Method for treating alkali metal sulfate solution

Abstract

It is disclosed a method for treating an alkali metal sulfate solution obtainable from an industrial process, the method comprising the steps of: (a) providing an alkali metal sulfate solution, preferably directly obtained from an industrial process, and a source of hydrogen chloride; (b) contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture; and (c) reacting the reaction mixture to produce a slurry, wherein the slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

Description

METHOD FOR TREATING ALKALI METAL SULFATE SOLUTIONTECHNICAL FIELD

[0001] In general, the present disclosure relates to the treatment of alkali metal sulfate obtained from an industrial process. The disclosed method is particularly suitable for treating alkali metal sulfate solutions.BACKGROUND

[0002] As battery materials manufacturing rapidly expands, the resulting byproducts, particularly alkali metal sulfates, are becoming an increasingly challenging environmental issue. These alkali metal sulfates primarily originate from the manufacturing of cathode active material precursors, which involves the coprecipitation of sulfate-based transition metal solutions with alkalis such as NaOH, KOH, or LiOH, resulting in waste solutions with high levels of the corresponding alkali metal sulfates. Particularly, such waste solution commonly originates from mother liquor of the precipitation process. In a precipitation reaction, the mother liquor is the liquid phase after the solid precipitate has been formed. This liquid phase contains alkali metal sulfates and may still contain some of the dissolved substances (solutes) that are not fully precipitated, as well as any impurities that were present in the original rection mixture.

[0003] The conventional approach has been to discharge alkali metal sulfate solutions or evaporate them and landfill the resulting solid alkali metal sulfate. Due to the environmental unsustainability of this activity, several prior art methods have been proposed to address this issue, motivated by sustainability goals and increasing raw material costs. Instead of discharging or landfilling, circular processing methods should be pursued. However, there is still a need for closed-loop and / or semi-closed-loop alkali sulfate treatment solutions that prevent salinization while improving industrial production efficiency.SUMMARY

[0004] An objective of this disclosure is to present improved methods for treating alkali metal sulfate solutions. Furthermore, another objective is to offer such a treatment method which would provide products suitable for reuse in an industrial process.

[0005] At least one object of the present disclosure is achieved by providing a method for treating an alkali metal sulfate solution obtained from an industrial process according to a first aspect. The method comprises the steps of:(a) providing an alkali metal sulfate solution, preferably directly obtained from an industrial process, and a source of hydrogen chloride;(b) contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture; and(c) reacting the reaction mixture to produce a slurry, said slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

[0006] Precisely, it is provided a method for treating an alkali metal sulfate solution obtained from an industrial process, the method comprising the steps of: - providing an alkali metal sulfate solution and a source of hydrogen chloride; wherein the alkali metal sulfate solution is an alkaline industrial mother liquor obtained from a process for precipitating transition-metal hydroxides and having a pH value of at least 10 and containing at least one of Ni / Mn / Co ions, at least one of Na+and K+, and sulfate ions,- contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture; and- reacting the reaction mixture to produce a slurry, said slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

[0007] It has been observed that treating the alkali metal sulfate solution according to the method of the first aspect substantially converts the alkali metal from the solution form into the formed solid fraction and leaves the sulfates in the liquid fraction, as demonstrated by the examples provided in this disclosure. The disclosed method addresses the drawbacks of prior art by providing a zero-waste, low-temperature treatment process for alkali metal sulfate, enabling cost-efficient implementation and processing. This method allows for the utilization of both products: the solid fraction containing alkali metal chloride and the liquid fraction containing sulfuric acid.

[0008] The disclosed method utilizes inexpensive chemicals and is simple to implement at any industrial location. It can supplement any industrial process that produces waste alkali metal sulfate with minimal investment. For example, the reactor or system can be installed near the source of waste alkali metal sulfate at low cost and operated without disrupting existing facilities and processes.

