JP2020027103A - Quantitatively measuring method of phosphorous in solution - Google Patents

Abstract

To precisely measure phosphorous contained in the solution even in a minute amount.SOLUTION: A quantitatively measuring method for phosphorous in the solution obtained by dissolving first metal in which hydroxide starts to form at pH greater than 2.5 and phosphorous includes: a precipitation step of adding into the solution a coprecipitant containing a second metal that starts to form hydroxide at pH of 2.5 or less, and precipitating hydroxide of the second metal containing phosphorous by adjusting pH of the solution to 2.5 or less; a preparation step of separating and collecting the hydroxide of the second metal, dissolving it in acid solution, and preparing measurement solution; and a quantitative measuring step of quantitatively measuring phosphorous contained in the measurement solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for determining phosphorus in a solution.

  Phosphorus is contained in a metal material constituting an electrode material of a lithium ion battery, for example. Since the characteristics of a metal material change depending on the phosphorus content, it is important to understand the phosphorus content in improving the characteristics of the metal material. Further, in controlling the content contained in the metal material as the final product, the content in the production process, for example, phosphorus contained in intermediates, various ores used as raw materials, or deposits obtained in wastewater treatment, etc. It is also important to understand the content of.

  However, when quantifying a trace amount of phosphorus contained in a metal compound such as a metal material or an intermediate, the analytical sensitivity of phosphorus is reduced due to the influence of the main component or coexisting element, and the quantification may not be performed accurately. Therefore, when quantifying a trace amount of phosphorus, it is common to separate and concentrate phosphorus to determine the amount.

  As this method, for example, a method of extracting phosphorus contained in a metal compound with a solvent is disclosed (for example, see Patent Document 1). However, this method may be toxic depending on the organic solvent used, or its safety may be impaired due to its low flash point or explosive limit concentration.

  Therefore, as another method, a method of dissolving a metal compound into a solution and then quantifying phosphorus contained in the solution has been studied. At this time, as a method for separating and concentrating the phosphorus contained in the solution, a method is disclosed in which the solution is heated and vaporized to form phosphorus-enriched vapor (for example, see Patent Document 2).

JP 2015-145820 A JP-A-9-98841

  However, in the enrichment method disclosed in Patent Document 2, although high analysis sensitivity is obtained, it is difficult to stably quantify a trace amount of phosphorus, so that the analysis accuracy may be low.

  The present invention has been made in view of the above problems, and has as its object to provide a technique for accurately measuring even a very small amount of phosphorus contained in a solution.

A first aspect of the present invention provides:
A method for quantifying phosphorus in a solution in which phosphorus and a first metal having a pH at which hydroxide formation is started is greater than 2.5 and phosphorus is dissolved,
By adding to the solution a coprecipitant containing a second metal whose pH at which hydroxide formation is initiated is 2.5 or less, and adjusting the pH of the solution to 2.5 or less, A precipitation step of precipitating the hydroxide of the second metal, comprising:
A preparation step of separately collecting and dissolving the hydroxide of the second metal in an acid solution to prepare a measurement solution;
And a quantification step of quantifying phosphorus contained in the measurement solution,
A method is provided for determining phosphorus in a solution.

According to a second aspect of the present invention, in the method for quantifying phosphorus according to the first aspect,
Before the precipitation step,
A preparing step of preparing a metal compound containing the first metal and phosphorus;
Dissolving the metal compound to obtain the solution.

A third aspect of the present invention provides the method for quantifying phosphorus according to the first aspect,
Before the precipitation step, there is provided a preparation step of preparing, as the solution, wastewater containing the first metal and phosphorus.

A fourth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to third aspects,
The second metal is at least one of titanium, zirconium, cerium, tin, niobium, tantalum and antimony.

A fifth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to fourth aspects,
The second metal is a tetravalent metal.

A sixth aspect of the present invention provides the method for quantifying phosphorus according to the fifth aspect,
The second metal is at least one of tetravalent titanium, tetravalent zirconium, and tetravalent cerium.

A seventh aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to sixth aspects,
In the precipitation step, the pH of the solution is adjusted to 1.5 or more and 2.5 or less.

An eighth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to seventh aspects,
The first metal is at least one of iron, aluminum, nickel, cobalt, manganese, zinc, copper, magnesium and chromium.

A ninth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to eighth aspects,
The first metal contains at least iron.

A tenth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to ninth aspects,
The acid solution used in the preparation step is a mixed solution containing hydrochloric acid, nitric acid, and hydrogen peroxide.

An eleventh aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to tenth aspects,
Before the precipitation step, there is a reduction step of adding a reducing agent to the solution to reduce metal ions contained in the solution.

A twelfth aspect of the present invention provides the method for quantifying phosphorus according to the eleventh aspect,
The reducing agent is sodium bisulfite.

A thirteenth aspect of the present invention provides the method for quantifying phosphorus according to the second aspect,
In the dissolving step, the metal compound is melted with an alkali salt, and the obtained melt is dissolved in an acid solution.

A fourteenth aspect of the present invention provides the method for quantifying phosphorus according to the thirteenth aspect,
The alkali salt is at least one of sodium peroxide and sodium carbonate.

A fifteenth aspect of the present invention provides the method for quantifying phosphorus according to any one of the first to fourteenth aspects,
In the quantifying step, phosphorus contained in the solution is quantified using any one of an ICP emission spectrometer, an ICP mass spectrometer, a flame atomic absorption device, a flameless atomic absorption device, and a spectrophotometer. .

