JP6094822B2 - Method for quantifying fat-soluble phosphorus compounds - Google Patents

Description

  The present invention relates to a method for quantifying a fat-soluble phosphorus compound contained in a trace amount in a metal salt.

  The following are known as industrial uses of nickel. For example, in addition to general electroplating, nickel sulfate is widely used for nickel electroless plating for hard disks in computers, and more recently, nickel sulfate has been widely used as a raw material for nickel for secondary batteries. Yes.

  As a general method for industrially producing nickel sulfate, there is a method of obtaining nickel sulfate crystals from a nickel sulfate solution by evaporating crystallization through a step of removing impurities after dissolving the raw material in an acid solution. In the step of removing the impurities, a solvent extraction method is used. As the extractant, for example, an organic phosphoric acid-based acidic extractant, that is, an acidic phosphonic acid ester or an acidic phosphinic acid ester is used.

  Patent Document 1 discloses a method for separating cobalt from an aqueous solution containing cobalt and nickel using an alkylphosphonic acid monoalkyl ester as an extractant.

  Patent Document 2 discloses a method of purifying nickel sulfate by extracting cobalt by solvent extraction using the trade name PC-88A (manufactured by Daihachi Chemical Co., Ltd.) as an extractant and separating nickel and cobalt. Has been.

  In the solvent extraction step, the organic phase and the aqueous phase are phase-separated by gravity, but if the phase separation property is poor, the extractant may be mixed into the aqueous phase. For example, when an extractant is mixed in nickel sulfate, which is the final product of Patent Document 2, the extractant has some adverse effects downstream of the manufacturing process of a product that uses nickel sulfate as a raw material.

  Conventionally, in a manufacturing process of a product using nickel sulfate as a raw material, contamination of the extractant has been evaluated by quantifying organic carbon using a total organic carbon meter (TOC meter). The TOC meter measures the total amount of organic substances present in water, and cannot detect organic substances that are not eluted or mixed in water. Since the extractant mixed in nickel sulfate is fat-soluble, the TOC meter is not suitable as an apparatus for evaluating the mixing of the extractant into nickel sulfate.

  On the other hand, since the extractant is a fat-soluble organic phosphorus compound, the mixing of the extractant into nickel sulfate can be evaluated by quantitative determination of phosphorus. Patent Document 3 discloses a method for quantifying phosphorus. In Patent Document 3, an organophosphorus compound is decomposed into phosphoric acid in a wet manner, and phosphorus is quantified by a high frequency inductively coupled plasma double focusing mass spectrometer (ICP-MS) or a high frequency inductively coupled plasma emission spectrometer (ICP-AES). doing.

  The organic phosphorus compound derived from the extractant contained in the metal salt such as nickel sulfate is extremely small amount (several ppm order). When the wet decomposition solution of nickel sulfate is assumed to be measured by ICP-MS or ICP-AES, it must be diluted to a salt concentration that does not cause the effects of device contamination and plasma fluctuation. Furthermore, when the sensitivity of the apparatus is taken into consideration, the lower limit of quantification as phosphorus is about 10 to 100 ppm, so the lower limit of quantification of the organophosphorus compound contained in the metal salt is higher than this. For these reasons, a method for analyzing an organophosphorus compound contained in a metal salt on the order of several ppm using ICP-MS or ICP-AES has not been known. Therefore, it has been desired to develop a quantitative method for evaluating organophosphorus compounds in the order of several ppm in metal salts.

JP-A-60-231420 JP-A-10-310437 JP 2004-317141 A

  An object of the present invention is to provide a method for quantifying a fat-soluble phosphorus compound for evaluating a trace amount of a fat-soluble phosphorus compound contained in a metal salt.

  In order to solve the above-mentioned problems, the first means according to the present invention includes an aqueous solution step of dissolving a metal salt containing a fat-soluble phosphorus compound in water, an organic solvent is added to the obtained aqueous solution, and the fat-soluble phosphorus compound Extraction step of extracting the organic solvent with the organic solvent, a recovery volatilization step of recovering and volatilizing the organic solvent phase-separated from the aqueous solution, and a generation step of generating a water-soluble phosphorus compound from the sample remaining after volatilization of the organic solvent And a measuring step of measuring an aqueous solution of the water-soluble phosphorus compound with an elemental analyzer, and a method for quantifying a fat-soluble phosphorus compound.

