Method for detecting purity of lithium salt

Abstract

The invention discloses a lithium salt purity detection method, which comprises the following steps: uniformly mixing a dried sample and oxalic acid, adding an organic solvent, and carrying out heating reaction to obtain a primary reactant; reacting the primary reactant with oxalic acid in the organic solvent for multiple times to obtain a reactant; dissolving reactants, adjusting the pH value to be greater than or equal to 7, carrying out suction filtration, adding a sodium phosphate solution into filtrate, then adding absolute ethyl alcohol, and continuously stirring to obtain reaction liquid; and carrying out suction filtration, washing and drying on the reaction liquid to constant weight, and calculating the purity of the sample. The method is wide in measuring range, and can be synchronously used for measuring the purity of lithium carbonate, lithium hydroxide and lithium chloride; according to the method, the required equipment is low in price, the operation is simple, and the requirement on personnel operation is relatively low; according to the method, the steps of measuring lithium carbonate, lithium hydroxide and lithium chloride are simplified, and the content of potassium, sodium, calcium and magnesium does not need to be deducted.

Description

Technical Field

[0001] The present invention relates to the field of compound detection, and in particular to a method for detecting the purity of a lithium salt. Background Art

[0002] Lithium carbonate, lithium hydroxide monohydrate, and lithium chloride raw materials play a vital role in positive electrode materials and additives, but the detection methods for the purity of such raw materials are always unsatisfactory. At present, the purity detection of lithium carbonate and lithium hydroxide mainly relies on acid-base titration; the purity detection of lithium chloride mainly relies on potentiometric titration. The national standard method GB / T11064-2013 "Chemical Analysis Methods for Lithium Carbonate, Lithium Hydroxide Monohydrate, and Lithium Chloride" discloses three parts of detection methods, as follows:

[0003] Part 1: Determination of lithium carbonate content - Acid-base titration method,

[0004] Part 2: Determination of lithium hydroxide content - Acid-base titration method,

[0005] Part 3: Determination of the amount of lithium chloride The potentiometric titration method specifies the specific operating details.

[0006] However, the prior art has the following shortcomings:

[0007] 1. If manual titration is used, the titration result will be affected by human sensory factors and the data reproducibility will be poor;

[0008] 2. Automatic titration by instrument can eliminate human interference, but the equipment is expensive;

[0009] 3. When the purity of lithium carbonate and lithium hydroxide is determined by acid-base titration, it is necessary to deduct potassium, sodium, calcium and magnesium to varying degrees to convert the corresponding lithium carbonate and lithium hydroxide content, and the operation is relatively inconvenient;

[0010] 4. When the purity of lithium chloride is determined by potentiometric titration, it is also necessary to deduct potassium, sodium, calcium and magnesium to varying degrees to convert the corresponding lithium chloride content.

[0011] In addition, the purity of lithium carbonate is calculated by measuring the lithium content in lithium carbonate by ICP, but this method is prone to introduce large dilution errors. The lithium carbonate is titrated with a standard sulfuric acid solution, and methyl orange is used as an indicator to calculate the lithium carbonate content by sulfuric acid consumption. This method has the same shortcomings as the hydrochloric acid titration of lithium carbonate. Summary of the invention

[0012] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for detecting the purity of lithium salts. When the method of the present invention is used to measure the purity of a product, the equipment required is low-cost and easily available. In addition, the purity is calculated by weighing, and no indicator is required for endpoint confirmation, and the result is not affected by sensory factors.

