JP2018159560A - Quantification method for trace amount of zinc in solution having high concentration of nickel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a trace amount of zinc contained in a solution having a high concentration of nickel with excellent precision.SOLUTION: A quantification method for quantifying a trace amount of zinc contained in a solution having a high concentration of nickel comprises: a preparation step of preparing the solution having the high concentration of the nickel containing the nickel and the trace amount of the zinc relative to an amount of the nickel as a sample solution; a wash step of bringing an organic solvent used for solvent extraction into contact with an acidic solution; an extraction step of bringing the organic solvent after the wash obtained in the wash step into contact with the sample solution to solvent-extract the zinc contained in the sample solution into the organic solvent after the wash; a back extraction step of bringing the organic solvent after the extraction obtained in the extraction step into contact with an acidic solution to back-extract the zinc contained in the organic solvent after the extraction into the acidic solution; and a quantification step of quantifying the zinc contained in the acidic solution obtained in the back extraction step.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for determining a trace amount of zinc in a high concentration nickel solution.

  In the wet metallurgy of nickel (Ni), there is a smelting method using a sulfuric acid bath and a chloride bath, and one of the processes is an electrowinning method in a chloride bath. In this process, first, in a leaching step, nickel sulfide as a raw material is leached with chlorine, and after a purification step, nickel electrolytic solution (hereinafter also simply referred to as electrolytic solution) is electrolyzed to obtain nickel (for example, Patent Document 1). And 2). The nickel thus obtained is referred to as electric nickel.

  When obtaining electric nickel, it is required to cope with impurity elements other than Ni. In particular, among impurity elements, zinc (Zn) is contained in nickel sulfide as a raw material at a concentration of several hundred ppm to several wt%. In order to cope with this, a method of separating Zn from nickel sulfide as a raw material has been proposed (see, for example, Patent Document 3). Patent Document 3 discloses that zinc is separated and removed by ion exchange from an electrolytic solution having a nickel concentration of 90 to 120 g / L, a zinc concentration of 1 to 10 mg / L, and 100 mg / L.

Japanese Patent Publication No.7-91599 Japanese Patent Laid-Open No. 11-236630 JP 2008-38236 A

  Residual zinc after separation and removal of the above zinc has a low concentration, and there is a need for a method capable of accurately measuring a very small amount of zinc.

  As a measuring method, for example, there is a method of measuring using an inductively coupled plasma emission spectrometer (ICP-AES) or an inductively coupled plasma mass spectrometer (ICP-MS). However, in ICP-AES and ICP-MS, when a high-concentration nickel solution is introduced, for example, high-concentration components (nickel, sodium, etc.) are clogged in the nebulizer, and the plasma fluctuates to stabilize the zinc concentration. Measurement may not be possible. Further, when measuring a very small amount of zinc concentration, it is considered that various interferences are received from high concentration components, and the reliability of the obtained measurement value is low.

  On the other hand, in order to reduce the influence of high concentration components, it is conceivable to measure after diluting the electrolyte solution, but in ICP-AES and ICP-MS, it is necessary to dilute several tens to several hundred times, In this case, the concentration of zinc is also reduced, and the measurement is difficult to exceed the lower limit of detection by ICP-AES or ICP-MS.

  In addition, in order to reduce the influence of high concentration components, it may be possible to separate high concentration components from the electrolyte before measurement, for example, by precipitation separation or ion exchange, but in this case, many steps are required before the separation. Therefore, zinc is likely to be mixed in from the instruments, reagents, work environment, etc. used, and a very small amount of zinc concentration in the electrolyte cannot be measured with high accuracy.

  In addition, in order to separate a small amount of zinc from high-concentration components, a method of solvent extraction of zinc from the electrolytic solution is conceivable, but according to the study of the present inventors, zinc may be mixed from the solvent used for extraction. In some cases, a trace amount of zinc originally contained in a high-concentration nickel solution cannot be accurately measured.

