Method for treating waste sodium sulfate obtained from an industrial process, use of waste sodium sulfate obtained from an industrial process, and industrial treatment plant

Abstract

A method for treating waste sodium sulfate obtained from an industrial process is disclosed. The method includes preparing a solution of waste sodium sulfate, preparing potassium hydroxide, either in solid form or as a solution having a potassium hydroxide concentration of 25% by weight or more, and mixing it with the waste sodium sulfate solution to obtain a reaction mixture for converting the waste sodium sulfate to potassium sulfate and sodium hydroxide, and recovering the potassium sulfate and sodium hydroxide formed. Uses of the waste sodium sulfate and an industrial treatment plant are also disclosed.

Description

[Technical Field]

[0001] The present disclosure relates to a method for treating waste sodium sulfate obtained from an industrial process, and to an industrial processing plant. The present disclosure also relates to uses of the waste sodium sulfate obtained from an industrial process. The present disclosure also relates to a fertilizer product. [Background technology]

[0002] The release of sulfates can increase the salinity of the water and increase eutrophication. Soluble sulfates, such as sodium sulfate (Na2SO4), increase the salinity of the water. Saltier wastewater has a higher density than lake water. Due to the density difference, the water easily forms two layers: salty water at the bottom and less salty water on top. This phenomenon is called stratification and reduces natural water mixing with the bottom and surface layers.

[0003] Several industrial activities, such as metal refining and pulping, produce metal sulfates, which are increasingly restricted by strict limits on sulfate wastewater concentrations. For example, kraft pulp wastewater contains sodium sulfate due to the use of NaOH and NaS as cooking chemicals. Sulfate concentrations in effluent are typically at levels of 54,000 kg / day. In older pulp mills, sulfate emissions in effluent can be up to 1500 mg / L. Sulfate has not been considered as a pulp mill effluent parameter. Therefore, sulfate is rarely removed during biological wastewater treatment. The WHO guideline for the maximum sulfate content in drinking water is 250 mg / L.

[0004] One new and rapidly growing industry is the production of lithium-ion battery precursors, which are typically prepared by co-precipitation from sulfate-based metal solutions. In Finland, for example, the sulfate limit for wastewater and the required treatment method are determined by the company's environmental permit. A typical limit for sulfate concentration in sewage is 400 mg / L. The sulfate limit is in place to reduce the environmental burden caused by the increasing salinity of natural waters, especially freshwater.

[0005] In the prior art, sodium sulfate is converted to potassium sulfate or Glauber salt or is disposed of by landfill, but these are not practical solutions to solve the problem of generated waste sodium sulfate. Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need to increase industrial production while avoiding the generation of sulfate-based waste and chlorides, which requires more efficient methods for wastewater and process water treatment, both for sulfate removal and for reuse of sulfate-containing wastewater and process water. [Means for solving the problem]

[0007] We have discovered a process that utilizes waste sodium sulfate from industrial sources and converts it back into usable chemicals. This process overcomes the shortcomings of the prior art, provides a zero-waste, low-temperature process, and allows for cost-effective implementation and processing. This process allows for utilization of both the NaOH and KSO products derived from sodium sulfate.

[0008] The present disclosure provides a method for treating waste sodium sulfate obtained from an industrial process, the method comprising: - preparing a solution of waste sodium sulfate; - providing potassium hydroxide in solid form or as a solution having a potassium hydroxide concentration of 25% by weight or more and mixing it with a solution of waste sodium sulfate to obtain a reaction mixture and convert the waste sodium sulfate into potassium sulfate and sodium hydroxide; - recovering the potassium sulfate and sodium hydroxide formed; Includes.

[0009] The present disclosure also provides the use of waste sodium sulfate obtained from an industrial process for preparing sodium hydroxide using the present method.

[0010] The present disclosure also provides for the use of waste sodium sulfate obtained from an industrial process for preparing potassium sulfate with a method for preparing a fertilizer product.

[0011] The present disclosure provides: - industrial processes utilizing sodium hydroxide; - a source of a solution of waste sodium sulfate; a device configured to carry out the method, the device comprising: - reactor, - mixing means, - comprising a heating means; a device in which said mixing means and said heating means are electrically controllable; Including, a source of waste sodium sulfate is conveyed and / or transported to said reactor; - the sodium hydroxide obtained from the reactor is conveyed and / or transported to an industrial process that utilizes sodium hydroxide; and - the potassium sulfate obtained is recovered from the reactor. The present invention provides an industrial processing plant comprising:

[0012] The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples disclosed herein can be freely combined with each other, unless otherwise stated.

[0013] The method of the present invention utilizes inexpensive chemicals and is simple to implement at any industrial site, and therefore any applicable industrial process that provides waste sodium sulfate can be supplemented by the present process with little investment, for example, the present reactor or system can be implemented near the source of waste sodium sulfate at low cost and can be operated without disturbing existing equipment and processes.

[0014] The process improves on current solutions with a completely zero waste approach, as all products obtained from the process can be utilized, making it possible to use the obtained NaOH, for example, as a cooking chemical or precipitant, and the obtained KSO, for example, for fertilizer. [Brief explanation of the drawings]

[0015] [Figure 1] Figure 1 shows an example of this process. [Figure 2] FIG. 2 shows an example of a method for treating waste sodium sulfate. [Figure 3] FIG. 3 shows the measured XRD spectrum of the solid product obtained from this process. DETAILED DESCRIPTION OF THE INVENTION

[0016] As used herein, percentage values ​​are by weight (w / w, by weight, or % by weight) unless specifically indicated otherwise. When any numerical range is provided, the range is inclusive of the upper and lower limits. The open term "comprise" also includes the closed term "consisting of" as an alternative.

[0017] As mentioned above, large amounts of metal sulfates are formed annually in industrial activities. Sulfate recovery methods have been extensively researched to reduce sulfate concentrations in process water or wastewater in a commercially viable and efficient manner. To date, no cost-effective technical method exists for treating alkaline sulfate waste streams. Acidic sulfate waste streams are typically precipitated with calcium, and the resulting gypsum sludge is recovered. Again, a technical and economical solution is lacking.

