Treatment method of ferro-nickel alloy

Abstract

The invention discloses a treatment method of a nickel-iron alloy, which comprises the following steps: first-stage leaching: mixing acid and the nickel-iron alloy for first-time leaching, and then carrying out solid-liquid separation to obtain a first nickel-iron-containing solution and first nickel-iron alloy slag; coarse ferrite crystals are prepared, specifically, the first nickel-iron-containing solution is subjected to cooling crystallization, and the coarse ferrite crystals and a second nickel-iron-containing solution are obtained; second-stage leaching is conducted, specifically, the second nickel-iron-containing solution and the first nickel-iron alloy slag are mixed for second-time leaching, then solid-liquid separation is conducted, and a third nickel-iron-containing solution and second nickel-iron alloy slag are obtained; the first initial H < + > concentration of the first-stage leaching reaction liquid is 4.0-24.0 mol / L, and the first leaching is completed when the H < + > concentration is 2.0-4.0 mol / L; the first-stage leaching is carried out under the condition of high acid concentration, the difficulty of continuously leaching ferronickel after a period of time is continuously increased, cooling crystallization is carried out on the first ferronickel-containing solution, and high leaching efficiency of the second-stage leaching is favorably kept.

Description

Technical Field

[0001] This application relates to the technical field of comprehensive utilization of nickel and iron in nickel-iron alloys, and more specifically, to a method for treating nickel-iron alloys. Background Art

[0002] Nickel-iron alloys are hard, corrosion-resistant, and have good plasticity, and are widely used in fields such as machinery, overflow materials, national defense, new energy, and light industry.

[0003] The nickel and iron resources in nickel-iron alloys can be recovered through a hydrometallurgical process. However, the leaching efficiency of nickel and iron is low, and the process economy is low.

[0004] In view of this, this application is specifically proposed. Summary of the Invention

[0005] The purpose of this application is to provide a method for treating nickel-iron alloys to improve the leaching rate of nickel and iron in nickel-iron alloys per unit time.

[0006] This application provides a method for treating nickel-iron alloys, including:

[0007] First-stage leaching: After mixing an acid with a nickel-iron alloy for the first leaching, solid-liquid separation is performed to obtain a first nickel-iron-containing solution and a first nickel-iron alloy slag;

[0008] Crude ferrous salt crystallization: Cooling crystallization is performed on the first nickel-iron-containing solution to obtain crude ferrous salt crystals and a second nickel-iron-containing solution;

[0009] Second-stage leaching: After mixing the second nickel-iron-containing solution with the first nickel-iron alloy slag for the second leaching, solid-liquid separation is performed to obtain a third nickel-iron-containing solution and a second nickel-iron alloy slag;

[0010] In the reaction solution of the first-stage leaching step, the initial concentration of H + is 4.0 - 24.0 mol / L, and the first leaching is completed when the concentration of H + is 2.0 - 4.0 mol / L.

[0011] The first-stage leaching is carried out at a high acid concentration, and a large amount of nickel and iron in the nickel-iron alloy are leached. Restricted by the decrease in hydrogen ion concentration and chemical equilibrium, the difficulty of continuous leaching of nickel and iron increases continuously, and the components in the obtained first nickel-iron-containing solution, especially ferrous salts, gradually approach saturation. Controlling the end-point concentration of H + in the first leaching and performing cooling crystallization on the first nickel-iron-containing solution to precipitate the ferrous salts therein, and then using the second nickel-iron-containing solution to continue dissolving the first nickel-iron alloy slag is beneficial to shortening the leaching time in the two-stage leaching and obtaining a high leaching rate, so as to improve the leaching rate of nickel and iron per unit time and improve the leaching efficiency.

[0012] Adopt a two-stage leaching process. In the first-stage leaching, at a high acid concentration, nickel and iron in the nickel-iron alloy can be leached without crushing the raw materials, which can improve the leaching rate and effectively increase the leaching rate of valuable metals in the nickel-iron alloy, enabling most of the iron, nickel, and cobalt to dissolve into the liquid phase. At the same time, a high acid concentration is conducive to preventing the oxidation of ferrous ions in the solution, reducing the loss of valuable metals, and improving the leaching efficiency and process economy of nickel-iron.

[0013] In an optional embodiment, the leaching temperature of the first-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h.

[0014] Optionally, in the first-stage leaching step, first mix the nickel-iron alloy with water at a liquid-solid ratio of 3 - 10:1 mL / g, and then add acid to it until the first initial H + concentration.

[0015] Optionally, in the reaction solution of the first-stage leaching step, the first initial H + concentration is 6.0 - 12.0 mol / L.

[0016] Optionally, the H + concentration when the first leaching is completed is 3.0 - 4.0 mol / L.

[0017] Optionally, the leaching temperature of the second-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h.

[0018] Optionally, the acid includes one or more of hydrochloric acid, nitric acid, and sulfuric acid; optionally, the acid is sulfuric acid.

[0019] Optionally, the second-stage leaching step further includes adding acid to make the second initial H + concentration in the reaction system 6.0 - 12.0 mol / L, and the second leaching is completed when the H + concentration is 2.0 - 4.0 mol / L.

[0020] Optionally, the second initial H + concentration is 6.0 - 12.0 mol / L.

[0021] Optionally, the H + concentration when the second leaching is completed is 3.0 - 4.0 mol / L.

[0022] Optionally, the temperature of the cooling crystallization is 10 - 25 °C, and the time is 1 - 8 h;

[0023] Optionally, the cooling crystallization adopts vacuum cooling crystallization.

[0024] In an optional embodiment, it further includes impurity removal:

[0025] Mix the third nickel-containing iron solution, crude ferrous salt crystals and water to dissolve the crude ferrous salt crystals, obtaining a fourth nickel-containing iron solution; add a purification agent to the fourth nickel-containing iron solution and adjust the pH of the solution to 0.5 - 4.5 for purification, and filter to obtain a fifth nickel-containing iron solution and purification residues.

[0026] In an optional embodiment, the content of ferrous ions in the fourth nickel-containing iron solution is 65 - 130 g / L.

[0027] Optionally, in the purification step, the purification agent includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium phosphate.

[0028] Optionally, the addition amount of the purification agent is 1.1 - 1.5 times the theoretical amount of chromium removal, and the theoretical amount of chromium removal is the amount of the purification agent that just reacts completely with chromium to form a precipitate.

[0029] In an optional embodiment, in the purification step, a neutralizing agent is used to adjust the pH of the solution to 0.5 - 4.5, and the neutralizing agent includes at least one of ferronickel, nickel matte, nickel powder and iron powder.

[0030] Optionally, a neutralizing agent is used to adjust the pH of the solution to 1.0 - 3.5.

[0031] Optionally, the ferronickel includes Fe 50 wt% - 80 wt%, Ni 15 wt% - 40 wt%, Co 0.1 wt% - 1.0 wt%, Cr 0.01 wt% - 1.0 wt%, S 5 wt% - 10 wt%.

[0032] Optionally, the nickel matte includes Fe ≤ 5 wt%, Ni 55 wt% - 65 wt%, Co 0.5 wt% - 1.2 wt%, Cr 0.01 wt% - 1.0 wt%, S 22 wt% - 27 wt%.

[0033] In an optional embodiment, it further includes iron precipitation: add phosphate, ammonia water and hydrogen peroxide to the fifth nickel-containing iron solution to precipitate iron, obtaining crude iron phosphate and the solution after iron precipitation.

[0034] Optionally, the phosphate includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium phosphate.

[0035] Optionally, the iron precipitation step includes adding a mixed solution containing phosphate, ammonia water and hydrogen peroxide with a pH of 5.0 - 7.0 to the fifth nickel-containing iron solution with a pH of 1.0 - 3.5, reacting for 1 - 2 h, and ending the reaction when the pH reaches 0.8 - 2.4.

[0036] Optionally, the addition time of the mixed solution lasts for 0.5 - 1.0 h.

[0037] Optionally, the temperature of the iron precipitation step is 30-60°C.

[0038] Optionally, the molar ratio of iron element in the fifth nickel-containing iron solution to phosphorus element in the mixed solution is 0.96-1.04:1.

[0039] Optionally, the molar ratio of ferrous ions in the fifth nickel-containing iron solution to hydrogen peroxide in the mixed solution is 0.68-0.78:1.

[0040] In an optional embodiment, it further includes pickling the crude iron phosphate and solid-liquid separation. The pickling includes mixing the crude iron phosphate and pure water according to a solid-liquid ratio of 1:14-18 g / mL for pulping, and adding sulfuric acid or hydrochloric acid to adjust the pH to 0.5-3.0.

[0041] Optionally, adding sulfuric acid or hydrochloric acid to adjust the pH to 1.0-1.5 can dissolve and wash out the acid-soluble impurities in the crude iron phosphate.

[0042] Optionally, the pickling time is 0.5-1.0 h and the temperature is 50-90°C.

[0043] In an optional embodiment, it further includes aging, water washing, drying and calcining the pickled iron phosphate in sequence to obtain iron phosphate for battery use.

[0044] Optionally, the aging includes mixing the pickled iron phosphate with phosphoric acid and water for pulping, and solid-liquid separation to obtain the aged iron phosphate. The mass ratio of phosphoric acid to the pickled iron phosphate is 0.10-0.24:1.0, and the concentration of phosphoric acid is 70%-90%; the aging temperature is 85-100°C and the aging time is 1.5-3.5 h.