  This invention is made | formed in view of the said subject, and it aims at providing the technique which measures the trace amount zinc contained in a high concentration nickel solution accurately.

  The present inventor further studied the case of solvent extraction of a high concentration nickel solution. As a result, zinc may be mixed in the organic solvent used for solvent extraction. Even if an attempt is made to measure the zinc concentration in a high concentration nickel solution using such an organic solvent for solvent extraction, the high concentration nickel solution is used. It was found that the trace amount of zinc in the sample could not be measured accurately.

  For this reason, the present inventor uses a container in which the organic solvent is washed in advance and the zinc does not elute in order to avoid zinc from being mixed into the measuring apparatus from other than the sample to be measured. Thus, the inventors have found that a very small amount of zinc in a high-concentration nickel solution can be accurately measured by solvent extraction, and have completed the present invention.

That is, the first aspect of the present invention is:
A quantitative method for quantifying a trace amount of zinc contained in a high-concentration nickel solution,
As a sample solution, a preparation step of preparing a high-concentration nickel solution containing a trace amount of zinc with respect to nickel and nickel;
A washing step in which an organic solvent used for solvent extraction is brought into contact with an acidic solution;
An extraction step of bringing the organic solvent after washing obtained in the washing step into contact with the sample solution, and extracting the zinc contained in the sample solution into the organic solvent after washing;
A back extraction step of bringing the organic solvent after extraction obtained in the extraction step into contact with an acidic solution and back extracting zinc contained in the organic solvent after the extraction into the acidic solution;
There is provided a method for quantifying a trace amount of zinc in a high-concentration nickel solution, comprising a quantification step of quantifying zinc contained in the acidic solution obtained in the back extraction step.

According to a second aspect of the present invention, in the quantification method of the first aspect,
In the extraction step, the pH of the sample solution is 2.0 or more and 4.0 or less.

According to a third aspect of the present invention, in the quantification method of the first or second aspect,
In the washing step, the acidic solution has a pH of 2.0 or less.

According to a fourth aspect of the present invention, in the quantification method according to any one of the first to third aspects,
The organic solvent is at least one of 2-ethylhexyl (2-ethylhexyl) phosphonate and bis (2-ethylhexyl) hydrogen phosphate.

According to a fifth aspect of the present invention, in the quantification method according to any one of the first to fourth aspects,
The instrument in contact with the sample solution and the purification solvent is made of resin.

  According to the present invention, a very small amount of zinc contained in a high-concentration nickel solution can be accurately measured.

FIG. 1 shows a process chart of a method for determining a trace amount of zinc in a high concentration nickel solution according to an embodiment of the present invention. FIG. 2 shows a process diagram of a method for quantifying trace amounts of zinc in Examples. FIG. 3 shows the correlation between the pH of the sample solution and the zinc recovery rate during solvent extraction. FIG. 4 is a diagram showing the correlation between the pH of the sample solution and the nickel residual concentration during solvent extraction. FIG. 5 is a diagram for explaining the difference in zinc elution amount depending on the material of the test tube. FIG. 6 is a diagram for explaining the difference in the elution amount of zinc depending on the material of the general-purpose container.

<One Embodiment of the Present Invention>
Hereinafter, a method for determining a trace amount of zinc in a high concentration nickel solution according to an embodiment of the present invention will be described. The quantitative method of the present embodiment includes a preparation process, a cleaning process, an extraction process, a back extraction process, and a quantitative process. Hereafter, each process is explained in full detail using FIG. FIG. 1 shows a process chart of a method for determining a trace amount of zinc in a high concentration nickel solution according to an embodiment of the present invention. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

(Preparation step S10)
First, as shown in FIG. 1, a high concentration nickel solution is prepared as a sample solution to be analyzed.

  The high-concentration nickel solution is, for example, a solution in the process of producing metallic nickel, a nickel plating solution used for processing electronic materials or electronic components, and the like. The concentration of zinc and nickel in the high concentration nickel solution is not particularly limited. In this embodiment, as will be described later, a very small amount of zinc can be quantified with respect to nickel.

