A method for separating and purifying nickel sulfate and lithium sulfate

Abstract

The present invention discloses a separation and purification method of nickel sulfate and lithium sulfate, and belongs to the technical field of resource recovery. The separation and purification method provided by the present invention comprises the following steps: S1. Evaporating and concentrating the stock solution including nickel sulfate and lithium sulfate, and then cooling and crystallizing the obtained concentrated solution to obtain a crude nickel sulfate product and a first crystallization mother liquor; the end point of evaporation and concentration is the first one of the following two standards: (1) critical precipitation of crystals; (2) at the temperature of cooling and crystallization, the difference between the saturation concentration of lithium sulfate and the concentration of lithium sulfate in the concentrated solution is between 1 and 2.5 g / L; S2. Concentrating and crystallizing the first crystallization mother liquor to obtain a second crystallization mother liquor and a crude lithium sulfate product; the temperature of concentrated crystallization is ≥90°C; the second crystallization mother liquor returns to step S1 and is mixed with the concentrated solution. The separation and purification method provided by the present invention has many advantages such as low cost, short process, high recovery rate of target elements, and high purity of target products.

Description

Technical Field

[0001] The invention relates to the technical field of resource recovery, and in particular to a method for separating and purifying nickel sulfate and lithium sulfate. Background Art

[0002] In the circular economy, battery waste is a valuable resource that can be recycled. Its main valuable elements are cobalt, nickel, manganese and lithium. In traditional technology, there are three main methods for treating waste battery waste: wet method, pyrolysis and direct recycling. Among them, recycling is mainly for battery waste with complete structure, which is relatively limited; pyrolysis requires a large amount of reducing agent and high temperature, which has high energy consumption and cost consumption. Therefore, the industry usually adopts wet method to recycle battery waste.

[0003] In traditional technology, the steps of wet recovery include leaching to obtain mixed metal ion solution, extraction to separate metal ions, and subsequent precipitation to obtain corresponding products. However, this method requires more extractants and bulky extraction equipment; the overall cost is also high.

[0004] In addition, both the wet method and the pyrometallurgical method have technical problems such as poor recovery rate of lithium and nickel, low efficiency of separation from each other and high cost. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a separation and purification method of nickel sulfate and lithium sulfate, which can effectively reduce the cost of hydrometallurgy of battery waste, reduce the site area requirement, and improve the recovery efficiency of lithium and nickel, as well as the purity of the obtained lithium sulfate and nickel sulfate.

[0006] According to an embodiment of the first aspect of the present invention, a method for separating and purifying nickel sulfate and lithium sulfate is provided, wherein the stock solution used in the separation and purification method includes nickel sulfate and lithium sulfate; the separation and purification method comprises the following steps:

[0007] S1. The stock solution is evaporated and concentrated to obtain a concentrated solution, and then the concentrated solution is cooled and crystallized to obtain a crude nickel sulfate product and a first crystallization mother liquor; the endpoint of the evaporation and concentration is the first one of the following two criteria:

[0008] (1) Critical crystal precipitation;

[0009] (2) at the cooling crystallization temperature, the difference between the saturated concentration of lithium in the system and the concentration of lithium in the concentrated solution is between 1 and 2.5 g / L;

[0010] S2. Concentrate and crystallize the first crystallization mother liquor to obtain a second crystallization mother liquor and a crude lithium sulfate product; the temperature of the concentrated crystallization is ≥90°C;

[0011] The second crystallization mother liquor is returned to step S1 and mixed with the concentrated liquor.

[0012] The mechanism of the separation and purification method is as follows:

[0013] The solubility of nickel sulfate in water increases with increasing temperature, while the solubility of lithium sulfate decreases with increasing temperature. Therefore, after evaporation and concentration in step S1 until critical precipitation of lithium sulfate, during cooling and crystallization, lithium sulfate is undersaturated in the concentrated solution and will not precipitate. At the same time, the solubility of nickel sulfate decreases and it will precipitate from the system, thereby obtaining a crude nickel sulfate product.

[0014] In the first crystallization mother liquor obtained, the concentration of nickel sulfate is far from saturated, while the concentration of lithium sulfate is close to or has been saturated. Therefore, after further concentration, lithium sulfate will be supersaturated and precipitated.

