A method for treating waste sodium sulphate obtained from an industrial process, use of waste sodium sulphate obtained from an industrial process and an industrial processing plant

Abstract

The present disclosure provides a method for treating waste sodium sulphate obtained from an industrial process (10), the method comprising providing waste sodium sulphate, providing potassium carbonate, and mixing with the waste5 sodium sulphate to obtain a reaction mixture (12), reacting the reaction mixture to convert the waste sodium sulphate to potassium sulphate and sodium carbonate, and recovering the formed potassium sulphate and / or the sodium carbonate. The present disclosure also provides an industrial processing plant comprising an industrial process (10) utilizing sodium carbonate, a source of a solution of waste0 sodium sulphate, and a device arranged to carry out the method. The present disclosure also provides use of waste sodium sulphate obtained from an industrial process (10) for preparing sodium carbonate and potassium sulphate.

Description

[0001] A method for treating waste sodium sulphate obtained from an industrial process, use of waste sodium sulphate obtained from an industrial process and an industrial processing plant

[0002] Field of the application

[0003] The present disclosure relates to a method for treating waste sodium sulphate obtained from an industrial process and to an industrial processing plant. The present disclosure also relates to use of waste sodium sulphate obtained from an industrial process.

[0004] Background

[0005] Sulphate emissions increase the water salinity and may increase eutrophication. Soluble sulphate salts, such as sodium sulphate (Na2SO4) increase the water salinity. The more saline waste water has a higher density than lake water. Due to the density differences, water forms easily two layers: saline water in the bottom and less saline water above. This phenomenon is referred as stratification, which decreases the natural water mixing with the bottom and the surface layer.

[0006] Several industrial activities, such as metal refining industry and pulping industry, produce metal sulphates that are increasingly controlled by strict limitations for wastewater concentrations of sulphate. For example, Kraft pulping wastewaters contain sodium sulphates because of the use of NaOH and Na2S as cooking chemicals. Sulphate concentrations in effluents are typically at the level of 54,000 kg / day. In old pulp mills, sulphate emissions in effluent can be up to 1500 mg / l. Sulphates have not been considered as an effluent parameter of a pulp mill. Therefore, sulphates are seldom removed in the biological waste water treatment. WHO guideline for maximum sulphate content in drinking water is 250 mg / l.

[0007] One emerging and quickly increasing industrial area is the production of lithium-ion battery precursors, which are typically prepared by coprecipitation from sulphate- based metal solutions. For example, in Finland, the limits of wastewater sulphate concentrations and the required treatment methods are determined by the environmental permit of the company. The common limit for sulphate concentrations in sewer water is 400 mg / l. Sulphate limitations are placed to reduce the environmental strain caused by the increase in saline concentrations of natural waters, especially in fresh waters. In prior art sodium sulphate has been converted to Glauber salt, or it has been landfilled, which are not practical solutions to solve the issues with emerging waste sodium sulphate.

[0008] There is a need to avoid production of sulphate-based waste and salination while increasing industrial production. This requires more efficient methods for wastewater and process water treatment, both for sulphate removal and for the reuse of sulphate-containing wastewaters and process waters. There is also a need to obtain chemicals from waste material, which are directly usable in industrial processes.

[0009] Summary

[0010] A process was found out for the utilization of waste sodium sulphate from industrial sources, and to convert it back to usable chemicals. The present process overcomes drawbacks of prior art, and provides a zero-waste, low-temperature process, enabling cost-efficient implementing and processing. The process enables the utilization of both products potassium sulphate and sodium carbonate obtained from sodium sulphate. Especially in cases wherein sodium carbonate can be utilized in a process, it was found advantageous to convert the sodium sulphate directly to sodium carbonate.

[0011] The present disclosure provides a method for treating a solution of waste sodium sulphate directly obtained from an industrial process 10 generating the sodium sulphate, the method comprising

[0012] -providing a solution of waste sodium sulphate directly obtained from an industrial process 10 generating the sodium sulphate,

[0013] -providing potassium carbonate as solid or as a solution having a concentration of potassium carbonate of 10% by weight or more, and mixing with the waste sodium sulphate to obtain a reaction mixture 12,

[0014] -reacting the reaction mixture to convert the waste sodium sulphate to potassium sulphate and sodium carbonate,

[0015] -cooling the solution to obtain crystallized potassium sulphate and a solution of sodium carbonate, and

[0016] -recovering the formed crystallized potassium sulphate and the solution of sodium carbonate. The present disclosure also provides use of waste sodium sulphate obtained from an industrial process for preparing sodium carbonate with the method.

[0017] The present disclosure also provides use of waste sodium sulphate obtained from an industrial process for preparing potassium sulphate with the method.

[0018] The present disclosure provides an industrial processing plant comprising -an industrial process 10 utilizing sodium carbonate,

[0019] -a source of a solution of waste sodium sulphate directly obtained from an industrial process 10 generating the sodium sulphate,

[0020] -a device arranged to carry out the method, the device comprising

[0021] -a reactor,

[0022] -mixing means,

[0023] -heating means,

[0024] -an inlet for solid potassium carbonate,

[0025] -wherein the mixing means and heating means are electrically controllable and preferably operatively connected to a control unit arranged to carry out the method steps, such as at least controlling the temperature in the reactor and / or controlling the mixing,

[0026] -the source of waste sodium sulphate directly obtained from an industrial process 10 generating the sodium sulphate being arranged to be conveyed and / or transported to the reactor,

[0027] -the obtained solution of sodium carbonate from the reactor being arranged to be conveyed and / or transported to the industrial process 10 utilizing sodium carbonate, and

[0028] -the obtained crystallized potassium sulphate being arranged to be recovered from the reactor.

[0029] The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples disclosed herein are mutually freely combinable unless otherwise explicitly stated. Any examples or embodiments not in the scope of the claims may be considered as examples or embodiments useful for understanding the invention.

[0030] The present method utilizes inexpensive chemicals and is simple to implement at any industrial location, so any applicable industrial process providing the waste sodium sulphate can be supplemented with the present process with low investments. For example, the present reactor or system can be implemented at vicinity of the source of waste sodium sulphate with low costs and can be operated without disturbing the existing facilities and processes.

