A method for removing iron and arsenic impurities from nickel sulfate based on two-stage directional reaction and adsorption mechanism

Abstract

The application discloses a method for removing iron and arsenic impurities from nickel sulfate based on two-stage directional reaction and adsorption mechanism, and belongs to the technical field of hydrometallurgy. The nickel sulfate to be removed is dissolved in water to prepare a nickel sulfate solution with a nickel concentration of 60-80 g / L; the nickel sulfate solution to be removed is heated to 60-85 DEG C, and a hydrogen peroxide solution equivalent to 1.0-1.5 times of the total molar amount of iron and arsenic is added, the temperature is kept at 60-85 DEG C, and oxidation is carried out for 20-40 min; then, 15-25% of an alkaline nickel carbonate suspension is added, and the pH value of the reaction system is adjusted to 3.5-5.5; then, aging is carried out at 70-85 DEG C for 30-90 min; and after the reaction, solid-liquid separation is carried out to obtain a nickel sulfate solution after impurity removal and a filter residue containing iron and arsenic. The method adopts two-stage directional reaction and adsorption mechanism, and combines with undisturbed and accurate pH value control of the reaction system, so that deep removal of arsenic is realized, the amount of iron residue is reduced, the loss of nickel entrainment is reduced, and meanwhile, high stability and wide applicability of the whole process flow are ensured.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for removing iron and arsenic impurities from nickel sulfate based on a two-stage directional reaction and adsorption mechanism. Background Technology

[0002] Nickel sulfate is a key raw material for preparing cathode materials for lithium-ion batteries, and its purity directly affects the battery's electrochemical performance and lifespan. During the preparation of nickel sulfate, the raw materials often contain impurities such as iron and arsenic, which can reduce the battery's energy density and cycle stability; therefore, they must be effectively removed.

[0003] Currently, the commonly used industrial methods for removing iron and arsenic impurities mainly include: 1. Traditional methods typically involve controlling the molar ratio of iron to arsenic and adding an oxidizing agent (such as hydrogen peroxide) to neutralize ferrous ions (Fe). 2+ ) is oxidized to iron ions (Fe 3+ ), trivalent arsenic (As 3+ ) is oxidized to pentavalent arsenic (As 5+ Then, the pH of the solution is adjusted to cause iron and arsenic to form insoluble ferric arsenate (FeAsO4) precipitate, while arsenic is removed by adsorption of Fe(OH)3 colloid generated by the hydrolysis of ferric salt.

[0004] 2. CN111533185A discloses a method for removing arsenic from crude nickel sulfate. This method involves controlling the iron-arsenic molar ratio and the amount of hydrogen peroxide added, as well as adjusting the temperature and pH of the iron removal section, to allow arsenic to combine with iron to form FeAsO4 precipitate. While this method is effective in removing arsenic, it suffers from drawbacks such as strict requirements on the iron-arsenic molar ratio and the generation of large amounts of solid waste.

[0005] 3. CN146846A discloses a method for arsenic removal in a nickel electrolysis mixed acid system. This method removes arsenic at different stages by controlling the parameters of the iron and cobalt removal processes in stages. In the cobalt removal stage, the oxidation potential and pH value are controlled to cause residual arsenic to co-precipitate with cobalt hydroxide, achieving an arsenic removal rate of over 98% in the system solution. However, this method is complex, requires multi-stage control, and the sulfiding agent itself poses potential safety risks.

[0006] In summary, traditional methods for removing iron and arsenic impurities mainly have the following problems: 1. Using strong alkaline substances such as sodium hydroxide and calcium carbonate to adjust pH can easily lead to local over-alkalinity, causing loss of nickel ions through co-precipitation and potentially introducing new impurity ions.

[0007] 2. Single arsenic removal methods are insufficient to reduce arsenic content to battery-grade standards, i.e., As content <0.0001g / L.

[0008] 3. Traditional impurity removal methods produce a large amount of arsenic-containing iron slag, which is costly to treat and can easily cause secondary pollution.

[0009] Given the shortcomings of existing technologies, there is an urgent need to develop a highly efficient, economical, and environmentally friendly method for the deep removal of iron and arsenic impurities from nickel sulfate solutions. This method would address the bottlenecks of existing technologies, such as incomplete iron and arsenic removal, high nickel loss rates, large amounts of solid waste generated, and narrow operating windows. Summary of the Invention

[0010] The purpose of this invention is to provide a method for removing iron and arsenic impurities from nickel sulfate based on a two-stage directional reaction and adsorption mechanism.

