JP4608612B2 - Method and apparatus for measuring iron sulfide content in solid components - Google Patents

Description

The present invention relates to a method and an apparatus for measuring the content of iron sulfide in a solid component.
The present invention relates to a method that can be measured at a measurement site and that can accurately measure the iron sulfide content in a solid component that causes sludge in a short time, and the measurement apparatus.

In the inner bay where the tidal current is poor, bottom mud tends to accumulate on the sea bottom surface layer of the inner bay, and oxygen-free water is generated above the accumulated sludge. These bottom mud and generated oxygen-free water diffuse into the bay due to storms, wind and rain, etc., causing serious environmental pollution such as marine product damage. Especially in recent years, the damage of this sludge and oxygen-free water has been increasing.
For this reason, it is required to quickly grasp the state of sludge contamination on the bottom surface layer in the above-mentioned inner bay, sea, lakes and rivers.

Since sludge is mainly composed of organic compounds, methods for measuring the concentration of organic substances, such as chemical oxygen demand COD measurement, have been carried out in order to grasp the sludge contamination state on the bottom surface layer.
However, this COD measurement has a problem that it takes a sample taken at a measurement point, requires a measurement time of about two weeks, and is an expensive measurement method.

In order to solve the above-mentioned problems, the applicant of the present application has created a method for measuring the degree of contamination by sludge that can be measured at a measurement site and is simple and low-cost in a short time (for example, patent document). 1).
The invention of this Patent Document 1 uses a measuring device (twin electrode) having two electrodes, and measures the iron ion concentration by the chronoamperometry method, thereby causing sludge contamination (sludge contamination) of water and seawater. It is invention of the method of measuring. Further, the applicant of the present application has created a measurement method for measuring the molar fraction and concentration of an electrochemically active substance in a solution using a twin electrode, and a measurement program by a computer used in this measurement method (patent) Reference 2).

  However, in the inventions described in the above cited references 1 and 2, the value of the chemical oxygen demand CODSED, which is an indicator of the degree of contamination at the measurement site, is estimated from the iron ions (electrochemically active substances) in the sample solution. This method has the problem that it is not possible to measure the weight percent in iron sulfide (FeS) samples (especially in solid components) that are the direct cause of contamination and the black color of sludge. It was.

JP 2003-50228 A JP 2003-65995 A

The present invention has been made in view of such circumstances, and can be measured at a measurement site, and can be measured in a short time, easily and at low cost, and the content of iron sulfide in a solid component (in a collected sample) that causes sludge. Provided are a method and a measuring apparatus for accurately measuring the temperature.

The invention according to claim 1 is a method for measuring the iron sulfide content in a solid component, wherein the first electrical conductivity k ₁ which is the electrical conductivity of a dispersion medium in which the solid is dispersed is measured, and the dispersion The second electrical conductivity k ₂ , which is the electrical conductivity of the suspension in which the solid is dispersed in the medium, is measured, and the first and second electrical conductivities (k ₁ and k ₂ ) are used for the suspension. Calculate the volume percentage x of the solid, measure the iron ion concentration w of the suspension by chronoamperometry, and calculate the weight percentage y of iron sulfide to the suspension from the iron ion concentration w. , solid component, which comprises calculating the iron sulfide content z (= y / x) by the ratio of the weight percentages y of the iron sulfide relative to the suspension and the volume percentage x of the solid relative to the suspension A method for measuring the iron sulfide content of is provided.

  When measuring the iron ion concentration w, the invention according to claim 2 includes a working electrode composed of a first working electrode and a second working electrode, which are opposed to each other with a distance d, a reference electrode, and a counter electrode. The method for measuring the iron sulfide content in the solid component according to claim 1, wherein a measuring device is used.

The invention according to claim 3 is characterized in that the volume percentage x of the solid with respect to the suspension is obtained from the first and second electric conductivities (k ₁ and k ₂ ) by the following equation (Equation 1). The measuring method of the iron sulfide content rate in the solid component of Claim 1 is provided.

The invention according to claim 4 calculates the solid (weight / volume) percentage v of the solid with respect to the suspension from the first and second electrical conductivities (k ₁ and k ₂ ) according to the following equation (Equation ₂ ): of the solid relative to the suspension (weight / volume) percentage v and the solids from the density d of the iron sulfide content according to claim 1, wherein the determination of the capacity percentage x of the solid relative to the suspension Provide a measuring method.

The invention according to claim 5 is characterized in that the weight percentage y of the iron sulfide with respect to the suspension is obtained from the iron ion concentration w by the following formula (Equation 3). A method for measuring iron sulfide content is provided.

