Method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate and application

Abstract

The invention discloses a method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate and application. The method comprises the following steps: preparing an iron source solution; the method comprises the following steps: dissolving ferric phosphate in a sulfuric acid solution, reducing ferric iron into ferrous iron, adjusting the pH value of an obtained liquid phase to 0-1, and carrying out alcohol precipitation, solid-liquid separation and washing to obtain ferrous sulfate coarse crystals; and carrying out impurity removal treatment on the ferrous sulfate coarse crystal to obtain a ferrous sulfate product. According to the method for preparing the ferrous sulfate from the iron-containing waste, targeted removal paths are formed for different types of impurities such as alkali metal, transition metal and non-metal phosphorus in all the steps, all the steps cooperatively remove the impurities, and finally efficient and low-cost conversion from the iron-containing waste to high-quality ferrous sulfate heptahydrate is achieved; in addition, deep removal of various impurities and comprehensive standard reaching of the product purity are achieved, the purity of the ferrous sulfate heptahydrate is 99.99% or above, and the yield of the ferrous sulfate heptahydrate is larger than or equal to 80%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste treatment, in particular to a method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate and application. BACKGROUND

[0002] Recovery of iron from solid waste (such as titanium dioxide slag, steel slag, battery black powder and copper smelting slag, etc.) and preparation of ferrous sulfate is an important way to realize resource recycling and environmental protection, and the prepared ferrous sulfate is widely used in water treatment, agricultural fertilizer, battery material and other fields, and its purity directly determines the performance and application safety of downstream products.

[0003] In the process of recovering iron from solid waste to prepare ferrous sulfate, the solid waste often contains transition metal impurities such as nickel, cobalt and manganese in addition to iron elements, for example, nickel-cobalt-manganese lithium in the positive electrode material of waste batteries (battery black powder), and nickel-cobalt-manganese alloy residues in steel slag. In the process of acid leaching iron, nickel ions (Ni 2+ ), cobalt ions (Co 2+ ) and manganese ions (Mn 2+ ) will enter the leaching solution together with iron ions, and will be co-precipitated or crystallized with them in the subsequent preparation of ferrous sulfate. The existing impurity removal treatment for the recovery process cannot completely separate nickel, cobalt and manganese, resulting in excessive impurity ions in the product.

[0004] The above problems result in that the nickel-cobalt-manganese impurity ions in the ferrous sulfate recovered from solid waste cannot be completely removed, and the purity is insufficient, which limits the industrial application of solid waste recovery and preparation of ferrous sulfate. For water treatment, it will affect the flocculation effect and cause secondary pollution, for battery material, it will reduce the electrode stability, and for fertilizer, it will accumulate in the soil and harm crops. Therefore, there is an urgent need for an impurity removal scheme that is suitable for solid waste recovery scenarios and can efficiently and completely remove nickel, cobalt and manganese impurities, to promote the industrial application of solid waste recovery and preparation of ferrous sulfate. SUMMARY

[0005] The present application discloses a method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate and application, to solve the technical problem that nickel-cobalt-manganese impurity ions cannot be completely removed in the preparation of ferrous sulfate from solid waste recovery of iron in the related art.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows: In a first aspect, the embodiments of the present application provide a method for preparing ferrous sulfate from iron-containing waste, comprising the following steps: Step S10: providing iron-containing waste, dissolving the iron-containing waste in acid solution to prepare an iron source solution; Step S20: adding a phosphorus source and an oxidizing agent to the iron source solution to oxidize the ferrous iron to ferric iron; adjusting the pH to 1.7 to 2.5 to generate a ferric phosphate-containing precipitate, and after the reaction is completed, performing solid-liquid separation and washing to obtain a ferric phosphate-containing solid phase; Step S30: dissolving the ferric phosphate-containing solid phase obtained in step S20 in a sulfuric acid solution, removing insoluble substances through solid-liquid separation, adjusting the pH to 1.7 to 2.5 to generate a ferric phosphate-containing precipitate, and after the reaction is completed, performing solid-liquid separation and washing to obtain a ferric phosphate-containing solid phase; Step S40: dissolving the ferric phosphate-containing solid phase obtained in step S30 in a sulfuric acid solution, adding a reducing agent to reduce the ferric iron to ferrous iron, and after the reaction is completed, performing solid-liquid separation to obtain a ferrous sulfate-containing liquid phase; Step S50: adjusting the pH of the ferrous sulfate-containing liquid phase obtained in step S40 to 0 to 1, and performing alcohol precipitation, solid-liquid separation, and washing to obtain a ferrous sulfate coarse crystal; Step S60: dissolving the ferrous sulfate coarse crystal in water, adjusting the pH to 5 to 7 under the protection of an inert gas, and after the reaction is completed, performing solid-liquid separation to obtain a ferrous sulfate-containing liquid phase; Step S70: adjusting the pH of the ferrous sulfate-containing liquid phase obtained in step S60 to 1 to 2, and then performing final impurity removal treatment, wherein the final impurity removal treatment is performed at least twice; at least one alcohol precipitation is performed in the at least twice impurity removal operations; and a ferrous sulfate product is obtained.

[0007] In a second aspect, the embodiments of the present application provide a ferrous sulfate product prepared by the above method.

[0008] In a third aspect, the embodiments of the present application provide an application of the above ferrous sulfate product in preparing high-purity iron single substance or high-purity iron-containing compound, wherein the iron-containing compound includes any one of ferric oxide, ferric hydroxide, ferrous hydroxide, lithium ferric phosphate, and nano Fe3O4. The high-purity iron single substance refers to an iron single substance with a purity of 3N or higher; and the high-purity iron-containing compound refers to an iron-containing compound with a purity of 3N or higher.

[0009] The technical solutions adopted by the embodiments of the present application can achieve the following beneficial effects: ① In step S20, iron and multiple impurities are preliminarily separated by phosphoric acid, so that the iron phosphate solid phase is separated from the dispersed impurity solution, realizing the enrichment and preliminary removal of iron; in step S30, the iron phosphate solid phase is subjected to acid dissolution and reprecipitation recrystallization operation, which is aimed at deep removal of alkali metal impurities that are easily dissolved in acid. Such impurities re-enter the liquid phase in the acid dissolution stage and are difficult to re-embed in the iron phosphate crystal lattice during the reprecipitation process, thereby realizing effective separation; for transition metals and heavy metals such as manganese, cobalt, nickel, and copper, they are stripped from the crystal lattice interstices through the regular growth of iron phosphate crystals during recrystallization, realizing substantial removal; the cooperation of steps S20 and S30 not only guarantees a high yield of iron element, but also greatly reduces the impurity treatment load for subsequent steps.

[0010] ② In step S40, the reduction of iron powder is used to convert trivalent iron to divalent iron (adapting to the valence state requirement of ferrous sulfate); in step S50, the alcohol precipitation effect of alcohol solvent is used to realize the precipitation of ferrous sulfate coarse crystals. First, the phosphorus impurity in the system is greatly reduced, and the intervention of alcohol solvent will weaken the complexing ability of phosphate and metal ions, making it difficult for them to enter the crystal phase with ferrous sulfate, thereby realizing the effective separation of phosphorus and ferrous sulfate coarse crystals; at the same time, the selective interception of alkali metal impurities in the liquid is formed, and by means of the dielectric properties of the alcohol solvent and water mixed system, most of the alkali metal ions remain in the liquid, while the ferrous sulfate is preferentially crystallized and precipitated, which can realize preliminary purification. The core function of step S40 is to complete the valence state conversion of iron to adapt to the product form of ferrous sulfate; step S50 utilizes the alcohol precipitation effect of alcohol solvent to realize the preliminary enrichment of ferrous sulfate crystal phase while efficiently removing a large amount of phosphorus impurities in step S40 system. The two steps cooperatively complete the valence state adjustment, phosphorus impurity removal, and target enrichment, which not only solves the separation problem of phosphorus and iron, but also lays a foundation for high-purity crystal phase for subsequent refining.

[0011] ​③In step S60, the stubborn impurities in the ferrous sulfate coarse crystal are deeply removed under weak alkaline conditions. First, the complete removal of phosphorus impurities is achieved. The trace amount of phosphate ions remaining in the weak alkaline environment will form stable precipitates with metal ions in the system, completely separating from the liquid phase. At the same time, high-valence metal impurities such as titanium, vanadium, aluminum, and chromium can be removed. Such impurities are easy to form hydroxide precipitates under weak alkaline conditions, while ferrous sulfate can remain stable in solution in this pH range, achieving precise separation of impurities and target substances. In addition, magnesium, calcium, cobalt, nickel, and copper are deeply purified, reducing their residual amount to a very low level. In step S70, through the final impurity removal treatment (at least one alcohol precipitation removal), the final impurity removal and product purification are completed. First, the residual alkali metal impurities in the system are removed. Alcohol precipitation can trap most of the alkali metal ions, and other impurities can be further removed from the ferrous sulfate lattice, achieving ultra-low residual. At the same time, trace amounts of residual alkaline earth metals and transition metal impurities can be trapped again. Through the screening effect of the crystallization process, the purity of the target product reaches the application standard. Thus, the complete removal of sodium, aluminum, potassium, phosphorus, vanadium, and other types of impurities is achieved. The heavy metal impurities such as cobalt, nickel, and copper are also reduced to below the detection limit, obtaining high-quality ferrous sulfate heptahydrate.

[0012] ④Steps S50 and S70 form a step-by-step impurity removal process that first enriches and removes alkali metals, and then refines and purifies. In step S50, the metastable effect of the alcohol solvent is used to achieve directional enrichment of ferrous sulfate, while most of the easily soluble alkali metal impurities are trapped in the liquid, completing the preliminary removal of alkali metals and the concentration of iron-based products, reducing the impurity load for subsequent refinement. The final purification treatment in step S70 (at least one alcohol precipitation treatment) further reduces the residual amount of alkali metals, ensuring the product crystal form and purity. The two-step process cooperates to not only avoid iron loss caused by single impurity removal, but also solve the technical problem of simultaneous purification of multiple types of impurities, achieving a balance between impurity removal efficiency and product yield. It is the key process synergy to ensure that the final product meets the standards.

[0013] (2) The method for preparing ferrous sulfate from iron-containing waste provided by the embodiment of the present application can prepare ferrous sulfate with a purity of more than 99.99%, which belongs to high-quality ferrous sulfate. The high-quality ferrous sulfate can be used in high-end fields that are extremely sensitive to impurity content. For example, the electronic industry, for preparing high-purity iron-based functional materials such as magnetic materials, ferrite, etc.; as an iron source precursor in the process of semiconductor manufacturing or thin film deposition (the content of metal impurities such as Cu, Zn, Ni, Cr, etc. needs to be strictly controlled); for preparing cleaning or etching liquid (as a reducing agent or complexing component in a specific process); new energy material research and development: as a high-purity iron source for synthesizing lithium iron phosphate (LiFePO4) positive electrode material. Battery-grade iron phosphate has strict requirements for the purity of iron and impurities (especially heavy metals) in raw materials; for preparing iron-based catalysts or electrode materials, used in fuel cells, supercapacitors, etc.; scientific research and analytical chemistry: used as a standard substance or reference reagent for titration analysis (such as the determination of iron content by potassium dichromate method); used as a raw material for preparing calibration solutions in spectral analysis (ICP-MS, AAS, etc.); used as a starting material for synthesizing other high-purity iron compounds (such as high-purity iron oxide, nano Fe3O4, etc.); preparation of special optical / magnetic materials: preparation of high-purity red iron oxide, yellow iron oxide and other pigments, used in high-end coatings, ceramics or optical coatings; used for growing single crystals or preparing magnetic recording materials. DETAILED DESCRIPTION

[0014] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of the present application.