[0013] To achieve the above purpose, the present invention determines the purity of lithium salt by weight method, which is applicable to lithium salt types including but not limited to lithium carbonate, lithium hydroxide, and lithium chloride. The specific steps are as follows:

[0014] The present invention provides a method for detecting the purity of lithium salt, comprising the following steps:

[0015] 1) Mix the dried sample and oxalic acid evenly, add an organic solvent, and heat to react to obtain a primary reactant;

[0016] 2) mixing the primary reactant and oxalic acid uniformly, adding an organic solvent, heating and reacting to obtain a product; wherein the amounts of oxalic acid and organic solvent used in this step are the same as those used in step 1);

[0017] 3) Repeat step 2) 1 to 2 times with the product; after adding the organic solvent for the last time, heat and evaporate to near dryness to obtain the reactant;

[0018] 4) After the mixture is cooled slightly, ultrapure water is added to the reactant, and the mixture is heated and dissolved at high temperature to obtain a solution;

[0019] 5) adjusting the pH value of the solution to ≥7 while hot, then cooling to room temperature and filtering, collecting the liquid, and washing the container with ultrapure water for multiple times, and filtering the washing liquid simultaneously and adding it to the liquid to obtain a filtrate;

[0020] 6) adding sodium phosphate solution to the filtrate under stirring, and then adding anhydrous ethanol, and continuing to stir to obtain a reaction solution;

[0021] 7) Use filter paper with a mass of m0 that has been pre-treated with constant weight to filter the reaction solution, wash the precipitate on the filter paper with ethanol solution or ammonia water, further filter, and then transfer the filter paper with the precipitate to a weighing bottle with a mass of m1 that has been pre-treated with constant weight, dry to constant weight, and record the constant weight as m2;

[0022] 8) Calculate the purity of the sample according to the following formula:

[0023]

[0024] Where: ω is the purity percentage of the sample, %;

[0025] m is the mass of the dried sample, g;

[0026] m0 is the mass of the filter paper, g;

[0027] m1 is the mass of the weighing bottle, g;

[0028] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0029] When the sample is lithium carbonate, K = 0.95717;

[0030] Or, when the sample is lithium hydroxide, K = 0.62045;

[0031] Alternatively, when the sample is lithium chloride, K = 1.09824.

[0032] Furthermore, in the step 1), the mass ratio of the sample to oxalic acid is 1:2.5-5.0.

[0033] Furthermore, in step 1) and step 2), the organic solvent is one or more of methanol, ethanol and acetone; and the mass ratio of oxalic acid to the organic solvent is 1:4.0-8.0; the heating temperature is 80-100° C., and the heating time is 5-10 min.

[0034] Furthermore, in the step 3), the temperature of heating and evaporation is 110-130°C.

[0035] Furthermore, in the step 4), the mass ratio of the sample to ultrapure water is 1:10-20, and the high temperature heating temperature is 90-100°C.

[0036] Furthermore, in step 5), the pH regulator is any one of potassium hydroxide, sodium hydroxide and ammonia water.

[0037] Furthermore, the concentration of the solution prepared with sodium hydroxide is 0.1-0.2 mol / L.

[0038] Furthermore, in step 6), the mass ratio of sodium phosphate in the sodium phosphate solution to the sample is 4-10:1; and the concentration of the sodium phosphate solution is 100-200 g / L.

[0039] Furthermore, the volume ratio of anhydrous ethanol to the filtrate is 1:10-20.

[0040] Furthermore, in step 7), the volume fraction of the ethanol solution is 10%-20%, the mass fraction of the ammonia water is 30%, and the drying temperature is 105±5°C.

[0041] Beneficial effects of the present invention:

[0042] (1) The present invention has a wide determination range and can be used to simultaneously determine the purity of lithium carbonate, lithium hydroxide, and lithium chloride;

[0043] (2) The equipment required by the present invention is cheap, easy to operate, and has low requirements on personnel operation;

[0044] (3) The present invention simplifies the steps of determining lithium carbonate, lithium hydroxide, and lithium chloride, and there is no need to deduct the contents of potassium, sodium, calcium, and magnesium. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand.

