Acid circulation process in rare earth mineral sulfation decomposition process

Abstract

The invention discloses an acid circulation process in a process of sulfating and decomposing rare earth minerals, which comprises the following steps: 1) mixing the sulfated and decomposed rare earth minerals with slurry mixing liquid to obtain primary leaching residues A1 and an acid solution B containing rare earth; 2) mixing the rare earth-containing acidic solution B with an amine-containing extractant I to obtain a sulfuric acid-loaded organic solution C and a rare earth-containing raffinate D; 3) mixing the raffinate D with an acidic phosphorus type extractant II to obtain a rare earth-loaded organic solution X and raffinate E containing dilute sulphuric acid; 4) mixing the organic solution C loaded with the sulfuric acid with water to obtain an organic solution Y containing the extracting agent I and a sulfuric acid strip liquor Z; and (5) returning the raffinate E containing dilute sulphuric acid to the step (1), mixing the raffinate E with the primary leaching residue A1, and repeating the steps (1)-(5) for n-1 times in total. According to the method, recycling of sulfuric acid is achieved, and the use amount of water in the leaching process is reduced.

Description

Technical Field

[0001] This invention relates to an acid cycling process in the sulfation decomposition of rare earth minerals. Background Technology

[0002] The sulfation decomposition technology for rare earth minerals is widely used due to its strong applicability to rare earth minerals, and its technological development continues to move towards comprehensive resource utilization. The tail gas produced during the sulfation decomposition process contains sulfur oxides (such as SO2 and SO3), which can be absorbed and separated to obtain a certain concentration of sulfuric acid solution, which can then be reused for the sulfation decomposition of minerals.

[0003] Rare earth sulfate, after sulfation and decomposition, requires industrial leaching with an aqueous solution to obtain a rare earth sulfate solution, which is then converted to a rare earth chloride solution. During this conversion process, some companies use extractant P204 for saponification and extraction. This process generates a large amount of dilute sulfuric acid wastewater, currently treated with lime neutralization. While the neutralized filtrate can be reused for rare earth sulfate leaching, it also produces a large amount of calcium sulfate solid waste. This treatment method not only increases the cost of transporting and storing solid waste but also wastes valuable resources such as calcium and sulfur.

[0004] Therefore, realizing the recycling of valuable resources, especially acid resources in dilute sulfuric acid wastewater, in the process of sulfation decomposition of rare earth minerals has become a key issue of current process focus. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide an acid recycling process in the sulfation decomposition of rare earth minerals. This process can convert solutions containing sulfuric acid from different steps into a sulfuric acid solution of a certain concentration, which can be reused for the leaching of sulfated rare earth minerals or for the sulfation decomposition of rare earth minerals. Furthermore, this process can also recover the extractant for the extraction of acidic solutions containing rare earth elements. In addition, this process can reduce the amount of leachate used during the leaching of sulfated rare earth minerals.

[0006] The present invention achieves the above objectives through the following technical methods.

[0007] This invention provides an acid cycling process in the sulfation decomposition of rare earth minerals, comprising the following steps:

[0008] 1) The rare earth minerals after sulfation and decomposition are mixed with the slurry, and the solid and liquid are separated to obtain primary leaching residue A1 and acidic solution B containing rare earth elements.

[0009] 2) Mix acidic solution B containing rare earth elements with extractant I containing amine, and after extraction, separate the phases to obtain organic solution C loaded with sulfuric acid and raffinate D containing rare earth elements.

[0010] 3) Mix the raffinate D containing rare earth elements with acidic phosphorus-type extractant II, and after extraction, separate the phases to obtain an organic solution X loaded with rare earth elements and a raffinate E containing dilute sulfuric acid.

[0011] 4) Mix the organic solution C loaded with sulfuric acid with water, extract and separate the phases to obtain an organic solution Y containing extractant I and a sulfuric acid back-extraction solution Z;

[0012] 5) Return the raffinate E containing dilute sulfuric acid to step 1) as a slurry, mix it with the primary leaching residue A1, and then repeat steps 1) to 5) a total of n-1 times until the REO content in the nth leaching residue An is ≤5wt%; where n is a positive integer greater than or equal to 2;

[0013] Steps 3) and 4) are not in any particular order.