(Washing step S20)
Subsequently, before the solvent extraction of zinc from the sample solution, the organic solvent used for the solvent extraction is washed in the washing step S20. According to this washing, even if zinc is mixed in the organic solvent used in the solvent extraction, the zinc is removed from the organic solvent before the solvent extraction to suppress the influence on the determination of zinc. Can do.

  Specifically, an organic solvent and an acidic solution are mixed and shaken. Thus, zinc mixed in the organic solvent is leached into the acidic solution and removed from the organic solvent. Then, after shaking, the organic layer and the aqueous layer are separated by standing or centrifuging, and the organic layer is taken out to remove the zinc, so that the zinc concentration becomes, for example, 1 μg / L or less. Obtain the solvent.

  The organic solvent is not particularly limited as long as zinc can be extracted from the sample solution in the extraction step S30 described later, but at least one of (2-ethylhexyl) phosphonic acid 2-ethylhexyl and hydrogen phosphate bis (2-ethylhexyl). It is preferable to use one. According to these organic solvents, zinc can be sufficiently extracted by one solvent extraction. In addition, in order to adjust the density, these organic solvents may be mixed with other organic solvents and used as a mixed solvent.

  Any acidic solution may be used as long as it can extract zinc mixed in the organic solvent. For example, an acidic solution having a pH of 2.0 or less is preferably used. Moreover, the mixing ratio of the organic solvent and the acidic solution is not particularly limited. However, from the viewpoint of preventing zinc from remaining in the organic solvent, the acidic solution is preferably 10% by volume or more based on the organic solvent.

  It is preferable that a container or an instrument (such as a pipette for collecting) used for washing the organic solvent in the washing step S20 is made of resin. This is because, as will be described later in Examples, resin-made containers and instruments have less zinc elution than glass and can maintain high measurement accuracy. Similarly, in the extraction step S30, the back extraction step S40, and the quantification step S50 described later, it is preferable to use a resin container or instrument.

  In the cleaning step S20, the cleaning operation may be performed at least once by bringing the acidic solution into contact with the organic solvent, and if necessary, the cleaning may be performed a plurality of times with the acidic solution. Further, in the washing step S20, the shaking of the organic solvent and the acidic solution can be carried out by shaking or using a device such as a shaker, and the shaking time (contact time) is It is good to set it as about 30 seconds-1 minute.

(Extraction step S30)
Subsequently, a small amount of zinc contained in the sample solution is subjected to solvent extraction using the washed organic solvent obtained in the washing step S20. Specifically, the washed organic solvent and the sample solution are mixed and shaken. Thereby, a trace amount of zinc in the sample solution is leached into the organic solvent. Then, after shaking, the organic layer and the aqueous layer are separated by standing or centrifuging, and the organic layer is taken out to obtain an organic solvent from which zinc has been extracted. In the extraction step S30, nickel may be extracted together with zinc, but the nickel concentration is low and does not affect the determination of zinc.

  In this embodiment, by washing the organic solvent in advance before extraction, even when zinc is mixed in the organic solvent before extraction, the zinc is removed from the organic solvent, and the mixed amount is included in the sample solution. It is reduced to a negligible amount with respect to a small amount of zinc. Therefore, the organic solvent after extraction accurately reflects the concentration of trace amount zinc contained in the sample solution.

In the extraction step S30, the sample solution may be subjected to solvent extraction as it is, but it is preferable to perform solvent extraction by adjusting the pH of the sample solution so that zinc can be extracted efficiently.
As shown in FIG. 3, the higher the pH of the sample solution, the easier it is to extract zinc from the sample solution and the higher the zinc recovery rate. Specifically, the pH of the sample solution is preferably 2.0 or more, and more preferably 2.3 or more. Thereby, the recovery rate of the trace amount zinc from the sample solution can be 80% or more, or 94% or more.
On the other hand, as shown in FIG. 4, the higher the pH of the sample solution, the higher the nickel concentration extracted into the organic solvent. When the nickel concentration is high, it is difficult to accurately determine a minute amount of zinc concentration. From the viewpoint of maintaining high accuracy of the determination, it is preferable to lower the pH by lowering the pH. Specifically, the pH of the sample solution is preferably 4.0 or less, and more preferably 3.0 or less.
Thus, by adjusting the pH of the sample solution within a predetermined range, extraction of nickel that affects the determination of zinc can be suppressed while extracting zinc from the sample solution with a high recovery rate.

