Method for deep removal of calcium and magnesium from a battery-grade manganese sulfate solution

Abstract

This invention discloses a method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution, belonging to the field of hydrometallurgical technology. The invention employs a three-stage purification process: pretreatment for impurity removal, gradient precipitation with manganese fluoride, selective extraction, and chelating resin refinement. First, the manganese sulfate leachate undergoes pretreatment to remove iron, aluminum, and heavy metals. Then, an in-situ / direct addition of manganese fluoride precipitation system using magnesium fluoride seeding and gradient fluoride supplementation efficiently removes most calcium and magnesium impurities from the solution, achieving a single-precipitation rate of over 93% for magnesium ions. Subsequently, a P507 / Cyanex272 / TBP compound saponification organic system is used with a reverse extraction logic of "extracting calcium and magnesium while retaining manganese in the aqueous phase" to precisely remove residual calcium and magnesium, avoiding the problems of competition between manganese and calcium and low magnesium extraction efficiency in traditional extraction methods. Finally, trace amounts of calcium, magnesium, and residual fluoride ions are completely removed through aluminum salt complexation for fluoride removal combined with deep refinement using aminocarboxylic acid chelating resin. This invention introduces no foreign impurities such as sodium and ammonium throughout the entire process, has a wide process window and strong industrial stability, and the final purified manganese sulfate solution can stably meet the high-end battery-grade index requirements of Ca²⁺≤5mg / l, Mg²⁺≤5mg / l, and F⁻≤1mg / l, making it suitable for the large-scale production of high-purity manganese sulfate, a raw material for lithium battery cathodes.

Description

Technical Field

[0001] This invention belongs to the field of manganese compound preparation technology, specifically a method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution. Background Technology

[0002] Battery-grade manganese sulfate is the core manganese source for lithium-ion battery cathode materials, and market demand continues to grow. Industry standards and mainstream cathode manufacturers require the following internal control indicators: Ca²⁺ ≤ 10 mg / kg, Mg²⁺ ≤ 10 mg / kg, with some high-end customers requiring Ca²⁺ ≤ 5 mg / kg and Mg²⁺ ≤ 5 mg / kg. Meanwhile, F⁻, as an introducing impurity, must also be controlled to ≤ 1 mg / kg; otherwise, it will form a LiF coating with Li⁺ during subsequent crystallization or cathode sintering, deteriorating ionic conductivity.

[0003] In manganese sulfate leaching solution, Ca and Mg mainly come from ore-associated carbonates / silicates and leaching water, with concentrations generally in the range of 200–800 mg / L (Ca) and 300–1200 mg / L (Mg), which is far from meeting battery-grade requirements and must undergo deep purification.

[0004] The existing mainstream purification methods and their technical problems are as follows: (1) Fluoride salt precipitation method: By generating CaF2 (Ksp≈3.9×10⁻¹²) and MgF2 (Ksp≈6.4×10⁻¹²), 9 Precipitation removes calcium and magnesium. The problem with this method is: Alkali metal / ammonium ions such as Na⁺ and NH₄⁺ are introduced with fluoride salts and need to be removed in subsequent processes. The solubility product of MgF2 is about three orders of magnitude higher than that of CaF2. It is difficult to reduce Mg to below 10 ppm by a single precipitation, and often excessive fluoride is required, resulting in excessive F⁻ in the filtrate. Fluoride salts are expensive, and excess fluoride remains in the manganese sulfate system in the form of HF2⁻, AlF6³⁻, etc., affecting product purity.

[0005] (2) Improvement route for manganese-based fluorides: Using MnF2 can avoid the introduction of Na⁺ / NH4⁺, but existing literature still relies on the direct addition of MnF2 powder followed by a single reaction, which has the following drawbacks: Solid MnF2 exhibits poor dispersibility in concentrated manganese sulfate solution, with localized F⁻ supersaturation. Without seeding to take advantage of the high solubility product of MgF2, the primary precipitation rate of Mg is generally only 75-82%. When feeding in a single batch at 1.2–1.5 times n(F) / n(Ca+Mg), even after filtering out excess MnF2, there will still be dissolved F⁻ residue. The so-called fluorine-free residue lacks a closed-loop process.

[0006] (3) Extraction method: The extraction order of P507 (H2A2) in a sulfuric acid system is Fe³⁺ >> Zn²⁺ > Mn²⁺ ≈ Ca²⁺ > Mg²⁺. If the approach of extracting manganese and retaining calcium and magnesium in the aqueous phase is adopted, the extraction competition between Mn and Ca is strong in the pH range of 3–4, Ca will be partially co-extracted, and Mg is almost not extracted by P507 alone (single agent extraction rate <40%), making it difficult to achieve deep removal. If the approach is changed to extracting calcium and magnesium and retaining manganese in the aqueous phase, the pH and saponification rate need to be precisely controlled, and a co-extractant is needed for Mg. Existing patents do not adequately address this coupling design.