[0014] This invention, through research and experimentation, reveals that by treating an acidic solution B containing rare earth elements with extractant I, an organic solution C loaded with sulfuric acid and a raffinate D containing rare earth elements can be obtained. Then, the organic solution C loaded with sulfuric acid is back-extracted with water to recover sulfuric acid back-extractant Z (i.e., recovered sulfuric acid solution) and an organic solution Y containing extractant I (i.e., recovered extractant I). The raffinate D containing rare earth elements is then mixed with extractant II for extraction to obtain an organic solution X loaded with rare earth elements and a raffinate E containing dilute sulfuric acid (i.e., recovered dilute sulfuric acid solution). The organic solution X containing rare earth elements can be back-extracted and separated with hydrochloric acid to obtain a rare earth chloride solution. This invention achieves the recovery and recycling of sulfuric acid.

[0015] In this invention, the amine-containing extractant I is composed of an amine compound, a diluent, and an additive. The amine compound is selected from one or more of trioctylamine, triisooctylamine, trioctyldecyl tertiary amine (N235), and secondary primary amine (N1923). The diluent is white oil or kerosene. The additive is selected from one or more of isooctanol, n-octanol, n-heptol, and n-decanol.

[0016] Acidic phosphorus-type extractant II consists of an acidic phosphorus-type compound and a diluent, wherein the acidic phosphorus-type compound is selected from one or more of di(2-ethylhexyl)phosphoric acid and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester. The diluent is white oil or kerosene. According to a specific embodiment of the present invention, acidic phosphorus-type extractant II is a mixture formed by di(2-ethylhexyl)phosphoric acid (P2O4) and kerosene.

[0017] In this invention, the raffinate E containing dilute sulfuric acid is returned to step 1) as the slurry preparation solution for step 1), mixed with the primary leaching residue A1, and subjected to solid-liquid separation to obtain secondary leaching residue A2 and an acidic solution B' containing rare earth elements, thus repeating step 1). In some embodiments, the raffinate E containing dilute sulfuric acid is used directly as the raw material for secondary leaching without dilution with water, and solid-liquid separation is performed to obtain secondary leaching residue A2 and an acidic solution B' containing rare earth elements. In other embodiments, a small amount of water is added to the raffinate E containing dilute sulfuric acid and stirred, then mixed with the primary leaching residue A1, and solid-liquid separation is performed to obtain secondary leaching residue A2 and an acidic solution B' containing rare earth elements.

[0018] According to the acid cycle process of the present invention, preferably, in step 1), the rare earth minerals after sulfation decomposition are obtained by decomposing rare earth minerals with sulfuric acid.

[0019] In this invention, the rare earth minerals after sulfation decomposition can be obtained by roasting with concentrated sulfuric acid, sulfation roasting, leaching with sulfuric acid at atmospheric pressure, or leaching with sulfuric acid under pressure. Preferably, the rare earth minerals after sulfation decomposition are obtained through concentrated sulfuric acid roasting or atmospheric pressure sulfuric acid leaching. In some embodiments, the rare earth minerals after sulfation decomposition are obtained through concentrated sulfuric acid roasting. In other embodiments, the rare earth minerals after sulfation decomposition are obtained through atmospheric pressure sulfuric acid leaching. The rare earth minerals can be rare earth concentrates.

[0020] According to the acid cycling process of the present invention, preferably, in step 1), the solid-liquid ratio when the rare earth minerals after sulfation decomposition are mixed with the slurry is 1 kg:(0.5-5) L. The preferred solid-liquid ratio is 1 kg:(1-4) L. Such a solid-liquid ratio can reduce the amount of slurry (e.g., water) used.

[0021] In some embodiments, the sulfated rare earth minerals are mixed with water at a solid-liquid ratio of 1 kg:1 L. In other embodiments, the sulfated rare earth minerals are mixed with water at a solid-liquid ratio of 1 kg:2 L. In still other embodiments, the sulfated rare earth minerals are mixed with water at a solid-liquid ratio of 1 kg:4 L.

[0022] In step 1), when the rare earth minerals after sulfation decomposition are mixed with water for leaching, the amount of water added is reduced by 50 wt% compared to the amount of water added in the existing process.

[0023] According to the acid cycling process of the present invention, preferably, in step 1), the slurry is water or raffinate E containing dilute sulfuric acid.

[0024] In this invention, the slurry used for the first leaching of rare earth minerals after sulfation decomposition is water, and in the leaching process of the nth leaching residue, the slurry used is the raffinate E containing dilute sulfuric acid.