  The mixing ratio between the sample solution and the organic solvent after washing is not particularly limited, but the pH of the sample solution varies depending on the mixing with the organic solvent, so that the pH of the sample solution does not deviate from the optimum range. It is good to change. As a reagent for adjusting the pH of the sample solution, for example, an aqueous ammonia solution or nitric acid can be used. Moreover, you may add a buffer solution to a sample solution so that pH may be adjusted easily as needed.

  Further, in the extraction step S30, the shaking of the sample solution and the washed organic solvent can be performed by shaking by hand or using a device such as a shaker. The time is preferably about 30 seconds to 1 minute.

(Back extraction step S40)
Subsequently, the extracted organic solvent is back-extracted with an acidic solution, and zinc contained in the extracted organic solvent is leached into the acidic solution. When the organic solvent after extraction is directly measured by ICP-AES or ICP-MS, the organic solvent makes plasma unstable and lowers the measurement accuracy. Therefore, in this embodiment, zinc to be quantified is converted into an acidic solvent. Let it be extracted. Here, the back extraction is performed by mixing the extracted organic solvent and the acidic solution, shaking in the same manner as in the extraction step S30, and then removing the separated aqueous layer to extract the zinc back-extracted acidic solution. Get.

  As the acidic solution used in the back extraction step S40, the same acidic solution used in the washing step S20 can be used.

(Quantitative process S50)
Subsequently, a predetermined amount is collected from the aqueous layer (acidic solution) from which zinc is back-extracted in the back extraction step S40, and used as a measurement solution. By supplying this measuring solution to an analyzer, the concentration of zinc contained in the measuring solution is measured. In the quantification step S50, for example, an absolute calibration curve method obtained from a peak area detected by injecting a fixed amount of a measuring solution, or a standard substance different from the target component is added, and an internal value obtained from a ratio of both detected peak areas The zinc concentration may be obtained by a known method such as a standard method or a standard addition method. As the analyzer, for example, a known device such as ICP-AES, ICP-MS, or atomic absorption spectrometer can be used.

  In the measurement solution, nickel may be extracted and mixed with zinc in the extraction step S30 and the back extraction step S40, but in this embodiment, the concentration of the mixed nickel (also referred to as nickel residual concentration) is kept low. Therefore, zinc can be quantified with high accuracy.

<Effect according to this embodiment>
According to the present embodiment, the following one or more effects are achieved.

  In this embodiment, the organic solvent used for solvent extraction is washed, and by using this washed organic solvent, a trace amount of zinc contained in the high-concentration nickel solution (sample solution) is solvent-extracted and back-extracted. The zinc concentration is measured. Even if zinc is mixed in the organic solvent before use by washing the organic solvent, the influence of zinc mixed in the organic solvent is suppressed, and a small amount of zinc contained in the high-concentration nickel solution Can be accurately quantified.

  Further, the pH of the sample solution is preferably 2.0 to 4.0, and more preferably 2.3 to 3.0, when performing solvent extraction. By setting the pH to 2.0 or more, zinc can be efficiently recovered from the sample solution, while by setting the pH to 4.0 or less, recovery of nickel can be suppressed and the zinc concentration can be measured with higher accuracy.

  As the organic solvent, it is preferable to use at least one of 2-ethylhexyl (2-ethylhexyl) phosphonate and bis (2-ethylhexyl) hydrogen phosphate. According to such an organic solvent, zinc can be efficiently extracted from the sample solution.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.

