Valence-specific quantitative determination of transition metal elements

Abstract

To provide a method for classifying and quantitating, a transition metal element included in a transition metal compound or a salt thereof for each valence.SOLUTION: There is provided a valence classification quantitation method of a transition metal element comprising: a preparation step for preparing a measurement sample which includes, a transition metal compound including a transition metal element which may take a plurality of oxidation numbers and is stabilized when the oxidation number is lowest, or a salt of the transition metal compound; an adjustment step for, mixing the measurement sample, a solvent, a halide acid or a salt thereof and thionic acids, for dissolving the measurement samples, for isolating a simple halogen by an oxidation reduction reaction of the transition metal element which exists in a format in which the transition metal element has a higher oxidation number higher than an oxidation number at which the transition metal element is stabilized in the measurement sample and the halide acid or the salt thereof, and performing the oxidation reduction reaction of the simple halogen and the thionic acids for acquiring a reaction solution; and a first quantitation step for, on the basis of a content of the thionic acids left in the reaction solution, quantitating the transition metal element which exists in the high oxidation number format.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for quantitatively determining transition metal elements by valence. [Background technology]

[0002] The transition metal element contained in a transition metal compound or a salt thereof can have a plurality of different oxidation numbers, including relatively stable oxidation numbers and unstable oxidation numbers, depending on the counter ion species constituting the transition metal compound or salt, the form of the solute, the redox atmosphere of the solvent, etc. Therefore, a transition metal compound or a salt thereof may contain a mixture of transition metal elements with different oxidation numbers.

[0003] It is necessary to understand the amount of each transition metal element with a different oxidation number contained in the transition metal compound or its salt.

[0004] Methods for quantifying metal elements contained in compounds include spectroscopic analysis, such as ICP emission spectroscopy, as well as gravimetric and volumetric methods.

[0005] However, when quantifying the metal elements contained in a compound, if the method includes chemical pretreatment involving an oxidation-reduction reaction, the oxidation number of the transition metal element changes, and it may not be possible to determine the original oxidation number of the transition metal element.

[0006] If a transition metal compound is readily soluble, it can be dissolved in a solvent that does not change the oxidation number of the solute, such as deoxygenated water, to keep the oxidation number of the transition metal element constant. In this case, quantification can be performed by an appropriate volumetric method or absorptiometry, which utilizes the specific color change.

[0007] For example, Patent Document 1 proposes a method for quantifying iron ions by separating them according to their valence using absorptiometry. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 06-281582 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the above-mentioned quantitative method cannot be applied to transition metal compounds or salts thereof containing transition metal elements such as nickel and cobalt, which are stable when they have the lowest oxidation number.

[0010] Such transition metal compounds or salts thereof cannot be dissolved in a state where the oxidation number is fixed, so that it is considered that they can be quantitatively determined by spectroscopic analysis.

[0011] However, in spectroscopic analysis, it is difficult to obtain high-purity standard samples with different oxidation states, and even if they were obtained and spectroscopic analysis was performed, it was difficult to determine the valence assignment from the different spectra obtained for each valence state, and accurate quantification was not possible.In addition, spectroscopic analysis equipment was extremely expensive.

[0012] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for quantitatively determining the transition metal elements contained in a transition metal compound or a salt thereof by separating them according to their valence. [Means for solving the problem]

[0013] A first aspect of the present invention is a preparation step of preparing a measurement sample containing a transition metal compound or a salt thereof containing a transition metal element that can have multiple oxidation numbers and is stable when the oxidation number is the lowest; a preparation step of mixing the measurement sample, a solvent, a hydrohalic acid or its salt, and a thionic acid to dissolve the measurement sample, and then liberating elemental halogen through an oxidation-reduction reaction between the hydrohalic acid or its salt and a transition metal element present in a higher oxidation number form than the oxidation number that is stable in the measurement sample, and the elemental halogen and the thionic acid to cause an oxidation-reduction reaction, thereby obtaining a reaction solution; a first quantification step of quantifying the transition metal element present in the high oxidation state based on the content of the thionic acids remaining in the reaction solution; This is a method for quantitatively determining the valence of transition metal elements.

