Process for separating nickel from iron in nickel-containing ferric chloride and use thereof

Abstract

This invention provides a method for separating nickel and iron in nickel-containing ferric chloride and its application. The method includes: preparing a solution of nickel-containing ferric chloride obtained by chlorination and roasting of a nickel-iron alloy; performing solid-liquid separation via iron precipitation reaction to obtain ferric phosphate dihydrate and a nickel-containing filtrate; adjusting the pH of the nickel-containing filtrate to 5-6 and then performing solid-liquid separation to obtain a nickel solution; adding a sulfur source to the nickel solution, and then performing solid-liquid separation after reaction to obtain nickel sulfide. This invention, through stepwise precipitation and precise pH control, simultaneously achieves high-purity iron production and efficient nickel enrichment within an ammonia-based system. The process is simple, low-cost, and suitable for the preparation of battery-grade ferric phosphate and the recycling of nickel resources.

Description

Technical Field

[0001] This invention belongs to the field of separation technology, specifically relating to a method for separating nickel and iron in nickel-containing ferric chloride and its application. Background Technology

[0002] With the growth of the new energy vehicle industry, the demand for lithium iron phosphate (LFP) batteries has surged, driving the development of a huge market for its key precursor—battery-grade iron phosphate. Meanwhile, the resource security of nickel, an important strategic metal, is receiving increasing attention. Against this backdrop, how to economically and environmentally obtain high-purity iron phosphate and efficiently recover the associated nickel resources has become a hot topic in industrial technology research and development.

[0003] The applicant's R&D team has developed a short-process chlorination roasting process for nickel-iron alloys, which can efficiently produce products mainly composed of nickel-containing ferric chloride. Furthermore, among various ferric phosphate preparation processes, the ammonia method has become the industry mainstream due to its low cost and high-value byproducts. Therefore, the natural and ideal technical route is to integrate the applicant's proprietary chlorination roasting process with the mature ammonia-based ferric phosphate process. However, when implementing this integration, a key technical obstacle immediately becomes apparent: the trace amounts of nickel (approximately 0.3%-0.5%) contained in the chlorination roasting product will form stable soluble nickel-ammonia complexes (such as [Ni(NH3)6]) in the alkaline or ammoniacal environment of the ammonia method. 2+ ).

[0004] This nickel-ammonia complex exists stably in solution, and it is difficult to effectively separate and enrich it using conventional simple methods such as alkaline precipitation, resulting in the loss of valuable nickel.

[0005] Existing technologies either circumvent the ammonia process by using other methods or add complex subsequent extraction steps, both of which increase process complexity and cost. Therefore, there is an urgent need for a technology embedded within the ammonia process system that can simultaneously achieve the preparation of high-purity iron phosphate and the efficient separation and enrichment of nickel, in order to alleviate or solve the aforementioned problems. Summary of the Invention

[0006] Aiming to solve the technical problem of how to simultaneously achieve the preparation of high-purity ferric phosphate and the efficient separation and enrichment of nickel within the ammonia process system, the present invention provides a method for separating nickel and iron in nickel-containing ferric chloride, comprising the following steps: S1. Prepare the nickel-containing ferric chloride into a nickel-containing ferric chloride solution; S2. The nickel-containing ferric chloride solution undergoes a precipitation reaction followed by solid-liquid separation to obtain ferric phosphate dihydrate and a nickel-containing filtrate. The pH during the precipitation reaction is 1.5-1.8. S3. After adjusting the pH of the nickel-containing filtrate to 5-6, perform solid-liquid separation to obtain nickel-iron slag and nickel liquid; S4. Add a sulfur source to the nickel liquid, and separate the solid and liquid to obtain nickel sulfide.

[0007] Furthermore, the chemical composition of the nickel-containing ferric chloride, by mass fraction, includes: ferric chloride ≥ 98%, nickel 0.3-0.5%, and cobalt 0.03-0.05%.