The invention of claim 6, wherein, there is provided a device for measuring the iron sulfide content in the solid component, the first measurement for measuring a first electrical conductivity k ₁ is an electric conductivity of the dispersion medium for dispersing the solid Means, a second measuring means for measuring a second electrical conductivity k ₂ which is an electrical conductivity of a suspension obtained by dispersing the solid in the dispersion medium, and the first and second electrical conductivities (k _1). And k ₂ ), a first computing means for calculating the volume percentage x of the solid relative to the suspension, a third measuring means for measuring the iron ion concentration w of the suspension by chronoamperometry, a second calculating means for calculating the weight percentage y of iron sulfide relative to the suspension from the iron ion concentration w, the weight percentages y of the iron sulfide relative to the suspension and the volume percentage x of the solid relative to the suspension A third calculating means for calculating the iron sulfide content z (= y / x) by the ratio of An apparatus for measuring the content of iron sulfide in a solid component is provided.
By providing these inventions, the above problems can be solved.

By the measuring method provided by the present invention, a method for accurately measuring the iron sulfide content in a solid component (in a collected sample) that can be measured at a measurement site, in a short time and at a low cost, and that causes sludge. Can be provided.

An apparatus for accurately measuring the content of iron sulfide in a solid component (in a collected sample) that can be measured in a short time, in a short time, at a simple and low cost by the measuring apparatus provided by the present invention. Can be provided.

Embodiments of the present invention will be described with reference to the drawings.
The structure of the sensor (10) used by this invention is demonstrated referring drawings.
FIG. 1 is a schematic view of a measuring apparatus used in the present invention, FIG. 2 is a view showing a working electrode, (a) is an exploded view thereof, and (b) is a sectional side view of the working electrode. (C) is a plan view of the working electrode.
The sensor (10) used in the present invention includes a working electrode (11), a reference electrode (12), and a counter electrode (13).
As shown in FIG. 1, the working electrode (11) includes a first working electrode (11a), a second working electrode (11b), and a spacer (11c). The first working electrode (11a) and the second working electrode (11b) have the same shape as shown in FIG.
The material of the first and second working electrodes (11a) and (11b) is not particularly limited, and it is preferable to use a platinum plate.
The spacer (11c) is not particularly limited as long as it is an insulating material, and the shape of the spacer (11c) is configured such that the measurement liquid can freely enter and exit between the first working electrode (11a) and the second working electrode (11b). It does not matter as long as the distance between the first working electrode (11a) and the second working electrode (11b) and the working area can be kept constant. The material of the spacer (11c) is not particularly limited, and may be polypropylene, polytetrafluoroethylene, phenol resin, or the like.
The distance d between the first working electrode (11a) and the second working electrode (11b) and the working area A are appropriately set in consideration of easiness of entering and exiting the measurement liquid, accuracy of measurement of the electrode current value, and the like. The distance d is 50 to 1000 μm, more preferably 100 to 600 μm, and the working area A (actually the opening area of the spacer) may be 1 to 100 cm ² .
As a method of feeding the measurement liquid between the first and second working electrodes (11a) and (11b), the sensor (10) may be simply immersed in the liquid, and the sensor (10) is accommodated in a case. Forcibly sending and discharging using a pump may be used.

  The first working electrode (11a), the second working electrode (11b), the reference electrode (12), and the counter electrode (13) are connected to the potentiostat (3), and the first working electrode (11a), the second working electrode (11b) are set to independent potentials.

  The reference electrode (12) is not particularly limited as long as it is an electrode used as a reference electrode in the electrochemical technical field, and a calomel electrode is preferably used. The counter electrode (13) is not particularly limited as long as it is an electrode generally used in the electrochemical technical field, but a platinum electrode is preferably used.

A measurement method according to the present invention will be described.
A solid containing iron sulfide and a dispersion medium for dispersing the solid are prepared. In actual measurement, seawater containing sludge (seawater at the measurement site) may be collected.
First, a first electrical conductivity k ₁ that is an electrical conductivity of a dispersion medium in which a solid containing iron sulfide is dispersed is measured. The method for measuring the first electrical conductivity k ₁ is not particularly limited, but may be measured using a Kohlrausch bridge.
Next, the second electrical conductivity k ₂ that is the electrical conductivity of the dispersion medium in which the solid containing iron sulfide is dispersed is measured. The method of measuring the electrical conductivity k ₂ is not particularly limited, but may be measured using a Kohlrausch bridge as in the case of measuring the first electrical conductivity k ₁ .
From the first and second electric conductivities (k ₁ and k ₂ ), the volume percentage x of the solid with respect to the suspension is obtained by the formula (Equation 4).

Further, the method from the first conductivity k ₁ and the second conductivity k ₂ solid for suspension using equation (5) (weight to determine the capacity percentage x of the solid relative to the suspension The volume percentage x of the solid to the suspension is determined from the (weight / volume) percentage v of the solid for this suspension and the density d of the solid.