[0007] (4) Ion exchange / membrane separation: Chelating resins are effective for trace amounts of Ca / Mg, but at high Mn²⁺ concentrations, the resin capacity decays rapidly and regeneration is frequent. Nanofiltration is selective for divalent / monovalent molecules, but Mn²⁺ and Ca²⁺ have similar radii, making it difficult to achieve a balance between retention rates. Furthermore, membrane fouling is severe, resulting in high industrialization costs. Summary of the Invention

[0008] To address the needs and problems mentioned in the background above, the present invention provides a method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution, thereby at least partially solving the above problems.

[0009] According to the technical solution of the present invention, a method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution is provided, comprising the following steps: (a) Pretreatment: The manganese sulfate leaching solution is subjected to iron and aluminum removal and heavy metal removal treatment to obtain a pretreated solution; (b) Primary precipitation removal: Manganese fluoride precipitant is added to the pretreatment solution to cause most of the calcium and magnesium ions in the solution to form fluoride precipitates, and the primary purified solution is obtained by solid-liquid separation. (c) Secondary extraction and removal: The primary purified liquid is contacted with a saponified organic extraction system for liquid-liquid extraction, so that calcium and magnesium ions are extracted into the organic phase, while manganese ions are retained in the aqueous phase. The secondary purified liquid is obtained by phase separation. (d) Tertiary Refinement and Removal: The secondary purified liquid is passed through a chelating ion exchange resin to further adsorb residual calcium and magnesium ions, resulting in a battery-grade manganese sulfate purified liquid with deep removal of calcium and magnesium.

[0010] Preferably, in step (b), the manganese fluoride precipitant is added in situ: Fluorine-containing raw materials and manganese source are added to the pretreatment liquid to generate manganese fluoride in situ within the system; or, the manganese fluoride precipitant is added directly in the form of solid manganese fluoride powder.

[0011] Preferably, step (b) further includes: Before or simultaneously with the addition of the manganese fluoride precipitant, magnesium fluoride seed crystals are added to the pretreatment solution, wherein the amount of magnesium fluoride seed crystals added is 0.01–0.5 wt% of the total mass of the pretreatment solution.

[0012] Preferably, in step (b), the molar ratio of fluorine to the total amount of calcium and magnesium ions is 2-3:1, and the manganese fluoride precipitant is added in a gradient of 2-5 batches, with a time interval of 5-30 minutes between adjacent batches; after the reaction is completed, aging is carried out for 10-60 minutes, followed by solid-liquid separation.

[0013] Preferably, in step (c), the saponified organic extraction system comprises an acidic phosphorus extractant and a co-extractant; the acidic phosphorus extractant is selected from one or more of P507, P204, and Cyanex272, and the co-extractant is selected from one or more of Cyanex272, TBP, and TOPO; the saponification rate of the organic extraction system is 30–70%.

[0014] Preferably, in step (c), the organic extraction system comprises, by volume fraction: 15–30% P507, 5–20% Cyanex272, 1–8% TBP, with the balance being diluent; The saponification rate is 40–65%; the pH of the aqueous phase is controlled at 3.5–5.0 during extraction, the volume ratio of the organic phase to the aqueous phase is 1–5:1, and the number of extraction stages is 3–7.

[0015] Preferably, before step (d), a defluorination step is also included: adding an aluminum source to the secondary purification liquid to generate aluminum-fluorine complexes or precipitates from residual fluoride ions, and after solid-liquid separation, the liquid is then sent to the chelating ion exchange resin.

[0016] Preferably, the aluminum source is aluminum sulfate or polyaluminum chloride, and the molar ratio of aluminum to fluorine is 0.5-1.5:1; the chelating ion exchange resin is an aminocarboxylic acid chelating resin.

[0017] Preferably, in step (a), the iron and aluminum removal treatment uses an oxidizing agent to oxidize Fe²⁺ to Fe³⁺, and then adjusts the pH to 3.0–4.5 to cause iron and aluminum to form hydroxide precipitates; the heavy metal removal treatment uses a sulfiding agent to cause heavy metal ions to form sulfide precipitates; and the concentration of Mn²⁺ in the pretreatment solution is 30–55 g / L.

[0018] On the other hand, the present invention also provides a method for preparing battery-grade manganese sulfate solution, comprising: Using the above method, a manganese sulfate purified solution with deep removal of calcium and magnesium was obtained, wherein Ca²⁺≤5mg / l, Mg²⁺≤5mg / l, and F⁻≤1mg / l; The purified manganese sulfate solution was evaporated and crystallized to obtain battery-grade manganese sulfate solution crystals.