[0015] The separation and purification method according to the embodiment of the present invention has at least the following beneficial effects:

[0016] The present invention utilizes the difference in solubility of nickel sulfate and lithium sulfate in water, and selects two-step crystallization to separate and detach them from the stock solution. Compared with the traditional wet method of extraction (extraction to achieve nickel-lithium separation) or precipitation (nickel precipitation to achieve nickel-lithium separation), the cost of extraction, the cost of the site required for multi-stage extraction and / or the cost of the precipitant are saved, and both evaporation concentration and evaporation crystallization are for the stock solution, and no other liquid is added during the process, so the cost of the evaporation process is also low. That is, the present invention significantly saves costs and sites through the adjustment of the separation and purification method, and is more convenient for industrial implementation. Specifically, a simple calculation shows that when the raw materials used are the same and the same amount of lithium is obtained, the separation and purification method provided by the present invention can save more than 80% of the cost compared with the traditional full extraction wet method, and saves more than 81% of the cost compared with the precipitation wet method.

[0017] In the separation and purification method provided by the present invention, the second crystallization mother liquor is returned and mixed with the concentrated solution, that is to say, except for the water vapor evaporated by evaporation concentration and evaporation crystallization, as well as the crude nickel sulfate and the crude lithium sulfate, no substance is discharged from the separation and purification system as a whole. After multiple cycles of crystallization, the yields of lithium and nickel in the stock solution are ≥99%, for example, up to 99.5%. In comparison, in the wet process including the extraction step, the yields of lithium and nickel are generally ≤99%, and the lower limit is uncertain. That is, the separation and purification method provided by the present invention significantly improves the recovery rate of lithium and nickel through the design of the process.

[0018] In the separation and purification method provided by the present invention, since in actual production, the system of the stock solution, and the temperature difference of the heating concentration and the cooling crystallization may be different, the above two standards are set, and whichever is reached first shall prevail. The setting of the end point of evaporation and concentration in step S1 will reduce the amount of lithium entrained in the obtained nickel sulfate crude product to a certain extent, that is, improve the purity of its nickel sulfate, and simultaneously improve the yield of nickel sulfate and lithium sulfate; specifically, during the cooling crystallization process, nickel sulfate will be separated in the form of hydrated nickel sulfate, that is, it will take away a certain amount of water. If the evaporation and concentration cause the lithium sulfate to be supersaturated, the lithium sulfate will also be precipitated in small amounts during the cooling crystallization process. In step S2, the temperature of concentrated crystallization will also significantly affect the difference in solubility between nickel sulfate and lithium sulfate, thereby affecting the amount of lithium sulfate precipitated and the nickel content entrained in lithium sulfate. On the whole, the present invention significantly improves the recovery rate of lithium and nickel, as well as the purity of the obtained lithium sulfate and nickel sulfate through parameter limitation.

[0019] The separation and purification method provided by the present invention generates distilled water as waste water, which can be directly reused in industry and does not generate waste gas; that is, it is more environmentally friendly and safe.

[0020] According to some embodiments of the present invention, in step S1, during the evaporation and concentration process, the lithium sulfate first reaches a saturated concentration. By limiting the concentration ratio of lithium sulfate to nickel sulfate in the stock solution, the entrainment of lithium sulfate by the crude nickel sulfate obtained by cooling crystallization can be avoided, and the purity of the obtained nickel sulfate can be significantly improved.

[0021] According to some embodiments of the present invention, in step S1, the stock solution comes from the leachate of battery waste. Specifically, the battery waste includes positive electrode materials of lithium-ion batteries. Therefore, among the battery waste, the waste with the highest nickel content is lithium nickelate (LiNiO2), and other types of battery materials, such as NCM523, have a nickel-to-lithium ratio lower than that of lithium nickelate; therefore, the mass concentration ratio of lithium and nickel after leaching of lithium nickelate is about 7:59 (molar ratio is about 1:1). Taking the evaporation and concentration temperature of 100°C in step S1 as an example, lithium sulfate still reaches the saturation concentration first. In other words, the stock solution derived from the leachate of battery waste does not need to adjust the concentrations of nickel sulfate and lithium sulfate, and can adapt to the separation and purification method provided by the present invention.

[0022] According to some embodiments of the present invention, the pH of the stock solution is 1-7.

[0023] According to some embodiments of the present invention, in step S1, the concentration of lithium in the stock solution is 5 to 20 g / L, for example, about 8 g / L, 10 g / L, 15 g / L or about 18 g / L.