[0046] Example 1

[0047] The method for detecting the purity of lithium chloride comprises the following steps:

[0048] (1) Weigh 2.0021 g of a dried lithium chloride sample and put it into a 100 mL polytetrafluoroethylene crucible; then weigh 5.0082 g of oxalic acid and put it into a 100 mL polytetrafluoroethylene crucible to mix with the sample, and add 25 g of methanol, adjust the temperature of the hot plate to 80° C., place it on the hot plate and heat it for 10 minutes to obtain a primary reactant;

[0049] (2) adding oxalic acid to a container to mix the primary reactant and oxalic acid evenly, then adding methanol, adjusting the temperature of the electric hot plate to 80° C., and heating on the electric hot plate for 10 minutes to obtain a product; wherein the amount of oxalic acid and the organic solvent used in this step is the same as that used in step (1);

[0050] (3) Repeat step (2) with the product until methanol is added, adjust the temperature of the hot plate to 110° C., place it on the hot plate and heat it until it is almost dry to obtain a reactant;

[0051] (4) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 25 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 90° C., and heat to dissolve to obtain a solution;

[0052] (5) while hot, adjust the pH value of the solution to 7 with 0.1 mol / L sodium hydroxide solution, remove and cool to room temperature, and then use a circulating water vacuum pump to filter, collect the liquid in a 250 mL conical flask, and wash the polytetrafluoroethylene crucible three times with 15 mL of ultrapure water, and filter the washing liquid simultaneously and add it to the liquid to obtain a filtrate;

[0053] (6) Add 50 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 5 min to obtain a reaction solution;

[0054] (7) Select filter paper with a mass m0 of 0.1099 g that has been pre-treated with constant weight, filter the reaction solution in step (6) using a circulating water vacuum pump, wash the precipitate on the filter paper with a volume fraction of 20% ethanol solution, further filter, and then transfer the filter paper with the precipitate to a weighing bottle with a mass m1 of 62.0793 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 63.9817 g;

[0055] (8) The purity calculation formula of lithium chloride is as follows:

[0056]

[0057] Where: ω------purity percentage of lithium chloride, %;

[0058] m------Weigh the mass of lithium chloride, g;

[0059] m0 is the mass of the filter paper, g;

[0060] m1 is the mass of the weighing bottle, g;

[0061] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0062] K=1.09824.

[0063] Example 2

[0064] The method for detecting the purity of lithium carbonate comprises the following steps:

[0065] (1) Weigh 2.0134 g of a dried lithium carbonate sample and put it into a 100 mL polytetrafluoroethylene crucible; then weigh 6.0378 g of oxalic acid and put it into a 100 mL polytetrafluoroethylene crucible to mix with the sample, and add 25 g of methanol, adjust the temperature of the hot plate to 90° C., place it on the hot plate and heat it for 8 minutes to obtain a primary reactant;

[0066] (2) adding oxalic acid to the container to mix the primary reactant and oxalic acid evenly, then adding methanol, adjusting the temperature of the electric hot plate to 90° C., placing the mixture on the electric hot plate and heating it for 8 minutes to obtain a product; wherein the amount of oxalic acid and the organic solvent used in this step is the same as that used in step (1);

[0067] (3) Repeat step (2) with the product until methanol is added, adjust the temperature of the hot plate to 120° C., place it on the hot plate and heat it until it is almost dry to obtain a reactant;

[0068] (4) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 30 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 100° C., and heat to dissolve to obtain a solution;

[0069] (5) While hot, adjust the pH value of the solution to 9 with 0.2 mol / L sodium hydroxide solution, remove and cool to room temperature, and filter with a circulating water vacuum pump. Collect the liquid in a 250 mL conical flask, and wash the polytetrafluoroethylene crucible three times with 15 mL of ultrapure water. Simultaneously, filter the washing liquid and add it to the liquid to obtain a filtrate;

[0070] (6) Add 100 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 10 min to obtain a reaction solution;

[0071] (7) Select filter paper with a mass m0 of 0.1097 g that has been pre-treated with constant weight, filter the reaction solution in step (6) using a circulating water vacuum pump, wash the precipitate on the filter paper with a volume fraction of 20% ethanol solution, further filter, and then transfer the filter paper with the precipitate to a weighing bottle with a mass m1 of 62.0848 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 64.2941 g;

[0072] (8) The purity calculation formula of lithium carbonate is as follows:

[0073]

[0074] Where: ω------purity percentage of lithium carbonate, %;

[0075] m------Weigh the mass of lithium carbonate, g;

[0076] m0 is the mass of the filter paper, g;

[0077] m1 is the mass of the weighing bottle, g;

[0078] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0079] K=0.95717.