[0008] Furthermore, step S4 includes: adding an iron precipitation agent to the nickel-containing ferric chloride solution to induce an iron precipitation reaction, followed by solid-liquid separation to obtain ferric phosphate dihydrate and a nickel-containing filtrate; The iron-precipitating agent includes a phosphorus agent and an alkaline agent; The phosphoric acid agent includes at least one of monoammonium phosphate solution and phosphoric acid solution, and the alkaline agent includes at least one of ammonia water, nickel hydroxide, and iron hydroxide.

[0009] Furthermore, the temperature during the iron deposition reaction is controlled at 80℃-90℃, and the duration is 3-6 hours.

[0010] Furthermore, during the iron precipitation reaction, the molar ratio of iron in the nickel-containing ferric chloride solution to phosphorus in the phosphorus agent is 1:1.15-1.35.

[0011] Furthermore, the nickel-iron slag is used as the alkaline agent in the iron precipitation reaction in step S2.

[0012] Furthermore, the sulfur source includes at least one of ammonium sulfide, sodium sulfide, and potassium sulfide, and the molar ratio of sulfur in the sulfur source to nickel in the nickel melt is 2-4:1.

[0013] Furthermore, the ferric phosphate dihydrate is subjected to washing and drying processes in sequence to obtain battery-grade ferric phosphate; The cleaning process includes: cleaning the ferric phosphate at a liquid-to-solid ratio of 5-10:1 for 0.5-1 hours, and repeating the cleaning 3-5 times; The drying process includes drying the product of the cleaning process at 75-80°C to a constant weight to obtain the battery-grade iron phosphate.

[0014] Furthermore, the yield of the battery-grade iron phosphate is not less than 98%, and the chemical composition of the battery-grade iron phosphate includes: Fe: 28.5-30%, P: 16.2-17.2%, Ni < 0.005%, Co < 0.005%; wherein, the iron-phosphorus molar ratio is 0.96-1; The nickel recovery rate in the nickel sulfide is not less than 97%.

[0015] This invention provides an application of the nickel and iron separation method in nickel-containing ferric chloride as described in any of the preceding claims in the production of lithium iron phosphate batteries.

[0016] Compared with the prior art, the present invention has at least the following advantages: This invention, through the iron precipitation reaction under specific conditions in step S2, can preferentially and selectively precipitate more than 98% of the ferric chloride in the raw material in the form of ferric phosphate dihydrate (FePO4·2H2O). The product can directly meet the standard of "Ferric Phosphate for Batteries" (HG / T4701-2021), and the content of the key impurity nickel is consistently below 0.005%, realizing the commercialization of high-value iron products.

[0017] Steps S3 and S4 of this invention constitute a proprietary recovery pathway for trace nickel. First, the solution is preliminarily purified by precisely adjusting the pH of the nickel-containing filtrate to 5-6 (as shown in the comparative example, this range can effectively precipitate residual iron and avoid nickel loss); then, a sulfur source is added for selective precipitation, which can efficiently enrich and recover more than 97% of the nickel in the form of nickel sulfide, solving the problem of trace nickel being dispersed in solution and difficult to recover.

[0018] This invention systematically solves the problem of nickel-iron separation within the framework of the ammonia process through the following progressive technical design: First, in the iron precipitation stage (step S2), the pH of the reaction system is precisely controlled within a strongly acidic range of 1.5-1.8. Under this condition, iron is preferentially and completely precipitated as ferric phosphate, while nickel remains in the solution due to the high acidity and the lack of a stable precipitate. This achieves efficient separation of iron and retention of nickel at the source. Subsequently, in the nickel-rich purification stage (step S3), the pH of the nickel-containing filtrate is adjusted to a weakly acidic range of 5-6. This pH condition effectively precipitates residual small amounts of iron impurities (forming nickel-iron slag), avoids co-precipitation of nickel ions and iron, and prevents a decrease in nickel recovery rate caused by nickel complexation and dissolution in ammonia, creating a favorable environment for subsequent nickel enrichment. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a schematic flowchart of a method for separating nickel and iron in nickel-containing ferric chloride according to an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0023] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0024] Among commonly used technologies, numerous processes have been explored for separating and recovering nickel and iron from nickel-iron alloys. For example, a typical hydrometallurgical route usually involves complex steps such as acid leaching, multi-step precipitation, crystallization, and even solvent extraction. Although such methods can achieve separation, they are initially designed for mixed raw materials with high nickel and iron content (such as nickel-iron alloys themselves), resulting in lengthy process designs, high reagent and energy consumption, and poor overall economic efficiency, especially when processing materials with low nickel content.