The materials used in this example are as follows.
As the sample solution, a solution adjusted to a predetermined concentration in a nickel concentration range of 50 to 150 g / L was used.
As a reagent for preparing the buffer solution, diammonium hydrogen citrate (manufactured by Wako Pure Chemical Industries, Ltd., for atomic absorption analysis) was used.
Nitric acid (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was used as the acidic solution.
A 20 vol% aqueous ammonia solution (manufactured by Kanto Chemical Co., Inc., for atomic absorption analysis) was used as a reagent for pH adjustment.
As a zinc extraction solvent, PC-88A ((2-ethylhexyl) phosphonic acid 2-ethylhexyl manufactured by Daihachi Chemical Industry Co., Ltd.) and Teklin N20 (manufactured by JX Nippon Mining & Energy Corporation) are in a volume ratio of 20:80. A mixed organic solvent (hereinafter also simply referred to as an organic solvent) mixed in (1) was used.
A zinc standard solution (manufactured by Kanto Chemical Co., Inc., 1000 mg / L) was used as the standard solution for zinc.
As a reagent for the internal standard solution, a cesium standard solution (manufactured by Kanto Chemical Co., Inc., 100 mg / L) was used.

<Example>
(Selection of measurement container)
First, for each of a measurement container (hereinafter also referred to as a test tube) for use in the analyzer used in the examples and a general-purpose container for use in solvent extraction and reagent subdivision, the material is appropriately changed to make zinc The amount of elution was measured, and one with less zinc contamination was selected.

  As a measurement container having a volume of about 10 to 15 mL used for automatic analysis with an ICP-MS apparatus, polystyrene (volume 12 mL, test tube A), glass (volume 14 mL, test tube B), and polypropylene (volume 14 mL) Three types of test tubes C) and C) were prepared. Nitric acid and pure water were added to each test tube so that the concentration of nitric acid was 2.8 N and the liquid volume was 10 mL, and left overnight. Thereafter, the contents of the test tube were measured for the zinc concentration using an ICP-MS apparatus. At this time, as a standard solution for the calibration curve, a standard solution containing 2.8N nitric acid and zinc added so as to have a zinc concentration of 5 μg / L was prepared. The concentration of zinc in was measured.

  The measurement results are shown in FIG. FIG. 5 is a diagram for explaining the difference in zinc elution amount depending on the material of the test tube. The error bars in FIG. 5 indicate standard deviation (n = 8), and the unit of zinc concentration is μg / L. According to FIG. 5, it was confirmed that the resin test tubes A and C had a smaller zinc elution amount and a smaller variation than the glass test tube B. Among the resins, polypropylene test tube C had an elution amount of zinc of 0.2 μg / L or less, and was confirmed to be more suitable for determination of trace amounts of zinc than polystyrene test tube A. Therefore, in this example, the test tube C was used as the measurement container.

(Selection of general-purpose containers)
As general-purpose containers used for solvent extraction and reagent subdivision, three types of containers made of polypropylene (volume 50 mL, container A), polypropylene (volume 100 mL, container B), and PFA (volume 100 mL, container C) Got ready. Nitric acid and pure water were added to each container so that the amount of nitric acid was 2.8 N and the liquid volume was about 80%, and left overnight. Thereafter, the contents of each container were measured for the zinc concentration using an ICP-MS apparatus. At this time, as a standard solution for the calibration curve, a standard solution with zinc added so that the concentration of nitric acid is 2.8 N and the zinc concentration is 5 μg / L is prepared. The concentration of zinc was measured.

  The measurement results are shown in FIG. FIG. 6 is a diagram for explaining the difference in the elution amount of zinc depending on the material of the general-purpose container. The error bars in FIG. 6 indicate standard deviation (n = 3), and the unit of zinc concentration is μg / L. According to FIG. 6, it was confirmed that the containers B and C had a small zinc elution amount of 0.1 μg / L or less and were suitable for the determination of trace amounts of zinc. In this example, since the container B is less expensive than the container C, the container B was used as a general-purpose container.