[0031] All the products obtained from the present process can be utilized, so the process improves the current solutions with fully zero-waste approach, and enables the use of obtained sodium carbonate, for example as a cooking chemical or a precipitant, and the obtained potassium sulphate, for example for fertilizers.

[0032] The use of undesired additional chemicals can be avoided, for example chloride- containing substances, such as potassium chloride. Therefore, accumulation of chloride in the end product can be avoided, which makes it suitable for a variety of uses.

[0033] Thus, the present invention enables providing a safe and simple method for converting an untreated industrial liquid waste stream comprising a solution of waste sodium sulphate directly obtained from an industrial process generating the waste stream into such valuable product(s), which can be used in the industrial process as such. The present process can be carried out as one-step process and with a device arrangement implemented at the industrial processing plant generating the sodium sulphate and / or utilizing sodium carbonate. The present invention also enables providing an apparatus capable of converting an untreated industrial liquid waste stream comprising a solution of waste sodium sulphate into useful products, which can be recycled back to the industrial process as such and used in the process. The present invention thus enables providing an industrial processing plant capable of utilizing an untreated industrial liquid waste stream comprising a solution of waste sodium sulphate in the industrial process.

[0034] Brief description of the figures

[0035] Figure 1 shows one example of the present method

[0036] Detailed description

[0037] In this specification, percentage values, unless specifically indicated otherwise, are based on weight (w / w, by weight, or wt%). If any numerical ranges are provided, the ranges include also the upper and lower values. In specific examples the embodiments and examples specified with the open term “comprise” may be further limited with a closed term “consisting of’.

[0038] As discussed, large amounts of metal sulphates are formed yearly in industrial activities. Sulphate recovery methods, which reduce the sulphate concentration of process waters or wastewaters in commercially viable and efficient ways, have been widely studied. Until now, there has not been a cost-efficient technical method for the treatment of alkaline sulphate waste streams. Acidic sulphate waste streams are typically precipitated with calcium, and the formed gypsum sludge is recovered. Also, in this case techno-economic solutions are missing.

[0039] Alkaline waste sodium sulphate solution is formed as a by-product in chemical and pulping industry. One example is precipitation of battery precursors from metal sulphate solutions using NaOH as precipitator. As an example, the concentrations of the main elements in waste sodium sulphate are described in Table 1. In addition to the elements mentioned in Table 1 , the solution contained ammonium ions with the concentration of 4 g / l as a residue from the chemical coprecipitation.

[0040] Table 1. The physicochemical characteristics of a waste sodium sulphate solution (pH 12.5). The values are presented as mg / l, and only values above 1 .0 mg / l were reported.

[0041] The present disclosure relates to a process for the utilization, i.e. valorization, of waste sodium sulphate by reaction with potassium carbonate and water to produce potassium sulphate and sodium carbonate. Potassium sulphate is a chemical used for fertilizers and it is currently produced via high-temperature processing. Na2COs can be recycled back to be used for example as a precipitator in chemical industry. The obtained potassium sulphate may comprise and / or be in the form of crystals, and it may comprise for example sodium. For example at least part, or all, of the potassium sulphate may comprise and / or be in the form of glaserite (KsNa(SO4)2). It was found out in tests that the recovered solid potassium sulphate in most cases contained some sodium sulphate. The glaserite may be further processed to obtain more pure potassium sulphate, if necessary. The glaserite may be also considered as waste sodium sulphate, and it may be treated with a suitable purification method, such as it may be subjected to the present method, especially if the content of the sodium sulphate is high enough.

[0042] The method may comprise using the recovered sodium carbonate as a precipitant or a precipitating chemical, such as in an industrial process, and / or in battery industry and / or in pulping and paper industry.

[0043] In one embodiment the industrial process 10 is a process of battery industry. The method may comprise using the recovered sodium carbonate as a precipitator for precipitation of battery precursors from metal sulphate solutions.

[0044] The present disclosure provides a method for treating waste sodium sulphate obtained from an industrial process. An example of the method is disclosed in Figure 1. The industrial process 10 may be any applicable industrial process, which provides sodium sulphate (Na2SO4) in a suitable form, which may be an effluent of an industrial process, or which may be crystalline / solid form of sodium sulphate. Preferably the waste sodium sulphate solution is alkaline waste sodium sulphate solution, wherein the pH of the waste solution is at an alkaline range, such as pH of 8 or more, 9 or more, 10 or more, 11 or more, or 12 or more. The sodium sulphate shall be concentrated enough, so for example waste waters containing minor amounts of sodium sulphate are excluded, such as sodium sulphate below 50 g / l, below 30 g / l or below 10 g / l.

[0045] The method comprises providing the sodium sulphate. The sodium sulphate is provided in a suitable form, for example as a solution or as solid. If the sodium sulphate is provided as solid, it is solubilized in aqueous solution, which may be water or a solution of potassium carbonate. The method may comprise providing the water or aqueous solution, and optionally adjusting pH to alkaline range, if necessary.

[0046] The method comprises providing an amount of potassium carbonate and mixing the potassium carbonate with the sodium sulphate obtain a reaction mixture. The reaction mixture is a solution. The potassium carbonate may be provided as solid or as a solution, such as a concentrated solution. The reaction(s) take(s) place in the reaction mixture 12, and a mixture of end products is obtained. The mixture of end products comprises a formed solution. The potassium sulphate crystallizes in the method, i.e. solid potassium sulphate is obtained, and can be separated from the sodium carbonate, which remains solubilized in the formed solution. The method may comprise converting the waste sodium sulphate to potassium sulphate with the reaction:

[0047] (I) Na2SO4+ K2CO3 K2SO4 + Na2CO3.

[0048] This equation may be also considered as a general equation describing the overall process of the present method, which can be carried out as the one-step reaction. The reaction conditions and ratios of reagents may be selected to control the reaction, for example to facilitate the reaction (I).

[0049] The present method preferably does not involve or does not substantially involve other reagents, especially other reagents contributing to the conversion. Preferably the present method does not involve, or is carried out in absence of, chloride- containing compounds, such as potassium chloride. The method may therefore be a chloride-free method. If chloride would be involved, it would result in chloride remains in the end products, which is not desired. For example, fertilizer products shall not contain chloride, as it would be detrimental to growth of certain plants.