[0024] According to some embodiments of the present invention, in step S1, the concentration of nickel in the stock solution is 90-100 g / L, for example, about 92 g / L, 93 g / L, 95 g / L, 97 g / L or about 98 g / L.

[0025] According to some embodiments of the present invention, in step S1, the concentration of sodium ions and / or potassium ions in the stock solution is ≤10 g / L, thereby preventing the sodium and potassium ions from having a significant effect on the solubility of lithium and nickel.

[0026] According to some embodiments of the present invention, in step S1, the total concentration of metal impurities in the stock solution is allowed to be ≤0.005 g / L. The metal impurities allowed here are metal ions other than sodium, potassium, lithium and nickel. This can further avoid the entrainment of metal impurities by the obtained lithium sulfate and nickel sulfate. If the purity of the stock solution cannot reach the above index, the stock solution needs to be impurity-removed before the separation and purification method is performed.

[0027] According to some embodiments of the present invention, in step S1, in the system of the stock solution at 100° C., the saturated concentration of lithium is 21 g / L; and / or the saturated concentration of nickel is 220 g / L.

[0028] According to some embodiments of the present invention, in step S1, in the system of the stock solution at 80° C., the saturated concentration of lithium is 21.5 g / L; and / or, the saturated concentration of nickel is 170 g / L.

[0029] According to some embodiments of the present invention, in step S1, in the system of the stock solution at 60° C., the saturated concentration of lithium is 22 g / L; and / or the saturated concentration of nickel is 150 g / L.

[0030] According to some embodiments of the present invention, in step S1, in the system of the stock solution at 35° C., the saturated concentration of lithium is 22.5 g / L; and / or the saturated concentration of nickel is 120 g / L.

[0031] According to some embodiments of the present invention, in step S1, the temperature of the evaporation concentration is ≥ 90° C. For example, it may be about 100° C. This can increase the rate of the evaporation concentration.

[0032] According to some embodiments of the present invention, in step S1, the concentration of lithium in the concentrated solution is 18-19 g / L. Thus, when the cooling crystallization temperature is about 35°C, the difference between the saturated concentration of lithium sulfate and the concentration of lithium sulfate in the concentrated solution is 1-2 g / L, which can significantly improve the yield and purity of the crude nickel sulfate.

[0033] Furthermore, if the lithium concentration in the second crystallization mother liquor is higher than the above range, it may be necessary to add the stock solution or water to adjust the concentration.

[0034] According to some embodiments of the present invention, in step S1, the nickel content in the concentrated solution is between 120 and 190 g / L, which is just lower than the saturation concentration at the temperature corresponding to the evaporation concentration and higher than the saturation concentration at the temperature corresponding to the cooling crystallization, thereby ensuring smooth precipitation in the cooling crystallization step and avoiding affecting the determination of the heating concentration endpoint.

[0035] According to some embodiments of the present invention, in step S1, the temperature of the cooling crystallization is ≤40°C.

[0036] According to some embodiments of the present invention, in step S1, the temperature of the cooling crystallization is 32 to 40°C (including endpoint values). For example, it can be about 35°C. Within this temperature range, the product obtained by cooling crystallization is nickel sulfate hexahydrate. The temperature of the cooling crystallization has little effect on the purity of the obtained crude nickel sulfate, but it will affect the yield of the crude nickel sulfate. Specifically, the lower the temperature, the lower the solubility of nickel sulfate, and more nickel can be precipitated; thereby reducing the nickel content in the first crystallization mother liquor, so that in the concentrated crystallization in the subsequent step S2, more lithium can be precipitated, or the nickel content in lithium sulfate can be reduced when the precipitated lithium is the same.

[0037] According to some embodiments of the present invention, in step S1, the cooling crystallization temperature is 0 to 32° C. (excluding the upper endpoint value). The trend within this temperature range is equivalent to the trend at 32 to 40° C., except that the main product precipitated within this temperature range is nickel sulfate heptahydrate.

[0038] According to some embodiments of the present invention, in step S1, the cooling crystallization includes sequentially performing cooling and solid-liquid separation while cold.