[0018] Alkaline waste sodium sulfate solutions are formed as by-products in the chemical and pulp industries. One example is the precipitation of battery precursors from metal sulfate solutions using NaOH as the precipitant. As an example, the concentrations of major elements in waste sodium sulfate are listed in Table 1. In addition to the elements mentioned in Table 1, the solution contained ammonium ions at a concentration of 4 g / L as residue from chemical coprecipitation.

[0019] [Table 1]

[0020] This disclosure relates to a process for the utilization, or valorization, of waste sodium sulfate by reacting potassium hydroxide with water to produce potassium sulfate and sodium hydroxide. Potassium sulfate is a chemical used in fertilizer and is currently produced by high-temperature processing. NaOH can be recycled for use, for example, as a precipitant in the chemical industry or as a cooking chemical in the pulp industry.

[0021] The present disclosure provides a method for treating waste sodium sulfate obtained from an industrial process. An example of the method is disclosed in FIG. 1. The industrial process 10 can be any applicable industrial process that provides sodium sulfate (NaSO) in a suitable form, which can be an industrial process effluent. Preferably, the waste sodium sulfate is alkaline waste sodium sulfate, and the pH of the waste solution is in the alkaline range, e.g., a pH of 8 or greater, 9 or greater, 10 or greater, 11 or greater, or 12 or greater. The sodium sulfate must be sufficiently concentrated; wastewater containing small amounts of sodium sulfate, e.g., less than 50 g / L, less than 30 g / L, or less than 10 g / L of sodium sulfate, is rejected.

[0022] The method includes providing sodium sulfate in solution, providing an amount of potassium hydroxide, and mixing the potassium hydroxide with the sodium sulfate solution to obtain a reaction mixture. Reaction(s) occur in reaction mixture 12 to obtain a final product mixture. The potassium sulfate and sodium hydroxide formed are recovered from the final product mixture. The method may include washing the resulting solid material containing potassium sulfate, thereby reducing the sodium content.

[0023] Potassium hydroxide may be provided, e.g., added, in molar excess relative to sodium sulfate, however, it may be possible to obtain appropriate final concentrations of potassium sulfate and sodium hydroxide for a particular application (other than a battery application) by using a stoichiometric or sub-stoichiometric ratio of potassium hydroxide to sodium sulfate.

[0024] The method may include converting waste sodium sulfate to potassium sulfate and sodium hydroxide in a one-step reaction. Na2SO4+2KOH → K2SO4+2NaOH

[0025] This formula can also be considered as a general formula describing the overall process of the method of the present invention, which can be carried out as a one-step reaction or as a two-step reaction.

[0026] The method may also be carried out using a two-step reaction having a first step (1) and a subsequent step (2): (1)2Na2SO4+3KOH → K3Na(SO4)2+3NaOH (2)K3Na(SO4)2+KOH → 2K2SO4+NaOH

[0027] The method may include controlling the stoichiometry of the reactants in step (1) or step (2) to control the reaction. More specifically, the reaction in step (1) may be carried out to the extent that less than all of the reactants react, i.e., to effect a partial reaction. This can be done by maintaining a substoichiometric ratio of KOH to sodium sulfate. In step (1), a precipitation mixture is obtained, which is shown in the reaction as K3Na(SO4)2. More specifically, the precipitation mixture contains primarily K3Na(SO4)2 but may also contain K2SO4. It may also be referred to as "impure potassium sulfate" or "impure K2SO4," for example, in FIG. 2. The precipitation mixture is then fed to step (2).

[0028] In step (2), potassium hydroxide can be provided in molar excess (superstoichiometric ratio) relative to sodium sulfate. This has been found to substantially increase the amount of solid KSO obtained from the reaction and reduce the amount of SO residue in the resulting NaOH (i.e., the resulting liquid phase), respectively, allowing the NaOH to be used as such, i.e., without further purification, in a variety of applications or industrial processes, including purity-sensitive applications and technical fields such as the battery industry.

[0029] In one embodiment, the molar excess is a molar ratio of potassium hydroxide to sodium sulfate, e.g., a molar ratio of KOH to NaSO and / or KNa(SO), of 4:1 or greater, preferably 5.1 or greater. Molar ratios of 5:1 or greater, e.g., 6:1 or greater, have been shown to efficiently precipitate almost all sulfate from the sodium sulfate solution. Additionally, the amount of sodium in the final solid precipitate is low, making it suitable for use as a fertilizer.

[0030] The potassium sulfate can be crystallized and separated from the sodium hydroxide in this process, with the sodium hydroxide remaining solubilized in solution. The resulting solid potassium sulfate can be recovered and used, for example, as a fertilizer product or for the preparation of fertilizer product 14, which can be performed in the same process or a separate process. Other products containing or based on potassium sulfate can be prepared as well. The resulting solid potassium sulfate can be shipped to another location for further processing, for example, to prepare additional products, such as a fertilizer manufacturer, to prepare a fertilizer product.

[0031] The resulting sodium hydroxide can be recovered and reused, for example, as a chemical, in the same industrial process 10 or in a process related to the same industrial process 10. The industrial process is an industrial process that utilizes sodium hydroxide, for example, using sodium hydroxide as a process chemical and / or for other purposes in the process or a related process. The industrial process can be carried out in the same facility or plant, for example, in a factory, mill, or any other applicable processing site. However, it is possible to provide the sodium hydroxide for another use and / or industrial process, and preferably, such use and / or process is located near the location where the method is carried out. Transport or conveyance of the resulting sodium hydroxide can be arranged in most industrial plants or other facilities, for example, by providing piping or other conveyance means, or by arranging transport in containers, for example, by using dedicated conveyors or other transport means, for example, by using vehicles and / or transport chains.