[0015] In the related art, the impurities in ferrous sulfate are mainly divalent ions such as nickel, cobalt, and manganese, which are difficult to remove. Since the pH of the trivalent iron phosphate precipitate is much lower than that of the divalent ions such as nickel, cobalt, and manganese, most of the divalent ion impurities can be removed by the method of oxidizing and precipitating iron phosphate and then washing. However, since the precipitation process is in a solution system with a high impurity concentration, some impurity ions inevitably form interstitial solid solutions and enter the iron phosphate lattice, which cannot be removed by washing. When the iron phosphate is redissolved in pure sulfuric acid to release the impurity ions in the lattice, the divalent impurity ions such as nickel, cobalt, and manganese are almost impossible to form interstitial solid solutions again and thus be removed by washing.

[0016] Therefore, the present application provides a method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate, and application. The method for preparing ferrous sulfate from iron-containing waste, ferrous sulfate, and application provided by the present application will be described in detail below through specific embodiments and application scenarios.

[0017] This application provides a method for preparing ferrous sulfate from iron-containing waste, comprising the following steps: Step S10: Provide iron-containing waste, dissolve the iron-containing waste in acid solution to obtain iron source solution; Step S20: Add phosphorus source to the iron source solution to form a first mixed solution. Heat the first mixed solution to 40°C to 60°C. Add oxidant to the first mixed solution to oxidize ferrous iron to ferric iron. Adjust the pH to 1.7 to 2.5 to generate a precipitate containing ferric phosphate. After the reaction is complete, perform solid-liquid separation and washing to obtain a solid phase containing ferric phosphate. When the first mixed solution contains aluminum, the solid phase obtained in this step also contains aluminum phosphate.

[0018] In this step, the reaction that occurs after adding the oxidant can be represented as (using hydrogen peroxide as an example): 2Fe 2+ +H₂O₂ + 2H₂ + →2Fe 3+ +2H2O.

[0019] Then, by precisely controlling the pH value, ferric phosphate is completely precipitated; the reaction that occurs can be represented as: Fe 3+ +PO4 3- →FePO4↓.

[0020] Step S30: Dissolve the iron phosphate-containing solid phase obtained in step S20 in sulfuric acid solution, remove insoluble matter by solid-liquid separation, adjust pH to 1.7 to 2.5, generate iron phosphate-containing precipitate, and after solid-liquid separation and washing, obtain iron phosphate-containing solid phase; In this step, the solid phase containing ferric phosphate (FePO4) reacts with sulfuric acid to produce water-soluble ferric sulfate and phosphoric acid, preparing for subsequent recrystallization. The reaction formula is as follows: 2FePO4+3H2SO4→Fe2(SO4)3+2H3PO4; In this reaction, sulfuric acid provides H₂. + This disrupts the precipitation equilibrium of ferric phosphate, causing it to dissolve into Fe. 3+ and PO4 3- (PO4) 3- With H + (Combined to form H3PO4), and with trace amounts of intermittent solid solution impurities Ni 2+ Co 2+ Mn 2+ Once all the divalent transition metal ions have entered the solution, the insoluble impurities in the solid phase containing ferric phosphate (metal ion hydroxides with strong hydrolytic ability, such as hydrated titanium dioxide and boehmite) are insoluble in dilute sulfuric acid and can be removed by solid-liquid separation.

[0021] When the pH is adjusted to 1.7 to 2.5, the Fe in the solution... 3+ With PO4 3- (From the ionization of H3PO4) they recombine to form a relatively pure ferric phosphate precipitate, the reaction formula is: Fe2(SO4)3+2H3PO4→2FePO4↓+3H2SO4; The optimal pH range for iron phosphate precipitation is 1.7 to 2.5, at which point Fe... 3+ With PO4 3- The binding ability is strong, and the precipitation is more complete; while Ni previously dissolved in the solution 2+ Co 2+ Mn 2+ At this pH, divalent transition metal ions are unlikely to form precipitates and will remain in the liquid phase, where they can be completely removed by subsequent washing.

[0022] Step S40: Dissolve the solid phase containing ferric phosphate obtained in step S30 in sulfuric acid solution, add a reducing agent to reduce ferric iron to ferrous iron, and after the reaction is completed, separate the solid and liquid phase to obtain the liquid phase containing ferrous sulfate. In this step, the solid phase containing ferric phosphate (FePO4) reacts with sulfuric acid to produce water-soluble ferric sulfate and phosphoric acid, preparing for the subsequent reduction reaction. The reaction formula is as follows: 2FePO4+3H2SO4→Fe2(SO4)3+2H3PO4; In this reaction, sulfuric acid provides H₂. + This disrupts the precipitation equilibrium of ferric phosphate, causing it to completely dissolve into Fe. 3+ and PO4 3- (PO4) 3- With H + (Combined to form H3PO4), ensuring Fe 3+ It can react fully with reducing agents.

[0023] Under stirring conditions at 40-60℃, high-purity iron powder (Fe) reacts with Fe in the solution. 3+ A redox reaction occurs, Fe 3+ Reduced to Fe 2+ High-purity iron powder itself is oxidized into Fe. 2+ Reaction formula: Fe + Fe2(SO4)3 → 3FeSO4; Sulfuric acid provides H₂ in the dissolution reaction. + The reduction reaction does not consume sulfuric acid, and the final solution mainly consists of FeSO4 and H3PO4. Solid-liquid separation can remove trace amounts of unreacted high-purity iron powder (insoluble matter) and obtain a relatively pure liquid phase containing ferrous sulfate.

[0024] Step S50: Adjust the pH of the liquid phase containing ferrous sulfate obtained in step S40 to 0 to 1, and obtain crude ferrous sulfate crystals through alcohol precipitation, solid-liquid separation, and washing. In this step, sulfuric acid is added to the liquid phase containing ferrous sulfate (containing FeSO4 and H3PO4) to adjust the pH to 0 to 1, the purpose of which is to maintain the strong acidity of the system. A strong acidic environment inhibits the ionization of phosphoric acid (avoiding the formation of Fe3(PO4)2 precipitate) and does not react chemically with any components in the solution, ensuring the stable presence of ferrous ions and phosphoric acid in the solution. During alcohol precipitation, because ferrous sulfate (FeSO4) is readily soluble in water but sparingly soluble in alcohol solvents such as ethanol and n-propanol, adding 1.2 to 1.8 times its mass of alcohol solvent to the liquid phase containing ferrous sulfate will reduce the polarity of the liquid phase containing ferrous sulfate and destroy the Fe... 2+ The solvation reaction with water molecules causes a sharp decrease in the solubility of ferrous sulfate, leading to crystallization and precipitation from the solution (forming coarse ferrous sulfate crystals). Meanwhile, phosphoric acid (H3PO4), miscible with alcohol or water, remains dissolved and separates from the ferrous sulfate crystals along with the liquid phase, achieving "phosphorus-iron separation." This significantly reduces phosphorus impurities in the system. The presence of the alcohol solvent weakens the complexation ability of phosphate ions with metal ions, making it difficult for them to enter the crystal phase with ferrous sulfate, thus effectively separating phosphorus from the coarse ferrous sulfate crystals. Simultaneously, it selectively retains alkali metal impurities in the solution. Utilizing the dielectric properties of the alcohol-water mixture, most alkali metal ions remain in the liquid, while ferrous sulfate preferentially crystallizes out, achieving preliminary purification. Furthermore, the alcohol solvent used can be recycled and reused, reducing costs.

[0025] Step S60: Dissolve the crude ferrous sulfate crystals in water, adjust the pH to 5 to 7 under the protection of an inert gas, and after the reaction is completed, separate the solid and liquid phases to obtain a liquid phase containing ferrous sulfate. This step achieves complete removal of phosphorus impurities. The trace amounts of phosphate remaining under a weakly alkaline environment will form a stable precipitate with metal ions in the system, completely detaching from the liquid phase. This process is carried out under an inert gas (such as nitrogen) to prevent Fe... 2+ It is oxidized to Fe by oxygen in the air. 3+ (To prevent the formation of Fe(OH)3 precipitate, which would lead to the loss of ferrous sulfate); when the pH is adjusted to 5 to 7, ferrous sulfate can be completely dissolved, while residual trace heavy metal impurities (such as aluminum, titanium, vanadium) and OH groups released from water dissociation will be lost. - The ferrous sulfate precipitate is formed by the combination of the two substances, which can be removed by solid-liquid separation. Furthermore, it deeply purifies alkaline earth metals such as magnesium and calcium, as well as heavy metals such as cobalt, nickel, and copper, reducing their residual levels to extremely low levels. The resulting liquid phase containing ferrous sulfate is a high-purity ferrous sulfate solution.

[0026] Step S70: Adjust the pH of the liquid phase containing ferrous sulfate obtained in step S60 to 1 to 2, and then perform final impurity removal treatment to obtain the ferrous sulfate product.

[0027] In this step, the final impurity removal and product purification are achieved through a secondary purification process (at least one alcohol precipitation). First, alcohol precipitation is used to specifically remove residual alkali metal impurities from the system. Alcohol precipitation can retain most alkali metal ions, and combined with other purification methods, it can further remove alkali metals from the ferrous sulfate lattice, achieving ultra-low residue. At the same time, it can also retain trace amounts of residual alkaline earth metals and transition metal impurities. Through the sieving effect of the crystallization process, the purity of the target product meets the application standards. Thus, the complete removal of various impurities such as sodium, aluminum, potassium, phosphorus, and vanadium is achieved, and heavy metal impurities such as cobalt, nickel, and copper are reduced to below the detection limit, resulting in high-quality ferrous sulfate heptahydrate.

[0028] In some embodiments, in step S70, the remaining purification operations in the final purification process are selected from at least one of the following (a) and (b): (a) alcohol precipitation for purification; (b) evaporation, concentration, cooling, and crystallization for purification. Furthermore, in the final impurity removal process, the combination method and implementation order of each impurity removal operation can be freely selected.

[0029] In some embodiments, in step S70, the final impurity removal process is selected from any combination of the following (1), (2), (3), and (4): (1) A combination of one-time alcohol precipitation for impurity removal and one-time evaporation, concentration, cooling, and crystallization for impurity removal; (2) A combination of two alcohol precipitation purification processes and one evaporation, concentration, cooling, and crystallization purification process; (3) A combination of one-time alcohol precipitation for impurity removal and two-time evaporation, concentration, cooling, and crystallization for impurity removal; (4) A combination of two alcohol precipitation to remove impurities.