[0025] According to the acid cycling process of the present invention, preferably, in step 2), the amine-containing extractant I is composed of an amine compound, a diluent, and an additive, wherein the amine compound is selected from one or more of trioctylamine, triisooctylamine, trioctyldecyl tertiary amine, and secondary primary amine. More preferably, in step 2), the amine compound is selected from one or more of trioctylamine, triisooctylamine, and secondary primary amine (N1923). The diluent is selected from white oil or kerosene, preferably kerosene. The additive is selected from one or more of isooctanol, n-octanol, n-heptol, and n-decanol, preferably one or more of isooctanol, n-octanol, and n-heptol, and more preferably isooctanol.

[0026] In this invention, the volume ratio of the amino compound, diluent, and additive is 40–45:40–45:20, preferably 40:40:20. According to one embodiment of the invention, kerosene is used as the diluent, isooctanol as the additive, and the volume ratio of the amino compound, kerosene, and isooctanol is 40:40:20. In some embodiments, the amino compound can be trioctylamine. In other embodiments, the amino compound can be triisooctylamine. In still other embodiments, the amino compound can be a secondary primary amine (N1923). This invention has found that the sulfuric acid back-extraction solution Z obtained using extractant I containing a secondary primary amine (N1923) has a higher concentration and fewer cycles.

[0027] In step 2) of this invention, the acidic solution B containing rare earth elements is used as the aqueous phase, and the extractant I containing amines is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 0.5 to 5:1. This ratio is beneficial for the complete separation of rare earth elements from sulfuric acid.

[0028] In some embodiments, the acidic solution B containing rare earth elements is used as the aqueous phase, and the amine-containing extractant I is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 0.5:1. In other embodiments, the acidic solution B containing rare earth elements is used as the aqueous phase, and the amine-containing extractant I is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 2:1. In still other embodiments, the acidic solution B containing rare earth elements is used as the aqueous phase, and the amine-containing extractant I is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 5:1.

[0029] According to the acid cycling process of the present invention, preferably, in step 3), the acidic phosphorus extractant II is composed of an acidic phosphorus compound and a diluent, wherein the acidic phosphorus compound is selected from one or more of di(2-ethylhexyl)phosphoric acid and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, preferably di(2-ethylhexyl)phosphoric acid. The diluent is white oil or kerosene, preferably kerosene. Specifically, di(2-ethylhexyl)phosphoric acid is P204, and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is P507. The volume ratio of the acidic phosphorus compound to the diluent is 1 to 1.5:1, preferably 1:1.

[0030] According to the acid cycling process of the present invention, preferably, in step 3), the raffinate D containing rare earth elements is used as the aqueous phase, and the acidic phosphorus-type extractant II is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 0.5 to 5:1. More preferably, the raffinate D containing rare earth elements is used as the aqueous phase, and the acidic phosphorus-type extractant II is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 1 to 5:1. This ratio is beneficial for complete rare earth extraction.

[0031] In some embodiments, the rare earth-containing raffinate D is used as the aqueous phase, and the acidic phosphorus-type extractant II is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 1:1. In other embodiments, the rare earth-containing raffinate D is used as the aqueous phase, and the acidic phosphorus-type extractant II is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 3:1. In still other embodiments, the rare earth-containing raffinate D is used as the aqueous phase, and the acidic phosphorus-type extractant II is used as the organic phase, with a volume ratio of organic phase to aqueous phase of 5:1.

[0032] In step 3) of the present invention, the obtained rare earth-loaded organic solution X can be back-extracted and separated into solid and liquid components using hydrochloric acid to obtain a single rare earth chloride solution.

[0033] According to the acid cycling process of the present invention, preferably, in step 4), when the organic solution C loaded with sulfuric acid is mixed with water, the volume ratio of the organic phase to the aqueous phase is 2 to 6:1. Such a ratio is beneficial for providing a suitable sulfuric acid concentration.

[0034] In some embodiments, when the sulfuric acid-loaded organic solution C is mixed with water, the volume ratio of the organic phase to the aqueous phase is 2:1. In other embodiments, the volume ratio of the organic phase to the aqueous phase is 4:1. In still other embodiments, the volume ratio of the organic phase to the aqueous phase is 6:1.

[0035] In step 4), the concentration of the sulfuric acid back-extraction solution Z obtained by the present invention can be 0.5–5 mol / L, preferably 1–4 mol / L. In some embodiments, the concentration of the sulfuric acid back-extraction solution Z obtained by the present invention is 1 mol / L. In other embodiments, the concentration of the sulfuric acid back-extraction solution Z obtained by the present invention is 3 mol / L. In still other embodiments, the concentration of the sulfuric acid back-extraction solution Z obtained by the present invention is 4 mol / L.