[0025] When the applicant integrates its proprietary nickel-iron alloy chlorination roasting process (which can efficiently produce a product mainly containing nickel-containing ferric chloride with trace amounts of nickel) with the downstream mainstream ammonia-based ferric phosphate preparation process, it faces a specific and prominent technical contradiction: in the ammonia environment of the ammonia process, the trace amounts of nickel in the product will be transformed into stable soluble nickel-ammonia complexes. The stability of such complexes makes the subsequent separation of nickel from the solution extremely difficult. Conventional alkaline precipitation methods are inefficient, resulting in low nickel recovery rates and the inability to concentrate nickel, causing intangible losses and waste of strategic metal resources.

[0026] The aforementioned problem of "nickel interference and loss in the ammonia process system" arising from process integration lacks a targeted and efficient solution in existing commonly used separation technologies. Existing technologies are either too complex and costly to economically process such specific intermediate products with low nickel content, or they cannot simultaneously achieve high-purity iron production and efficient nickel recovery within the ammonia process system.

[0027] like Figure 1 As shown, to address the shortcomings of the aforementioned commonly used techniques, this invention provides a method for separating nickel and iron in nickel-containing ferric chloride, comprising the following steps: S1. Prepare the nickel-containing ferric chloride into a nickel-containing ferric chloride solution.

[0028] In this invention, the anhydrous ferric chloride comprises, by mass fraction: ferric chloride ≥ 98%, nickel 0.3-0.5%, and cobalt 0.03-0.05%.

[0029] In this invention, the preparation of the nickel-containing ferric chloride includes the following steps: nickel-iron alloy is subjected to chlorination roasting treatment to obtain nickel-containing ferric chloride.

[0030] In some embodiments, the chemical composition of the nickel-iron alloy, by mass fraction, comprises: 80%-85% iron, 10%-15% nickel, and 0.4%-0.6% cobalt.

[0031] In some embodiments, the chlorination roasting temperature is 650-850℃, the mass ratio of nickel-iron alloy to chlorine is 1:1.66-2.5, the chlorine flow rate is 1.45kg / min-2.2kg / min, and the chlorination reaction time is 2.5h-3h.

[0032] For example, the temperature of the chlorination roasting treatment can be 650°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 850°C, and any value between such a minimum and maximum value, or a range of any two values.

[0033] For example, the mass ratio of the nickel-iron alloy to chlorine gas can be 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, and any value between such a minimum and maximum value, or a range of any two values.

[0034] In this invention, step S1 includes: adding water to nickel-containing ferric chloride to prepare a nickel-containing ferric chloride solution, wherein the concentration of the nickel-containing ferric chloride solution can be 0.5-1.5 mol / L.

[0035] S2. The nickel-containing ferric chloride solution undergoes solid-liquid separation after an iron precipitation reaction to obtain ferric phosphate dihydrate and a nickel-containing filtrate.