[0032] The solid potassium sulfate and sodium hydroxide solutions can be separated and recovered by using any suitable method and apparatus for separating and recovering solids and liquids. The separated and recovered fractions can be analyzed for purity using any suitable means. For example, the purity of the potassium sulfate may be analyzed from a sample using X-ray powder diffraction (XRD) and related equipment, such as an X-ray powder diffractometer or a versatile XRD system for R&D, to obtain an XRD spectrum or pattern, which can be used to evaluate the purity of the potassium sulfate and / or the degree of conversion in the process, the success of the process, etc. The resulting potassium sulfate and sodium hydroxide can be identified by analyzing the fractions. The progress of the reaction, such as the degree of conversion during the reaction, can also be monitored and / or estimated by using other means, such as monitoring the absorbance and / or turbidity of the reaction mixture, detecting precipitates formed, etc.

[0033] In one embodiment, the method comprises using the recovered sodium hydroxide in an industrial process and / or a process related to an industrial process.

[0034] Thus, a closed or substantially closed process can be provided, particularly with regard to sodium sulfate, which utilizes all or substantially all of the materials provided to the method, particularly sodium hydroxide, and the materials obtained from the method. This makes it possible to provide an industrial process with little or no waste. Because sodium sulfate is considered a problematic waste product with respect to further use and the material is primarily discarded, the method makes it possible to utilize the waste and obtain valuable raw materials for the process. Because all the waste sodium sulfate can be utilized, there is no need to find a waste disposal site or apply for any permits to dispose of the waste. This reduces environmental issues, reduces permits, requires fewer wastewater purification units or plants, and allows the industrial process and plant to be implemented in a variety of locations.

[0035] In one embodiment, the method is a waste-free method, involving utilizing all or substantially all reaction products and / or reagents, including waste sodium sulfate. Waste-free refers to a process for treating sodium sulfate that generates no or substantially no waste. For example, a small amount of waste may be obtained that includes or consists of impurities present in the waste sodium sulfate that may have been separated in the process. However, residual impurities may not be a problem in all cases, and therefore, removal of impurities from the final product may not be necessary.

[0036] Sodium sulfate can be fed into the reactor or similar vessel as a solution, such as an aqueous solution. The sodium sulfate solution must have a sufficiently high concentration, such as 50 g / L or more, e.g., 80 g / L or more, 100 g / L or more, and preferably 120 g / L or more. In one embodiment, sodium sulfate is provided as an aqueous solution having a concentration of 100 g / L or more. The solution can have a sodium sulfate concentration in the range of 100 to 450 g / L or 120 to 450 g / L, e.g., 120 to 400 g / L, or 140 to 300 g / L. Sodium sulfate can be obtained directly from a corresponding industrial process that generates sodium sulfate; therefore, the waste sodium sulfate does not need to be purified or otherwise treated before being fed to the present method. However, the waste sodium sulfate solution can be concentrated and / or is concentrated during the present method. The present method can include measuring and / or obtaining the concentration of sodium sulfate in the waste sodium sulfate solution. This can be used to determine the required amount of potassium hydroxide, the suitability of the waste liquid for the method, the need to concentrate the waste liquid, and / or the need to adjust any other process parameters, and a corresponding decision on whether and / or to what extent to perform such action can be made based on the determined and / or obtained concentration. The method can include providing waste sodium sulfate from an industrial process or from a process step that generates waste sodium sulfate, for example by conveying and / or transporting it in a container. The waste sodium sulfate can contain small amounts of impurities, but in tests it has been found that the impurities do not interfere with the process and that, if necessary, the impurities can even be separated from the sodium sulfate.

[0037] The sodium sulfate concentration can be adjusted to obtain optimal potassium sulfate precipitation. A suitable sodium sulfate concentration may be obtained after concentration, or the original wastewater may already have such a concentration, e.g., 2 mol / L or less, or 1.8 mol / L or less, e.g., 0.3-2.0 mol / L, 0.5-2.0 mol / L (71-284 g / L), or 1-1.8 mol / L (142-256 g / L). At concentrations above 2.5 mol / L, sodium sulfate tends to precipitate, which interferes with the process. In most cases, a concentration in the range of 1.0-2.0 mol / L (142-284 g / L) has been found to be optimal.

[0038] The potassium hydroxide can be provided in solid form or as a solution, such as an aqueous solution. The solution can be concentrated, such as having a KOH concentration of 25% by weight or more, e.g., 30% by weight or more, e.g., in the range of 30-50% by weight, e.g., about 30% by weight. Preferably, the potassium hydroxide is provided in solid form, such as in granular or powder form. Solid potassium hydroxide generates heat when solubilized in aqueous solution, which facilitates the process. Furthermore, providing the KOH in solid or concentrated form allows the method to be carried out in a simple, safe, and compact manner. This has advantages in water and solution management, as well as in the implementation of devices and systems that can be more compact because large amounts of KOH are not required.

[0039] Potassium hydroxide is mixed with sodium sulfate. This can be done in a reactor, which may be equipped with one or more mixing means, such as one or more mixers, which may be equipped with one or more mixing blades, agitators, fluid flow effects, etc., or may utilize the fluid flow effects of liquids to achieve mixing. A reaction mixture is obtained. The reaction mixture and / or the contents of the reactor are preferably heated by using one or more heating means, such as one or more heaters arranged to heat the contents of the reactor. Mixing and / or heating can be performed to achieve a homogeneous solution. The reaction mixture can be heated to or have a temperature below 100°C, for example, 95°C or less, or 90°C or less. The temperature can be 60°C or higher, for example, 70°C or higher, or 80°C or higher. The temperature can be in the range of 60-90°C, for example, 60-80°C, 70-90°C, or 80-90°C. Alternatively, or additionally, the sodium sulfate solution can be provided at an elevated temperature and / or heated.

[0040] The solubilities of the sodium and potassium salts differ substantially at temperatures above 60°C, as shown in Table 2.

[0041] [Table 2]

[0042] Heating and / or mixing may be carried out for a time necessary to react all or substantially all of the reactants, e.g., a time necessary to allow complete or substantially complete conversion of sodium sulfate to potassium sulfate, e.g., 90% or greater, or 95% or greater.