  ADVANTAGE OF THE INVENTION According to this invention, even a trace amount of phosphorus contained in a solution can be measured accurately.

FIG. 1 is a diagram showing a change in the amount of phosphorus trapped by the pH of a coprecipitant. FIG. 2 is a flowchart showing steps of a method for quantifying phosphorus in Example 1.

  The present inventors have focused on coprecipitation separation as a pretreatment operation for separating and concentrating phosphorus from a solution in order to solve the above problems.

  In the coprecipitation separation, the target phosphorus is precipitated as a hydroxide together with the coprecipitant by adding a coprecipitant to a solution in which the metal and phosphorus are dissolved. By separating and collecting the precipitate and measuring the content of phosphorus contained therein, the amount of phosphorus contained in the solution can be determined. According to the coprecipitation separation, it is possible not only to separate a trace component quickly but also to perform the separation easily, as compared with other pretreatment operations.

  As the coprecipitant, for example, hydroxides such as lanthanum, iron, manganese, aluminum, and magnesium are known. However, according to the study of the present inventor, when these coprecipitants dissolve metals which form hydroxides and precipitate easily in a wide pH range in the solution, these metals precipitate together with phosphorus. Therefore, it was found that it was difficult to coprecipitate and separate phosphorus, and that phosphorus could not be accurately quantified. For example, iron, aluminum, nickel and the like tend to form hydroxides and precipitate in the pH range of greater than 2.5, so that in a solution containing many of these metals, trace amounts of phosphorus can be accurately quantified. It becomes difficult.

  From this, in order to accurately quantify the trace amount of phosphorus contained in the solution, it is difficult to precipitate iron and aluminum, etc., and when the pH is within the range of 2.5 or less, the metal containing the metal that initiates the formation of hydroxide is used. It has been found that a precipitant should be used. According to such a coprecipitant, even when the solution contains a metal which easily forms a hydroxide and forms a precipitate in a range where the pH is higher than 2.5, the coprecipitation of these metals is performed. And the hydroxide containing phosphorus can be precipitated. That is, even if the amount of phosphorus contained in the solution is very small, it can be accurately determined.

  The present invention has been made based on the above findings.

<One embodiment of the present invention>
Hereinafter, a method for determining phosphorus contained in a solution according to an embodiment of the present invention will be described.

  In the present embodiment, the solution refers to a solution in which at least the first metal at which the formation of hydroxide is started and the pH is higher than 2.5 and phosphorus are dissolved. The solution includes, for example, a solution in which a metal compound containing a first metal and phosphorus is dissolved, or a waste solution containing these components. Hereinafter, a case will be described as an example where the metal compound is dissolved to determine the phosphorus contained in the solution in order to determine the phosphorus in the metal compound.

  The method for quantifying phosphorus according to the present embodiment includes a preparation step, a dissolution step, a reduction step, a precipitation step, a preparation step, and a quantification step. Hereinafter, each step will be described in detail.

(Preparation process)
First, a metal compound for obtaining a solution to be quantified is prepared.

  The metal compound refers to, for example, a product made of a metal material, an intermediate product obtained in a manufacturing process of the product, various ores serving as the raw material, a deposit in wastewater treatment, and the like. The metal compound includes at least a first metal having a pH of more than 2.5 at which hydroxide formation is initiated and phosphorus.

  Here, the pH at which the formation of hydroxide starts is the pH at which metal ions start to precipitate as hydroxide. The term “precipitate as hydroxide” means that the solubility of the hydroxide at 25 ° C. is 0.1 mol / l or less. That is, the first metal dissolves when the pH of the solution is 2.5 or lower, but when the pH is higher than 2.5, the solubility of the hydroxide becomes 0.1 mol / l or lower, so that the first metal is dissolved. It is a metal that begins to precipitate as an oxide. The range of the pH at which the formation of the hydroxide of the first metal is started is not particularly limited, but is preferably, for example, greater than 2.5 and 11.0 or less.

  Such a first metal is a metal other than phosphorus, for example, at least one of iron, aluminum, nickel, cobalt, manganese, zinc, copper, magnesium, and chromium. The metal compound may contain components other than the first metal and phosphorus, such as silicic acid and sulfur.

  Also prepare a coprecipitant.

  In the present embodiment, as described above, a coprecipitant containing a second metal that starts to form a hydroxide at a pH of 2.5 or less is used. The second metal is a metal that starts to precipitate as a hydroxide when the solubility of the hydroxide becomes 0.1 mol / l or less, even when the pH of the solution is in the range of 2.5 or less. That is, the second metal is a metal whose pH at which precipitation as hydroxide starts to be lower than that of the first metal. The pH at which the formation of the second metal hydroxide is started is not particularly limited, but is preferably, for example, 1.5 or more and 2.5 or less.

  The second metal is not particularly limited as long as it starts to form a hydroxide at a pH of 2.5 or less and can precipitate while collecting phosphorus. As such a second metal, for example, at least one of titanium, zirconium, cerium, tin, niobium, tantalum, and antimony can be used. Among them, titanium, zirconium, cerium, and tin are preferable because hydroxides are easily formed stably in a pH range of 2.5 or less, and phosphorus is easily collected and precipitated. Further, it is more preferably at least one of titanium, zirconium and cerium, and more preferably titanium, because of low solubility and easy precipitation, rapid precipitation and easy filtration of the precipitate. These second metals can have a plurality of valences, but are preferably tetravalent from the viewpoint of more stably depositing phosphorus, and are preferably tetravalent titanium, tetravalent zirconium, and tetravalent zirconium. Preferably, it is at least one of cerium. Specifically, examples of the titanium (IV) compound include a titanium (IV) chloride solution (titanium tetrachloride solution) and titanium (IV) oxysulfate.n hydrate. Examples of the zirconium (IV) compound include a zirconium (IV) chloride solution (zirconium tetrachloride solution) and zirconium (IV) oxychloride octahydrate. Examples of the cerium (IV) compound include ceric ammonium nitrate (IV).

