r / min to obtain iron-removing phosphoric acid and an iron-loaded extractant; the first extraction is a single-stage extraction;

[0068] (2) mixing the second extraction system with the iron-removing phosphoric acid described in step (1) at a volume ratio of 5:1, performing a second extraction for 50 minutes at 70° C. and a second stirring rate of 250 r / min to obtain an iron-removing aluminum phosphoric acid and an aluminum-loaded extractant; the second extraction is a multi-stage extraction with 5 extraction stages;

[0069] Wherein, the first extraction system is composed of dimethylheptyl methylphosphonate extractant and sulfonated kerosene diluent in a volume ratio of 1:1;

[0070] The second extraction system is consistent with the first extraction system.

[0071] Example 3

[0072] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps, the method comprising the following steps:

[0073] (1) mixing a first extraction system and wet-process phosphoric acid at a volume ratio of 1:3, performing a first extraction for 20 minutes at 20° C. and a first stirring rate of 180 r / min to obtain iron-removing phosphoric acid and an iron-loaded extractant; the first extraction is a single-stage extraction;

[0074] (2) mixing the second extraction system with the iron-removing phosphoric acid described in step (1) at a volume ratio of 4:1, performing a second extraction for 40 minutes at 90° C. and a second stirring rate of 200 r / min to obtain an iron-removing aluminum phosphoric acid and an aluminum-loaded extractant; the second extraction is a multi-stage extraction with 5 extraction stages;

[0075] Wherein, the first extraction system is composed of 2-ethylhexyl diphenyl phosphate extractant and sulfonated kerosene diluent in a volume ratio of 1:1.5;

[0076] The second extraction system is consistent with the first extraction system.

[0077] Example 4

[0078] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1 except that in step (1), the volume ratio of the first extraction system to the wet-process phosphoric acid is 1:0.5.

[0079] Example 5

[0080] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1 except that in step (1), the volume ratio of the first extraction system to the wet-process phosphoric acid is 1:3.5.

[0081] Example 6

[0082] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1, except that the volume ratio of the second extraction system in step (2) to the iron-removing phosphoric acid in step (1) is 3.5:1.

[0083] Example 7

[0084] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1, except that the volume ratio of the second extraction system in step (2) to the iron-removing phosphoric acid in step (1) is 6.5:1.

[0085] Example 8

[0086] This embodiment provides a method for stepwise extraction of iron and aluminum from wet-process phosphoric acid. The method is the same as that of Example 1, except that the volume ratio of dimethylheptyl methylphosphonate extractant to sulfonated kerosene diluent in the first extraction system is 1:2.

[0087] Example 9

[0088] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1, except that the second stirring rate in the second extraction process is 180 r / min.

[0089] Example 10

[0090] This embodiment provides a method for extracting iron and aluminum from wet-process phosphoric acid in steps. The method is the same as that of Example 1 except that the second extraction is a single-stage extraction.

[0091] 2. Comparative Example

[0092] Comparative Example 1

[0093] This comparative example provides a method for extracting iron and aluminum from wet-process phosphoric acid. The method is the same as Example 1 except that the volume ratio of the first extraction system to the wet-process phosphoric acid is 5:1.

[0094] Comparative Example 2

[0095] This comparative example provides a method for extracting iron and aluminum from wet-process phosphoric acid. The method is the same as Example 1 except that the volume ratio of the second extraction system to the iron-free phosphoric acid is 1:1.

[0096] 3. Test and its results

[0097] The extraction rates of iron ions and aluminum ions in the methods provided in the above examples and comparative examples were tested and calculated, and the results are shown in Table 2.

[0098] Table 2

[0099]

[0100]

[0101] From Table 2 we can see that:

[0102] (1) It can be seen from Examples 1 to 3 that the present invention achieves step-by-step extraction of iron ions and aluminum ions in wet-process phosphoric acid by adjusting the O / A ratio of the first extraction and the second extraction, extracting iron ions in wet-process phosphoric acid at a lower O / A ratio, and further extracting aluminum ions in the iron-removing phosphoric acid at a higher O / A ratio, and the extraction rate of iron ions is as high as 95.31% or more, and the extraction rate of aluminum ions is as high as 85.90% or more; so that aluminum ions and iron ions with similar properties can be recovered separately in the subsequent process, which is conducive to the high-quality utilization of the subsequent iron-removing aluminum phosphoric acid.