[0043] The reaction mixture may be concentrated to remove water. Concentration may be by evaporation, which may be carried out at elevated temperatures. In one embodiment, the method includes concentrating the reaction mixture, preferably by evaporation. This may be done before and / or after adding potassium hydroxide.

[0044] The solution is cooled or allowed to cool, for example to below 50°C, for example below 40°C, preferably to room temperature, for example below 25°C, for example 20-22°C, to obtain crystallized potassium sulfate and a solution of sodium hydroxide. During cooling, potassium sulfate crystallizes in high purity (>90%), and the formed NaOH remains in solution. The crystallized potassium sulfate forms a suspension and can be precipitated to obtain a solid potassium sulfate precipitate, which can be separated from the remaining NaOH solution.

[0045] Preferably, the solution is cooled or allowed to cool to a temperature of 2°C or higher, for example 5°C or higher, for example 10°C or higher. Advantageously, cooling is above 1.8°C, which may prevent solidification of the sodium sulfate. The temperature may be, for example, in the range of 2 to 50°C, for example 2 to 40°C or 2 to 25°C, preferably 5 to 50°C, for example 5 to 40°C or 5 to 25°C, for example 10 to 50°C, for example 10 to 40°C or 10 to 25°C, for example about 30°C.

[0046] In one embodiment, the method comprises: - heating the reaction mixture to 60-90°C to obtain a preferably homogeneous solution; - cooling the solution to below 50°C to obtain a crystallized potassium sulfate and sodium hydroxide solution; Includes.

[0047] The method may be performed in a device comprising the means disclosed herein, which may be controllable, such as electronically controllable. The device may be an automated or semi-automated device and may be part of a complex or system. The device or system may be a pulping and / or papermaking process and / or industry device or system, or a battery industry device or system.

[0048] In one example, the device a reactor; - a mixing means; - temperature control means, such as heating and / or cooling means, such as heating and optionally cooling means, The mixing means and the temperature control means are electrically controllable and preferably operably connected to control means, such as one or more control units, arranged to carry out the method steps disclosed herein, such as controlling at least the temperature in the reactor and / or controlling the mixing. The control means may be operably connected to one or more means, devices, actuators, etc. disclosed herein, so that the control means can controllably operate the means, and / or to one or more sensors and other devices arranged to monitor the process, i.e., obtain information from the process, e.g., from the reactor / reaction mixture. This device may include cooling means, e.g., one or more coolers, e.g., implemented with a liquid flow within the reactor envelope. The cooling means may be used to cool the reactor mixture or homogeneous solution to initiate precipitation. The cooling means may be operably connected to the control unit.

[0049] The device may also include one or more of the following: - inlet for waste sodium sulfate solution, - an inlet for potassium hydroxide, - outlet for the obtained solid potassium sulfate, - an outlet for the resulting sodium hydroxide solution, - one or more sensors positioned to monitor one or more properties of the reaction mixture and / or reactor, such as temperature, pH, turbidity, absorbance, flow rate, liquid level, conductivity, etc.; - one or more pumps for conveying the solution, which may be operably connected to the control unit; - one or more further vessels as disclosed herein and the necessary connections such as pipes, - one or more valves for controlling the flow of solutions and / or solids, and / or - one or more actuators connected to one or more moving members for mixing, moving, and / or otherwise controlling the process, the actuators being operably connected to a control unit. The valves may be electrically controllable valves with actuators operably connected to the control unit. The device may comprise a container for potassium hydroxide, the container being connected via a controllable valve or other control means, e.g., operably connected to the control unit so that the input of potassium hydroxide can be controlled. The container may comprise a funnel for allowing the flow of solid potassium hydroxide. The device may comprise means for discharging the resulting solid potassium sulfate, such as at the bottom of the reactor, e.g., actuators connected to one or more moving members for moving the solid potassium sulfate, which means may be operably connected to the control unit.

[0050] The device may include an inlet for solid potassium hydroxide or an inlet for a concentrated solution of potassium hydroxide, which may have the concentrations disclosed herein.

[0051] The device utilizes mixing means, such as a mixer, to ensure immediate solubilization of the concentrated solution of solid KOH or potassium hydroxide, facilitating the avoidance of local concentration gradients. Even if heating or cooling is not necessarily required initially, for example, due to heat generation from solubilizing KOH or the need to reduce the temperature, the reaction can be easily controlled by maintaining the temperature of the reaction mixture optimally during the process using temperature control means. The temperature control means may include one or more heating and / or cooling elements arranged to control the temperature of the reactor and / or the reaction mixture within the reactor.

[0052] The inlet for solid potassium hydroxide or the inlet for concentrated potassium hydroxide solution can be connected to a container for solid potassium hydroxide or concentrated potassium hydroxide solution. The use of concentrated potassium hydroxide allows for a relatively small volume container to be provided, allowing the system and device to be implemented in a compact form.

[0053] The industrial processing plant may be an industrial processing plant for pulping and / or paper manufacturing processes and / or industries, or an industrial processing plant for the battery industry.

[0054] The control unit may be an electronic control unit, which may be programmable, comprising one or more processors, memory, and software configured, when executed on the processor in the control unit, to perform one or more operations for carrying out the method, e.g., to regulate the temperature of the reaction mixture by controlling temperature control means such as heating and / or cooling means, to control mixing means to obtain a desired mixture of the reaction mixture, to monitor the temperature and / or other properties of the reaction mixture using one or more sensors in the reactor, and similar operations. The control unit may be arranged, e.g., programmed, to monitor one or more properties from the device, system, and / or reactor, e.g., as a function of time, and, as feedback on the monitored properties, to perform one or more control actions in the device or system to adjust the function of the device to carry out the method. Properties such as temperature, pH, turbidity, absorbance, conductivity, flow rate, liquid level, control of substance addition, mixing rate, etc., may be monitored using one or more sensors arranged to monitor the property. For example, temperature may be controlled to be within a predetermined range and / or to increase and / or decrease in a controlled manner to carry out the method.