[0011] The objective of this invention is achieved as follows: the method for removing iron and arsenic impurities from nickel sulfate based on a two-stage directional reaction and adsorption mechanism includes the following steps: Dissolve the nickel sulfate to be purified in water to prepare a nickel sulfate solution with a nickel concentration of 60-80 g / L; heat the nickel sulfate solution to be purified to 60-85°C, add hydrogen peroxide solution equivalent to 1.0-1.5 times the total molar amount of iron and arsenic, maintain the temperature at 60-85°C, and oxidize for 20-40 min; then add 15-25% basic nickel carbonate suspension to adjust the pH of the reaction system to 3.5-5.5; then age at 70-85°C for 30-90 min; perform solid-liquid separation on the reactants to obtain the purified nickel sulfate solution and filter residue containing iron and arsenic.

[0012] Compared with the prior art, the technical solution described in this invention has the following advantages: 1. Oxidation-precipitation-adsorption synergistic mechanism: This invention uses hydrogen peroxide to oxidize iron and arsenic in low valence states, converting them into higher valence states that are easier to precipitate; it generates stable FeAsO4 compounds through chemical precipitation; and it further captures residual arsenic through colloidal adsorption, forming a triple synergistic arsenic removal mechanism to ensure a deep purification effect.

[0013] 2. Furthermore, the technical solution described in this invention employs a two-stage directional reaction and adsorption mechanism. Within a lower pH range, highly selective chemical precipitation is preferentially ensured. Under these conditions, excess iron ions and arsenate ions primarily generate crystalline FeAsO4 and basic nickel arsenate double salt precipitates. This also avoids the explosive nucleation of large quantities of Fe(OH)3 colloids.

[0014] 3. Within a higher pH range, excess iron salts can be controlled to hydrolyze, generating highly surface-active Fe(OH)3 colloids that adsorb and deeply remove residual arsenate ions. Segmented pH control of the reaction system allows for more precise matching of the optimal reaction pathway for different arsenic removal stages.

[0015] 4. Regarding the selection of neutralizing agents, basic nickel carbonate (chemical formula NiCO3·2Ni(OH)2·4H2O), as a weakly basic nickel salt, can slowly release carbonate and hydroxide ions in aqueous solution, avoiding the problem of excessively high local pH caused by the use of strong alkalis. Its slow hydrolysis characteristics make pH adjustment more uniform and stable, preventing the co-precipitation loss of nickel ions, and at the same time, it will not introduce foreign cation impurities other than nickel.

[0016] 5. Low nickel loss rate: The technical solution uses basic nickel carbonate as a pH adjuster and adds it slowly at a rate of 0.25-0.75 mL / min, which avoids nickel hydrolysis loss caused by local over-alkaliness. The nickel recovery rate is as high as 99.5% or more, which is about 2-3% higher than the traditional sodium hydroxide adjustment method.

[0017] 6. Wide operating window: The proposed technical solution has relatively relaxed requirements on the molar ratio of iron to arsenic (2~5:1), making it highly adaptable and easier to implement industrially. Traditional methods, on the other hand, lack precise control over the pH range, and precipitation and adsorption reactions tend to occur disorderly and simultaneously within a single pH range. The entire process is highly dependent on the stoichiometric ratio of the reactants, inevitably resulting in a narrow operating window.

[0018] 7. Excellent impurity removal effect: The technical solution can reduce the arsenic content in nickel sulfate solution to below 0.0001 g / L and the iron content to below 0.0005 g / L, which is far below the standard requirements for battery-grade nickel sulfate (As < 0.0005 g / L, Fe < 0.001 g / L).

[0019] 8. It is environmentally friendly, reduces the generation of solid waste, reduces the volume of nickel-iron slag, and fixes arsenic in a stable chemical state in the slag, thus reducing environmental risks.

[0020] 9. Low cost: Basic nickel carbonate can use intermediate products from the production system, and hydrogen peroxide is a common industrial oxidant. The raw materials are readily available and have low cost.