[0039] According to some embodiments of the present invention, in step S1, the concentration of lithium in the first crystallization mother liquor is affected by the concentration of lithium in the concentrated solution, and is slightly higher than the concentration of the concentrated solution, for example, it can be 20 to 21 g / L; the concentration of nickel is affected by the cooling crystallization temperature, for example, it can be 120 to 130 g / L.

[0040] According to some embodiments of the present invention, in step S1, the concentration of nickel in the first crystallization mother solution is the saturated concentration of nickel at the temperature corresponding to the cooling crystallization, for example, specifically about 120 g / L.

[0041] According to some embodiments of the present invention, the separation and purification method further comprises purifying the crude nickel sulfate.

[0042] According to some embodiments of the present invention, the purification of the crude nickel sulfate includes recrystallization to obtain purified nickel sulfate and recrystallization mother liquor.

[0043] According to some embodiments of the present invention, the recrystallization comprises dissolving the crude nickel sulfate in a solvent and then cooling the solution.

[0044] in,

[0045] The solvent of choice includes water.

[0046] The mass ratio of the crude nickel sulfate to the solvent is 1:2-3. For example, it can be about 1:2.3, 1:2.4, 1:2.5 or about 1:2.7.

[0047] The dissolving temperature is 95-100° C., for example, specifically about 98° C.

[0048] The cooling temperature is 32-35° C. For example, it can be about 33° C. or about 34° C. Within this temperature, it can be ensured that the crystallized product is purified nickel sulfate hexahydrate.

[0049] According to some embodiments of the present invention, during the recrystallization, the precipitation rate of the impurity lithium is ≥ 90%, for example, about 92%, 93%, 95%, 96%, 97% or about 98%.

[0050] According to some embodiments of the present invention, the recrystallization mother liquor is returned to step S1 and mixed with the raw liquor.

[0051] According to some embodiments of the present invention, in step S2, the temperature of the concentrated crystallization is 95-100° C. This can significantly increase the evaporation rate during the evaporative crystallization process and improve the purity of the obtained crude lithium sulfate (reduce nickel entrainment therein).

[0052] According to some embodiments of the present invention, in step S2, the concentrated crystallization includes heating concentration and hot solid-liquid separation in sequence. The concentration of nickel in the concentrated liquid obtained by the heating concentration is between 120 and 190 g / L; for example, it can be about 150 g / L or about 180 g / L. That is, it is lower than the saturation concentration at the corresponding temperature of the concentrated crystallization, so that in the hot solid-liquid separation process, the lithium sulfate produced will not carry a large amount of nickel; the concentration exceeding 120 g / L indicates that the first crystallization mother liquor has been concentrated, which can increase the amount of lithium precipitation in the concentrated crystallization process.

[0053] According to some embodiments of the present invention, the separation and purification method further comprises purifying the crude lithium sulfate.

[0054] According to some embodiments of the present invention, the purification of the crude lithium sulfate includes hot water washing to obtain purified lithium sulfate and a washing mother liquor. The temperature of the hot water used for the hot water washing is 90 to 100° C. The end point of the hot water washing is when the conductivity of the washing mother liquor is ≤10 μs / m 2 .

[0055] According to some embodiments of the present invention, the hot water washing has a nickel removal efficiency of ≥ 97% in the crude lithium sulfate product.

[0056] According to some embodiments of the present invention, the washing mother liquor is returned to step S1 and mixed with the raw liquor.

[0057] According to some embodiments of the present invention, in the separation and purification method, the recovery rate of nickel is ≥ 99%, for example, about 99.5%, 99.8% or about 110%.

[0058] According to some embodiments of the present invention, in the separation and purification method, the grade of the purified nickel sulfate obtained reaches battery grade.

[0059] According to some embodiments of the present invention, in the separation and purification method, the lithium recovery efficiency is ≥ 99%, for example, about 99.5%, 99.8% or about 100%.

[0060] According to some embodiments of the present invention, in the separation and purification method, the purified lithium sulfate crystals obtained can be used to produce battery-grade lithium carbonate.

[0061] If there is no special explanation, the actual meaning of “about” in the present invention is that the error is allowed to be within the range of ±2%, for example, about 100 is actually 100±2%×100.

