FR 3144170 A1 20240628 FR 2312739 A 20231120 Disclosed is a separation reagent and a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, which belong to the field of hydrometallurgy technology. The separation reagent includes an extracting agent and a co-extracting agent; the extracting agent includes BC196 and the co-extracting agent includes Mextral 6103H. Through the combination of BC196 and Mextral 6103H, the pH value of an water phase solution is reduced, such that the separation reagent can be applied to iron-containing solutions, and the loading capacity and separation coefficient are increased, thereby realizing an effective separation of cobalt from iron, zinc, calcium, silicon and magnesium. The method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon includes extracting the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon with the separation reagent. The recovery rate of cobalt can reach 99%. According to the method, no dangerous chemicals are introduced and no hazardous wastes are produced; and the method has the advantages of high extraction efficiency, large separation coefficient, short technological process, and less investment in equipment. SEPARATION REAGENT AND METHOD FOR RESOURCE UTILIZATION OF MAGNESIUM SULFATE SOLUTION CONTAINING COBALT, IRON, ZINC, CALCIUM AND SILICON The present disclosure relates to the field of hydrometallurgy technology, and in particular, to a separation reagent and a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon. BACKGROUND With the rapid development of new energy technology, 5G and other related electronic technologies, there is an increasing demand for batteries in the future. Nickel, cobalt, manganese, lithium and magnesium, as the most important elements in battery components, will also be increasingly demanded. Therefore, some low-grade nickel-cobalt ores, salt lakes, nickel-cobalt intermediates, etc., that are rarely exploited or not exploited will also be exploited gradually to improve the resource utilization level of low-grade mines and salt lakes and obtain high-purity nickel-cobalt-manganese-lithium-magnesium products, which will greatly reduce the exploitation cost, improve the competitiveness, and occupy the market share. In the existing technology, nickel-cobalt bioleach solutions are extracted with a reagent containing Versatic10. However, because of a high solubility of Versatic 10 in water and a dissolution loss of the Versatic10 after multiple extractions, the components that form the extracting agent have changed greatly and the extraction performance has changed greatly, which cannot be used in the large-scale production. In some cases, fluorides are used to remove calcium and magnesium. This method requires an excessively high cost in the industrial production, and the cost for the environment treatment of the introduced fluoride ions is also high. In some cases, all magnesium is extracted directly with P204. When P204 is used to extract all magnesium, due to a very low separation coefficient of nickel, cobalt and magnesium, on one hand, the amount of extracting agent used will be large, and part of nickel and cobalt will enter the extraction on other hand. The treatment process for the extraction liquid of extracted magnesium, part of the nickel and cobalt is to add liquid alkali to cause flocculation and precipitation to treat the wastewater, but during the precipitation, not only nickel and cobalt are recovered but also magnesium. When the recovered material is returned to production for reuse, a small amount of magnesium is enriched continuously, which ultimately affect the extraction efficiency, and leads to an increased amount of extracting agent and an increased production cost. In some other cases, sodium sulfide is used to precipitate wastewater to recover metals, such as nickel, cobalt and manganese, and precipitate magnesium. In the method, although the wastewater can meet the standard (with nickel and cobalt less than or equal to 0.5 ppm), hydrogen sulfide will be generated when sodium sulfide is added, which is extremely dangerous, unsatisfactory in controllability. Moreover, the wastewater is yellowish and do not meet the requirements of environmental protection. That is, the technical schemes of the existing technology of using sodium sulfide have the problems such as environmental risks, long process flow, low metal recovery rate, high water solubility of extracting agent, low loading capacity, and the like. In view of the above, the present