[0021] In summary, the technical solution described in this invention employs a two-stage directional reaction and adsorption mechanism, combined with undisturbed and precise control of the pH value of the reaction system. This achieves deep removal of arsenic while reducing the amount of iron slag and minimizing nickel entrainment loss, while ensuring high stability and wide applicability of the entire process. Detailed Implementation

[0022] The present invention will be further described below, but this is not intended to limit the invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the scope of protection of the present invention.

[0023] The method for removing iron and arsenic impurities from nickel sulfate based on a two-stage directional reaction and adsorption mechanism, as described in this invention, includes the following steps: Dissolve the nickel sulfate to be purified in water to prepare a nickel sulfate solution with a nickel concentration of 60-80 g / L; heat the nickel sulfate solution to be purified to 60-85°C, add hydrogen peroxide solution equivalent to 1.0-1.5 times the total molar amount of iron and arsenic, maintain the temperature at 60-85°C, and oxidize for 20-40 min; then add 15-25% basic nickel carbonate suspension to adjust the pH of the reaction system to 3.5-5.5; then age at 70-85°C for 30-90 min; perform solid-liquid separation on the reactants to obtain the purified nickel sulfate solution and filter residue containing iron and arsenic.

[0024] If the nickel sulfate solution to be purified has a high organic content, it can be pretreated with activated carbon adsorption; if there are insoluble substances such as CaSO4, it can be quickly filtered using a vacuum filtration device.

[0025] The preferred heating temperature is 70~80℃, that is, the preferred temperature for the oxidation reaction is 70~80℃.

[0026] The molar ratio of iron to arsenic is 2 to 5:1, preferably 3:1.

[0027] The preferred amount of hydrogen peroxide solution added is equivalent to 1.2 times the total molar amount of iron and arsenic.

[0028] The concentration of the hydrogen peroxide solution is 10-30%.

[0029] The oxidation time is preferably 25-30 min.

[0030] The oxidation reaction was carried out with stirring at a speed of 200 rpm.

[0031] The concentration of the basic nickel carbonate suspension is preferably 20%.

[0032] The basic nickel carbonate suspension is added at a rate of 0.25~0.75 mL / min.

[0033] The pH adjustment of the reaction system is carried out in two stages: In the first stage, 15-25% of basic nickel carbonate suspension is added to the reaction system to adjust the pH to 3.5-4.5. During this stage, the basic nickel carbonate neutralizes the H⁺ ions released by the reaction, avoiding excessively high local pH. At the same time, it reacts with arsenate and iron ions to form ferric arsenate (FeAsO4) and basic nickel arsenate double salt precipitates. In the second stage, 15-25% of basic nickel carbonate suspension is added to the reaction system to adjust the pH to 4.5-5.5, and the system is aged at 70-85℃ for 40-80 minutes. During this stage, excess iron salts hydrolyze to form Fe(OH)3 colloid. This colloid has a huge specific surface area and can effectively adsorb residual arsenate ions in the solution, achieving deep removal of arsenic.

[0034] The preferred aging temperature is 75~80℃.

[0035] The preferred aging time is 50-70 minutes.

[0036] The solid-liquid separation is performed by vacuum filtration. The filter residue, after washing, can be safely landfilled as waste or sent to a specialized arsenic treatment plant to recover arsenic, while the washing liquid is returned to the dissolution process.

[0037] Example 1

[0038] A crude nickel sulfate sample provided by a smelter was dissolved in water to prepare a nickel sulfate solution with a nickel concentration of 80 g / L, containing 0.25 g / L As, 0.45 g / L Fe, 0.15 g / L Cu, and 0.08 g / L Zn. 500 mL of the nickel sulfate solution to be purified was placed in a 1 L beaker, heated to 70 °C, and filtered using rapid filter paper before use.

[0039] Add 10.5 mL of 10% hydrogen peroxide solution, which is equivalent to 1.2 times the total molar amount of iron and arsenic. Maintain the temperature at 70°C and stir at 200 rpm for 30 min.

[0040] Next, under stirring conditions, a 20% basic nickel carbonate suspension was slowly added dropwise at a rate of 0.50 mL / min to adjust the pH of the reaction system to 4.0; then, a basic nickel carbonate suspension of the same concentration was slowly added dropwise at the same rate to gradually increase the pH of the reaction system to 4.5.