[0030] In some embodiments, the alcohol solvent used for alcohol precipitation to remove impurities is selected from at least one of ethanol, n-propanol, and isopropanol. It is understood that the selected alcohol solvent can be a single solvent or a mixture of multiple solvents in any proportion; of course, the selection of the alcohol solvent is not limited to the alcohol solvents disclosed in this application, and other alcohol solvents suitable for the alcohol precipitation process can also be used. The alcohol solvent used for alcohol precipitation to remove impurities can be recycled and reused to reduce costs.

[0031] In some embodiments, the alcohol precipitation for impurity removal includes: adding an alcohol solvent to a liquid phase containing ferrous sulfate, wherein the mass ratio of the liquid phase containing ferrous sulfate to the alcohol solvent is 1:0.3 to 1:0.5; after the alcohol solvent is added, stirring is continued until no precipitate is formed, and then solid-liquid separation is performed.

[0032] In some embodiments, the evaporation, concentration, cooling, crystallization, and impurity removal includes: evaporating and concentrating the liquid phase containing ferrous sulfate until the iron content is 10% to 12% by mass, cooling to 0°C to 5°C for cooling and crystallization until no precipitate is formed. The process can be adjusted appropriately according to the specific process, and then solid-liquid separation is performed.

[0033] In some embodiments, in step S70, the pH is adjusted to 1 to 2, and the pH adjuster used is sulfuric acid; wherein the sulfuric acid can be sulfuric acid of any mass percentage concentration, preferably concentrated sulfuric acid with a mass percentage concentration of 98%, which can reduce the amount of water added. If an evaporation and concentration process is subsequently used for impurity removal, the amount of water evaporated can be reduced.

[0034] In some embodiments, in step S20, the phosphorus source is selected from at least one of phosphorus-containing waste and phosphorus-containing compounds; the phosphorus-containing compound is selected from at least one of phosphoric acid, monoammonium phosphate, ammonium dihydrogen phosphate, ammonium orthophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium orthophosphate. It is understood that the phosphorus source can be phosphorus-containing waste or a commercially available compound reagent. Of course, it is not limited to the types of phosphorus sources disclosed in this application, and other phosphorus-containing compounds can also be used.

[0035] In some embodiments, in step S20, the amount of phosphorus source added is such that the molar ratio of iron to phosphorus in the mixed solution formed by the phosphorus source and the iron source solution is 1:1 to 1:1.05.

[0036] In some embodiments, in step S20, the oxidant is selected from at least one of hydrogen peroxide, air, ozone, sodium persulfate, sodium ferrate, and high-purity oxygen; the amount of oxidant added is 1.0 to 1.2 times the theoretical molar amount, based on the oxidization of all ferrous iron to ferric iron.

[0037] In some embodiments, in step S20, the pH is adjusted to 1.7 to 2.5, and the pH adjuster used is selected from at least one of ammonia, sodium hydroxide, sodium carbonate and sodium bicarbonate; after adjusting the pH to 1.7 to 2.5, the mixture is stirred and reacted at a temperature of 40°C to 60°C for 15 min to 60 min until no more precipitate is formed. The pH can be adjusted appropriately according to the specific process.

[0038] In some embodiments, in step S20, when the iron-containing waste contains phosphorus and the molar amount of phosphorus in the iron source solution is greater than or equal to the molar amount of iron after the iron source solution is prepared, there is no need to supplement the phosphorus source. It is understood that when the phosphorus content in the iron-containing waste is high, the iron-containing waste is used as both an iron source and a phosphorus source.

[0039] In some embodiments, in step S30, the solid phase containing ferric phosphate is dissolved in a sulfuric acid solution with a mass percentage concentration of 10% to 30%. In this step, the solid phase containing ferric phosphate can be directly dissolved in the 10% to 30% sulfuric acid solution; alternatively, the solid phase containing ferric phosphate can be first dispersed in water, and then concentrated sulfuric acid with a mass percentage concentration of 98% can be added to completely dissolve the solid phase containing ferric phosphate. The molar ratio of the solid phase containing ferric phosphate to sulfuric acid is 1:0.8 to 1:1.2, and the amount of sulfuric acid solution used is based on concentrated sulfuric acid with a mass percentage of 98%.

[0040] In some embodiments, in step S30, the pH is adjusted to 1.7 to 2.5, and the pH adjuster used is selected from at least one of ammonia, sodium hydroxide, sodium carbonate and sodium bicarbonate; wherein the mass percentage concentration of ammonia is 25% to 28%.

[0041] In some embodiments, in step S30, after adjusting the pH to 1.7 to 2.5, the mixture is stirred and reacted at a temperature of 40°C to 60°C for 15 to 60 minutes until no more precipitate is formed. The reaction can be adjusted appropriately according to the specific process.

[0042] In some embodiments, in step S40, the solid phase containing ferric phosphate is dissolved in a sulfuric acid solution with a mass percentage concentration of 10% to 30%. In this step, the solid phase containing ferric phosphate can be directly dissolved in the 10% to 30% sulfuric acid solution; alternatively, the solid phase containing ferric phosphate can be first dispersed in water, and then concentrated sulfuric acid with a mass percentage concentration of 98% can be added to completely dissolve the solid phase containing ferric phosphate. The molar ratio of the solid phase containing ferric phosphate to sulfuric acid is 1:0.8 to 1:1.2, and the amount of sulfuric acid solution used is based on concentrated sulfuric acid with a mass percentage of 98%.

[0043] In some embodiments, in step S40, the reducing agent is selected from at least one of high-purity iron powder, hydrogen sulfide, sodium sulfite, and sodium thiosulfate; the amount of reducing agent added is 1.0 to 1.2 times the theoretical molar amount, based on the reduction of all trivalent iron to divalent iron.

[0044] In some embodiments, in step S40, after the reducing agent is added, the mixture is stirred and reacted at a temperature of 40°C to 60°C for 1.5 to 3 hours.

[0045] In some embodiments, in step S50, the pH is adjusted to 0 to 1, and sulfuric acid is used as the pH adjuster.

[0046] In some embodiments, in step S50, the alcohol solvent used for alcohol precipitation is selected from at least one of ethanol, n-propanol, and isopropanol.

[0047] In some embodiments, in step S50, an alcohol solvent is added to the liquid phase containing ferrous sulfate. The alcohol solvent can be added dropwise. The mass ratio of the liquid phase containing ferrous sulfate to the alcohol solvent is 1:1.2 to 1:1.8. After the alcohol solvent is added, the mixture is stirred continuously until no precipitate is formed, and then solid-liquid separation is performed.

[0048] In some embodiments, in step S50, the crude ferrous sulfate crystals are washed with an alcohol solvent. The mass ratio of ferrous sulfate to the alcohol solvent is 1:0.8 to 1:2. The alcohol solvent is selected from at least one of ethanol, n-propanol, and isopropanol, and can be the same as the alcohol solvent used for alcohol precipitation. It is understood that the crude ferrous sulfate crystals are moist and may contain trace amounts of free sulfuric acid and phosphoric acid (floating acid). When washed with an alcohol solvent, the alcohol solvent does not dissolve the ferrous sulfate, but it can dissolve acidic impurities adsorbed on the crystal surface. Impurities are removed through solid-liquid separation, resulting in relatively pure crude ferrous sulfate crystals.

[0049] In some embodiments, in step S60, the mass ratio of crude ferrous sulfate crystals to pure water is 1:2 to 1:3.

[0050] In some embodiments, in step S60, the pH is adjusted to 5 to 7, and the pH adjuster used is selected from at least one of ammonia, sodium hydroxide, sodium carbonate, and sodium bicarbonate; wherein the mass percentage concentration of ammonia is 25% to 28%. In some embodiments, in step S60, after adjusting the pH to 5 to 7, the reaction is stirred at room temperature for 15 to 60 minutes until no more precipitate is formed.

[0051] In some embodiments, in step S10, the iron-containing waste is selected from at least one of lithium slag, battery black powder, ferrophosphate slag, sulfuric acid slag, titanium dioxide slag, copper smelting slag, blast furnace slag, steel slag, fly ash, nickel slag, chromium slag, and lead-zinc slag; generally, as long as the waste contains recyclable iron, it can be used in this application to prepare high-purity ferrous sulfate.

[0052] In some embodiments, in step S10, the acid solution is a sulfuric acid solution with a mass percentage concentration of 10% to 40%; and the mass percentage content of iron in the final iron source solution is controlled to be 5% to 6%.

[0053] The following detailed embodiments illustrate a method for preparing ferrous sulfate from iron-containing waste and the ferrous sulfate itself, as provided in this application.

[0054] I. Description of Raw Materials, Reagents, and Testing Standards: (1) Iron source: Sulfuric acid residue: originating from sulfuric acid plants, it is a waste residue from sulfuric acid production. The main component of sulfuric acid residue is ferric oxide. Specifically, the iron content in sulfuric acid residue is 53.86% by mass. It also contains significant amounts of other elements, including 5802 ppm sodium, 4331 ppm magnesium, 4609 ppm aluminum, 2253 ppm potassium, 14839 ppm calcium, 2504 ppm titanium, 3080 ppm chromium, 1110 ppm manganese, 430 ppm cobalt, 270 ppm nickel, 1465 ppm copper, 3105 ppm zinc, 43 ppm arsenic, 437 ppm cadmium, and 231 ppm lead.

[0055] Copper smelting slag: a byproduct of the smelting or blowing stage in copper ore smelting. Copper smelting slag contains a large amount of ferric oxide (Fe2O3). Specifically, the mass percentage of iron in copper smelting slag is 34.79%. Copper smelting slag also contains significant amounts of other elements, including 7772 ppm sodium, 277 ppm magnesium, 4807 ppm aluminum, 445 ppm potassium, 7481 ppm calcium, 2812 ppm titanium, 309 ppm chromium, 769 ppm manganese, 164 ppm cobalt, 557 ppm nickel, 4007 ppm copper, 6 ppm zinc, 9 ppm arsenic, 0.1 ppm cadmium, and 3 ppm lead.

[0056] Ferrous sulfate, a byproduct of titanium dioxide production, is derived from the evaporation of the mother liquor after acid leaching of ilmenite for titanium removal. Its main component is ferrous sulfate. Specifically, the iron content in ferrous sulfate produced from titanium dioxide is 18.37% by mass. It also contains significant amounts of other elements, including 770 ppm sodium, 1005 ppm magnesium, 1802 ppm aluminum, 184 ppm potassium, 1168 ppm calcium, 7417 ppm titanium, 147 ppm chromium, 5762 ppm manganese, 33 ppm cobalt, 32 ppm nickel, 0.2 ppm copper, 90 ppm zinc, 0.6 ppm arsenic, 0.1 ppm cadmium, and 8 ppm lead.