[0055] The present disclosure provides: - industrial processes utilizing sodium hydroxide; a source of waste sodium sulfate, which may be an industrial process utilizing sodium hydroxide, an associated industrial process and / or a separate industrial process; a device arranged to carry out the method, the device comprising: - reactor, - mixing means, - temperature control means, e.g. heating and / or cooling means, - the mixing means and the temperature control means are electrically controllable and preferably operably connected to a control unit arranged to carry out at least the method steps of controlling the temperature in the reactor and / or controlling the mixing; - a source of waste sodium sulfate arranged to be delivered and / or transported to the reactor; - sodium hydroxide obtained from the reactor, which is arranged to be conveyed and / or transported to an industrial process that utilizes sodium hydroxide; - the resulting potassium sulfate, which is arranged to be withdrawn from the reactor; The present invention provides an industrial treatment plant, or a system or device arrangement in an industrial process plant, or similar treatment site, comprising:

[0056] The method and overall process may be performed in different ways by different operators, and the method may facilitate an entire production chain, including actions performed by different operators. The method may be performed by one operator or by two or more operators. For example, a first operator may generate waste sodium sulfate. Such an operator may perform an industrial process, which may be performed in a factory, plant, or other applicable production or processing location, and may be an industrial process that utilizes sodium hydroxide 10. The waste sodium sulfate may be collected in a container or provided directly from the process via a conveying means, such as a pipe. The first operator may also provide the waste sodium sulfate to the location where the reaction is performed (which may be referred to as the point of use). For example, another operator could provide the waste sodium sulfate when the waste sodium sulfate is collected in a container and transported to the point of use. The reaction(s) 12 may be performed by the first or second operator, but may also be performed by a third operator who operates the reactor, charges potassium hydroxide, and recovers the reaction product. This operator may also provide the reaction product for further use, and the operator may also perform one or both of the further uses, i.e., using sodium hydroxide as a compound and / or providing potassium sulfate for the preparation of fertilizer 14 or preparing the fertilizer. However, it is also possible that one or two further operators perform these steps and / or that the first operator performs the step of using sodium hydroxide as a compound in industrial process 10. An operator that may utilize the resulting potassium sulfate may be a fertilizer manufacturer.

[0057] An example of a method of the present invention for treating waste sodium sulfate is shown in Figure 2. This process utilizes two precipitation steps and can provide a high purity final product. The process of Figure 2 can be included in step 12 of Figure 1.

[0058] In step 20, sodium sulfate (NaSO) waste liquor is fed to a reactor, concentrated (30%) potassium hydroxide (KOH) in solid form as pellets is added, and the resulting solution is mixed and heated to 80°C to obtain a homogeneous solution. The solution is concentrated by evaporation at high temperature. When the mixture is cooled to 50°C in step 22, potassium sulfate (KSO) crystallizes and contains some residual sodium sulfate. This resulting impure potassium sulfate is solubilized in a minimum amount of water at 80°C and crystallized by cooling to 50°C for purification crystallization step 26. Pure potassium sulfate is obtained from step 26 and can be recovered.

[0059] The remaining solution from steps 22 and 26 is crystallized in a second crystallization step 24 by cooling to 0-20°C. Regenerated NaOH, Na2SO4, and residual K2SO4 are obtained in step 30. NaOH can be recovered and reused, for example, transported to an industrial process. The residual solution containing Na2SO4 and residual K2SO4 from step 30 is returned to step 20. Alternatively, the residual solution containing Na2SO4 and residual K2SO4 from step 26 can be returned directly to step 20 to avoid dilution of the NaOH solution in the second crystallization step 24.

[0060] The method may be applied to a variety of industrial processes 10 that provide waste sodium sulfate.

[0061] In one embodiment, the industrial process 10 is a pulping process. A pulping process refers to a process or system setup that includes or involves pulping and / or cooking in a pulping process, including the production of cooking chemicals. One such source of sodium sulfate is removal of sodium sulfate from the recovery cycle due to excess sulfur. A conventional method of controlling the sodium and sulfur balance is to remove a portion of the recovery boiler fly ash, which contains primarily sodium sulfate and sodium carbonate. Sodium sulfate has traditionally been dissolved in wastewater or utilized as a make-up chemical. When sodium sulfate is dissolved in wastewater, sulfate emissions increase. On the other hand, when it is used as a make-up chemical, it can increase excess sulfur in the Na / S equilibrium. Excess sulfur can increase fly ash purge, which also increases sulfate emissions.

[0062] The method of the present invention allows for a reduction in the sodium sulfate content of the pulping process or pulping mill wastewater or other emissions, and allows for better process control since there is no need to use sodium sulfate as a make-up chemical.

[0063] In one embodiment, the method includes using the recovered sodium hydroxide as cooking chemicals in a pulping process, such as caustic soda, for example, in white liquor and / or bleaching.

[0064] Sodium hydroxide may be used in paper manufacturing processes, such as paper recycling to separate ink from recycled paper. In one embodiment, industrial process 10 is a paper manufacturing process.

[0065] In one embodiment, the industrial process 10 is a battery industry process. In such a case, the method may include using the recovered sodium hydroxide as a precipitating agent, such as to precipitate a battery precursor from a metal sulfate solution.

[0066] In certain processes in the battery industry, transition metal (M) sulfates, such as nickel sulfate, are treated with sodium hydroxide to precipitate the transition metal hydroxides in the following reaction: MSO4+2NaOH → M(OH)2+Na2SO4

[0067] Sodium sulfate is generated in the process as a waste liquid.

[0068] In one example, nickel hydroxide is prepared as a precursor for producing LiNiO (LNO), which is used as a cathode material in Li-ion batteries. A spherical Ni(OH) precursor is synthesized using alkali metal hydroxide coprecipitation in an inert gas atmosphere. This reaction also uses NaOH to precipitate nickel hydroxide in the following reaction: Formation of metal-ammonia complexes Ni 2+ +nNH3 → [Ni(NH3)n] 2+ Metal-hydroxide precipitation reaction [Ni(NH3)n] 2+ +2OH - → Ni(OH)2+nNH3

[0069] In one embodiment, the method includes using the recovered sodium hydroxide as a precipitating chemical and / or pH adjuster to treat the wastewater.