[0050] The formed potassium sulphate and / or the sodium carbonate are recovered from the mixture of end products, such as substantially at the same time or separately, for example subsequently. For example, the obtained solution may be separated thus leaving the solid material. The obtained fractions may be further processed, such as purified. The method may comprise washing the obtained solid material comprising the potassium sulphate, for example to decrease sodium content, such as with a solution comprising or consisting of ethanol, water or aqueous solution.

[0051] The obtained and recovered solid potassium sulphate may be provided for example as a fertilizer product or for preparation of a fertilizer product 14, which may be carried out in the same process or in a separate process. Other products comprising or based on potassium sulphate may be prepared as well. The obtained solid potassium sulphate may be provided and / or transported to another location for further processing, such as for preparing the further product, for example to a fertilizer manufacturer to prepare a fertilizer product.

[0052] If the crystal ized / sol id potassium sulphate comprises and / or is in the form of glaserite, it may be further purified to obtain pure potassium sulphate. This may comprise treating the obtained and recovered solid potassium sulphate with a suitable purification method. In one example the purification is carried out with a solution of potassium chloride, such as with the reaction:

[0053] K3Na(SO4)2+ KCI 2K2SO4+ NaCI

[0054] The obtained sodium carbonate is recovered, and it can be reused as industrial chemical, for example in the same industrial process 10 or a process relating to the same industrial process 10 or the same industry. The industrial process is an industrial process utilizing sodium carbonate, for example using sodium carbonate as a process chemical and / or for other purposes in the process or in a related process. The industrial process may utilize the obtained sodium carbonate directly and / or without further processing. The industrial process may be carried out at the same facilities or plant, such as a factory, a mill or any other applicable processing site. However it is possible to provide the sodium carbonate to another use and / or industrial process, preferably wherein such a use and / or process is located near the site of carrying out the method. Transporting or conveying the obtained sodium carbonate can be arranged in most industrial plants or other facilities, for example by providing piping or other conveying means, or by arranging transport in containers, for example by using a dedicated conveyer or other transport means, such as vehicle(s), and / or transporting chain.

[0055] The solid potassium sulphate and the sodium carbonate solution can be separated and recovered by using any suitable methods and devices for separating and recovering solids and liquids. This may be carried out for example by filtering, such as by using a suitable filtering device and / or a suitable filter having a cut-off value enabling recovering the formed solids. The recovered solids may be washed, for example with absolute ethanol or with aqueous ethanol solution. The separated and recovered fractions may be analysed for purity with any suitable means. For example the purity of (washed) potassium sulphate may be analysed from a sample by using X-ray Powder Diffraction (XRD) and related instrumentation, such as an X-ray powder diffractometer or versatile XRD systems for R&D, to obtain XRD spectra or pattern, which can be used for evaluating the purity of the potassium sulphate and / or the conversion degree in the method, success of the method and the like. The obtained potassium sulphate and sodium carbonate may be recognized by analysing the fractions. The proceeding of the reaction, such as the conversion degree during the reaction, may be also monitored, determined and / or estimated by using other means, such as monitoring absorbance and / or turbidity of the reaction mixture, detecting formed precipitate and the like. In one embodiment the method comprises using the recovered sodium carbonate in the industrial process 10 and / or in a process relating to the industrial process 10.

[0056] In one embodiment the industrial process 10 is a pulping and / or papermaking process

[0057] In one embodiment the industrial process 10 utilizing sodium carbonate is the same industrial process 10 or a process relating to the same industrial process 10 that generates the sodium sulphate, as shown in Figure 1 .

[0058] In one embodiment the method comprises using the recovered sodium carbonate as a precipitating chemical and / or pH adjusting agent for treating waste water.

[0059] With the present method and process a closed or a substantially closed process can be provided, especially in respect of sodium sulphate, which process utilizes all or substantially all of the materials provided to the method, especially the sodium carbonate, and materials obtained from the method. This enables providing industrial processes, which provide less or no waste. As sodium sulphate has been considered as a problematic waste in respect of further usage, and the material has been mainly discarded, the present method enables utilizing the waste and obtaining valuable raw material for the processes. As all the waste sodium sulphate can be utilized, there is no need to find disposal site for the waste, or to apply for any authorization to dispose waste. This enables implementing industrial processes and plants with less environmental issues, less authorizations, less waste water purification units or plants, and to a variety of locations.

[0060] In one embodiment the method is a waste-free method comprising utilizing all or substantially all the reaction products and / or reagents, including the waste sodium sulphate. The reaction products may be provided, for example provided directly, to processes utilizing all or substantially all the reaction products. Waste-free refers to a process of treating sodium sulphate, wherein no or substantially no waste is generated. For example a small amount of waste may be obtained comprising or consisting of the impurities present in the waste sodium sulphate, which may have been washed or otherwise separated in the process. However residual impurities are not problematic in all cases, so it may not be necessary to remove the impurities from the final products.

[0061] The sodium sulphate may be provided in a reactor or the like container as a solution, such as an aqueous solution, or as solid. The sodium sulphate solution shall have a high enough concentration, wherein the concentration of the sodium sulphate is 50 g / l or more, such as 80 g / l or more, 100 g / l or more, preferably 120 g / l or more. In one embodiment the sodium sulphate is provided as an aqueous solution having a concentration of 100 g / l or more. The solution may have a concentration of sodium sulphate in the range of 100-450 g / l or 120-450 g / l, such as 120-400 g / l. It can be directly obtained from the corresponding industrial process generating the sodium sulphate, so the waste sodium sulphate may have not been treated, such as purified and / or neutralised, for example treated or precipitated with calcium, before providing to the present method.