[0080] Example 3

[0081] The method for detecting the purity of lithium hydroxide comprises the following steps:

[0082] (1) Weighing 2.0125 g of a dried lithium hydroxide sample and placing it in a 100 mL polytetrafluoroethylene crucible; then weighing 5.834 g of oxalic acid and placing it in a 100 mL polytetrafluoroethylene crucible to mix with the sample, and adding 30 g of methanol, adjusting the temperature of the hot plate to 80° C., placing it on the hot plate and heating it for 10 minutes to obtain a primary reactant;

[0083] (2) adding oxalic acid to a container to mix the primary reactant and oxalic acid evenly, then adding methanol, adjusting the temperature of the electric hot plate to 80° C., and heating on the electric hot plate for 10 minutes to obtain a product; wherein the amount of oxalic acid and the organic solvent used in this step is the same as that used in step (1);

[0084] (3) Repeat step (2) with the product until methanol is added for the last time, adjust the temperature of the hot plate to 110° C., place it on the hot plate and heat it until it is almost dry to obtain a reactant;

[0085] (4) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 30 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 90° C., and heat to dissolve to obtain a solution;

[0086] (5) While hot, the pH value of the solution was adjusted to 10 with 0.2 mol / L sodium hydroxide solution, and after cooling to room temperature, the solution was filtered using a circulating water vacuum pump, and the liquid was collected in a 250 mL conical flask, and the polytetrafluoroethylene crucible was washed three times with 15 mL of ultrapure water, and the washing liquid was simultaneously filtered and added to the liquid to obtain a filtrate;

[0087] (6) Add 80 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 5 min to obtain a reaction solution;

[0088] (7) Select filter paper with a mass m0 of 0.1098 g that has been pre-treated with constant weight, filter the reaction solution in step (6) using a circulating water vacuum pump, wash the precipitate on the filter paper with a volume fraction of 20% ethanol solution, further filter, and then transfer the filter paper with the precipitate to a weighing bottle with a mass m1 of 62.1018 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 65.3972 g;

[0089] (8) The purity calculation formula of lithium hydroxide is as follows:

[0090]

[0091] Where: ω------purity percentage of lithium hydroxide, %;

[0092] m------Weigh the mass of lithium hydroxide, g;

[0093] m0 is the mass of the filter paper, g;

[0094] m1 is the mass of the weighing bottle, g;

[0095] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0096] K=0.62045.

[0097] Example 4

[0098] The method for detecting the purity of lithium chloride comprises the following steps:

[0099] (1) Weigh 2.0230 g of a dried lithium chloride sample and put it into a 100 mL polytetrafluoroethylene crucible; then weigh 8.0331 g of oxalic acid and put it into a 100 mL polytetrafluoroethylene crucible to mix with the sample, and add 50 g of ethanol, adjust the temperature of the hot plate to 100° C., place it on the hot plate and heat it for 10 minutes to obtain a primary reactant;

[0100] (2) adding oxalic acid to a container to mix the primary reactant and oxalic acid evenly, then adding methanol, adjusting the temperature of the electric hot plate to 100° C., placing on the electric hot plate and heating for 10 minutes to obtain a product; wherein the amount of oxalic acid and the organic solvent used in this step is the same as that used in step (1);

[0101] (3) Repeat step 2) with the product until methanol is added, adjust the temperature of the hot plate to 120° C., place it on the hot plate and heat until it is almost dry to obtain a reactant;

[0102] (4) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 40 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 100° C., and heat to dissolve to obtain a solution;

