Method for treating sulphate in an industrial process

Abstract

A method for treating sulfate salts in an industrial process is disclosed, the method comprising the steps of: a) contacting a first solution containing a metal sulfate, preferably a transition metal sulfate, with a second solution containing potassium hydroxide, thereby obtaining: a. a first precipitate material comprising a metal hydroxide, and b. a third solution containing potassium sulfate; b) recovering the third solution; c) providing a salting-out agent, preferably containing at least one of a potassium hydroxide source and an ammonia source; d) adding the salting-out agent to the third solution and mixing, thereby obtaining: a. a second precipitate material comprising potassium sulfate, and b. a fourth solution containing the salting-out agent; and e) recovering the second precipitate material and the fourth solution.

Description

Technical Field

[0001] Generally speaking, the present invention relates to a method for treating sulfates in an industrial process. Background Technology

[0002] In various industries, the treatment of metal sulfates with alkali metal hydroxides often results in the formation of alkali metal sulfates. These byproducts are typically considered waste process streams or solutions. A common example of this is seen in the battery industry, where potassium hydroxide is used as a pH control agent or as a precipitant in the co-precipitation of sulfate-based transition metal feedstocks to prepare precursors for cathode active materials. This process leaves behind a residual solution, called the mother liquor, which contains high levels of potassium sulfate.

[0003] Given the increasing emphasis on sustainability goals and rising raw material costs, there is growing interest in reusing these waste process streams rather than simply discharging or landfilling them. For example, if a waste process stream contains potassium sulfate, it could potentially be processed into fertilizer compounds. However, for this to be economically viable, the potassium sulfate must be pure and obtained in high yields.

[0004] Currently, the most common method for obtaining this type of potassium sulfate is evaporative crystallization. In evaporative crystallization, potassium sulfate crystals are formed by the evaporation of the solvent. Therefore, this process produces a suspension of vapor and potassium sulfate crystals in the mother liquor. However, this process is energy-intensive and not particularly efficient. Therefore, a more efficient and sustainable method for treating waste process solutions containing potassium sulfate is clearly needed. This is particularly important in industries such as the battery industry, which generate large quantities of potassium sulfate as a byproduct. Summary of the Invention

[0005] It has been found that crystallization yield can be improved by strategically altering, in particular reducing, the solubility of potassium sulfate in a solution derived from a coprecipitation reaction of a metal sulfate, preferably a transition metal sulfate (referred to as the precipitate mother liquor). This is achieved by introducing a solubilizing agent into the solution and mixing thoroughly until potassium sulfate precipitation is obtained. Essentially, the method involves salting out dissolved potassium sulfate by adding a solubilizing agent or a synonymous salting-out agent (e.g., potassium hydroxide and / or an ammonium source) until successful crystallization is achieved. Experiments have shown that the method according to the invention helps to obtain high-purity crystalline potassium sulfate with significant yields. The solution remaining after the salting-out reaction can be effectively reused in the coprecipitation process, either entirely or alternatively separated into a solution containing ammonia and another solution containing potassium hydroxide. Using one or both of these portions for the coprecipitation and / or salting-out reactions enables efficient and recyclable material handling, thereby improving the sustainability of the entire process.

[0006] Therefore, the present invention provides a method for treating sulfates in an industrial process, the method comprising the following steps:

[0007] a) Contact a first solution containing a metal sulfate, preferably a transition metal sulfate, with a second solution containing potassium hydroxide to obtain o Contains a first precipitated material of metal hydroxide, and o A third solution containing potassium sulfate; b) Recover the third solution; c) Provide a salting-out agent, preferably containing at least one of a potassium hydroxide source and an ammonia source; d) Add the salting-out agent to the third solution and mix to obtain o contains a second precipitating material containing potassium sulfate, and o A fourth solution containing a salting-out agent; and The second precipitate and the fourth solution were recovered.

[0008] Step a) is a precipitation process, which can be, for example, a process used to prepare a precursor for a secondary battery cathode active material. For example, the first solution can be an aqueous solution of a transition metal prepared by dissolving one or more transition metal raw materials such as nickel sulfate, cobalt sulfate, or manganese sulfate in water. For example, the second solution can be an aqueous solution of potassium sulfate prepared by dissolving potassium sulfate in water. The first solution, the second solution, and optionally a solution containing ammonium ions are introduced into a reactor to carry out a coprecipitation reaction. The reaction conditions and methods used for precipitation or coprecipitation are generally known. The material obtained from the coprecipitation process is a slurry containing a precipitate containing a metal hydroxide and a solution containing potassium sulfate.