[0062] However the waste sodium sulphate solution may have been concentrated, such as it may be provided as solid, and / or it is concentrated in the present method, and / or the concentration of the sodium sulphate in the reaction mixture may be adjusted and / or controlled. The method may comprise determining and / or obtaining the concentration of the sodium sulphate in the waste sodium sulphate solution. This can be used to determine the required amount of potassium carbonate, the suitability of the waste solution for the present method, the need for concentrating the waste solution, the need for solubilizing solid sodium sulphate to obtain a desired concentration in a solution, and / or the need to adjust any other process parameters, and a corresponding decision whether or not to carry out said action, and / or in which extent, can be made based on the determined and / or obtained concentration. The method may comprise providing, such as conveying and / or transporting, waste sodium sulphate from the industrial process, or a process step generating sodium sulphate waste, for example to the container. The waste sodium sulphate may contain small amounts of impurities, but it was found out in the tests that the impurities did not interfere the process and they could be even separated from the sodium sulphate, if necessary.

[0063] Potassium carbonate may be provided, such as added, in an excess molar amount to the sodium sulphate. The method may comprise controlling the stoichiometry of the reactants. For example, it may be possible to obtain adequate final concentrations of potassium sulphate and sodium carbonate for certain applications by using stoichiometric or substoichiometric ratios of potassium carbonate to sodium sulphate. The molar ratio of potassium carbonate to sodium sulphate may be about 1 :1 or more, or about 2:1 or more, such as about 4:1 or more, for example about 6:1 or more.

[0064] The potassium carbonate may be provided as solid form or as a solution, such as an aqueous solution. The solution may be concentrated solution, such as having a concentration of K2CO3 of 10% by weight or more, such as 20% by weight or more, 25% by weight or more, for example 30% by weight or more. The concentration of potassium carbonate may be up to 70% by weight, but in most cases concentrations up to 50% by weight are readily available. The concentration of K2CO3 may be in the range of 20-50% by weight, such as 25-50% by weight or 30-50% by weight.

[0065] Preferably potassium carbonate is provided in solid form, such as in the form of granules or powder. Solid potassium carbonate generates heat when solubilized in the aqueous solution, which facilitates the process. Solid potassium carbonate is also safe to use and handle. Providing potassium carbonate in solid or concentrated form enables implementing the method in a simple and compact form. Further, with solid potassium carbonate the desired stoichiometric ratio can be easily achieved.

[0066] The potassium carbonate is mixed with the sodium sulphate. Either one or both reactants may be provided as a solution or as solid, and water or aqueous solution may be added if necessary, such as to obtain an aqueous solution / reaction mixture and / or to obtain desired concentrations in the reaction mixture. This can be carried out in the reactor, which may be equipped with one or more mixing means, such as one or more mixers, which may comprise one or more mixing blades, agitators, effect of flow and / or the like, and also the effect of flow of liquids may be utilized for obtaining mixing. A reaction mixture is obtained. The reaction mixture, and / or the content of the reactor, is heated, preferably by using one or more heating means, such as one or more heaters, arranged to heat the content of the reactor. The mixing and / or heating may be carried out to obtain a homogenous solution. The reaction mixture may be heated to, or have, a temperature below 100°C, such as 95°C or less, or 90°C or less. The temperature is 60°C or more, such as 70 °C or more, or 80°C or more. The temperature may be in the range of 60-90°C, such as 60-80°C, 70-90°C or 80-90°C. Alternatively, or in addition, the solution of sodium sulphate may be provided at elevated temperature and / or may be heated. One example provides a method for treating waste sodium sulphate obtained from an industrial process, the method comprising -providing a solution of waste sodium sulphate,

[0067] -providing potassium carbonate in solid form or as a solution having a concentration of potassium carbonate of 20% by weight or more, and mixing with the waste sodium sulphate to obtain a reaction mixture,

[0068] -reacting the reaction mixture to convert the waste sodium sulphate to potassium sulphate and sodium carbonate, and

[0069] -recovering the formed potassium sulphate and / or the sodium carbonate.

[0070] The solubilities of sodium and potassium salts are substantially different at temperatures of 60°C or above, as presented in Table 2.

[0071] Table 2. Approximate solubilities of key Na and K salts in water as a function of temperature

[0072] The heating and / or mixing may be carried out for a time period required to allow reacting all or substantially all of the reagents, such as to allow full or substantially full conversion of sodium sulphate to potassium sulphate, for example 90% or more, or 95% or more. The time period may be 20 minutes or more, such as 30 minutes or more, for example 20-60 minutes or 30-60 minutes.

[0073] The reaction mixture may be concentrated to remove water. The concentrating may be carried out by evaporating, which takes place at the elevated temperature. In one embodiment the method comprises concentrating the reaction mixture, preferably by evaporating. This may be carried out before and / or after adding the potassium carbonate.

[0074] The solution is cooled or allowed to cool, such as to 40°C or less, for example to 30°C or less, preferably to room temperature, such as to 25°C or less, for example 20-22°C, to obtain crystallized potassium sulphate and a solution of sodium carbonate. During the cooling, potassium sulphate is crystallized with high purity (> 90%) and formed sodium carbonate remains in the solution. The crystallized potassium sulphate forms a suspension, and is allowed to precipitate to obtain solid potassium sulphate precipitate, which can be separated from the remaining sodium carbonate solution. The cooling may be carried out for a time period required to obtain a desired crystallization degree of the potassium sulphate, such as complete or substantially complete crystallization. The cooling time may include the time required to lower the temperature and / or the time required to obtain the desired crystallization degree, i.e. maturation of the reaction mixture. The cooling time may be 60 minutes or more, such as 100 minutes or more, 120 minutes or more, or 150 minutes or more.

[0075] The method may comprise

[0076] -heating the reaction mixture (12) to 60-90°C, preferably to obtain a homogenous solution,

[0077] -cooling the solution to 30°C or less, such as to 25°C or less, preferably for a time required to obtain (desired) crystallization of the potassium sulphate, to obtain crystallized potassium sulphate and a solution of sodium carbonate.

[0078] Preferably the solution is cooled or allowed to cool to a temperature of not less than 5°C, such as not less than 10°C, for example not less than 15°C, to prevent solidifying sodium carbonate. The temperature may be for example in the range of 5-40°C, such as 5-30°C, or 5-25°C, preferably 10-40°C, such as 10-30°C, or 10-25°C, for example 15-40°C, such as 15-30°C, or 15-25°C, for example to about 30°C.