[0036] According to the acid cycling process of the present invention, preferably, in step 5), the solid-liquid ratio when the raffinate E containing dilute sulfuric acid is mixed with the primary leaching residue A1 is 1 kg:(0.5-5) L. The preferred solid-liquid ratio is 1 kg:(1-4) L. This ratio is beneficial for the leaching of rare earth elements.

[0037] In some embodiments, the solid-liquid ratio of the raffinate E containing dilute sulfuric acid to the primary leaching residue A1 is 1 kg:1 L. In other embodiments, the solid-liquid ratio of the raffinate E containing dilute sulfuric acid to the primary leaching residue A1 is 1 kg:2 L. In still other embodiments, the solid-liquid ratio of the raffinate E containing dilute sulfuric acid to the primary leaching residue A1 is 1 kg:4 L.

[0038] In step 5), steps 1) to 5) are repeated n-1 times until the REO content in the leaching residue An is ≤5wt%; where n is a positive integer greater than or equal to 2. The number of times steps 1) to 5) are repeated is preferably 2 to 5 times. In some embodiments, steps 1) to 5) are repeated 2 times. In other embodiments, steps 1) to 5) are repeated 3 times. In still other embodiments, steps 1) to 5) are repeated 4 times.

[0039] In step 5), the REO content in the leaching residue An obtained n times is preferably less than or equal to 5 wt%; more preferably less than or equal to 4 wt%.

[0040] In some embodiments, the REO content in the leaching residue An obtained after n leaching cycles is 3.95 wt%. In other embodiments, the REO content in the leaching residue An obtained after n leaching cycles is 3.25 wt%. In still other embodiments, the REO content in the leaching residue An obtained after n leaching cycles is 3.29 wt%.

[0041] According to the acid cycle process of the present invention, preferably, the organic solution Y containing extractant I obtained in step 4) is recycled to step 2) to extract the acidic solution B containing rare earth; the sulfuric acid back-extraction solution Z is used to decompose the rare earth minerals to obtain the rare earth minerals after sulfation and decomposition.

[0042] The acid recycling process of this invention employs a back-extraction method, using water to extract a sulfuric acid solution containing extractant I. This enriches the sulfuric acid for mineral decomposition and allows extractant I to be recycled for extraction of acidic solutions containing rare earth elements. The acid recycling process uses extractant II containing P2O4 to extract the sulfuric acid rare earth solution. The resulting dilute sulfuric acid raffinate can be recycled for re-leaching of the primary leaching residue of the rare earth minerals after sulfation decomposition, achieving sulfuric acid enrichment and improving rare earth recovery. This acid recycling process reduces water consumption during rare earth leaching, saving process costs. Attached Figure Description

[0043] Figure 1 The above are schematic flowcharts of Embodiments 1, 2 and 3 of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0045] The sources of some raw materials in the following examples are explained below:

[0046] N1923: Chengdu Aikeda Chemical Reagent Co., Ltd.

[0047] P204: Chengdu Aikeda Chemical Reagent Co., Ltd.

[0048] Kerosene: Chengdu Aikeda Chemical Reagent Co., Ltd.

[0049] Isooctyl alcohol: Chengdu Aikeda Chemical Reagent Co., Ltd.

[0050] The testing method and calculation formula are described below:

[0051] REO content: The test was conducted using the method specified in GB / T 18114.1-2010.

[0052] REO recovery rate (wt%) = total rare earth content in the P204 organic solution loaded with rare earth / rare earth content in rare earth minerals × 100%.

[0053] Example 1

[0054] 1) The rare earth mineral roasted ore obtained by roasting and decomposing rare earth concentrate with concentrated sulfuric acid (i.e. rare earth mineral after sulfation and decomposition) is mixed with water at a solid-liquid ratio of 1 kg: 4 L, filtered, and a primary leaching residue A1 and an acidic solution B containing rare earth are obtained.

[0055] 2) An acidic solution B containing rare earth elements (as the aqueous phase) and an amine-containing extractant I (as the organic phase; wherein the amine-containing extractant I is composed of N1923, kerosene and isooctanol in a volume ratio of 4:4:2) are mixed and extracted at a volume ratio of 0.5:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain an organic solution C loaded with sulfuric acid and a raffinate D containing rare earth elements.

[0056] 3) The raffinate D containing rare earth elements (as the aqueous phase) and the acidic phosphorus-type extractant II (as the organic phase; wherein the acidic phosphorus-type extractant II is composed of P204 and kerosene in a volume ratio of 1:1) are mixed and extracted at a volume ratio of 1:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain a rare earth-loaded P204 organic solution (i.e., rare earth-loaded organic solution X) and a raffinate E containing dilute sulfuric acid.