[0009] All products obtained from the disclosed process can be utilized, enhancing prior art solutions with a fully zero-waste approach. The obtained sulfuric acid can be used, for example, as a leaching chemical, while the obtained alkali metal chloride can be further processed, for example by a chlor-alkali process, into hydrogen chloride for reuse in the disclosed process and into alkali metal hydroxide for use in an industrial process, for example as a precipitant or a pulping chemical.

[0010] Various embodiments are disclosed in the claims and the description of the present disclosure. The embodiments and examples recited in the claims and description are freely combinable with one another, unless otherwise expressly stated. Throughout the disclosure, where numerical ranges are given, the ranges include endpoint values unless otherwise expressly stated.DETAILED DESCRIPTION

[0011] In the following detailed description, preferred embodiments are described in detail to enable the disclosure to be practiced. Although the technology of the disclosure is described with reference to these specific embodiments, it will be understood that the disclosure is not limited to these embodiments. To the contrary, the disclosure includes numerous alternatives, modifications, and equivalents, as will become apparent upon consideration of the following detailed description.

[0012] The term "comprising", as used herein and in the claims, should not be interpreted as being limited to the means set for below; it does not exclude other elements or steps. It is to be interpreted as specifying the presence of the specified features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a composition comprising components A and B" should not be limited to compositions consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the composition are A and B. This same applies to the terms "including" and "containing". Accordingly, the terms "comprising", "containing" and "including" encompass the more restrictive terms "consisting essentially of" and "consisting of".

[0013] As used herein, the term "and / or", when used in a list of two or more items, means that any one of the listed items can be used alone, or any combination of two or more of the listed items can be used. For example, when a composition is described as containing components X, Y and / or Z, the composition may contain Xalone; Y alone; Z alone; X and Y in combination; X and Z in combination; Y and Z in combination; or X, Y and Z in combination.

[0014] In this disclosure, percentage values, unless specifically indicated otherwise, are based on weight (w / w, by weight, or wt%).

[0015] In the present disclosure all given pH values refer to values which are measured at a temperature of 20 °C, unless otherwise stated.

[0016] In one aspect, the present disclosure relates to a method for treating an alkali metal sulfate solution obtainable or obtained from an industrial process. The method comprises the steps of:(a) providing an alkali metal sulfate solution, preferably directly obtained from an industrial process, and a source of hydrogen chloride;(b) contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture; and(c) reacting the reaction mixture to produce a slurry, said slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

[0017] Precisely, it is provided a method for treating an alkali metal sulfate solution obtained from an industrial process, the method comprising the steps of: - providing an alkali metal sulfate solution and a source of hydrogen chloride; wherein the alkali metal sulfate solution is an alkaline industrial mother liquor obtained from a process for precipitating transition-metal hydroxides and having a pH value of at least 10 and containing at least one of Ni / Mn / Co ions, at least one of Na+and K+, and sulfate ions, in the step (a)- contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture, in the step (b); and- reacting the reaction mixture, in the step (c), to produce a slurry, said slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

[0018] Accordingly, the method comprises at least three steps, hereinafter also referred to as step (a), step (b) and step (c). The method may include further optional steps.

[0019] The further optional steps may include, for example, a step following step (c). Such a step (d) may comprise recovering the formed solid fraction and / or liquid fraction from the mixture of end products, e.g. substantially simultaneously or separately, e.g. subsequently. For example, the recovering may comprise separatingthe obtained solution, thus leaving the solid material. The recovery may alternatively or additionally comprise separating the formed solid fraction and liquid fraction, for example by filtering. There may also be further steps for the separated fractions, some of which are described hereinbelow.

[0020] The obtained solid fraction comprises alkali metal chloride and the obtained liquid fraction comprises sulfuric acid, and they may be separated and recovered by any suitable solid-liquid separation process and apparatus. This process may be carried out, for example, by filtration using a suitable filtering device and / or a filter with a cut-off value which allows the recovery of the solids formed. The recovered solids may then be washed.