[0036] In this invention, the pH of the iron precipitation reaction can be controlled at 1.5-1.8, the temperature at 80℃-90℃, and the reaction time at 3-6 hours. These reaction conditions are crucial for achieving preferential, efficient, and selective precipitation of iron. Under these strongly acidic conditions (pH 1.5-1.8) and relatively high temperatures (80-90℃), iron ions can rapidly react with phosphate ions to form pure iron phosphate dihydrate crystals, while nickel and cobalt ions remain largely in the solution due to the high acidity and lack of precipitate formation. The reaction time (3-6 hours) ensures complete precipitation and good crystal growth. If the pH is too low (e.g., Comparative Example 4, pH=1.3), incomplete iron precipitation and reduced yield will occur; if the pH is too high (e.g., Comparative Example 5, pH=2.0), co-precipitation of nickel and cobalt impurities may occur, affecting product purity. Insufficient temperature (e.g., Comparative Example 6, 70℃) or excessively short time (e.g., Comparative Example 9, 2 hours) will result in substandard chemical composition, abnormal crystal structure, or abnormal morphology in the product.

[0037] For example, the pH during the iron deposition reaction can be 1.5, 1.6, 1.7, 1.8, or any value between such a minimum and maximum value, or a range of any two values.

[0038] In this invention, during the iron precipitation reaction, the molar ratio of iron in the nickel-containing ferric chloride solution to phosphorus in the phosphating agent is 1:1.15-1.35. This iron-phosphorus ratio range is necessary to obtain stoichiometrically accurate and high-purity ferric phosphate dihydrate. An appropriate excess of phosphorus (1.15-1.35) ensures complete precipitation of iron ions, preventing insufficient phosphorus from causing excessive iron content in the product (e.g., in Comparative Example 7, the iron-phosphorus ratio of 1:1 results in insufficient phosphorus content and abnormal color). Conversely, an excessively high phosphorus ratio (e.g., in Comparative Example 8, the iron-phosphorus ratio of 1:1.4) will lead to excessive phosphorus content in the product, which also fails to meet battery-grade standards.

[0039] For example, the molar ratio of iron in the nickel-containing ferric chloride solution to phosphorus in the phosphorus agent can be 1:1.15, 1:1.2, 1:1.25, 1:1.30, 1:1.35, or any value between such a minimum and maximum value, or a range of any two values.

[0040] In this invention, the ferric phosphate dihydrate is sequentially washed and dried to obtain battery-grade ferric phosphate. The cleaning process includes: cleaning the ferric phosphate at a liquid-to-solid ratio of 5-10:1 for 0.5-1 hour, repeating the cleaning 3-5 times. The specific steps are as follows: The ferric phosphate is subjected to a three-stage countercurrent washing process to obtain the washed product; wherein, the first-stage washing water is collected; the first-stage washing water contains ammonium ions, chloride ions, and nickel and cobalt soluble impurities remaining on the surface of the ferric phosphate dihydrate.

[0041] The primary washing water and the nickel-containing filtrate obtained in step S2 are combined for subsequent nickel separation and enrichment steps. For example, the system obtained by combining the primary washing water and the nickel-containing filtrate obtained in step S2 can be referred to as a mixture.

[0042] The drying process includes drying the product from the cleaning process at 75-80°C to a constant weight to obtain the battery-grade iron phosphate. A drying temperature not exceeding 80°C ensures effective removal of free moisture from the material while preventing iron phosphate dihydrate (FePO4·2H2O) from losing its water of crystallization, thereby guaranteeing the stability of the final product's chemical composition.

[0043] It should be noted that the iron phosphate products involved in this invention, including their wet form (iron phosphate wet material) and the final battery-grade iron phosphate, all have iron phosphate dihydrate (FePO4·2H2O) as their core chemical component.

[0044] In this invention, the yield of the battery-grade iron phosphate is not less than 98%, and the chemical composition of the battery-grade iron phosphate includes: Fe: 28.5-30%, P: 16.2-17.2%, Ni < 0.005%, Co < 0.005%; wherein, the iron-phosphorus molar ratio is 0.96-1; The nickel recovery rate in the nickel sulfide is not less than 97%.