disclosure is hereby provided. SUMMARY A first object of the present disclosure is to provide a separation reagent for separating cobalt from iron, zinc, calcium, silicon and magnesium, which has low water solubility, a large separation coefficient and a low organic loss, and can effectively realize the separation of cobalt from iron, zinc, calcium, silicon and magnesium. A second object of the present disclosure is to provide use of the separation reagent in separating cobalt from iron, zinc, calcium, silicon and magnesium. A third object of the present disclosure is to provide a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, which has a short flow, a low cost, a high metal recovery rate and a satisfactory solution quality. The present disclosure can be achieved by the technical scheme as follows. In a first aspect, the present disclosure provides a separation reagent for separating cobalt from iron, zinc, calcium, silicon and magnesium, wherein the separation reagent includes an extracting agent and a co-extracting agent; and the extracting agent includes BC196, and the co-extracting agent includes Mextral 6103H. In an alternative embodiment, a volume percentage of the BC196 in the separation reagent is 5-15%, and/or, a volume percentage of the Mextral 6103H in the separation reagent is 5-8%. In an alternative embodiment, the separation reagent further includes a diluent, and a volume percentage of the diluent in the separation reagent is a balance after subtracting the volume percentages of the extracting agent and the co-extracting agent. In an alternative embodiment, the diluent includes at least one of kerosene, sulfonated kerosene, Escaid 110, heptane, hexane, dodecane, or sec-octanol. In a second aspect, the present disclosure provides use of the separation reagent of any one of the above embodiments in separating cobalt from iron, zinc, calcium, silicon and magnesium. In a third aspect, the present disclosure provides a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, including the following steps: extracting a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon with the separation reagent of any one of the above embodiments to obtain a loaded organic phase and a raffinate water phase. In an alternative embodiment, a volume ratio of the separation reagent to the magnesium sulfate solution containing cobalt, iron, zinc, calcium, and silicon is 1:0.5to1:20; In an alternative embodiment, the extracting includes a single-stage extraction or a multi-stage counter-current extraction. In an alternative embodiment, the raffinate water phase has a pH value of 4.5-5. In an alternative embodiment, the method further includes subjecting the separation reagent to a saponification treatment prior to the step of extracting. In an alternative embodiment, a saponifying agent used for the saponification treatment is an alkaline solution. In an alternative embodiment, the alkaline solution includes at least one of a sodium hydroxide solution, ammonia water, a potassium hydroxide solution, or a magnesium hydroxide solution. In an alternative embodiment, the alkaline solution has a concentration of 5-10 mol/L. In an alternative embodiment, a degree of saponification after the saponification treatment is greater than 0 but not greater than 50%. In an alternative embodiment, the method further includes carrying out a reverse extraction on the loaded organic phase with a reverse extracting agent to obtain a battery-grade cobalt sulfate solution. In an alternative embodiment, the reverse extracting agent includes at least one of a sulfuric acid solution, or a hydrochloric acid solution. In an alternative embodiment, a concentration of H + in the reverse extracting agent is 3-5 mol/L. In an alternative embodiment, a number of stages of the reverse extraction is 1-5. In an alternative embodiment, the method further includes washing the loaded organic phase with a washing liquid prior to the reverse extraction. In an alternative embodiment, the washing liquid used for washing includes at least one of water, a sulfuric acid solution, a hydrochloric acid solution, a phosphoric acid solution, or an oxalic acid solution. In an alternative embodiment, a concentration of H + in the washing liquid is not greater than 1 mol/L. In an alternative embodiment, a volume ratio of the washing liquid to the loaded organic phase is 0.05:1 to 0.5:1. In an alternative embodiment, the washing treatment method is a multi-stage counter-current washing. In an alternative