[0079] The formed solution can be regenerated by using potassium sulphite, which may be added as solid.

[0080] The method may comprise

[0081] -providing Na2SOs solution as a reductant to the formed solution to convert Na2SC>3 to Na2SC>4. -removing the formed sulphate, and

[0082] -regenerating the solution by adding solid K2SO3 to the solution to produce solid potassium sulphate and Na2SO3solution.

[0083] The formed solution may refer to the solution formed as a result from reacting the reaction mixture to convert the waste sodium sulphate to potassium sulphate and sodium carbonate. The formed solution may further refer to the solution that remains after the potassium sulphate is removed.

[0084] The Na2SO4 may be heated, for example to about 50°C or more, such as to about 60°C or more, preferably in inert atmosphere, such as in nitrogen atmosphere. After adding the potassium sulphite, the formed mixture may be heated, for example to about 70°C or more, such as to about 80°C or more, for example for about 30 minutes. After the reaction had proceeded at the elevated temperature, the mixture may be cooled, for example to about 20°C, and may be allowed to mature, such as for 2 hours or more, for example for about 2 hours 30 minutes. The formed solids may be separated, such as by vacuum filtration, and they may be washed, such as by using ethanol or other suitable washing solution. A glaserite precipitate is obtained.

[0085] The process may be carried out as a one-step process / reaction, with sodium sulphate and potassium sulphite as follows:

[0086] (II) Na2SO4(aq) + K2SO3(s) -> K2SO4(s) + Na2SO3(aq)

[0087] The reactions disclosed herein can be carried out by using one solid starting material and one aqueous starting material or both starting materials in aqueous form. K2SO4is component in the solution exhibiting lowest solubility in all cases and therefore crystallizes first in proper conditions. If necessary, solution may be concentrated by evaporating water.

[0088] The method may be carried out in a device comprising the means disclosed herein, which means may be controllable, such as electronically controllable. The device may be automated or semi-automated device, and it may be a part of a complex or a system. The device or the system may be a device or a system of pulping and / or papermaking process and / or industry, or battery industry.

[0089] In one example the device comprises -a reactor,

[0090] -mixing means,

[0091] -temperature controlling means, such as heating and / or cooling means, for example heating and optionally cooling means,

[0092] -wherein the mixing means and the temperature controlling means are electrically controllable and preferably operatively connected to controlling means, such as one or more control units, arranged to carry out the method steps disclosed herein, such as at least controlling the temperature in the reactor and / or controlling the mixing. The controlling means may be operatively connected to one or more means, devices, actuators, and the like disclosed herein, so that the controlling means can controllably operate the means, and / or connected to one or more sensors and other devices arranged to monitor the process, i.e. to obtain information from the process, such as from the reactor / reaction mixture. The device may comprise cooling means, such as one or more cooler, for example implemented with liquid flow in a rector envelope. The cooling means may be used for cooling the reactor mixture or the homogenous solution to initiate the precipitation. The cooling means may be operatively connected to the control unit.

[0093] The device may also comprise one or more of the following:

[0094] -inlet for the waste sodium sulphate solution,

[0095] -inlet for potassium carbonate,

[0096] -outlet for obtained solid potassium sulphate,

[0097] -outlet for obtained sodium carbonate solution,

[0098] -one or more sensors arranged to monitor one or more properties of the reaction mixture and / or the reactor, such as temperature, pH, turbidity, absorbance, flow rate, liquid level, conductivity or the like,

[0099] -one or more pumps for conveying the solutions, which pumps may be operatively connected to the control unit,

[0100] -one or more further containers disclosed herein and required connections, such as pipes,

[0101] -one or more valves for controlling flow of the solutions and / or solids, and / or

[0102] -one or more actuators connected to one or more moving members for mixing, moving and / or otherwise controlling the process, which actuators may be operatively connected to the control unit. The valves may be electrically controllable valves comprising an actuator operatively connected to the control unit. The device may comprise a container for potassium carbonate, which is connected via a controllable valve or other controlling means, for example operatively connected to the control unit, so that dosing of the potassium carbonate can be controlled. The container may comprise a funnel for allowing flow of solid potassium carbonate. The device may comprise means for outletting the obtained solid potassium sulphate, such as at the bottom of the reactor, for example an actuator connected to one or more movable members for moving the solid potassium sulphate, which means may be operatively connected to the control unit.

[0103] The device may comprise an inlet for solid potassium carbonate or an inlet for concentrated solution of potassium carbonate, which may have a concentration disclosed herein.

[0104] The present device utilizes the mixing means, such as a mixer, to confirm immediate solubilization of the solid carbonate or the concentrated solution of potassium carbonate, which facilitates avoiding local concentration gradients. Even though heating or cooling is not necessarily required at first, for example due to generation of heat by the solubilization of carbonate or due to need for lowering the temperature, using the temperature controlling means enable a simple control of the reaction by maintaining the temperature of the reaction mixture optimal during the process. The temperature controlling means may comprise one or more heating and / or cooling elements arranged to control the temperature of the rector and / or the reaction mixture in the reactor.

[0105] The inlet for solid potassium carbonate or the inlet for concentrated solution of potassium carbonate may be connected to a container for the solid potassium carbonate or the concentrated solution of potassium carbonate. The use of the concentrated potassium carbonate enables providing a container with a relatively small volume, which enables implementing the system and the device in a compact form.

[0106] The device may comprise or be connected to means for separating solids and liquid, such as filtering means, for example a suitable filtering device and / or filter with a suitable cut-off value.

[0107] The industrial processing plant may be an industrial processing plant of pulping and / or papermaking process and / or industry, or an industrial processing plant of battery industry. The control unit may be electronic control unit, which may be programmable, comprising one or more processors, memory, and software configured, when executed with a processor in the control unit, to carry out one or more operations to implement the method, for example to adjust the temperature of the reaction mixture by controlling the temperature controlling means, such as the heating and / or the cooling means, to control the mixing means to obtain a desired mixing of the reaction mixture, monitor the temperature and / or other properties of the reaction mixture with one or more sensors in the reactor, and the like operations. The control unit may be arranged, such as programmed, to monitor one or more properties from the device, the system, and / or the reactor, for example as a function of time, and as feedback to the monitored properties carry out one or more control actions in the device or the system to adjust the function of the device to carry out the present method. Properties such as temperature, pH, turbidity, absorbance, conductivity, flow rate, liquid level, control of addition of substances, mixing rate, and the like may be monitored with one or more sensors arranged to monitor said properties. For example, temperature may be controlled to be at a predetermined range and / or to increase and / or decrease in a controlled manner to carry out the method.