(Dissolution process)
Subsequently, the metal compound is dissolved to obtain a solution. In this solution, the first metal, phosphorus and the like derived from the metal compound are present as ions.

  The method of dissolving the metal compound is not particularly limited, but from the viewpoint of easily dissolving the metal compound, it is preferable to dissolve the metal compound and then dissolve the melt with an acid solution. Specifically, after the metal compound and the alkali salt are put in a container and mixed, the mixture is heated and heated to, for example, 800 ° C. to melt the metal compound. After allowing the obtained melt to cool to room temperature, the melt is dissolved with an acid solution to obtain a solution.

  As the alkali salt used for melting, for example, sodium peroxide, sodium carbonate, sodium nitrate, potassium disulfate and the like can be used. Among them, sodium peroxide and sodium carbonate are preferable from the viewpoint of oxidizing power. Each of these may be used alone or in combination to adjust the oxidizing power.

  As a heating method at the time of melting, for example, heating may be performed using an electric muffle furnace, a Bunsen burner, or the like.

  Further, as a container used for melting, a high-purity alumina, high-purity nickel, a crucible made of a material such as high-purity zirconia can be used, but from the viewpoint of obtaining high durability, the crucible is made of high-purity alumina. Crucibles are preferred.

  As the acid solution used for dissolving the melt, for example, hydrochloric acid, sulfuric acid, nitric acid and the like can be used. From the viewpoint of performing the reduction operation efficiently in the reduction step described below, it is preferable to use a non-oxidizing acid such as hydrochloric acid in the dissolving step, rather than an oxidizing acid such as nitric acid or sulfuric acid.

  In addition, when an undissolved residue is generated without dissolving the melt, it is preferable to heat the mixture of the melt and the acid solution at a low temperature to promote the dissolution. In addition, when the first metal constituting the metal compound contains silicic acid, particularly when the first metal is contained at a high concentration, a gel-like silicic acid compound may be formed, and the melt may not be sufficiently dissolved. In this case, the melt may be dissolved while cooling the mixture of the melt and the acid solution in, for example, a water bath.

(Reduction process)
Subsequently, a reduction treatment is performed on the obtained solution. Specifically, a reducing agent is added to the solution and the mixture is heated until the color no longer changes. According to this reduction treatment, the range of the pH at which the first metal starts to precipitate can be changed to a higher pH side, so that the precipitation of the first metal can be suppressed in the later-described precipitation step. This will be specifically described below.

  In the solution, the first metal, phosphorus, and the like derived from the metal compound are dissolved and exist as ions. If the first metal contains a metal having a plurality of valences, such as iron or nickel, a plurality of ions having the same valence but different valences exist in the solution. For example, iron and nickel are present in the form of divalent or trivalent metal ions. Such a metal ion having a different valence has a different pH range at which precipitation starts depending on the valence, even if the kind of metal is the same. For example, trivalent iron ions are present as ions when the pH of the solution is less than 2.0, but begin to precipitate by forming hydroxides in the range of 2.0 or more. On the other hand, divalent iron ions exist as ions when the pH is less than 6.0, but start to precipitate when the pH is in a range of 6.0 or more. That is, trivalent iron ions are more likely to precipitate at a lower pH than divalent iron ions. Such a metal ion that easily precipitates at a low pH may precipitate together with phosphorus in a precipitation step described below, impeding coprecipitation separation by a coprecipitant, and possibly lowering the quantification accuracy. In particular, among the first metal ions, iron ions form hydroxides in a wide pH range and easily precipitate, which greatly affects the determination accuracy of phosphorus. In this regard, a reduction step is provided before the precipitation step to reduce the first metal ion derived from the first metal, for example, to make trivalent metal ions divalent and tetravalent metal ions trivalent. Thereby, the precipitation of the first metal in the precipitation step can be suppressed, and the quantification accuracy can be kept high.

  As the reducing agent, those having a necessary reducing power according to the type and content of the coexisting element may be used, such as sodium hydrogen sulfite, sodium sulfite, ascorbic acid, or a hydrazine compound having a strong reducing power. Can be used.

(Precipitation step)
Subsequently, a coprecipitant is added to the solution after reduction. In the present embodiment, as described above, the coprecipitant containing the second metal is used. Further, a buffer is added to the solution, and the pH is adjusted to a range of 2.5 or less, preferably 1.5 to 2.5. As a result, the second metal contained in the coprecipitant forms a hydroxide while trapping phosphorus in the solution, and the hydroxide precipitates in the solution. This precipitate is composed of a hydroxide of a second metal containing phosphorus. For example, when the second metal is titanium or the like, it exhibits white, and when it is cerium or the like, it exhibits yellow. The solution also contains first metal ions derived from the first metal, but these metal ions are less likely to form hydroxides in the pH range of 2.5 or less, and are therefore less likely to precipitate as hydroxides.

  In the precipitation step, after adjusting the pH of the solution, a coprecipitant may be added.