[0019] This invention has at least the following beneficial effects: 1. This invention removes 90% of Ca and 80% of Mg in the precipitation stage, and increases the primary precipitation rate of Mg to >93% by using MgF2 seed crystals and gradient fluorination; in the co-extraction stage, P507 + Cyanex272 are used to selectively extract Ca / Mg in the pH range of 3.6-4.6 (manganese remains in the aqueous phase), which solves the problems of low Mg extraction rate of single agent P507 and competition between Ca and Mn in the manganese extraction route.

[0020] 2. The precipitant used in this invention is MnF2 (in situ or externally added), and the only cation is Mn. 2+ Without introducing Na + / NH4 + This avoids the risk of new impurities in battery-grade products. Detailed Implementation

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

[0022] This invention provides a method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution, comprising the following steps: (1) Pretreatment to remove impurities: The manganese sulfate leaching solution was processed sequentially: Iron removal by oxidation: Add pyrolusite (MnO2) or hydrogen peroxide to oxidize Fe²⁺ to Fe³⁺; then add limestone powder and / or lime milk to adjust the pH to 3.2–4.2, stir for 20–40 min to precipitate Fe³⁺ and Al³⁺ as hydroxides, and filter to obtain the iron and aluminum removed liquid; Sulfide removal: Add 5–10 wt% MnS suspension to the liquid after iron and aluminum removal, stir for 10–30 min, so that heavy metals such as Cu, Zn, Pb, and Cd form sulfide precipitates, and then filter. The concentration of Mn²⁺ in the pretreated solution was controlled at 30–55 g / l, Fe ≤ 5 mg / l, Al ≤ 3 mg / l, and Cu / Zn / Pb ≤ 1 mg / l.

[0023] (2) In-situ precipitation stage of manganese fluoride (primary removal): Heat the solution obtained in step (1) to 80–95°C and proceed with the following sub-steps: Add MgF2 seed crystals: Add MgF2 seed crystals (particle size 1–10 μm) at 0.03–0.20 wt% of the total solution mass to induce subsequent MgF2 co-precipitation growth; In-situ generation of MnF2: Add fluorine-containing raw materials (selected from one or more of fluorosilicic acid, hydrofluoric acid, and sodium fluorosilicate) and manganese sources (selected from one or more of MnCO3, MnO, and Mn(OH)2) to the system to generate active MnF2 precipitate in-situ within the system; or, commercially available MnF2 powder can be added directly, and either the in-situ generation method or the other can be used. Gradient fluoride addition: Add fluoride in 2–4 batches according to the total amount of fluoride n(F):n(Ca+Mg) = 2.1:1 to 2.6:1, with an interval of 10–20 min between adjacent batches, where n(F) and n(Ca+Mg) represent the molar amount of F and the molar amount of Ca plus Mg, respectively; Stirring rate 80–160 r / min, total reaction time 60–100 min, after reaction, age for 20–40 min and then filter.

[0024] (3) Saponification and extraction stage (secondary removal – calcium, magnesium, and manganese are extracted and retained in the aqueous phase): After filtration in step (2), the liquid is introduced into the extraction process. The logic here is the opposite of the conventional manganese extraction route: the goal of this step is to extract the residual Ca / Mg into the organic phase, while keeping Mn in the aqueous phase as much as possible. Specifically: Organic phase composition (volume fraction): P507: 18–28%; Cyanex272 (bis(2,4,4-trimethylpentyl)phosphonic acid): 8–16%; TBP (tributyl phosphate) as a modifier: 2–6%; Sulfonated kerosene or 260 # The solvent oil level was replenished to 100%. Saponification: The organic phase is saponified with 20–35 wt% NaOH solution or NH4OH solution, and the saponification rate is controlled at 40–65%. Aqueous phase conditions: Adjust the pH to 3.6–4.6 using Na2CO3 or dilute ammonia (within this range, the distribution ratio of P507 / Cyanex272 to Ca is D). Ca It is D Mn 2–5 times that of Mg D Mg (with Cyanex 272 coenzyme, it can be increased from <10 to >40), where D Ca D represents the distribution ratio of Ca in the aqueous phase. Mn Indicates the distribution ratio of Mn in the aqueous phase; D Mg This indicates the distribution ratio of Mg in the aqueous phase.

[0025] Flow ratio and number of stages: O / A = 1.5:1 to 4:1, 3–6 stages of countercurrent extraction, single-stage mixing time 3–8 min, temperature 25–40℃; The raffinate (aqueous phase) after extraction is a manganese sulfate-rich solution with significantly reduced calcium and magnesium content, Ca≤8mg / L and Mg≤8mg / L; After the supported organic phase is washed with 0.3–1.0 mol / L dilute H2SO4 to remove entrained Mn, Ca / Mg is back-extracted with 2.0–3.5 mol / L H2SO4. The unloaded organic phase after back-extraction is returned to the saponification-extraction cycle.