この式（数５）に示される比例定数Ａは、懸濁液中の電気伝導率及び固体画分容量から求められる定数である。図３は、懸濁液中の電気伝導率比（分散媒の電気伝導率k ₁ 、分散媒を使用して固体を懸濁させた懸濁液の電気伝導率k ₂ ）及び液体画分容量の関係を示すグラフであり、縦軸に電気伝導率比、横軸に固体画分容量の容量比（懸濁液に対する固体の（重量／容量）百分率）を示している。図３から判断すると、電気伝導率比と懸濁液に対する固体の（重量／容量）百分率との間には、式（数５）で示される如く、懸濁液に対する固体の（重量／容量）百分率が増加するにともない電気伝導率比が低下する関係が得られる。
尚、式（数５）の比例定数Ａは、約−０．０１８であるが、この比例定数Ａは、−０．０２〜−０．０１の範囲の定数である。
また、懸濁液に対する固体の（重量／容量）百分率ｖから固体の密度ｄにより懸濁液に対する固体の容量百分率ｘを求める方法は、懸濁液に対する固体の（重量／容量）百分率ｖに密度ｄの逆数を掛け合わせることによって、懸濁液に対する固体の容量百分率ｘを求める（ｘ＝ｖ／ｄ）。

The proportionality constant A shown in this equation (Equation 5) is a constant determined from the electrical conductivity in the suspension and the solid fraction volume. FIG. 3 shows the electrical conductivity ratio in the suspension (the electrical conductivity k _{1 of} the dispersion medium, the electrical conductivity k _{2 of} the suspension obtained by suspending the solid using the dispersion medium) and the liquid fraction volume. The vertical axis represents the electric conductivity ratio, and the horizontal axis represents the volume ratio of the solid fraction volume (percentage of solid (weight / volume) relative to the suspension ). Judging from FIG. 3, between the electrical conductivity ratio and the (weight / volume) percentage of solid to suspension, the solid (weight / volume) to suspension , as shown in equation (5) A relationship is obtained in which the electrical conductivity ratio decreases as the percentage increases.
In addition, although the proportionality constant A of Formula (Formula 5) is about -0.018, this proportionality constant A is a constant in the range of -0.02 to -0.01.
The density method, the (weight / volume) percent v solid for suspension to obtain a weight / volume percentage v of the solid with respect to the suspension by density d of the solid from the capacitance percentage x of the solid with respect to the suspension Multiply the reciprocal of d to determine the volume percentage x of the solid to the suspension (x = v / d).

Next, the iron ion concentration w of the suspension is measured by the chronoamperometry method.
First, the first and second working electrodes (11a) (11a) such that the electrode potentials of the first working electrode (11a) and the second working electrode (11b) with respect to the reference electrode (12) become the first potential E ₁ (V). 11b) and a counter electrode (13) are loaded with a voltage for a first predetermined time.
The electrode potential (first working electrode and second working electrode) is set to the second potential E ₂ (V) for a second predetermined time.
Next, the electrode potential of the first working electrode (11a) is set to the iron ion oxidation potential E ₃ (V), and the electrode potential of the second working electrode (11b) is set to the iron ion reduction potential E ₄ (V) simultaneously. change.
At this time, the electrode current value (second electrode current I) is detected in any of the following cases.
When the second potential E ₂ is the oxidation potential of iron ions, the reduced iron ions generated at the second working electrode (11b) diffuse and move to reach the first working electrode (11a) and are oxidized. When the second electrode current I (A) generated by becoming iron oxide ions or the second potential E ₂ is the reduction potential of the iron ions, it is generated at the first working electrode (11b). Iron oxide ions diffuse and move to the second working electrode (11b), reach the second working electrode (11b), and are reduced to become reduced iron ions. The two-electrode current I (A) is measured.

The iron ion concentration w is obtained based on the time change of the second electrode current I (A) from the second electrode current I (A).
First, let t be the time from the start of current value measurement, and give the extreme value I (t _m ) and the extreme value I (t _m ) of the second electrode current I (A) in the graph of the relationship between I / t and t. Find the time t _m .
From this t _{m, the} diffusion coefficient D is obtained by calculation based on the following equation (Equation 6).

尚、上記した条件下で測定を行った場合に於いて、関数Ｇ（τ）が極値を取るときのτの値＝K₁は、０．１６６６７５．．．と計算され、実測においては、適宜小数点以下を切り捨て、例えばK₁＝０．１６６６７５として計算する。

When measurement is performed under the above-described conditions, the value of τ = K ₁ when the function G (τ) takes an extreme value is 0.166675. . . In the actual measurement, the decimal part is appropriately rounded down, for example, K ₁ = 0.166675.

