Method for treating sodium sulfate-containing residual process streams from battery manufacturing facilities, battery recycling facilities, or steel plants

Abstract

The present invention relates to a method for producing a potassium sulfate containing fertilizer composition from a sodium sulfate containing residual process stream of a battery manufacturing facility, a battery recycling facility or a steel plant, comprising providing a residual process stream from a battery manufacturing facility, a battery recycling facility or a steel plant; optionally providing water; providing potassium chloride; providing a reaction mixture comprising said optional water, potassium chloride and the residual process stream, and reacting to obtain potassium sulfate.

Description

[Technical field]

[0001] The present invention relates to a process for providing value-added products from residual process streams from battery manufacturing or recycling facilities or steel plants. [Background technology]

[0002] Currently, there is an increasing interest in providing more sustainable products and processes. Various industries aim to make better use of the earth's finite resources.

[0003] Increasing awareness of climate change and limited supplies of fossil fuels are current major concerns.

[0004] This awareness and limited supply has led to an increased demand for alternative energy sources, for example for driving cars. The demand for batteries based on lithium-ion technology is growing rapidly. This also means that the emissions and solid and liquid residues from the battery manufacturing are increasing. Therefore, recycling and material optimization have become important issues in recent years. Resource optimization is something that most countries consider necessary for the continued use of lithium-ion batteries now and in the future.

[0005] Many industries want to improve the sustainability of their products and processes and limit the amount of waste generated from their facilities.

[0006] The battery manufacturing industry is continually working to minimize the generation of residuals and also aims to recycle process essential chemicals such as cobalt, lithium and manganese to reduce the operational costs of the facility. Residuals from the battery manufacturing process are hazardous wastes such as aqueous wastewater streams, ammonia, n-methylpyrrolidone and battery metal components. However, because residual streams, especially wastewater streams, can be quite large, reducing the amount of residuals and providing value-added components from streams that would be classified as waste is desirable to improve the overall operation of the battery manufacturing facility in terms of cost and raw material usage, and to allow reuse of the Earth's finite resources. Also, local and national regulations may dictate whether battery manufacturing is permitted to discharge residuals and process emissions, especially to bodies of water. Undesirable elements such as sulfates and sodium may be present at high levels in various production processes such as steel making in steel plants or battery production and recycling, and the undesirable elements have a negative impact on residual process streams as they are expensive to dispose of and, if sent directly to sewers or wastewater treatment plants, place a significant burden on the downstream processes. Today, permits are not granted for battery manufacturing or battery recycling facilities where significant amounts of sulfate and sodium are present or expected to be present. Sodium sulfate is a problematic by-product for battery manufacturers, battery recyclers, and steel manufacturers. Given the volume of production, the costs of handling sodium sulfate can be significant, and not addressing the chemicals can prevent companies from obtaining the permits they need to continue production or new permits to increase production or build new production facilities.

[0007] The battery recycling industry is also continually working to minimise its waste stream, as is the steel industry.

[0008] Currently, sodium sulfate present in residual process streams may be discharged into wastewater systems, e.g., via drains and sewers, landfilled, or separated from the residual stream and sold as a lower grade chemical. Residual process streams from battery manufacturing facilities containing sodium sulfate come primarily from the oxidation step of cathode production. Residual process streams from steel plants containing sodium sulfate come primarily from vanadium recovery. Even though sodium sulfate is considered a waste product, it could be a valuable asset if a use for it were provided, due to the potentially large amounts of sodium sulfate present. For battery manufacturing facilities, battery recycling facilities, and steel plants, handling the resulting sodium sulfate is problematic. However, if the sodium sulfate were to be utilized, it could be a valuable additive to the overall process.

[0009] The problem with current residual process streams in battery manufacturing facilities is that potentially valuable chemicals are not recovered or recycled from them. In reality, large amounts of chemicals are always discharged to landfills, disposed as low-grade chemicals, or sent to wastewater systems. The same is true for battery recycling facilities, for example, processing lithium batteries for recycling purposes, such as batteries for electric vehicles (EVs). This is another focus of the present invention. Also, in steel plants, potentially valuable chemicals contained in residual process streams are not recovered or recycled from them. Again, in reality, large amounts of chemicals may be discharged to landfills, disposed as low-grade chemicals, or sent to wastewater systems.