[0045] In this invention, the formula for calculating the yield of the battery-grade iron phosphate is as follows: Yield (%) = (Mass of iron in battery-grade iron phosphate ÷ Total mass of iron in raw materials) × 100%.

[0046] The formula for calculating the nickel recovery rate in the nickel sulfide is as follows: Nickel recovery rate (%) = (mass of nickel in nickel sulfide ÷ total mass of nickel in raw material) × 100%.

[0047] S3. After adjusting the pH of the nickel-containing filtrate to 5-6, solid-liquid separation is performed to obtain nickel-iron slag and nickel liquid. Precise control of this pH range is a key step in achieving efficient separation and enrichment of nickel and iron. Adjusting the pH to a weakly acidic range of 5-6 allows the trace iron ions that were not completely precipitated in step S2, as well as iron impurities introduced from ferric phosphate washing, to precipitate completely in the form of ferric hydroxide, etc. (forming nickel-iron slag), thereby ensuring that the iron content in the subsequent nickel liquid is extremely low, creating conditions for obtaining high-purity nickel sulfide products (as shown in Comparative Example 1, iron removal is incomplete at pH=4.5, resulting in a high iron content in the final nickel sulfide); on the other hand, this pH environment can effectively inhibit the formation of precipitates between nickel ions and hydroxide ions, allowing them to remain in the solution as free ions, avoiding the loss of nickel due to precipitation, and laying the foundation for the efficient and selective precipitation of nickel sulfide in the subsequent step S4.

[0048] For example, the pH of the nickel-containing filtrate can be adjusted to 5-6 using ammonia.

[0049] In this invention, the nickel-iron slag can be used as the alkaline agent in the iron precipitation reaction in step S2.

[0050] It should be noted that the main component of the nickel-iron slag is ferric hydroxide, which may contain a small amount of precipitated nickel. Its reuse as an alkali agent allows for material recycling.

[0051] S4. Add a sulfur source to the nickel liquid, and separate the solid and liquid to obtain nickel sulfide.

[0052] In this invention, step S4 includes: adding an iron precipitation agent to the nickel-containing ferric chloride solution to induce an iron precipitation reaction, followed by solid-liquid separation to obtain ferric phosphate dihydrate and a nickel-containing filtrate. The iron-precipitating agent includes a phosphorus agent and an alkaline agent; The phosphoric acid agent includes at least one of monoammonium phosphate solution and phosphoric acid solution, and the alkaline agent includes at least one of ammonia water, nickel hydroxide, and iron hydroxide.

[0053] In this invention, the sulfur source includes at least one of ammonium sulfide, sodium sulfide, and potassium sulfide, and the molar ratio of sulfur in the sulfur source to nickel in the nickel solution is (2-4):1. This excess sulfur-nickel ratio (2-4:1) is crucial for ensuring that trace amounts of nickel in the solution are efficiently and completely precipitated as nickel sulfide. In the weakly acidic nickel-rich solution purified in step S3, the excess sulfur ions effectively overcome the dissolution equilibrium limitation, driving the nickel precipitation reaction to completion, thereby achieving a high nickel recovery rate (>97%). If the sulfur-nickel ratio is insufficient (e.g., in Comparative Example 3, S:Ni = 1:1), incomplete nickel precipitation will occur, and the nickel recovery rate will decrease significantly.

[0054] The present invention also provides an application of the nickel and iron separation method in nickel-containing ferric chloride as described in any of the preceding claims in the production of lithium iron phosphate batteries.

[0055] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided: Example 1 S1. Weigh 162.5g of nickel-containing ferric chloride, dissolve it in 1L of water, and prepare a 1mol / L ferric chloride solution for later use; the chemical composition of the nickel-containing ferric chloride, by mass fraction, includes: ferric chloride 98.5%, nickel 0.37%, and cobalt 0.034%.