[0045] Optionally, the water washing includes mixing the aged iron phosphate with water according to a solid-liquid mass ratio of 1:16-22 for pulping and solid-liquid separation to obtain the water-washed iron phosphate. The water washing time is 0.5-1.0 h and the temperature is 50-90°C.

[0046] In an optional embodiment, the post-iron-precipitation solution is sequentially filtered, subjected to extraction for impurity removal and degreasing to obtain battery-grade nickel sulfate solution.

[0047] Optionally, the extractant used for extraction includes any one of P204, P507, and Cyanex272.

[0048] Optionally, the addition amount of the extractant used for extraction is 20%-30% of the volume of the aqueous phase.

[0049] Optionally, the time for extraction and impurity removal is 5-10 min and the temperature is 30-40°C.

[0050] In an alternative embodiment, the nickel-iron alloy includes Fe and Ni, and further includes at least one of impurity elements Co, Cr, Cu, Mn, Zn, and P.

[0051] Optionally, the nickel-iron alloy includes 50 wt% to 80 wt% of Fe, 15 wt% to 40 wt% of Ni, 0.1 wt% to 1.0 wt% of Co, 0.01 wt% to 1.0 wt% of Cr, and 0.01 wt to 1 wt% of S.

[0052] Optionally, the particle size of the nickel-iron alloy is 1 to 10 cm. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0054] Figure 1 It is a flowchart of the leaching step in the treatment method of the nickel-iron alloy provided in some embodiments of the present application;

[0055] Figure 2 It is a flowchart of the treatment method of the nickel-iron alloy provided in some embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0058] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0059] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, a method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0060] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean only including or comprising the listed components.

[0061] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or present) and B is false (or absent); A is false (or absent) while B is true (or present); or both A and B are true (or present).

[0062] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by purchasing in the market.

[0063] In this application, matte refers to a mixture containing metallic elements such as nickel and iron and optional sulfides. The sulfides can be, for example, FeS, Ni3S2, etc. According to the different nickel contents in matte, matte can be divided into low-grade matte and high-grade matte. The nickel content in low-grade matte is usually below 40 wt%, and the iron content is usually below 80 wt%. The nickel content in high-grade matte is usually above 40%, and the iron content is usually below 5 wt%. In some examples, both low-grade matte and high-grade matte can be intermediate products in the nickel smelting process, such as a sulfide eutectic melt of metals such as nickel, copper, and cobalt obtained by smelting nickel concentrate in an electric furnace and a converter.

[0064] The main components of nickel-iron alloy are Ni and Fe, and it may also contain at least one element among Co, Cr, Cu, Si, S, P, and C. In some examples, nickel-iron alloy can be obtained by pyrometallurgy, reducing nickel oxide ore at high temperature.

[0065] Battery-grade nickel sulfate refers to nickel sulfate that complies with the "Battery-grade Nickel Sulfate Standard" with the standard number T / ATCRR 12—2020, and iron phosphate for batteries refers to iron phosphate that complies with the "Iron Phosphate Standard for Batteries" with the standard number HG / T 4701-2021.

[0066] This application provides a method for treating nickel-iron alloy, including:

[0067] First-stage leaching: After mixing an acid with nickel-iron alloy for the first leaching, solid-liquid separation is carried out to obtain a first nickel-iron-containing solution and a first nickel-iron alloy slag;

[0068] Crude ferrous salt crystallization: Cooling and crystallizing the first nickel-iron-containing solution to obtain crude ferrous salt crystals and a second nickel-iron-containing solution;

[0069] Two-stage leaching: After the second nickel-iron-containing solution is mixed with the first nickel-iron alloy slag for the second leaching, solid-liquid separation is carried out to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0070] In the reaction solution of the first-stage leaching step, the initial concentration of H + is 4.0 - 24.0 mol / L, and the first leaching is completed when the concentration of H + is 2.0 - 4.0 mol / L.

[0071] Taking the two-stage leaching of nickel-iron alloy with sulfuric acid as an example, the reaction equations mainly involved in the leaching of nickel-iron alloy may include:

[0072] Ni + H2SO4 = NiSO4 + H2↑

[0073] Ni + H2SO4 + (1 / 2)O2 = NiSO4 + H2O

[0074] Fe + H2SO4 = FeSO4 + H2↑

[0075] FeS + H2SO4 = FeSO4 + H2S↑

[0076] Among them, the first-stage leaching at high acid concentration is beneficial to preventing the oxidation of components in the solution (such as ferrous ions), reducing the leaching rate of valuable metals, shortening the leaching time, and improving the leaching efficiency. However, if the hydrogen ion concentration is too high, for example, when the hydrogen ion concentration is greater than 24.0 mol / L, it is easy to cause metal passivation, which is not conducive to leaching.

[0077] The first-stage leaching is carried out at high acid concentration, and a large amount of nickel and iron in the nickel-iron alloy are leached. Restricted by the decrease in hydrogen ion concentration and chemical equilibrium, the difficulty of continuous leaching of nickel and iron increases, and the components in the obtained first nickel-iron-containing solution, especially ferrous salts, gradually approach saturation. Controlling the end-point H + concentration of the first leaching, and cooling and crystallizing the first nickel-iron-containing solution to precipitate ferrous salts therein, and then using the second nickel-iron-containing solution to continue dissolving the first nickel-iron alloy slag is beneficial to shortening the leaching time and obtaining a higher leaching rate in the two-stage leaching.

[0078] In addition, adopting the two-stage leaching process, at high acid concentration, without raw material crushing, nickel and iron in the nickel-iron alloy can be leached simultaneously, which can improve the leaching rate and effectively increase the leaching rate of valuable metals in the nickel-iron alloy, enabling most of the iron, nickel, and cobalt to dissolve into the liquid phase. When the concentration of H + is lower than 2.0 mol / L, the content of ferrous ions in the reaction solution of the first-stage leaching step is relatively large, which is not conducive to continuous leaching. Controlling the end-point H + concentration of the first-stage leaching can ensure a high leaching rate and leaching efficiency, and improve the economic efficiency of the process.

[0079] In an alternative embodiment, the leaching temperature for the first-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h. Appropriately increasing the leaching temperature is beneficial to improving the leaching rate and increasing the amount of ferrous salt dissolved in the solution.

[0080] Optionally, in the first-stage leaching step, first mix the nickel-iron alloy with water at a liquid-solid ratio of 3 - 10:1 mL / g, and then add acid to the mixture until the first initial H + concentration. Exemplarily, the liquid-solid ratio of the nickel-iron alloy to water can be 3 mL:1 g, 5 mL:1 g, 7 mL:1 g, 9 mL:1 g, 10 mL:1 g.

[0081] Optionally, in the reaction solution of the first-stage leaching step, the first initial H + concentration is 6.0 - 12.0 mol / L. Within this concentration range, it is beneficial for efficiently leaching valuable metals from the nickel-iron alloy, reducing the pH adjustment during subsequent treatment of the valuable metal leaching solution, and reducing the requirements for the acid resistance or oxidation resistance of the equipment, thereby reducing production costs.

[0082] Optionally, the H + concentration at the end of the first leaching is 3.0 - 4.0 mol / L. Exemplarily, the H + concentration at the end of the first leaching can be 3.0 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, 4.0 mol / L.

[0083] In an alternative embodiment, the leaching temperature for the second-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h. Appropriately increasing the leaching temperature is beneficial to improving the leaching rate and increasing the amount of ferrous salt dissolved in the solution.

[0084] Optionally, the acid includes one or more of hydrochloric acid, nitric acid, and sulfuric acid; optionally, the acid is sulfuric acid, which is convenient for the subsequent recovery of sulfates such as nickel sulfate.

[0085] Optionally, the second-stage leaching step further includes adding acid to make the second initial H + concentration in the reaction system 4.0 - 24.0 mol / L. When the H + concentration is 2.0 - 4.0 mol / L at the end of the second leaching, the hydrogen ion concentration in the second nickel-iron-containing solution is higher than 2.0 mol / L, and the nickel-iron alloy can continue to be dissolved. However, for improving the leaching efficiency, the second-stage leaching is carried out at a high acid concentration. Carrying out the second-stage leaching at a high acid concentration is also beneficial to preventing the components in the solution from being oxidized, reducing the leaching time, improving the leaching efficiency, reducing the loss of valuable metals, and facilitating the pH adjustment in the subsequent impurity removal step.

[0086] Optionally, the second initial H + concentration is 6.0 - 12.0 mol / L. Within this concentration range, it is beneficial for further efficiently leaching valuable metals in the nickel-iron alloy, reducing the pH adjustment during subsequent treatment of the valuable metal leaching solution, and reducing the acid resistance or oxidation resistance of the equipment, etc., thereby reducing production costs. Exemplarily, the second initial H + concentration can be 6.0 mol / L, 7.0 mol / L, 8.0 mol / L, 9.0 mol / L, 10.0 mol / L, 11.0 mol / L, 12.0 mol / L.

[0087] In some alternative embodiments, the second nickel-iron alloy slag can be returned to the first-stage leaching.

[0088] Optionally, the H + concentration at the completion of the second leaching is 3.0 - 4.0 mol / L.