[0108] The present disclosure provides an industrial processing plant, or a system or a device arrangement in the industrial process plant, or the like processing site, comprising

[0109] -an industrial process utilizing sodium carbonate,

[0110] -a source of waste sodium sulphate, which may be the industrial process utilizing sodium carbonate, a related industrial process and / or a separate industrial process,

[0111] -a device arranged to carry out the method, the device comprising

[0112] -a reactor,

[0113] -mixing means,

[0114] -temperature controlling means, such as heating and / or cooling means,

[0115] -wherein the mixing means and heating means are electrically controllable and preferably operatively connected to a control unit arranged to carry out the method steps, such as at least controlling the temperature in the reactor and / or controlling the mixing,

[0116] -the source of waste sodium sulphate being arranged to be conveyed and / or transported to the reactor, such as waste sodium sulphate from the source of waste sodium sulphate being arranged to be conveyed and / or transported to the reactor,

[0117] -the obtained sodium carbonate from the reactor being arranged to be conveyed and / or transported to the industrial process utilizing sodium carbonate, and / or -the obtained potassium sulphate being arranged to be separated and / or recovered from the reactor.

[0118] The industrial process utilizing sodium carbonate may comprise one or more systems, device arrangements, and / or plants arranged to carry out one or more processes utilizing sodium carbonate.

[0119] The present method and overall process may be implemented in different ways by different operators, and the whole production chain, such as the actions carried out by different operators, can be facilitated with the method. The method may be carried out by one operator, or it may be carried out by two or more operators. For example a first operator may generate the waste sodium sulphate. Such an operator may run the industrial process, which may be carried out in a factory, a plant or other applicable production or processing site, and which may be an industrial process utilizing sodium carbonate 10. The waste sodium sulphate may be collected into containers, or it may be provided directly from the process, for example via a pipe or the like conveying means. The first operator may also provide the waste sodium sulphate to the site, wherein the present reaction is carried out, which may be called site of use. It is also possible that another operator provides the waste sodium sulphate, for example when the waste sodium sulphate is collected into containers and transported to the site of use. The present reaction(s) 12 may be carried out by the first or the second operator, but it / they may be also carried out by another, third operator. This operator operates the reactor, doses potassium carbonate, and recovers the reaction products. This operator may also provide the reaction products to further use, and the operator may also carry out one or both of the further uses, namely using the sodium carbonate as industrial chemical and / or providing the potassium sulphate to preparation of a fertilizer 14, or preparing the fertilizer. However, it is also possible that one or two further operators carry out these steps, and / or that the first operator carries out the step of using the sodium carbonate as industrial chemical in an industrial process 10. An operator which may utilize the obtained potassium sulphate may be a fertilizer manufacturer. One example of the present process of treating the waste sodium sulphate utilizes two precipitations steps and can provide end products with high purity. This process may be included in step 12 of Figure 1 .

[0120] Sodium sulphate (Na2SO4) waste solution is fed to a reactor, concentrated (30%) potassium carbonate (K2CO3) in solid form is added, and the obtained solution is mixed and heated to 80°C to obtain a homogenous solution. The solution is concentrated by evaporating at the increased temperature. The mixture is cooled, for example to 20-25°C, wherein potassium sulphate crystallizes and contains some residual sodium sulphate. This obtained impure potassium sulphate, which may be glaserite, is solubilized to a minimum amount of water at 80°C for purification crystallization step and crystallized by cooling. Substantially pure potassium sulphate is obtained, and can be recovered and washed.

[0121] The remaining solutions from previous steps may be crystallized in a second crystallization step by cooling, for example to 2-20°C. Regenerated Na2COs, Na2SC>4 and residual potassium sulphate are obtained at further step. The Na2COs can be recovered and reused, such as conveyed to an industrial process. The residual solution comprising Na2SO4 and residual potassium sulphate from this step is conveyed back to the reactor. Alternatively, the residual solution comprising Na2SO4 and residual potassium sulphate may be conveyed directly back to the reactor to avoid diluting the Na2COs solution of the second crystallization step.

[0122] The present method may be applied to different industrial processes 10, which provide waste sodium sulphate.

[0123] In one embodiment the industrial process 10 is a pulping process. A pulping process refers to a process, or a system setup, including or involving pulping and / or cooking in the pulping process, including the production of cooking chemicals. One such a source of sodium sulphate is the removal of sodium sulphate from the recovery cycle due to excess sulphur. The traditional way to control sodium and sulphur balance is to remove a part of recovery boiler fly ash, which includes mainly sodium sulphate and sodium carbonate. Sodium sulphate has been conventionally either dissolved in waste water or utilized as a make-up chemical. If the sodium sulphate is dissolved in waste water, it increases the sulphate emissions. On the other hand, if it is used as a make-up chemical, it may increase the excess sulphur in the Na / S-balance. The excess sulphur may lead to increased fly ash purging, which also increases the sulphate emissions. With the present method it is possible to lower the sodium sulphate content of waste waters or other emissions of pulping processes, or pulping mills, and to allow better control of the process as there is no need to use sodium sulphate as a make-up chemical.

[0124] In one embodiment the method comprises using the recovered sodium carbonate as a cooking chemical in the pulping process, such as with caustic soda, for example in white liquor and / or in bleaching.

[0125] Sodium carbonate may be used in papermaking process, such as paper recycling to separate ink form recycled paper. In one embodiment the industrial process 10 is a papermaking process

[0126] In one embodiment the industrial process 10 is a process of battery industry. In such case the method may comprise using the recovered sodium carbonate as a precipitator, such as for precipitation of battery precursors from metal sulphate solutions.