[0056] S2. Measure 650 ml of 1 mol / L nickel-containing ferric chloride solution into a beaker, turn on the stirrer, heat to 80℃, add 1 mol / L monoammonium phosphate solution and ammonia water at an iron-to-phosphorus ratio of 1:1.15 to carry out the iron precipitation reaction. Adjust the amount of ammonia water to control the reaction pH to 1.8 and the temperature to 80℃. React for 3 hours to obtain ferric phosphate dihydrate and nickel-containing filtrate. Ferric phosphate dihydrate was washed in a liquid-solid ratio of 5:1 using a three-stage countercurrent washing process for 1 hour, and the washing was repeated 3 times. The first-stage washing water was collected, and the phosphate was dried at 80°C to constant weight to obtain battery-grade ferric phosphate.

[0057] S3. After mixing the nickel-containing filtrate and primary cleaning water, the composition and content of the mixture are shown in Table 1. Ammonia water is added to adjust the pH to 5.5. Solid-liquid separation is performed to obtain nickel-iron slag and nickel liquid. The iron content in the nickel liquid is 0 mg / L, and the nickel content is 251.5 mg / L. The nickel-iron slag can be returned to step S2 as an iron-precipitating agent for recycling.

[0058] Table 1. Composition content of the mixture

[0059] S4. Add sodium sulfide to the nickel liquid at a molar ratio of S:Ni of 4:1, and separate the solid and liquid to obtain nickel slag and nickel-removed liquid.

[0060] Results: The yield of battery-grade iron phosphate was 99.8%, with Fe: 29.2%, P: 16.6%, iron-to-phosphorus ratio: 0.98, Ni: 0.0040%, and Co: 0.0035%. The product met the technical requirements of "Iron Phosphate for Batteries" (HG / T4701-2021), as shown in Table 2 (and to ensure the quality of battery-grade iron phosphate, the nickel content was required to be no higher than 0.005%). The final nickel content of the obtained nickel-free solution was 4.75 mg / L. In the final nickel-iron alloy chlorination roasting product, 99.8% of the iron in the nickel-iron chloride was enriched in the battery-grade iron phosphate product, and 97.5% of the nickel was separated and enriched in the nickel slag in the form of nickel sulfide. The nickel slag did not contain iron.

[0061] Table 2 is selected from the technical requirements of "Iron Phosphate for Batteries" (HG / T4701-2021).

[0062] Example 2 S1. Weigh 162.5g of nickel-containing ferric chloride from Example 1, dissolve it in 1L of water until fully dissolved, and prepare a 1mol / L nickel-containing ferric chloride solution for later use.

[0063] S2. Measure 300 ml of 1 mol / L ferric chloride solution into a beaker, turn on the stirrer, heat to 80°C, add 1 mol / L monoammonium phosphate solution and ammonia (iron precipitation agent) at an iron-to-phosphorus ratio of 1:1.2 to carry out the iron precipitation reaction. Control the reaction pH to 1.6 and the temperature to 80°C by adjusting the amount of ammonia. React for 4 hours to obtain ferric phosphate dihydrate and nickel-containing filtrate.

[0064] Ferric phosphate dihydrate was washed for 1 hour at a liquid-to-solid ratio of 5:1, and then washed three times. The phosphate was dried at 80°C to constant weight to obtain battery-grade ferric phosphate.

[0065] S3. After mixing the nickel-containing filtrate and primary washing water, the content and composition of the mixture are shown in Table 3. Ammonia water is added to adjust the pH to 6, and solid-liquid separation is performed to obtain nickel-iron slag and nickel liquid. The nickel liquid has an iron content of 0 mg / L and a nickel content of 249.42 mg / L. The nickel-iron slag is used in step S2 as an iron-settling agent for recovery.

[0066] Table 3. Composition content of the mixture

[0067] S4. Add sodium sulfide to the nickel liquid at a molar ratio of S:Ni of 3:1, and separate the solid and liquid to obtain nickel slag and nickel removal liquid.