[0026] (4) Residual fluoride ring-closing + resin finishing stage (three-stage removal): In step (3), the outlet of the raffinate is set up as follows: Online defluorination unit: Add Al³⁺ source (aluminum sulfate or polyaluminum chloride) to the raffinate, with an Al / Molar-F molar ratio of 0.8–1.2:1 and a natural pH (3.5–4.5), to generate AlF₆³⁻ / Al(OH)₂. x Fᵧ micro-fibers are filtered and retained (≤0.45μm); Chelating resin refinement: The filtered liquid is passed through an aminocarboxylic acid chelating resin column (such as DOWEX-2, Purolite S930 or domestic 601 type) at a flow rate of 5–15 BV / h to further adsorb trace amounts of Ca²⁺, Mg²⁺ and residual Al³⁺. The eluent obtained is battery-grade manganese sulfate purified solution, with the following specifications: Ca²⁺≤5mg / kg, Mg²⁺≤5mg / kg, F⁻≤1mg / kg, Mn²⁺30–55g / L; It can be directly fed into MnSO4·H2O for evaporation and crystallization or used as a precursor for LMFP.

[0027] It should be noted that the solubility product constant of CaF2 is Ksp≈3.9×10⁻¹², and that of MgF2 is Ksp≈6.4×10⁻ 9 The difference between the two is approximately three orders of magnitude. This means that at the same F⁻ concentration, Ca²⁺ precipitates more easily and completely, while Mg²⁺ requires a higher F⁻ supersaturation to precipitate effectively.

[0028] In this embodiment of the invention, MgF2 seed induction is used: the pre-added MgF2 microcrystals provide a heterogeneous nucleation surface for the subsequently generated MgF2, reducing the nucleation barrier and enabling Mg²⁺ to begin precipitation at a lower F⁻ supersaturation, thereby increasing the primary precipitation rate of Mg from the conventional 75–82% to over 93%.

[0029] Gradient fluoride replenishment avoids excessive MnF2 dissolution and F⁻ waste caused by excessively high local F⁻ concentrations, allowing the precipitation reaction to proceed under mild and controllable supersaturation, while reducing the formation of colloidal precipitates and improving filtration performance.

[0030] Aging allows fine precipitate particles to grow larger and their crystal form to become more complete under the Ostwald ripening process, further improving filtration efficiency and precipitation stability.

[0031] Utilizing the selectivity of liquid-liquid extraction, residual Ca²⁺ and Mg²⁺ that were not completely removed in the first stage are separated from the manganese sulfate solution, while ensuring that Mn²⁺ is retained in the aqueous phase to the maximum extent. This section adopts an extraction logic opposite to the conventional "manganese extraction" route: In the conventional P507 extraction system, the extraction order is Fe³⁺ >> Zn²⁺ > Mn²⁺ ≈ Ca²⁺ > Mg²⁺. If the approach of "extracting manganese and retaining calcium and magnesium in the aqueous phase" is followed, the extraction competition between Mn and Ca is very intense in the pH range of 3–4, and a large amount of Ca will co-extract into the organic phase, making it impossible to achieve deep removal of calcium and magnesium.

[0032] In this embodiment of the invention, a modified strategy is used to extract calcium, magnesium, and manganese while retaining them in the aqueous phase: by saponifying the organic phase (40–65% saponification rate), the extractant molecules exist in the form of sodium salts (or ammonium salts), thereby increasing their exchange affinity for Ca²⁺ and Mg²⁺; simultaneously, the pH of the aqueous phase is precisely controlled within the range of 3.6–4.6—at this pH, the distribution ratio of P507 to Ca²⁺ (D... Ca The chelating power of Mg²⁺ is 2–5 times that of Mn²⁺, while the extraction of Mg²⁺ depends on the synergistic effect of Cyanex 272: Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphonic acid) has a higher pKa than P507, exhibits stronger chelating ability for Mg²⁺ under weakly acidic conditions, and can significantly improve the partition coefficient (D) of Mg²⁺ after forming a mixed extraction system with P507. Mg (Increased from <10 to >40).

[0033] After extraction, Mn²⁺ remains in the aqueous phase (raffinate), while Ca²⁺ and Mg²⁺ enter the organic phase. Ca / Mg can then be eluted by back-extraction with dilute sulfuric acid, and the organic phase can be regenerated and reused.

[0034] The fluoride removal unit utilizes the strong complexing ability of Al³⁺ with F⁻ (Al³⁺ + 6F⁻ ⇌ AlF₆³⁻, stability constant logβ₆ ≈ 19.8). Under pH conditions of 3.5–4.5, a trace amount of Al³⁺ (in the form of aluminum sulfate or polyaluminum chloride) is added to convert free F⁻ into AlF₆³⁻ complex ions or Al(OH)₂. x The F⁻ mixture is precipitated and then filtered through a precision filter (≤0.45μm) for retention. This step can achieve a removal rate of 85–95% for F⁻.