[0021] The separated and recovered fractions may be analyzed by any suitable method with respect to their composition and a rate of completion of the reaction (i.e., how much of the provided sulfate is converted from the solid reagent to the final product of the liquid fraction, for example). For example, the solid fraction may be analyzed by X-ray diffraction (XR.D) or X-ray fluorescence (XRF), while the liquid fraction may be analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). Other analytical tools and methods may also be used depending on the specific requirements of the use case.

[0022] The method may comprise converting the solution form alkali metal sulfate to solid alkali metal chloride, for example with the reaction:Me2SO4(aq) + 2HCI(aq) -> 2MeCI(s) + H2SO4(aq),where "Me" represents an alkali metal. This equation may be also considered as a general equation describing the overall process of the disclosed method, which can be carried out as the one-step reaction. The reaction conditions and reagent ratios may be selected to control the reaction, for example to facilitate the reaction.

[0023] The disclosed method preferably does not include or substantially does not include other reagents, particularly those that contribute to the conversion of alkali metal sulfate solution into a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid. Thus, the disclosed process is compact, uses inexpensive chemicals, and is easy to implement at any industrial site.

[0024] The apparatus and / or means for performing steps (b) and (c) is not particularly limited. These steps may be carried out in a vessel equipped with one or more mixing / contacting means, such as mixers with mixing blades, agitators, and / or utilizing the flow of reagents to achieve mixing. By ensuring adequate contactbetween the provided reagents, a homogeneous reaction mixture can be obtained. Steps (b) and (c) may be performed, for example, in a stirred reaction tank.

[0025] During the treatment in step (c), it is advantageous to mix the provided reagents, such as by stirring, to ensure an efficient reaction between the provided reagents. This mixing prevents sedimentation of solids formed and ensures that all alkali metal sulfate experience uniform treatment conditions. In some embodiments, reacting the reaction mixture is conducted at room temperature, such as a temperature between 15-30 °C. The experiments of the present disclosure demonstrate that reacting can be conducted at room temperature to achieve the satisfactory results. Operating at room temperature promotes selective NaCI / KCI precipitation, keeps transition metals in solution, improves safety, reduces corrosion and energy costs.

[0026] The mixing and / or step (c) may be carried out for a period of time necessary to allow all or substantially all of the alkali metal sulfate reagent to react, such as to allow sufficient or complete or substantially complete conversion of the alkali metal to the solid fraction formed, for example 70% or more, or 80% or more. The time period may vary depending on a number of factors, such as the concentration of the alkali metal sulfate solution and / or the concentration of the hydrogen chloride in the reaction mixture. It can be 30 minutes or more, such as 45 minutes or more, such as 1-10 hours.

[0027] In one embodiment of the present disclosure, the alkali metal of the alkali metal sulfate solution provided in step (a) is selected from the group consisting of at least Na, K and Li, optionally wherein the alkali metal comprises at least two different alkali metals. In one embodiment, the alkali metal is at least one of Na, K, and Li, preferably Na and K. In one embodiment, the alkali metal of the provided alkali metal sulfate is Na. In one embodiment, the alkali metal of the provided alkali metal sulfate is K.

[0028] The alkali metal sulfate solution provided in step (a) is alkaline, having a pH value 10 or more. In some preferred embodiments, the pH value is 11 or more, or 12 or more.

[0029] The alkali metal sulfate solution may have an alkali metal concentration of 7 g / l or more, such as in the range of 7-200 g / l. In some embodiments, the alkali metal concentration is at least 10 g / l, at least 15 g / l, or at least 20 g / l. In some embodiments, the alkali metal concentration is at most 100 g / l, at most 80 g / l, or at most 60 g / l.

[0030] The alkali metal sulfate solution may have a sulfur content of 5 g / l or more, such as in the range of 5-100 g / l. In some embodiments, the sulfur content is at least 7 g / l, at least 8 g / l, or at least 10 g / l. In some embodiments, the sulfur content is at most 70 g / l, at most 60 g / l, or at most 50 g / l.