[0010] Today, the emphasis is on having environmentally sustainable processes and on obtaining as many value-added and recyclable products as possible from the processes in order to avoid as much waste and loss as possible.

[0011] Thus, there is a need to obtain more efficient processes. There is a demand for processes that reduce the need to landfill waste or discharge valuable chemicals into wastewater systems. There is also a need to provide value-added products from waste from battery manufacturing facilities, battery recycling facilities, or steel plants, improving the overall economics of the battery manufacturing facilities, battery recycling facilities, or steel plants, respectively. Summary of the Invention [Problem to be solved by the invention]

[0012] The process of the present invention provides an environmentally sustainable solution to waste disposal while at the same time obtaining a high value-added product. By providing a high value-added product that has a market demand and can be sold, the overall economics of a battery manufacturing facility, a battery recycling facility or a steel mill are improved and Mother Nature's resources are used carefully. This process also allows the possibility to meet the requirements and regulations related to battery manufacturing and waste disposal for recycling. [Means for solving the problem]

[0013] The residual process stream from battery manufacturing used in the present process may be from the oxidation step of cathode manufacturing in (lithium ion) battery manufacturing, in which sodium sulfate is formed. The residual process stream may be wastewater from the oxidation step of cathode manufacturing. Residual process streams from battery manufacturing, which today are sent to landfills or wastewater systems or are concentrated to solid residues, can be treated with potassium chloride to produce K2SO4, a high-value fertilizer, and by-product NaCl, which can be used for various applications, for example as road salt. The residual process stream containing sodium sulfate from the oxidation step of lithium ion battery cathode manufacturing may be in the form of an aqueous wastewater. Such wastewater may be concentrated by evaporation of at least a portion of the water before proceeding to the present process. Such wastewater may be dried to provide a dry residual process stream.

[0014] The residual process stream from battery recycling may be derived from the processing of lithium-containing batteries. The residual process stream may be obtained from a black agglomerate material containing lithium iron phosphate.

[0015] Residual process streams from steelmaking may come from slag processing with vanadium recovery.

[0016] This invention allows the use of large amounts of a chemical present in residual process streams (from battery manufacturing, battery recycling or steel making as described herein), namely sodium sulfate, eliminating the adverse environmental impacts from battery manufacturing residual process streams, battery recycling residual process streams or steel plant residual process streams. This invention provides high quality fertilizer, allowing nutrient chemicals to be delivered to plants in need instead of being flushed down the drain, sewers, landfilled or separated as lower quality chemicals.

[0017] The present invention is applicable to and can be implemented in any battery manufacturing facility, battery recycling facility or steel mill that provides a residual process stream or that processes a residual process stream, such as an aqueous residual process stream, comprising sodium sulfate in a residual processing system or that processes an aqueous residual process stream comprising sodium sulfate in a residual processing system.

[0018] The scope of the invention is defined by the appended claims.

[0019] The present invention relates to a method for producing a fertilizer composition containing potassium sulfate (K2SO4) from a residual process stream of a battery manufacturing facility, a battery recycling facility, or a steel plant, comprising the steps of: providing a residual process stream from a battery manufacturing facility, a battery recycling facility or a steel plant; optionally providing water if the residual process stream does not contain water or does not contain a sufficient amount of water; Provide potassium chloride; providing a mixture comprising the optional water, potassium chloride and a residual process stream to react to obtain potassium sulfate; The present invention relates to a method for producing a fertilizer composition.

[0020] According to one embodiment, potassium chloride and a residue process stream are provided in any order or simultaneously to provide said mixture. Potassium chloride, optional water and a residue process stream may be provided and mixed in any order or simultaneously to provide said mixture. Residual process stream, potassium chloride and optional water may be provided in any order or simultaneously to provide said mixture, and said components may be contacted and mixed in any order or simultaneously. To provide said mixture, a mixture of potassium chloride, residue process stream and optional water may be provided by simultaneous addition or sequential addition and mixing in any order. The mixture may be obtained by first mixing the provided residue process stream with optional water, and then adding and mixing potassium chloride. Alternatively, the mixture may be obtained by first mixing the provided residue process stream with potassium chloride, and then adding and mixing optional water. Alternatively, the mixture may be obtained by first mixing the provided optional water with potassium chloride, and then adding and mixing the residue process stream. Alternatively, the mixture can be obtained by first mixing the provided residual process stream with optional water, followed by adding and mixing potassium chloride, optionally mixed with additional optional water. Preferably, the optional water and the residual process stream are added before the potassium chloride. Both the residual process stream and the potassium chloride may be combined with the optional water before being combined and mixed with each other to form said mixture, i.e. the residual process stream, potassium chloride and optional water may be combined and mixed. In one preferred embodiment, the residual process stream is combined and mixed with optional water before being contacted and mixed with potassium chloride to form said mixture.