[0089] Optionally, the temperature of the cooling crystallization is 10 - 25 °C and the time is 1 - 8 h.

[0090] Optionally, the cooling crystallization is carried out by vacuum cooling crystallization. By using vacuum cooling crystallization, the solution is cooled and evaporated without contacting the cooling surface, and no heat exchange surface of the equipment is required, avoiding the generation of a large amount of crystal scale in the equipment, which is beneficial to the improvement of production efficiency. The specific conditions of the cooling crystallization are related to the type of ferrous salt. When the ferrous salt is mainly ferrous sulfate, the temperature of the cooling crystallization is 10 - 25 °C and the time is 1 - 8 h.

[0091] In this embodiment, two-stage leaching combined with crude ferrous sulfate crystallization is adopted, which can fully leach nickel and iron in the solid phase, and the obtained second nickel-iron alloy slag can also be returned to the first-stage leaching step for continuous leaching as needed, improving the leaching rate of nickel and iron in the nickel-iron alloy. In alternative embodiments, impurity removal is also included:

[0092] Mix the third nickel-iron-containing solution, crude ferrous salt crystals and water to dissolve the crude ferrous salt crystals, obtaining a fourth nickel-iron-containing solution; add an impurity remover to the fourth nickel-iron-containing solution and adjust the pH of the solution to 0.5 - 4.5 for impurity removal, and filter to obtain a fifth nickel-iron-containing solution and impurity removal slag.

[0093] In alternative embodiments, the content of ferrous ions in the fourth nickel-iron-containing solution is 65 - 130 g / L. If the concentration is too high, the ferrous sulfate crystals cannot be fully dissolved, and if the concentration is too low, the subsequent iron precipitation step is difficult.

[0094] Optionally, in the impurity removal step, the impurity remover includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium phosphate.

[0095] Optionally, the addition amount of the impurity removing agent is 1.1 - 1.5 times the theoretical amount of chromium removal. The theoretical amount of chromium removal is the amount of the impurity removing agent that exactly reacts with chromium to form a precipitate. Excessive addition of the impurity removing agent can, on the one hand, ensure that chromium is fully removed, and on the other hand, a small amount of other elements such as nickel in the system will also combine with the impurity removing agent, increasing the consumption of the impurity removing agent.

[0096] In an optional embodiment, in the impurity removing step, a neutralizing agent is used to adjust the pH of the solution to 0.5 - 4.5. The neutralizing agent includes at least one of ferronickel, nickel matte, nickel powder, and iron powder.

[0097] Optionally, a neutralizing agent is used to adjust the pH of the solution to 1.0 - 3.5.

[0098] Optionally, the ferronickel contains 50wt% - 80wt% Fe, 15wt% - 40wt% Ni, 0.1wt% - 1.0wt% Co, 0.01wt% - 1.0wt% Cr, and 5wt% - 10wt% S.

[0099] Optionally, the nickel matte contains Fe ≤ 5wt%, 55wt% - 65wt% Ni, 0.5wt% - 1.2wt% Co, 0.01wt% - 1.0wt% Cr, and 22wt% - 27wt% S. In addition, ferronickel and nickel matte may also contain other impurity elements such as copper.

[0100] The reaction equations involved in the impurity removing step may include:

[0101] FeS + H2SO4 = FeSO4 + H2S↑

[0102] Fe + H2SO4 = FeSO4 + H2↑

[0103] Ni + H2SO4 = NiSO4 + H2↑

[0104] Co + H2SO4 = CoSO4 + H2↑

[0105] Ni + H2SO4 + (1 / 2)O2 = NiSO4 + H2O

[0106] Ni 2+ + FeS = NiS↓ + Fe 2+

[0107] Co 2+ + FeS = CoS↓ + Fe 2+

[0108] Mn 2+ + FeS = MnS↓ + Fe 2+

[0109] Cu 2+ +FeS=CuS↓+Fe 2+

[0110] Zn 2+ +FeS=ZnS↓+Fe 2+

[0111] Fe 3+ +PO4 3- =FePO4↓

[0112] 3Ni 2+ +2PO4 3- =Ni3(PO4)2↓

[0113] 3Co 2+ +2PO4 3- =Co3(PO4)2↓

[0114] 3Cr 2+ +2PO4 3- =Cr3(PO4)2↓

[0115] During the impurity removal process, a phosphate-containing impurity remover is used in combination with pH adjustment to remove the impurity metal ions Fe 3+ 、Ni 2+ 、Co 2 + Cr 2+ , Cu 2+ , Mn 2+ 、Zn 2+ Precipitate out, and because the subsequent iron precipitation step also requires the use of phosphate, the addition of the impurity remover will not produce new impurities.

[0116] When the neutralizer can be at least one of high-grade nickel matte or low-grade nickel matte, both high-grade nickel matte and low-grade nickel matte contain nickel, iron and ferrous sulfide. On the one hand, the nickel and iron can be used to adjust the pH, and the iron can be used to replace and remove Ni. 2+ 、Co 2+ Cr 2+ , Cu 2+ , Mn 2+ 、Zn 2+ On the other hand, the ferrous sulfide in the solution can be used to convert the Co 2+ Cr 2+ , Cu 2+ , Mn 2+ 、Zn 2+The iron is precipitated as metal sulfide precipitate. In addition, high-ice nickel and low-ice nickel have good filtration performance. Reducing substances contained therein such as Ni3S2 can inhibit the oxidation of ferrous ions to a certain extent, thereby reducing the formation of iron hydroxide, shortening the filtration time, and improving the filtration efficiency and the yield of iron phosphate. It can be seen that using high-ice nickel and low-ice nickel as neutralizing agents can not only adjust the pH, but also remove some impurity metal ions, improve the filtration efficiency and the yield of iron phosphate, introduce relatively few impurities, and at the same time realize the utilization of low-ice nickel and high-ice nickel, improving the economy of the process.

[0117] In an alternative embodiment, the method for treating nickel-iron alloy further includes iron precipitation: adding phosphate, ammonia water and hydrogen peroxide to the fifth nickel-iron-containing solution to precipitate iron, obtaining crude iron phosphate and the solution after iron precipitation.

[0118] Optionally, the phosphate includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium phosphate.

[0119] Optionally, in the iron precipitation step, a mixed solution containing phosphate, ammonia water and hydrogen peroxide with a pH of 5.0 - 7.0 is added to the fifth nickel-iron-containing solution with a pH of 1.0 - 3.5, and the reaction is carried out for 1 - 2 h until the pH reaches 0.8 - 2.4 to end the reaction. During this process, the reaction of ferrous sulfate with phosphate salt causes an increase in hydrogen ions and a decrease in pH.

[0120] Optionally, the time for adding the mixed solution lasts for 0.5 - 1.0 h.

[0121] Optionally, the temperature of the iron precipitation step is 30 - 60 °C.

[0122] Optionally, the molar ratio of iron element in the fifth nickel-iron-containing solution to phosphorus element in the mixed solution is 0.96 - 1.04:1.

[0123] Optionally, the molar ratio of ferrous ions in the fifth nickel-iron-containing solution to hydrogen peroxide in the mixed solution is 0.68 - 0.78:1.

[0124] In the iron precipitation step, adding the mixed solution slowly to the fifth nickel-iron-containing solution and adjusting the adding rate of the mixed solution can avoid excessive local concentration and too fast precipitation as much as possible, preventing the inclusion of impurity components, which is beneficial to improving the purity of the obtained crude iron phosphate and reducing the difficulty of subsequent refining steps.

[0125] In an alternative embodiment, it further includes pickling the crude iron phosphate and performing solid-liquid separation. The pickling includes mixing and pulping the crude iron phosphate and pure water at a solid-liquid ratio of 1:14-18 g / mL, and adding sulfuric acid or hydrochloric acid to adjust the pH to 0.5-3.0. Exemplarily, the solid-liquid ratio of the crude iron phosphate and pure water for mixing and pulping can be 1 g:14 mL, 1 g:15 mL, 1 g:16 mL, 1 g:17 mL, 1 g:18 mL, and any ratio between 1:14-18 g / mL.

[0126] Optionally, adding sulfuric acid or hydrochloric acid to adjust the pH to 1.0-1.5 can dissolve and wash out the acid-soluble impurities in the crude iron phosphate.

[0127] Optionally, the pickling time is 0.5-1.0 h, and the temperature is 50-90 °C.

[0128] In an alternative embodiment, it further includes aging, water washing, drying, and calcining the pickled iron phosphate in sequence to obtain iron phosphate for batteries.

[0129] Optionally, the aging includes mixing and pulping the pickled iron phosphate with phosphoric acid and water, and performing solid-liquid separation to obtain the aged iron phosphate. The mass ratio of phosphoric acid to the pickled iron phosphate is 0.10-0.24:1.0, the concentration of phosphoric acid is 70%-90%, the aging temperature is 85-100 °C, and the aging time is 1.5-3.5 h. The aging step can adjust the crystal form of the iron phosphate and remove some of the impurities therein.

[0130] Optionally, the water washing includes mixing and pulping the aged iron phosphate with water at a solid-liquid mass ratio of 1:16-22, and performing solid-liquid separation to obtain the water-washed iron phosphate. The water washing time is 0.5-1.0 h, and the temperature is 50-90 °C.