From I (t _m ) and D, the iron ion concentration w (molar concentration) is obtained by the following equation (Equation 8).

K₂は、上記した条件下では、K₂＝０．６１６７５６．．．と計算されるが、実測においては、適宜小数点以下を切り捨て、例えばK₂＝０．６１６７５６として鉄イオン濃度wを求める。

K ₂ is K ₂ = 0.616756. . . In actual measurement, the fractional part is appropriately rounded down, and the iron ion concentration w is obtained by setting K ₂ = 0.616756, for example.

Based on the time change of the second electrode current I (A) to the second electrode current I (A), the iron ion concentration w can be obtained by other methods, and the method is described below.
The time from the start of current value measurement is t, and I (t) is differentiated twice at t, and the inflection point current value I (t _f ) at which the differential value becomes 0 and the inflection point current value I (t _f ) Find the time t _f giving.
Next, the diffusion coefficient D is obtained from t _f by calculation based on the following equation (Equation 9).

I（ｔ_f）とDとから、次式（数１１）により鉄イオン濃度w（モル濃度）を求める。

From I (t _f ) and D, the iron ion concentration w (molar concentration) is obtained by the following equation (Equation 11).

The weight percentage y of iron sulfide to the suspension is calculated from the iron ion concentration w obtained by the method described above.
The method for obtaining the iron ion concentration w is not particularly limited, but the weight percentage y of iron sulfide with respect to the suspension is obtained using the following equation (Equation 12).

The iron sulfide content z (= y / x) is calculated using the solid volume percentage x with respect to the suspension and the weight percentage y of iron sulfide with respect to the suspension determined by the above method.
The above is the method for measuring the iron sulfide content z according to the present invention.

The correlation between the first and second electric conductivities (k ₁ and k ₂ ) used in the measurement method of the present invention and the volume percentage x of the solid to the suspension is examined.
A solid containing iron sulfide and a dispersion medium for dispersing the solid are prepared. The solid was prepared by grinding iron sulfate, silicon dioxide, and alumina for 3 minutes, and the dispersion medium was a 0.5 M sodium chloride solution to which polyvinylpyrrolidone was added.
First, the first electrical conductivity k ₁ that is the electrical conductivity of the dispersion medium is measured.
Next, the solid is mixed in the dispersion medium, substituted with N _{2 for} 10 minutes, and then stirred for 5 minutes to be suspended. This suspension is injected into the sensor (10) .
A second electrical conductivity k ₂ , which is the electrical conductivity of this suspension, is measured using a Colelausch bridge.
At this time, the ratio of iron sulfide (FeS) and silicon dioxide (SiO ₂ ) to the volume percentage of the solid with respect to the suspension, and the electric conductivity ratio of the first electric conductivity k ₁ and the second electric conductivity k ₂ (k ₁ / K ₂ ) is shown in FIG.
4A shows the relationship between iron sulfide and the electrical conductivity ratio, and FIG. 4B shows the relationship between silicon dioxide and the electrical conductivity ratio.
From FIG. 4, the decreasing rate of the electrical conductivity ratio (k ₁ / k ₂ ) can be calculated. FIG. 5 shows the correlation of the electrical conductivity ratio. From these graphs, the correlation between the first and second electrical conductivities (k ₁ and k ₂ ) and the solid volume percentage x with respect to the suspension is shown below. The relationship of equation (Equation 13) is obtained.

The correlation between the first and second electrical conductivity ratio (k ₁ / k ₂ ) used in the measurement method of the present invention and the solid (weight / volume) percentage v of the suspension is examined.
As described above, the electrical conductivity ratio ( k ₁ / k ₂ ) and the (weight / volume) percentage v of the solid to the suspension increase as the (weight / volume) percentage v to the suspension increases. It is known that ( k ₁ / k ₂ ) shows a tendency of a downward slope (see FIG. 3).
Also, FIG. 6 is a graph showing the electric conductivity ratio (k ₁ / k ₂₎ of the solid relative to the suspension (weight / volume) percent of the relationship, the iron sulfide (FeS), silicon dioxide (SiO ₂₎ and iron sulfide and silicon dioxide (the mixing ratio of 1: 9) shows the case of each of the mixtures.
From FIG. 6, the electric conductivity ratio and a suspension for the solid (weight / volume) relationship percentage is shown in equation (14), the rate of decrease in electric conductivity ratio of the solid body for suspension ( The weight / volume) percentage can be calculated.
A is a proportionality constant, which is a negative number from the slope of the graph. In FIG. 3, it is calculated that A is about −0.018.

Also, as described above, the solid (weight / volume) percentage v of the suspension can be calculated by giving the density d to the solid volume percentage x of the suspension .
When the sludge accumulated on the sea floor is targeted, the solid density d is set in the range of 2.4 to 2.6.