[0068] Results: The yield of the obtained battery-grade iron phosphate product was 98.1%, with Fe: 28.6%, P: 16.4%, iron-to-phosphorus ratio: 0.97, Ni: 0.0043%, and Co: 0.0031%. The product met the technical requirements of "Iron Phosphate for Batteries" (HG / T4701-2021). The final nickel content of the obtained nickel-free solution was 5.12 mg / L. In the final nickel-iron alloy chlorination roasting product, 98.1% of the iron in the nickel ferric chloride was separated and enriched in the form of iron phosphate, and 97.3% of the nickel was separated and enriched in the form of nickel sulfide in the nickel slag. The nickel slag did not contain iron.

[0069] Comparative Example 1 Compared to Example 1, this comparative example only adjusts step S3: ammonia is added to the mixture of primary cleaning water and nickel-containing filtrate to adjust the pH to 4.5; the other steps remain unchanged.

[0070] In this comparative example, the yield of battery-grade iron phosphate was 99.8%, with Fe: 29.2%, P: 16.6%, iron-phosphorus ratio: 0.98, Ni: 0.0040%, and Co: 0.0035%, meeting the standards. However, the nickel solution still contained 46.1 mg / L of iron ions that were not completely removed, resulting in nickel sulfide containing 15.6% iron sulfide, indicating incomplete iron-nickel separation.

[0071] Comparative Example 2 Compared to Example 1, this comparative example only adjusts step S4: sodium sulfide is replaced with sodium hydroxide, sodium hydroxide is added to the nickel solution to precipitate nickel ions, and the pH is adjusted to 10.5.

[0072] In this comparative example, the yield of battery-grade iron phosphate was 99.8%, with Fe: 29.2%, P: 16.6%, iron-to-phosphorus ratio: 0.98, Ni: 0.0040%, and Co: 0.0035%, meeting the standards. However, the nickel solution still contained 134.63 mg / L of unprecipitated nickel ions, and only 39.0% of the nickel was ultimately separated and enriched as nickel hydroxide. This indicates that simply using ammonia or sodium hydroxide to precipitate nickel ions cannot completely separate and enrich the nickel in the nickel solution; sodium sulfide must be used to completely break the complex.

[0073] Comparative Example 3 Compared to Example 1, this comparative example only adjusts step S4: sodium sulfide is added to the nickel liquid at a molar ratio of S:Ni of 1:1; the other steps remain unchanged.

[0074] In this comparative example, the yield of battery-grade iron phosphate was 99.8%, with Fe: 29.2%, P: 16.6%, iron-to-phosphorus ratio: 0.98, Ni: 0.0040%, and Co: 0.0035%, meeting the standards. However, 21.14 mg / L of unprecipitated nickel ions remained in the nickel solution, and ultimately 92.9% of the nickel was separated and enriched as nickel sulfide, indicating incomplete nickel separation and enrichment.

[0075] Comparative Example 4 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the pH of the iron precipitation reaction in step S2 is adjusted to 1.3.

[0076] Results: The yield of battery-grade iron phosphate product was 88.9%, with Ni: 0.0029% and Co: 0.0009%.

[0077] Comparative Example 5 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the pH of the iron precipitation reaction in step S2 is adjusted to 2.0.

[0078] In this comparative example, the yield of battery-grade iron phosphate product was 99.5%, with Co content of 0.006% and Ni content of 0.01%, which does not meet the product standard.

[0079] Comparative Example 6 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the iron deposition reaction temperature in step S2 is adjusted to 70°C.

[0080] In this comparative example, the battery-grade iron phosphate product obtained had an Fe content of 31.28%, which does not meet the product standard, and the product was reddish-brown.

[0081] Comparative Example 7 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the amount of monoammonium phosphate added in step S1 is adjusted to adjust the iron-phosphorus ratio to 1:1.

[0082] In this comparative example, the battery-grade iron phosphate product obtained had a P content of 15.5%, was reddish-brown, a Ni content of 0.0037%, and a Co content of 0.0015%, which did not meet the product standard.