[0014] A second aspect of the present invention is a method for producing a composition comprising the steps of: The method further includes a second quantification step of quantifying the total amount of the transition metal elements contained in the measurement sample, The amount of the transition metal element present in the lowest oxidation state in the measurement sample is determined by subtracting the amount of the transition metal element present in the higher oxidation state from the total amount.

[0015] A third aspect of the present invention is the first or second aspect, The transition metal element is at least one of nickel, cobalt, chromium, and manganese.

[0016] A fourth aspect of the present invention is the method according to any one of the first to third aspects, The hydrohalic acid is hydrogen chloride.

[0017] A fifth aspect of the present invention is the method according to any one of the first to fourth aspects, In the first quantification step, the content of the thionic acids is quantified by an indirect iodine method.

[0018] A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, In the preparation step, the measurement sample, the solvent, and the thionic acids are mixed together, and then the hydrohalic acid is added. [Effects of the Invention]

[0019] According to the present invention, the transition metal elements contained in the transition metal compound or salt thereof can be separated and quantified according to their valence. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a flowchart showing the operation procedure of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present inventors have investigated the above-mentioned problems and have found that when a transition metal compound or a salt thereof containing a transition metal element that is stable at its lowest oxidation number coexists with a hydrohalic acid under strongly acidic conditions, a simple halogen is quantitatively liberated through an oxidation-reduction reaction between the transition metal element present in an unstable high oxidation number form and the hydrohalic acid. By quantifying this simple halogen, it is possible to quantify the transition metal element present in a high oxidation number form contained in the transition metal compound or a salt thereof.

[0022] To quantify the released elemental halogens, it is necessary to reliably separate hydrogen halide from elemental halogen in the reaction system. Methods for collecting elemental halogen include gas collection methods, but in a reaction system where hydrohalic acid coexists under strongly acidic conditions, it is difficult to reliably separate and fix only elemental halogen.

[0023] The present inventors have further investigated this method of capturing elemental halogens and found that using thionic acids as a capture agent is effective. By including thionic acids in the reaction system, elemental halogens liberated by oxidation-reduction reactions can be quickly captured by the thionic acids. Therefore, for example, the amount of elemental halogens lost (amount consumed) from a known amount of thionic acids can be used to indirectly quantify the amount of transition metal elements present in higher oxidation states.

[0024] The present invention was made based on the above findings.

[0025] <One embodiment of the present invention> Hereinafter, a method for quantitatively determining transition metal elements by valence according to one embodiment of the present invention will be described.

[0026] (preparation process) First, a measurement sample to be quantified is prepared.

[0027] The measurement sample of this embodiment contains a transition metal compound or a salt thereof containing a transition metal element that can assume multiple oxidation numbers and is stable at its lowest oxidation number but unstable at higher oxidation numbers. Specifically, the measurement sample is a metal compound or salt thereof containing the transition metal element, a mixture of these metal compounds or salts, or a composite metal oxide. In the measurement sample, the transition metal element exists in a stable form with the lowest oxidation number, an unstable form with a higher oxidation number, or both of these forms. Furthermore, the transition metal element can be dissolved as a metal ion while maintaining its oxidation number in a solvent or a mineral acid that does not have oxidizing power. The lowest and most stable form refers to a form in which the transition metal element contained in the measurement sample is resistant to oxidation and does not change its oxidation number when the measurement sample is placed in a room temperature and normal pressure environment. Hereinafter, the form with the lowest oxidation number will be simply referred to as a low oxidation form, and the form with a higher oxidation number will be referred to as a high oxidation form.

[0028] Examples of transition metal elements that can have multiple oxidation numbers and are stable at their lowest oxidation number include nickel, cobalt, chromium, and manganese. The number of oxidation numbers that transition metal elements can have varies depending on the type of transition metal element and is not limited to two, but may be three or more. Nickel can have oxidation numbers 2 and 3, cobalt can have oxidation numbers 2 and 3, chromium can have oxidation numbers 3 and 6, and manganese can have oxidation numbers 2, 4, 6, and 7. Stable oxidation numbers are 2 for nickel, 2 for cobalt, 3 for chromium, and 2 for manganese. While iron is an example of a transition metal element, iron is a transition metal element that is stable at its highest oxidation number and is not subject to quantification. However, transition metal elements such as iron that are stable at their highest oxidation number may be contained in the measurement sample. The type of counter ion that constitutes a transition metal compound or its salt is not particularly limited, and examples include compounds that form amorphous complexes or complex salts, such as sulfates, hydrochlorides, carbonates, and hydroxides.