[0021] According to one embodiment, an acid is added to the mixture. Preferably, sulfuric acid and / or hydrochloric acid are used, more preferably sulfuric acid is used. Preferably, the acid is added before the addition of potassium chloride. Such addition may be performed to adjust the pH of the mixture.

[0022] According to one embodiment, the residual process stream is contacted with potassium chloride.

[0023] Residual process streams comprising sodium sulfate, originating from battery manufacturing, battery recycling or steel plants, may contain water, may be mixed with water or may be at least partially dissolved in water. The residual process stream may be a solution. To produce a dry residual process stream, the residual process stream may be pre-treated with an evaporation step. Such pre-treated dry residual process stream may then be contacted with water and then with potassium chloride. Alternatively, such pre-treated dry residual process stream may then be contacted with potassium chloride and then with water. Alternatively, such pre-treated dry residual process stream may then be contacted with potassium chloride that has already been contacted with water.

[0024] According to one embodiment, sodium hydroxide and / or potassium hydroxide is added to the mixture of water, potassium chloride and residual process stream, for example to adjust the pH when acid has been added.

[0025] According to one embodiment, the reaction of water, potassium chloride and a residual process stream produces glaserite, which is removed, admixed with additional potassium chloride and / or leached with water to provide potassium sulfate. The potassium sulfate can then be removed for further use or sale. It is noted that the admixture of potassium chloride and the leaching with water may be performed in any order. However, in a preferred embodiment, the reaction with potassium chloride is performed first, followed by the leaching with water.

[0026] According to one embodiment, the mixture remaining after removal of the potassium sulfate is concentrated and then the sodium chloride present is removed, e.g. for further use.

[0027] According to one embodiment, the removed sodium chloride is sent to a cell membrane process that converts it into sodium hydroxide, hydrogen and chlorine.

[0028] According to one embodiment, the removed sodium chloride is sent to a cell membrane process that converts it into sodium hydroxide, hydrogen and chlorine.

[0029] According to one embodiment, the residual process stream from a battery manufacturing facility originates from a lithium battery manufacturing facility, for example, a battery manufacturing facility that manufactures batteries selected from lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium titanate, or any combination thereof, preferably a battery manufacturing facility that manufactures lithium nickel manganese cobalt oxide batteries.

[0030] According to one embodiment, the residual process stream from the battery recycling facility originates from a battery recycling facility for lithium-containing batteries. The recycled lithium-containing batteries can be selected from batteries containing lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium titanate, or any combination thereof, and preferably from batteries containing lithium nickel manganese cobalt oxide.

[0031] According to one embodiment, the sodium sulfate containing residue process stream from a steel plant originates from the treatment of slag for vanadium recovery. The vanadium recovery may include vanadium purification by addition of sodium hydroxide, thereby providing vanadium pentoxide as one product stream and a sodium sulfate containing residue process stream as another product stream. The sulfuric acid containing residue process stream from a steel plant may be obtained by addition of sulfuric acid and / or aluminum sulfate after vanadium purification.

[0032] According to one embodiment, the potassium chloride added to the residue process stream is subjected to a pre-treatment step involving washing with water and optionally subsequent evaporation to remove impurities present in the potassium chloride.

[0033] The present invention also relates to the use of the process for the manufacture of a fertilizer comprising potassium sulphate. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 discloses a schematic embodiment of the process of the present invention. [Diagram 2] FIG. 2 discloses a schematic of the cathode oxidation step in battery manufacturing where sodium sulfate is sent to the process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The present invention relates to providing valuable components from residual process streams of battery manufacturing, battery recycling or steel plants. The present invention provides a high value fertilizer, K2SO4, and also a by-product, NaCl, which can be used for various applications, e.g. road salt.