[0035] Chelating resin refinement: Aminocarboxylic acid chelating resins (such as DOWEX-2 and Purolite S930) contain iminodiacetic acid (IDA) or similar functional groups, exhibiting high selective chelating ability for Ca²⁺ and Mg²⁺. In a high Mn²⁺ background, the resin's partition coefficient for Ca²⁺ / Mg²⁺ is much higher than that for Mn²⁺ (selectivity coefficient α(Ca / Mn)≈5–15). Therefore, even in solutions with Mn²⁺ concentrations as high as 30–50 g / L, trace amounts of Ca²⁺ and Mg²⁺ (<10 mg / L) can be further adsorbed to ≤5 mg / L. After resin saturation, it is regenerated with dilute hydrochloric acid and recycled.

[0036] The three levels are not simply a series of additions, but rather each level compensates for the inherent shortcomings of the previous level: The precipitation section removes more than 90% of Ca / Mg, so that the extraction section does not have to face the emulsification risk caused by high concentrations of Ca / Mg. The extraction section overcomes the bottleneck of the precipitation section, which cannot reduce Mg to below 10 mg / L (due to the limitation of MgF2Ksp). The resin section solves the problem that the extraction section cannot completely remove trace amounts of Ca / Mg and F⁻ residues (due to extraction equilibrium limitations and F⁻ dissolution equilibrium in the precipitation section).

[0037] This relay-style division of labor enables each stage to operate efficiently within its optimal concentration window. The overall process achieves superior calcium and magnesium removal depth (≤5mg / l) and fluorine control level (≤1mg / l) compared to any existing single-stage or two-stage process. Furthermore, it has a wide process window, high operational flexibility, and significant industrial application value. Example

[0038] (1) Pretreatment: Take 10L of manganese sulfate leaching solution, in which the concentration of Mn²⁺ is 42.3g / L, the concentration of Ca²⁺ is 456mg / L, the concentration of Mg²⁺ is 618mg / L, the total amount of Fe is 287mg / L, the concentration of Al is 153mg / L, and the total concentration of Cu / Zn / Pb is 89mg / L.

[0039] Add 12g of pyrolusite powder (MnO2 content ≥65%) to the leachate and stir for 20min to oxidize Fe²⁺ to Fe³⁺; then slowly add lime milk (Ca(OH)2 content 20wt%) to adjust the pH to 3.8 and continue stirring for 30min to generate Fe(OH)3 and Al(OH)3 precipitates. Filter the solution through a plate and frame filter to obtain the liquid after iron and aluminum removal.

[0040] 180 mL of 8 wt% MnS solution was added to the iron and aluminum removed solution and stirred for 20 min to allow Cu, Zn, and Pb to precipitate as sulfides. The precipitate was then obtained by precision filtration. The concentrations of Mn²⁺, Ca²⁺, and Mg²⁺ in the pretreated solution were measured to be 41.6 g / L, 452 mg / L, 615 mg / L, Fe ≤ 2 mg / L, Al ≤ 1 mg / L, and Cu / Zn / Pb ≤ 0.5 mg / L.

[0041] (2) In-situ precipitation stage of manganese fluoride (first-stage removal): The pretreated solution was transferred to a reaction vessel equipped with a stirring and heating jacket, and the temperature was raised to 88°C. MgF2 seed crystals (average particle size 3 μm) were added at 0.08 wt% of the total solution mass, and the mixture was stirred and dispersed for 5 min.

[0042] The method for in-situ generation of MnF2 was adopted: 68.5 g of solid MnCO3 (industrial grade, Mn content ≥44%) and 112 mL of 40 wt% hydrofluoric acid (analytical grade) were weighed and added to the reactor in three batches, alternatingly. The first batch consisted of half the total amount of MnCO3 and half the total amount of HF. After a 15-minute interval, the second batch (each containing 1 / 4 of the total amount) was added, and after another 15-minute interval, the third batch (each containing 1 / 4 of the total amount) was added. The total n(F):n(Ca+Mg) ratio was 2.4:1. The stirring speed was 130 r / min, and the total reaction time was 90 min. After the reaction was completed, stirring was stopped, and the mixture was aged for 30 min. The mixture was then filtered while hot using a plate and frame filter press. The filter cake was washed with a small amount of 85°C hot water, and the filtrate and washings were combined to obtain the first-stage purified solution.

[0043] The concentrations of the primary purification solution were as follows: Ca²⁺ 21.3 mg / L, Mg²⁺ 37.8 mg / L, F⁻ 14.6 mg / L, and Mn²⁺ 40.8 g / L.

[0044] (3) Saponification and extraction stage (secondary removal): The organic phase (volume fraction) was prepared as follows: 24% P507, 12% Cyanex 272, 4% TBP, and 60% sulfonated kerosene. Saponification was carried out using a 28wt% NaOH solution, with the saponification rate controlled at 52%.