  As the buffer, conventionally known buffers can be used. For example, an aqueous acetic acid solution or a mixed solution of acetic acid and sodium acetate can be used. The pH of the solution may be finely adjusted by adding, for example, hydrochloric acid or sodium hydroxide solution.

(Preparation process)
Subsequently, a precipitate of hydroxide precipitated in the solution is separated and collected. An acid solution is added to the resulting precipitate and heated at low temperature. Thus, the precipitate is dissolved to obtain a solution in which phosphorus and the second metal are dissolved. Next, an internal standard solution containing yttrium, which is an internal standard substance (also referred to as an internal standard substance), is added to the solution, and the volume is adjusted to prepare a measurement solution.

  As the acid solution for dissolving the precipitate in the preparation step, sulfuric acid can also be used, but from the viewpoint of reducing the load on the analyzer in the quantification step described below, a mixed solution containing hydrochloric acid, nitric acid and aqueous hydrogen peroxide is used. It is preferable to use

  In the preparation step, the solution is preferably heated at a low temperature before separating and collecting the precipitate, and the precipitate is preferably heated and aged. The separation and collection may be performed by a known method such as suction filtration. In addition, as a filter paper used at the time of filtration, for example, a normal quantitative filter paper, a cellulose acetate filter paper, a hydrophilic PTFE filter paper, or the like may be used. From the viewpoint of convenience in dissolving the precipitate, it is preferable to use hydrophilic PTFE filter paper. The separated and collected precipitate may be washed, for example, with pure water 5 or 6 times.

(Analysis process)
Subsequently, the measurement solution is introduced into the analyzer to determine phosphorus. The method for determining phosphorus is not particularly limited, and may be determined by a known method such as an absolute calibration curve method, a standard addition method, or an internal standard method. When a large amount of coprecipitant is added in the above-mentioned precipitation step, the absolute calibration curve method and the internal standard method use the same amount as the amount contained in the standard solution for preparing the calibration curve to further improve the measurement accuracy. A matrix matching method (also called an equal composition method) for adjusting the composition of the solution by adding an amount of a coprecipitant may be applied.

  The analyzer is not particularly limited as long as it can quantify phosphorus, and an ICP emission analyzer, an ICP mass spectrometer, a flame atomic absorption device, a flameless atomic absorption device, a spectrophotometer, and the like can be used. . Among them, an ICP emission spectrometer is preferable because a trace amount of phosphorus can be easily and accurately quantified.

  As described above, the amount of phosphorus contained in the metal compound can be determined.

<Effects according to the present embodiment>
According to the present embodiment, one or more of the following effects can be obtained.

(A) In the present embodiment, hydroxide formation is started in a solution in which a metal compound containing a first metal and phosphorus having a pH at which hydroxide formation is started is larger than 2.5 and phosphorus is dissolved. A coprecipitant containing a second metal having a pH of 2.5 or less is added, and the pH of the solution is adjusted to 2.5 or less. Thereby, while suppressing precipitation of the first metal contained in the metal compound, phosphorus contained in the metal compound can be collected and precipitated as a hydroxide of the second metal. By measuring the content of phosphorus contained in the precipitate of the hydroxide, the amount of phosphorus contained in the metal compound can be accurately determined. In addition, since the collection of metals other than phosphorus can be suppressed, even a trace amount of phosphorus can be accurately quantified.

(B) In the present embodiment, before performing the precipitation step by adding the coprecipitant to the solution in which the metal compound is dissolved, a reducing agent is added to the solution to reduce metal ions contained in the solution. . Thereby, among the first metal ions, metal ions that form hydroxides and easily precipitate in the range of pH 2.5 or less can be reduced to metal ions that do not precipitate in the range of pH 2.5 or less. . For example, trivalent iron ions can be reduced to divalent iron ions. As a result, even if the pH is adjusted to 2.5 or less in the precipitation step, precipitation of metal ions other than phosphorus can be suppressed, and the accuracy of phosphorus quantification can be improved.

(C) In the precipitation step, the pH of the solution is preferably adjusted to 1.5 or more and 2.5 or less. By adjusting the pH to such a range and collecting phosphorus with a coprecipitant, it is possible to collect phosphorus present in the solution at a higher recovery rate than in the case where the pH is adjusted to a range other than the above range. Can be precipitated.

  This will be specifically described with reference to FIG. FIG. 1 is a diagram showing the change in the amount of phosphorus collected by the pH of the coprecipitant. The horizontal axis indicates the pH of the solution, and the vertical axis indicates the amount of phosphorus collected by the coprecipitant [mmol / g]. Is shown. The square plot (□) indicates the amount collected when titanium hydroxide (IV) was used as the coprecipitant, and the circle plot (○) indicates the amount collected when zirconium hydroxide (IV) was used. The asterisk plot (*) indicates the amount collected when cerium (IV) hydroxide was used.

In FIG. 1, the collection amount of titanium hydroxide (IV) was measured by the following procedure.
Specifically, first, about 0.33 g (about 0.08 g of titanium) of a titanium (IV) chloride solution (titanium tetrachloride solution) was collected in a 300 ml beaker with a Komagome pipette, and dissolved in 200 ml of pure water. Next, the pH was adjusted to a predetermined value using a sodium hydroxide solution and hydrochloric acid to produce about 0.2 g of a white precipitate of titanium (IV) hydroxide, which was used as a test solution. Next, 0.4 ml of a 1 mol / l solution of phosphorus (ammonium dihydrogen phosphate) was added to the test solution, and the mixture was reacted at room temperature for 24 hours or more with stirring. Finally, after the final pH of the test solution was measured, the precipitate was sedimented, and the amount of phosphorus collected in the precipitate was measured by analyzing the residual phosphorus concentration of the collected supernatant by ICP emission spectrometry. This measurement was repeated by adjusting the amounts of sodium hydroxide and hydrochloric acid to change the pH, and the amount of phosphorus collected by the titanium (IV) hydroxide at each pH was determined.