[0057] (2) Phosphorus source: Agricultural-grade monoammonium phosphate contains 4799 ppm sodium, 1041 ppm magnesium, 119 ppm aluminum, 5969 ppm potassium, 2083 ppm calcium, 219000 ppm phosphorus, 48 ​​ppm titanium, 14 ppm chromium, 651 ppm manganese, 13 ppm cobalt, 17 ppm nickel, 9 ppm copper, 49 ppm zinc, 35 ppm arsenic, 0.2 ppm cadmium, and 15 ppm lead.

[0058] Industrial waste phosphoric acid contains 377.79 ppm sodium, 84.94 ppm magnesium, 8085.89 ppm aluminum, 124.05 ppm potassium, 446.58 ppm calcium, 108000 ppm phosphorus, 95.83 ppm titanium, 1.34 ppm vanadium, 1.85 ppm chromium, 2.47 ppm manganese, 0.07 ppm cobalt, 42.67 ppm nickel, 3.78 ppm copper, 11.88 ppm zinc, 0.11 ppm cadmium, and 0.71 ppm lead.

[0059] It also serves as a source of iron and phosphorus: Phosphorus-iron slag: Specifically, it contains 65.05% iron by mass, 21.54% phosphorus by mass, and also includes: 158 ppm sodium, 816 ppm magnesium, 757 ppm aluminum, 311 ppm potassium, 15072 ppm calcium, 6028 ppm titanium, 2139 ppm vanadium, 1451 ppm chromium, 24781 ppm manganese, 207 ppm cobalt, 1005 ppm nickel, 688 ppm copper, 72 ppm zinc, 5 ppm arsenic, 0 ppm cadmium, and 152 ppm lead.

[0060] The black powder for lithium iron phosphate batteries consists of 24.25% iron and 13.34% phosphorus by mass, and also includes: 26590.91 ppm lithium, 1409 ppm sodium, 71 ppm magnesium, 7504 ppm aluminum, 235 ppm potassium, 791 ppm calcium, 10 ppm titanium, 18 ppm chromium, 298 ppm manganese, 117 ppm cobalt, 365 ppm nickel, 579 ppm copper, 11 ppm zinc, 6 ppm arsenic, 0.1 ppm cadmium, and 3 ppm lead.

[0061] Battery black powder lithium extraction slag: Specifically, the iron mass percentage concentration is 24.19%, the phosphorus mass percentage concentration is 11.66%, including 821 ppm lithium, 374 ppm sodium, 18 ppm magnesium, 359 ppm aluminum, 38 ppm potassium, 165 ppm calcium, 1205 ppm titanium, 26 ppm chromium, 173 ppm manganese, 2 ppm cobalt, 8 ppm nickel, 13 ppm copper, 13 ppm zinc, 0.8 ppm arsenic, 0 ppm cadmium, and 1 ppm lead.

[0062] In the following examples and comparative examples: phosphoric acid, monoammonium phosphate, ammonium dihydrogen phosphate, ammonium orthophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium orthophosphate, ethanol, n-propanol and isopropanol were all of analytical grade; and pure water was used.

[0063] II. Implementation Examples Example 1: This application provides a method for preparing ferrous sulfate from iron-containing waste, comprising the following steps: Step S10: Dissolve 100g of lithium extraction residue from battery black powder in 300g of sulfuric acid solution with a mass percentage concentration of 30%, dilute with water, and control the mass percentage content of iron in the final iron source solution to be 5% to obtain the iron source solution.

[0064] Step S20: 6.5g of 85% phosphoric acid was added to the iron source solution to form a first mixed solution; the pH was adjusted to 2.0 using a 20% sodium hydroxide solution to generate a precipitate containing iron phosphate and aluminum phosphate. The mixture was stirred at 50°C for 30 minutes until no more precipitate was generated. After filtration and washing, 161.5g of a solid phase containing iron phosphate and aluminum phosphate was obtained. The solid phase containing iron phosphate and aluminum phosphate obtained in this step was found to contain: iron 14.82% (mass percentage), lithium 7.85 ppm, sodium 2984.63 ppm, magnesium 4.85 ppm, aluminum 87.58 ppm, potassium 7.95 ppm, calcium 42.08 ppm, phosphorus 85800 ppm, titanium 289.97 ppm, vanadium 20.17 ppm, chromium 6.61 ppm, manganese 44.16 ppm, cobalt 43.56 ppm, nickel 41.03 ppm, copper 3.07 ppm, zinc 2.86 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. Iron was determined by potassium dichromate titration, while the other elements were determined by ICP-MS (inductively coupled plasma mass spectrometry).

[0065] Step S30: Dissolve 150g of the ferric phosphate solid phase obtained in step S20 in 200g of a 20% sulfuric acid solution until all the ferric phosphate solid phase is dissolved. Then filter to remove insoluble matter. Adjust the pH to 2.0 using a 20% sodium hydroxide solution to generate a precipitate containing ferric phosphate and aluminum phosphate. Stir the reaction at 50℃ for 30 minutes until no more precipitate is generated. After filtration and washing, obtain 154.4g of the ferric phosphate and aluminum phosphate solid phase. Analysis revealed that the solid phase containing iron phosphate and aluminum phosphate obtained in this step contained: iron 14.37% (mass percentage), lithium 0.17 ppm, sodium 2427.43 ppm, magnesium 2.98 ppm, aluminum 67.24 ppm, potassium 5.59 ppm, calcium 39.50 ppm, phosphorus 87200 ppm, titanium 285.64 ppm, vanadium 15.86 ppm, chromium 6.89 ppm, manganese 0.38 ppm, cobalt 0.06 ppm, nickel 0.13 ppm, copper 0.17 ppm, zinc 0.87 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0066] Step S40: Dissolve 150g of the solid phase containing ferric phosphate and aluminum phosphate obtained in step S30 in 200g of sulfuric acid solution with a mass percentage concentration of 20% until the solid phase containing ferric phosphate is completely dissolved; add 12.3g of 3N grade iron powder to reduce ferric iron to ferrous iron. After adding the 3N grade iron powder, stir the reaction at 50℃ for 2.5h. After filtration, obtain 361.1g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 9.29% (mass percentage), lithium 0.03 ppm, sodium 1347.79 ppm, magnesium 1.2 ppm, aluminum 42.01 ppm, potassium 2.74 ppm, calcium 14.47 ppm, phosphorus 41800 ppm, titanium 134.01 ppm, vanadium 7.20 ppm, chromium 4.13 ppm, manganese 0.06 ppm, cobalt 0.01 ppm, nickel 0.05 ppm, copper 0.04 ppm, zinc 0.35 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0067] Step S50: The pH of the 300g liquid phase containing ferrous sulfate obtained in step S40 is adjusted to 0.5 using sulfuric acid with a mass percentage concentration of 98%; then 480g of ethanol is added to the liquid phase containing ferrous sulfate. The ethanol can be added dropwise. After the ethanol is added, the mixture is stirred continuously at room temperature until no precipitate is formed, then filtered. The mixture is then washed with ethanol at a solid-liquid mass ratio of 1:1 to obtain 158.3g of crude ferrous sulfate crystals. Analysis revealed that the crude ferrous sulfate crystals obtained in this step contained: 17.48% (mass percentage) iron, 0.00 ppm lithium, 120.86 ppm sodium, 1.93 ppm magnesium, 68.14 ppm aluminum, 3.24 ppm potassium, 8.39 ppm calcium, 1300 ppm phosphorus, 193.36 ppm titanium, 8.04 ppm vanadium, 6.53 ppm chromium, 0.24 ppm manganese, 0.67 ppm cobalt, 0.28 ppm nickel, 0.10 ppm copper, 0.67 ppm zinc, 0.01 ppm cadmium, and 0.00 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0068] Step S60: Dissolve 100g of crude ferrous sulfate crystals in 200g of water. Under nitrogen protection, adjust the pH to 6 with a 40% sodium hydroxide solution. Stir the reaction at room temperature for 30min until no more precipitate is formed. Then filter to obtain 308.5g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 5.62% (mass percentage), lithium 0.00 ppm, sodium 3564.53 ppm, magnesium 0.79 ppm, aluminum 0.22 ppm, potassium 2.08 ppm, calcium 3.65 ppm, phosphorus 0.00 ppm, titanium 0.17 ppm, vanadium 0.03 ppm, chromium 0.02 ppm, manganese 0.06 ppm, cobalt 0.02 ppm, nickel 0.09 ppm, copper 0.01 ppm, zinc 0.04 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0069] Step S70: Adjust the pH of the ferrous sulfate-containing liquid phase obtained in step S60 to 0.5, and then perform a final impurity removal treatment. The final impurity removal treatment involves two impurity removal operations, namely, alcohol precipitation and evaporation concentration followed by cooling crystallization in sequence; wherein: The alcohol precipitation for impurity removal specifically involves adding 120g of ethanol to 300g of liquid phase containing ferrous sulfate. After the ethanol is added, the mixture is stirred continuously at room temperature until no precipitate is formed, followed by solid-liquid separation to obtain 95.2g of solid phase containing ferrous sulfate, with an iron content of 17.71% by mass. The evaporation, concentration, cooling, crystallization and impurity removal process is as follows: 95.2g of solid phase containing ferrous sulfate is dissolved in 238g of water at a solid-liquid ratio of 1:2.5 to obtain a liquid phase containing ferrous sulfate. The liquid phase is evaporated and concentrated until the mass percentage of iron is 10%. Then, the temperature is lowered to 3℃ for cooling and crystallization until no precipitate is formed. Finally, solid-liquid separation is performed to obtain a solid phase containing ferrous sulfate. The solid phase containing ferrous sulfate obtained after final impurity removal was dried under reduced pressure at 80℃ to obtain 74.61g of ferrous sulfate heptahydrate (FeSO4·7H2O).

[0070] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was determined by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.50 ppm, magnesium 2.68 ppm, aluminum 0.00 ppm, potassium 0.00 ppm, calcium 4.00 ppm, phosphorus 0.00 ppm, titanium 0.32 ppm, vanadium 0.00 ppm, chromium 0.02 ppm, manganese 0.10 ppm, cobalt 0.03 ppm, nickel 0.06 ppm, copper 0.01 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) is determined by the formula: 1 - total impurities (1). The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9987% (based on FeSO4·7H2O). The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated using formula (1) in Examples 2-20 and Comparative Examples 1-2 described below.

[0071] Meanwhile, the total iron yield was calculated by multiplying the iron yields of each step: 85.73%.

[0072] Example 2: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed twice, namely, evaporation concentration, cooling crystallization for impurity removal and alcohol precipitation for impurity removal in sequence. The rest was the same as in Example 1, and 73.18 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0073] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 17.52 ppm, magnesium 4.20 ppm, aluminum 0.73 ppm, potassium 0.63 ppm, calcium 2.79 ppm, phosphorus 0.00 ppm, titanium 0.42 ppm, vanadium 0.00 ppm, chromium 0.03 ppm, manganese 0.11 ppm, cobalt 0.03 ppm, nickel 0.05 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9973% using formula (1). The total iron yield was calculated to be 84.09% by multiplying the iron yields of each step.