[0057] 4) The organic solution C loaded with sulfuric acid was mixed with water at a volume ratio of organic phase to aqueous phase of 6:1 and extracted. After extraction, the phases were separated to obtain an organic solution containing N1923 (i.e., an organic solution Y containing extractant I) and a sulfuric acid back-extraction solution Z. The concentration of the sulfuric acid back-extraction solution Z was 4 mol / L. The organic solution containing N1923 can be used for the extraction of rare earth acidic solution B. The sulfuric acid back-extraction solution Z can be used to decompose rare earth minerals.

[0058] 5) Mix the raffinate E containing dilute sulfuric acid with the primary leaching residue A1 at a solid-liquid ratio of 1 kg: 4 L, and then repeat steps 1) to 5) twice. The REO content in the resulting tertiary leaching residue A3 is 3.95 wt%.

[0059] Example 2

[0060] 1) The rare earth sulfate obtained by slurry decomposition of rare earth concentrate with concentrated sulfuric acid (i.e. rare earth minerals after sulfation decomposition) is mixed with water at a solid-liquid ratio of 1 kg: 1 L, filtered, and a primary leaching residue A1 and an acidic solution B containing rare earth are obtained.

[0061] 2) An acidic solution B containing rare earth elements (as the aqueous phase) and an amine-containing extractant I (as the organic phase; wherein the amine-containing extractant I is composed of N1923, kerosene and isooctanol in a volume ratio of 4:2:4) are mixed and extracted at a volume ratio of 5:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain an organic solution C loaded with sulfuric acid and a raffinate D containing rare earth elements.

[0062] 3) The raffinate D containing rare earth (as the aqueous phase) and the acidic phosphorus extractant II (as the organic phase; wherein the acidic phosphorus extractant II is composed of P204 and kerosene in a volume ratio of 1:1) are mixed and extracted at a volume ratio of 5:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain a rare earth-loaded P204 organic solution (i.e., rare earth-loaded organic solution X) and a raffinate E containing dilute sulfuric acid.

[0063] 4) The organic solution C loaded with sulfuric acid was mixed with water at a volume ratio of organic phase to aqueous phase of 4:1 and extracted. After extraction, the phases were separated to obtain an organic solution containing N1923 (i.e., an organic solution Y containing extractant I) and a sulfuric acid back-extraction solution Z. The concentration of the sulfuric acid back-extraction solution Z was 3 mol / L. The organic solution containing N1923 can be used for the extraction of rare earth acidic solution B. The sulfuric acid back-extraction solution Z can be used to decompose rare earth minerals.

[0064] 5) Mix the raffinate E containing dilute sulfuric acid with the primary leaching residue A1 at a solid-liquid ratio of 1 kg: 1 L, and then repeat steps 1) to 5) a total of 4 times. The REO content in the five-stage leaching residue A5 is 3.25 wt%.

[0065] Example 3

[0066] 1) The rare earth sulfate (i.e. rare earth minerals after sulfation and decomposition) after slurrying and decomposing rare earth concentrate with concentrated sulfuric acid is mixed with water at a solid-liquid ratio of 1kg:2L, filtered, and the resulting primary leaching residue A1 and acidic solution B containing rare earth are obtained.

[0067] 2) An acidic solution B containing rare earth elements (as the aqueous phase) and an amine-containing extractant I (as the organic phase; wherein the amine-containing extractant I is composed of triisooctylamine, kerosene and isooctanol in a volume ratio of 4:4:2) are mixed and extracted at a volume ratio of 2:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain an organic solution C loaded with sulfuric acid and a raffinate D containing rare earth elements.

[0068] 3) The raffinate D containing rare earth (as the aqueous phase) and the acidic phosphorus extractant II (as the organic phase; wherein the acidic phosphorus extractant II is composed of P204 and kerosene in a volume ratio of 1:1) are mixed and extracted at a volume ratio of 3:1 between the organic phase and the aqueous phase. After extraction, the phases are separated to obtain a rare earth-loaded P204 organic solution (i.e., rare earth-loaded organic solution X) and a raffinate E containing dilute sulfuric acid.