The amount of zirconium hydroxide (IV) collected was measured in the same manner as described above.
Specifically, about 0.39 g (about 0.11 g as zirconium) of zirconium (IV) oxychloride octahydrate was collected in a 300 ml beaker and dissolved in 200 ml of pure water. Next, the pH was adjusted to a predetermined value using a sodium hydroxide solution and hydrochloric acid to produce about 0.2 g of a white precipitate of zirconium (IV) hydroxide, which was used as a test solution. Then, by performing the same operation as described above, the amount of phosphorus collected at each pH of zirconium (IV) hydroxide was determined.

The amount of cerium (IV) hydroxide collected was measured in the same manner as described above.
Specifically, about 0.53 g (about 0.13 g as cerium) of diceric ammonium (IV) nitrate was collected in a 300 ml beaker and dissolved in 200 ml of pure water. Next, the pH was adjusted to a predetermined value using a sodium hydroxide solution and hydrochloric acid to produce about 0.2 g of a yellow precipitate of cerium (IV) hydroxide, which was used as a test solution. Then, by performing the same operation as described above, the amount of phosphorus collected at each pH of cerium (IV) hydroxide was determined.

  As shown in FIG. 1, it can be confirmed that according to the coprecipitant of the present embodiment, the amount of trapped phosphorus can be increased even when the pH is in the range of 1.5 to 2.5. In particular, when titanium hydroxide was used, the trapping amount was 2.0 mmol / g, and it was confirmed that the phosphorus recovery rate was 100%. As described above, by adjusting the pH of the solution to 1.5 to 2.5, phosphorus can be collected from the metal compound at a high recovery rate and quantified with higher accuracy. In addition, when the concentration of the second metal contained in the coprecipitant was measured in a test solution in which the pH was adjusted to about 2.0 by adding the coprecipitant, the titanium concentration was <1 mg / l and the zirconium concentration was 55 mg. / L, the cerium concentration was 68 mg / l, and it was confirmed that these metals were precipitated without being dissolved. That is, these second metal hydroxides are hardly dissolved even in a low pH range, and are excellent in acid resistance. Among these, hydroxides of titanium are particularly excellent in acid resistance.

(D) The second metal contained in the coprecipitant is preferably at least one of titanium, zirconium, cerium, tin, niobium, tantalum and antimony. Among them, a tetravalent metal is more preferable, and at least one of tetravalent titanium, tetravalent zirconium and tetravalent cerium is more preferable. According to such a coprecipitant containing the second metal, the hydroxide is easily formed stably in the pH range of 2.5 or less, and the phosphorus is easily collected and precipitated. Can be higher.

(E) The first metal constituting the metal compound is at least one of iron, aluminum, nickel, silicate, sulfur, cobalt, manganese, zinc, copper, magnesium and chromium, and contains at least iron. Since iron easily forms a hydroxide in a wide pH range and precipitates, it is impossible to accurately determine phosphorus in a metal compound containing iron. In this regard, in this embodiment, a coprecipitant that forms a hydroxide and easily precipitates even in the range of pH 2.5 or less is used, and the pH of the solution is set to 2.5 or less, so that iron ions can be converted to water. Phosphorus contained in the solution can be trapped and precipitated as hydroxide while suppressing trapping as oxide. That is, phosphorus can be concentrated and collected, and can be accurately quantified.

(F) The acid solution for dissolving the phosphorus-containing hydroxide precipitated by the coprecipitant is preferably dissolved in a mixed solution containing hydrochloric acid, nitric acid and hydrogen peroxide. According to such an acid solution, the viscosity of the finally obtained measurement solution can be kept lower than in the case of using sulfuric acid. Thereby, the efficiency of introduction of the measurement solution into the measurement unit of the analytical instrument, for example, does not significantly impair the spray efficiency when introduced by spraying, so it is possible to suppress a decrease in measurement accuracy due to a decrease in the introduction efficiency. it can.

(G) Further, by using a coprecipitant, it is possible to use an organic solvent having toxicity or a low flash point as compared with, for example, the case where phosphorus is solvent-extracted from a metal compound using an organic solvent. Since there is no such information, work safety can be ensured.

<Another embodiment of the present invention>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  In the above embodiment, the case where the amount of phosphorus contained in the solution in which the metal compound is dissolved is determined as the solution has been described, but the present invention is not limited to this. For example, as a solution, wastewater containing at least a first metal at which formation of hydroxide is started and having a pH of more than 2.5 and phosphorus, and wastewater discharged in the process of manufacturing an electrode material for a lithium ion battery Can be quantified.

  When quantifying phosphorus contained in these wastewaters, the wastewater is subjected to a reduction treatment by adding a reducing agent as necessary, and then, as described above, a precipitation step, a preparation step, and a quantification step are performed. Good.

  The preferred embodiments of the present invention are as follows.