  According to a second means of the present invention, in the first means, the pH of the aqueous solution in the extraction step is 1.0 or less.

  A third means according to the present invention is characterized in that, in the first or second means, the metal salt containing the fat-soluble phosphorus compound is nickel sulfate.

  A fourth means according to the present invention is characterized in that, in the third means, the fat-soluble phosphorus compound is an organic phosphate extractant used in the purification step of the nickel sulfate.

  According to a fifth means of the present invention, in any one of the first to fourth means, the organic solvent is n-hexane or chloroform.

  A sixth means according to the present invention is the method according to any one of the first to fifth means, wherein in the production step, a water decomposition is performed from a sample remaining after volatilization of the organic solvent by a wet decomposition method or a closed pressure decomposition method. It is characterized by producing a functional phosphorus compound.

  A seventh means according to the present invention is the sixth means characterized in that the wet decomposition method is white smoke treatment with nitric acid and sulfuric acid.

  According to an eighth means of the present invention, in any one of the first to seventh means, the elemental analyzer is a high frequency inductively coupled plasma mass spectrometer or a high frequency inductively coupled plasma emission spectrometer. It is.

  According to a ninth means of the present invention, in the eighth means, the high-frequency inductively coupled plasma mass spectrometer is a double-focusing mass spectrometer.

  In the present invention, since a metal salt containing a fat-soluble phosphorus compound as an impurity is made into an aqueous solution, and the fat-soluble phosphorus compound is liquid-liquid extracted from the aqueous solution with an organic solvent, even a very small amount of the fat-soluble phosphorus compound in the metal salt is extracted. Can do. Moreover, since the metal ion which is the main component of the metal salt is not distributed to the organic phase, only the fat-soluble phosphorus compound which is the target component can be separated and recovered. Further, the fat-soluble phosphorus compound can be concentrated by volatilization of the organic solvent. Moreover, since the decomposition liquid obtained by wet-decomposing the extracted fat-soluble phosphorus compound does not contain a metal ion having a high salt concentration, it can be measured by ICP-MS or ICP-AES without dilution. And according to this invention, in the quantitative analysis of the fat-soluble phosphorus compound in a metal salt, the lower limit of quantification of 0.1 ppm or less can be achieved as phosphorus.

It is a flowchart which shows the determination method of the fat-soluble phosphorus compound which concerns on this invention. It is a flowchart which shows the determination method of the trace amount fat-soluble phosphorus compound contained in a nickel sulfate crystal (Example 1).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a flowchart showing each step in the method for quantifying a fat-soluble phosphorus compound according to the present invention. The method for quantifying a fat-soluble phosphorus compound according to the present invention includes an aqueous solution step in which a metal salt containing a small amount of a fat-soluble phosphorus compound is dissolved in water, and an extraction in which an organic solvent is added to the aqueous solution to extract the fat-soluble phosphorus compound. Process, recovery and volatilization process for recovering and volatilizing the organic solvent phase-separated from the aqueous solution, and wet decomposition method or closed pressure decomposition method (microwave) for the sample (oil-soluble phosphorus compound) remaining after volatilization of the organic solvent And a measuring step of measuring an aqueous solution containing the water-soluble phosphorus compound with an elemental analyzer.

  The metal salt contains a fat-soluble phosphorus compound. For example, in the purification process of transition metals such as Co, Cu, Ni, or Zn, or salts thereof, a fat-soluble phosphorus compound may be used to remove impurities in the raw material. Therefore, a trace amount of a fat-soluble phosphorus compound may remain in these transition metal salts. The present invention can be applied to salts of these transition metals. The present invention can also be applied to alkali metals such as Na or K or alkaline earth metals such as Mg or K.

  The metal salt is preferably one that is readily soluble in water, that is, one that is soluble in water only by a normal stirring operation. In the case of a metal salt that is sparingly soluble in water, some kind of decomposition treatment is required, and there is a possibility that the fat-soluble phosphorus compound as the target component is not extracted into the organic solvent.