[0070] Sodium hydroxide may be used as an industrial cleaning agent, as it can dissolve grease, oil, fat and protein-based depots and can be used to clean process equipment, storage tanks, etc. It may also be used to make soaps and other detergents.

[0071] The resulting sodium hydroxide, or a portion thereof, may be used for purposes other than the discussed industrial process 10, such as in or to prepare cement (e.g., in plasticizers), detergents, water treatment agents, food treatment agents, esterification and / or transesterification reagents, solvents for amphoteric metals and compounds, or reagents for making man-made textile fibers. The method may include separating and / or recovering a portion of the resulting sodium hydroxide and using it as any of the agents disclosed herein, or to prepare any of the agents disclosed herein, and / or for any of the uses disclosed herein.

[0072] In one embodiment, the method includes providing crystallized potassium sulfate for the preparation of a fertilizer product, preferably by combining it with one or more substances that act as fertilizers, bulking agents, and / or stabilizers. In one example, the fertilizer is an NPK fertilizer. NPK fertilizers contain nitrogen, phosphorus, and potassium and can be produced by steam granulation, chemical granulation, compaction, or bulk blending. The potassium sulfate obtained by the present invention can be provided as a formulation ingredient for preparing such fertilizers or other types of fertilizers. Preparing the fertilizer product can include providing potassium sulfate, providing one or more substances that act as fertilizers, bulking agents, and / or stabilizers, mixing to obtain a mixture, and forming the mixture into a fertilizer product. The fertilizer product can be formed into granules, powder, or any other applicable form. In one embodiment, the method includes preparing a fertilizer product containing crystallized potassium sulfate.

[0073] Disclosed is a fertilizer product comprising potassium sulfate obtainable by the method disclosed herein. The fertilizer product can be in the form of a dry powder or dry granules, which can have a moisture content of 20% by weight or less, e.g., 15% by weight or less, or 10% by weight or less.

[0074] The present disclosure relates to treating waste sodium sulfate by the following reaction: Na2SO4+2KOH → K2SO4+2NaOH into potassium sulfate and sodium hydroxide by means of a process comprising recovering the potassium sulfate and providing it as a fertilizer product or providing it for preparing a fertilizer product, and / or recovering the sodium hydroxide and preferably using it in the industrial process and / or in a process related to the industrial process.

[0075] A process comprising converting waste sodium sulfate to potassium sulfate and sodium hydroxide can include any of the methods disclosed herein and / or can include using any of the devices disclosed herein.

[0076] The present disclosure provides for the use of waste sodium sulfate obtained from an industrial process to prepare sodium hydroxide using the methods disclosed herein. The sodium hydroxide is preferably used in and / or in processes related to the industrial process, as described above.

[0077] The present disclosure provides for the use of waste sodium sulfate obtained from an industrial process for preparing potassium sulfate using the methods disclosed herein. Preferably, the potassium sulfate is for preparing a fertilizer product. [Example]

[0078] Example 1 The process of the present invention is carried out as a one-step process using sodium sulfate and potassium hydroxide as follows: Na2SO4+2KOH → K2SO4+2NaOH

[0079] Alkaline waste sodium sulfate solution (250 mL) obtained from a process for preparing metal hydroxides for batteries is mixed with excess KOH solution (21 g KOH pellets in water) by stirring and heated to a maximum of 80-90 °C to form a completely homogeneous solution. The reaction is cooled to 50 °C, whereupon potassium sulfate is precipitated (evaporation of approximately 125 mL), resulting in the formation of nearly pure potassium sulfate (white powder) and a concentrated NaOH solution (supernatant solution), which are separated and recovered.

[0080] Example 2 The process of the present invention is carried out as a two-step process using sodium sulfate and potassium hydroxide as follows: 2Na2SO4+3KOH → K3Na(SO4)2+3NaOH K3Na(SO4)2+KOH → 2K2SO4+NaOH

[0081] An alkaline waste sodium sulfate solution (250 mL) obtained from a process for preparing metal hydroxides for batteries is mixed with an excess of KOH solution (21 g of KOH pellets in water) by stirring and heated to a maximum of 80-90 °C to form a completely homogeneous solution. The reaction is cooled to 50 °C, whereupon potassium sulfate is precipitated (evaporation of approximately 125 mL), resulting in the formation of nearly pure potassium sulfate (white powder) and a solution of NaOH (supernatant solution), which are separated and recovered.

[0082] The X-ray powder diffraction (XRD) spectrum of the obtained crystalline potassium sulfate was measured using a PANalytical Powder XRD apparatus, and is shown in Figure 3. From the spectrum, it can be seen that most of the peaks represent potassium sulfate, and only trace amounts of impurities, mainly unreacted sodium sulfate and sodium potassium sulfate, are present.

[0083] Example 3: One-step reaction A 1M Na2SO4 solution was prepared by dissolving solid Na2SO4 in deionized water. Eight separate Examples 3.1-3.8 were then performed. In each example, 200 mL of the prepared Na2SO4 solution was added to an Erlenmeyer flask, and the initial temperature of the solution was measured. The amount of KOH pellets listed in Table 3 below was then added in small increments to the flask and continuously stirred with a magnetic stirrer to form a completely homogeneous solution. After all the KOH was added, the temperature of the solution was recorded. Mixing was then terminated, and the solution was cooled to 30°C and subsequently filtered to separate the resulting solid and liquid fractions.

[0084] Analyses of the resulting solid and liquid fractions, including X-ray diffraction (XRD) for the solid and inductively coupled plasma (ICP) for elemental composition analysis for the solid and liquid, were performed as described below and the results are shown in Table 4.