embodiment, a volume ratio of the reverse extracting agent to the loaded organic phase after washing is 0.05:1 to 0.5:1. In an alternative embodiment, the method further includes performing ion adsorption on the raffinate water phase to obtain a refined magnesium sulfate solution. In an alternative embodiment, an ion exchange resin used for the ion adsorption is a sodium-type resin. In an alternative embodiment, the sodium- type resin includes at least one of D467, SepliteD001, LSC850, or D503. The present disclosure can achieve the following beneficial effects. In the present disclosure, two reagents, i.e., BC196 and Mextral 6103H, are creatively used to extract cobalt, which effectively solves the problem that BC196 is not applicable to iron-containing solutions and has high equilibrium pH, and Mextral 6103H has a small load and a low separation coefficient, and therefore an effective separation of cobalt from iron, zinc, calcium, silicon and magnesium can be achieved. Moreover, BC196 and Mextral 6103H have large separation coefficients for impurities such as cobalt, magnesium, iron, zinc, calcium, and silicon, and have low water solubility and low organic loss. Extraction of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon using the above separation reagent can achieve a recovery rate up to 99% of the cobalt. According to the method, no dangerous chemicals are introduced and no hazardous wastes are produced. In addition, the method has the advantages of high extraction efficiency, large separation coefficient, short technological process, and less investment in equipment. In order to illustrate the technical schemes of examples of the present disclosure more clearly, the accompanying drawings used in the examples will be briefly described below. It should be understood that the accompanying drawings in the following description are only a part of embodiments of the present disclosure and should not be considered as a limitation to the present disclosure. For those having ordinary skills in the art, other drawings can be obtained based on these accompanying drawings without creative efforts. is a flowchart of a method for resource utilization of a magnesium sulfate solution in Example 1 of the present disclosure. DETAILED DESCRIPTION In order to illustrate the objects, technical schemes, and advantages of the examples of the present disclosure more clearly, a clear and complete description of the technical schemes in the examples of the present disclosure will be made below. The conventional conditions or conditions recommended by the manufacturers shall be followed unless specific conditions are specified in the examples. The reagents or instruments used of which the manufacturers are not indicated are conventional products commercially available. A separation reagent and a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon provided by the present disclosure will be described in detail below. The present disclosure provides a separation reagent for separating cobalt from iron, zinc, calcium, silicon and magnesium, which includes an extracting agent and a co-extracting agent. The extracting agent includes BC196, and the co-extracting agent includes Mextral 6103H. That is, compositions of the separation reagent provided in the present disclosure include both BC196 and Mextral 6103H. Furthermore, other extracting agents and co-extracting agents can be added on the basis of BC196 and Mextral 6103H as required. The BC196 is an acid compound, a colorless or light-yellow liquid with a density of 0.85-0.88 g/mL and a purity greater than or equal to 90%, and can be purchased from Suzhou Bocui Circulation Technology Co., Ltd. Mextral 6103H is a lipid extracting agent, a brown transparent liquid with a density of 0.97±0.005 g/mL and a flash point greater than 70°C, and can be purchased from Kopper Chemical Industry Corp., Ltd. Referentially, a volume percentage of the BC196 in the separation reagent may be 5-15%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., or may be any other value within the range of 5-15%. A volume percentage of the Mextral 6103H in the separation reagent may be 5-8%, for example, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%, etc., or may be any other value within the range of 5-8%. Further, the separation reagent further includes a diluent, and a volume percentage of the diluent in the separation reagent is a balance after subtracting the volume percentages of the extracting agent and the co-extracting