[0131] Furthermore, after pickling, primary wash water can be obtained. The primary wash water can be recycled for pickling until the acid in the primary wash water is insufficient to adjust the pH to the specified value, so as to make full use of the acid and reduce wastewater discharge.

[0132] Furthermore, after aging, aged liquid can be obtained. The aged liquid contains phosphoric acid and can be used to prepare phosphate solutions.

[0133] Furthermore, after water washing, secondary wash water can be obtained. The secondary wash water can be recycled for pickling to improve the metal recovery rate and economy.

[0134] In an alternative embodiment, the post-iron-precipitation liquid is sequentially filtered, subjected to impurity removal by extraction, and degreased to obtain a battery-grade nickel sulfate solution.

[0135] Optionally, the extractant used in the extraction includes any one of P204, P507, and Cyanex272.

[0136] Optionally, the addition amount of the extractant used in the extraction is 20%-30% of the volume of the aqueous phase.

[0137] Optionally, the time for impurity removal by extraction is 5-10 min, and the temperature is 30-40 °C.

[0138] In this embodiment, the filtration is carried out in a precision filter. After the extraction is completed, cobalt sulfate is transferred into the organic phase, and nickel sulfate remains in the aqueous phase. After phase separation, the extracted solution obtained can be defatted with activated carbon to obtain a battery-grade nickel sulfate solution. The organic phase can be reused after separating cobalt sulfate therein.

[0139] In an alternative embodiment, the nickel-iron alloy includes Fe, Ni, and at least one of the impurity elements Co, Cr, Cu, Mn, Zn, and P.

[0140] Optionally, in the nickel-iron alloy, Fe is 50 wt% - 80 wt%, Ni is 15 wt% - 40 wt%, Co is 0.1 wt% - 1.0 wt%, Cr is 0.01 wt% - 1.0 wt%, and S is 0.01 wt - 1 wt%.

[0141] Optionally, the particle size of the nickel-iron alloy is 1 - 10 cm.

[0142] In some alternative embodiments, when the particle size of the nickel-iron alloy used is 1 - 10 cm, the nickel-iron alloy can be directly used without being crushed or ball-milled, reducing the raw material crushing cost.

[0143] In the method for treating nickel-iron alloy of the present application, the iron element in the nickel-iron alloy can be relatively fully separated to obtain battery-grade iron phosphate with high purity. For the nickel and other possible element components such as cobalt in the nickel-iron alloy, resource recycling and utilization are also carried out. The process is simple, the wastewater discharge is small, the cost is low, the resource utilization rate is high, and it has strong practicability and high economic efficiency.

[0144] The features and properties of the present application will be further described in detail below in conjunction with examples.

[0145] Example 1

[0146] A method for treating nickel-iron alloy, as Figure 1 and Figure 2 shown, includes the following steps:

[0147] Mix a nickel-iron alloy with a particle size of 5 cm and pure water according to a liquid-solid ratio (unit: mL / g) of 3:1, and add concentrated sulfuric acid to make the first initial H+ With a concentration of 12 mol / L, start stirring and heat to 80 °C under normal pressure for the first leaching. When the H + concentration in the solution is 3 mol / L, the reaction ends. Filter to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0148] After the first nickel-iron-containing solution is cooled and crystallized (cooled and crystallized at 18 °C for 2 h), filter to obtain the second nickel-iron-containing solution and crude ferrous salt crystals. Mix the first nickel-iron alloy slag and the second nickel-iron-containing solution, and add concentrated sulfuric acid to make the initial H + concentration 12 mol / L, and heat to 80 °C under normal pressure for the second leaching. When the H + concentration in the solution is 3.0 mol / L, the reaction ends. Filter to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0149] Mix the crude ferrous salt crystals and the third nickel-iron-containing solution, then add pure water to dissolve them, so that the ferrous ion content reaches 70 g / L to obtain the fourth nickel-iron-containing solution;

[0150] Add ferronickel to the fourth nickel-iron-containing solution, control the temperature at 50 °C and stir, adjust the pH value of the solution to 2.0, filter to obtain ferronickel slag and the solution after pH adjustment. Add sodium phosphate with 1.2 times the theoretical amount to the solution after pH adjustment for impurity removal, and filter to obtain the fifth nickel-iron-containing solution and the impurity removal slag;

[0151] Add pure water to the fifth nickel-iron-containing solution until the ferrous ion content is 50 g / L, and heat to 40 °C to obtain Product 10 (solution);

[0152] Take 1.03 times the theoretical amount (the amount required for stoichiometric reaction) of ammonium dihydrogen phosphate (i.e., monoammonium phosphate) for precipitating ferrous ions, add pure water, heat to 40 °C, dissolve to obtain a phosphate solution with a concentration of 68 g / L, add ammonia water to adjust the pH to 6.90, and add hydrogen peroxide according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-iron-containing solution being 0.7, stir evenly to obtain the mixed liquid Product 11 (solution);

[0153] Dropwise add Product 11 (solution) to Product 10 (solution) at a controlled addition rate. Product 11 (solution) is added dropwise within 30 min, and continue to react for 1.5 h to obtain Product 12 (slurry);

[0154] Filter Product 12 (slurry) to obtain the solution after iron precipitation and crude iron phosphate;

[0155] The crude iron phosphate was slurried with pure water at a solid-liquid ratio (g / mL) of crude iron phosphate: pure water = 1:15, and sulfuric acid solution was added to adjust the pH to 1.2. Then it was heated to 60 °C for the first stirring and washing for 30 min, and filtered to obtain Product 15 (filtrate) and Product 16 (filter residue, i.e., pickled iron phosphate).

[0156] Product 16 (filter residue) was added with pure water for slurrying, and the liquid-solid ratio was controlled to be the same as that of Product 12 (slurry). Phosphoric acid was added so that the mass ratio of phosphoric acid to pickled iron phosphate was 0.12. Then it was heated to 95 °C and aged for 2.0 h, and filtered to obtain Product 17 (filtrate) and Product 18 (filter residue, i.e., aged iron phosphate).

[0157] Product 18 (filter residue) was added with pure water for slurrying according to the solid-liquid mass ratio of aged iron phosphate: pure water = 1:21, and heated to 60 °C for the second stirring and washing for 30 min, and filtered to obtain Product 19 (filtrate) and Product 20 (filter residue, i.e., washed iron phosphate).

[0158] Product 20 (filter residue) was dried and calcined to obtain Product 21 (solid), and Product 21 (solid) is iron phosphate for batteries.

[0159] After Product 13 (filtrate) was filtered through a precision filter, extractant P507 was added for impurity extraction. The organic phase composition was 20% P507 + 80% 260# solvent oil (volume ratio). The organic phase recovered cobalt sulfate products, and the raffinate was deoiled with activated carbon to obtain Product 22 (solution), and Product 22 (solution) is battery-grade nickel sulfate solution.

[0160] Example 2

[0161] The difference between this example and Example 1 is that in this example, after obtaining the crude iron phosphate, the pickling step is not used, and the rest of the operations are the same as in Example 1, that is, after obtaining the crude iron phosphate, sulfuric acid solution is not added to adjust the pH to 1.2. The specific steps are as follows:

[0162] A method for treating nickel-iron alloy includes the following steps:

[0163] Nickel-iron alloy with a particle size of 5 cm was mixed with pure water at a liquid-solid ratio (unit: mL / g) of 3:1, and concentrated sulfuric acid was added to make the first initial H + concentration be 12 mol / L, stirring was started, and it was heated to 80 °C under atmospheric pressure for the first leaching. When the H + concentration in the solution was 3 mol / L, the reaction ended, and it was filtered to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag.

[0164] The first nickel-containing iron solution is filtered after cooling crystallization (cooling crystallization at 18 °C for 2 h) to obtain a second nickel-containing iron solution and crude ferrous salt crystals. The first nickel-iron alloy slag and the second nickel-containing iron solution are mixed, and concentrated sulfuric acid is added to make the initial H + concentration 12 mol / L, and heated to 80 °C under atmospheric pressure for the second leaching. When the H + concentration in the solution is 3.0 mol / L, the reaction ends, and the third nickel-containing iron solution and the second nickel-iron alloy slag are obtained by filtration;

[0165] The crude ferrous salt crystals and the third nickel-containing iron solution are mixed and then dissolved in pure water to make the ferrous ion content reach 70 g / L, obtaining a fourth nickel-containing iron solution;

[0166] Ferronickel is added to the fourth nickel-containing iron solution, the temperature is controlled at 50 °C and stirred, the pH value of the solution is adjusted to 2.0, and after filtration, ferronickel slag and the solution after pH adjustment are obtained. The solution after pH adjustment is added with sodium phosphate at 1.2 times the theoretical amount for impurity removal, and after filtration, a fifth nickel-containing iron solution and impurity removal slag are obtained;

[0167] Pure water is added to the fifth nickel-containing iron solution until the ferrous ion content is 50 g / L, and the temperature is raised to 40 °C to obtain Product 10 (solution);

[0168] 1.03 times the theoretical amount (the amount required for reaction according to the stoichiometric ratio) of ammonium dihydrogen phosphate for precipitating ferrous ions is taken, added to pure water, heated to 40 °C, dissolved to obtain a phosphate solution with a concentration of 68 g / L, ammonia water is added to adjust the pH to 6.90, and hydrogen peroxide is added according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-containing iron solution being 0.7, and stirred evenly to obtain a mixed liquid Product 11 (solution);