[0029] A solvent is also prepared to dissolve the components of the measurement sample. The solvent is not particularly limited as long as it can maintain the oxidation number of the transition metal element without changing it. Examples of the solvent include pure water, a mineral acid with no oxidizing power, or a mineral acid with low concentration that does not cause a change in the oxidation number even if it has oxidizing power. It is preferable to use a solvent from which dissolved oxygen has been removed in order to suppress a change in the oxidation number of the transition metal element. Examples of the mineral acid with no oxidizing power include sulfuric acid and hydrochloric acid.

[0030] Furthermore, a hydrohalic acid or its salt is prepared to liberate the elemental halogen. The hydrohalic acid is not particularly limited as long as it undergoes an oxidation-reduction reaction with a transition metal element present in a high oxidation state. The hydrohalic acid or its salt not only dissolves the measurement sample but also acts as a halogen generating source through the oxidation-reduction reaction described below. From the viewpoints of ease of handling and reactivity, hydrogen chloride is preferred. Hydrogen chloride is preferably added as hydrochloric acid, a mineral acid. Hydrogen chloride is a strong acidic solution, and can directly act on the dissolution of the measurement sample. When adding the hydrohalic acid as an aqueous solution, it is preferable to prepare it appropriately so that the hydrohalic acid completely dissociates hydrogen ions in the aqueous solution.

[0031] Furthermore, thionic acids are prepared. The thionic acids generate thiosulfate ions upon dissolution and capture elemental halogens as described below. The thionic acids are not particularly limited as long as they can be dissolved in the reaction solution and can oxidize elemental halogens. Examples of thionic acids that can be used include thiosulfates, dithionites, trithionates, and tetrathionates. Among these, thiosulfates are preferred from the viewpoint of ease of handling, and specifically, sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate are preferred. Note that one type of thionic acid may be used alone, or two or more types may be used in combination.

[0032] (Preparation process) Next, the measurement sample, solvent, hydrohalic acid, and thionic acids are mixed and dissolved to prepare a reaction solution.

[0033] By this mixing, first, the measurement sample dissolves, and then a redox reaction occurs between the transition metal elements present in a high oxidation state contained in the measurement sample and the hydrohalic acid, liberating elemental halogens. Specifically, the reaction shown in the following formula (1) proceeds. In formula (1), Me a+ represents the transition metal element present in the measurement sample in a higher oxidation state, a is an integer and its oxidation state, HX represents hydrohalic acid, and MeX bindicates a halide salt of Me, and X2 indicates an elemental halogen. When the transition metal element is trivalent, the reaction shown in formula (2) below occurs. The reaction solution is an acidic solution containing a metal halide salt (MeX2) such as a metal chloride salt and a mineral acid such as hydrochloric acid, but the metal halide salt does not affect the redox reaction. In the measurement sample, transition metal elements that exist in a form with a low oxidation number do not contribute to the redox reaction, and remain dissolved, maintaining their valence. Me a+ +aHX → MeX b +(a / 2-b / 2)X2+aH + ···(1) Me 3+ +3HX → MeX2+1 / 2X2+3H + ···(2)

[0034] When a transition metal element contained in a measurement sample can take three or more oxidation states, such as chromium or manganese, the lowest oxidation state does not react, while the two or more higher oxidation states react as described above. For example, in the case of chromium, chromium with an oxidation state of 3 exists in a stable form, while chromium with an oxidation state of 6 liberates elemental halogen through the above reaction. In the case of manganese, manganese with an oxidation state of 2 exists in a stable form, while manganese with oxidation states of 4 and 7 liberate elemental halogen through the above reaction.