[0062] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0063] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0065] Figure 1 It is a schematic diagram of the process of Example 1 of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0067] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0068] Example 1

[0069] refer to Figure 1 This example provides a method for separating and purifying nickel sulfate and lithium sulfate, and the specific steps are as follows:

[0070] S1. Evaporate and concentrate the stock solution at about 100°C to obtain a concentrated solution, and then cool and crystallize the obtained concentrated solution (including sequential cooling and solid-liquid separation while cold) to obtain crude nickel sulfate and the first crystallization mother liquor; and recrystallize the crude nickel sulfate to obtain purified nickel sulfate and recrystallization mother liquor; the recrystallization step is to dissolve the crude nickel sulfate and water at a mass ratio of 1:2.4 at 100°C, and then cool and crystallize in the range of 32-33°C, and the crystallized product is purified nickel sulfate (actually nickel sulfate hexahydrate). The steps of returning the recrystallization mother liquor for circulation and circulating the stock solution are followed by evaporation and concentration; wherein,

[0071] In the stock solution, the nickel concentration is 92.5g / L and the lithium concentration is 10g / L. The stock solution in this example is obtained by leaching, extraction, separation and purification of waste battery ternary materials. The total content of sodium and potassium is less than 10g / L; except for sodium, potassium, lithium and nickel, other metal impurities are less than 0.005g / L.

[0072] In the concentrated solution, the lithium concentration is 20.54 g / L and the nickel concentration is 190 g / L. Among them, 20.54 g / L is the critical point of evaporation concentration, that is, the saturated concentration of lithium in the system is 22.5 g / L at 35°C; 22.5-20.5=2 g / L; this critical point is earlier than the critical precipitation of crystals.

[0073] The cooling crystallization temperature is 35°C;

[0074] The first crystallization mother liquor has a lithium content of 22.5 g / L and a nickel content of 120 g / L; the concentrations of nickel sulfate and lithium sulfate are approximately the saturation concentrations at the temperature, and lithium is enriched compared to the original liquor.

[0075] In this step, the process parameters of nickel sulfate recrystallization are shown in Table 1.

[0076] S2. At 100° C., the solubility of nickel sulfate increases, while the solubility of lithium sulfate remains substantially unchanged. Therefore, the crystallization mother liquor obtained in step S1 is concentrated and crystallized at 100° C. (including heating concentration and hot solid-liquid separation in sequence) to obtain a crude lithium sulfate product and a second crystallization mother liquor; the second crystallization mother liquor is mixed with the stock solution (or pure water) to reduce the lithium concentration to 18-19 g / L, and then returned to step S1 for cooling and crystallization to separate nickel sulfate; the crude lithium sulfate is washed with 100° C. hot water to obtain purified lithium sulfate and a water-washing mother liquor; the end point of the hot water washing is that the conductivity of the water-washing mother liquor is ≤10 μs / m 2 The mother solution of water washing is returned for circulation and the original solution of step S1 is circulated before evaporation and concentration. The parameters of hot water washing are shown in Table 2.

[0077] The endpoint of evaporation crystallization is that the concentration of nickel sulfate is 190g / L; at the same time, lithium is supersaturated with a concentration of 35.6g / L;

[0078] In the second crystallization mother liquor, the lithium content is 21g / L and the nickel content is slightly greater than 190g / L (since lithium sulfate crystals take away water, but the amount taken away is small, the nickel concentration will not change significantly);

[0079] Repeat steps S1 to S2 until the nickel and lithium in the stock solution are completely crystallized and precipitated. Use ICP-OES to test the composition of the purified nickel sulfate and lithium sulfate to obtain the purity. Calculate the ratio of lithium content in the purified lithium sulfate to lithium content in the stock solution to obtain the lithium yield; calculate the ratio of nickel content in the purified nickel sulfate to nickel content in the stock solution to obtain the nickel yield. The results are shown in Table 3.

[0080] Example 2

[0081] This example provides a method for separating and purifying nickel sulfate and lithium sulfate, which is different from Example 1 in that:

[0082] The concentrations of lithium and nickel in the original solution are slightly different. Correspondingly, the concentrations of lithium and nickel in the obtained concentrated solution and the subsequent mother solution are slightly different.

[0083] Furthermore, considering the difference in lithium nickel concentration in the stock solution, there may be no precipitation of nickel sulfate (or a very small amount of precipitation) in step S1 of the first cycle, and the next step can be continued.

[0084] The results are shown in Tables 1 and 3.