[0074] Example 3: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as alcohol precipitation impurity removal, alcohol precipitation impurity removal, and evaporation, concentration, cooling and crystallization impurity removal. The rest was the same as in Example 1, and 72.26 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0075] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.24 ppm, magnesium 1.22 ppm, aluminum 0.00 ppm, potassium 0.03 ppm, calcium 1.92 ppm, phosphorus 0.00 ppm, titanium 0.02 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 0.03 ppm, cobalt 0.01 ppm, nickel 0.02 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9991% using formula (1). Meanwhile, the total iron yield was calculated by multiplying the iron yields of each step: 83.03%.

[0076] Example 4: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as alcohol precipitation impurity removal, evaporation concentration cooling crystallization impurity removal, and alcohol precipitation impurity removal. The rest was the same as in Example 1, and 74.52 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0077] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 6.01 ppm, magnesium 2.51 ppm, aluminum 0.93 ppm, potassium 0.98 ppm, calcium 2.41 ppm, phosphorus 0.00 ppm, titanium 0.12 ppm, vanadium 0.00 ppm, chromium 0.00 ppm, manganese 0.5 ppm, cobalt 0.02 ppm, nickel 0.01 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9986% using formula (1). The total iron yield was calculated to be 85.63% by multiplying the iron yields of each step.

[0078] Example 5: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as follows: evaporation concentration, cooling crystallization impurity removal, alcohol precipitation impurity removal, and alcohol precipitation impurity removal. The rest was the same as in Example 1, and 74.10 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0079] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 6.01 ppm, magnesium 2.51 ppm, aluminum 0.93 ppm, potassium 0.98 ppm, calcium 2.41 ppm, phosphorus 0.00 ppm, titanium 0.12 ppm, vanadium 0.00 ppm, chromium 0.00 ppm, manganese 0.05 ppm, cobalt 0.02 ppm, nickel 0.01 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9987% using formula (1). The total iron yield was calculated to be 85.15% by multiplying the iron yields of each step.

[0080] Example 6: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as follows: evaporation concentration cooling crystallization impurity removal, evaporation concentration cooling crystallization impurity removal, and alcohol precipitation impurity removal. The rest was the same as in Example 1, and 73.35 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0081] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 14.35 ppm, magnesium 3.87 ppm, aluminum 0.28 ppm, potassium 0.07 ppm, calcium 3.86 ppm, phosphorus 0.00 ppm, titanium 0.18 ppm, vanadium 0.00 ppm, chromium 0.03 ppm, manganese 0.04 ppm, cobalt 0.00 ppm, nickel 0.03 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9977% using formula (1). The total iron yield was calculated to be 84.28% by multiplying the iron yields of each step.

[0082] Example 7: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as follows: evaporation concentration, cooling and crystallization impurity removal, alcohol precipitation impurity removal, and evaporation concentration, cooling and crystallization impurity removal. The rest was the same as in Example 1, and 72.93 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0083] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 8.37 ppm, magnesium 1.84 ppm, aluminum 0.41 ppm, potassium 0.74 ppm, calcium 2.16 ppm, phosphorus 0.00 ppm, titanium 0.17 ppm, vanadium 0.00 ppm, chromium 0.02 ppm, manganese 0.03 ppm, cobalt 0.07 ppm, nickel 0.04 ppm, copper 0.01 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9986% using formula (1). The total iron yield was calculated to be 83.80% by multiplying the iron yields of each step.

[0084] Example 8: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process is performed in three impurity removal operations, which are carried out in sequence as alcohol precipitation, evaporation concentration and cooling crystallization, and evaporation concentration and cooling crystallization. The rest was the same as in Example 1, and 70.24 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0085] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 7.44 ppm, magnesium 2.74 ppm, aluminum 0.86 ppm, potassium 1.25 ppm, calcium 2.68 ppm, phosphorus 0.00 ppm, titanium 0.04 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 0.04 ppm, cobalt 0.02 ppm, nickel 0.05 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9984% using formula (1). The total iron yield was calculated to be 80.71% by multiplying the iron yields of each step.

[0086] Example 9: The difference between this embodiment and embodiment 1 is that in step S70, the final impurity removal process performs two impurity removal operations, both of which are alcohol precipitation for impurity removal. The rest was the same as in Example 1, and 80.4 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0087] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 11.47 ppm, magnesium 2.07 ppm, aluminum 1.02 ppm, potassium 1.41 ppm, calcium 3.54 ppm, phosphorus 0.00 ppm, titanium 0.47 ppm, vanadium 0.01 ppm, chromium 0.04 ppm, manganese 0.03 ppm, cobalt 0.01 ppm, nickel 0.01 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9979% using formula (1). The total iron yield was calculated to be 92.38% by multiplying the iron yields of each step.

[0088] Example 10: The difference between this embodiment and Example 1 is that in step S50, the alcohol solvent used for alcohol precipitation and washing is n-propanol; in this step, 159.1g of crude ferrous sulfate crystals are obtained. The crude ferrous sulfate crystals obtained in step S50 were found to contain: 17.74% (mass percentage concentration) iron, 0.00 ppm lithium, 127.58 ppm sodium, 2.14 ppm magnesium, 76.36 ppm aluminum, 3.85 ppm potassium, 8.49 ppm calcium, 1300 ppm phosphorus, 179.35 ppm titanium, 8.55 ppm vanadium, 6.28 ppm chromium, 0.49 ppm manganese, 0.36 ppm cobalt, 0.38 ppm nickel, 0.04 ppm copper, 0.18 ppm zinc, 0.00 ppm cadmium, and 0.01 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were determined by ICP-MS (inductively coupled plasma mass spectrometry).

[0089] In step S70, the alcohol solvent used for alcohol precipitation is n-propanol; The rest was the same as in Example 1, and 73.59 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0090] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 8.41 ppm, magnesium 1.62 ppm, aluminum 0.46 ppm, potassium 0.96 ppm, calcium 2.84 ppm, phosphorus 0.00 ppm, titanium 0.14 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 0.02 ppm, cobalt 0.03 ppm, nickel 0.02 ppm, copper 0.01 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9985% using formula (1). The total iron yield, calculated by multiplying the iron yields of each step, was 84.56%.

[0091] Example 11: The difference between this embodiment and Example 1 is that in step S50, isopropanol is used as the alcohol solvent for both alcohol precipitation and washing; in this step, 158.8g of crude ferrous sulfate crystals are obtained. Analysis revealed that the crude ferrous sulfate crystals obtained in step S50 contained: 17.49% iron, 0.00 ppm lithium (mass percentage concentration), 118.86 ppm sodium, 2.08 ppm magnesium, 76.35 ppm aluminum, 3.36 ppm potassium, 8.57 ppm calcium, 1100 ppm phosphorus, 185.25 ppm titanium, 8.47 ppm vanadium, 6.14 ppm chromium, 0.58 ppm manganese, 0.24 ppm cobalt, 0.25 ppm nickel, 0.08 ppm copper, 0.14 ppm zinc, 0.00 ppm cadmium, and 0.00 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0092] In step S70, isopropanol is used as the alcohol solvent for alcohol precipitation. The rest was the same as in Example 1, and 72.67 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0093] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.26 ppm, magnesium 0.95 ppm, aluminum 0.58 ppm, potassium 0.91 ppm, calcium 2.48 ppm, phosphorus 0.00 ppm, titanium 0.09 ppm, vanadium 0.00 ppm, chromium 0.02 ppm, manganese 0.05 ppm, cobalt 0.02 ppm, nickel 0.02 ppm, copper 0.01 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9989% using formula (1). The total iron yield was calculated to be 83.50% by multiplying the iron yields of each step.

[0094] Example 12: The difference between this embodiment and Embodiment 1 is that in step S50, the alcohol solvent used for alcohol precipitation and washing is a mixed solvent of n-propanol and isopropanol in a volume ratio of 1:2; in this step, 159.4g of crude ferrous sulfate crystals are obtained. The crude ferrous sulfate crystals obtained in step S50 were found to contain: 17.67% (mass percentage concentration) iron, 0.00 ppm lithium, 138.69 ppm sodium, 3.32 ppm magnesium, 82.36 ppm aluminum, 5.52 ppm potassium, 12.29 ppm calcium, 1200 ppm phosphorus, 195.25 ppm titanium, 6.57 ppm vanadium, 6.05 ppm chromium, 0.68 ppm manganese, 0.39 ppm cobalt, 0.52 ppm nickel, 0.04 ppm copper, 0.25 ppm zinc, 0.00 ppm cadmium, and 0.02 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were determined by ICP-MS (inductively coupled plasma mass spectrometry).

[0095] In step S70, the alcohol solvent used for alcohol precipitation is a mixed solvent of n-propanol and isopropanol in a volume ratio of 1:2. The rest was the same as in Example 1, and 73.84 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0096] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 10.85 ppm, magnesium 1.69 ppm, aluminum 0.77 ppm, potassium 0.26 ppm, calcium 4.31 ppm, phosphorus 0.00 ppm, titanium 0.14 ppm, vanadium 0.00 ppm, chromium 0.06 ppm, manganese 0.09 ppm, cobalt 0.00 ppm, nickel 0.00 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9981% using formula (1). The total iron yield was calculated to be 84.85% by multiplying the iron yields of each step.

[0097] Example 13: The difference between this embodiment and Embodiment 1 is that in step S50, the alcohol solvent used for alcohol precipitation and washing is a mixed solvent of ethanol and isopropanol in a volume ratio of 3:5; in this step, 159.3g of crude ferrous sulfate crystals are obtained. Analysis revealed that the crude ferrous sulfate crystals obtained in step S50 contained: 17.52% (mass percentage concentration) iron, 0.00 ppm lithium, 51.22 ppm sodium, 6.24 ppm magnesium, 86.55 ppm aluminum, 2.56 ppm potassium, 6.11 ppm calcium, 900 ppm phosphorus, 177.02 ppm titanium, 8.64 ppm vanadium, 5.50 ppm chromium, 0.49 ppm manganese, 0.28 ppm cobalt, 0.20 ppm nickel, 0.09 ppm copper, 0.21 ppm zinc, 0.00 ppm cadmium, and 0.00 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0098] In step S70, the alcohol solvent used for alcohol precipitation is a mixed solvent of isopropanol, ethanol and isopropanol mixed in a volume ratio of 3:5. The rest was the same as in Example 1, and 73.51 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0099] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 8.26 ppm, magnesium 2.59 ppm, aluminum 0.74 ppm, potassium 0.28 ppm, calcium 4.36 ppm, phosphorus 0.00 ppm, titanium 0.16 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 0.03 ppm, cobalt 0.02 ppm, nickel 0.02 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9983% using formula (1). The total iron yield was calculated to be 84.47% by multiplying the iron yields of each step.