(Measurement of the lower limit of determination of zinc)
In order to calculate the lower limit of quantification in the zinc quantification method, a blank test using pure water as a sample solution is performed according to the procedure shown in FIG. 2, and the variation in signal intensity of the sample solution obtained in the blank test and the measurement of zinc are performed. The lower limit of quantification was calculated from the sensitivity. Specifically, it is as follows.

  First, as shown in FIG. 2 (a), an organic solvent that is an extraction solvent for zinc was washed as a washing step. In this example, an organic solvent and 2 mol / L nitric acid were mixed at a volume ratio of 4: 1, and the lid was closed and shaken by hand for 1 minute. Thereafter, the layers were separated by a centrifuge (5000 rpm, 1 minute). Further, the organic solvent was transferred to another container, 2 mol / L nitric acid was mixed at a volume ratio of 4: 1 and shaken by hand. Thereafter, the layers were separated by a centrifuge (5000 rpm, 1 minute). That is, the organic solvent was washed twice in total. After the layers were separated, the upper liquid was collected to obtain an organic solvent after washing.

  Subsequently, as shown in FIG. 2B, as an extraction process, 30 mL of pure water as a sample solution was collected and transferred to a general-purpose container (volume: 50 mL), and 2 mL of 200 g / L aqueous solution of diammonium hydrogen citrate was added. . The pH was adjusted to 3-4 by adding 0.15 mL of an aqueous ammonium solution to this solution. Next, 15 mL of the washed organic solvent was collected and added to the above solution, and the lid of the general-purpose container was closed and shaken by hand for 1 minute. Thereafter, the layers were separated by a centrifuge (5000 rpm, 1 minute). The pH of the aqueous layer at the time of extraction was 2.6 to 2.8.

  Then, as shown in FIG.2 (c), 10 mL of organic solvents (upper liquid) which extracted zinc were extract | collected as a back extraction process, and it moved to another general purpose container (volume 50mL). 10 mL of 2 mol / L nitric acid was added to the container, the lid was closed, and the mixture was shaken by hand for 1 minute, and then separated into layers by a centrifuge (5000 rpm, 1 minute). Thereafter, as shown in FIG. 2 (d), 5 mL of the aqueous layer (lower solution) was collected and transferred to a resin test tube (volume: 15 mL), and 1 mL of a 100 μg / L cesium standard solution was used as an internal standard substance there. In addition, the volume was adjusted to 10 mL. The solution was used as a measurement solution. In this example, the same operation was performed to prepare 10 measurement solutions.

Subsequently, the prepared 10 measurement solutions and the standard solution for the calibration curve prepared in advance were subjected to ICP-MS, and the signal strength of zinc, the standard deviation, by the internal standard method using cesium as an internal standard substance, The slope of the calibration curve (mg ⁻¹ · L) and the lower limit of quantification (mg / L) were determined. The results are shown in Table 1 below.
Although there are a plurality of methods for obtaining the lower limit of quantification, in this example, a value obtained by dividing 10 times the standard deviation of the signal intensity of zinc obtained by the blank test by the slope of the calibration curve as the measurement sensitivity is used. And obtained by the following formula (1).
Lower limit of quantification (mg / L) = 10 × standard deviation / slope of calibration curve (mg ⁻¹ · L) (1)

  As shown in Table 1, the lower limit of quantification calculated from 10 blank tests was 0.0021 mg / L, which was 0.01 mg / L or less, and it was confirmed that a trace amount of zinc could be accurately quantified.