  A preparing step of preparing a metal compound containing a first metal having a pH at which formation of hydroxide is greater than 2.5 and phosphorus, and a dissolving step of dissolving the metal compound to obtain a solution; By adding to the solution a coprecipitant containing a second metal whose pH at which hydroxide formation is initiated is 2.5 or less, and adjusting the pH of the solution to 2.5 or less, A precipitating step of precipitating the second metal hydroxide, comprising: separating and collecting the second metal hydroxide and dissolving it in an acid solution to prepare a measurement solution; A method for quantifying phosphorus in a metal compound, comprising: a quantification step of quantifying phosphorus contained.

  A preparing step of preparing wastewater containing a first metal and phosphorus whose pH at which hydroxide formation is started is larger than 2.5; and a pH at which hydroxide formation is started in the solution as the wastewater. A coprecipitant containing a second metal of 2.5 or less is added, and the pH of the solution is adjusted to 2.5 or less to precipitate a hydroxide of the second metal containing phosphorus. A step of preparing a measurement solution by separating and collecting the hydroxide of the second metal and dissolving it in an acid solution, and a quantification step of quantifying phosphorus contained in the measurement solution. This is a method for determining phosphorus in a compound.

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

<Example 1>
In this example, a measurement solution was prepared according to the flow shown in FIG. 2, and the amount of phosphorus contained in the metal compound was determined.

(Preparation of measurement solution)
Specifically, first, a metal compound having a matrix composition as shown in Table 1 below was prepared as an analysis target. As shown in Table 1, the metal compound contains Fe, Mg, Ni, or the like as a main component as a first metal having a pH at which formation of a hydroxide is started and is higher than 2.5.

  In this example, this metal compound was processed in the following manner in parallel with three samples to prepare samples 1 to 3. First, 0.5 g of this metal compound was weighed and added to a high-purity alumina crucible. In addition, 2.5 g of sodium peroxide and 2.5 g of sodium carbonate were weighed as alkali salts, and added and mixed in a crucible. Thereafter, the mixture was heated to melt the metal compound.

  Next, after the crucible was cooled to room temperature, it was transferred to a 300 ml beaker, and 100 ml of warm water and 30 ml of hydrochloric acid were added, and the melt was sufficiently dissolved by heat of neutralization. At this time, when there is an undissolved residue, heating was performed at a low temperature of 80 ° C to 120 ° C. When the metal compound contained a high concentration of silicic acid, the melt was dissolved while cooling the beaker in a water bath.

  Next, the obtained solution was cooled, and the crucible was taken out from the beaker and washed. Thereafter, 2 g of sodium bisulfite as a reducing agent was added to the solution, and the solution was heated until its color did not change, thereby performing a reduction treatment.

  Next, after the solution subjected to the reduction treatment was cooled again, 10 ml of a titanium tetrachloride solution containing titanium tetrachloride as a coprecipitant (containing 1 g / l as titanium) was added, and sufficiently stirred. Subsequently, 5 ml of acetic acid (acetic acid (1 + 10)) diluted 11-fold was added as a buffer, and 15 ml of a 50% sodium hydroxide solution was added to roughly adjust the pH. The pH was finely adjusted to a range of 1.5 to 2.5 using hydrochloric acid (hydrochloric acid (1 + 1)) diluted twice and a 25% sodium hydroxide solution. This produced a white precipitate (hydroxide).

  Next, the resulting white precipitate was heated and aged in the range of 80 ° C to 120 ° C for 30 minutes or more. Thereafter, suction filtration was performed using hydrophilic PTFE filter paper (pore diameter (grain size: 0.1 μm, diameter: 47 mm)) to separate and collect a white precipitate, which was washed 5 or 6 times with pure water. The filtered white precipitate was transferred to a beaker together with filter paper, and 8 ml of hydrochloric acid, 4 ml of nitric acid, and 2 ml of hydrogen peroxide solution were added as an acid solution, and the mixture was heated at 120 ° C. to dissolve the white precipitate. The solution of the precipitate was transferred to a polypropylene container, 0.2 ml of an yttrium solution (1 g / l) for the internal standard method was added, and the volume was adjusted to 20 ml with pure water, whereby the measurement solution of Example 1 was used. Obtained.

  In this example, apart from the samples 1 to 3, phosphorus-added samples 4 and 5 were prepared as samples for evaluating the recovery rate of phosphorus. Specifically, first, 0.2 ml (a phosphorus equivalent to 20 μg) of a phosphorus standard solution having a concentration of 100 mg / L was added to a high-purity alumina crucible, dried at 60 ° C., and then cooled. Subsequently, a metal compound is weighed into a crucible containing dried phosphorus according to the flow shown in FIG. 2 and alkali melting is performed. , 5 were produced.

  In this example, blank samples 6 and 7 for blank test were prepared separately from samples 1 to 3. Specifically, blank samples 6 and 7 were prepared by performing the same operation as the preparation of samples 1 to 3 according to the flow of FIG. 2 except that the metal compound was not weighed in the high-purity aluminum crucible.

(Phosphorus determination)
Next, each sample was introduced into an ICP emission spectrometer (ICP-OES “Agilent730-ES” manufactured by Agilent Technologies Inc.), and phosphorus contained in each sample was measured under the measurement conditions shown in Table 2 below. The measurement wavelength of phosphorus was 213.618 nm.

  The measured values of phosphorus contained in each sample are shown in Table 3 below. The measured value of phosphorus was determined using a calibration curve prepared by changing the phosphorus concentration to 0 mg / l, 0.5 mg / l, 1 mg / l, and 2 mg / l.