  Examples of the fat-soluble phosphorus compound contained in the metal salt include an organic phosphoric acid-based extractant used in a nickel sulfate purification step. Specifically, trade names such as Cyanex 277, D2EHPA, or PC-88A.

  The water used in the aqueous solution process is preferably pure water from which salts and residual chlorine have been removed. When the metal salt is nickel sulfate, as long as the concentration is not too high, the nickel sulfate is completely dissolved by simply adding the nickel sulfate to water at room temperature and stirring.

  It is preferable that the pH of the aqueous solution in the extraction step is 1 or less by adding a strong acid to the aqueous solution of the metal salt in the aqueous solution step or the extraction step. When the base in the metal salt is a transition metal such as Co, Cu, Ni, or Zn, when the pH in the extraction process exceeds 1.0, the fat-soluble phosphorus compound in the metal salt becomes complex with the transition metal. Since a metal complex may be formed and the degree of hydrophobicity varies, the fat-soluble phosphorus compound may not be sufficiently extracted into an organic solvent.

  Examples of the strong acid added to the aqueous metal salt solution include hydrogen bromide, hydrochloric acid, nitric acid, and sulfuric acid. When the metal salt is nickel sulfate, it is preferable to use sulfuric acid so that the fat-soluble phosphorus compound does not form a complex organometallic complex. The strong acid may be added in advance to the aqueous solvent before the metal salt is dissolved in water in the aqueous solution process.

  The organic solvent added to the aqueous solution in the extraction step is preferably n-hexane or chloroform. In consideration of toxicity and environmental burden, n-hexane is preferable. In a mixed solution of an aqueous solution and an organic solvent, metal ions are not distributed to the organic solvent. Therefore, if the aqueous phase and the organic phase are phase-separated, the fat-soluble phosphorus compound is selectively extracted into the organic phase.

  In the extraction step, it is preferable to stir or shake the mixed solution of the aqueous solution and the organic solvent for 5 to 30 minutes so that the fat-soluble phosphorus compound is completely extracted into the organic solvent. Then, after this operation, the mixed solution is allowed to stand until the aqueous phase and the organic phase are completely separated. The organic solvent after phase separation in the extraction step is recovered in a beaker or the like using a separatory funnel or the like.

  Next, in the recovery and volatilization process, the organic solvent has high volatility compared to the fat-soluble phosphorus compound that is the target component for recovery, so it is simple to heat it to 90 ° C to 100 ° C and maintain this temperature for about 1 hour. Can be volatilized and removed. And after an organic solvent volatilizes completely, only a fat-soluble phosphorus compound remains as a dry solid. In the recovery and volatilization step, it is preferable to completely remove the organic solvent.

  Next, in the production step, a water-soluble phosphorus compound is produced from the dry solid of the fat-soluble phosphorus compound. An elemental analyzer such as ICP-MS or ICP-AES used in the subsequent measurement process can measure only an aqueous solution. Therefore, in order to perform quantitative analysis with these apparatuses, it is necessary to denature the fat-soluble phosphorus compound, which is a measurement object, to be water-soluble. Examples of a method for modifying a fat-soluble phosphorus compound into a water-soluble phosphorus compound include a wet decomposition method or a closed pressure decomposition method (microwave method). The wet decomposition method is preferable because the container containing the dry solid used in the recovery and volatilization step can be used as it is. If the container containing the dry solid is used as it is in the wet decomposition method, not only the workability of the present invention can be improved, but also a decrease in the yield of the fat-soluble phosphorus compound can be prevented. The acid for decomposition used in the wet decomposition method is preferably a combination of a plurality of acids rather than a single acid. For example, a combination of nitric acid and sulfuric acid or a combination of nitric acid and perchloric acid can be used. In the wet decomposition method, it is preferable to continue the white smoke treatment for 10 to 30 minutes after white smoke starts to be generated so that the fat-soluble phosphorus compound is completely decomposed by the acid. In order to measure with higher sensitivity, the decomposition solution containing the water-soluble phosphorus compound is heated and concentrated by white smoke treatment, etc., and then re-dissolved by adding a predetermined amount of water or acid to obtain an aqueous solution of the water-soluble phosphorus compound. It is preferable to create.