[0169] Product 11 (solution) is added dropwise to Product 10 (solution) at a controlled addition rate, and the addition of Product 11 (solution) is completed in 30 min, and the reaction continues for 1.5 h to obtain Product 12 (slurry);

[0170] Product 12 (slurry) is filtered to obtain the iron-precipitated liquid and crude iron phosphate;

[0171] According to the solid-liquid ratio (g / mL) of crude iron phosphate: pure water = 1:15, the crude iron phosphate is slurried with pure water, heated to 60 °C for the first stirring and washing, washed for 30 min, and filtered to obtain Product 15 (filtrate) and Product 16 (filter residue, i.e., pickled iron phosphate);

[0172] Product 16 (filter residue) is slurried with pure water, the liquid-solid ratio is controlled to be the same as that of Product 12 (slurry), and phosphoric acid is added to make the mass ratio of phosphoric acid to pickled iron phosphate 0.12, heated to 95 °C, and aged for 2.0 h, and filtered to obtain Product 17 (filtrate) and Product 18 (filter residue, i.e., aged iron phosphate);

[0173] The product 18 (filter residue) was slurried with pure water according to the solid-liquid mass ratio of aged iron phosphate: pure water = 1:21, heated to 60 °C for secondary stirring and washing for 30 min, and then filtered to obtain product 19 (filtrate) and product 20 (filter residue, i.e., iron phosphate after water washing).

[0174] The product 20 (filter residue) was dried and calcined to obtain product 21 (solid), and product 21 (solid) is iron phosphate for batteries.

[0175] After the product 13 (filtrate) was filtered through a precision filter, extractant P507 was added for impurity extraction. The organic phase composition was 20% P507 + 80% solvent oil 260# (volume ratio). The organic phase recovered cobalt sulfate products, and the raffinate was degreased with activated carbon to obtain product 22 (solution), and product 22 (solution) is nickel sulfate solution of battery grade.

[0176] Example 3

[0177] This example has the same processing steps as Example 1, except that the parameters of each step are different, and the neutralizing agent used in the impurity removal step is different. In this example, nickel matte is used as the neutralizing agent. The specific steps are as follows:

[0178] A method for treating nickel-iron alloy, comprising the following steps:

[0179] A nickel-iron alloy with a particle size of 5 cm was mixed with pure water according to a liquid-solid ratio (unit: mL / g) of 3:1, and concentrated sulfuric acid was added to make the first initial H + concentration 8 mol / L, and heated to 80 °C under atmospheric pressure for the first leaching. When the H + concentration in the solution was 3.0 mol / L, the reaction ended, and the first nickel-iron-containing solution and the first nickel-iron alloy slag were obtained by filtration;

[0180] After the first nickel-iron-containing solution was cooled and crystallized (cooled and crystallized at 18 °C for 2 h), it was filtered to obtain the second nickel-iron-containing solution and crude ferrous salt crystals. The first nickel-iron alloy slag and the second nickel-iron-containing solution were mixed, and concentrated sulfuric acid was added to make the second initial H + concentration 8 mol / L, and heated to 80 °C under atmospheric pressure for the second leaching. When the H + concentration in the solution was 3.0 mol / L, the reaction ended, and the third nickel-iron-containing solution and the second nickel-iron alloy slag were obtained by filtration;

[0181] The crude ferrous salt crystals and the third nickel-iron-containing solution were mixed and then dissolved in pure water to make the ferrous ion content reach 70 g / L to obtain the fourth nickel-iron-containing solution;

[0182] Add nickel matte to the fourth nickel-containing iron solution, control the temperature at 80 °C and stir, adjust the pH of the solution to 2.5, filter to obtain nickel matte slag and the solution after pH adjustment. Add 1.3 times the theoretical amount of monoammonium phosphate to the solution after pH adjustment for impurity removal, and filter to obtain the fifth nickel-containing iron solution and impurity removal slag;

[0183] Add pure water to the fifth nickel-containing iron solution until the ferrous ion content is 50 g / L, and heat up to 40 °C to obtain Product 10 (solution);

[0184] Take 1.0 times the theoretical amount of ammonium dihydrogen phosphate required for precipitating ferrous ions, add pure water and heat up to 40 °C to dissolve to obtain a phosphate solution of 68 g / L, add ammonia water to adjust the pH to 6.93, and add hydrogen peroxide according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-containing iron solution being 0.75, stir evenly to obtain the mixed liquid Product 11 (solution);

[0185] Dropwise add Product 11 (solution) to Product 10 (solution) at a controlled addition rate. Product 11 (solution) is added dropwise within 30 min, and continue to react for 1.5 h to obtain Product 12 (slurry);

[0186] Filter Product 12 (slurry) to obtain the solution after iron precipitation and crude iron phosphate;

[0187] Slurry crude iron phosphate with pure water according to the solid-liquid ratio (g / mL) of crude iron phosphate: pure water = 1:15, add sulfuric acid solution to adjust the pH to 1.0, heat up to 80 °C for the first stirring and washing, wash for 40 min, and filter to obtain Product 15 (filtrate) and Product 16 (filter residue, i.e., pickled iron phosphate);

[0188] Slurry Product 16 (filter residue) with pure water, control the liquid-solid ratio to be the same as that of Product 12 (slurry), and add phosphoric acid so that the mass ratio of phosphoric acid to pickled iron phosphate is 0.13, heat up to 95 °C, age for 1.5 h, and filter to obtain Product 17 (filtrate) and Product 18 (filter residue, i.e., aged iron phosphate);

[0189] Slurry Product 18 (filter residue) with pure water according to the solid-liquid mass ratio of aged iron phosphate: pure water = 1:22, heat up to 80 °C for the second stirring and washing, wash for 40 min, and filter to obtain Product 19 (filtrate) and Product 20 (filter residue, i.e., washed iron phosphate);

[0190] Dry and calcine Product 20 (filter residue) to obtain Product 21 (solid), and Product 21 (solid) is iron phosphate for batteries;

[0191] After the product 13 (filtrate) is filtered through a precision filter, extractant Cyanex272 is added to remove impurities. The organic phase composition is 20% Cyanex272 + 80% solvent oil 260# (volume ratio). The raffinate is deoiled by activated carbon to obtain product 22 (solution), and product 22 (solution) is a battery-grade nickel sulfate solution.

[0192] Example 4

[0193] The difference between this example and Example 1 is that during the first leaching process, when the H + concentration in the solution is 4 mol / L, the reaction ends and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag; and this example does not include the step of subsequent treatment of the fourth nickel-iron-containing solution. Other steps are the same as those in Example 1, and the specific steps are as follows:

[0194] A method for treating nickel-iron alloy, as Figure 1 and Figure 2 shown, includes the following steps:

[0195] Mix nickel-iron alloy with a particle size of 5 cm and pure water at a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the first initial H + concentration 12 mol / L, start stirring, heat to 80 °C under normal pressure for the first leaching. When the H + concentration in the solution is 4 mol / L, the reaction ends, and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0196] After the first nickel-iron-containing solution is cooled and crystallized (cooled and crystallized at 18 °C for 2 h), filtration is carried out to obtain the second nickel-iron-containing solution and crude ferrous salt crystals. Mix the first nickel-iron alloy slag and the second nickel-iron-containing solution, add concentrated sulfuric acid to make the second initial H + concentration 12 mol / L, heat to 80 °C under normal pressure for the second leaching. When the H + concentration in the solution is 3.0 mol / L, the reaction ends, and filtration is carried out to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0197] Mix the crude ferrous salt crystals and the third nickel-iron-containing solution, then add pure water to dissolve them to make the ferrous ion content reach 70 g / L to obtain the fourth nickel-iron-containing solution.

[0198] Example 5

[0199] The difference between this example and Example 1 is that during the first leaching process, when the H + concentration in the solution is 2 mol / L, the reaction ends and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag; and this example does not include the step of subsequent treatment of the fourth nickel-iron-containing solution. Other steps are the same as those in Example 1, and the specific steps are as follows:

[0200] A method for treating nickel-iron alloy, comprising the following steps:

[0201] Mix nickel-iron alloy with a particle size of 5 cm and pure water according to a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the first initial H + concentration 12 mol / L, start stirring, heat to 80 °C under normal pressure for the first leaching, when the H + concentration in the solution is 2 mol / L, the reaction ends, filter to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0202] After cooling and crystallization (cooling and crystallizing at 18 °C for 2 h) of the first nickel-iron-containing solution, filter to obtain the second nickel-iron-containing solution and crude ferrous salt crystals, mix the first nickel-iron alloy slag and the second nickel-iron-containing solution, add concentrated sulfuric acid to make the second initial H + concentration 12 mol / L, heat to 80 °C under normal pressure for the second leaching, when the H + concentration in the solution is 3.0 mol / L, the reaction ends, filter to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0203] Mix the crude ferrous salt crystals and the third nickel-iron-containing solution, then add pure water to dissolve, so that the content of ferrous ions reaches 70 g / L to obtain the fourth nickel-iron-containing solution.