agent. In an embodiment, the diluent may include for example at least one of kerosene, sulfonated kerosene, Escaid 110, heptane, hexane, dodecane, or sec-octanol. In some preferred embodiments, the separation reagent is composed of an extracting agent, a co-extracting agent and a diluent, wherein the extracting agent is BC196, and the co-extracting agent is Mextral 6103H. Calculated by volume percentage, BC196 accounts for 5-15% of the separation reagent, Mextral 6103H accounts for 5-8% of the separation reagent, and the balance is the diluent. It should be noted that BC196 usually has a high equilibrium pH when used for extracting cobalt and is not suitable for iron-containing systems. Meanwhile, BC196 has a high water solubility and a large organic loss, which will bring environmental problems. In contrast, Mextral 6103H has a small load and a low separation coefficient for separating cobalt from iron and silicon. The inventor creatively uses two reagents, i.e., BC196 and Mextral 6103H, to extract cobalt, which effectively solves the problem that BC196 is not suitable for iron-containing solutions and has a high equilibrium pH and Mextral 6103H has a small load and a low separation coefficient, thereby realizing an effective separation of cobalt from iron, zinc, calcium, silicon and magnesium. Moreover, BC196 and Mextral 6103H have a large separation coefficient for impurities such as cobalt, magnesium, iron, zinc, calcium, and silicon, and have a low water solubility and a low organic loss. Accordingly, the present disclosure further provides use of the separation reagent, for example, in the separation of cobalt from iron, zinc, calcium, silicon and magnesium. Specifically, the separation reagent can be used to extract a substance containing cobalt, iron, zinc, calcium, silicon and magnesium to be separated. Additionally, the present disclosure further provides a method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, which includes the following steps: extracting a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon with the separation reagent to obtain a loaded organic phase and a raffinate water phase. In some embodiments, the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon is a battery waste or a reverse extracting solution produced by removing iron, aluminum and copper, and then extracting and removing impurities with P507 from a leaching solution of nickel-cobalt intermediate. In the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, magnesium has a concentration of 25-45 g/L, calcium has a concentration of 0.05-0.15 g/L, zinc has a concentration of 0.01-0.5 g/L, cobalt has a concentration of 0.2-5 g/L, silicon has a concentration of 0.01-0.1 g/L, sodium has a concentration of 0.02-0.05 g/L, and iron has a concentration of 0.05-0.1 g/L. Referentially, a volume ratio of the separation reagent to the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon may be 1:0.5 to 1:20, for example, 1:0.5, 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, or 1:20, etc., or any other value within the range of 1:0.5 to 1:20. The extraction method can be a single-stage extraction or a multi-stage counter-current extraction, with stages of greater than or equal to 2. After extraction, the raffinate water phase has a pH of approximately 4.5-5. In some preferred embodiments, the method further includes subjecting the separation reagent to a saponification treatment prior to the step of extracting. Referentially, the saponifying agent used for the saponification treatment is an alkaline solution, for example, may include at least one of a sodium hydroxide solution, ammonia water, a potassium hydroxide solution, or a magnesium hydroxide solution. The alkaline solution may have a concentration of 5-10 mol/L, for example, 5 mol/L, 5.5 mol/L, 6 mol/L, 6.5 mol/L, 7 mol/L, 7.5 mol/L, 8 mol/L, 8.5 mol/L, 9 mol/L, 9.5 mol/L, or 10 mol/L, etc., or any other value within the range of 5-10 mol/L. Preferably, a degree of saponification after the saponification treatment is greater than 0 but not greater than 50%, for example, 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., or any other value within the range of greater than 0 but not greater than 50%. Further, the method further includes carrying out a reverse extraction on the loaded organic phase with a reverse extracting agent to obtain a battery-grade cobalt sulfate solution. The battery-grade cobalt sulfate solution can be directly used in the synthesis of a ternary