[0127] In certain processes of battery industry transition metal (M) sulphates, such as nickel sulphates, are treated with sodium hydroxide to precipitate transition metal hydroxides with the reaction:

[0128] MSO4+ 2 NaOH M(OH)2+ Na2SO4

[0129] Sodium sulphate is generated in the process as a waste solution.

[0130] In one example nickel hydroxide is prepared as a precursor for manufacturing LiNiO2(LNO) to be used as cathode material in Li-ion batteries. Spherical Ni(OH)2precursors are synthetized using alkali metal hydroxide coprecipitation in an inert gas atmosphere. Also this reaction uses NaOH for precipitating nickel hydroxide in the following reactions:

[0131] Metal-ammonia complex formation Ni2++ nNHs [Ni(NHs)n]2+

[0132] Metal-hydroxide precipitation reaction [Ni(NHs)n]2++ 2OH’ Ni(OH)2+ nNHs In one embodiment the method comprises using the recovered sodium carbonate as a precipitating chemical and / or pH adjusting agent for treating waste water.

[0133] The sodium carbonate may be also used as or for making cleaning agents, such as industrial cleaning agents, which may be used to clean process equipment, storage tanks and the like, as sodium carbonate can dissolve grease, oils, fats and protein-based depots. It may be also used for making soaps and other detergents. Sodium carbonate is also called as washing soda.

[0134] The obtained sodium carbonate may be used for other purposes than the discussed industrial process 10, such as in, or for preparing, cement (for example in a plasticizer), water treatment agent, food treatment agent, esterification and / or transesterification reagent, solvent for amphoteric metals and compounds, or a reagent for making artificial textile fibres. The method may comprise separating and / or recovering part of the obtained sodium carbonate, and using it as, or for preparing, any of the agents disclosed herein, and / or for any of the uses disclosed herein.

[0135] In one embodiment the method comprises providing the crystallized potassium sulphate for preparation of a fertilizer product, preferably by combining with one or more substances acting as, and / or selected from, a fertilizer, a filler, and / or a stabilizer. In one example the fertilizer is a NPK fertilizer. NPK fertilizers comprise nitrogen, phosphorus and potassium, and they can be manufactured by steam granulation, by chemical granulation, by compaction, or by bulk blending. The present obtained potassium sulphate may be provided as an ingredient for preparing such fertilizers or other types of fertilizers. The preparation of the fertilizer product may comprise providing the potassium sulphate, providing one or more substances acting as, and / or selected from, a fertilizer, a filler, and / or a stabilizer, mixing to obtain a mixture, and forming the mixture into a fertilizer product. The fertilizer products may be formed into granules, powder, or to any other applicable form. In one embodiment the method comprises preparing a fertilizer product comprising the crystallized potassium sulphate.

[0136] Disclosed is a fertilizer product comprising potassium sulphate obtained with the method disclosed herein. The fertilizer product may be in a form of dry powder or dry granules, which may have a moisture content of 20% by weight or less, such as 15% by weight or less or 10% by weight or less. The fertilizer product may be chloride-free or it contains only traces of chloride. The present disclosure provides use of waste sodium sulphate obtained from an industrial process in the process comprising converting the waste sodium sulphate to potassium sulphate and sodium carbonate, for example with the reaction:

[0137] Na2SO4 + K2CO3 — > K2SO4 + Na2COs, wherein the potassium sulphate is recovered and provided as, or for preparing, a fertilizer product, and / or wherein the sodium carbonate is recovered and preferably used in the industrial process and / or in a process relating to the industrial process.

[0138] The process comprising converting the waste sodium sulphate to potassium sulphate and sodium carbonate may comprise any of the methods and / or using any of the devices disclosed herein.

[0139] The present disclosure provides use of waste sodium sulphate obtained from an industrial process for preparing sodium carbonate with the method disclosed herein. The sodium carbonate is preferably used in the industrial process and / or in a process relating to the industrial process, as discussed.

[0140] The present disclosure provides use of waste sodium sulphate obtained from an industrial process for preparing potassium sulphate with the method disclosed herein. Preferably the potassium sulphate is used for preparing or manufacturing a fertilizer product and / or as a fertilizer product. The preparing or manufacturing may comprise formulating the potassium sulphate into fertilizer product, such as into granules, powder or the like form. Further fertilizing agent(s), fillers, binders and / or other additives may be provided and combined with the potassium sulphate to obtain a fertilizer composition.

[0141] Disclosed is use of the solid potassium sulphate obtained from the method for preparing or manufacturing a fertilizer product.

[0142] Examples

[0143] Example 1

[0144] The present process was carried out as a one-step process, with sodium sulphate and potassium carbonate as follows: Na2SO4 + K2CO3 — > K2SO4 + Na2COs

[0145] Waste sodium sulphate solution (250 ml) was mixed by stirring with excess of solid K2CO3 (34 g of K2CO3 powder) and heated up to 80°C to form a fully homogenous solution. Approximately 125 ml of water was evaporated to concentrate the solution. Potassium sulphate was then separated by cooling the reaction system down to 20°C, leading to the formation of almost pure potassium sulphate (white powder) and a solution of almost concentrated Na2COs (supernatant solution). These were recovered. In practice, the recovered solid potassium sulphate always contained some sodium sulphate (mineral glaserite).

[0146] Example 2: Regeneration of the solution

[0147] Na2SOs solution was used as reductant, wherein Na2SOs was converted to Na2SO4. 450 ml of 1.8 M Na2SO4 solution was heated to 60°C in nitrogen atmosphere. The formed sulfate was removed, and solution was regenerated by adding K2SO3 solids to the solution to produce solid potassium sulfate and Na2SOs solution. 128.2 grams of potassium sulfite was added to beaker containing sodium sulfate solution. Mixture was heated to 80°C for 30 minutes. After reaction time was passed, mixture was cooled to 20°C and allowed to mature for 2 hours and 30 minutes. Solids were separated by vacuum filtration and washed with 30 ml of absolute ethanol. Reaction yielded 108 grams of glaserite precipitate.