  Next, in the measurement step, phosphorus in the aqueous solution of the water-soluble phosphorus compound is quantified using an elemental analyzer. Examples of the element analyzer include ICP-MS and ICP-AES. The ICP-MS is preferably a double-focusing ICP-MS that can be separated from molecular ions that interfere with phosphorus. On the basis of the measurement liquid, it is expected that quantification of about 0.1 mg / L with ICP-AES and about 1 ng / ml with double convergence ICP-MS is possible.

  The phosphorus concentration is calculated from the measurement results obtained by these apparatuses. An absolute calibration curve method, an internal standard method, or a standard addition method can be applied to calculate the phosphorus concentration. Examples of the internal standard substance include yttrium, rhodium, and cesium. However, cesium cannot be used in ICP-AES.

  In the following examples, a method for quantifying a fat-soluble phosphorus compound derived from the trade name PC-88A, which is an organic phosphoric acid-based extractant used in the nickel sulfate purification step, is shown. The metal salt to be analyzed is nickel sulfate crystals.

  The compound name of PC-88A is mono-2-ethylhexyl 2-ethylhexylphosphonate and is represented by the following general formula.

  PC-88A is soluble in general organic solvents and slightly soluble in water. When the purity of PC-88A is 100%, the phosphorus content is 10%. Therefore, when the lower limit of quantification of PC-88A is 1 ppm, the lower limit of quantification converted to phosphorus is 0.1 ppm.

<Example 1>
(Measurement of phosphorus recovery rate)
A nickel sulfate aqueous solution was prepared by weighing 40 g of nickel sulfate crystals in a beaker and dissolving in water. This aqueous nickel sulfate solution was evenly distributed between the two separatory funnels. At this time, 0.5 ml (phosphorus content 50 μg) of an ethanol solution (hereinafter referred to as “standard solution”) having a phosphorus concentration of 100 mg / L prepared from PC-88A was added to only one separatory funnel. Next, water was added to both separatory funnels to make up to about 100 ml, 5 ml of hydrochloric acid and 50 ml of n-hexane were further added, and the mixture was shaken for about 5 minutes. After standing for about 10 minutes, the organic phases in both separatory funnels were collected in separate beakers, and the separatory funnel washed with 5 ml of n-hexane was also collected. The recovered organic phase was heated on a hot plate at about 100 ° C. to evaporate the organic solvent and dry it. Next, 2 ml of nitric acid and 2 ml of (1 + 1) sulfuric acid were added to both beakers, heated and concentrated on a hot plate at about 300 ° C., and heated for about 10 minutes after white smoke sulfate began to appear. After allowing to cool, 1 ml of nitric acid added to both beakers and redissolved were separately transferred to test tubes. Next, 1 ml of an yttrium solution having an yttrium concentration of 100 mg / L, whose internal standard substance is yttrium, was added to both test tubes. Furthermore, water was added to both test tubes to make a constant volume of 10 ml, and these were used as measurement solutions. The phosphorus concentration in the two measurement solutions was quantified using ICP-AES by the internal standard method. A series of these phosphorus concentration measurement steps is shown in the flowchart of FIG.

The series of phosphorus concentration measurement steps shown in FIG. 2 was repeated 10 times. In the n-th measurement, the quantitative value of phosphorus in the measurement solution to which the standard solution was not added is expressed as Xn [μg], and the quantitative value of phosphorus in the measurement solution to which the standard solution was added is X′n [μg. ], Since the amount of phosphorus added by the standard solution is 50 μg, the phosphorus recovery rate is calculated by the following equation (1).
Recovery [%] = (X′n−Xn) / 50 × 100 (1)

  The recovery rate of phosphorus calculated from the measurement results of the phosphorus concentration from the first to the tenth time using the formula (1) is shown in “Table 1”. Table 1 also shows the average value [%] of phosphorus recovery based on the measurement results of all 10 times, its standard deviation [%], and its coefficient of variation.

  As shown in Table 1, the average recovery rate of phosphorus in Example 1 was 102%, its standard deviation was 9.04%, and its coefficient of variation was 8.87. Here, the variation coefficient is obtained by dividing the standard deviation value by the average value, and is an index indicating relative variation. The value of the coefficient of variation of 8.87 is a good value and indicates that the measured value has little variation. Therefore, it can be said that the phosphorus recovery rate calculated in Example 1 is highly reliable.