[0036] In particular, the present invention relates to residual process streams from lithium ion battery manufacturing or battery recycling, for example selected from lithium cobalt oxide (LiCoO2 or LCO), lithium manganese oxide (LiMn2O4 or LMO), lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC), lithium iron phosphate (LiFePO4 or LFP), lithium nickel cobalt aluminum oxide (LiNiCoAlO2 or NCA), lithium titanate (Li2TiO3 or LTO). In particular, the present invention relates to providing valuable components from residual process streams of lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) battery manufacturing or battery recycling.

[0037] As mentioned above, the residual process stream from battery manufacturing used in the present process can be from the oxidation step of cathode manufacturing in (lithium ion) battery manufacturing, where sodium sulfate is formed. The residual process stream can be wastewater from the oxidation step of cathode manufacturing. The residual process stream used in the present process is preferably obtained from the cathode manufacturing step in the battery manufacturing process, more specifically, the residual process stream is sourced from the oxidation step of cathode manufacturing. In the cathode manufacturing process, sodium hydroxide and sulfuric acid are used. The said residual process stream from the battery manufacturing facility mainly contains sodium, sulfates, and trace amounts of some metals and elements, nickel, cobalt, ammonia and lithium. Figure 2 discloses a schematic diagram of the cathode manufacturing process.

[0038] As can be seen from the above, lithium-containing batteries are one focus area according to the present invention. Furthermore, according to another embodiment, a residual process stream from a battery recycling facility is obtained from black agglomerate material containing lithium iron phosphate. Furthermore, according to another embodiment, the concentration of lithium is increased relative to the sum of lithium, iron and phosphate, preferably by separating iron and / or phosphate, before being provided as a residual process stream from the battery recycling facility.

[0039] The residual process stream from a steel plant used in the process may be a sodium sulfate-containing residual process stream from slag processing with vanadium recovery. In this regard, according to one embodiment, it can be mentioned that the sodium sulfate-containing residual process stream originates from the processing of slag for vanadium recovery. Furthermore, according to yet another embodiment, the vanadium recovery comprises vanadium purification by addition of sodium hydroxide, thereby providing vanadium pentoxide as one product stream and a sodium sulfate-containing residual process stream as another product stream. Furthermore, according to one specific embodiment, the sulfate-containing residual process stream is obtained by addition of sulfuric acid and / or aluminum sulfate after vanadium purification.

[0040] In the present process, the residual process stream, optional water, and potassium chloride may be provided and mixed in any order, or may be provided and mixed simultaneously, to provide the mixture. That is, the residual process stream, optional water, and potassium chloride may be contacted and mixed in any order or simultaneously to provide the mixture. The mixture may be provided by: Simultaneously providing and mixing potassium chloride, optional water, and a residue process stream; providing and mixing a residual process stream and optional water, and then adding and mixing potassium chloride; providing and mixing a residue process stream and potassium chloride, and then adding and mixing optional water; providing and mixing a residue process stream and optional water, providing and mixing potassium chloride and optional water, and then mixing the potassium chloride and optional water with the residue process stream and optional water; or Providing and mixing potassium chloride and optional water, then adding and mixing a residual process stream.

[0041] Residual process streams comprising sodium sulfate, originating from battery manufacturing, battery recycling or steel plants, may be mixed with water and at least partially dissolved in water. Preferably, the residual process stream is in solution. The components of the residual process stream are preferably dissolved. The aqueous mixture of the residual process stream may optionally be treated with an acid, preferably sulfuric acid. The optional use of an acid may depend on the composition of the residual process stream.

[0042] Residual process streams vary in chemical content and may contain the following impurities: Where residual process streams come from a battery manufacturing facility: Na2SO4, nickel, cobalt, ammonia, lithium, and NaOH; If the residual process stream is provided by a battery recycling facility: Na2SO4, calcium, lithium, aluminum, iron, and manganese; or When the residual process stream comes from a steel plant: Na2SO4, silicon, iron, potassium and calcium.

[0043] Optionally, a subsequent step of pH adjustment using an alkaline compound can be used, for example when the above-mentioned acids are added in the process. Preferably, KOH and / or NaOH are used as alkaline compounds. The addition of an alkaline compound can be used to raise the pH and achieve the correct stoichiometric relationship with respect to K2SO4 and NaCl.

[0044] To obtain potassium sulfate, potassium chloride (KCl) is added to the aqueous mixture constituting the residual process stream. The solid phase obtained in this process may contain a salt called glaserite, which consists of potassium sulfate and sodium sulfate (K3Na(SO4)2). In one embodiment, the intermediate product obtained in this process after the first addition of potassium chloride is glaserite.