[0045] The pH of the primary purified solution was adjusted to 4.2 using a 10wt% Na₂CO₃ solution and then pumped into the extraction tank. The organic and aqueous phases were subjected to a 5-stage countercurrent extraction at an O / A ratio of 3:1, with each stage lasting 5 minutes at 32°C. After extraction, the mixture was allowed to stand and separate, and the raffinate (aqueous phase) was collected as the secondary purified solution.

[0046] The supported organic phase was first washed with 0.5 mol / L H2SO4 (O / A=2:1, stage 1) to remove entrained Mn, and then back-extracted with 2.5 mol / L H2SO4 (O / A=3:1, stage 3) to elute Ca / Mg. The empty organic phase was returned to the saponification-extraction cycle.

[0047] The secondary purification solution tested showed the following concentrations: Ca²⁺ 5.7 mg / L, Mg²⁺ 6.8 mg / L, F⁻ 12.1 mg / L, and Mn²⁺ 39.5 g / L.

[0048] (4) Residual fluoride closed-loop + resin finishing stage (three-stage removal): Add aluminum sulfate solution (Al2O3 content ≥17%) to the secondary purification solution at an Al:F molar ratio of 1.0:1. Stir for 15 min, let stand for 20 min, and then filter through a 0.45μm precision filter.

[0049] The filtered liquid was passed at a flow rate of 10 BV / h through an ion exchange column (50 mm diameter, 500 mm resin bed height) packed with aminocarboxylic acid chelating resin (DOWEX-2), with the breakthrough point controlled at an outlet Ca²⁺ concentration ≤ 5 mg / L. After 8 hours of operation, the resin needed to be regenerated with 1 mol / L HCl.

[0050] The collected column liquid is the finished purified liquid. Example

[0051] The difference from Example 1 is as follows: In step (2), the manganese fluoride precipitant is added directly as MnF2 powder (purity ≥98%, particle size 10–20 μm) instead of in-situ generation; the total n(F):n(Ca+Mg) = 2.4:1, added in one go, without gradient replenishment. Example

[0052] The difference from Example 1 is as follows: In step (2), no MgF2 seed crystals are added. Example

[0053] The difference from Example 1 is as follows: In step (2), the total n(F):n(Ca+Mg) = 2.0:1, and it is added in two batches in a gradient. Example

[0054] The difference from Example 1 is as follows: In step (2), the total n(F):n(Ca+Mg) = 3.0:1, and it is added in 5 batches in a gradient. Example

[0055] The difference from Example 1 is as follows: In step (3), the organic phase composition (volume fraction) is: 28% P507, 8% Cyanex272, 3% TBP, and 61% sulfonated kerosene; the saponification rate is 65%; the pH of the aqueous phase is controlled at 3.6; O / A = 4:1, and there is a 4-stage countercurrent. Example

[0056] The difference from Example 1 is as follows: In step (3), the organic phase composition (volume fraction) is: 18% P507, 16% Cyanex272, 6% TBP, and 60% sulfonated kerosene; saponification rate is 40%; the pH of the aqueous phase is controlled at 4.6; O / A = 2:1, and there is 6-stage countercurrent. Example

[0057] The difference from Example 1 is as follows: In step (4), the defluorination step is omitted (i.e., aluminum sulfate is not added, and the product is directly fed into the chelating resin column). Example

[0058] The difference from Example 1 is as follows: In step (4), the chelating resin is replaced with PuroliteS930 (iminodiacetic acid type), and the other parameters remain unchanged. Example

[0059] The difference from Example 1 is as follows: In step (1), the concentration of Mn²⁺ in the pretreatment solution was adjusted to 30.5 g / L (obtained by dilution), the concentration of Ca²⁺ was 335 mg / L, and the concentration of Mg²⁺ was 458 mg / L; In step (2), the amount of MgF2 seed crystals added is adjusted to 0.20 wt% of the total mass of the solution, and the total n(F):n(Ca+Mg) = 2.4:1, and is added in 3 batches; In step (3), the pH of the aqueous phase is controlled at 3.8, O / A = 3:1, and there is a 5-stage countercurrent.

[0060] Comparative Example 1 The difference from Example 1 is as follows: In step (2): MnF2 powder is added directly, with a total n(F):n(Ca+Mg) ratio of 1.3:1 (corresponding to the original median value). It is added all at once without adding MgF2 seed crystals or gradient addition. After reacting for 60 minutes, it is filtered immediately without aging. Steps (3) extraction and (4) resin are omitted, meaning only the precipitation stage is used to obtain the finished product.

[0061] Comparative Example 2 The difference from Example 1 is as follows: Step (2) uses the same precipitation section parameters as in Example 1; Step (3) is changed to: the organic phase is 25 vol% P204 + 75 vol% sulfonated kerosene, which is not saponified; the pH of the aqueous phase is controlled at 1.8 (typical conditions for manganese extraction from P204), O / A = 2:1, and 5-stage countercurrent extraction is used to extract Mn into the organic phase, while Ca / Mg remains in the raffinate (i.e., the route of extracting manganese while retaining calcium and magnesium). Step (4) is omitted (because the raffinate is a Ca / Mg enrichment solution, not the target product).