precursor. Referentially, the reverse extracting agent may include at least one of a sulfuric acid solution, or a hydrochloric acid solution. A concentration of H + in the reverse extracting agent may be 3-5 mol/L, for example, 3 mol/L, 3.5 mol/L, 4 mol/L, 4.5 mol/L or 5 mol/L, etc., or any other value within the range of 3-5 mol/L. The number of stages of the reverse extraction may be, for example, 1 to 5 stages, specifically 1 stage, 2 stages, 3 stages, 4 stages or 5 stages. In some preferred embodiments, the method further includes washing the loaded organic phase with a washing liquid prior to the reverse extraction. Referentially, the washing liquid used for washing may include, for example, at least one of water, a sulfuric acid solution, a hydrochloric acid solution, a phosphoric acid solution, or an oxalic acid solution. The concentration of H + in the washing liquid is not greater than 1 mol/L, for example, 0 mol/L, 0.1 mol/L, 0.2 mol/L, 0.3 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, 0.7 mol/L, 0.8 mol/L, 0.9 mol/L or 1 mol/L, etc., or may be any other value within the range of not greater than 1 mol/L. A volume ratio of the washing liquid to the loaded organic phase may be 0.05:1 to 0.5:1, for example, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4: 1, 0.45:1 or 0.5:1, etc., or any other value within the range of 0.05:1 to 0.5:1. The washing treatment method is preferably a multi-stage counter-current washing. The volume ratio of the reverse extracting agent to the loaded organic phase after washing may be 0.05:1 to 0.5:1, for example, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1, etc., or any other value within the range of 0.05:1 to 0.5:1. Further, the method further includes performing ion adsorption on the raffinate water phase to obtain a refined magnesium sulfate solution. A pH value of the refined magnesium sulfate solution after removing iron, zinc, calcium and silicon by ion exchange is controlled at 4.5-5. Referentially, an ion exchange resin used for the ion adsorption is preferably a sodium- type resin, which may include for example at least one of D467, SepliteD001, LSC850, or D503. The resin is light yellow or beige particles, which can be purchased from Xi’an Sunresin Technology Co., Ltd. The ion adsorption principle includes that: resins such as D467 or LSC850 do not adsorb magnesium under acidic conditions but can completely adsorb iron, zinc, calcium and silicon, achieving 99% recovery of cobalt and magnesium. For example, in the obtained battery-grade cobalt sulfate solution, a content of cobalt is greater than 100 g/L, a content of copper and zinc is less than 0.5 ppm, a content of calcium and magnesium is less than 3 ppm, a content of chromium is less than 2 ppm, a content of silicon is less than 8 ppm, a content of sodium is less than 100 ppm, and a content of iron is less than 1 ppm. In the obtained refined magnesium sulfate solution, a content of magnesium is greater than 25 g/L, a content of cobalt is less than 0.5ppm, a content of nickel is less than 0.5 ppm, a content of zinc is less than 2 ppm, a content of calcium is less than 1 ppm, a content of silicon is less than 1 ppm, and a content of iron is less than 5 ppm. As described above, the method for separating magnesium from cobalt, iron, zinc, calcium, and silicon realizes the separation of magnesium from cobalt, iron, zinc, calcium, and silicon through the combination of extraction method and ion exchange method, thus obtaining a battery-grade cobalt sulfate solution and a refined magnesium sulfate solution. The battery-grade cobalt sulfate solution can be directly used in the synthesis of a ternary precursor. According to the method, no dangerous chemicals are introduced and no hazardous wastes are produced, and the method has the advantages of high extraction efficiency, large separation coefficient, short technological process, low cost, less investment in equipment, high metal recovery rate, and satisfactory solution quality, thus realizing the efficient recovery of cobalt and the resources utilization of magnesium. The characteristics and performance of the present disclosure will be further described in detail below in conjunction with the examples. Example 1 Referring to , this example provided a method for resource utilization of a magnesium sulfate solution, including the following steps: Step (1): mixing an extracting agent BC196, a co-extracting agent Mextral 6103H and a diluent (Escaid110) in a volume ratio of 5:5:90 to prepare