[0045] The resulting glaserite salt is removed from the treated residual process stream and the liquid remaining portion of the mixture can be further treated with KCl to produce K2SO4, which may then be removed.

[0046] The reactions involved in the production of the intermediates glaserite and K2SO4 are shown below. [ka]

[0047] As an alternative treatment, the resulting glaserite salt may be removed from the treated residual process stream and then leached in water to provide K2SO4.

[0048] However, in further embodiments, the process may include a combination of both of the above treatment steps for glaserite, in any order. The resulting glaserite salt may then be first treated with KCl and then leached in water to produce K2SO4, or the order may be reversed.

[0049] The potassium chloride used in the process may be subjected to a pretreatment step, including washing and optionally evaporation, before addition to the residue process stream. Pretreatment by washing with water allows the removal of by-products or impurities present. Potassium chloride products offered on the market often contain by-products and impurities, such as sodium chloride. By subjecting the potassium chloride to a water wash, the impurities present can be removed from the potassium chloride and the quality of the potassium chloride added to the residue process stream can be improved. By pretreatment with a water wash and optionally subsequent evaporation of the water, the quality of the potassium chloride can be improved, for example, from one containing about 4 wt. % sodium chloride to one containing at most 1 wt. % sodium chloride. Such an improvement in the purity of the potassium chloride used in the process increases the yield of potassium sulfate obtained in the conversion step by at least 5 times, when the conversion to potassium sulfate is carried out at a pH of about 5-9, for example about 6-8, preferably about 6-7.

[0050] The treated residual process stream remaining after separation of the K2SO4 can be further processed, for example by a cooling step, to precipitate sodium sulfate and increase the sulfate yield by returning the sulfate to the process.

[0051] The residual process stream remaining after separation of the K2SO4 can be further processed, for example by evaporation, to precipitate sodium chloride (NaCl) which can be removed as a solid phase and used, for example, as road salt.

[0052] The invention can be further complemented by the use of a membrane cell process to convert the resulting NaCl into NaOH, H2 and Cl2. NaOH is a valuable chemical and is used in battery manufacturing plants, battery recycling plants or steel plants, for example in vanadium purification in steel plants. The other two products, H2 and Cl2, can be recovered and, in the case of H2, used as energy or sold to third parties, improving the economics and profitability of battery production or the process as a whole.

[0053] In this way, a product with higher added value than the manufactured fertilizer is obtained and can be reused or sold in the battery manufacturing process, battery recycling process, total steelmaking process, or other processes.

[0054] Referring to FIG. 1, in step 1, the residual process stream and water are added and mixed. If the residual process stream already contains a sufficient amount of water, the addition of water is optional. Alternatively, if the residual process stream already contains some amount of water, only a small amount of water may be added. In one embodiment, the residual process stream and water may replace or be combined with the removal from the pre-treatment residual process stream treatment system. Optionally, an acid, such as sulfuric acid, may also be added in step 1.

[0055] The residual process stream containing the mixture may optionally be mixed with KOH and / or NaOH in step 2, where the pH of the mixture is raised and the solution can reach the correct stoichiometric relationship with respect to the resulting K2SO4 and NaCl, for example, if no acid was added in step 1. An alkaline compound may not be required in step 2.

[0056] Then, in step 3, the residual process stream mixture is mixed with KCl to obtain K2SO4. This process produces a mixed salt of potassium and sodium sulfate called glaserite. This glaserite salt is then removed and proceeds to step 4 where it is reacted with additional KCl in aqueous solution and then further leached in water in step 5 to produce the final product K2SO4. Note that either steps 4 and 5 may be used alone or in combination. The solid phase K2SO4 may be separated from the treated residual process stream and recycled.

[0057] The remaining liquids from steps 3, 4 and 5 can be recycled countercurrently to the precipitated salts to the previous steps in the process. In step 3, where glaserite may be formed, the treated residual process stream from this step is sent to cooling step 6 for further precipitation of sulfates, which are separated and recycled to step 3.

[0058] The solution remaining after cooling step 6, which contains small amounts of sodium sulfate and potassium but also sodium and chloride, is sent to evaporation step 7 where water is removed to increase the salt concentration, precipitate NaCl as a solid phase, and separate the salt from solution. The water driven off in the evaporation step, where NaCl is precipitated and removed from solution, is recycled back into the process to close the system and can be used to dilute or dissolve fresh residual process streams.