[0204] Example 6

[0205] A method for treating nickel-iron alloy, comprising the following steps:

[0206] Mix nickel-iron alloy with a particle size of 5 cm and pure water according to a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the first initial H + concentration 12 mol / L, start stirring, heat to 90 °C under normal pressure for the first leaching, when the H + concentration in the solution is 4 mol / L, the reaction ends, filter to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0207] After cooling and crystallization (cooling and crystallizing at 18 °C for 2 h) of the first nickel-iron-containing solution, filter to obtain the second nickel-iron-containing solution and crude ferrous salt crystals, mix the first nickel-iron alloy slag and the second nickel-iron-containing solution, heat to 90 °C under normal pressure for the second leaching, when the H + concentration in the solution is 2.0 mol / L, the reaction ends, filter to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0208] Mix the crude ferrous salt crystals and the third nickel-iron-containing solution, then add pure water to dissolve, so that the content of ferrous ions reaches 70 g / L to obtain the fourth nickel-iron-containing solution.

[0209] Comparative Example 1

[0210] The difference between this comparative example and Example 1 is as follows: Only one-stage leaching is adopted, and the leaching ends when the leaching time reaches that of Example 1 (the first leaching + the second leaching in Example 1), without a cooling crystallization step. The remaining steps and parameters are the same as those in Example 1. The specific steps are as follows:

[0211] A method for treating nickel-iron alloy includes the following steps:

[0212] Mix nickel-iron alloy with a particle size of 5 cm and pure water at a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the initial H + concentration 12 mol / L, start stirring, heat to 80 °C under atmospheric pressure for leaching, and end the leaching when the leaching time of Example 1 is reached. After the leaching ends, filter to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0213] Dissolve the first nickel-iron-containing solution in pure water to make the ferrous ion content reach 70 g / L to obtain the fourth nickel-iron-containing solution;

[0214] Add ferronickel to the fourth nickel-iron-containing solution, control the temperature at 50 °C and stir, adjust the pH value of the solution to 2.0, filter to obtain ferronickel slag and the solution after pH adjustment. Add sodium phosphate at 1.2 times the theoretical amount to the solution after pH adjustment for impurity removal, and filter to obtain the fifth nickel-iron-containing solution and the impurity removal slag;

[0215] Add pure water to the fifth nickel-iron-containing solution until the ferrous ion content is 50 g / L, and heat to 40 °C to obtain Product 5 (solution);

[0216] Take 1.03 times the theoretical amount (the amount required for reaction according to the stoichiometric ratio) of ammonium dihydrogen phosphate for precipitating ferrous ions, add pure water and heat to 40 °C to dissolve to obtain a phosphate solution with a concentration of 68 g / L, add ammonia water to adjust the pH to 6.90, and add hydrogen peroxide according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-iron-containing solution being 0.7, stir evenly to obtain the mixed liquid Product 6 (solution);

[0217] Dropwise add Product 7 (solution) to Product 6 (solution) at a controlled addition rate. The addition of Product 7 (solution) is completed in 30 min, and continue to react for 1.5 h to obtain Product 8 (slurry);

[0218] Filter Product 8 (slurry) to obtain the solution after iron precipitation and crude iron phosphate;

[0219] The crude iron phosphate is slurried with pure water at a solid-liquid ratio (g / mL) of crude iron phosphate: pure water = 1:15, and sulfuric acid solution is added to adjust the pH to 1.2. The temperature is raised to 60 °C for the first stirring and washing for 30 min, and then filtered to obtain Product 11 (filtrate) and Product 12 (filter residue, i.e., pickled iron phosphate).

[0220] Product 12 (filter residue) is added with pure water for slurrying. The amount of pure water added is controlled to have the same liquid-solid ratio as Product 8 (slurry), and phosphoric acid is added so that the mass ratio of phosphoric acid to pickled iron phosphate is 0.12. The temperature is raised to 95 °C and aged for 2.0 h, and then filtered to obtain Product 13 (filtrate) and Product 14 (filter residue, aged iron phosphate).

[0221] Product 14 (filter residue) is slurried with pure water at a solid-liquid mass ratio of aged iron phosphate: pure water = 1:21, and the temperature is raised to 60 °C for the second stirring and washing for 30 min, and then filtered to obtain Product 15 (filtrate) and Product 16 (filter residue, i.e., washed iron phosphate).

[0222] Product 16 (filter residue) is dried and calcined to obtain Product 17 (solid), and Product 17 (solid) is iron phosphate for batteries.

[0223] After Product 9 (filtrate) is filtered through a precision filter, extractant P507 is added for impurity extraction. The organic phase recovers cobalt sulfate product, and the raffinate is deoiled by activated carbon to obtain Product 18 (solution), and Product 22 (solution) is nickel sulfate solution for battery grade.

[0224] Comparative Example 2

[0225] The difference between this example and Example 3 is that: the first initial H + concentration is different in the first-stage leaching step, the second initial H + concentration is different in the second-stage leaching step, and the second initial H + concentration in the first-stage leaching step is less than the first initial H + concentration in the second-stage leaching step, and the remaining steps and parameters are the same as those in Example 3. The specific steps are as follows:

[0226] A method for treating nickel-iron alloy, comprising the following steps:

[0227] Nickel-iron alloy with a particle size of 5 cm is mixed with pure water at a liquid-solid ratio (unit: mL / g) of 3:1, and concentrated sulfuric acid is added to make the first initial H + concentration 4 mol / L. It is heated to 80 °C under atmospheric pressure for the first leaching. The leaching time is the same as that in Example 3. After reaching the leaching time, it is filtered to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag.

[0228] The first nickel-iron-containing solution is filtered after cooling crystallization (cooling crystallization at 18 °C for 2 h) to obtain a second nickel-iron-containing solution and crude ferrous salt crystals. The first nickel-iron alloy slag and the second nickel-iron-containing solution are mixed, and concentrated sulfuric acid is added to make the initial H + concentration 7 mol / L, and heated to 80 °C under atmospheric pressure for the second leaching. When the H + concentration in the solution is 3.0 mol / L, the reaction ends, and the third nickel-iron-containing solution and the second nickel-iron alloy slag are obtained by filtration;

[0229] The crude ferrous salt crystals and the third nickel-iron-containing solution are mixed and then dissolved in pure water to make the ferrous ion content reach 70 g / L, obtaining a fourth nickel-iron-containing solution;

[0230] High-grade nickel matte is added to the fourth nickel-iron-containing solution, the temperature is controlled at 80 °C and stirred, the pH of the solution is adjusted to 2.5, and after filtration, high-grade nickel matte slag and the solution after pH adjustment are obtained. The solution after pH adjustment is added with 1.3 times the theoretical amount of monoammonium phosphate for impurity removal, and after filtration, a fifth nickel-iron-containing solution and impurity removal slag are obtained;

[0231] Pure water is added to the fifth nickel-iron-containing solution until the ferrous ion content is 50 g / L, and the temperature is raised to 40 °C to obtain Product 10 (solution);

[0232] 1.0 times the theoretical amount of ammonium dihydrogen phosphate required for precipitating ferrous ions is taken, added to pure water, heated to 40 °C, dissolved to obtain a phosphate solution of 68 g / L, ammonia water is added to adjust the pH to 6.93, and hydrogen peroxide is added according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-iron-containing solution being 0.75, and after stirring evenly, a mixed liquid Product 11 (solution) is obtained;

[0233] Product 11 (solution) is added dropwise to Product 10 (solution) at a controlled addition rate. Product 11 (solution) is added dropwise within 30 min, and the reaction continues for 1.5 h to obtain Product 12 (slurry);

[0234] Product 12 (slurry) is filtered to obtain the iron-precipitated liquid and crude iron phosphate;

[0235] The crude iron phosphate is slurried with pure water according to a solid-liquid ratio (g / mL) of crude iron phosphate: pure water = 1:15, and sulfuric acid solution is added to adjust the pH to 1.0, and heated to 80 °C for the first stirring and washing for 40 min, and after filtration, Product 15 (filtrate) and Product 16 (filter residue, i.e., pickled iron phosphate) are obtained;

[0236] Product 16 (filter residue) is slurried with pure water, the liquid-solid ratio is controlled to be the same as that of Product 12 (slurry), and phosphoric acid is added to make the mass ratio of phosphoric acid to pickled iron phosphate 0.13, heated to 95 °C, aged for 1.5 h, and after filtration, Product 17 (filtrate) and Product 18 (filter residue, i.e., aged iron phosphate) are obtained;

[0237] The product 18 (filter residue) was slurried with pure water according to the solid-liquid mass ratio of aged iron phosphate: pure water = 1:22, heated to 80 °C for secondary stirring and washing for 40 min, and filtered to obtain product 19 (filtrate) and product 20 (filter residue);

[0238] The product 20 (filter residue) was dried and calcined to obtain product 21 (solid), and product 21 (solid) is iron phosphate for batteries;

[0239] After the product 13 (filtrate) was filtered through a precision filter, the extractant Cyanex272 was added for impurity extraction. The organic phase composition was 20% Cyanex272 + 80% 260# solvent oil (volume ratio). The raffinate was degreased with activated carbon to obtain product 22 (solution), and product 22 (solution) is battery-grade nickel sulfate solution.