(Measurement of zinc recovery rate)
Next, in order to evaluate the recovery rate of zinc, an additional recovery test of zinc was performed. In addition to the analysis of the normal sample solution, the additional recovery test prepares a sample solution in which a known amount of zinc is added to the sample solution (hereinafter also referred to as an additional sample solution), and performs the same analysis as the normal sample solution. This is a test in which the quantitative value of the sample solution is subtracted from the quantitative value obtained from the additional sample solution, and whether or not the subtracted value matches the added amount of zinc. According to the additional recovery test, in the process of quantitative analysis, failure factors such as loss due to poor extraction of zinc and loss during back-extraction can be confirmed, and if a recovery rate close to 100% is obtained, there is a failure. It can be judged that there is no factor. In addition, as a sample solution, the liquid adjusted to the predetermined density | concentration among the nickel density | concentration of 50-150 g / L was used.

  In the additional recovery test, as shown in FIG. 2 (b), 30 mL of the sample solution was sampled and transferred to each of five general-purpose containers (volume: 50 mL), and 200 g / L aqueous solution of diammonium hydrogen citrate was added to each. 2 mL was added. 0.5 mL of a zinc aqueous solution (containing 1% nitric acid) prepared at a predetermined concentration was added to three of the five sample solutions to obtain an additional sample solution. Then, as shown in FIGS. 2B to 2D, in the same manner as the measurement of the lower limit of quantification of zinc described above, pH adjustment, solvent extraction with an organic solvent after washing, back extraction with an acidic solution, and cesium Five measurement solutions were prepared by adding the standard solution.

Subsequently, the three measurement solutions to which the zinc standard solution was added, the two measurement solutions to which the zinc standard solution was not added, and the standard solution for the calibration curve were subjected to ICP-MS, and cesium was used as the internal standard substance. The concentration of zinc in each measurement solution was measured by an internal standard method. And the recovery rate of zinc was computed from the obtained measured value based on following formula (2). Three measurement values obtained from the measurement solution containing the additional sample solution are An (μg), two measurement values obtained from the measurement solution containing the sample solution are B (μg), and the amount of zinc added is C (μg). Then, the recovery rate (%) of zinc was calculated by the following formula (2).
Recovery rate (%) = (An−B) / C × 100 (2)

  When the recovery rates were calculated from the measurement results of the three additional sample solutions, it was confirmed that the recovery rates were as shown in Table 2 below. Moreover, the average value (%), standard deviation (%), and relative standard deviation (%) of the recovery rate are shown.

  According to Table 2, the recovery rate of zinc was 98% on average, its standard deviation was 1.4%, and the relative standard deviation was 1.4%. From this result, since the recovery rate is close to 100% and the variation is small, it is possible to recover a small amount of zinc from a high concentration nickel solution without losing it during solvent extraction or back extraction, and to accurately determine the zinc concentration. Was confirmed.

(Change in zinc recovery rate due to pH during solvent extraction)
Next, in order to evaluate the optimum pH range for the sample solution for solvent extraction of a trace amount of zinc, the pH of the sample solution was changed and the zinc recovery rate was measured. The sample solution used was the same as the sample solution used in the measurement of zinc recovery.

  Specifically, in order to change the pH at the time of solvent extraction, in the measurement of the zinc recovery rate described above, the amount of the aqueous ammonia solution added to the sample solution is appropriately changed, and the pH of the sample solution before the extraction is 1.5 to A total of 7 pieces were prepared, one at each level, varying from 7 to 3.0. To each of these, 0.8 mL of a standard zinc solution having a predetermined concentration was added to obtain an additional sample solution.

  For each prepared solution, the zinc recovery rate was calculated in the same manner as the measurement of the zinc recovery rate described above, and there was a correlation as shown in FIG. 3 between the pH of the sample solution and the zinc recovery rate. Was confirmed. FIG. 3 is a diagram showing the correlation between the pH of the sample solution during the solvent extraction and the zinc recovery rate. According to FIG. 3, the higher the pH of the sample solution, the better the zinc recovery rate. From the viewpoint of efficiently recovering zinc by setting the recovery rate to 94% or higher, the pH of the sample solution should be 2.3 or higher. I understand that.

(Change in residual nickel concentration due to pH during solvent extraction)
Next, in order to evaluate the change in nickel concentration in the aqueous layer after back extraction due to the pH during solvent extraction, the nickel concentration remaining in the aqueous layer after back extraction by appropriately changing the pH during solvent extraction It was measured.