[0059] To further facilitate the reaction of glaserite to potassium sulfate in step 4, the KCl is washed to remove impurities to produce high purity KCl, which increases the yield in step 4 by up to five times.

[0060] Since almost all reactions occur at room temperature or slightly above, the process according to the present invention does not require much energy, except for the evaporation of water in the NaCl precipitation step 7.

[0061] A membrane cell process can be further added to this process to provide NaOH from the produced by-product NaCl to battery manufacturing facilities, battery recycling facilities, or steel plants, such as vanadium refining.

Claims

1. 1. A method for producing a potassium sulfate-containing fertilizer composition from a sodium sulfate-containing residual process stream of a battery manufacturing facility, a battery recycling facility, or a steel plant, comprising: Providing a residual process stream from a battery manufacturing facility, a battery recycling facility, or a steel plant; Optionally providing water; providing potassium chloride; providing a mixture comprising the optional water, potassium chloride and a residual process stream and reacting to obtain potassium sulfate; A method for producing a potassium sulfate-containing fertilizer composition.

2. 2. The method of claim 1, wherein the potassium chloride, the residue process stream, and optionally water are provided and mixed in any order or simultaneously to provide the mixture, preferably the mixture is provided by: - simultaneously providing and mixing said potassium chloride, optional water, and residual process streams; providing and mixing said residual process stream and optional water, and then adding and mixing said potassium chloride; providing and mixing said residual process stream and potassium chloride, and then adding and mixing optional water; providing and mixing said residue process stream and optional water, providing and mixing said potassium chloride and optional water, and then mixing said potassium chloride and optional water with said residue process stream and optional water; or - Providing and mixing the potassium chloride and optional water, then adding and mixing the residual process stream.

3. 10. The method of claim 1 , wherein the residue process stream and optional water are added prior to the potassium chloride.

4. 2. The method of claim 1, wherein an acid is admixed to the mixture, preferably prior to the addition of the potassium chloride.

5. 10. The method of claim 1, wherein the residual process stream is pretreated with an evaporation step to produce a dry product for contacting with the water and thereafter with the potassium chloride.

6. 10. The method of claim 1 , wherein sodium hydroxide and / or potassium hydroxide is added to the mixture of water, potassium chloride and a residual process stream.

7. 2. The method of claim 1, wherein the reaction of the water, the potassium chloride and the residual process stream produces glaserite, which is removed, admixed with additional potassium chloride and / or leached with water to provide potassium sulfate.

8. 8. The process according to claim 7, in which the mixture remaining after removal of the potassium sulfate is concentrated and then the sodium chloride present is removed.

9. 9. The method of claim 8, wherein the removed sodium chloride is sent to a cell membrane process that converts it to sodium hydroxide, hydrogen and chlorine.

10. 2. The method of claim 1, wherein the residual process stream from a battery manufacturing facility originates from a lithium battery manufacturing facility, preferably a battery manufacturing facility that manufactures batteries selected from lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium titanate, or any combination thereof, preferably a battery manufacturing facility that manufactures lithium nickel manganese cobalt oxide batteries.

11. 10. The method of claim 1 , wherein the residual process stream from a battery recycling facility is derived from a battery recycling facility for lithium-containing batteries.

12. 12. The method of claim 11, wherein the lithium-containing batteries being recycled can be selected from batteries containing lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium titanate, or any combination thereof, and preferably from batteries containing lithium nickel manganese cobalt oxide.

13. 2. The method of claim 1 , wherein the sodium sulfate containing residual process stream from a steel plant is derived from the processing of slag for vanadium recovery.

14. 14. The method of claim 13, wherein the vanadium recovery comprises vanadium purification by addition of sodium hydroxide to provide vanadium pentoxide as one product stream and a sodium sulfate containing residue process stream as another product stream.

15. 14. The method of claim 13, wherein the sulfate-containing residual process stream from a steel plant is obtained by addition of sulfuric acid and / or aluminum sulfate after vanadium purification.

16. 10. The method of claim 1, wherein the potassium chloride added to the residue process stream is subjected to a pretreatment step comprising washing with water and optionally subsequent evaporation to remove impurities present in the potassium chloride.

17. Use of the method according to any one of claims 1 to 16 for producing a fertiliser comprising potassium sulphate.

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