[0103] (2) It can be seen from Examples 1 and 4 to 7 that, since the volume ratio of the first extraction system to the wet-process phosphoric acid in Example 4 is relatively high, the iron ions and aluminum ions in the wet-process phosphoric acid are extracted simultaneously during the first extraction process in step (1) and cannot be recovered separately; and the volume ratio of the first extraction system to the wet-process phosphoric acid in Example 5 is relatively low, resulting in the iron ion extraction rate being reduced to 65.02%, and iron ions still remaining in the iron-free phosphoric acid; since the volume ratio of the second extraction system to the iron-free phosphoric acid in Example 6 is relatively low, the aluminum ion extraction is incomplete, and the aluminum ion extraction rate is reduced to 70.51%; and the volume ratio of the second extraction system to the iron-free phosphoric acid in Example 7 is relatively high, the aluminum ion extraction effect is not significantly improved, but the extractant is wasted; thus, the present invention further preferably has a volume ratio of the first extraction system to the wet-process phosphoric acid of 1:(1-3), and preferably has a volume ratio of the second extraction system to the iron-free phosphoric acid of (4-6):1, which synergistically further improves the efficient extraction and selective separation and recovery of iron ions and aluminum ions in the wet-process phosphoric acid.

[0104] (3) It can be seen from Examples 1 and 8 that, due to the large proportion of the diluent content in the first extraction system in Example 8, the iron ion extraction effect is poor, only 81.24%, and some iron ions still remain; the present invention further prefers that the volume ratio of the extractant to the diluent in the first extraction system is 1: (0.5-1.5), which further improves the extraction effect of iron ions and aluminum ions in wet-process phosphoric acid.

[0105] (4) It can be seen from Examples 1 and 9-10 that the second stirring rate in the second extraction process in Example 9 is relatively low, and the extraction rate of aluminum ions decreases to 84.22%. In Example 10, the second extraction is a single-stage extraction, resulting in a poor extraction effect of aluminum ions, which decreases to 46.19%. It can be seen that the present invention further optimizes the extraction temperature, stirring rate and extraction stage in the second extraction process, further improving the extraction rate of aluminum ions in wet-process phosphoric acid.

[0106] (5) It can be seen from Example 1 and Comparative Examples 1 to 2 that, since the first extraction and the second extraction in Comparative Example 1 were both carried out under a relatively large O / A ratio, both iron ions and aluminum ions were extracted during the first extraction process, making it difficult to achieve separate extraction and recovery of iron ions and aluminum ions in wet-process phosphoric acid; whereas, in Comparative Example 2, the first extraction and the second extraction were both carried out under a relatively small O / A ratio, resulting in insufficient extraction of aluminum ions or almost no extraction of aluminum ions during the second extraction process, making it impossible to achieve recovery and reuse of aluminum ions in wet-process phosphoric acid.

[0107] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for extracting iron and aluminum from wet-process phosphoric acid in steps, characterized in that: The method comprises the following steps: (1) mixing the first extraction system and wet-process phosphoric acid in a volume ratio of 1:(1-6) to perform a first extraction to obtain iron-removing phosphoric acid; (2) mixing the second extraction system and the iron-removing phosphoric acid in step (1) at a volume ratio of (1.2-6):1 to perform a second extraction to obtain iron-removing aluminum phosphoric acid; Wherein, the first extraction system and the second extraction system each independently comprise an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus hydroxyl group.

2. The method according to claim 1, characterized in that In step (1), the volume ratio of the first extraction system to wet-process phosphoric acid is 1:(1-3).

3. The method according to claim 1, characterized in that The volume ratio of the second extraction system in step (2) to the iron-removing phosphoric acid in step (1) is (4-6):

1.

4. The method according to claim 1, wherein Calculated by weight percentage, the content of iron ions in the wet-process phosphoric acid in step (1) is 0.10-0.50 wt%.

5. The method according to claim 1, wherein Calculated by weight percentage, the content of aluminum ions in the wet-process phosphoric acid in step (1) is 0.60-3.0 wt%.