[0062] Comparative Example 3 The difference from Example 1 is as follows: Step (4) is omitted, that is, after completing the extraction stage of step (3), it is used as the finished product liquid, without defluorination and resin finishing.

[0063] The following methods were used to test each embodiment and comparative example: The determination of calcium in manganese ore was performed according to GB / T1506-2016 "Methods for Chemical Analysis of Manganese Ore". 2+ Residue detection: The sample was diluted with 1% HNO3 to Mn²⁺ ≤ 1 g / L (to avoid matrix inhibition) so that Ca fell into the middle of the calibration curve (0–5 mg / L working curve); The spectral lines selected for analysis were Ca 317.933 nm or 393.366 nm, and spectral interference was corrected using the Mn matrix matching method. The detection limit can reach 0.05 mg / L, which meets the quantitative requirement of ≤5 ppm.

[0064] The determination of Mg by YS / T1007-2014 "Manganese Sulfate for Batteries" (ICP-OES Determination of Mg) 2+ Residue detection: Analyze the spectral lines for Mg at 285.213 nm or 279.553 nm; Similarly, it was diluted with 1% HNO3 and matched with the Mn matrix; The detection limit can reach 0.02 mg / L.

[0065] F- residue was detected according to GB / T6730.28-2016 "Determination of Fluorine Content in Iron Ore by Ion Chromatography": concentrated manganese sulfate matrix can damage IC column, so NaOH must be added to adjust to near neutral +0.45μm filter membrane first, or perchloric acid distillation pretreatment (according to GB / T6730). IC conditions: anion exchange column, eluent Na2CO3 / NaHCO3 system, F⁻ retention time ~3–5 min; The fluoride ion-selective electrode method is faster: the sample is diluted 1:1 with TISAB (total ionic strength adjustment buffer containing CDTA to mask Al³⁺), read directly, and the detection limit is ~0.05 mg / L.

[0066] Manganese content in manganese ore was determined using GB / T1506-2016, "Chemical Analysis Methods for Manganese Ore - Determination of Manganese Content" (EDTA titration). 2+ Detection: EDTA titration: pH 10 NH3-NH4Cl buffer, Chrome Black T indicator (or Acid Chrome Blue K-Naphthol Green B mixed indicator), endpoint changes from red to purple → blue.

[0067] The test results are shown in Table 1 below: Table 1 Example 1 3.2 4.1 0.6 39.2 Example 2 4.8 5.9 2.3 39.0 Example 3 4.1 7.2 0.8 39.1 Example 4 4.5 5.3 0.5 38.9 Example 5 2.8 3.5 1.8 38.6 Example 6 4.3 4.9 0.7 38.8 Example 7 3.5 4.6 0.6 39.3 Example 8 3.4 4.3 2.8 39.1 Example 9 3.8 4.5 0.7 39.0 Example 10 2.5 3.2 0.4 28.7 Comparative Example 1 34.6 86.2 19.5 41.0 Comparative Example 2 328 446 — 4.2 Comparative Example 3 5.7 6.8 12.1 39.5 As shown in Table 1 above, comparing Example 1 and Comparative Example 3, it is evident that relying solely on two stages of precipitation and extraction (without resin refinement), Mg can only be reduced to 6.8 mg / L (exceeding the standard), while F... - The concentration was as high as 12.1 mg / L (exceeding the standard), requiring the addition of a resin stage and a defluorination step to achieve stable compliance. A comparison between Example 1 and Comparative Example 1 provides a clearer picture: the original single-stage precipitation scheme showed that all three parameters (Ca, Mg, and F) exceeded the standards, rendering it completely unfeasible for industrial application.

[0068] In Example 2 (direct addition of MnF2 powder, one-time feeding), the Mg content was 5.9 mg / L and the F content was 2.3 mg / L, both worse than in Example 1, proving that in-situ generation combined with gradient addition is helpful in reducing Mg and controlling fluorine content. In Example 3 (without MgF2 seed crystals), the Mg content increased to 7.2 mg / L, directly proving that the seed crystals are indispensable for inducing MgF2 precipitation. Examples 4 and 5 show that the Ca / Mg ratio can meet the standard in the range of n(F):n(Ca+Mg) from 2.0:1 to 3.0:1, but the risk of F⁻ residue increases significantly when it exceeds 3.0:1 (F⁻=1.8 mg / L in Example 5 exceeds the standard), so the optimal range is 2.1-2.6:1.

[0069] Comparative Example 2 used the traditional P204 manganese extraction route, and the result was that the Mn loss exceeded 90% and Ca / Mg was almost not removed. This shows that the route is not suitable for deep calcium and magnesium removal scenarios, and also proves the advantages of the present invention's calcium and magnesium extraction and manganese retention aqueous phase extraction logic.