[0100] Example 14: The difference between this embodiment and Embodiment 1 is that in step S50, the alcohol solvent used for alcohol precipitation and washing is a mixed solvent of ethanol, n-propanol and isopropanol in a volume ratio of 1:1:1; in this step, 158.5g of crude ferrous sulfate crystals are obtained. The crude ferrous sulfate crystals obtained in step S50 were found to contain: 17.47% (mass percentage concentration) iron, 0.00 ppm lithium, 51.22 ppm sodium, 6.24 ppm magnesium, 86.55 ppm aluminum, 2.56 ppm potassium, 6.11 ppm calcium, 900 ppm phosphorus, 177.02 ppm titanium, 8.64 ppm vanadium, 5.50 ppm chromium, 0.49 ppm manganese, 0.28 ppm cobalt, 0.20 ppm nickel, 0.09 ppm copper, 0.21 ppm zinc, 0.00 ppm cadmium, and 0.00 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were determined by ICP-MS (inductively coupled plasma mass spectrometry).

[0101] In step S70, the alcohol solvent used for alcohol precipitation is a mixed solvent of ethanol, n-propanol and isopropanol in a volume ratio of 1:1:1. The rest was the same as in Example 1, and 73.34 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0102] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.69 ppm, magnesium 2.25 ppm, aluminum 0.33 ppm, potassium 0.51 ppm, calcium 2.71 ppm, phosphorus 0.00 ppm, titanium 0.18 ppm, vanadium 0.00 ppm, chromium 0.04 ppm, manganese 0.08 ppm, cobalt 0.08 ppm, nickel 0.06 ppm, copper 0.02 ppm, zinc 0.00 ppm, cadmium 0.01 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9988% using formula (1). The total iron yield was calculated to be 84.27% by multiplying the iron yields of each step.

[0103] Example 15: The difference between this embodiment and Embodiment 1 is that: In step S10, the iron-containing waste material is: sulfuric acid residue, 100g; In step S20, the phosphorus source is sodium orthophosphate, 158g; the oxidant is ozone. In step S40, hydrogen sulfide is used as the reducing agent; The rest was the same as in Example 1, and 72.41 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0104] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 11.50 ppm, magnesium 1.99 ppm, aluminum 0.02 ppm, potassium 0.82 ppm, calcium 2.11 ppm, phosphorus 0.00 ppm, titanium 0.16 ppm, vanadium 0.00 ppm, chromium 0.07 ppm, manganese 0.11 ppm, cobalt 0.03 ppm, nickel 0.06 ppm, copper 0.02 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9983% using formula (1). The total iron yield was calculated to be 83.21% by multiplying the iron yields of each step.

[0105] Example 16: The difference between this embodiment and Embodiment 1 is that: In step S10, the iron-containing waste material is: phosphorus-iron slag, 100g; In step S20, the phosphorus source is monoammonium phosphate, 66.1 g; the oxidant is sodium persulfate, 416.4 g. In step S40, the reducing agent is sodium sulfite, 27.7g. The rest was the same as in Example 1, and 73.34 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0106] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 10.85 ppm, magnesium 1.69 ppm, aluminum 0.77 ppm, potassium 0.26 ppm, calcium 4.31 ppm, phosphorus 0.00 ppm, titanium 0.14 ppm, vanadium 0.00 ppm, chromium 0.06 ppm, manganese 0.09 ppm, cobalt 0.00 ppm, nickel 0.06 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9981% using formula (1). The total iron yield was calculated to be 84.27% by multiplying the iron yields of each step.

[0107] Example 17: The difference between this embodiment and Embodiment 1 is that: In step S10, the iron-containing waste is titanium dioxide residue, 500g. In step S20, the phosphorus source is monoammonium phosphate, 183.5 g; The rest was the same as in Example 1, and 73.76 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0108] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 6.85 ppm, magnesium 1.95 ppm, aluminum 0.74 ppm, potassium 0.36 ppm, calcium 4.32 ppm, phosphorus 0.00 ppm, titanium 0.21 ppm, vanadium 0.00 ppm, chromium 0.06 ppm, manganese 0.08 ppm, cobalt 0.04 ppm, nickel 0.02 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9985% using formula (1). The total iron yield was calculated to be 84.76% by multiplying the iron yields of each step.

[0109] Example 18: The difference between this embodiment and Embodiment 1 is that: In step S10, the iron-containing waste material is copper smelting slag, 200g. In step S20, the phosphorus source is ammonium orthophosphate, 185g. The rest was the same as in Example 1, and 74.1 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0110] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.11 ppm, magnesium 0.98 ppm, aluminum 0.77 ppm, potassium 0.26 ppm, calcium 4.27 ppm, phosphorus 0.00 ppm, titanium 0.19 ppm, vanadium 0.00 ppm, chromium 0.05 ppm, manganese 0.09 ppm, cobalt 0.03 ppm, nickel 0.03 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9988% using formula (1). The total iron yield was calculated to be 85.14% by multiplying the iron yields of each step.

[0111] Example 19: This application provides a method for preparing ferrous sulfate from iron-containing waste, comprising the following steps: Step S10: Dissolve 100g of lithium iron phosphate battery black powder in 400g of sulfuric acid solution with a mass percentage concentration of 20% to obtain an iron source solution; control the mass percentage content of iron in the final iron source solution to be 6%.

[0112] Step S20: The iron source solution is heated to 40°C, and 37.6g of sodium ferrate is added to the first mixed solution; the pH is adjusted to 2.5 using a 10% sodium carbonate solution to generate a precipitate containing iron phosphate and aluminum phosphate. The mixture is stirred at 40°C for 60 minutes until no more precipitate is generated. After filtration and washing, 214.5g of solid phase containing iron phosphate and aluminum phosphate is obtained. Analysis revealed that the solid phase containing iron phosphate and aluminum phosphate obtained in this step contained: iron 14.69% (mass percentage), lithium 37.27 ppm, sodium 2861.24 ppm, magnesium 4.98 ppm, aluminum 1528.64 ppm, potassium 48.26 ppm, calcium 38.26 ppm, phosphorus 86900 ppm, titanium 483.12 ppm, vanadium 27.25 ppm, chromium 49.69 ppm, manganese 15.87 ppm, cobalt 13.57 ppm, nickel 18.62 ppm, copper 5.99 ppm, zinc 0.54 ppm, cadmium 0.05 ppm, and lead 4.58 ppm. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0113] Step S30: Dissolve 214.5g of the solid phase containing ferric phosphate and aluminum phosphate obtained in step S20 in 622g of a 10% sulfuric acid solution until all the ferric phosphate solid phase is dissolved. Then filter to remove insoluble matter. Heat to 40℃ and adjust the pH to 2.5 with a 10% sodium carbonate solution to generate a precipitate containing ferric phosphate and aluminum phosphate. Stir the reaction at 40℃ for 60min until no more precipitate is generated. After filtration and washing, 214.0g of the solid phase containing ferric phosphate and aluminum phosphate is obtained. Analysis revealed that the solid phase containing iron phosphate and aluminum phosphate obtained in this step contained: iron 14.38% (mass percentage), lithium 20.21 ppm, sodium 2427.43 ppm, magnesium 2.98 ppm, aluminum 264.59 ppm, potassium 19.18 ppm, calcium 37.36 ppm, phosphorus 85900 ppm, titanium 285.64 ppm, vanadium 2.23 ppm, chromium 24.39 ppm, manganese 0.38 ppm, cobalt 0.06 ppm, nickel 0.13 ppm, copper 0.17 ppm, zinc 0.87 ppm, cadmium 0.01 ppm, and lead 2.38 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0114] Step S40: Dissolve 150g of the solid phase containing ferric phosphate and aluminum phosphate obtained in step S30 in 720g of sulfuric acid solution with a mass percentage concentration of 10%; add 30.4g of sodium thiosulfate to reduce ferric iron to ferrous iron. After adding sodium thiosulfate, raise the temperature to 40℃ and stir the reaction at 40℃ for 3h. After filtration, obtain 867.9g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 2.47% (mass percentage), lithium 5.62 ppm, sodium 1347.79 ppm, magnesium 1.20 ppm, aluminum 138.28 ppm, potassium 16.21 ppm, calcium 8.99 ppm, phosphorus 86700 ppm, titanium 147.84 ppm, vanadium 1.19 ppm, chromium 13.32 ppm, manganese 0.22 ppm, cobalt 0.29 ppm, nickel 0.19 ppm, copper 0.23 ppm, zinc 0.17 ppm, cadmium 0.01 ppm, and lead 0.18 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0115] Step S50: The pH of 800g of the ferrous sulfate-containing liquid phase obtained in step S40 is adjusted to 0 using sulfuric acid with a mass percentage concentration of 50%; then 960g of alcohol solvent is added to the ferrous sulfate-containing liquid phase. The alcohol solvent is a mixed solution of ethanol and n-propanol in a volume ratio of 1:1. The alcohol solvent can be added dropwise. After the alcohol solvent is added, the mixture is stirred continuously at room temperature until no precipitate is formed, then filtered. The mixture is then washed with alcohol solvent, which is a mixed solution of ethanol and n-propanol in a volume ratio of 1:1. The solid-liquid mass ratio during washing is 1:1.2, yielding 106.7g of crude ferrous sulfate crystals. Analysis revealed that the crude ferrous sulfate crystals obtained in this step contained: 18.41% (mass percentage) iron, 0.41 ppm lithium, 120.86 ppm sodium, 4.93 ppm magnesium, 12.12 ppm aluminum, 4.86 ppm potassium, 24.86 ppm calcium, 1300 ppm phosphorus, 17.92 ppm titanium, 0.09 ppm vanadium, 1.00 ppm chromium, 0.24 ppm manganese, 0.67 ppm cobalt, 0.28 ppm nickel, 0.38 ppm copper, 0.19 ppm zinc, 0.01 ppm cadmium, and 0.12 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0116] Step S60: Dissolve 100g of crude ferrous sulfate crystals in 300g of water. Under nitrogen protection, adjust the pH to 7 with a 10% sodium carbonate solution. Stir the reaction at room temperature for 15min until no more precipitate is formed. Then filter to obtain 410.2g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 4.41% (mass percentage), lithium 0.07 ppm, sodium 3618.28 ppm, magnesium 0.64 ppm, aluminum 0.31 ppm, potassium 1.96 ppm, calcium 4.08 ppm, phosphorus 0.00 ppm, titanium 0.12 ppm, vanadium 0.02 ppm, chromium 0.01 ppm, manganese 0.07 ppm, cobalt 0.01 ppm, nickel 0.06 ppm, copper 0.00 ppm, zinc 0.02 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0117] Step S70: Adjust the pH of the ferrous sulfate-containing liquid phase obtained in step S60 to 1, and then perform a final impurity removal treatment. The final impurity removal treatment involves two impurity removal operations, namely, alcohol precipitation and evaporation concentration followed by cooling crystallization in sequence; wherein: The alcohol precipitation and impurity removal process specifically involves adding 150g of alcohol solvent to 300g of liquid phase containing ferrous sulfate. The alcohol solvent is a mixed solution of ethanol and n-propanol in a volume ratio of 1:1. After the alcohol solvent is added, the mixture is stirred continuously at room temperature until no precipitate is formed, and then solid-liquid separation is performed to obtain a solid phase containing ferrous sulfate 93.5 (iron mass percentage content is 14.12%). The specific steps of evaporation, concentration, cooling, crystallization, and impurity removal are as follows: 93.5g of a solid phase containing ferrous sulfate is dissolved in 300g of water to obtain a liquid phase containing ferrous sulfate. This liquid phase is evaporated and concentrated until the iron content is 10% by mass. Then, it is cooled to 0℃ for cooling and crystallization until no precipitate is formed. Finally, solid-liquid separation is performed to obtain a solid phase containing ferrous sulfate. The solid phase containing ferrous sulfate obtained after final impurity removal was dried under reduced pressure at 80℃ to obtain 57.54 g of ferrous sulfate heptahydrate (FeSO4·7H2O).