[0031] The alkali metal sulfate solution may have a transition-metal ion concentration of 0.001 g / l or more, such as in the range of 0.001-10 g / l. In some embodiments, the transition-metal ion concentration is at least 0.002 g / l, at least 0.003 g / l, or at least 0.004 g / l. In some embodiments, the transition-metal ion concentration is at most 5 g / l, at most 3 g / l, or at most 1 g / l.

[0032] To ensure an efficient reaction in step (c), hydrogen chloride may be added in an excess molar amount relative to the alkaline metal sulfate. The method may involve controlling the stoichiometry of the reactants. For example, it may be possible to achieve an adequate conversion rate of alkali metal to the solid fraction formed for certain applications by using stoichiometric ratio of hydrogen chloride to alkaline metal sulfate. In one embodiment, the method involves contacting hydrogen chloride in step (b) in excess of the molar amount of alkali metal sulfate, preferably a twofold or threefold excess, or more, such as about a sixfold excess or more.

[0033] The source of hydrogen chloride may be provided, at least in part, as an aqueous solution, preferably having a concentration of HCI at least 30 % or more, such as 32 % or 34 %. When the HCI concentration of the aqueous solution is in such ranges, the reaction is effective and / or the conversion rate of sulfate is adequate.

[0034] In one embodiment, the source of hydrogen chloride is hydrogen chloride gas. In one embodiment of the present disclosure, hydrogen chloride gas is added to the reaction mixture, whereto the hydrochloric acid has been added. Providing some of the hydrogen chloride in the reaction in gaseous form can increase reaction efficiency, in part due to avoiding dilution of the reaction mixture. In some embodiments all of the hydrogen chloride or a majority of the hydrogen chloride, such as over 50 % or over 60 % or 70 or 80 % or even more, is provided in gaseous form.

[0035] In one embodiment of the present disclosure, step (b) or step (c) or both are carried out at least in part at a pressure above atmospheric pressure, preferably more than 5 mbar above atmospheric pressure, such as in the range of 1.05 to 6 bar or 2 to 6 bar above atmospheric pressure. Such pressurization can increase reaction efficiency.

[0036] In one embodiment of the present disclosure, the method comprises treating the recovered solid fraction in a chlor-alkali process to convert the alkali metal chloride into alkaline metal hydroxide and chlorine gas.

[0037] The alkaline metal hydroxide obtained from the chlor-alkali process may be used in an industrial process, such as a battery material process, including the coprecipitation process of transition metals, or such as a mining or pulping process, for example.

[0038] The chlorine gas obtained from the chlor-alkali process may be converted into hydrogen chloride or hydrochloric acid. This resulting hydrogen chloride or hydrochloric acid may then be provided as a source of hydrogen chloride in step (a).

[0039] The liquid fraction may comprise, in addition to sulfuric acid (and / or sulfate ions), hydrogen chloride (and / or chloride ions). These sulfuric and chloride components can be separated for example by evaporating the liquid fraction, preferably through gas-liquid separation, so that the sulfuric acid is recovered as one fraction and the hydrogen chloride as another. The recovered hydrogen chloride can then be used upstream in the disclosed process, and the recovered sulfuric acid can be used in an industrial process, such as a leaching chemical.

[0040] All products obtained from the disclosed process can be thus utilized, enhancing prior art solutions with a fully zero-waste approach.

[0041] The alkali metal sulfate treated in the disclosed method is advantageously obtained directly from an industrial process that produces alkali metal sulfate, such as a process in the battery, mining, or pulp industries. In this context, "directly obtained" means that the alkali metal sulfate may not have been treated, e.g. purified, before being supplied to the disclosed process. In other words, the alkali metal sulfate is obtained directly as a waste and / or by-product from the industrial process and it is not processed / refined before being supplied to the present process.