[0085] [Table 3]

[0086] [Table 4] α For NaK3(SO4)2, ICDD reference number 00-020-0928 was used. β For K2SO4, ICDD reference number 04-005-7905 was used. γ Mass fraction calculated based on Rietveld refinement analysis.

[0087] In Example 3.1, where the molar ratio of KOH to Na2SO4 was 1:1, no solid material was obtained.

[0088] Example 3.2, with a 1.5:1 molar ratio of KOH to Na2SO4, yielded a small amount of solid that was not sufficient for ICP analysis.

[0089] In Examples 3.2 and 3.3, the main solid phase obtained was NaK3(SO4)2.

[0090] In Examples 3.6, 3.7, and 3.8, a large excess of KOH was used to precipitate almost all of the sulfate from the sodium sulfate solution, with K2SO4 being the predominant solid phase obtained.

[0091] Using a large excess (4:1) of KOH produced primarily K2(SO4) as a solid material along with some impurities.

[0092] The resulting solid material can be washed (not done in this example) to reduce the sodium content.

[0093] Example 4: Two-step reaction First, in Example 4.1, a 1 M NaSO solution was prepared by dissolving solid NaSO in deionized water. Then, 1 L of the prepared NaSO solution was added to an Erlenmeyer flask and mixed with 112.21 g of KOH pellets using a magnetic stirrer to form a completely homogeneous solution. After all the KOH was added, a solution temperature of 33.2°C was recorded. Then, mixing was stopped, and the solution was cooled to 25°C, followed by filtration to separate the resulting solid and liquid fractions.

[0094] Analyses of the resulting solid and liquid fractions, including X-ray diffraction (XRD) for the solid and inductively coupled plasma (ICP) elemental composition analysis for the solid and liquid, were performed as described below, and the results are shown in Table 6. As reported in Table 6, the major phase of the resulting solid material of Example 4.1 was NaK3(SO4)2.

[0095] Four separate Examples 4.2 to 4.5 were further carried out, in which 4.0 g of the resulting solid material (i.e., the precipitate mixture containing NaK3(SO4)2) and 12 mL of deionized water were added to an Erlenmeyer flask and mixed. Subsequently, KOH pellets in the amount listed in Table 5 below were added to the flask in small portions and continuously stirred with a magnetic stirrer to form a completely homogeneous solution. After all the KOH was added, the temperature of the solution was recorded, and then mixing was terminated and the solution was cooled to 30°C, followed by filtration to separate the resulting solid and liquid fractions.

[0096] Analyses of the resulting solid and liquid fractions, including X-ray diffraction (XRD) for the solid and inductively coupled plasma (ICP) for elemental composition analysis for the solid and liquid, were performed as described below and the results are shown in Table 6.

[0097] [Table 5]

[0098] [Table 6] α For NaK3(SO4)2, ICDD reference number 00-020-0928 was used. β For K2SO4, ICDD reference number 04-005-7905 was used. γ Mass fraction calculated based on Rietveld refinement analysis. * There were problems with the measurements, and reliable results were not obtained.

[0099] According to XRD and ICP analysis in Example 4.1, the resulting solid material was NaK3(SO4)2.

[0100] In Example 4.2, the resulting solid material is primarily K2SO4 with some NaK3(SO4)2.

[0101] The resulting solid material can be washed (not done in this example) to reduce the sodium content.

[0102] Example 5: Na 2 SO 4 Concentration effect First, in Example 5.1, three different Na2SO4 solutions with concentrations of 0.5M, 1M, and 1.5M were prepared by dissolving solid Na2SO4 in deionized water. Three sets of examples were then performed and analyzed in the same manner as Example 5.1 (Examples 5.2-5.12) by using three Na2SO4 solutions with four different KOH:Na2SO4 molar ratios of 2:1, 4:1, 6:1, and 8:1. Table 7 shows the concentrations of the Na2SO4 solutions, the KOH:Na2SO4 molar ratios, and the amounts of KOH pellets used in Examples 5.1-5.12, and the analytical results are shown in Table 8.

[0103] [Table 7]

[0104] [Table 8] α For NaK3(SO4)2, ICDD reference number 00-020-0928 was used. β For K2SO4, ICDD reference number 04-005-7905 was used. γ Mass fraction calculated based on Rietveld refinement analysis. * There were problems with the measurements, and reliable results were not obtained.

[0105] Examples 5.1-5.12 show that increasing the concentration of the Na2(SO4) solution increases the amount of solid fraction obtained at the same molar ratio of KOH:Na2SO4.

[0106] Examples 5.1-5.12 show that increasing the amount of KOH decreases the sulfate content in the liquid fraction.

[0107] The resulting solid material can be washed (not done in this example) to reduce the sodium content.

[0108] X-ray diffraction analysis of Examples 3 to 5 The XRD spectrum of the sample was measured using an X-ray diffractometer EMPYREAN (registered trademark) manufactured by PANalytical under the conditions shown in Table 9 below.

[0109] [Table 9]

[0110] Elemental composition analysis of Examples 3 to 5 The contents of K, Na, and S in the obtained solid and liquid fraction samples were measured by inductively coupled plasma-optical emission spectrometry (ICP-OES) using a Thermo iCAP 6000 Series ICP-OES instrument.

[0111] For solid samples, the measurement sample was prepared as follows: 0.25 grams of powder sample of each example was dissolved in deionized (DI) water in a 100 mL volumetric flask. The volumetric flask was filled with deionized (DI) water up to the 100 mL mark, followed by thorough homogenization. 1 mL of the solution was pipetted and transferred to a 100 mL volumetric flask for a second dilution. An appropriate amount of concentrated nitric acid was added by pipet, the volume was adjusted with deionized (DI) water, and then homogenized to make a 5% HNO3 solution. Finally, this solution was used for ICP-OES measurement. The contents of K, Na, and S are expressed in % units.