[0009] According to the present invention, a third solution containing potassium sulfate is recovered and mixed with a salting-out agent. Step d) is a precipitation process. The resulting material is a slurry containing a precipitate containing potassium sulfate and a solution containing a salting-out agent. The obtained precipitate containing potassium sulfate can be used in fertilizer products and therefore has high commercial value, and the obtained solution containing the salting-out agent can be reused in the method according to the present invention.

[0010] Therefore, the present invention enables efficient material recycling, thereby contributing to improved process sustainability.

[0011] The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. Unless otherwise expressly stated, the embodiments and examples described in the claims and specification can be freely combined with each other. Detailed Implementation

[0012] In the following detailed description, preferred embodiments are described in detail to enable the practice of the invention. Although the invention has been described with reference to these specific preferred embodiments, it should be understood that the invention is not limited to these preferred embodiments. Rather, the invention includes numerous alternatives, modifications, and equivalents, as will become apparent from consideration of the following detailed description and drawings.

[0013] As used herein and in the claims, the term “comprising” should not be construed as limited to the manner listed thereafter; it does not exclude other elements or steps. It should be interpreted as specifying the presence of the stated features, integers, steps, or components as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Therefore, the scope of the expression “composition comprising components A and B” should not be limited to compositions consisting solely of components A and B. This means that, for the purposes of this invention, the only relevant components of the composition are A and B. Therefore, the terms “comprising” and “including” encompass the more restrictive terms “consistently composed of” and “composed of”.

[0014] In this specification, if any numerical range is provided, the range also includes an upper limit and a lower limit. It should be understood that in this specification, the term "at least" covers the concept of "equal to and / or greater than," and the term "at most" covers the concept of "equal to and / or less than."

[0015] In this disclosure, the solution is preferably an aqueous solution when applicable.

[0016] As mentioned above, this invention enables efficient material recycling, thereby contributing to improved process sustainability. A method for treating sulfates in an industrial process is provided, comprising the following steps: a) Contact a first solution containing a metal sulfate, preferably a transition metal sulfate, with a second solution containing potassium hydroxide to obtain a. A first precipitated material containing metal hydroxides, and b. A third solution containing potassium sulfate; b) Recover the third solution; c) Provide a salting-out agent, preferably containing at least one of a potassium hydroxide source and an ammonia source; d) Add the salting-out agent to the third solution and mix to obtain a. A secondary precipitating material containing potassium sulfate, and b. A fourth solution containing a salting-out agent; and The second precipitate and the fourth solution were recovered.

[0017] Step a) can be a precipitation process, such as a process for preparing a precursor for a secondary battery cathode active material. For example, the first solution can be an aqueous solution of a transition metal prepared by dissolving one or more transition metal raw materials, such as nickel sulfate, cobalt sulfate, or manganese sulfate, in water. For example, the second solution can be an aqueous solution of potassium sulfate prepared by dissolving potassium sulfate in water. The first solution, the second solution, and optionally a solution containing ammonium ions are introduced into a reactor to carry out a coprecipitation reaction. The reaction conditions and methods used for precipitation or coprecipitation are generally known. The material obtained from the coprecipitation process is a slurry containing a precipitate containing a metal hydroxide and a solution containing potassium sulfate.

[0018] The first solution containing the metal sulfate is preferably a solution containing a transition metal cation, wherein the transition metal may be one or more of nickel (Ni), cobalt (Co), and manganese (Mn). For example, the first solution may be an aqueous solution of the transition metal prepared by dissolving NiSO4, CoSO4, and MnSO4 in deionized water in a desired stoichiometric ratio, such that the molar ratio of Ni:Mn:Co is x:y:z, where 0.10≤x≤0.99, 0.00≤y≤0.85, 0.00≤z≤0.40, and x+y+z≤1.

[0019] The second solution containing potassium hydroxide can be an alkaline solution. Alkalinity means that the pH of the solution is within an alkaline range, such as pH 8 or higher, 9 or higher, 10 or higher, 11 or higher, or 12 or higher. Preferably, the step of contacting the first solution containing a metal sulfate, preferably a transition metal sulfate, with the second solution containing potassium hydroxide includes forming and mixing a reaction mixture containing the first solution containing a metal sulfate, preferably a transition metal sulfate, and the second solution containing potassium hydroxide. The reaction mixture is preferably alkaline. In such cases, the second solution containing potassium hydroxide can act as a pH control agent and / or a precipitant in the co-precipitation process.