[0042] In step (c), the slurry may be cooled or allowed to cool to 40°C or less, for example, to 30°C or less, preferably to room temperature or below, such as to 25°C or less, or even to 20-0.1°C. This cooling process promotes obtaining a better yield in a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid. The cooling time may include the duration needed to lower the temperature and / or to achieve the desired degree of crystallization, i.e., maturation of the reaction mixture. The cooling time may be 30 minutes or more,such as 1 hour or more, 2 hours or more, or 3 hours or more. Cooling during and / or after step (c), may enhance the reaction efficiency.

[0043] In one embodiment of the present disclosure, the step (c) comprises cooling the reaction mixture, preferably to 30°C or less, such as in the range of 20-0.1°C.

[0044] In one embodiment of the present disclosure, the method comprises heating the reaction mixture before the cooling, preferably to higher than 30°C, such as in the range of 40-50°C. In some applications, such heating of the reaction mixture prior to cooling may improve sulfate removal from the solid fraction, i.e., more pure alkali chloride is obtained as a solid fraction. In addition, such heating may improve reaction efficiency.

[0045] In some embodiments, the obtained solid fraction is washed, advantageously with a washing liquid containing hydrogen chloride. Such washing may improve the purity of the alkali chloride solid fraction obtained.

[0046] With the disclosed process, it is possible to achieve a closed or substantially closed or semi-closed process, in particular with respect to alkaline metal sulfate. This process utilizes all or nearly all of the materials provided, in particular the liquid fraction comprising sulfuric acid and / or the solid fraction comprising alkaline metal chloride obtained from the process. This allows industrial processes that produce little or no waste. Since alkaline metal sulfate has been considered a problematic waste due to its limited further use and has often been discarded, this process allows it to be utilized, turning it into a valuable raw material for industrial processes, particularly those that produce it as a by-product. By using all or nearly all of the waste alkali metal sulfate, there is no need to find disposal sites or obtain waste disposal permits. This facilitates the implementation of industrial processes and facilities with fewer environmental concerns, fewer permitting requirements, reduced need for wastewater treatment units or facilities, and suitability for a variety of sites.

[0047] In one aspect, the present disclosure provides use of alkali metal sulfate solution obtainable or obtained from an industrial process to prepare alkali metal chloride and / or sulfuric acid with the method disclosed herein. The alkali metal chloride obtained is preferably used as is or treated into a form suitable for industrial use, such as being converted into alkali metal hydroxide and hydrogen chloride as described herein. The sulfuric acid obtained is preferably used in the industrial process, as discussed elsewhere in this disclosure.

[0048] Modifications of the disclosure will occur to those skilled in the art and to those who make or use the disclosure. Therefore, it is understood that the embodiments described above are merely for illustrative purposes and not intended to limit the scope of the disclosure, which is defined by the following claims, as interpreted according to the principles of patent law, including the doctrine of equivalents.EXPERIMENTAL ANALYSIS USED IN THE EXAMPLES

[0049] The following analysis methods are used in the Examples and the Comparative Example:A) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) measurement

[0050] The contents of alkali metals (Na, K, and Li) and S and Cl in the obtained solid fraction and liquid fraction samples were measured by the Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) method using an Thermo iCAP 6000 Series ICP-OES instrument.

[0051] The test sample was prepared as follows for solid samples: 0.25 gram of a powder sample of 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 completely homogenized. 1 ml of the solution was removed with a pipette and transferred to a 100 ml volumetric flask for the second dilution. An appropriate amount of concentrated nitric acid was added with a pipette to obtain a 5% HNO3 solution when made up to volume with deionized water (DI) and then homogenized. This solution was then used for the ICP-OES measurement. The contents of alkali metals (Na, K and Li), S and Cl are expressed in %.