[0085] Example 3

[0086] This example provides a method for separating and purifying nickel sulfate and lithium sulfate, which is different from Example 1 in that:

[0087] The concentrations of lithium and nickel in the original solution are slightly different. Correspondingly, the concentrations of lithium and nickel in the obtained concentrated solution and the subsequent mother solution are slightly different.

[0088] The results are shown in Tables 1 and 3.

[0089] Table 1 Recrystallization process parameters of crude nickel sulfate

[0090]

[0091] Table 2 Hot water washing parameters of crude lithium sulfate

[0092]

[0093]

[0094] Table 3 Partial results in Example 1

[0095]

[0096] If there is no special explanation, in the present invention, the calculation method of recovery rate is as follows:

[0097] In Example 1, the yield of lithium = (1-(quality of nickel sulfate hexahydrate crystal product × 0.005%) / (volume of stock solution * 10.04)) * 100% = 99.79%%;

[0098] The yield of nickel = (1-(mass of lithium sulfate crystal product × 0.005%) / (volume of original solution * 92.5)) * 100% = 99.94%.

[0099] Example 4

[0100] This example provides a method for separating and purifying nickel sulfate and lithium sulfate, which is different from Example 1 in that:

[0101] In step S1, the temperature of cooling crystallization is 60°C.

[0102] This temperature has no significant effect on the purity of the obtained nickel sulfate and lithium sulfate, and the overall yield, but compared with Example 1, it significantly reduces the yield of nickel sulfate in the single cooling crystallization step, which in turn increases the number of cycles of step S1 and step S2, increasing the time cost and economic cost. The specific comparison is shown in Table 4.

[0103] Table 4 Comparison of some parameters and results of the cooling crystallization method in step S1 of Example 1 and Example 4

[0104] Example 1 Example 4 Cooling crystallization temperature ℃ 35 60 Cooling crystallization temperature corresponds to nickel and lithium saturation concentration Li=22.5g / L、Ni=120g / L Li=22g / L、Ni=150g / L Nickel and lithium concentration in concentrate Li=20.5g / L、Ni=190g / L Li=20.5g / L、Ni=190g / L Volume before crystallization Measured by 1L Measured by 1L Volume after crystallization 0.86L 0.92L The amount of crystallization corresponding to different temperatures g 320 181 Lithium nickel content in nickel sulfate crystals Li: 0.005%, Ni: 22% Li: 0.005%, Ni: 22%

[0105] It should be noted that in the present invention, the yield of lithium and nickel is the overall calculation result after all the stock solution is consumed, or all the lithium and nickel in the stock solution are consumed. Table 4 is only the result of a single step and the yield cannot be calculated based on this. Other similar situations refer to the explanation here.

[0106] Example 5

[0107] This example provides a method for separating and purifying nickel sulfate and lithium sulfate, which is different from Example 1 in that:

[0108] The concentration of the first crystallization mother liquor was adjusted. The specific concentration is shown in Table 5. The subsequent parameter changes caused by the concentration are also listed in Table 5.

[0109] The results show that the change in the lithium-nickel concentration ratio in the first crystallization mother liquor will not affect the purity of the obtained lithium sulfate, nor will it affect the final recovery rate of lithium sulfate and nickel sulfate; but it will affect the yield of lithium sulfate in step S2 to a certain extent, which is equivalent to increasing the number of cycles of the separation and purification method and increasing the operating cost of the separation and purification method within a certain range.

[0110] Table 5 Comparison of the first crystallization mother solution used in step S2 of Example 1 and Example 5 and subsequent parameters

[0111] Example 1 Example 5 Lithium and nickel concentration in the first crystallization mother liquor (25℃) Li=22.5g / L、Ni=120g / L Li=12g / L、Ni=120g / L Solubility of lithium and nickel at 100℃ Li=21g / L、Ni=220g / L Li=21g / L、Ni=220g / L Volume of the first crystallization mother liquor 1L 1L Volume of concentrated liquid after evaporation and crystallization 0.63L 0.63L Lithium and nickel concentration after concentration (unfiltered) Li=35.6g / L、Ni=190g / L Li=19g / L、Ni=190g / L The amount of crystals precipitated from the concentrated liquid g 70 0.2 Lithium nickel content in lithium sulfate crystals Li: 10.7%, Ni: 0.005% Li: 10.7%, Ni: 0.005% The proportion of lithium and nickel in lithium sulfate crystals 1:0.0005 1:0.0005 Lithium-nickel separation factor <![CDATA[β Li / Ni =1900]]> <![CDATA[β Li / Ni =1]]>

[0112] Comparative Example 1

[0113] This example provides a method for separating and purifying nickel sulfate and lithium sulfate, which is different from Example 1 in that:

[0114] In step S2, the temperature of the concentrated crystallization is 80°C, not 100°C.