[0083] Comparative Example 8 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the amount of monoammonium phosphate added in step S2 is adjusted to adjust the phosphorus-iron ratio to 1:1.4.

[0084] In this comparative example, the battery-grade iron phosphate product obtained had a P content of 18.3%, a Ni content of 0.0096%, and a Co content of 0.0058%, which did not meet the product standard.

[0085] Comparative Example 9 Compared to Example 1, the remaining steps in this comparative example remain unchanged, except that the iron deposition reaction time in step S2 is designed to be 2 hours.

[0086] In this comparative example, the battery-grade iron phosphate product had an Fe content of 30.7%, a Ni content of 0.0050%, and a Co content of 0.0010%, which did not meet the product standard.

[0087] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for separating nickel and iron in nickel-containing ferric chloride, characterized in that, Including the following steps: S1. Prepare the nickel-containing ferric chloride into a nickel-containing ferric chloride solution; S2. The nickel-containing ferric chloride solution undergoes solid-liquid separation after an iron precipitation reaction to obtain ferric phosphate dihydrate and a nickel-containing filtrate. The pH during the iron precipitation reaction is 1.5-1.

8. S3. After adjusting the pH of the nickel-containing filtrate to 5-6, perform solid-liquid separation to obtain nickel-iron slag and nickel liquid; S4. Add a sulfur source to the nickel liquid, and separate the solid and liquid to obtain nickel sulfide.

2. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 1, characterized in that, The chemical composition of the nickel-containing ferric chloride, by mass fraction, includes: ferric chloride ≥ 98%, nickel 0.3-0.5%, and cobalt 0.03-0.05%.

3. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 1, characterized in that, Step S2 includes: adding an iron precipitation agent to the nickel-containing ferric chloride solution to induce an iron precipitation reaction, separating the solid and liquid to obtain ferric phosphate dihydrate and a nickel-containing filtrate. The iron-precipitating agent includes a phosphorus agent and an alkaline agent; The phosphoric acid agent includes at least one of monoammonium phosphate solution and phosphoric acid solution, and the alkaline agent includes at least one of ammonia water, nickel hydroxide, and iron hydroxide.

4. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 3, characterized in that, The temperature during the iron deposition reaction is controlled at 80℃-90℃, and the duration is 3-6 hours.

5. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 3, characterized in that, During the iron precipitation reaction, the molar ratio of iron in the nickel-containing ferric chloride solution to phosphorus in the phosphorus agent is 1:1.15-1.

35.

6. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 3, characterized in that, The nickel-iron slag is used as the alkaline agent in the iron precipitation reaction in step S2.

7. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 1, characterized in that, The sulfur source includes at least one of ammonium sulfide, sodium sulfide, and potassium sulfide, and the molar ratio of sulfur in the sulfur source to nickel in the nickel melt is 2-4:

1.

8. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 1, characterized in that, The ferric phosphate dihydrate was sequentially cleaned and dried to obtain battery-grade ferric phosphate. The cleaning process includes: cleaning the ferric phosphate at a liquid-to-solid ratio of 5-10:1 for 0.5-1 hours, and repeating the cleaning 3-5 times; The drying process includes drying the product of the cleaning process at 75-80°C to a constant weight to obtain the battery-grade iron phosphate.

9. The method for separating nickel and iron in nickel-containing ferric chloride according to claim 8, characterized in that, The yield of the battery-grade iron phosphate is not less than 98%, and the chemical composition of the battery-grade iron phosphate includes: Fe: 28.5-30%, P: 16.2-17.2%, Ni < 0.005%, Co < 0.005%; wherein the iron-phosphorus molar ratio is 0.96-1. The nickel recovery rate in the nickel sulfide is not less than 97%.

10. The application of the method for separating nickel and iron in nickel-containing ferric chloride as described in any one of claims 1-9 in the production of lithium iron phosphate batteries.

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