[0070] In Example 8 (without defluorination step), the F⁻ level exceeded the standard by 2.8 mg / L, while in Example 1 (with Al³⁺ online coagulation), the F⁻ level was reduced to 0.6 mg / L. This indicates that the defluorination step is crucial to achieving the goal of F⁻≤1 mg / L and is not an optional additional step.

[0071] Examples 6, 7, 9, and 10 show that the finished product consistently meets the standards even when parameters such as organic phase ratio, saponification rate, pH, resin type, and initial Mn concentration change. This demonstrates that the present invention has a wide process window, strong industrial adaptability, and large-scale promotion value.

[0072] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for deep removal of calcium and magnesium from battery-grade manganese sulfate solution, characterized in that, Includes the following steps: (a) Pretreatment: The manganese sulfate leaching solution is subjected to iron and aluminum removal and heavy metal removal treatment to obtain a pretreated solution; (b) Primary precipitation removal: Manganese fluoride precipitant is added to the pretreatment solution to cause most of the calcium and magnesium ions in the solution to form fluoride precipitates, and the primary purified solution is obtained by solid-liquid separation. (c) Secondary extraction and removal: The primary purified liquid is contacted with a saponified organic extraction system for liquid-liquid extraction, so that calcium and magnesium ions are extracted into the organic phase, while manganese ions are retained in the aqueous phase. The secondary purified liquid is obtained by phase separation. (d) Tertiary Refinement and Removal: The secondary purified liquid is passed through a chelating ion exchange resin to further adsorb residual calcium and magnesium ions, resulting in a battery-grade manganese sulfate purified liquid with deep removal of calcium and magnesium.

2. The method according to claim 1, characterized in that, In step (b), the manganese fluoride precipitant is added in situ: Fluorine-containing raw materials and manganese source are added to the pretreatment liquid to generate manganese fluoride in situ within the system; or, the manganese fluoride precipitant is added directly in the form of solid manganese fluoride powder.

3. The method according to claim 1, characterized in that, Step (b) also includes: Before or simultaneously with the addition of the manganese fluoride precipitant, magnesium fluoride seed crystals are added to the pretreatment solution, wherein the amount of magnesium fluoride seed crystals added is 0.01–0.5 wt% of the total mass of the pretreatment solution.

4. The method according to claim 1, characterized in that, In step (b), the molar ratio of fluorine to total calcium and magnesium ions is 2-3:1, and the manganese fluoride precipitant is added in a gradient of 2-5 batches, with a time interval of 5-30 minutes between adjacent batches; after the reaction is completed, aging is carried out for 10-60 minutes, followed by solid-liquid separation.

5. The method according to claim 1, characterized in that, In step (c), the saponified organic extraction system comprises an acidic phosphorus extractant and a co-extractant; the acidic phosphorus extractant is selected from one or more of P507, P204, and Cyanex272, and the co-extractant is selected from one or more of Cyanex272, TBP, and TOPO; the saponification rate of the organic extraction system is 30–70%.

6. The method according to claim 5, characterized in that, In step (c), the organic extraction system comprises, by volume fraction: 15–30% P507, 5–20% Cyanex272, 1–8% TBP, with the balance being diluent; The saponification rate is 40–65%; the pH of the aqueous phase is controlled at 3.5–5.0 during extraction, the volume ratio of the organic phase to the aqueous phase is 1–5:1, and the number of extraction stages is 3–7.

7. The method according to claim 1, characterized in that, Before step (d), a defluorination step is also included: adding an aluminum source to the secondary purification liquid to generate aluminum-fluorine complexes or precipitates from residual fluoride ions, and after solid-liquid separation, the liquid is then sent to the chelating ion exchange resin.

8. The method according to claim 7, characterized in that, The aluminum source is aluminum sulfate or polyaluminum chloride, and the molar ratio of aluminum to fluorine is 0.5-1.5:1; the chelating ion exchange resin is an aminocarboxylic acid chelating resin.

9. The method according to claim 1, characterized in that, In step (a), the iron and aluminum removal treatment uses an oxidizing agent to oxidize Fe²⁺ to Fe³⁺, and then adjusts the pH to 3.0–4.5 to cause iron and aluminum to form hydroxide precipitates; the heavy metal removal treatment uses a sulfiding agent to cause heavy metal ions to form sulfide precipitates; the concentration of Mn²⁺ in the pretreatment solution is 30–55 g / L.

10. A method for preparing battery-grade manganese sulfate solution, characterized in that, include: Using the method of any one of claims 1-9, a manganese sulfate purified solution with deep removal of calcium and magnesium is obtained, wherein Ca²⁺≤5mg / l, Mg²⁺≤5mg / l, and F⁻≤1mg / l; The purified manganese sulfate solution was evaporated and crystallized to obtain battery-grade manganese sulfate solution crystals.