[0052] The test sample was prepared as follows: for liquid samples, 1 ml of liquid sample was taken with a pipette and transferred to a 100 ml volumetric flask. The volumetric flask was filled to the 100 ml mark with deionized (DI) water and then completely homogenized. An appropriate amount of the solution was pipetted and transferred to a 100 ml or 250 ml volumetric flask for the second dilution. An appropriate amount of concentrated nitric acid was pipetted to obtain a 5% HNO3 solution when made up to volume with deionized (DI) water and then homogenized. Finally, the solution was used for the ICP-OES measurement. The contents of alkali metals (Na, K and Li), S and Cl are expressed in g / l.B) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) measurement

[0053] 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.Table 1. XRD measurement conditionsC) X-ray fluorescence spectroscopy (XRF) analysis

[0054] The chloride (Cl) content of the solid fractions obtained in the examples was analyzed by the XRF method. Approximately 20 g of the solid fraction was mixed with binder (mixture of cellulose and emu powder) and then milled and pressed into a briquette. The briquette XRF samples were measured using a PW2404 XRF spectrometer manufactured by Phillips under the conditions described in Table 2 below.Table 2. XRF measurement conditionsEXAMPLES AND COMPARATIVE EXAMPLES

[0055] The present disclosure is further illustrated in the following examples.

[0056] Four separate examples, designated Examples 1.1 through 1.4, were performed. In each example, 100 ml of mother liquor, pH 12.5, whose content analysis is summarized in Table 2, obtained from the co-precipitation process of Ni, Mn, and Co sulfate solution with a sodium hydroxide solution to produce the corresponding tertiary transition metal hydroxide, pCAM, which is to be mixed with a lithium source and sintered to obtain cathode active material for batteries, was combined with 100 ml (Example 1.1), 200 ml (Example 1.2), 400 ml (Example 1.3), and 600 ml (Example 1.4) of 32% hydrochloric acid in an Erlenmeyer flask to form a reaction mixture. The mixture was then stirred with a magnetic stirrer for one hour at room temperature. Visual inspection revealed that the mixture began to contain white solids as the mixing process progressed. After mixing, the mixture was filtered through a Buchner funnel to separate the solid and liquid fractions obtained.

[0057] The analysis of the obtained solid and liquid fractions, including XR.D and XRF for the solid fraction and ICP of the elemental composition analysis for the solid and liquid fractions, was performed as described above and the results are presented in Table 3. Table 3 also shows the amount (in grams) of solid fraction obtained and the percentage conversion of sulfate from the provided sodium sulfate to the analyzed liquid fraction obtained, calculated from the sodium content in the provided sodium sulfate solution and the measured sodium content in the obtained solid fraction.

[0058] Two separate examples, designated Examples 2.1 and 2.2, were performed. In both example, 100 ml of mother liquor, pH 12.25, whose content analysis is summarized in Table 2, obtained from the co-precipitation process of Ni, Mn, and Co sulfate solution with a potassium hydroxide solution to produce the corresponding tertiary transition metal hydroxide, pCAM, which is to be mixed with a lithium source and sintered to obtain cathode active material for batteries, was combined with 200 ml (Example 2.1), and 400 ml (Example 2.2) of 32% hydrochloric acid in an Erlenmeyer flask to form a reaction mixture. The mixture was then stirred with a magnetic stirrer for one hour at room temperature. Visual inspection revealed that the mixture began to contain white solids as the mixing process progressed. After mixing, the mixture was filtered through a Buchner funnel to separate the solid and liquid fractions obtained. The results are presented in Table 3.Example 3 (EX3)