[0035] Furthermore, the liberated elemental halogen undergoes an oxidation-reduction reaction shown in the following formula (3) with thionic acids (thiosulfate ions) dissolved in the reaction solution under strong acidic conditions. 2S2O3 - +X2→2X - +S4O6 2- ···(3)

[0036] In this way, in the reaction solution, the elemental halogen (X2) liberated by the hydrohalic acid is converted into thionic acids (S2O3 -) can be used to capture the metals. In this reaction, thionic acids are quantitatively consumed depending on the amount of transition metal elements present in high oxidation states in the measurement sample. The reaction solution contains transition metal elements in low oxidation states in the measurement sample, halides of the transition metal elements, and residual hydrohalic acids and thionic acids that did not completely react.

[0037] Although the measurement sample, solvent, hydrohalic acid, and thionic acids may be mixed simultaneously, it is preferable to mix the measurement sample, solvent, and thionic acids in advance, and then add the hydrohalic acid and mix them. In this case, when the measurement sample is dissolved by the addition of hydrohalic acid and elemental halogens are liberated, the elemental halogens can be quickly and efficiently captured by the thionic acids dissolved in the solvent.

[0038] The amounts of the hydrohalic acid and thionic acids added are preferably in excess of the amounts required for the reaction.

[0039] (1st quantitative step) Subsequently, after the reactions of the above formulas (1) and (3) are completed, the content of thionic acids contained in the resulting reaction solution that remain unreacted in the above formula (3) is quantified. Based on this content, the content of transition metal elements present in a high oxidation state among the transition metal elements contained in the measurement sample is quantified.

[0040] The method for quantifying the remaining thionic acids is not particularly limited, but examples include the indirect iodine method, the direct iodine method, and titration using potassium permanganate (IV) or potassium dichromate. Among these, the indirect iodine method is preferred from the perspective of accurate and easy quantification. In the direct iodine method, iodine in the dropping solution may volatilize during the procedure, so the operating atmosphere must be controlled to prevent iodine volatilization. Furthermore, in titration methods using potassium permanganate (IV), etc., if the reaction solution contains iron and hydrogen chloride, a Zimmerman-Leithardt solution must be used as the titrant. Depending on the reaction solution, a specific titrant must be selected. In contrast, the indirect iodine method uses a strong oxidizing agent to quantitatively liberate iodine, which is easily volatilized in the solution, through an oxidation reaction. Furthermore, the liberated iodine can be quickly consumed by the sodium thiosulfate already present, thereby minimizing quantitative errors. That is, in the indirect iodine method, there are no limitations on the atmospheric conditions or reaction solution compared to the direct iodine method, and quantitative determination can be carried out easily and accurately.

[0041] Specifically, in the indirect iodine method, potassium iodide is first added to and dissolved in the reaction solution, and a titrant is then added dropwise to perform potentiometric titration. Known titrants such as potassium iodate solution and potassium iodide solution can be used as the titrant. Among these, potassium iodate solution is preferred. Potassium iodide solution can sometimes cause unintended reactions during titration, impairing quantitative accuracy. In contrast, potassium iodate solution can suppress unintended reactions and maintain high quantitative accuracy. The reactions when potassium iodate solution is used are represented by the following equations (4) and (5). The amount of thionic acids remaining in the reaction solution is then quantified. KIO3+5KI+6HX→6KX+3H2O+3I2...(4) 2S2O3 2- +I2→2NaI+S4O6 2- ···(5)

[0042] Then, based on the amount of remaining thionic acids, the content of transition metal elements present in higher oxidation states among the transition metal elements contained in the measurement sample is determined. Specifically, the amount of thionic acids consumed in the reaction of the above formula (3) is determined by subtracting the amount of remaining thionic acids from the amount of added thionic acids. The amount of consumed thionic acids corresponds to the amount of elemental halogen liberated, and the content of transition metal elements present in higher oxidation states in the measurement sample can be determined based on the amount of elemental halogen liberated and the above formula (1).

[0043] The content of transition metal elements present in higher oxidation states quantified here refers to the content of the higher oxidation state if the transition metal element has two oxidation states, or the total content of the two or more higher oxidation states excluding the lowest oxidation state if the transition metal element has three or more oxidation states.