[0115] At the same time, the above-mentioned concentration crystallization temperature has an impact on the subsequent recovery of lithium sulfate, etc., and the changes in the parameters are shown in Table 6.

[0116] Table 6 Differences caused by concentration crystallization temperature in step S2

[0117]

[0118]

[0119] According to the above comparison, the temperature of concentrated crystallization will significantly affect the purity of the obtained lithium sulfate and reduce the lithium-nickel distribution coefficient. The reason is that at a lower concentrated crystallization temperature, the solubility of nickel sulfate is not high enough to be far from the saturated concentration of nickel at that temperature. Therefore, the precipitated crystals contain not only lithium sulfate but also nickel sulfate.

[0120] Comparative Example 2

[0121] This example provides a method for separating and purifying lithium sulfate and nickel sulfate, which is different from Example 1 in that:

[0122] In step S1, the concentration ratio of lithium to nickel in the stock solution is adjusted, and the critical point of lithium concentration (reached first) during the evaporation concentration process is ignored, and the critical precipitation of crystals reached later is taken as the end point of evaporation concentration.

[0123] The specific conditions of the concentrated liquid and the corresponding parameter changes are shown in Table 7.

[0124] Table 7 Effect of concentrate composition on purification and separation process

[0125] Example 1 Comparative Example 2 Lithium and nickel concentration in concentrate (100℃) Li=20.5g / L、Ni=190g / L Li=22g / L、Ni=190g / L Solubility of lithium and nickel at 35℃ Li=22.5g / L、Ni=120g / L Li=22.5g / L、Ni=120g / L Volume before cooling crystallization 1L 1L Volume after cooling and crystallization 0.86L 0.82L Cooling crystallization precipitation amount g 320 370 Lithium nickel content in nickel sulfate crystals Li: 0.005%, Ni: 22% Li: 0.1%, Ni: 21.5% The proportion of lithium nickel in nickel sulfate crystals 1：4400 1：215

[0126] According to the above comparison, when nickel sulfate crystallizes, nickel sulfate will form crystalline hydrates to take away part of the water. Therefore, the lithium concentration cannot be too close to the saturation concentration, otherwise the process of water loss will lead to supersaturation of lithium, which will then precipitate with the precipitation of nickel sulfate, resulting in a decrease in lithium yield and a decrease in the purity of the obtained nickel sulfate.

[0127] Test Case

[0128] In the first aspect of this example, the cost and yield of lithium extraction by carbon reduction (pyrometallurgy), full extraction (full extraction wet method, nickel-lithium extraction and separation), crystallization (precipitation wet method, nickel precipitation to achieve nickel-lithium separation, and then crystallization to obtain lithium) and the method provided by the present invention are calculated. The specific comparison is shown in Table 8. The specific calculation process is calculated based on the use of the same ternary battery waste as raw material and the same mass of lithium.

[0129] Table 8 Comparison of parameter calculation results of several lithium extraction methods

[0130]

[0131] In Table 8, the carbon reduction lithium extraction process needs to be first carbon reduction roasting, and the roasting product still needs to be wet leached and recovered; the second wet stage can use full extraction lithium extraction, crystallization lithium extraction and new methods to extract lithium. Therefore, in the cost column, the pyrolysis method increases, indicating that the pyrolysis roasting process has increased costs compared with other technical solutions; the wet method remains unchanged, which means that the cost of the wet stage of carbon reduction lithium extraction is equivalent to the corresponding other wet methods of lithium extraction.

[0132] Specifically, the process cost accounting of using crystallization lithium extraction and the separation and purification method of the present invention is shown in Tables 9 to 10.