  The chronoamperometry method, which is an electrochemical analysis, is described in detail in Japanese Patent Application No. 2001-240722 (Japanese Patent Application Laid-Open No. 2003-50228) filed by the applicant of the present application, and the iron ion concentration w can be determined by the method described above. it can.

As shown in FIG. 7, it can be seen that the relationship between the weight percentage y of iron sulfide and the iron ion concentration w with respect to the suspension has a certain correlation as shown in FIG. This correlation is expressed by the following equation (Equation 15). Note that 3.23 corresponds to B in (Expression 12) described above, and 1.90 corresponds to C in (Expression 12). In addition, this measurement result is a case where the method of calculating | requiring the solid volume percentage with respect to suspension directly from electrical conductivity ratio is used.

Similarly, when the volume percentage of the solid to the suspension is obtained using the electrical conductivity ratio (k ₁ / k ₂ ) and the (weight / volume) percentage of the solid to the suspension , the same applies to the suspension. The relationship between the iron sulfide weight percentage y and the iron ion concentration w was measured with a standard reagent (see FIG. 8). Although the iron ion concentration varies depending on the time during which the current to be applied is applied based on the measurement result, the calibration curve indicated by the weight percentage y of iron sulfide and the iron ion concentration w with respect to the suspension is a straight line passing through the origin (see equation (16) )) And a certain correlation.

また、図９には標準試薬を利用した場合の検量線の一実施例を示す。図９（ａ）は電気伝導率比と懸濁液に対する固体の（重量／容量）百分率の関係を示し、（ｂ）は懸濁液に対する硫化鉄の重量百分率と鉄イオン濃度の関係を示す。
上記する如く、電気伝導率比と懸濁液に対する固体の（重量／容量）百分率の関係から硫化鉄と鉄イオンの一定の相関関係が成立している。

FIG. 9 shows an example of a calibration curve when a standard reagent is used. 9 (a) shows a solid body (weight / volume) percentage relationship to the suspension and the electrical conductivity ratio, indicating the (b) the percentage by weight and the iron ion concentration of the iron sulfide for suspension relationship .
As described above, a certain correlation between iron sulfide and iron ions is established from the relationship between the electrical conductivity ratio and the solid (weight / volume) percentage of the suspension .

The measuring device (1) according to the present invention will be described. The measuring device (1) is composed of the sensor (10), the potentiostat (3), the digital recorder (4), and the computer (5).
The potentiostat (3) detects a current signal. The digital recorder (4) records the current signal detected by the potentiostat (3) and the change over time of the detected current value.
The computer (5) is connected to the digital recorder (4) and calculates by a predetermined method based on the signal recorded in the digital recorder (4) in order to measure the iron sulfide content rate.
This predetermined method refers to calculation by substituting a given numerical value for the following calculation formula.
The computer (5) is connected to a display device (not shown) and can display (output) the result calculated by the computer (5).

The computer (5) of the measuring device (1) includes a first measuring means (51), a second measuring means (52), a first calculating means (53), a third measuring means (54), 2 calculating means (55) and 3rd calculating means (56). FIG. 10 shows a block diagram of the measuring apparatus.
First measuring means (51) measures the first conductivity k ₁ is an electric conductivity of the dispersion medium for dispersing the solid.
Second measuring means (52) measures the second electrical conductivity k ₂ is an electric conductivity of the suspension obtained by dispersing the solid in the dispersion medium.
The first calculating means (53) includes a first electrical conductivity k ₁ measured by the first measuring means (51) and a second electrical conductivity k measured by the second measuring means (52). _{From 2} the volume percentage x of the solid to the suspension is calculated using the formula (Equation 13).

Further, the first computing means (53) includes a first electrical conductivity k ₁ measured at the first measuring means (51), a second electrical measured at the second measuring means (52) From the conductivity k ₂ , using the formula (Equation 5) (using A = −0.018), the solid (weight / volume) percentage v of the suspension is calculated and the solids for this suspension are calculated . It may be used to calculate the volume percentage x of the solid with respect to the suspension from the (weight / volume) percentage v and density d.

The third measuring means (54) measures the iron ion concentration w of the suspension by the chronoamperometry method.
In the third measuring means (54), first, the electrode potential of the first working electrode (11a) and the second working electrode (11b) with respect to the reference electrode (12) is set to the first potential E ₁ (V). In addition, a voltage is applied between the first and second working electrodes (11a) and (11b) and the counter electrode (13) for a first predetermined time. Thereafter, the electrode potential (first working electrode and second working electrode) is set to the second potential E ₂ (V) for a second predetermined time.
Next, the electrode potential of the first working electrode (11a) is set to the iron ion oxidation potential E ₃ (V), and the electrode potential of the second working electrode (11b) is set to the iron ion reduction potential E ₄ (V) simultaneously. Then, the electrode current value (second electrode current I (A)) is measured.
The second electrode current I this is measured (A), the at when the second potential E ₂ is the oxidation potential of iron ions, the reduced iron ions produced by the second working electrode (11b) is diffuse and move In the case where the current reaches the first working electrode (11a) and is oxidized to become iron oxide ions, or the second potential E ₂ is the reduction potential of iron ions, The iron oxide ions generated at one working electrode (11b) are diffused and moved to the second working electrode (11b), reach the second working electrode (11b), and are reduced to become reduced iron ions. Measure either current.