[0044] (Second quantitative step) In the first quantification step described above, only those transition metal elements present in high oxidation number forms were quantified among the transition metal elements contained in the measurement sample, but in the second quantification step, the content of transition metal elements present in low oxidation number forms can be determined by subtracting the content of transition metal elements present in high oxidation number forms quantified in the first quantification step from the total amount of transition metal elements contained in the measurement sample.

[0045] The total amount of transition metal elements contained in a measurement sample can be quantified by methods such as ICP atomic emission spectroscopy, atomic absorption spectroscopy, absorptiometry, volumetric methods, and gravimetric methods. These methods can be selected appropriately depending on the required quantitative accuracy. If high accuracy, for example, an error of less than 0.5% in relative standard deviation, is required, volumetric or gravimetric methods should be used. Furthermore, if a certain degree of accuracy, for example, an error of about 5% in relative standard deviation, is acceptable, ICP atomic emission spectroscopy or other methods should be used.

[0046] Specifically, the total amount of transition metal elements contained in a measurement sample is determined by first decomposing a separately prepared identical measurement sample using mineral acid to form a solution. Then, in ICP atomic emission spectrometry and atomic absorption spectrometry, the volume is measured in a volumetric flask, followed by dilution, if necessary, to prepare a dilute solution, which is then measured using an ICP atomic emission spectrometry analyzer, atomic absorption spectrometer, or absorption spectrophotometer. In volumetric methods, the decomposed solution is converted into a form suitable for redox reactions and subjected to redox titration. In gravimetric methods, the transition metal elements are captured by a chelating agent, filtered, and then converted from the recovered sample weight, or electrolytic gravimetry can be used.

[0047] As a result, transition metal elements that can take multiple oxidation states contained in a measurement sample can be separated into those present in the lowest and most stable oxidation states and those present in the higher oxidation states, and their respective contents can be quantified. Furthermore, the composition ratio of each oxidation state can be calculated from the respective contents, and the average oxidation state of the transition metal elements contained in the measurement sample can be determined.

[0048] If a transition metal element has two oxidation states, the average oxidation number is the average of the two oxidation states. On the other hand, if a transition metal element has three or more oxidation states, the average oxidation number is the average of the transition metal element present in the lowest oxidation state and the transition metal element present in the highest oxidation state.

[0049] <Effects of this embodiment> According to this embodiment, one or more of the following effects are achieved.

[0050] In this embodiment, a measurement sample containing a transition metal element, a solvent, a hydrohalic acid, and a thionic acid are mixed, and an oxidation-reduction reaction between the transition metal element present in a high oxidation state in the measurement sample and the hydrohalic acid liberates elemental halogen, which is then captured by the thionic acid. The amount of thionic acid remaining in the reaction solution is then quantified and subtracted from the known amount of thionic acid added, thereby determining the amount of transition metal element present in a high oxidation state among the transition metal elements present in the measurement sample. In this way, even when transition metal elements of different oxidation states are present in the measurement sample, the transition metal element present in an unstable high oxidation state can be selectively oxidized and reduced, and its content can be accurately quantified through a simple operation.

[0051] In addition, the amount of transition metal elements present in the low oxidation state can be determined by quantifying the total amount of transition metal elements present in the low oxidation state and the high oxidation state in the measurement sample and subtracting the amount of transition metal elements present in the high oxidation state. Furthermore, based on the amounts of the low oxidation state and the high oxidation state, the ratio of the low oxidation state to the high oxidation state can be calculated, and the average oxidation state of the transition metal elements in the measurement sample can be determined.

[0052] Furthermore, conventional fractional quantification methods are limited to cases where the measurement sample is a transition metal element-containing sulfate or the like that is soluble in a solvent that does not cause a redox reaction. Furthermore, the quantification range of the content may be limited depending on the quantification method. In this regard, the quantification method of the present embodiment allows for the quantification of a wider range of transition metal elements, as long as the measurement sample is a transition metal compound or its salt containing a transition metal element that is stable at its lowest oxidation state, without limiting the type of counter ion constituting the compound or salt. Furthermore, the quantification range of the transition metal element contained in the measurement sample is not particularly limited and can be adjusted appropriately by the concentration of the oxidizing agent added during quantification and the volume of the quantification device. The quantification range can be selected from a wide range, for example, from 0.1 mg / L or more to several g / L or less.