a separation reagent; Step (2): saponifying the separation reagent with an alkaline solution (aqueous sodium hydroxide solution) at a concentration of 10 mol/L, with a degree of saponification of 50%, to obtain a saponified separation reagent; Step (3): carrying out a 4-stage counter-current extraction according to a volume ratio of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon (pH 3.0) to the saponified separation reagent of 2:1, and standing for 5 minutes to separate an upper organic phase and a lower water phase to obtain a loaded organic phase and a raffinate water phase; Step (4): carrying out a 4-stage counter-current washing according to a volume ratio of 0.5mol/L dilute sulfuric acid as a washing liquid to the loaded organic phase of 1:20 to obtain a washed loaded organic phase; and carrying out a 3-stage counter-current reverse extraction according to a volume ratio of 2.5 mol/L sulfuric acid to the washed loaded organic phase of 1:20, and after cyclic enrichment, a battery-grade cobalt sulfate solution was obtained; and Step (5): passing the raffinate water phase (magnesium sulfate solution containing iron, zinc, calcium and silicon, pH 4.6) through a D467 resin bed at 2 BV/h for adsorption of iron, zinc, calcium and silicon to obtain a refined magnesium sulfate solution. Example 2 This example provided a method for resource utilization of a magnesium sulfate solution, including the following steps: Step (1): mixing an extracting agent BC196, a co-extracting agent Mextral 6103H and a diluent (Escaid110) in a volume ratio of 10:5:85 to prepare a separation reagent; Step (2): saponifying the separation reagent with an alkaline solution (aqueous sodium hydroxide solution) at a concentration of 10 mol/L, with a degree of saponification of 50%, to obtain a saponified separation reagent; Step (3): carrying out a 4-stage counter-current extraction according to a volume ratio of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon (pH 3.2) to the saponified separation reagent of 4:1, and standing for 5 minutes to separate an upper organic phase and a lower water phase to obtain a loaded organic phase and a raffinate water phase; and Step (4) and step (5) were the same as those in Example 1. Example 3 This example provided a method for resource utilization of a magnesium sulfate solution, including the following steps: Step (1) and step (2) were the same as those in Example 1; Step (3): carrying out a 4-stage counter-current extraction according to a volume ratio of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon (pH 4.0) to the saponified organic phase of 2:1, and standing for 5 minutes to separate an upper organic phase and a lower water phase to obtain a loaded organic phase; Step (4) was the same as that in Example 1; and Step (5): passing the raffinate water phase (magnesium sulfate solution containing iron, zinc, calcium and silicon, pH 4.7) through a D467 resin bed at 2 BV/h for adsorption of iron, zinc, calcium and silicon to obtain a refined magnesium sulfate solution. Example 4 Referring to , this example provided a method for resource utilization of a magnesium sulfate solution, including the following steps: Step (1): mixing an extracting agent BC196, a co-extracting agent Mextral 6103H and a diluent (kerosene) in a volume ratio of 15:6:79 to prepare a separation reagent; Step (2): saponifying the separation reagent with an alkaline solution (aqueous sodium hydroxide solution) at a concentration of 5 mol/L, with a degree of saponification of 5%, to obtain a saponified separation reagent; Step (3): carrying out a single-stage extraction according to a volume ratio of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon (pH 3.0) to the saponified separation reagent of 10:1, and standing for 5 minutes to separate an upper organic phase and a lower water phase to obtain a loaded organic phase and a raffinate water phase; Step (4): carrying out a 3-stage counter-current washing according to a volume ratio of 0.5 mol/L hydrochloric acid as a washing liquid to the loaded organic phase of 0.5:1 to obtain a washed loaded organic phase; and carrying out a 5-stage counter-current reverse extraction according to a volume ratio of 3 mol/L hydrochloric acid to the washed loaded organic phase of 0.5:1, and after cyclic enrichment, a battery-grade cobalt sulfate solution was obtained; and Step (5): passing the raffinate water phase (magnesium sulfate solution containing iron, zinc, calcium and silicon, pH 4.6) through a