[0118] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 5.64 ppm, magnesium 0.62 ppm, aluminum 0.41 ppm, potassium 0.18 ppm, calcium 3.36 ppm, phosphorus 0.00 ppm, titanium 0.14 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 0.03 ppm, cobalt 0.03 ppm, nickel 0.02 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9989% using formula (1). The total iron yield was calculated to be 82.83% by multiplying the iron yields of each step.

[0119] Example 20: This application provides a method for preparing ferrous sulfate from iron-containing waste, comprising the following steps: Step S10: Dissolve 30g of lithium extraction slag, 30g of phosphorus iron slag and 40g of sulfuric acid slag in 200g of sulfuric acid solution with a mass percentage concentration of 40%, dilute with water, and control the mass percentage content of iron in the final iron source solution to be 5% to obtain the iron source solution.

[0120] Step S20: 65.3g of monoammonium phosphate is added to the iron source solution to form a first mixed solution; the first mixed solution is heated to 60°C, and high-purity oxygen is added to the first mixed solution to oxidize ferrous iron to ferric iron; wherein, the amount of high-purity oxygen added is 1.0 times the theoretical molar amount, based on the oxidation of all ferrous iron to ferric iron; the temperature is raised to 60°C, and the pH is adjusted to 1.7 with ammonia water with a mass percentage concentration of 25%, generating a precipitate containing ferric phosphate and aluminum phosphate; the reaction is stirred at 60°C for 15 minutes, and no more precipitate is generated; after centrifugation and washing, a solid phase containing ferric phosphate and aluminum phosphate is obtained. Analysis revealed that the solid phase containing iron phosphate and aluminum phosphate obtained in this step contained: iron 14.47% (mass percentage), lithium 28.69 ppm, sodium 62.47 ppm, magnesium 4.94 ppm, aluminum 1547.69 ppm, potassium 47.58 ppm, calcium 39.44 ppm, phosphorus 87100 ppm, titanium 483.12 ppm, vanadium 27.25 ppm, chromium 49.69 ppm, manganese 15.87 ppm, cobalt 13.57 ppm, nickel 18.62 ppm, copper 5.99 ppm, zinc 0.54 ppm, cadmium 0.05 ppm, and lead 4.58 ppm. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0121] Step S30: Dissolve 200g of the solid phase containing ferric phosphate and aluminum phosphate obtained in step S20 in 200g of sulfuric acid solution with a mass percentage concentration of 30% until all the solid phase containing ferric phosphate is dissolved. Then filter to remove insoluble matter. Heat to 60℃ and adjust the pH to 1.7 with ammonia solution with a mass percentage concentration of 25% to generate a precipitate containing ferric phosphate and aluminum phosphate. Stir the reaction at 60℃ for 15min until no more precipitate is generated. After filtration and washing, 195.3g of solid phase containing ferric phosphate and aluminum phosphate is obtained. Analysis revealed that the solid phase containing iron phosphate and aluminum phosphate obtained in this step contained: 14.62% (mass percentage), lithium 13.73 ppm, sodium 38.01 ppm, magnesium 2.89 ppm, aluminum 258.78 ppm, potassium 20.47 ppm, calcium 34.42 ppm, phosphorus 86300 ppm, titanium 287.58 ppm, vanadium 2.41 ppm, chromium 24.96 ppm, manganese 0.47 ppm, cobalt 0.07 ppm, nickel 0.12 ppm, copper 0.18 ppm, zinc 0.69 ppm, cadmium 0.00 ppm, and lead 1.86 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0122] Step S40: Dissolve 150g of the solid phase containing ferric phosphate and aluminum phosphate obtained in step S30 in 150g of sulfuric acid solution with a mass percentage concentration of 30% until the solid phase containing ferric phosphate is completely dissolved; add sodium sulfite to reduce ferric iron to ferrous iron. After adding sodium sulfite, raise the temperature to 60℃ and stir the reaction at 60℃ for 1.5h. After centrifugation, obtain 301.5g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 7.26% (mass percentage), lithium 5.62 ppm, sodium 47.25 ppm, magnesium 1.51 ppm, aluminum 136.88 ppm, potassium 11.68 ppm, calcium 8.78 ppm, phosphorus 84300 ppm, titanium 155.36 ppm, vanadium 1.24 ppm, chromium 14.15 ppm, manganese 0.17 ppm, cobalt 0.24 ppm, nickel 0.14 ppm, copper 0.24 ppm, zinc 0.19 ppm, cadmium 0.00 ppm, and lead 0.08 ppm. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0123] Step S50: The pH of 300g of the ferrous sulfate-containing liquid phase obtained in step S40 is adjusted to 1 using sulfuric acid with a mass percentage concentration of 98%; then 540g of ethanol is added to the ferrous sulfate-containing liquid phase. The ethanol can be added dropwise. After the ethanol is added, the mixture is stirred continuously at room temperature until no precipitate is formed, then filtered. The mixture is then washed with ethanol at a solid-liquid mass ratio of 1:0.8 to obtain 116.3g of crude ferrous sulfate crystals. Analysis revealed that the crude ferrous sulfate crystals obtained in this step contained: 18.66% (mass percentage) iron, 0.27 ppm lithium, 12.66 ppm sodium, 4.57 ppm magnesium, 12.01 ppm aluminum, 5.58 ppm potassium, 20.16 ppm calcium, 1100 ppm phosphorus, 18.22 ppm titanium, 0.07 ppm vanadium, 1.52 ppm chromium, 0.13 ppm manganese, 0.37 ppm cobalt, 0.24 ppm nickel, 0.15 ppm copper, 0.14 ppm zinc, 0.01 ppm cadmium, and 0.11 ppm lead. Iron was determined by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0124] Step S60: Dissolve 100g of crude ferrous sulfate crystals in 250g of water. Under nitrogen protection, adjust the pH to 5 with 25% ammonia solution. Heat to 60℃ and stir at 60℃ for 15min until no more precipitate is formed. Then centrifuge to obtain 349.7g of liquid phase containing ferrous sulfate. Analysis revealed that the ferrous sulfate-containing liquid phase obtained in this step contained: iron 5.32% (mass percentage), lithium 0.27 ppm, sodium 12.66 ppm, magnesium 4.57 ppm, aluminum 12.01 ppm, potassium 5.58 ppm, calcium 20.16 ppm, phosphorus 1100 ppm, titanium 18.22 ppm, vanadium 0.07 ppm, chromium 1.52 ppm, manganese 0.13 ppm, cobalt 0.37 ppm, nickel 0.24 ppm, copper 0.15 ppm, zinc 0.14 ppm, cadmium 0.01 ppm, and lead 0.11 ppm. Iron was detected by potassium dichromate titration, while the other elements were detected by ICP-MS (inductively coupled plasma mass spectrometry).

[0125] Step S70: Adjust the pH of the ferrous sulfate-containing liquid phase obtained in step S60 to 1.5, and then perform a final impurity removal treatment. The final impurity removal treatment involves two impurity removal operations, namely, alcohol precipitation and evaporation concentration followed by cooling crystallization. The alcohol precipitation and impurity removal process is as follows: 150g of ethanol is added to 300g of liquid phase containing ferrous sulfate. After the ethanol is added, the mixture is stirred continuously at room temperature until no precipitate is formed, and then solid-liquid separation is performed to obtain 111.8g of solid phase containing ferrous sulfate (iron content is 14.25% by mass). The evaporation, concentration, cooling, crystallization, and impurity removal process is as follows: 111.8g of a solid phase containing ferrous sulfate is dissolved in 279.5g of water to obtain a liquid phase containing ferrous sulfate. This liquid phase is evaporated and concentrated until the iron content is 12% by mass. Then, it is cooled to 5℃ for cooling and crystallization until no precipitate is formed. Finally, solid-liquid separation is performed to obtain a solid phase containing ferrous sulfate. The solid phase containing ferrous sulfate obtained after final impurity removal was dried under reduced pressure at 80℃ to obtain 68.2g of ferrous sulfate heptahydrate (FeSO4·7H2O).

[0126] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 2.04 ppm, magnesium 0.18 ppm, aluminum 0.24 ppm, potassium 1.16 ppm, calcium 3.57 ppm, phosphorus 0.00 ppm, titanium 0.04 ppm, vanadium 0.00 ppm, chromium 0.00 ppm, manganese 0.02 ppm, cobalt 0.01 ppm, nickel 0.02 ppm, copper 0.00 ppm, zinc 0.00 ppm, cadmium 0.00 ppm, and lead 0.00 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 97.9992% using formula (1). The total iron yield was calculated to be 83.98% by multiplying the iron yields of each step.

[0127] III. Comparative Example Comparative Example 1: The difference between this comparative example and Example 1 is that step S30 is omitted. The procedure was the same as in Example 1, and 74.18 g of ferrous sulfate heptahydrate (FeSO4·7H2O) was obtained.

[0128] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 37.98 ppm, magnesium 1.34 ppm, aluminum 2.77 ppm, potassium 10.14 ppm, calcium 20.99 ppm, phosphorus 0.00 ppm, titanium 0.03 ppm, vanadium 0.00 ppm, chromium 0.01 ppm, manganese 10.55 ppm, cobalt 10.8 ppm, nickel 12.29 ppm, copper 0.08 ppm, zinc 0.08 ppm, cadmium 0.00 ppm, and lead 0.04 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9892% using formula (1). The total iron yield was calculated to be 85.24% by multiplying the iron yields of each step.

[0129] Comparative Example 2: The difference between this comparative example and Example 1 is that in step S70, alcohol precipitation to remove impurities is replaced by evaporation, concentration, cooling, and crystallization to remove impurities. The procedure was the same as in Example 1, yielding 64.44 g of ferrous sulfate heptahydrate (FeSO4·7H2O).