[0020] Optionally, step a) includes contacting the ammonium-containing solution with a first solution containing a metal sulfate, preferably a transition metal sulfate, and a second solution containing potassium hydroxide. The ammonium-containing solution acting as a complexing agent may include, but is not limited to, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof. For example, the ammonium-containing solution may be an aqueous ammonia solution, also known as ammonia water, ammonium hydroxide, ammonia-containing liquid, ammonia solution, aqueous ammonia solution, or aqueous ammonia, i.e., a solution of ammonia in water. It can be represented by the symbol NH3(aq).

[0021] The material obtained from the co-precipitation process is a slurry comprising a precipitate containing a metal hydroxide and a solution containing potassium sulfate. The first precipitate containing the metal hydroxide can be a precursor for a secondary battery cathode active material; therefore, the metal hydroxide is preferably a transition metal hydroxide. Thus, in some embodiments of the invention, the industrial process is a battery industrial process, preferably wherein the first solution is an aqueous solution of a metal sulfate of M, preferably a transition metal sulfate, wherein M comprises at least one of Ni, Mn, and Co, and wherein the obtained first precipitate is a particulate hydroxide or hydroxyl oxide of M. Therefore, the first precipitate containing the metal hydroxide may contain… - Ni with a content of x, wherein 10.0 mol% ≤ x ≤ 99.0 mol%. - Mn with a content of y, where 0 mol% ≤ y ≤ 85.0 mol%. - Co with a content of z, where 0 mol% ≤ z ≤ 40.0 mol%. - Al with a content of q, where 0 mol% ≤ q ≤ 10.0 mol%, and - One or more additional elements with a content of r, wherein the additional element is an element from the list of B, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W, Zn, and Zr, wherein 0 mol% ≤ r ≤ 5.0 mol%. And where x + y + z + q + r = 100.0 mol%.

[0022] The third solution containing potassium sulfate can be a solution derived from a coprecipitation reaction of a metal sulfate, preferably a transition metal sulfate, or a residual solution left over from the coprecipitation process. It is referred to as the mother liquor. Therefore, the first precipitate and the third solution can be separated and recovered using any suitable method and apparatus for separating and recovering the solids and liquids, such as by filtration.

[0023] The recovered third solution containing potassium sulfate is then mixed with a salting-out agent. Salting-out, also known as salt-induced precipitation, salt fractionation, antisolvent crystallization, precipitation crystallization, or precipitation crystallization, is a purification technique that utilizes the property that certain molecules have reduced solubility in solutions with very high ionic strength. Step d) can be a precipitation process. The resulting material is a slurry containing a precipitate containing potassium sulfate and a solution containing a salting-out agent. Therefore, in the context of this disclosure, a salting-out agent refers to a chemical substance that reduces the solubility of potassium sulfate in the third solution (precipitate mother liquor). Examples of such salting-out agents include, but are not limited to, potassium hydroxide and ammonia sources. Preferably, the salting-out agent contains at least one of a potassium hydroxide source and an ammonia source, and more preferably, the salting-out agent contains both a potassium hydroxide source and an ammonia source.

[0024] In this document, ammonia source refers to ammonia and its derivatives in any form. Examples of ammonia sources include, but are not limited to, ammonia gas, ammonia solutions, and ammonium salts such as ammonium sulfate. Therefore, an ammonia source can be a solution containing ammonium ions as defined above. In some embodiments, the salting-out agent contains an ammonia source, and in step d), after mixing with the third solution, the ammonia concentration is equal to or greater than 90 g / L, preferably equal to or greater than 95 g / L, more preferably equal to or greater than 100 g / L, and most preferably equal to or greater than 130 g / L. It has been observed that the higher the ammonia concentration, the better the sulfate conversion rate. Therefore, using ammonia gas as the ammonia source is advantageous because it is easier to adjust the ammonia concentration on-site, especially when higher concentrations (e.g., greater than 100 g / L or greater than 120 g / L) are required, as commercially available ammonia solutions have concentration limitations due to practical reasons (e.g., transportation).

[0025] The potassium hydroxide source is preferably provided in solid form and / or as a solution containing 25% by weight or more, such as in the range of 25% to 75% by weight. In some embodiments, the salting-out agent comprises a potassium hydroxide source, and in step d), after mixing with the third solution, the potassium hydroxide concentration is equal to or greater than 50 g / L, for example equal to or greater than 100 g / L, or equal to or greater than 150 g / L, preferably equal to or greater than 200 g / L, for example equal to or greater than 250 g / L, and at most or equal to 650 g / L. It has been observed that the higher the KOH concentration, the better the sulfate conversion rate.