SepliteD001 resin bed at 2 BV/h for adsorption of iron, zinc, calcium and silicon to obtain a refined magnesium sulfate solution. Example 5 Referring to , this example provided a method for resource utilization of a magnesium sulfate solution, including the following steps: Step (1): mixing an extracting agent BC196, a co-extracting agent Mextral 6103H and a diluent (sec-octanol) in a volume ratio of 10:8:82 to prepare a separation reagent; Step (2): saponifying the separation reagent with an alkaline solution (potassium hydroxide solution) at a concentration of 7.5 mol/L, with a degree of saponification of 25%, to obtain a saponified separation reagent; Step (3): carrying out a 2-stage counter-current extraction according to a volume ratio of the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon (pH 3.0) to the saponified separation reagent of 20:1, and standing for 5 minutes to separate an upper organic phase and a lower water phase to obtain a loaded organic phase and a raffinate water phase; Step (4): carrying out a 2-stage counter-current washing according to a volume ratio of water as a washing liquid to the loaded organic phase of 0.1:1 to obtain a washed loaded organic phase; and carrying out a 1-stage reverse extraction according to a volume ratio 2 mol/L sulfuric acid to the washed loaded organic phase of 0.1:1 to obtain a battery-grade cobalt sulfate solution; and Step (5): passing the raffinate water phase (magnesium sulfate solution containing iron, zinc, calcium and silicon, pH 4.6) through a LSC850 resin bed at 2 BV/h for adsorption of iron, zinc, calcium and silicon to obtain a refined magnesium sulfate solution. Test example The contents of various elements in the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, the separated cobalt sulfate solution and magnesium sulfate solution obtained in the Examples 1 to 5 were tested. The results are shown in Table 1. Table 1: Effect of organic content and feed solution pH on extraction of elements Sample Mg Co Ca Zn Si Fe Magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon ( feed solution) mg/L 35620 1258 80 120 22 60 Example 1 Cobalt sulfate solution mg/L 2.2 101620 2.6 0.4 6.5 0.6 Magnesium sulfate solution mg/L 35410 0.4 0.8 1.6 0.8 3.2 Example 2 Cobalt sulfate solution mg/L 2.0 100250 2.5 0.4 6.2 0.7 Magnesium sulfate solution mg/L 35150 0.4 0.8 1.5 0.8 4.2 Example 3 Cobalt sulfate solution mg/L 1.5 100165 2.5 0.32 6.0 0.6 Magnesium sulfate solution mg/L 35260 0.35 0.6 1.2 0.6 3.8 Example 4 Cobalt sulfate solution mg/L 0.6 106824 2.8 0.5 6.5 0.7 Magnesium sulfate solution mg/L 35052 0.02 0.8 1.6 0.8 4.0 Example 5 Cobalt sulfate solution mg/L 1.8 108500 2.5 0.4 6.0 0.6 Magnesium sulfate solution mg/L 35060 0.2 0.6 1.4 0.7 4.1 As shown in Table 1, the methods provided in Examples 1 to 5 can achieve effective separation of magnesium from cobalt, iron, zinc, calcium and silicon. Comparative Example 1 The difference between this comparative example and Example 1 was that the extracting agent BC196 was replaced by C272. The results showed that magnesium cannot be effectively separated from cobalt, zinc and calcium. Comparative Example 2 The difference between this comparative example and Example 1 was that the separation reagent did not contain co-extracting agent Mextral 6103H, and the co-extracting agent Mextral 6103H was replaced with the same amount of the diluent. The results showed that, when the requirement of cobalt in the raffinate was met, the pH is about 6.9, the iron formed into colloid, and the organic phase and water phase were difficult to separate, so that the process could not continue. Comparative Example 3 The difference between this comparative example and Example 1 was that no ion adsorption was performed on the raffinate water phase. The results showed that magnesium could not be effectively separated from iron, zinc, calcium and silicon. In summary, in the present disclosure, the separation of magnesium from cobalt, iron, zinc, calcium, and silicon is realized through the combination of extraction method and ion exchange method, and a battery-grade cobalt sulfate solution and a refined magnesium sulfate solution are obtained. The battery-grade cobalt sulfate solution can be directly used in the synthesis of a ternary precursor, and the recovery rates of cobalt and magnesium can reach 99%. According to the method, no dangerous chemicals are introduced and no hazardous wastes are produced; and the method has the advantages of high extraction efficiency, large