(Measurement of the lower limit of quantification of phosphorus concentration)
The lower limit of quantification of the ICP-AES phosphorus concentration used in the measurement of phosphorus recovery was measured by an operational blank test. In this operation blank test, the phosphorus concentration of this yttrium solution was measured 10 times by ICP-AES using a blank sample not containing phosphorus, specifically, an yttrium solution having an yttrium concentration of 10 mg / L. The measurement results of the phosphorus concentration for all 10 times are shown in “Table 2”.

The average value of the measured values of phosphorus concentration for all 10 times was 0.0076 mg / L, its standard deviation was 0.0066 mg / L, and its lower limit of quantification was 0.0332 ppm. Here, the lower limit of quantification of the phosphorus concentration in Table 2 is obtained by multiplying the standard deviation (δ) by 10 and converting the unit to ppm. There are a plurality of methods for obtaining the lower limit of quantification of the solution concentration. Usually, a value obtained by multiplying the standard deviation of the operation blank test result by 10 is adopted as the lower limit of quantification. The lower limit of quantification of the phosphorus concentration in Table 2 is a value calculated by the following formula (2).
Lower limit of quantification [ppm] = 10 × standard deviation × constant volume / sample amount (2)

  The sample amount of 20 g in Table 2 is the amount of nickel sulfate crystals used in the measurement of phosphorus recovery rate of 20 g (the initial use amount is 40 g, but is 20 g because it is equally distributed thereafter). Yes, the constant volume of 10 ml in Table 2 is the amount of the measurement liquid measured by ICP-AES in the measurement of phosphorus recovery rate is 10 ml.

  Therefore, the lower limit of quantification of the phosphorus concentration calculated from the standard deviation of all 10 measurements was 0.0332 ppm, and the target value of 0.1 ppm or less was achieved. Therefore, according to the method for quantifying a fat-soluble phosphorus compound according to Example 1, a highly reliable content rate is obtained even for a very small amount of a fat-soluble phosphorus compound containing less than 1 ppm in a nickel sulfate crystal. Can do.

<Example 2>
(Measurement of phosphorus recovery rate)
5 g of nickel sulfate crystals were weighed into a vial, added with 20 ml of water and made into an aqueous solution by ultrasonic irradiation. This operation was repeated again to prepare two aqueous nickel sulfate solutions in the vial. Next, 0.1 ml of the standard solution was added to only one vial. Next, 1 ml of hydrochloric acid and 20 ml of n-hexane were added to both vials and shaken for about 5 minutes. After standing for about 10 minutes, 10 ml of the organic phase of both vials was collected in separate beakers and heated to dryness on a hot plate at about 100 ° C. Nitric acid (2 ml) and (1 + 1) sulfuric acid (2 ml) were added to both beakers, and the mixture was heated and concentrated on a hot plate at about 300 ° C., and heated for about 10 minutes after sulfuric acid white smoke began to appear. After allowing to cool, 1 ml of nitric acid added to both beakers and redissolved were transferred to separate test tubes. Subsequently, water was added to both beakers to make 10 ml, and then diluted 10 times to obtain a measurement solution. At the time of 10-fold dilution, 0.1 ml of a mixed solution having a mixed concentration of rhodium and cesium of 100 ng / ml was added to both beakers as an internal standard substance. The phosphorus concentration in the measurement solution was quantified using a double convergence ICP-MS by an internal standard method. In addition, it quantified with the resolution | decomposability 4000 which is not influenced by the molecular ion interference derived from nitrogen.

  For each of the measurement solution containing the standard solution and the measurement solution not containing the standard solution, the phosphorus concentration was measured once. The recovery rate of phosphorus was calculated from the measured value of phosphorus concentration using the above formula (1). As a result, the recovery rate of phosphorus was 87%. Although the phosphorus recovery rate of 87% is lower than that of Example 1, it is a value sufficiently tolerable for practical use.

(Measurement of the lower limit of quantification of phosphorus concentration)
By performing the same operation blank test as in Example 1, the lower limit of quantification of the phosphorus concentration of the double convergent ICP-MS was measured. Specifically, using a blank sample that does not contain phosphorus, that is, a mixed solution having a mixed concentration of rhodium and cesium of 1 ng / ml, the phosphorus concentration of this mixed solution was measured 6 times by double-focusing ICP-MS. The measurement results of the phosphorus concentration for all six times are shown in “Table 3”.