[0026] The potassium sulfate-containing precipitate obtained from step d) can be used in fertilizer products and therefore has high commercial value. The second precipitate and the fourth solution can be separated and recovered using any suitable method and apparatus for separating and recovering solids and liquids, such as by filtration. In some embodiments, recovering the second precipitate includes filtering it to obtain a composition containing potassium sulfate. Preferably, the composition contains at least 40% by weight of potassium and at least 17% by weight of sulfur, making the composition readily suitable for use as a fertilizer.

[0027] Filtration methods and apparatus are generally known in the art. An example is provided below. A slurry is filtered during a dewatering process to separate solid particles from the liquid. The dewatering process can be achieved using a belt filter with a moving annular filter cloth having a feed end to which the slurry is dispensed. The liquid slurry is filtered through the liquid-permeable filter cloth, thereby forming a filter cake containing the solid particles of the slurry on the filter cloth. The filter cake can then be washed in a washing stage by passing a washing liquid through it, while the filter cake remains on the moving filter cloth. Filtration through the filter cloth is typically enhanced by creating a partial vacuum on the other side of the filter cloth (rather than the side where the filter cake forms). At the discharge end of the belt filter, the filter cake is removed from the filter cloth and may be conveyed to further processing stages outside the belt filter, such as an additional drying stage.

[0028] Therefore, in some embodiments of the present invention, the method includes washing the filter cake containing the fourth solution and the second precipitate material with a washing liquid, which may contain ammonia.

[0029] The solution containing the salting-out agent obtained from step d), i.e., the fourth solution, can be recycled and used in one or more steps of the method. Therefore, the method according to the invention may include recycling the recovered fourth solution back to at least one of steps a) to d). Optionally, the concentration of the fourth solution may be adjusted to a level suitable for reuse. Therefore, in some embodiments, recovering the fourth solution preferably involves concentrating the fourth solution by evaporation.

[0030] In some embodiments, salting out includes an ammonia source and a potassium hydroxide source, therefore the fourth solution contains both an ammonia source and a potassium hydroxide source. In some embodiments, to efficiently reuse the ammonia and potassium hydroxide separately, the step of recovering the fourth solution may include, for example, separating the ammonia present in the fourth solution from the potassium hydroxide by ammonia stripping. Ammonia stripping is generally well known and is a desorption process used to reduce the ammonia content in aqueous solutions (e.g., wastewater streams). The fourth solution contains an ammonia source, which is in the form of ammonium ions (NH4+). + It exists as both NH4+ and dissolved ammonia (NH3). Typically, NH4+ exists in the pH range of 7 to 12. +Both NH3 and ammonia are present in the fourth solution, and the amount of dissolved gas (NH3) increases with temperature and pH. By adjusting the pH of the fourth solution to increase the proportion of NH3, and then contacting the fourth solution with air, ammonia is stripped and collected for reuse as an ammonia source, for example, as ammonia solution after dissolving the collected ammonia in water. Therefore, in some embodiments, recovering the fourth solution includes, preferably, ammonia separation by ammonia stripping, to obtain a fifth solution containing an ammonia source, and the remaining solution after ammonia separation is thus a sixth solution containing potassium hydroxide. After ammonia separation, the fifth solution can preferably be concentrated by evaporation, preferably to a concentration of ammonia in the fifth solution of 170 g / L or higher, such as in the range of 170 g / L to 550 g / L. As understood by those skilled in the art, NH3... 3（aq） The concentration can be measured using a commercially available titrator such as the Metrhom 848 Titrino Plus. The sixth solution can also preferably be concentrated by evaporation to a concentration of KOH of 100 g / L or higher, such as in the range of 100 g / L to 300 g / L or higher.

[0031] By contacting the fifth solution with the first and second solutions, the ammonia-containing fifth solution can be used as a chelating agent in step a) of this method. The ammonia-containing fifth solution can also be used as a salting-out agent in steps c)-d) of this method. The sixth solution can be used as the second solution in step a) of this method, optionally after concentration, preferably by evaporation. The sixth solution can also be used as a salting-out agent in steps c)-d) of this method.