[0103] (5) While hot, the pH value of the solution was adjusted to 10 with 0.1 mol / L sodium hydroxide solution, and after cooling to room temperature, the solution was filtered using a circulating water vacuum pump, and the liquid was collected in a 250 mL conical flask, and the polytetrafluoroethylene crucible was washed three times with 15 mL of ultrapure water, and the washing liquid was simultaneously filtered and added to the liquid to obtain a filtrate;

[0104] (6) Add 50 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 5 min to obtain a reaction solution;

[0105] (7) Select filter paper with a mass m0 of 0.1100 g that has been pre-treated with constant weight, filter the reaction solution in step (6) using a circulating water vacuum pump, wash the precipitate on the filter paper with a mass fraction of 30% ammonia solution, and further filter it, then put the filter paper with the precipitate into a weighing bottle with a mass m1 of 62.1252 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 64.0471 g;

[0106] (8) The purity calculation formula of lithium chloride is as follows:

[0107]

[0108] Where: ω------purity percentage of lithium chloride, %;

[0109] m------Weigh the mass of lithium chloride, g;

[0110] m0 is the mass of the filter paper, g;

[0111] m1 is the mass of the weighing bottle, g;

[0112] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0113] K=1.09824.

[0114] Comparative Example 1

[0115] (1) Weigh 2.0048 g of a dried lithium chloride sample and put it into a 100 mL polytetrafluoroethylene crucible; then weigh 5.0112 g of oxalic acid and put it into a 100 mL polytetrafluoroethylene crucible to mix with the sample, and add 25 g of methanol, adjust the temperature of the hot plate to 80° C., place it on the hot plate and heat it for 10 minutes to obtain a primary reactant;

[0116] (2) adding oxalic acid to a container to mix the primary reactant and oxalic acid evenly, then adding methanol, adjusting the temperature of the electric hot plate to 80° C., and heating on the electric hot plate for 10 minutes to obtain a product; wherein the amount of oxalic acid and the organic solvent used in this step is the same as that used in step (1);

[0117] (3) Repeat step (2) with the product until methanol is added, adjust the temperature of the hot plate to 110° C., place it on the hot plate and heat it until it is almost dry to obtain a reactant;

[0118] (4) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 25 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 90° C., and heat to dissolve to obtain a solution;

[0119] (5) while hot, adjust the pH value of the solution to 6.5 with 0.1 mol / L sodium hydroxide solution, remove and cool to room temperature, and filter with a circulating water vacuum pump. Collect the liquid in a 250 mL conical flask, and wash the polytetrafluoroethylene crucible three times with 15 mL of ultrapure water. Simultaneously, filter the washing liquid and add it to the liquid to obtain a filtrate;

[0120] (6) Add 50 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 5 min to obtain a reaction solution;

[0121] (7) Select filter paper with a mass m0 of 0.1099 g that has been pre-treated with constant weight, filter the reaction solution in step (6) using a circulating water vacuum pump, wash the precipitate on the filter paper with a volume fraction of 20% ethanol solution, and further filter it, then put the filter paper with the precipitate into a weighing bottle with a mass m1 of 62.0793 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 64.0010 g;

[0122] (8) The purity calculation formula of lithium chloride is as follows:

[0123]

[0124] Where: ω------purity percentage of lithium chloride, %;

[0125] m------Weigh the mass of lithium chloride, g;

[0126] m0 is the mass of the filter paper, g;

[0127] m1 is the mass of the weighing bottle, g;

[0128] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0129] K=1.09824.

[0130] If the pH value is less than 7, the solution is weakly acidic, and high-valent cations such as calcium and magnesium will not be completely precipitated and exist in the filtrate in a soluble form. After adding sodium phosphate solution, calcium phosphate, magnesium phosphate and other precipitates will be formed and precipitated together with lithium phosphate, resulting in a high final result.