In this example, 1 mL and 0.1 mL were collected from each water layer finally obtained by solvent extraction and back extraction based on the change in the zinc recovery rate due to pH described above, and transferred to another test tube. did. As an internal standard substance, 1 mL of a 100 mg / L yttrium standard solution was added to a test tube, 1 mL of concentrated nitric acid was added, and the volume was adjusted to 10 mL to prepare a 10-fold diluted solution and a 100-fold diluted solution. The adjusted 10-fold diluted solution corresponds to the measured value of the nickel residual concentration of 200 mg / L or less in FIG. 4, and the adjusted 100-fold diluted solution corresponds to the measured value of the nickel residual concentration of 200 mg / L or more in FIG. ing.
As a standard solution for preparing a calibration curve, 1 mL of concentrated nitric acid was placed in each of three test tubes, and 1 mL of 100 mg / L yttrium standard solution was added to each test tube as an internal standard substance. Thereafter, a nickel standard solution was added so that the nickel concentration levels were 0 mg / L, 10 mg / L, and 20 mg / L, and the volume was adjusted to 10 mL.

  The prepared measurement solution and standard solution were subjected to ICP-AES, the concentration of nickel was measured, and the residual concentration of nickel was calculated from the measured value. As a result, it was confirmed that there was a correlation as shown in FIG. 4 between the pH of the sample solution and the residual nickel concentration. FIG. 4 is a diagram showing the correlation between the pH of the sample solution and the nickel residual concentration during solvent extraction. As can be seen from FIG. 4, the nickel residual concentration increases as the pH of the sample solution increases. In an analysis apparatus such as ICP-MS, if the nickel residual concentration is higher than 250 μg / L, it is considered that the measurement result is affected. Therefore, the pH of the sample solution is adjusted so that the nickel residual concentration is 250 μg / L or less. It can be seen that the value is preferably 3.0 or less.

  As described above, a small amount of zinc is extracted from a high-concentration nickel solution using an organic solvent that has been previously washed to remove zinc, so that zinc can be efficiently separated from high-concentration nickel. It is possible to accurately quantify a small amount of zinc contained in the high-concentration nickel solution by suppressing external mixing. Further, by adjusting the pH of the high-concentration nickel solution to 2.3 to 3.0 at the time of solvent extraction, zinc can be efficiently recovered while suppressing the mixing of nickel.

Claims (5)

A quantitative method for quantifying a trace amount of zinc contained in a high-concentration nickel solution,
As a sample solution, a preparation step of preparing a high-concentration nickel solution containing a trace amount of zinc with respect to nickel and nickel;
A washing step in which an organic solvent used for solvent extraction is brought into contact with an acidic solution;
An extraction step of bringing the organic solvent after washing obtained in the washing step into contact with the sample solution, and extracting the zinc contained in the sample solution into the organic solvent after washing;
A back extraction step of bringing the organic solvent after extraction obtained in the extraction step into contact with an acidic solution and back extracting zinc contained in the organic solvent after the extraction into the acidic solution;
A quantification step of quantifying zinc contained in the acidic solution obtained in the back extraction step. In the extraction step, the pH of the sample solution is 2.0 or more and 4.0 or less.
The method for determining a trace amount of zinc in the high concentration nickel solution according to claim 1. In the washing step, the pH of the acidic solution is 2.0 or less.
A method for quantifying a trace amount of zinc in a high-concentration nickel solution according to claim 1 or 2. The organic solvent is at least one of 2-ethylhexyl (2-ethylhexyl) phosphonate and bis (2-ethylhexyl) hydrogen phosphate;
The method for determining a trace amount of zinc in the high-concentration nickel solution according to any one of claims 1 to 3. An instrument in contact with the sample solution and the purification solvent is made of resin.
The method for determining a trace amount of zinc in the high concentration nickel solution according to any one of claims 1 to 4.