[0032] According to this method, the salting-out process in step d) can be further improved, thereby increasing efficiency, by adjusting the concentration of the third solution containing potassium sulfate, for example, by concentrating (preferably by evaporation), before and / or during step d). Advantageously, the concentration of sulfur in the third solution in step d) is 15.00 g / L or higher, such as in the range of 15.00 g / L to 30.00 g / L, or 20.00 g / L or higher, such as in the range of 20.00 g / L to 50.00 g / L, as determined by ICP; and / or wherein the concentration of potassium in the third solution in step d) is 40.00 g / L or higher, such as in the range of 40.00 g / L to 80.00 g / L, or 50.00 g / L or higher, such as in the range of 50.00 g / L to 95.00 g / L, as determined by ICP.

[0033] Similarly, the concentration of the salting-out agent can be optimized. For example, when the salting-out agent contains an ammonia source as ammonia water, the salting-out agent can have an ammonia concentration of 170 g / L or higher, such as in the range of 170 g / L-550 g / L, or 300 g / L or higher, such as in the range of 300 g / L-550 g / L, or 400 g / L or higher, such as in the range of 400 g / L-550 g / L. Higher concentrations require less water, which is beneficial for water balance, especially when the method is implemented on an industrial scale. In some embodiments, the salting-out agent contains an ammonia source as ammonia gas, thus further improving water management. As understood by those skilled in the art, NH4+... 3（aq） Concentration can be measured using a commercially available titrator such as the Metrhom 848 Titrino Plus.

[0034] In some preferred embodiments, the salting-out agent comprises both an ammonia source and a potassium hydroxide source. The potassium hydroxide source and the ammonia source can be added and mixed in any order. For example, the potassium hydroxide source and the ammonia source can be added and mixed in such a way that at least a portion of the ammonia source is mixed into the third solution before mixing the potassium hydroxide source; at least a portion of the potassium hydroxide source is mixed into the third solution before mixing the ammonia source; or the potassium hydroxide source and the ammonia source are mixed simultaneously. Advantageously, at least a portion of the ammonia source is mixed into the third solution before mixing the potassium hydroxide source, because adding KOH increases the temperature of the mixture, and the solubility of NH3 decreases when the temperature of the mixture increases. Therefore, by adding NH3 before adding KOH, a more concentrated NH3 reaction mixture can be obtained. For the same reason, when the mixture of potassium hydroxide and the third solution is adjusted (e.g., by cooling) to a temperature favorable for NH3 dissolution before mixing the ammonia source, it is advantageous to mix at least a portion of the potassium hydroxide source into the third solution before mixing the ammonia source.

[0035] For the same reason, in embodiments in which the salting-out agent comprises at least one of an ammonia source and a potassium hydroxide source, after the third solution and the salting-out agent are mixed and have a temperature T1, it is advantageous to adjust the mixed solution containing the third solution and the salting-out agent to a temperature of 50°C or lower, such as to a temperature of 2°C-50°C, for example by cooling, when T1 is greater than 50°C; preferably, the method further includes adjusting the mixed solution to 30°C or lower, such as 2°C-25°C, when T1 is greater than 30°C.

[0036] When the salting-out agent contains both an ammonia source and a potassium hydroxide source, the molar ratio of ammonia to potassium hydroxide can be one of the following: -1:1 molar ratio; - The molar ratio of ammonia source to excess potassium hydroxide, such as 1.1:1 or higher, 1.5:1 or higher, 2:1 or higher, or 4:1 or higher; and - The molar ratio of potassium hydroxide to an excess of ammonia source is such as 1:1.1 or higher, 1:1.5 or higher, 1:2 or higher, or 1:4 or higher.

[0037] In some embodiments, the salting-out agent comprises an ammonia source and a potassium hydroxide source, and in step d), after mixing with the third solution, the potassium hydroxide concentration is equal to or greater than 5 g / L, for example, equal to or greater than 15 g / L, or equal to or greater than 25 g / L, preferably equal to or greater than 30 g / L, for example, equal to or greater than 65 g / L. It has been observed that the higher the KOH concentration, the better the sulfate conversion rate. It has also been observed that, with the same amount of KOH added, the conversion rate can be significantly improved by also adding an ammonia source compared to other reaction conditions with the same conditions but without the addition of ammonia. In other words, the combination of an ammonia source and a potassium hydroxide source as a salting-out agent produces a synergistic effect in the removal of sulfate from wastewater.

[0038] Example The present invention will be further described below with reference to some embodiments and comparative examples.

[0039] Measurement methods used in the embodiments NH 3 (aq) concentration analysis The concentration of NH3(aq) in the sample was measured by endpoint titration using a Metron 848 Titrino Plus instrument. 1 mL of a solution containing the NH3 concentration to be measured was added to the titration vessel, followed by 30-40 mL of deionized water and 1 mL of 1M NaOH. The resulting sample was then titrated to the endpoint with 0.1M HCl.