[0240] Comparative Example 3

[0241] The difference between this comparative example and Example 1 is that ferrous sulfide was used as the neutralizing agent, and other steps and parameters were the same as those in Example 1. The specific steps are as follows:

[0242] A method for treating nickel-iron alloy, comprising the following steps:

[0243] A certain amount of pure water was added to the nickel-iron alloy according to the liquid-solid ratio (unit mL / g) of 3:1, concentrated sulfuric acid was added to make the hydrogen ion concentration 12.0 mol / L, stirring was started, and it was heated to 80 °C under normal pressure for the first leaching. When the H + concentration in the solution was 3 mol / L, the reaction ended, and filtration was carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0244] After the first nickel-iron-containing solution was cooled and crystallized, filtration was carried out to obtain the second nickel-iron-containing solution and crude ferrous salt crystals. The first nickel-iron alloy slag and the second nickel-iron-containing solution were mixed, concentrated sulfuric acid was added to make the sulfuric acid concentration 6 mol / L, and it was heated to 80 °C under normal pressure for the second leaching. When the H + concentration in the solution was 3.0 mol / L, the reaction ended, and filtration was carried out to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0245] The crude ferrous salt crystals and the third nickel-iron-containing solution were mixed and then dissolved in pure water to make the ferrous ion content reach 70 g / L to obtain the fourth nickel-iron-containing solution;

[0246] Ferrous sulfide was added to the fourth nickel-iron-containing solution, the temperature was controlled at 50 °C and stirred, the pH value of the solution was adjusted to 2.0, filtration was carried out to obtain matte slag and the solution after pH adjustment. The solution after pH adjustment was added with sodium phosphate at 1.2 times the theoretical amount for impurity removal, and filtration was carried out to obtain the fifth nickel-iron-containing solution and the impurity removal slag;

[0247] The fifth nickel-containing iron solution is added with a certain amount of pure water according to 50 g / L of ferrous iron, and the temperature is raised to 40 °C to obtain Product 10 (solution);

[0248] Take 1.03 times of ammonium dihydrogen phosphate according to the theoretical amount required for precipitating ferrous ions (the amount required for reaction according to the stoichiometric ratio), add pure water and raise the temperature to 40 °C to dissolve and obtain a phosphate solution of 68 g / L. Add ammonia water to adjust the pH to 6.90, and add hydrogen peroxide according to the molar ratio of ferrous ions to hydrogen peroxide in the fifth nickel-containing iron solution being 0.7. Stir evenly to obtain the mixed liquid Product 11 (solution);

[0249] Control the addition rate of Product 11 (solution) and drop it into Product 10 (solution). Product 11 (solution) is added dropwise within 30 min, and continue to react for 1.5 h to obtain Product 12 (slurry);

[0250] Filter Product 12 (slurry) to obtain the iron-precipitated solution and crude iron phosphate;

[0251] According to the solid-liquid ratio of crude iron phosphate: pure water = 1:15 (g / mL), add pure water to slurry the crude iron phosphate, add sulfuric acid solution to adjust the pH to 1.2, raise the temperature to 60 °C for the first stirring and washing, wash for 30 min, and filter to obtain Product 15 (filtrate) and Product 16 (filter residue, i.e., pickled iron phosphate);

[0252] Slurry Product 16 (filter residue) with pure water. The amount of pure water added is controlled to have the same liquid-solid ratio as Product 12 (slurry), and add phosphoric acid so that the mass ratio of phosphoric acid to pickled iron phosphate is 0.12. Raise the temperature to 95 °C and age for 2.0 h, and filter to obtain Product 17 (filtrate) and Product 18 (filter residue, i.e., aged iron phosphate);

[0253] According to the solid-liquid mass ratio of aged iron phosphate: pure water = 1:21, add pure water to slurry Product 18 (filter residue), raise the temperature to 60 °C for the second stirring and washing, wash for 30 min, and filter to obtain Product 19 (filtrate) and Product 20 (filter residue, i.e., water-washed iron phosphate);

[0254] Dry and calcine Product 20 (filter residue) to obtain Product 21 (solid), and Product 21 (solid) is iron phosphate for batteries;

[0255] After Product 13 (filtrate) is filtered through a precision filter, add the extractant P507 to remove impurities. The organic phase recovers cobalt sulfate products. The organic phase composition is 20% P507 + 80% 260# solvent oil (volume ratio). The raffinate is deoiled with activated carbon to obtain Product 22 (solution), and Product 22 (solution) is battery-grade nickel sulfate solution.

[0256] Comparative Example 4

[0257] The difference between this embodiment and Embodiment 1 is that during the first leaching process, when the concentration of H in the solution + is 4.5 mol / L, the reaction ends and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag; and this embodiment does not include the step of performing subsequent treatment on the fourth nickel-iron-containing solution, and other steps are the same as those in Embodiment 1. The specific steps are as follows:

[0258] A method for treating a nickel-iron alloy, comprising the following steps:

[0259] Mix nickel-iron alloy with a particle size of 5 cm and pure water at a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the first initial H + concentration 12 mol / L, start stirring, heat to 80 °C under normal pressure for the first leaching. When the concentration of H in the solution + is 4.5 mol / L, the reaction ends, and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag;

[0260] After cooling crystallization (cooling crystallization at 18 °C for 2 h) of the first nickel-iron-containing solution, filtration is carried out to obtain the second nickel-iron-containing solution and crude ferrous salt crystals. Mix the first nickel-iron alloy slag and the second nickel-iron-containing solution, add concentrated sulfuric acid to make the second initial H + concentration 12 mol / L, heat to 80 °C under normal pressure for the second leaching. When the concentration of H in the solution + is 4.5 mol / L, the reaction ends, and filtration is carried out to obtain the third nickel-iron-containing solution and the second nickel-iron alloy slag;

[0261] Mix the crude ferrous salt crystals and the third nickel-iron-containing solution, then add pure water to dissolve them to make the ferrous ion content reach 70 g / L, obtaining the fourth nickel-iron-containing solution.

[0262] Comparative Example 5

[0263] The difference between this embodiment and Embodiment 1 is that during the first leaching process, when the concentration of H in the solution + is 0.5 mol / L, the reaction ends and filtration is carried out to obtain the first nickel-iron-containing solution and the first nickel-iron alloy slag; and this embodiment does not include the step of performing subsequent treatment on the fourth nickel-iron-containing solution, and other steps are the same as those in Embodiment 1. The specific steps are as follows:

[0264] A method for treating a nickel-iron alloy, comprising the following steps:

[0265] Mix nickel-iron alloy with a particle size of 5 cm and pure water at a liquid-solid ratio (unit: mL / g) of 3:1, add concentrated sulfuric acid to make the first initial H + concentration 12 mol / L, start stirring, heat to 80 °C under normal pressure for the first leaching. When the concentration of H in the solution+ The reaction ends when the concentration is 0.5 mol / L, and the first nickel-iron-containing solution and the first nickel-iron alloy slag are obtained by filtration;

[0266] After the first nickel-iron-containing solution is cooled and crystallized (cooled and crystallized at 18 °C for 2 h), the second nickel-iron-containing solution and crude ferrous salt crystals are obtained by filtration. The first nickel-iron alloy slag and the second nickel-iron-containing solution are mixed, and concentrated sulfuric acid is added to make the initial H of the second + The concentration is 12 mol / L, and it is heated to 80 °C under normal pressure for the second leaching. When the H in the solution + The reaction ends when the concentration is 3.0 mol / L, and the third nickel-iron-containing solution and the second nickel-iron alloy slag are obtained by filtration;

[0267] The crude ferrous salt crystals and the third nickel-iron-containing solution are mixed and then dissolved in pure water to make the ferrous ion content reach 70 g / L, obtaining the fourth nickel-iron-containing solution.

[0268] The following is a summary table of the production process data of 6 examples and 5 comparative examples:

[0269] Table 1: Summary table of the leaching rate and leaching time of each element in the leaching step

[0270]

[0271] The calculation method of the leaching rate of metal elements is as follows:

[0272] The leaching rate of metal elements = 1 - (volume of leaching solution * metal content in leaching solution) / (mass of nickel-iron alloy * content of metal elements in nickel-iron alloy)

[0273] It should be noted that the leaching time in Table 1 refers to the total time of the first leaching reaction and the second leaching reaction.

[0274] As can be seen from Table 1, the nickel-iron alloy has a high leaching rate and a short leaching time by two-stage high-acid leaching, and the process conditions are the best.

[0275] Table 2: Summary table of the impurity removal effect and time of the leaching solution

[0276]

[0277]

[0278] As can be seen from Table 2, the nickel-iron alloy leaching solution is not decontaminated, and the impurity content of the solution is very high; using ferrous sulfide as a neutralizing agent, the filtration time after solution decontamination is long, the production efficiency is low, and the economy is poor.

[0279] Table 3: Content of each component in iron phosphate for batteries

[0280]

[0281] As can be seen from Table 3, the iron phosphate prepared according to the present application meets the industry standards. The iron phosphate produced in Example 2 where pickling was not carried out during the preparation of iron phosphate has a high impurity content and does not meet the industry standards.

[0282] Table 4: Recovery rates of various elements in the entire process

[0283]

[0284] Recovery rate of nickel

[0285] Where: C1 is the concentration of nickel in the nickel-iron alloy leaching solution, V1 is the volume of the nickel-iron alloy leaching solution, C2 is the concentration of nickel in the battery-grade nickel sulfate solution, and V2 is the volume of the battery-grade nickel sulfate solution.