separation coefficient, short technological process, low cost, less investment in equipment, high metal recovery rate, and good solution quality, realizing the efficient recovery of cobalt and the resources utilization of magnesium. The above are merely preferred embodiments of the present disclosure, and is not intended to limit the present disclosure. Various modifications and changes may be made to the present disclosure. Any modifications, equivalent replacements, improvements, etc., made without departing from the scope and the principles of the present disclosure shall fall within the scope of protection of the present disclosure. A separation reagent for separating cobalt from iron, zinc, calcium, silicon and magnesium, comprising an extracting agent and a co-extracting agent; wherein the extracting agent comprises BC196, and the co-extracting agent comprises Mextral 6103H. The separation reagent of claim 1, wherein a volume percentage of the BC196 in the separation reagent is 5-15%, and/or, a volume percentage of the Mextral 6103H in the separation reagent is 5-8%. The separation reagent of claim 2, wherein the separation reagent further comprises a diluent; and a volume percentage of the diluent in the separation reagent is a balance after subtracting the volume percentages of the extracting agent and the co-extracting agent; and the diluent comprises at least one of kerosene, sulfonated kerosene, Escaid 110, heptane, hexane, dodecane, or sec-octanol. Use of the separation reagent of any one of claims 1 to 3 in separating cobalt from iron, zinc, calcium, silicon and magnesium. A method for resource utilization of a magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon, comprising a following step: extracting the magnesium sulfate solution containing cobalt, iron, zinc, calcium and silicon with the separation reagent of any one of claims 1 to 3, to obtain a loaded organic phase and a raffinate water phase; wherein a volume ratio of the separation reagent to the magnesium sulfate solution containing cobalt, iron, zinc, calcium, and silicon is 1:0.5 to1:20; the extracting comprises a single-stage extraction or a multi-stage counter-current extraction; and a pH value of the raffinate water phase is 4.5-5. The method for resource utilization of the magnesium sulfate solution of claim 5, further comprising subjecting the separation reagent to a saponification treatment prior to the step of extracting; wherein a saponifying agent used for the saponification treatment is an alkaline solution; the alkaline solution comprises at least one of a sodium hydroxide solution, ammonia water, a potassium hydroxide solution, or a magnesium hydroxide solution; the alkaline solution has a concentration of 5-10 mol/L; and a degree of saponification after the saponification treatment is greater than 0 but not greater than 50%. The method for resource utilization of the magnesium sulfate solution of claim 5 or 6, further comprising carrying out a reverse extraction on the loaded organic phase with a reverse extracting agent to obtain a battery-grade cobalt sulfate solution; wherein the reverse extracting agent comprises at least one of a sulfuric acid solution, or a hydrochloric acid solution; a concentration of H + in the reverse extracting agent is 3-5 mol/L; a number of stages of the reverse extraction is 1-5. The method for resource utilization of the magnesium sulfate solution of claim 7, further comprising washing the loaded organic phase with a washing liquid prior to the reverse extraction; wherein the washing liquid used for washing comprises at least one of water, a sulfuric acid solution, a hydrochloric acid solution, a phosphoric acid solution, or an oxalic acid solution; a concentration of H + in the washing liquid is not greater than 1 mol/L; a volume ratio of the washing liquid to the loaded organic phase is 0.05:1 to 0.5:1; the washing is multi-stage counter-current washing; a volume ratio of the reverse extracting agent to the loaded organic phase after washing is 0.05:1to 0.5:1. The method for resource utilization of the magnesium sulfate solution of claim 5 or 6, further comprising performing ion adsorption on the raffinate water phase to obtain a refined magnesium sulfate solution. The method for resource utilization of the magnesium sulfate solution of claim 9, wherein an ion exchange resin used for the ion adsorption is a sodium- type resin; and the sodium-type resin comprises at least one of D467, SepliteD001, LSC850, or D503.