Next, the iron ion concentration w is calculated based on the time change of the second electrode current I (A) from the measured second electrode current I (A).
The means for calculating the iron ion concentration w is the time from the start of current value measurement, t, and the extreme value I (t _m ) of the second electrode current I and its extreme value I in the graph of the relationship between I / t and t. The time t _m giving (t _m ) is measured, and the diffusion coefficient D is calculated from this t _m by the calculation based on the equations (Equation 6) and (Equation 7) according to the method described above.
When measurement is performed under the above-described conditions, the value of τ = K ₁ when the function G (τ) takes an extreme value is 0.166675. . . In the actual measurement, the decimal part is appropriately rounded down, for example, K ₁ = 0.166675.

From I (t _m ) and D, the iron ion concentration w (molar concentration) is calculated by the equation (Equation 8). (P is the number of electrons involved in the electrode reaction of iron ions, F is the Faraday constant (C / mol), A is the electrode area (cm ² ) of the first working electrode (11a) and the second working electrode (11b), K ₂ = K ₁ · G (K ₁ ).)
K ₂ is K ₂ = 0.616756. . . In actual measurement, the fractional part is appropriately rounded down to calculate the iron ion concentration w, for example, K ₂ = 0.616756.

Based on the time change of the second electrode current I (A) to the second electrode current I (A), the iron ion concentration w can be obtained by other means, which is shown below.
The time from the start of current value measurement is t, and I (t) is differentiated twice at t, and the inflection point current value I (t _f ) at which the differential value becomes 0 and the inflection point current value I (t _The time t _f giving _f ) is obtained, and then the diffusion coefficient D is obtained from t _f by calculation based on the equation (Equation 9).
Here, D is the diffusion coefficient of the iron ion to be measured, d is the distance between the first working electrode and the second working electrode (cm), and K ₃ is the τ when the equation expressed by the equation (Equation 10) holds Value. From I (t _f ) and D, the iron ion concentration w for obtaining the iron ion concentration w (molar concentration) is calculated by the equation (Equation 11). (P is the number of electrons involved in the electrode reaction of iron ions, F is the Faraday constant, A is the electrode area of the first working electrode (11a) and the second working electrode (11b), and K ₄ = K ₃ · G (K ₃ ).)

The second calculating means (55) calculates the weight percentage y of iron sulfide with respect to the suspension from the iron ion concentration w in the third measuring means (54) using the formula (Equation 12).
The third calculating means (56) is a solid volume percentage x with respect to the suspension calculated in the first calculating means (53) and the suspension with respect to the suspension calculated in the second calculating means (55) . The iron sulfide content z (= y / x) is calculated by the ratio of the weight percentage y of iron sulfide.
In each means, a storage means (not shown) for storing measurement or calculation results may be provided.
The above is the configuration of the measuring apparatus (1) according to the present invention.

(Test example)
A solid containing iron sulfide and silicon dioxide is prepared, a 0.5 M sodium chloride solution to which polyvinylpyrrolidone is added as a dispersion medium is prepared, and the content of iron sulfide in the solid component is determined by the method described above. This solid sample was prepared by mixing iron sulfide (FeS) and silicon dioxide (SiO ₂ ) so that the solid weight% was 10%.
First, the first electrical conductivity k ₁ of the dispersion medium is obtained. Next, the second electrical conductivity k ₂ of the dispersion medium in which the solid is suspended is measured.

From the first and second electric conductivities (k ₁ and k ₂ ), the solid volume percentage x with respect to the direct suspension is obtained using the formula (Equation 13).

Further, from this first and second electrical conductivities (k ₁ and k ₂ ), the formula (Equation 5) is used to determine the solid (weight / volume) percentage v of the suspension (where A = Using -0.018), the solid (weight / volume) percentage v to suspension and the sludge density d (= 2.5) are used to calculate the solid volume percentage x to suspension. .
In addition, since the density d of sludge is about 2.4-2.6, the numerical value which exists in this range can be used.