6. The method according to claim 1, wherein The extractant containing a phosphorus-oxygen double bond includes any one of trialkylphosphine oxide, tributyl phosphate, Cyanex 272, dimethylheptyl methylphosphonate or 2-ethylhexyl diphenyl phosphate, or a combination of at least two thereof.

7. The method according to claim 1, characterized in that The extractant containing phosphorus hydroxyl groups includes di(2-ethylhexyl) phosphate and / or 2-ethylhexyl phosphate.

8. The method according to claim 1, characterized in that In step (1), the first extraction system further includes a first diluent.

9. The method according to claim 8, characterized in that The volume ratio of the extractant to the first diluent in the first extraction system is 1:(1-4).

10. The method according to claim 9, characterized in that The volume ratio of the extractant to the first diluent in the first extraction system is 1:(1-2).

11. The method according to claim 8, characterized in that In step (2), the second extraction system further includes a second diluent.

12. The method according to claim 11, characterized in that The volume ratio of the extractant to the second diluent in the second extraction system is 1:(1-4).

13. The method according to claim 11, characterized in that The first diluent and the second diluent each independently include any one or a combination of at least two of kerosene, sulfonated kerosene, cyclohexane, xylene, n-heptane or ethyl acetate.

14. The method according to claim 1, wherein The temperature of the first extraction in step (1) is 20-50°C.

15. The method according to claim 1, wherein The time of the first extraction in step (1) is 5 to 30 minutes.

16. The method according to claim 1, characterized in that The first extraction process in step (1) is accompanied by a first stirring.

17. The method according to claim 16, wherein The first stirring speed is 50-200 r / min.

18. The method according to claim 17, wherein The first stirring rate is 100-180 r / min.

19. The method according to claim 1, wherein The temperature of the second extraction in step (2) is 20-90°C.

20. The method according to claim 19, characterized in that The temperature of the second extraction in step (2) is 60-90°C.

21. The method according to claim 1, wherein The second extraction time in step (2) is 5 to 60 minutes.

22. The method according to claim 1, wherein The second extraction process in step (2) is accompanied by a second stirring.

23. The method according to claim 22, wherein The second stirring speed is 50-300 r / min.

24. The method according to claim 23, wherein The second stirring speed is 200-300 r / min.

25. The method according to claim 11, wherein The first extraction and the second extraction methods each independently include single-stage extraction and / or multi-stage extraction.

26. The method according to claim 25, characterized in that The first extraction method is single-stage extraction.

27. The method according to claim 25, characterized in that The second extraction is performed in a multi-stage extraction manner.

28. The method according to claim 27, characterized in that The extraction stages of the multi-stage extraction are 2 to 5.

29. The method according to claim 1, wherein After the first extraction in step (1), an iron-loaded extractant is obtained.

30. The method according to claim 1, wherein After the second extraction in step (2), an aluminum-loaded extractant is obtained.

31. The method according to claim 1, wherein The method comprises the following steps: (1) mixing the first extraction system and wet-process phosphoric acid in a volume ratio of 1:(1-6), performing a first extraction for 5-30 minutes at 20-50° C. and a first stirring rate of 50-200 r / min to obtain iron-removing phosphoric acid and an iron-loaded extractant; (2) mixing the second extraction system and the iron-removing phosphoric acid described in step (1) at a volume ratio of (1.2-6):1, performing a second extraction for 5-60 minutes at 20-90° C. and a second stirring rate of 50-300 r / min to obtain an iron-removing aluminum phosphoric acid and an aluminum-loaded extractant; Wherein, the content of iron ions in the wet-process phosphoric acid in step (1) is 0.10-0.50 wt%, and the content of aluminum ions is 0.60-3.0 wt%. The first extraction and the second extraction are each independently a single-stage extraction and / or a multi-stage extraction, and the number of stages of the multi-stage extraction is 2-5. The first extraction system and the second extraction system each independently include an extractant containing a phosphorus-oxygen double bond and / or an extractant containing a phosphorus hydroxyl group; the first extraction system also includes a first diluent; the volume ratio of the extractant to the first diluent in the first extraction system is 1:(1~4); the second extraction system also includes a second diluent; the volume ratio of the extractant to the second diluent in the second extraction system is 1:(1~4).

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