Next, the quantitative value of phosphorus contained in the metal compound was calculated from the measured value of phosphorus contained in each sample. Specifically, a quantitative value of phosphorus was calculated from the measured values of phosphorus of the samples 1 to 3 (sample measured values) and the measured values of phosphorus of the blank samples 6 and 7 (blank test values) by the following equation (1). . Table 3 shows the quantitative values.
(Quantitative value of phosphorus [ppm]) = {(sample measured value [mg / l])-(blank test value [mg / l])} x (constant volume [ml]) / (sample amount [g])・ ・ (1)

Further, the recovery rate of phosphorus in Example 1 was calculated. Specifically, the recovery rate of phosphorus is calculated from the phosphorus measurement value (addition measurement value) of the phosphorus-added samples 4 and 5 and the phosphorus measurement value (sample measurement value) of the samples 1 to 3 by the following formula (2). did. Table 3 shows the recovery rates.
(Recovery rate [%]) = {(addition measured value [mg / l])-(sample measurement value [mg / l])} / (addition concentration [mg / l]) × 100 (2)

<Examples 2 and 3>
In Examples 2 and 3, the measurement was performed in the same manner as in Example 1 except that the type of the coprecipitant was changed from titanium tetrachloride (IV) to zirconium oxychloride (IV) or ceric ammonium nitrate (IV). The solution was prepared, and the quantitative value of phosphorus and the recovery were calculated.

<Comparative Example 1>
In Comparative Example 1, the type of the coprecipitant was changed from titanium tetrachloride (IV) to lanthanum (III) nitrate whose pH at which hydroxide formation starts was about 8.0, and A measurement solution was prepared in the same manner as in Example 1 except that the pH at the time of precipitation was adjusted to about 10, and a quantitative value of phosphorus and a recovery rate were calculated.

<Example 4>
In Example 4, wastewater was prepared as a solution to be quantified instead of a solution in which a metal compound was dissolved. The matrix composition of the wastewater is shown in Table 4 below. As shown in Table 4, the wastewater is strongly acidic, and contains Fe, Mg, Ni, or the like as a main component as a first metal having a pH at which formation of a hydroxide is started and is larger than 2.5.

  In this example, the preparation step and the dissolution step in Example 1 were omitted, 200 ml of the prepared wastewater was collected in a 300 ml beaker, 2 g of sodium bisulfite as a reducing agent was added to the solution, and the color of the solution was changed. The reduction treatment was performed by heating until no more change occurred. Thereafter, measurement solutions were prepared in the same manner as in Example 1 to prepare Samples 1 to 3.

  In this example, apart from the samples 1 to 3, phosphorus-added samples 4 and 5 were prepared as samples for evaluating the recovery rate of phosphorus. Specifically, 0.2 ml (a phosphorus equivalent to 20 μg) of a phosphorus standard solution having a concentration of 100 mg / l was added to a 300 ml beaker, and the same operation as in the preparation of samples 1 to 3 was performed. Was prepared.

  In this example, blank samples 6 and 7 for blank test were prepared separately from samples 1 to 3. Specifically, except that pure water was used instead of collecting wastewater, the same operation as in the preparation of samples 1 to 3 was performed, and blank samples 6 and 7 were prepared.

  Subsequently, in the same manner as in Example 1, phosphorus contained in each of the obtained specimens was measured. The measured values of phosphorus contained in each sample are shown in Table 5 below.

  Subsequently, in the same manner as in Example 1, the quantitative value of phosphorus contained in the waste liquid and the recovery rate of phosphorus were calculated from the measured values of phosphorus contained in each sample. Table 5 shows the respective numerical values. In Example 4, since the final constant volume is 20 ml with respect to the sample amount of wastewater of 200 ml, the concentration of phosphorus is 10 times that of the original wastewater.

<Examples 5 and 6>
In Examples 5 and 6, the measurement was performed in the same manner as in Example 4 except that the type of the coprecipitant was changed from titanium tetrachloride (IV) to zirconium oxychloride (IV) or ceric ammonium nitrate (IV). The solution was prepared, and the quantitative value of phosphorus and the recovery were calculated.

<Comparative Example 2>
In Comparative Example 2, the type of the coprecipitant was changed from titanium tetrachloride (IV) to lanthanum (III) nitrate whose pH at which hydroxide formation starts was about 8.0, and A measurement solution was prepared in the same manner as in Example 4 except that the pH at the time of precipitation was adjusted to about 10, and a quantitative value of phosphorus and a recovery rate were calculated.

<Evaluation results>
As shown in Table 3, according to Examples 1 to 3, it was confirmed that the amounts of phosphorus contained in the metal compounds were 9 ppm, 7 ppm, and 6 ppm, respectively. It was also confirmed that the recovery rates of phosphorus from the metal compound were 101%, 80%, and 72%, respectively. From this, it was confirmed that phosphorus was collected from the metal compound at a high recovery rate, and that the phosphorus contained in the metal compound could be accurately quantified.

  In particular, in Example 1 using the coprecipitant containing titanium, Example 2 using the coprecipitant containing zirconium, and in Example 3 using the coprecipitant containing cerium, phosphorus was removed from the metal compound. It was confirmed that phosphorus could be quantified more accurately by sampling at a higher recovery rate. The reason why the recovery of zirconium and cerium is lower than that of titanium is presumed to be that phosphorus was not completely formed in the hydroxide precipitate.