[0040] X-ray diffraction analysis The XRD spectra of the samples were measured using an EMPYREAN® X-ray diffractometer manufactured by PANalytical, under the conditions described in Table 1 below.

[0041]

[0042] Elemental composition analysis The contents of K, Na, and S in the obtained solid and liquid fractions were measured using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) instrument based on a Thermo iCAP 6000 series ICP-OES instrument.

[0043] For solid samples, the measurement samples were prepared as follows: 0.25 g of the powder sample from each example was dissolved in deionized (DI) water in a 100 mL volumetric flask. The volumetric flask was filled to the 100 mL mark with deionized (DI) water and then homogenized completely. 1 mL of the solution was taken out by pipette and transferred to a 100 mL volumetric flask for a second dilution. An appropriate amount of concentrated nitric acid was added by pipette to obtain a 5% HNO3 solution when diluted to volume with deionized (DI) water, and then homogenized. Finally, this solution was used for ICP-OES measurement. The contents of K, Na, and S are expressed as % (%).

[0044] For liquid samples, prepare the measurement sample as follows: Pipette 1 mL of the liquid sample and transfer it to a 100 mL volumetric flask. Fill the volumetric flask to the 100 mL mark with deionized (DI) water and then homogenize completely. Pipette an appropriate amount of solution and transfer it to a 100 mL or 250 mL volumetric flask for a second dilution. Add an appropriate amount of concentrated nitric acid via pipette to obtain a 5% HNO3 solution when diluted to volume with deionized (DI) water, and then homogenize. Finally, use this solution for ICP-OES measurement. The contents of Co, Mn, Ni, K, Na, and S are expressed in g / L.

[0045] Preparation Example 1 First, an aqueous solution of transition metals was prepared by dissolving NiSO4, CoSO4, and MnSO4 in deionized water at the desired stoichiometric ratio, resulting in a Ni:Mn:Co molar ratio of 0.90:0.05:0.05 in a 120 g / L solution. Then, the transition metal aqueous solution, 220 g / L ammonia, and 220 g / L potassium hydroxide aqueous solution were continuously fed into a reaction vessel equipped with baffles, a six-bladed turbine, and a concentrator (through which the mother liquor could be removed from the reaction vessel) to precipitate the transition metal hydroxides. The mixture was stirred to achieve an NH3 concentration of 3 g / L–5 g / L and a pH of 10.9 ± 0.2 in the reaction mixture (i.e., the aqueous slurry). Precipitation was terminated when the average particle size (D50) of the transition metal hydroxides reached a target value of approximately 5.0 μm. Throughout the precipitation process, mixing was performed by rotating the turbine at 1050 rpm, the slurry temperature within the reaction vessel was maintained at 85°C by heating, and an inert atmosphere was ensured by circulating nitrogen through the vessel. Thus, transition metal hydroxides were obtained, and the mother liquor was recovered from the slurry by filtration.

[0046] The recovered mother liquor was analyzed using the ICP-OES analytical method described above; the results are reported in Table 2.

[0047]

[0048] Example 1 First, 1.5 L of the mother liquor from Preparation Example 1 and 1.5 L of 25 wt% ammonia solution were added to a hermetically sealed conical flask and mixed for 30 minutes to obtain a well-stirred mixture. Then, after standing at room temperature (e.g., about 18°C ​​to 22°C) for two hours, the mixture was subjected to Buchner filtration to separate the solid and liquid fractions, and the solid fraction was washed with 25 mL of 25 wt% ammonia solution to remove any possible impurities, such as sodium residue. The NH3 concentration of the mixture was analyzed prior to filtration and found to be 97 g / L.

[0049] The obtained solid and liquid fractions were analyzed as described above, including X-ray diffraction (XRD) of the solid fraction and inductively coupled plasma (ICP) elemental composition analysis of both the solid and liquid fractions, and the results are given in Table 5. Table 5 also reports the amount of the obtained solid fraction (in grams) and the percentage of sulfate conversion from the mother liquor to the obtained solid fraction, which was calculated using ICP measurements of sulfur content in the mother liquor and filtrate.

[0050] Example 2 First, 3.0 L of the mother liquor from Preparation Example 1 was placed in an Erlenmeyer flask, followed by the addition of 625 g of potassium hydroxide (KOH) granules in small batches, while continuously stirring with a magnetic stirrer for 30 minutes. Then, the flask was sealed airtight, and the mixture was cooled to room temperature (22°C), followed by Buchner filtration to separate the solid and liquid fractions, and the solid was washed with 50 mL of 25% by weight ammonia.