[0053] The indirect iodine method is preferably used to quantify the thionic acids remaining in the reaction solution. In the indirect iodine method, for example, potentiometric titration can be used to accurately determine the titration equivalence point, thereby further improving the accuracy of the quantification.

[0054] The hydrohalic acid used is preferably hydrogen chloride, which is easy to handle and does not cause unnecessary fluctuations in the oxidation number of the transition metal elements, thereby maintaining high quantitative accuracy.

[0055] In addition, in the preparation step, it is preferable to first mix the measurement sample, the solvent, and the thionic acids, and then add the hydrohalic acid. The addition of the hydrohalic acid promotes the oxidation-reduction reaction of the transition metal elements present in higher oxidation states, and elemental halogens begin to be generated. Therefore, by dissolving the thionic acids in the solution in advance, the elemental halogens generated can be more efficiently collected. This allows the transition metal elements to be quantified with higher accuracy.

[0056] <Other embodiments> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention.

[0057] In the above-described embodiment, the measurement sample contains one type of transition metal element. However, the measurement sample may contain two or more types of transition metal elements, such as nickel, cobalt, chromium, and manganese. In this case, the two or more types of transition metal elements can be quantified as the total content of the transition metal elements present in a highly oxidized form. For example, when two types of transition metal elements A and B are contained, in the preparation step, the transition metal element A present in a highly oxidized form and the transition metal element B present in a highly oxidized form are each subjected to an oxidation-reduction reaction to liberate elemental halogens, which are then captured using thionic acids, thereby quantifying the total content of the transition metal elements A and B present in a highly oxidized form. [Example]

[0058] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0059] Example 1 In Example 1, the valence-specific determination of transition metal elements was carried out as shown in the flow chart of FIG.

[0060] Specifically, a mixture of nickel compounds containing nickel as a transition metal element, which is stable at its lowest oxidation state, was prepared as a measurement sample. This mixture included compounds with nickel oxidation states of 2 and 3, such as nickel hydroxide and nickel sulfate.

[0061] Next, a certain amount of the measurement sample was weighed, 100 mL of pure water was added, and then 20 mL of sodium thiosulfate solution, which had been prepared in advance to a concentration of 0.1 mol / L as thionic acids, was added in excess to prepare a mixed solution. The sodium thiosulfate solution was added so that the sodium thiosulfate concentration was 2 mmol.

[0062] Next, approximately 5 mL of hydrochloric acid (1 + 1) containing hydrogen chloride, a hydrohalic acid, was added to the mixture as a reaction initiator. After the addition, the mixture was gently stirred for several minutes to dissolve the measurement sample and simultaneously promote the reaction with the transition metal compound or its salt containing the transition metal element present in the measurement sample in a high oxidation state. After the reaction was completed, a reaction solution was obtained.

[0063] The reaction for preparing the reaction solution is as follows: Ni 3+ +3HCl → NiCl2 + 1 / 2Cl2 + 3H + ···(6) 2S2O3 - +Cl2 → 2Cl - +S4O6 2- ···(7)

[0064] Subsequently, 3 g of potassium iodide was dissolved in the resulting reaction solution, and then a 1 / 60 mol / L potassium iodate solution was used as the dropping solution for the automatic titrator, and potentiometric titration was carried out using a silver / silver oxide electrode.

[0065] The reaction in potentiometric titration is as follows: KIO3+5KI+6HCl→6KCl+3H2O+3I2...(8) 2S2O3 2- +I2→2NaI+S4O6 2- ···(9)

[0066] Potentiometric titration confirmed that the content of thionic acids remaining in the reaction solution was 1.5 mmol. This confirmed that the amount of thionic acids consumed in the reaction with the elemental halogen (Cl2) in the above formula (7) was 0.72 mmol, and that the content of nickel present in a higher oxidation state that reacted in the above formula (6) was 0.72 mmol. Note that the higher oxidation state of nickel here was assumed to be trivalent.