  The lower limit of quantification of the phosphorus concentration calculated from the measurement results of the six operation blank tests was 0.0578 ppm, and the target value of 0.1 ppm or less was achieved. Here, the lower limit of quantification of the phosphorus concentration is calculated using the above formula (2). In Example 2, after 5 g of nickel sulfate crystals are dissolved in 20 ml of n-hexane, only 10 ml of this organic phase is collected. Further, the collected organic phase is diluted 10 times before becoming a measurement solution. Therefore, in Example 2, the “sample amount” of the formula (2) is 5 g × 10 ml / 20 ml × 1/10 = 0.25 g of nickel sulfate crystals.

<Example 3>
In Example 2, the n-hexane added to the vial together with 1 ml of hydrochloric acid was changed to chloroform. Except this, the recovery rate of phosphorus contained in the standard solution was measured in the same manner as in Example 2. As a result, the phosphorus recovery rate was 87%, the same as in Example 2.

<Reference example>
In Example 2, 2 ml of nitric acid and 2 ml of (1 + 1) sulfuric acid added to the dry solid obtained by evaporating the organic solvent were changed to only 2 ml of nitric acid. Except this, the recovery rate of phosphorus contained in the standard solution was measured in the same manner as in Example 2. As a result, the average phosphorus recovery rate calculated from the measurement results was 57%. Therefore, in the reference example, 43% of the phosphorus contained in the standard solution could not be recovered. In other words, it is considered that nearly half of the fat-soluble phosphorus compound contained in the metal salt cannot be modified into a water-soluble phosphorus compound by the means of the reference example. Therefore, it is difficult to say that the measurement accuracy of the means of the reference example is sufficient as a method for quantifying the fat-soluble phosphorus compound.

  In a hydrometallurgical process having a solvent extraction step using an organic phosphate extractant, it can be used as a technique for evaluating the mixing of the extractant into the aqueous phase. It can be applied not only to product metal salts but also to management for process liquids and intermediates.

Claims (9)

An aqueous solution step of dissolving a metal salt containing a fat-soluble phosphorus compound in water;
An extraction step of adding an organic solvent to the obtained aqueous solution, and extracting the fat-soluble phosphorus compound with the organic solvent;
A recovery and volatilization step of recovering and volatilizing the organic solvent phase-separated from the aqueous solution;
A production step of producing a water-soluble phosphorus compound from the sample remaining after the volatilization of the organic solvent;
A measuring step of measuring an aqueous solution of the water-soluble phosphorus compound with an elemental analyzer, and a method for quantifying the fat-soluble phosphorus compound.   The method for quantifying a fat-soluble phosphorus compound according to claim 1, wherein the pH of the aqueous solution in the extraction step is 1.0 or less.   The method for quantifying a fat-soluble phosphorus compound according to claim 1 or 2, wherein the metal salt containing the fat-soluble phosphorus compound is nickel sulfate.   The method for quantifying a fat-soluble phosphorus compound according to claim 3, wherein the fat-soluble phosphorus compound is an organic phosphoric acid-based extractant used in the purification step of the nickel sulfate.   The method for quantifying a fat-soluble phosphorus compound according to any one of claims 1 to 4, wherein the organic solvent is n-hexane or chloroform.   In the said production | generation process, a water-soluble phosphorus compound is produced | generated from the sample which remain | survived after volatilization of the said organic solvent by the wet decomposition method or the closed pressure decomposition method. The quantification method of the fat-soluble phosphorus compound of description.   7. The method for quantifying a fat-soluble phosphorus compound according to claim 6, wherein the wet decomposition method is white smoke treatment with nitric acid and sulfuric acid.   The method for quantifying a fat-soluble phosphorus compound according to any one of claims 1 to 7, wherein the elemental analyzer is a high-frequency inductively coupled plasma mass spectrometer or a high-frequency inductively coupled plasma emission spectrometer.   The method for quantifying a fat-soluble phosphorus compound according to claim 8, wherein the high-frequency inductively coupled plasma mass spectrometer is a double-focusing mass spectrometer.

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