[0051] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0052] Example 3 First, 200 mL of the mother liquor from Preparation Example 1 was placed in an Erlenmeyer flask, which was hermetically connected via a gas line to a round-bottom flask containing 600 mL of 25% (w / w) ammonia solution. The round-bottom flask was then heated to boiling the ammonia solution to obtain gaseous ammonia (NH3), which was introduced into the Erlenmeyer flask below the surface of the mother liquor via the gas line. This contact between the NH3 gas and the mother liquor lasted for 3 hours. Then, after being left at room temperature (e.g., approximately 18°C ​​to 22°C) for two hours, the mixture obtained in the flask was subjected to Buchner filtration to separate the solid and liquid fractions, and the precipitate (i.e., the solid fraction) obtained in the Erlenmeyer flask was washed with 10 mL of 25% (w / w) ammonia solution. The NH3 concentration of the resulting mixture was analyzed prior to filtration and found to be 147 g / L.

[0053] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0054] Example 4 Eight separate examples, Examples 4.1-4.8, were conducted. In each example, 200 mL of the mother liquor from Example 1 was first placed in an Erlenmeyer flask, followed by the addition of small batches of potassium hydroxide (KOH) granules as described in Table 3, while continuously stirring with a magnetic stirrer for 30 minutes. The mixture was then cooled to 15°C, followed by Buchner filtration to separate the solid and liquid fractions, and the solid fraction was washed with 10 mL of 25% by weight ammonia.

[0055] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0056]

[0057] Example 5 Five separate examples, Examples 5.1-5.5, were conducted. In each example, 200 mL of the mother liquor from Example 1 was first placed in an Erlenmeyer flask, and then potassium hydroxide (KOH) granules as described in Table 4 were added in small batches while continuously stirring with a magnetic stirrer for 30 minutes. The mixture was then cooled to 22°C, followed by the addition of 200 mL of 25% by weight ammonia solution. The flask was then sealed airtight and continuously stirred with a magnetic stirrer for 60 minutes. The resulting mixture was then subjected to Buchner filtration to separate the solid and liquid fractions, and the solid fraction was washed with 10 mL of 25% by weight ammonia solution.

[0058] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0059]

[0060] Comparative Example 1 First, 200 mL of the mother liquor from Preparation Example 1 was placed in an Erlenmeyer flask, and then the liquid was evaporated until 50 mL remained in the flask. The remaining liquid in the flask was then cooled to 4.9°C, followed by Buchner filtration to separate the solid and liquid fractions, and the solid fraction was washed with 10 mL of 25% by weight ammonia.

[0061] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0062] Comparative Example 2 First, 200 mL of the mother liquor from Preparation Example 1 was placed in an Erlenmeyer flask, and the liquid was then cooled to 2°C. Next, the liquid was subjected to Buchner filtration to separate the solid and liquid fractions, and the solid fraction was washed with 10 mL of 25% by weight ammonia.

[0063] The obtained solid and liquid fractions were analyzed in a similar manner to that in Example 1, and the results are given in Table 5.

[0064]

[0065]

[0066]

[0067] Referring to Table 5, compared with the sulfate removal effect of Comparative Examples 1-2, the sulfate removal effect of Examples 1-5 on alkaline waste sulfate solution was improved.

Claims

1. A method for treating sulfates in an industrial process, the method comprising the following steps: a) Contacting a first solution containing a metal sulfate, preferably a transition metal sulfate, with a second solution containing potassium hydroxide to obtain a. A first precipitated material containing metal hydroxides, and b. A third solution containing potassium sulfate; b) Recover the third solution; c) Provide a salting-out agent, preferably containing at least one of a potassium hydroxide source and an ammonia source; d) The salting-out agent is added to the third solution and mixed to obtain... a. A secondary precipitating material containing potassium sulfate, and b. A fourth solution containing the salting-out agent; and e) Recover the second precipitated material and the fourth solution.

2. The method of claim 1, wherein the mixture of the third solution and the salting-out agent has a temperature T1, the method further comprising adjusting the mixture of the third solution and the salting-out agent to a temperature of 50°C or lower, such as adjusting to a temperature of 2°C-50°C, when T1 is greater than 50°C; preferably, the method further comprises adjusting the mixture to a temperature of 30°C or lower, such as 2°C-25°C, when T1 is greater than 30°C.