[0067] Meanwhile, the total amount of nickel contained in the measurement sample, that is, the total content of divalent nickel and trivalent nickel, was determined by ICP atomic emission spectrometry and was found to be 52 wt%. By subtracting the content of trivalent nickel from the total amount of nickel, the content of divalent nickel was found to be 18 wt%.

[0068] From the above results, it was confirmed that the composition ratio of divalent nickel, which is in a low oxidation state, and trivalent nickel, which is in a high oxidation state, in the measurement sample was as shown in Table 1 below. Furthermore, when the average oxidation state of nickel in the measurement sample was calculated from these ratios, it was confirmed to be 2.66.

[0069] Example 2 In Example 2, a sample obtained by removing the water-soluble nickel from the sample of Example 1 was similarly evaluated. The composition ratio of trivalent nickel, which is in a higher oxidation state, was confirmed to be as shown in Table 1 below, and the average oxidation number of nickel in the measurement sample was calculated from these ratios and confirmed to be 2.73.

[0070] Example 3 In Example 3, nickel sulfate hexahydrate (NiSO4·6H2O), a water-soluble nickel compound, was used as the standard substance and evaluated in the same manner as in Example 1. In Example 3, no trivalent nickel compounds in the form of higher oxidation states were detected.

[0071] Example 4 In Example 4, nickel hydroxide (Ni(OH)2) was used as the standard substance as an acid-soluble nickel compound, and evaluation was performed in the same manner as in Example 1. In Example 4, no trivalent nickel compounds in the form of higher oxidation states were detected.

[0072] Example 5 In Example 5, nickel oxyhydroxide (NiOOH) was used as the trivalent standard substance and evaluation was carried out in the same manner as in Example 1. The average oxidation number of nickel in the measurement sample was determined to be 2.96.

[0073] [Table 1]

[0074] As explained above, the transition metal elements present in the form of higher oxidation numbers contained in the measurement sample are selectively oxidized and reduced, the elemental halogens liberated in the course of the reaction are collected with thionic acids, and the content of the transition metal elements present in the form of higher oxidation numbers can be quantified from the amount of thionic acids consumed.

Claims

1. a preparation step of preparing a measurement sample containing a transition metal compound or a salt thereof containing a transition metal element that can have multiple oxidation numbers and is stable when the oxidation number is the lowest; a preparation step of mixing the measurement sample, a solvent, a hydrohalic acid or its salt, and a thionic acid to dissolve the measurement sample, and then liberating elemental halogen through an oxidation-reduction reaction between the hydrohalic acid or its salt and a transition metal element present in a higher oxidation number form than the oxidation number that is stable in the measurement sample, and the elemental halogen and the thionic acid to cause an oxidation-reduction reaction, thereby obtaining a reaction solution; a first quantification step of quantifying the amount of the transition metal element present in the high oxidation state based on the content of the thionic acids remaining in the reaction solution, the transition metal element is at least one of nickel, cobalt, chromium, and manganese; the solvent is water, the hydrohalic acid is hydrogen chloride, and the thionic acid is thiosulfate; In the preparation step, the elemental halogen is liberated and subjected to an oxidation-reduction reaction with thiosulfate ions under acidic conditions of hydrochloric acid in the reaction solution. A method for quantitative determination of transition metal elements by valence.

2. The method further includes a second quantification step of quantifying the total amount of the transition metal elements contained in the measurement sample, The amount of the transition metal element present in the lowest oxidation state in the measurement sample is determined by subtracting the amount of the transition metal element present in the higher oxidation state from the total amount. The method for quantitatively determining transition metal elements by valence according to claim 1.

3. In the first quantification step, the content of the thionic acids is quantified by an indirect iodine method. The method for quantitatively determining transition metal elements by valence according to claim 1 or 2.

4. In the preparation step, the measurement sample, the solvent, and the thionic acids are mixed together, and then the hydrohalic acid is added. The method for quantitatively determining transition metal elements by valence according to any one of claims 1 to 3.

Images