[0069] 4) The organic solution C loaded with sulfuric acid was mixed with water at a volume ratio of 5:1 (organic phase to aqueous phase) and extracted. After extraction, the phases were separated to obtain an organic solution containing triisooctylamine (i.e., organic solution Y containing extractant I) and a sulfuric acid back-extraction solution Z. The concentration of the sulfuric acid back-extraction solution Z was 3 mol / L. The organic solution containing triisooctylamine can be used for the extraction of rare earth acidic solution B. The sulfuric acid back-extraction solution Z can be used to decompose rare earth minerals.

[0070] 5) Mix the raffinate E containing dilute sulfuric acid with the primary leaching residue A1 at a solid-liquid ratio of 1 kg: 2 L, and repeat steps 1) to 5) three times. The REO content in the resulting fourth leaching residue A4 is 3.29 wt%.

[0071] The recovery rate of REO and the concentration of (dilute) sulfuric acid raffinate in Examples 1-3 are shown in Table 1.

[0072] Table 1

[0073]

[0074] Note: In Table 1, the H2SO4 concentrations of sulfuric acid back-extraction solution Z and raffinate E containing dilute sulfuric acid are obtained from a single treatment, excluding repeated steps 1) to 5).

[0075] In summary, the acid recycling process of the present invention realizes the recycling of sulfuric acid during the sulfation decomposition of rare earth minerals, and the extractants I and II used can also be recycled.

[0076] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A process for recycling acid in a process for the sulphatizing decomposition of rare earth minerals, characterized in that, Includes the following steps: 1) The rare earth minerals after sulfation and decomposition are mixed with the slurry, and the solid and liquid are separated to obtain primary leaching residue A1 and acidic solution B containing rare earth. 2) Mix acidic solution B containing rare earth elements with extractant I containing amine, and after extraction, separate the phases to obtain organic solution C loaded with sulfuric acid and raffinate D containing rare earth elements. 3) Mix the raffinate D containing rare earth elements with acidic phosphorus-type extractant II, and after extraction, separate the phases to obtain an organic solution X loaded with rare earth elements and a raffinate E containing dilute sulfuric acid. 4) Mix the organic solution C loaded with sulfuric acid with water, back-extract and separate the phases to obtain an organic solution Y containing extractant I and a sulfuric acid back-extract Z; 5) Return the raffinate E containing dilute sulfuric acid to step 1) as a slurry preparation solution, and mix it with the primary leaching residue A1. Then repeat steps 1) to 5) a total of n-1 times until the REO content in the leaching residue An is ≤5wt%; where n is a positive integer greater than or equal to 2; Steps 3) and 4) are not in any particular order.

2. The acid recycling process according to claim 1, characterized in that, In step 1), the rare earth minerals after sulfation decomposition are obtained by decomposing rare earth minerals with sulfuric acid.

3. The acid recycling process according to claim 1, characterized in that, In step 1), the solid-liquid ratio when the rare earth minerals after sulfation and decomposition are mixed with the slurry is 1 kg: (0.5-5) L.

4. The acid recycling process according to claim 1, characterized in that, In step 1), the slurry is water or raffinate E containing dilute sulfuric acid.

5. The acid recycling process according to claim 1, characterized in that, In step 2), the amine-containing extractant I is composed of an amine compound, a diluent, and an additive; wherein the amine compound is selected from one or more of trioctylamine, triisooctylamine, trioctyldecyl tertiary amine, and secondary carbon primary amine.

6. The acid recycling process according to claim 1, characterized in that, In step 3), the acidic phosphorus extractant II is composed of an acidic phosphorus compound and a diluent, wherein the acidic phosphorus compound is selected from one or more of di(2-ethylhexyl)phosphoric acid and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester.

7. The acid recycling process according to claim 1, characterized in that, In step 3), the raffinate D containing rare earth elements is used as the aqueous phase, and the acidic phosphorus extractant II is used as the organic phase. The volume ratio of the organic phase to the aqueous phase is 0.5 to 5:

1.

8. The acid recycling process according to claim 1, characterized in that, In step 4), when the organic solution C loaded with sulfuric acid is mixed with water, the volume ratio of the organic phase to the aqueous phase is 2 to 6:

1.

9. The acid recycling process according to claim 1, characterized in that, In step 5), the solid-liquid ratio when the raffinate E containing dilute sulfuric acid is mixed with the primary leaching residue A1 is 1 kg: (0.5-5) L.

10. The acid recycling process according to claim 1, characterized in that, It also includes the following steps: The organic solution Y containing extractant I obtained in step 4) is reused in step 2) to extract the acidic solution B containing rare earth elements. The sulfuric acid back-extraction solution Z was used to decompose rare earth minerals to obtain rare earth minerals after sulfation and decomposition.

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