3. The method according to claim 1 or 2, comprising, preferably, concentrating the third solution by evaporation before and / or during step d).

4. The method according to any one of the preceding claims, wherein the concentration of sulfur in the third solution in step d) is 15.00 g / L or higher, such as in the range of 15.00 g / L to 30.00 g / L, or 20.00 g / L or higher, such as in the range of 20.00 g / L to 50.00 g / L, as determined by ICP; and / or wherein the concentration of potassium in the third solution in step d) is 40.00 g / L or higher, such as in the range of 40.00 g / L to 80.00 g / L, or 50.00 g / L or higher, such as in the range of 50.00 g / L to 95.00 g / L, as determined by ICP.

5. The method according to any one of the preceding claims, wherein the salting-out agent comprises both the ammonia source and the potassium hydroxide source, preferably, the molar ratio of ammonia to potassium hydroxide is one of the following: -1:1 molar ratio; - The molar ratio of the ammonia source to the excess potassium hydroxide is, for example, 1.1:1 or higher, 1.5:1 or higher, 2:1 or higher, or 4:1 or higher; and - The molar ratio of potassium hydroxide to the excess ammonia source is, for example, 1:1.1 or higher, 1:1.5 or higher, 1:2 or higher, or 1:4 or higher.

6. The method of claim 5, wherein the potassium hydroxide source and the ammonia source are added and mixed in any order, optionally by means of: - Before mixing in the potassium hydroxide source, at least a portion of the ammonia source is mixed into the third solution; - Before mixing the ammonia source, at least a portion of the potassium hydroxide source is mixed into the third solution; or - Simultaneously mix the potassium hydroxide source and the ammonia source.

7. The method according to any one of the preceding claims, wherein the salting-out agent comprises the potassium hydroxide source, the potassium hydroxide source being provided in solid form and / or as a solution containing 25% by weight or more, such as in the range of 25% by weight to 75% by weight of potassium hydroxide.

8. The method according to any one of the preceding claims, wherein the salting-out agent comprises the ammonia source, the ammonia source being ammonia water, preferably the salting-out agent having an ammonia concentration of 170 g / L or higher, such as in the range of 170 g / L to 550 g / L, or 300 g / L or higher, such as in the range of 300 g / L to 550 g / L, or 400 g / L or higher, such as in the range of 400 g / L to 550 g / L.

9. The method according to any one of the preceding claims, wherein the salting-out agent comprises the ammonia source, the ammonia source being ammonia gas or an ammonium salt, such as ammonium sulfate.

10. The method according to any one of the preceding claims, wherein recovering the second precipitated material comprises filtering the second precipitated material to obtain a composition containing potassium sulfate, and optionally before and / or during the filtration, the method comprises washing the filter cake containing the second precipitated material with a washing solution containing ammonia; wherein the composition is suitable for use as a fertilizer.

11. The method according to any one of the preceding claims, comprising recycling the recovered fourth solution back to at least one of steps a) to d).

12. The method according to any one of the preceding claims, wherein recovering the fourth solution preferably comprises concentrating the fourth solution by evaporation.

13. The method according to any one of claims 1-12, wherein the salting-out agent comprises the ammonia source and the potassium hydroxide source, and wherein recovering the fourth solution preferably comprises ammonia separation by ammonia stripping to obtain a fifth solution containing the ammonia source and a sixth solution containing potassium hydroxide, and wherein the method further comprises at least one of the following: In step a), the fifth solution is used as a chelating agent by contacting the fifth solution with the first solution and the second solution; In steps c)-d), the fifth solution is used as the salting-out agent; Optionally, after the sixth solution is preferably concentrated by evaporation, it is used as the second solution in step a); or In steps c)-d), the sixth solution is used as the salting-out agent.

14. The method according to claim 13, wherein after ammonia separation, the fifth solution is preferably concentrated by evaporation, preferably concentrated to a concentration of ammonia in the fifth solution of 170 g / L or higher, such as in the range of 170 g / L to 550 g / L, and / or the sixth solution is preferably concentrated by evaporation, preferably concentrated to a concentration of KOH in the sixth solution of 100 g / L or higher, such as in the range of 100 g / L to 300 g / L or higher.

15. The method according to any one of the preceding claims, wherein the industrial process is a battery industrial process, preferably wherein the first solution is an aqueous solution of a metal sulfate of M, wherein M includes at least one of Ni, Mn and Co, wherein the first precipitated material obtained is a particulate hydroxide or hydroxyl oxide of M.

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