[0131] Comparative Example 2

[0132] (1) Weighing 2.0147 g of a dried lithium carbonate sample and placing it in a 100 mL polytetrafluoroethylene crucible; then weighing 5.0165 g of oxalic acid and placing it in a 100 mL polytetrafluoroethylene crucible to mix with the sample, and adding 25 g of methanol, adjusting the temperature of the electric hot plate to 110° C., placing it on the electric hot plate and heating it until it is almost dry, to obtain a reactant;

[0133] (2) Remove the polytetrafluoroethylene crucible containing the reactants, cool it slightly, add 25 g of ultrapure water to the crucible, place it on a hot plate, adjust the temperature of the hot plate to 90° C., and heat to dissolve to obtain a solution;

[0134] (3) while hot, adjust the pH value of the solution to 8 with 0.1 mol / L sodium hydroxide solution, remove and cool to room temperature, and then use a circulating water vacuum pump to filter, collect the liquid in a 250 mL conical flask, and wash the polytetrafluoroethylene crucible three times with 15 mL of ultrapure water, and filter the washing liquid simultaneously and merge it into the liquid to obtain a filtrate;

[0135] (4) Add 50 mL of 200 g / L sodium phosphate solution to the filtrate under stirring, then add 20 mL of anhydrous ethanol, and continue stirring for 5 min to obtain a reaction solution;

[0136] (5) Select filter paper with a mass m0 of 0.1099 g that has been pre-treated with constant weight, filter the reaction solution in step (4) using a circulating water vacuum pump, wash the precipitate on the filter paper with a volume fraction of 20% ethanol solution, further filter, and then put the filter paper with the precipitate into a weighing bottle with a mass m1 of 62.0793 g that has been pre-treated with constant weight, and dry it at 105±5°C to constant weight, and record the constant weight mass m2 as 64.2797 g;

[0137] (6) The purity calculation formula of lithium carbonate is as follows:

[0138]

[0139] Where: ω------purity percentage of lithium carbonate, %;

[0140] m------Weigh the mass of lithium carbonate, g;

[0141] m0 is the mass of the filter paper, g;

[0142] m1 is the mass of the weighing bottle, g;

[0143] m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g;

[0144] K=0.95717.

[0145] Table 1 Purity values ​​of various embodiments and comparative examples

[0146] Case Sample source Inspection report value Test purity value Deviation value Example 1 MACKLIN(LiCl) 98.518％ 98.326％ 0.195％ Example 2 <![CDATA[MACKLIN(Li2CO3)]]> 99.938％ 99.817％ 0.121％ Example 3 MACKLIN(LiOH) 98.389％ 98.211％ 0.181％ Example 4 MACKLIN(LiCl) 98.518％ 98.364％ 0.156％ Comparative Example 1 MACKLIN(LiCl) 98.518％ 99.251％ 0.744％ Comparative Example 2 <![CDATA[MACKLIN(Li2CO3)]]> 99.938％ 99.318％ 0.620％

[0147] Note: The test report value is determined by the method disclosed in the national standard method GB / T 11064-2013 "Chemical Analysis Method for Lithium Carbonate, Lithium Hydroxide Monohydrate and Lithium Chloride".

[0148] As shown in Table 1: According to the experimental results of Examples 1-4, the deviation between the sample inspection report value and the measured purity value is 0.1%-0.2%, which meets the test requirements (deviation within 0.5%), and the solution is determined to be feasible.

[0149] Compared with Example 1, Comparative Example 1 differs in that the pH value of the solution in step (4) is adjusted to 6.5, and other experimental conditions are the same. The deviation between the measured purity value and the test report value is 0.744%>0.5%, indicating that the pH value of the solution needs to be greater than 7 during the experiment. The reason is that when the pH value is less than 7, some calcium oxalate and magnesium oxalate will be incompletely precipitated. After the addition of sodium phosphate, they will precipitate out in the form of calcium phosphate and magnesium phosphate together with lithium phosphate, resulting in a larger result.