[0112] The measurement samples were prepared for liquid samples as follows: 1 mL of the liquid sample was pipetted and transferred to a 100 mL volumetric flask. The volumetric flask was filled with deionized (DI) water up to the 100 mL mark, followed by thorough homogenization. An appropriate amount of the solution was pipetted and transferred to a 100 mL or 250 mL volumetric flask for a second dilution. An appropriate amount of concentrated nitric acid was added by pipet, the volume was adjusted with deionized (DI) water, and then homogenized to make a 5% HNO3 solution. Finally, this solution was used for ICP-OES measurement. The contents of K, Na, and S are expressed in g / L.

Claims

1. 1. A process for treating waste sodium sulfate obtained from an industrial process (10), comprising the steps of: - providing a solution of waste sodium sulfate; - providing potassium hydroxide in solid form or as a solution having a potassium hydroxide concentration of 25% by weight or more and mixing it with said solution of waste sodium sulfate to obtain a reaction mixture (12) and convert the waste sodium sulfate into potassium sulfate and sodium hydroxide; - recovering said formed potassium sulfate and said sodium hydroxide; A method comprising:

2. The following reaction Na ２ OO ４ +2KOH → K ２ OO ４ +2111H 2. The method of claim 1, wherein the waste sodium sulfate is converted to potassium sulfate by

3. The waste sodium sulfate is subjected to the following two-step reaction: <h2 style=";text-align:left;direction:ltr">(1)22Na<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> 5O<h2 style=";text-align:left;direction:ltr"> ４ <h2 style=";text-align:left;direction:ltr"> +3KOH → K<h2 style=";text-align:left;direction:ltr"> ３ <h2 style=";text-align:left;direction:ltr"> Na(SO<h2 style=";text-align:left;direction:ltr"> ４ <h2 style=";text-align:left;direction:ltr"> )<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> +3NaOH、 (2)K ３ [OO ４ ) ２ +KOH → 2K ２ OO ４ ++OOH 3. The method of claim 1 or 2, wherein potassium sulfate is converted to potassium sulfate by

4. 4. The method of claim 1, wherein the potassium hydroxide is provided in molar excess relative to the sodium sulfate.

5. 4. The method of claim 3, wherein in step (2), the potassium hydroxide is provided in molar excess relative to the sodium sulfate.

6. 6. The method of claim 4 or 5, wherein the molar excess is a 4:1 molar ratio of potassium hydroxide to sodium sulfate or greater.

7. 7. The method of any one of claims 1 to 6, wherein the potassium hydroxide is provided in solid form.

8. 7. A method according to any one of claims 1 to 6, wherein the potassium hydroxide is provided as a solution having a potassium hydroxide concentration of 30% by weight or more, for example in the range of 30 to 50% by weight.

9. 9. The method according to claim 1, wherein the waste sodium sulfate solution is an alkaline waste sodium sulfate solution.

10. - heating the reaction mixture to 60-90°C; - cooling the solution below 50°C to obtain a crystallized potassium sulfate and sodium hydroxide solution; The method according to any one of claims 1 to 9, comprising:

11. 11. The method of any one of claims 1 to 10, wherein the sodium sulfate is provided as an aqueous solution having a concentration of 100 g / L or more, for example, a concentration in the range of 120 to 450 g / L, or 140 to 300 g / L.

12. A method according to any one of claims 1 to 11, comprising concentrating the reaction mixture, preferably by evaporation, for example before and / or after adding the potassium hydroxide.

13. 13. The method of any one of claims 1 to 12, comprising using the recovered sodium hydroxide in the industrial process (10) and / or in a process related to the industrial process (10).

14. The method according to any one of claims 1 to 13, wherein the industrial process (10) is a pulping and / or papermaking process.

15. 15. The method of claim 14, including using the recovered sodium hydroxide as a cooking chemical in a pulping process.

16. 14. The method according to any one of claims 1 to 13, wherein the industrial process (10) is a battery industry process, preferably the method comprising using the recovered sodium hydroxide as a precipitating agent for precipitating a battery precursor from a metal sulfate solution.

17. 17. The method of any one of claims 1 to 16, comprising using the recovered sodium hydroxide as a precipitating chemical and / or pH adjuster for treating wastewater.

18. 18. The process of any one of claims 1 to 17, which is a waste-free process involving utilisation of all reaction products.

19. 19. The method of any one of claims 1 to 18, comprising providing said crystallized potassium sulfate, preferably in combination with one or more substances acting as fertilizers, fillers and / or stabilizers, to prepare a fertilizer product (14).

20. 20. Use of waste sodium sulfate obtained from an industrial process (10) for preparing sodium hydroxide using the method according to any one of claims 1 to 19, preferably used in said industrial process (10) and / or in a process related to said industrial process (10).

21. 20. Use of waste sodium sulfate obtained from an industrial process (10) for preparing potassium sulfate using the method according to any one of claims 1 to 19 for preparing a fertilizer product (14).

22. - industrial processes utilizing sodium hydroxide (10); - a source of a solution of waste sodium sulfate; A device adapted to carry out the method according to any one of claims 1 to 19, a reactor; - a mixing means; - temperature control means (e.g. heating means and / or cooling means), - the mixing means and the temperature control means are electrically controllable and preferably operably connected to a control unit arranged to carry out the method steps, the mixing means and the temperature control means comprising, for example, devices for controlling the temperature and / or controlling the mixing at least in the reactor, - a source of waste sodium sulfate is conveyed and / or transported to said reactor; - the sodium hydroxide obtained from said reactor is conveyed and / or transported to an industrial process (10) that utilizes sodium hydroxide; and - the potassium sulfate obtained is recovered from the reactor.

1. An industrial processing plant comprising:

23. 23. An industrial processing plant for the battery industry according to claim 22, wherein the device comprises an inlet for solid potassium hydroxide or an inlet for a concentrated solution of potassium hydroxide.

24. 24. The battery industry industrial processing plant according to claim 22 or 23, wherein the industrial processing plant is a pulping and / or papermaking process industrial processing plant.

25. 24. The industrial process plant for the battery industry according to claim 22 or 23, wherein the industrial process plant is an industrial process plant for the battery industry.

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