[0133] Table 9 Process cost accounting of crystallization lithium extraction

[0134]

[0135]

[0136] Table 10 Specific cost accounting of the separation and purification process of the present invention

[0137] Process comparison New Technology Original raw material ingredients Li=10g / L、Ni=100g / L Li-Ni ratio before evaporation 1：10 Price per cubic meter of water evaporated / yuan 100 <![CDATA[Water carried away by nickel sulfate crystallization / m 3 > 14 <![CDATA[Water volume carried away by lithium sulfate crystallization / m 3 > 1 Amount of water evaporated per ton of lithium metal separation / t 80 Cost per ton of lithium metal consumption / t 8000 NTD

[0138] According to the above comparison, the separation and purification method provided by the present invention does not require pyrometallurgical costs, nickel precipitation costs, or frozen crystallization costs (the cooling crystallization temperature is near room temperature); it only requires the cost of evaporation and concentration, and the cost is relatively low. At the same time, in the process, no extraction, nickel precipitation, or frozen crystallization of nickel sulfate for sodium removal is required, which significantly saves the process. Most importantly, the separation and purification method provided by the present invention has a high recovery rate of lithium and nickel, and can be directly achieved to battery-grade purity, with a high purity.

[0139] In the second aspect of this example, the composition of lithium sulfate and nickel sulfate obtained in Example 1 was tested. Specifically, the results obtained in Example 1 were similar. For example, Tables 11 to 12 provide the composition of lithium sulfate and nickel sulfate obtained in Example 1.

[0140] Table 11 Composition of nickel sulfate hexahydrate obtained in Example 1

[0141]

[0142]

[0143] Table 12 Composition of hydrated lithium sulfate obtained in Example 1

[0144]

[0145] According to the above results, the purity of the lithium sulfate and nickel sulfate obtained by the present invention exceeds 99%, and the corresponding lithium nickel content and impurity content have exceeded the industrial requirements for battery-grade lithium sulfate and nickel sulfate.

[0146] In summary, the separation and purification method provided by the present invention not only has the advantages of simple steps, cost saving, environmental protection and high efficiency, but also has many advantages such as high lithium nickel recovery rate and high cost of obtained lithium sulfate and nickel sulfate. It is expected to be widely used in the fields of secondary battery waste recovery and mining and metallurgy.

[0147] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for separating and purifying nickel sulfate and lithium sulfate, characterized in that: The separation and purification method comprises the following steps: S1. The raw solution including nickel sulfate and lithium sulfate is evaporated and concentrated to obtain a concentrated solution, and then the concentrated solution is cooled and crystallized to obtain a crude nickel sulfate product and a first crystallization mother liquor; the endpoint of the evaporation and concentration is the first one of the following two standards: (1) Critical crystal precipitation; (2) at the cooling crystallization temperature, the difference between the saturated concentration of lithium in the system and the concentration of lithium in the concentrated solution is between 1 and 2.5 g / L; S2. Concentrate and crystallize the first crystallization mother liquor to obtain a second crystallization mother liquor and a crude lithium sulfate product; the temperature of the concentrated crystallization is ≥90°C; The second crystallization mother liquor is returned to step S1 and mixed with the concentrated liquor.

2. The separation and purification method according to claim 1, characterized in that: The separation and purification method also includes purifying the crude nickel sulfate.

3. The separation and purification method according to claim 2, characterized in that: The purification of the crude nickel sulfate includes recrystallization to obtain purified nickel sulfate and a recrystallization mother liquor; and / or the recrystallization mother liquor is returned to step S1 and mixed with the original liquor.

4. The separation and purification method according to claim 1, characterized in that: The separation and purification method also includes purifying the crude lithium sulfate product.

5. The separation and purification method according to claim 4, characterized in that: The purification of the crude lithium sulfate includes washing with hot water to obtain purified lithium sulfate and a washing mother liquor; and / or the washing mother liquor is returned to step S1 and mixed with the original liquor.

6. The separation and purification method according to any one of claims 1 to 5, characterized in that: In step S1, the temperature of the cooling crystallization is ≤40°C.

7. The separation and purification method according to any one of claims 1 to 5, characterized in that: In step S1, the temperature of the evaporation and concentration is ≥90°C.

8. The separation and purification method according to any one of claims 1 to 5, characterized in that: In step S1, the stock solution is a leaching solution of a positive electrode material of a lithium-ion battery.

9. The separation and purification method according to any one of claims 1 to 5, characterized in that: In the separation and purification method, the recovery rate of nickel is ≥99%.

10. The separation and purification method according to any one of claims 1 to 5, characterized in that: In the separation and purification method, the lithium recovery efficiency is ≥99%.

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