[0150] Compared with Example 1, Comparative Example 2 is different in that step 2 is not repeated, and other experimental conditions are the same. The deviation between the measured purity value and the test report value is 0.620%>0.5%, indicating that repeated operation is crucial to the experimental determination results of lithium carbonate. The reason is that oxalic acid is added once, and part of the lithium carbonate does not react with oxalic acid in time. When the first filtration is performed, the lithium carbonate that does not participate in the reaction is filtered out together with the precipitates such as calcium oxalate and magnesium oxalate. The number of repetitions has an impact on the experimental results of lithium carbonate and lithium hydroxide, but has little impact on the experimental results of lithium chloride.

[0151] Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for detecting the purity of a lithium salt, characterized in that: The following steps are involved: 1) Mix the dried sample and oxalic acid evenly, add an organic solvent, and heat to react to obtain a primary reactant; 2) mixing the primary reactant and oxalic acid uniformly, adding an organic solvent, heating and reacting to obtain a product; wherein the amounts of oxalic acid and organic solvent used in this step are the same as those used in step 1); 3) Repeat step 2) 1 to 2 times with the product; after adding the organic solvent for the last time, heat and evaporate to near dryness to obtain the reactant; 4) After the mixture is cooled slightly, ultrapure water is added to the reactant, and the mixture is heated and dissolved at high temperature to obtain a solution; 5) adjusting the pH value of the solution to ≥7 while hot, then cooling to room temperature and filtering, collecting the liquid, and washing the container with ultrapure water for multiple times, and filtering the washing liquid simultaneously and adding it to the liquid to obtain a filtrate; 6) adding sodium phosphate solution to the filtrate under stirring, and then adding anhydrous ethanol, and continuing to stir to obtain a reaction solution; 7) Use filter paper with a mass of m0 that has been pre-treated with constant weight to filter the reaction solution, wash the precipitate on the filter paper with ethanol solution or ammonia water, further filter, and then transfer the filter paper with the precipitate to a weighing bottle with a mass of m1 that has been pre-treated with constant weight, dry to constant weight, and record the constant weight as m2; 8) Calculate the purity of the sample according to the following formula: Where: ω is the purity percentage of the sample, %; m is the mass of the dried sample, g; m0 is the mass of the filter paper, g; m1 is the mass of the weighing bottle, g; m2 is the mass of the weighing bottle containing the filter paper and sediment after drying, g; When the sample is lithium carbonate, K = 0.95717; Or, when the sample is lithium hydroxide, K = 0.62045; Alternatively, when the sample is lithium chloride, K = 1.09824.

2. The detection method according to claim 1, characterized in that: In the step 1), the mass ratio of the sample to oxalic acid is 1:2.5-5.

0.

3. The detection method according to claim 1 or 2, characterized in that: In step 1) and step 2), the organic solvent is one or more of methanol, ethanol and acetone; and the mass ratio of oxalic acid to the organic solvent is 1:4.0-8.0; the heating temperature is 80-100° C., and the heating time is 5-10 min.

4. The detection method according to claim 1, characterized in that: In the step 3), the heating and evaporation temperature is 110-130°C.

5. The detection method according to claim 1, characterized in that: In the step 4), the mass ratio of the sample to ultrapure water is 1:10-20, and the high temperature heating temperature is 90-100°C.

6. The detection method according to claim 1, characterized in that: In the step 5), the pH regulator is any one of potassium hydroxide, sodium hydroxide and ammonia water.

7. The detection method according to claim 6, characterized in that: The concentration of the solution prepared with sodium hydroxide is 0.1-0.2 mol / L.

8. The detection method according to claim 1, characterized in that: In the step 6), the mass ratio of sodium phosphate in the sodium phosphate solution to the sample is 4-10:1; and the concentration of the sodium phosphate solution is 100-200 g / L.

9. The detection method according to claim 1 or 8, characterized in that: In the step 6), the volume ratio of anhydrous ethanol to the filtrate is 1:10-20.

10. The detection method according to claim 1, characterized in that: In the step 7), the volume fraction of the ethanol solution is 10%-20%, the mass fraction of the ammonia water is 30%; and the drying temperature is 105±5°C.

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