Next, the iron ion concentration w of the suspension is measured by the chronoamperometry method.
First, the electrode potentials of the first working electrode (11a) and the second working electrode (11b) with respect to the reference electrode (12) are set to the first potential E ₁ = 2.0 (V), and the first and second working electrodes (11a). A voltage is applied between (11b) and the counter electrode (13) for a first predetermined time (60 seconds).
The electrode potential (first working electrode and second working electrode) is set to the second potential E ₂ = 0.7 (V) for a second predetermined time.
Next, the electrode potential of the first working electrode (11a) is set to the iron ion oxidation potential E ₃ = 0.7 (V), and the electrode potential of the second working electrode (11b) is set to the iron ion reduction potential E ₄ = 0. Change to 3 (V) at the same time. At this time, when the second potential E ₂ is the oxidation potential of iron ions, the reduced iron ions generated at the second working electrode (11b) diffuse and move to reach the first working electrode (11a). When the second electrode current I (A) generated by oxidation to iron oxide ions or the second potential E ₂ is the reduction potential of iron ions, the first working electrode (11b) Any of the second electrode currents I (A) due to the iron oxide ions generated in this manner diffusing and moving to the second working electrode (11b), reaching the second working electrode (11b), and being reduced to become reduced iron ions. In this case, the electrode current value (second electrode current I (A)) is detected.
The iron ion concentration w is obtained using the second electrode current I (A). The iron ion concentration w may be obtained by either of the two methods described above.

When the iron ion concentration w is obtained, the weight percentage y of iron sulfide with respect to the suspension is obtained by the equation (Equation 15) obtained by using the standard reagent. When the weight percentage y of iron sulfide with respect to the suspension is determined, the iron sulfide content z (= y / x) in the solid component is determined from the weight percentage x of the solid with respect to the previously determined suspension .
At this time, the iron sulfide content z in the obtained solid component is shown in FIG. FIG. 11 is a graph showing the relationship between the charged value of iron sulfide content and the measured value when the measuring method of the present invention is used. From FIG. 11, it can be seen that by using the method and apparatus for measuring the iron sulfide content in the solid component according to the present invention, the charged content and the actually measured measured content are substantially the same. It proved to be a very accurate measurement method.

Further, from this first and second electrical conductivities (k ₁ and k ₂ ), the formula (Equation 5) is used to determine the solid (weight / volume) percentage v of the suspension (where A = Using -0.018), the solid (weight / volume) percentage v to suspension and the sludge density d (= 2.5) are used to calculate the solid volume percentage x to suspension. Also in the case, the iron ion concentration w is similarly obtained, and the weight percentage y of iron sulfide with respect to the suspension is obtained by the equation (Equation 16) obtained by using the standard reagent.
The solid content percentage z (= y / x) in the solid component is determined by the solid volume percentage x with respect to the previously determined suspension .
At this time, iron sulfide content z in the obtained solid component is shown in FIG. FIG. 12 is a graph showing the relationship between the charged value of iron sulfide content and the measured value when the measuring method of the present invention is used. From FIG. 12, it can be seen that by using the method and apparatus for measuring the iron sulfide content in the solid component according to the present invention, the charged content and the actually measured measured content are substantially the same. It proved to be a very accurate measurement method. As shown in FIG. 12, the calibration curve is a linear function passing through the origin.
Note that when obtaining the calibration curve, with using a glove box, filled with argon (Ar), was made adjustment of utmost preventing reagent oxidation of iron ions. Moreover, to fully eliminate such as by vacuum bubbles generated upon, prepare reagents.

(Example)
Using the method for measuring the content of iron sulfide in the solid component according to the present invention and this measuring apparatus, sludge was actually collected from 11 measurement points in Uranouchi Bay, Kochi Prefecture. Measurements were made. FIG. 13 is a graph showing the iron sulfide content at 11 measurement sites in Uranouchi Bay.
FIG. 14 shows the weight percentage of iron sulfide according to the present invention and the weight percentage of iron sulfide by the drying method at 11 measurement points in Uranouchi Bay, Kochi Prefecture.