[0130] The impurity content in ferrous sulfate heptahydrate (FeSO4·7H2O) was detected by ICP-MS (inductively coupled plasma mass spectrometry). The impurity ions were: lithium 0.00 ppm, sodium 208.79 ppm, magnesium 0.79 ppm, aluminum 1.91 ppm, potassium 0.96 ppm, calcium 5.51 ppm, phosphorus 0.00 ppm, titanium 0.07 ppm, vanadium 0.00 ppm, chromium 0.02 ppm, manganese 0.04 ppm, cobalt 0.01 ppm, nickel 0.01 ppm, copper 0.00 ppm, zinc 0.01 ppm, cadmium 0.00 ppm, and lead 0.01 ppm. The purity of ferrous sulfate heptahydrate (FeSO4·7H2O) was calculated to be 99.9781% using formula (1). The total iron yield was calculated to be 74.05% by multiplying the iron yields of each step.

[0131] Based on the data from Example 1, Comparative Example 1, and Comparative Example 2: In Example 1: Step S30 achieves deep pre-retention of heavy metals, and this step, in conjunction with step S20, achieves total removal rates of 99.93%, 99.85%, and 99.77% for cobalt, nickel, and manganese, respectively. Iron is lost only slightly during this process, achieving a synergistic balance between impurity removal and yield retention. In step S70, alkali metals are refined through alcohol precipitation and crystallization. This step, along with step S50, also forms a staged synergistic process for sodium removal. Step S50 performs coarse sodium removal (reducing sodium from 1347.79 ppm to 120.86 ppm), and S70 further reduces sodium to 5.50 ppm through final impurity removal (secondary alcohol precipitation), forming a staged synergy of coarse and fine removal. Simultaneously, ferrous sulfate is directionally enriched during alcohol precipitation, avoiding iron loss during crystallization and achieving a synergistic effect between impurity removal and yield retention. In summary, Embodiment 1 of this application achieves high yield, high purity, and low impurities through synergistic impurity removal in each step, possessing industrial application value and promising prospects for industrial application.

[0132] In Comparative Example 1: the purity was only 99.9892%. After omitting S30, the iron yield only decreased slightly by 0.49 percentage points, but the impurities of cobalt, nickel, and manganese increased by hundreds of times (cobalt increased from 0.03 ppm to 10.80 ppm), and aluminum also remained at 2.77 ppm. The product could not meet the impurity control requirements for battery-grade raw materials, and the process lost its core application significance.

[0133] In Comparative Example 2, the overall yield was only 74.05%, which was cost-effective. Although the purification capacity of cobalt, nickel and manganese was slightly improved after replacing alcohol precipitation with crystallization, the sodium impurity increased dramatically to 208.79 ppm (37.96 times that of Example 1), and the iron yield dropped sharply to 74.05% (a decrease of 11.68 percentage points). The raw material loss was too large, and it was not feasible for industrialization.

[0134] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for producing ferrous sulfate from an iron-containing waste material, characterized by, The method comprises the following steps: Step S10: providing iron-containing waste, dissolving the iron-containing waste in an acid solution to obtain an iron source solution; Step S20: adding a phosphorus source and an oxidizing agent to the iron source solution to oxidize the ferrous iron to ferric iron, adjusting the pH to 1.7-2.5 to generate a ferric phosphate-containing precipitate, and after the reaction is completed, performing solid-liquid separation and washing to obtain a ferric phosphate-containing solid phase; Step S30: dissolving the ferric phosphate-containing solid phase obtained in step S20 in a sulfuric acid solution, removing insoluble substances by solid-liquid separation, adjusting the pH to 1.7-2.5 to generate a ferric phosphate-containing precipitate, and after the reaction is completed, performing solid-liquid separation and washing to obtain a ferric phosphate-containing solid phase; Step S40: dissolving the ferric phosphate-containing solid phase obtained in step S30 in a sulfuric acid solution, adding a reducing agent to reduce the ferric iron to ferrous iron, and after the reaction is completed, performing solid-liquid separation to obtain a ferrous sulfate-containing liquid phase; Step S50: adjusting the pH of the ferrous sulfate-containing liquid phase obtained in step S40 to 0-1, performing alcohol precipitation, solid-liquid separation, and washing to obtain ferrous sulfate coarse crystals; Step S60: dissolving the ferrous sulfate coarse crystals in water, adjusting the pH to 5-7 under the protection of an inert gas, and after the reaction is completed, performing solid-liquid separation to obtain a ferrous sulfate-containing liquid phase; Step S70: adjusting the pH of the ferrous sulfate-containing liquid phase obtained in step S60 to ≤2, and performing final impurity removal treatment, wherein the final impurity removal treatment comprises at least two impurity removal operations, and at least one of the at least two impurity removal operations is alcohol precipitation impurity removal.

2. The process for producing ferrous sulfate from ferrous bearing scrap material as claimed in claim 1 wherein, In step S70, the impurity removal operations in the final impurity removal treatment are selected from at least one of (a) and (b): (a) alcohol precipitation impurity removal; and (b) evaporation concentration and cooling crystallization impurity removal. In step S70, the combination mode and implementation sequence of each impurity removal operation in the final impurity removal treatment can be freely selected.

3. The process for producing ferrous sulfate from ferrous bearing scrap material as claimed in claim 2 wherein, In step S70, the final impurity removal treatment is selected from any one of the following combination modes (1), (2), (3), and (4): (1) combination of one alcohol precipitation impurity removal and one evaporation concentration and cooling crystallization impurity removal; (2) combination of two alcohol precipitation impurity removals and one evaporation concentration and cooling crystallization impurity removal; (3) combination of one alcohol precipitation impurity removal and two evaporation concentration and cooling crystallization impurity removals; (4) combination of two alcohol precipitation impurity removals.

4. The process for producing ferrous sulfate from ferrous bearing scrap material as claimed in claim 3 wherein, The alcohol solvent used in the alcohol precipitation impurity removal is selected from at least one of ethanol, n-propanol, and isopropanol. The alcohol precipitation impurity removal comprises adding an alcohol solvent to the ferrous sulfate-containing liquid phase, the mass ratio of the ferrous sulfate-containing liquid phase to the alcohol solvent is 1:0.3-1:0.5, and after the addition of the alcohol solvent is completed, the stirring is continued until no precipitate is generated, and then solid-liquid separation is performed. The evaporation concentration and cooling crystallization impurity removal comprises evaporating and concentrating the ferrous sulfate-containing liquid phase until the mass percentage content of iron is 10%-12%, cooling to a temperature of 0-5°C for cooling crystallization until no precipitate is generated, and then performing solid-liquid separation. In step S70, the pH adjusting agent used for adjusting the pH to ≤2 is sulfuric acid.

5. The process for producing ferrous sulfate from ferrous bearing scrap material as claimed in claim 1 wherein, In step S30, the ferric phosphate-containing solid phase is dissolved in a sulfuric acid solution with a mass percentage concentration of 10%-30%. And / or, in the step S30, the pH is adjusted to 1.7 to 2.5, and the pH adjusting agent is at least one selected from ammonia, sodium hydroxide, sodium carbonate and sodium bicarbonate; And / or, in the step S30, after the pH is adjusted to 1.7 to 2.5, the reaction is stirred at a temperature of 40°C to 60°C for 15min to 60min until no more precipitate is generated; And / or, in the step S40, the solid phase containing ferric phosphate is dissolved in a 10% to 30% mass percentage concentration of sulfuric acid solution; And / or, in the step S40, the reducing agent is at least one selected from high-purity iron powder, hydrogen sulfide, sodium sulfide, sodium hydrosulfide, hydrogen, sodium sulfite, sodium bisulfite, sodium thiosulfate, ascorbic acid and sulfur dioxide; the amount of the reducing agent added is 1.0 to 1.2 times the theoretical molar amount, calculated based on the reduction of all the ferric iron to ferrous iron; And / or, in the step S40, after the reducing agent is added, the reaction is stirred at a temperature of 40°C to 60°C for 1.5h to 3h.

6. The process for producing ferrous sulfate from ferrous bearing scrap material as claimed in claim 1 wherein, In the step S20, the phosphorus source is at least one selected from phosphorus-containing waste and phosphorus-containing compounds; the phosphorus-containing compounds are at least one selected from phosphoric acid, monoammonium phosphate, ammonium dihydrogen phosphate, ammonium orthophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium orthophosphate; the amount of the phosphorus source added is such that the molar ratio of iron to phosphorus in the mixed solution formed after the phosphorus source is added to the iron source solution is 1:1 to 1:1.05; And / or, in the step S20, when the iron-containing waste contains phosphorus, and after the iron source solution is prepared, the molar amount of phosphorus in the iron source solution is greater than or equal to the molar amount of iron, no phosphorus source needs to be supplemented; And / or, in the step S20, the oxidizing agent is at least one selected from hydrogen peroxide, air, ozone, sodium persulfate, sodium ferrate and high-purity oxygen; the amount of the oxidizing agent added is 1.0 to 1.2 times the theoretical molar amount, calculated based on the oxidation of all the ferrous iron to ferric iron; And / or, in the step S20, the pH is adjusted to 1.7 to 2.5, and the pH adjusting agent is at least one selected from ammonia, sodium hydroxide, sodium carbonate and sodium bicarbonate; after the pH is adjusted to 1.7 to 2.5, the reaction is stirred at a temperature of 40°C to 60°C for 15min to 60min until no more precipitate is generated; And / or, in the step S30, after the phosphorus source is added to the iron source solution, a mixed solution is formed, and when the mixed solution contains aluminum, the solid phase obtained in this step also contains aluminum phosphate.

7. The process for producing ferrous sulfate from ferrous bearing materials as claimed in claim 1 wherein, In the step S50, the pH is adjusted to 0 to 1, and the pH adjusting agent is sulfuric acid; And / or, in the step S50, the alcohol solvent used in the alcohol precipitation is at least one selected from ethanol, n-propanol and isopropanol; And / or, in the step S50, the alcohol solvent is added to the liquid phase containing ferrous sulfate, the mass ratio of the liquid phase containing ferrous sulfate to the alcohol solvent is 1:1.2 to 1:1.8, and after the alcohol solvent is added, the stirring is continued until no precipitate is generated before the solid-liquid separation.

8. The process for producing ferrous sulfate from ferrous bearing materials as claimed in claim 1 wherein, In the step S60, the mass ratio of the ferrous sulfate coarse crystal to pure water is 1:2 to 1:

3. And / or, in the step S60, the pH is adjusted to 5-7 by using at least one of ammonia, sodium hydroxide, sodium carbonate and sodium bicarbonate as the pH regulator; after the pH is adjusted to 5-7, the reaction is stirred at room temperature for 15-60 minutes until no more precipitate is generated; And / or, in the step S10, the iron-containing waste is at least one of lithium extraction residue, battery black powder, phosphorus iron residue, sulfuric acid residue, titanium dioxide residue, copper smelting residue, blast furnace slag, steel slag, fly ash, nickel residue, chromium residue and lead-zinc residue; And / or, in the step S10, the acid solution is a sulfuric acid solution with a mass percentage concentration of 10%-30%.

9. A ferrous sulfate product prepared by the method of any one of claims 1-8.

10. Use of the ferrous sulfate product of claim 9 in the preparation of high-purity iron or high-purity iron-containing compounds, including any one of iron oxide, iron hydroxide, ferrous hydroxide, lithium iron phosphate and nano-Fe3O4.