  In contrast, in Comparative Example 1, an attempt was made to prepare a measurement solution in the same manner as in Examples 1 to 3 using a coprecipitant containing lanthanum, but iron ions contained in the solution formed hydroxides. As a result, the amount of phosphorus could not be determined.

  In addition, as shown in Examples 4 to 6, it was confirmed that phosphorus can be quantified even when the quantification target is wastewater. Specifically, as shown in Table 5, it was confirmed that the amounts of phosphorus contained in the wastewater were 0.015 mg / l, 0.012 mg / l, and 0.010 mg / l, respectively. Further, it was confirmed that the recovery rates of phosphorus from the wastewater were 100%, 86%, and 74%, respectively. From this, it was confirmed that phosphorus was collected from the wastewater at a high recovery rate, and it was confirmed that the phosphorus contained in the wastewater could be accurately quantified. In addition, the recovery rates of phosphorus for each coprecipitant were also measured in Examples 1 to 3. The same tendency as in the case of the metal compound was obtained.

  On the other hand, in Comparative Example 2, the measurement solution was prepared in the same manner as in Examples 4 to 6 using the coprecipitant containing lanthanum. Was formed and a large amount of precipitate was formed, so that the amount of phosphorus could not be determined.

As shown in Tables 6 and 7 below, the lower limit of quantification of phosphorus was determined to be up to 2.3 ppm in Examples 1 and 2 and 1.8 ppm in Example 3 after performing 10 blank tests. In Example 5, it was confirmed that up to 0.004 mg / l, in Example 5, up to 0.006 mg / l, and in Example 6, up to 0.007 mg / l. Regarding the lower limit of phosphorus quantification, Examples 1 to 3 were calculated based on the following equation (3), and Examples 4 to 6 were calculated based on the following equation (4).
(Quantification lower limit [ppm]) = {10 × (standard deviation σ) [mg / l]} × (constant volume [ml]) / (sample amount [g]) (3)
(Lower limit of quantification [mg / l]) = {10 × (standard deviation σ) [mg / l]} × (constant volume [ml]) / (sample amount [ml]) (4)

As described above, to the solution in which the metal compound is dissolved, a coprecipitant containing a second metal that starts to form hydroxide in the range of pH 2.5 or less is added, and the pH of the solution is adjusted to 2.5. By adjusting as follows, phosphorus contained in the metal compound can be precipitated as a hydroxide while suppressing precipitation of the metal component derived from the metal compound. Thereby, even if the amount of phosphorus contained in the metal compound is very small, it can be accurately determined. Further, similarly to the solution of the metal compound, even in the wastewater containing the first metal and phosphorus, the amount of phosphorus can be accurately determined.

Claims (15)

A method for quantifying phosphorus in a solution in which phosphorus and a first metal having a pH at which hydroxide formation is started is greater than 2.5 and phosphorus is dissolved,
By adding to the solution a coprecipitant containing a second metal whose pH at which hydroxide formation is initiated is 2.5 or less, and adjusting the pH of the solution to 2.5 or less, A precipitation step of precipitating the second metal hydroxide comprising:
A preparing step of separating and collecting the second metal hydroxide and dissolving it in an acid solution to prepare a measurement solution;
And a quantification step of quantifying phosphorus contained in the measurement solution,
Method for determining phosphorus in solution. Before the precipitation step,
A preparing step of preparing a metal compound containing the first metal and phosphorus;
Dissolving the metal compound to obtain the solution,
The method for determining phosphorus in a solution according to claim 1. Before the precipitation step, the method has a preparation step of preparing a wastewater containing the first metal and phosphorus as the solution,
The method for determining phosphorus in a solution according to claim 1. The second metal is at least one of titanium, zirconium, cerium, tin, niobium, tantalum and antimony;
The method for quantifying phosphorus in a solution according to claim 1. The second metal is a tetravalent metal;
The method for quantifying phosphorus in a solution according to claim 1. The second metal is at least one of tetravalent titanium, tetravalent zirconium, and tetravalent cerium;
The method for determining phosphorus in a solution according to claim 5. In the precipitation step, the pH of the solution is adjusted to 1.5 or more and 2.5 or less,
A method for determining phosphorus in a solution according to any one of claims 1 to 6. The first metal is at least one of iron, aluminum, nickel, cobalt, manganese, zinc, copper, magnesium and chromium;
A method for quantifying phosphorus in a solution according to any one of claims 1 to 7. The first metal includes at least iron;
The method for quantifying phosphorus in a solution according to claim 1. The acid solution used in the preparation step is a mixed solution containing hydrochloric acid, nitric acid and hydrogen peroxide solution,
A method for quantifying phosphorus in a solution according to any one of claims 1 to 9. Before the precipitation step, a reducing agent is added to the solution, and a reduction step of reducing metal ions contained in the solution is provided.
A method for determining phosphorus in a solution according to any one of claims 1 to 10. The reducing agent is sodium bisulfite,
A method for determining phosphorus in a solution according to claim 11. In the dissolving step, the metal compound is melted with an alkali salt, and the obtained melt is dissolved in an acid solution.
The method for determining phosphorus in a solution according to claim 2. The alkali salt is at least one of sodium peroxide and sodium carbonate;
The method for determining phosphorus in a solution according to claim 13. In the quantifying step, phosphorus contained in the solution is quantified using any one of an ICP emission spectrometer, an ICP mass spectrometer, a flame atomic absorption device, a flameless atomic absorption device, and a spectrophotometer. ,
A method for quantifying phosphorus in a solution according to any one of claims 1 to 14.