[0286] Recovery rate of iron

[0287] Where: C4 is the concentration of iron in the high Ni / Fe ratio solution, V4 is the volume of the high Ni / Fe ratio solution, and C3 is the concentration of iron in the nickel-iron alloy leaching solution.

[0288] Recovery rate of cobalt

[0289] Where: C5 is the concentration of cobalt in the raffinate, V4 is the volume of the raffinate solution, and C5 is the concentration of cobalt in the nickel-iron alloy leaching solution.

[0290] Note: The recovery rates of nickel, cobalt, and iron are calculated based on the target products of iron phosphate for batteries, battery-grade nickel sulfate solution, and cobalt in the organic phase.

[0291] After the solution after synthesizing iron phosphate is extracted with an extractant (P204 or 507 or Cyanex272) to remove impurities such as iron, the loaded organic phase is washed and stripped to obtain a cobalt-containing solution (such as cobalt sulfate solution, which is concentrated, crystallized, centrifuged, and dried to produce refined cobalt sulfate). The organic phase is then stripped with hydrochloric acid to obtain a ferric chloride solution, and the organic phase is washed and then sent for saponification. The raffinate is degreased, concentrated, crystallized, centrifuged, and dried to obtain a battery-grade nickel sulfate product.

[0292] Through the data comparison of the above examples and comparative examples, it can be shown that: the leaching rates of iron, nickel, and cobalt in this process are the best, with high leaching efficiency, high recovery rate, high rational utilization rate of resources, low production cost, low impurity content and better quality in the prepared iron phosphate product, and better economy.

[0293] The above are only optional embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for treating a nickel-iron alloy, characterized in that, Comprising: One-stage leaching: After mixing an acid with a nickel-iron alloy for the first leaching, solid-liquid separation is carried out to obtain a first nickel-iron-containing solution and a first nickel-iron alloy slag; Crude ferrous salt crystallization: The first nickel-iron-containing solution is cooled and crystallized to obtain crude ferrous salt crystals and a second nickel-iron-containing solution; Two-stage leaching: After mixing the second nickel-iron-containing solution with the first nickel-iron alloy slag for the second leaching, solid-liquid separation is carried out to obtain a third nickel-iron-containing solution and a second nickel-iron alloy slag; In the reaction solution of the one-stage leaching step, the first initial H + concentration is 4.0 - 24.0 mol / L, and the first leaching is completed when the H + concentration is 2.0 - 4.0 mol / L.

2. The method for treating nickel-iron alloy according to claim 1, characterized in that, The leaching temperature of the one-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h; Optionally, in the one-stage leaching step, first mix the nickel-iron alloy with water at a liquid-solid ratio of 3-10:1 mL / g, and then add acid thereto to a first initial H + concentration; Optionally, in the reaction solution of the one-stage leaching step, the initial concentration of H + is 6.0 - 12.0 mol / L; Optionally, the H concentration at the completion of the first leaching + is 3.0 - 4.0 mol / L; Optionally, the leaching temperature of the two-stage leaching is 50 - 100 °C, and the leaching time is 8 - 30 h; Optionally, the acid includes one or more of hydrochloric acid, nitric acid, and sulfuric acid; optionally, the acid is sulfuric acid; Optionally, the two-stage leaching step further includes adding an acid to make the second initial H in the reaction system + concentration be 4.0 - 24.0 mol / L, and the second leaching is completed when the H + concentration is 2.0 - 4.0 mol / L; Optionally, the second initial H + concentration is 6.0 - 12.0 mol / L; Optionally, the H concentration at the completion of the second leaching + is 3.0 - 4.0 mol / L; Optionally, the temperature of the cooling crystallization is 10 - 25 °C, and the time is 1 - 8 h; Optionally, the cooling crystallization adopts vacuum cooling crystallization.

3. The method for treating a nickel-iron alloy according to claim 2, wherein Also including impurity removal: Mixing the third nickel-iron-containing solution, crude ferrous salt crystals, and water to dissolve the crude ferrous salt crystals, obtaining a fourth nickel-iron-containing solution; adding an impurity remover to the fourth nickel-iron-containing solution and adjusting the pH of the solution to 0.5 - 4.5 for impurity removal, and filtering to obtain a fifth nickel-iron-containing solution and impurity removal slag.

4. The method for treating a nickel-iron alloy according to claim 3, wherein The content of ferrous ions in the fourth nickel-iron-containing solution is 65 - 130 g / L; Optionally, in the impurity removal step, the impurity remover includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; Optionally, the addition amount of the impurity remover is 1.1 - 1.5 times the theoretical amount of chromium removal, and the theoretical amount of chromium removal is the amount of the impurity remover that just reacts completely with chromium to form a precipitate.

5. The method for treating a nickel-iron alloy according to claim 3, characterized in that, In the impurity removal step, a neutralizing agent is used to adjust the pH of the solution to 0.5 - 4.5, and the neutralizing agent includes at least one of ferronickel, nickel matte, nickel powder, and iron powder; Optionally, a neutralizing agent is used to adjust the pH of the solution to 1.0 - 3.5; Optionally, the ferronickel includes Fe 50 wt% - 80 wt%, Ni 15 wt% - 40 wt%, Co 0.1 wt% - 1.0 wt%, Cr 0.01 wt% - 1.0 wt%, S 5 wt% - 10 wt%; Optionally, the nickel matte includes Fe ≤ 5 wt%, Ni 55 wt% - 65 wt%, Co 0.5 wt% - 1.2 wt%, Cr 0.01 wt% - 1.0 wt%, S 22 wt% - 27 wt%.

6. The method for treating nickel-iron alloy according to claim 3, characterized in that, Also including iron precipitation: Adding phosphate, ammonia water, and hydrogen peroxide to the fifth nickel-iron-containing solution to precipitate iron, obtaining crude iron phosphate and the solution after iron precipitation; Optionally, the phosphate includes at least one of monoammonium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; Optionally, the iron precipitation step includes adding a mixed solution containing phosphate, ammonia water, and hydrogen peroxide with a pH of 5.0 - 7.0 to the fifth nickel-iron-containing solution with a pH of 1.0 - 3.5, reacting for 1 - 2 h, and ending the reaction when the pH reaches 0.8 - 2.4; Optionally, the addition time of the mixed solution lasts for 0.5 - 1.0 h; Optionally, the temperature of the iron precipitation step is 30 - 60 °C; Optionally, the molar ratio of iron element in the fifth nickel - containing iron solution to phosphorus element in the mixed solution is 0.96 - 1.04:1; Optionally, the molar ratio of ferrous ions in the fifth nickel - containing iron solution to hydrogen peroxide in the mixed solution is 0.68 - 0.78:

1.

7. The method for treating a nickel-iron alloy according to claim 6, wherein It also includes pickling the crude iron phosphate and solid - liquid separation. The pickling includes mixing the crude iron phosphate and pure water according to a solid - liquid ratio of 1:14 - 18 g / mL to form a slurry, and adding sulfuric acid or hydrochloric acid to adjust the pH to 0.5 - 3.0; Optionally, sulfuric acid or hydrochloric acid is added to adjust the pH to 1.0 - 1.5; Optionally, the pickling time is 0.5 - 1.0 h and the temperature is 50 - 90 °C.

8. The method for treating a nickel-iron alloy according to claim 7, characterized in that, It also includes aging, water washing, drying and calcining the pickled iron phosphate in sequence to obtain iron phosphate for batteries; Optionally, the aging includes mixing the pickled iron phosphate with phosphoric acid and water to form a slurry and solid - liquid separation to obtain the aged iron phosphate, where the mass ratio of phosphoric acid to the pickled iron phosphate is 0.10 - 0.24:1.0, the concentration of phosphoric acid is 70% - 90%, the aging temperature is 85 - 100 °C, and the aging time is 1.5 - 3.5 h; Optionally, the water washing includes mixing the aged iron phosphate with water according to a solid - liquid mass ratio of 1:16 - 22 to form a slurry and solid - liquid separation to obtain the water - washed iron phosphate. The water washing time is 0.5 - 1.0 h and the temperature is 50 - 90 °C.

9. The method for treating a nickel-iron alloy according to claim 6, wherein, The post - iron - precipitation solution is sequentially filtered, subjected to extraction for impurity removal and degreasing to obtain a battery - grade nickel sulfate solution; Optionally, the extractant used for extraction includes any one of P204, P507, and Cyanex272; Optionally, the addition amount of the extractant used for extraction is 20% - 30% of the volume of the aqueous phase; Optionally, the time for extraction and impurity removal is 5 - 10 min and the temperature is 30 - 40 °C.

10. The method for treating nickel-iron alloy according to claim 1, characterized in that, The nickel - iron alloy includes Fe, Ni, and also includes at least one of impurity elements Co, Cr, Cu, Mn, Zn, and P; Optionally, the nickel - iron alloy includes 50 wt% - 80 wt% Fe, 15 wt% - 40 wt% Ni, 0.1 wt% - 1.0 wt% Co, 0.01 wt% - 1.0 wt% Cr, and 0.01 wt - 1 wt% S; Optionally, the particle size of the nickel - iron alloy is 1 - 10 cm.

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