The schematic of the measuring apparatus used by this invention is shown. It is a figure which shows a working electrode, (a) is these exploded views, (b) is a cross-sectional side view of a working electrode, (c) is a top view of a working electrode. The relationship between the electrical conductivity ratio in the suspension (the electrical conductivity k _{1 of} the dispersion medium, the electrical conductivity k ₂ of the suspension obtained by suspending the solid using the dispersion medium) and the liquid fraction volume is shown. It is a graph, and the vertical axis indicates the electric conductivity ratio, and the horizontal axis indicates the volume ratio of the solid fraction volume (percentage of solid (weight / volume) with respect to the suspension ). (A ) shows the relationship between iron sulfide and electrical conductivity ratio, and (b) shows the relationship between silicon dioxide and electrical conductivity ratio. The correlation of electrical conductivity ratio is shown. Electric conductivity ratio (k ₁ / k ₂₎ and a graph showing a weight / volume percentages of the relationship of the solid with respect to the suspension, the iron sulfide (FeS), silicon dioxide (SiO ₂₎ and iron sulphide and secondary Each case of a mixture of silicon oxide (mixing ratio 1: 9) is shown. It is a graph which shows the weight percentage of iron sulfide, and the relationship of iron ion concentration. Using the electrical conductivity ratio (k ₁ / k ₂ ) and the (weight / volume) percentage of the suspension , the relationship between the weight percentage of iron sulfide and the iron ion concentration when the weight percentage of the solid to the suspension is determined. It is a graph to show. Shows an embodiment of a calibration curve of the case of using the standard reagent, (a) shows the electrical conductivity and the solid body (weight / volume) percent relationship, (b) the weight percentage of iron ions of iron sulfide The concentration relationship is shown. 1 shows a block diagram of a computer according to the present invention. It is a graph which shows the relationship between the preparation value of an iron sulfide content rate when using the measuring method of this invention, and a measured value. It is a graph which shows the relationship between the preparation value of an iron sulfide content rate when using the measuring method of this invention, and a measured value. Is a graph showing the in iron sulfide content in the measurement locations 11 locations Uranouchi Inlet, the vertical axis represents the iron sulfide content mg of the solid in the component 1g of sediment, the horizontal axis is the sampling sites. The weight percentage of iron sulfide according to the present invention and the weight percentage of iron sulfide by the drying method at 11 measurement points in Uranouchi Bay, Kochi Prefecture are shown. The left side of each measurement point is the measurement result by the drying method, and the right side is the measurement result by the measurement method of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Measuring apparatus 10 ... Sensor 11 ... Working electrode 11a ... 1st working electrode 11b ... 2nd working electrode 12 ... Reference electrode 13 ... Counter electrode 51 ··· First measuring means 52 ··· Second measuring means 53 ··· First calculating means 54 ··· Third measuring means 55 ··· Second calculating means 56 ··· Third computing means

Claims (6)

A method for measuring the iron sulfide content in a solid component,
Measuring a first electrical conductivity k ₁ which is an electrical conductivity of a dispersion medium in which the solid is dispersed;
Measuring a second electrical conductivity k ₂ which is an electrical conductivity of a suspension in which the solid is dispersed in the dispersion medium;
Calculating the volume percentage x of the solid to the suspension from the first and second electrical conductivities (k ₁ and k ₂ );
By measuring the iron ion concentration w of the suspension by chronoamperometry,
Calculate the weight percentage y of iron sulfide to the suspension from the iron ion concentration w,
In the solid component, the iron sulfide content z (= y / x) is calculated by the ratio of the volume percentage x of the solid to the suspension and the weight percentage y of the iron sulfide to the suspension . Method for measuring iron sulfide content. When measuring the iron ion concentration w,
2. The solid component according to claim 1, wherein the measuring device comprises a working electrode composed of a first working electrode and a second working electrode arranged opposite to each other with a distance d, a reference electrode, and a counter electrode. Method for measuring iron sulfide content. 2. The solid component according to claim 1, wherein the volume percentage x of the solid with respect to the suspension is obtained from the first and second electrical conductivities (k ₁ and k ₂ ) by the following formula (Equation 1). Method for measuring the content of iron sulfide.

From the first and second electrical conductivities (k ₁ and k ₂ ), the (weight / volume) percentage v of the solid with respect to the suspension is calculated by the following equation (Equation ₂ ):
Iron sulfide content according to claim 1, wherein the determination of the capacity percentage x of the solid relative to the suspension from the density d of the solid (weight / volume) percent v and the solid relative to the suspension Measuring method.

2. The method for measuring the iron sulfide content in a solid component according to claim 1, wherein the weight percentage y of the iron sulfide relative to the suspension is obtained from the iron ion concentration w by the following equation (Equation 3). .

An apparatus for measuring the iron sulfide content in a solid component,
First measuring means for measuring a first electrical conductivity k ₁ which is an electrical conductivity of a dispersion medium for dispersing the solid;
A second measuring means for measuring a second electrical conductivity k ₂ which is an electrical conductivity of a suspension obtained by dispersing the solid in the dispersion medium;
First computing means for calculating a volume percentage x of the solid relative to the suspension from the first and second electrical conductivities (k ₁ and k ₂ );
A third measuring means for measuring the iron ion concentration w of the suspension by chronoamperometry;
Second computing means for calculating a weight percentage y of iron sulfide with respect to the suspension from the iron ion concentration w;
And third calculating means for calculating an iron sulfide content z (= y / x) based on a ratio of a volume percentage x of the solid to the suspension and a weight percentage y of the iron sulfide to the suspension. A device for measuring the content of iron sulfide in solid components.

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