[0059] Two separate examples, designated Examples 3.1 and 3.2, were performed. 25 ml (Example 3.1) and 15 ml (Example 3.2) of the same mother liquor used in Example 1 as a source of sodium sulfate solution was combined in a round flask with hydrogen chloride gas produced from the amount of 250 ml of 32% hydrochloric acid to form a reaction mixture. The mixture was then stirred with a magnetic stirrer for one hour at room temperature. Visual inspection revealed that the mixture began to contain white solids as the mixing process progressed. After mixing, the mixture was filtered through a Buchner funnel to separate the solid and liquid fractions obtained.Table 2. The content of the industrial process stream used in Examples 1-3Table 3. The analysis results of the obtained solid and liquid fractions of Examples 1-3Calculated from the sodium(Exl) / potassium(Ex2) / sodium(Ex3) content in the alkaline sulfate solution provided and the measured corresponding alkaline metal content in the solid fraction obtained.“ A mass fraction calculated based on the Rietveld refinement analysis, where X is Na in Ex 1.1-1.4 and in Ex 3.1-3.2 and K in Ex 2.1-2.2.Na in Ex 1.1-1.4 and in Ex 3.1-3.2 and K in Ex 2.1-2.2.

Claims

1. CLAIMS1. A method for treating an alkali metal sulfate solution obtained from an industrial process, the method comprising the steps of:(a) providing an alkali metal sulfate solution and a source of hydrogen chloride;wherein the alkali metal sulfate solution is an alkaline industrial mother liquor obtained from a process for precipitating transition-metal hydroxides and having a pH value of at least 10 and containing at least one of Ni / Mn / Co ions, at least one of Na+and K+, and sulfate ions,(b) contacting the alkali metal sulfate solution and the source of hydrogen chloride to obtain a reaction mixture; and(c) reacting the reaction mixture to produce a slurry, said slurry comprising a solid fraction comprising alkali metal chloride and a liquid fraction comprising sulfuric acid.

2. The method according to claim 1, wherein the alkali metal is at least one of Na and K, optionally wherein the alkali metal comprises at least two different alkali metals consisting of Na, K and Li.

3. The method according to claim 1 or 2, wherein the alkali metal sulfate solution is alkaline, preferably having a pH value of 11 or more, or 12 or more.

4. The method according to any of the preceding claims, wherein the alkali metal sulfate solution has an alkali metal concentration of 7 g / l or more, such as in the range of 7-200 g / l.

5. The method according to any of the preceding claims, wherein the hydrogen chloride in step (b) is in excess of the molar amount of alkali metal sulfate, preferably a twofold or threefold excess.

6. The method according to any of the preceding claims, wherein the source of hydrogen chloride is provided at least partially as an aqueous solution, preferably having a concentration of HCI at least 30 % or more, such as 32 % or 34 %.

7. The method according to any of the preceding claims, wherein the source of hydrogen chloride is provided at least partially as a gas.

8. The method according to any of the preceding claims, wherein step (b) or step (c) or both are carried out at least in part at a pressure above atmospheric pressure, preferably more than 5 mbar above atmospheric pressure, such as in the range of 1.05 to 6 bar or 2 to 6 bar above atmospheric pressure.

9. The method according to any of the preceding claims, comprising recovering the formed solid fraction and / or liquid fraction.

10. The method according to claim 9, comprising treating the recovered solid fraction in a chlor-alkali process to convert the alkali metal chloride into alkaline metal hydroxide and chlorine gas.

11. The method according to claim 10, comprising using the alkaline metal hydroxide obtained in an industrial process, such as a battery process, including the co-precipitation process of transition metals, or such as a mining or pulping process.

12. The method according to claim 10 or 11, comprising converting the obtained chlorine gas into hydrogen chloride.

13. The method according to claim 12, wherein the resulting hydrogen chloride is provided as a source of hydrogen chloride in step (a).

14. The method according to any of the preceding claims, wherein the alkali metal sulfate solution has a transition-metal ion concentration of 0.001 g / l or more, such as in the range of 0.001-10 g / l.

15. The method according to any of the preceding claims, comprising in the step (c), following the reacting the reaction mixture, cooling the slurry, preferably to 30°C or less, such as in the range of 20-0.1°C.

16. The method according to claim 15, wherein step (c) comprises heating the reaction mixture before the cooling, preferably to higher than 30°C, such as in the range of 40-50°C.

Images