[0041] Then, the temperature is raised to 80℃ and maintained for aging for 40 minutes. The reacted material is then filtered while hot to separate the solid and liquid phases, yielding a purified nickel sulfate solution and a filter residue containing iron and arsenic.

[0042] Example 2

[0043] Another sample of crude nickel sulfate provided by a smelter was dissolved in water to prepare a nickel sulfate solution with a nickel concentration of 60 g / L, containing 0.08 g / L As, 0.12 g / L Fe, 0.20 g / L Cu, and 0.12 g / L Zn. 500 mL of the nickel sulfate solution to be purified was placed in a 1 L beaker and heated to 65 °C for later use.

[0044] Add 1.2 mL of 30% hydrogen peroxide solution, which is equivalent to 1.5 times the total molar amount of iron and arsenic. Maintain the temperature at 65°C and stir at 200 rpm for 25 min.

[0045] Next, under stirring conditions, a 15% basic nickel carbonate suspension was slowly added dropwise at a rate of 0.75 mL / min to adjust the pH of the reaction system to 4.5; then, a basic nickel carbonate suspension of the same concentration was slowly added dropwise at the same rate to gradually increase the pH of the reaction system to 5.0.

[0046] Then, the temperature is raised to 75°C and maintained for aging for 45 minutes. The reacted material is then filtered while hot to separate the solid and liquid phases, yielding a purified nickel sulfate solution and a filter residue containing iron and arsenic.

[0047] Example 3

[0048] The crude nickel sulfate sample was dissolved in water as in Example 1 to prepare a nickel sulfate solution with a nickel concentration of 70 g / L. 500 mL of the nickel sulfate solution to be purified was placed in a 1 L beaker, heated to 75°C, and filtered using rapid filter paper before use.

[0049] Add 10.5 mL of 10% hydrogen peroxide solution, which is equivalent to 1.2 times the total molar amount of iron and arsenic. Maintain the temperature at 75°C and stir at 200 rpm for 35 min.

[0050] Next, under stirring conditions, a 25% basic nickel carbonate suspension was slowly added dropwise at a rate of 0.25 mL / min to adjust the pH of the reaction system to 3.5; then, a basic nickel carbonate suspension of the same concentration was slowly added dropwise at the same rate to gradually increase the pH of the reaction system to 4.5.

[0051] Then, the temperature is raised to 85℃ and maintained for 30 minutes. The reacted material is then filtered while hot to separate the solid and liquid phases, yielding a purified nickel sulfate solution and a filter residue containing iron and arsenic.

Claims

1. A method for removing iron and arsenic impurities from nickel sulfate based on a two-stage directional reaction and adsorption mechanism, characterized in that, The process includes the following steps: Dissolve the nickel sulfate to be purified in water to prepare a nickel sulfate solution with a nickel concentration of 60-80 g / L; heat the nickel sulfate solution to be purified to 60-85°C, add hydrogen peroxide solution equivalent to 1.0-1.5 times the total molar amount of iron and arsenic, maintain the temperature at 60-85°C, and oxidize for 20-40 min; then add 15-25% basic nickel carbonate suspension to adjust the pH of the reaction system to 3.5-5.5; then age at 70-85°C for 30-90 min; perform solid-liquid separation on the reactants to obtain the purified nickel sulfate solution and filter residue containing iron and arsenic.

2. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The heating temperature is 70~80℃.

3. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The molar ratio of iron to arsenic is 2~5:

1.

4. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The amount of hydrogen peroxide solution added is equivalent to 1.2 times the total molar amount of iron and arsenic.

5. The method for removing iron and arsenic impurities from nickel sulfate according to any one of claims 1 or 4, characterized in that, The concentration of the hydrogen peroxide solution is 10-30%.

6. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The oxidation time is 25-30 minutes.

7. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The concentration of the basic nickel carbonate suspension is 20%.

8. The method for removing iron and arsenic impurities from nickel sulfate according to any one of claims 1 or 7, characterized in that, The basic nickel carbonate suspension is added at a rate of 0.25~0.75 mL / min.

9. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The aging temperature is 75~80℃.

10. The method for removing iron and arsenic impurities from nickel sulfate according to claim 1, characterized in that, The aging time is 50-70 minutes.