[0148] The process was carried out as a one-step process, with sodium sulphate and potassium sulfite as follows:

[0149] Na2SC>4(aq) + K2SOs(s) -> K2SO4(s) + Na2SOs(aq)

[0150] Example 3

[0151] 142.4 grams of solid waste sodium sulphate was dissolved in water to obtain 500 ml of approximately 2 molar sodium sulphate solution. 450 milliliters of the sodium sulphate solution was added to a beaker and warmed up to 60°C. 124.9 grams of potassium carbonate was added to solution. The mixture was then heated to 80°C for 30 minutes reaction time. Afterwards the mixture was cooled to 25°C and allowed to mature for 150 minutes. Obtained solid was separated by filtration and solids were washed using 70% ethanol solution. Washed solid was obtained comprising 111 grams of glaserite crystals. Sulphur content of the obtained solution dropped from 64 to 17.9 g / l. Table 3 shows the composition of obtained crystals.

[0152] Example 4

[0153] 142.6 grams of solid waste sodium sulphate was dissolved in water to obtain 500 ml of approximately 2 molar sodium sulphate solution. 450 milliliters of sodium sulphate solution was added to a beaker and system warmed up to 60°C. 125 grams of potassium carbonate was added to solution. Mixture was then heated to 80°C for 30 minutes reaction time. Afterwards mixture was cooled to 25°C and allowed to mature for 120 minutes. The mixture was then cooled to 15°C and allowed to mature for 30 minutes. Obtained solid was separated by filtration and solids were washed using 70% ethanol solution. Washed solid was obtained comprising 113.6 grams of glaserite crystals. Sulphur content of the obtained solution was dropped from 60 to 17.5 g / l. Table 3 shows the composition of obtained crystals.

[0154] Table 3. ICP-OES analyses of glaserite crystals produced in the exemplary reactions.

Claims

Claims1. A method for treating a solution of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate, the method comprising-providing a solution of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate,-providing potassium carbonate as solid or as a solution having a concentration of potassium carbonate of 10% by weight or more, and mixing with the waste sodium sulphate to obtain a reaction mixture (12),-reacting the reaction mixture to convert the waste sodium sulphate to potassium sulphate and sodium carbonate,-cooling the solution to obtain crystallized potassium sulphate and a solution of sodium carbonate, and-recovering the formed crystallized potassium sulphate and the solution of sodium carbonate.

2. The method of claim 1 , wherein the waste sodium sulphate solution is a solution of alkaline waste sodium sulphate having pH of 8 or more, such as 9 or more3. The method of claim 1 or 2, wherein the waste sodium sulphate is converted to potassium sulphate with the reactionNa2SO4 + K2CO3 — > K2SO4 + Na2COs.

4. The method of any of preceding claims, wherein the potassium carbonate is provided as a solution having a concentration of potassium carbonate in the range of 10-50% by weight, for example 30-50% by weight.

5. The method of any of preceding claims, comprising-heating the reaction mixture (12) to 60-90°C,-cooling the solution to 30°C or less, such as to 25°C or less, to obtain crystallized potassium sulphate and a solution of sodium carbonate.

6. The method of any of preceding claims, wherein the sodium sulphate is provided as an aqueous solution having a concentration of 100 g / l or more, such as in the range of 120-450 g / l.

7. The method of any of preceding claims, comprising providing potassium carbonate in an excess molar amount to the sodium sulphate.

8. The method of any of preceding claims, wherein the method is a chloride-free method9. The method of any of preceding claims, comprising using the recovered sodium carbonate in the industrial process (10) and / or in a process relating to the industrial process (10).

10. The method of any of preceding claims, wherein the industrial process (10) is a pulping and / or papermaking process.11 . The method of any of claims 1-9, wherein the industrial process (10) is a process of battery industry, preferably wherein the method comprises using the recovered sodium carbonate as a precipitator for precipitation of battery precursors from metal sulphate solutions.

12. The method of any of preceding claims, comprising using the recovered sodium carbonate as a precipitating chemical, and / or pH adjusting agent for treating wastewater.

13. The method of any of preceding claims, wherein the method is a waste-free method comprising utilizing all the reaction products.

14. The method of any of preceding claims, comprising providing the formed potassium sulphate for preparation of a fertilizer product (14), preferably by combining with one or more substances selected from a fertilizer, a filler, and a stabilizer.

15. The method of any of preceding claims, comprising-providing Na2SOs solution as a reductant to the formed solution to convert Na2SC>3 to Na2SC>4,-removing the formed sulphate, and-regenerating the solution by adding solid K2SO3 to the solution to produce solid potassium sulphate and Na2SOs solution.

16. Use of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate for preparing sodium carbonate with the method of any of claims 1 -15.

17. The use of claim 16, wherein the sodium carbonate is used in the industrial process (10) and / or in a process relating to the industrial process (10).

18. Use of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate for preparing potassium sulphate with the method of any of claims 1-15.

19. The use of claim 18, wherein the potassium sulphate is for preparing a fertilizer product (14).

20. An industrial processing plant comprising-an industrial process (10) utilizing sodium carbonate,-a source of a solution of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate,-a device arranged to carry out the method of any of claims 1-15, the device comprising-a reactor,-mixing means,-heating means,-an inlet for solid potassium carbonate,-wherein the mixing means and heating means are electrically controllable,-the source of waste sodium sulphate directly obtained from an industrial process (10) generating the sodium sulphate being arranged to be conveyed and / or transported to the reactor,-the obtained solution of sodium carbonate from the reactor being arranged to be conveyed and / or transported to the industrial process (10) utilizing sodium carbonate, and-the obtained crystallized potassium sulphate being arranged to be recovered from the reactor.21 . The industrial processing plant of claim 20, wherein the mixing means and heating means are operatively connected to a control unit arranged to carryout the method steps, by at least controlling the temperature in the reactor and / or controlling the mixing.

22. The industrial processing plant of claim 20 or 21 , wherein the industrial process (10) utilizing sodium carbonate is the same industrial process(10) or a process relating to the same industrial process (10) that generates the sodium sulphate.

23. The industrial processing plant of any of claims 20-22, which is a processing plant of pulping and / or papermaking industry.

24. The industrial processing plant of any of claims 20-22, which is a processing plant of battery industry.

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