Pretreatment apparatus and pretreatment method

Abstract

To provide a pretreatment device capable of preparing a measurement sample suitable for highly accurately detecting the concentration of a treatment object by efficiently concentrating the treatment object in a simple process even when the concentration of the treatment object contained in a sample is extremely low or the sample contains a large amount of impurities, and a pretreatment method using the same.SOLUTION: A working electrode, a counter electrode, and a reference electrode that are disposed in the liquid tank, a stirring unit that stirs the treatment liquid in the liquid tank, and a control unit, wherein the control unit includes a voltage application unit that applies a voltage between the counter electrode and the working electrode, and the control unit applies the voltage after the ions of the treatment target contained in the treatment liquid are reduced and electrodeposited on the working electrode. The voltage application part is controlled so as to ionize again and dissolve the impurities except the object to be treated electrodeposited on the working electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pretreatment device for concentrating a treatment object from a treatment liquid containing the treatment object, and a pretreatment method using the same. [Background technology]

[0002] For example, pollutants such as heavy metals contained in soil can have a significant impact on human health. For this reason, the permissible limits of pollutants contained in soil are strictly regulated in many countries. For example, in Japan, Article 16, Paragraph 1 of the Basic Environment Law (Law No. 91 of 1993) prescribes standards for pollutants that are desirable to maintain in order to protect human health and preserve the living environment (hereinafter referred to as "environmental standards") regarding environmental conditions related to soil contamination.

[0003] Among these pollutants, substances containing cadmium, lead, copper, arsenic, and mercury, for example, have a significant impact on the human body and the environment even in minute amounts, and therefore strict environmental standards have been set for them.Taking mercury as an example of a pollutant, the Appendix to Article 16, Paragraph 1 of the Basic Environment Law (Law No. 91 of 1993) stipulates that the total mercury content must be 0.0005 mg (0.5 ppb) or less per liter of treatment liquid.

[0004] Conventionally, methods for accurately measuring trace concentrations of pollutants, such as those required by the environmental standards mentioned above, include, for example, a method in which a soil sample is subjected to multiple pretreatments to form a treated liquid, and then this treated liquid is analyzed using an inductively coupled plasma mass spectrometer (ICP-MS) or an atomic absorption spectrometer (AAS) (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Publication No. 60-017449 [Patent Document 2] Japanese Patent Application Publication No. 56-100360 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional heavy metal pretreatment methods such as those described in Patent Documents 1 and 2 require expensive, large-scale analytical equipment such as ICP-MS or AAS, which poses a problem of high analytical costs.

[0007] On the other hand, there are methods for easily analyzing pollutants, such as colorimetric quantification, but these methods have the problem of being difficult to accurately detect when the pollutant concentration is extremely small, such as 1 ppb or less.Furthermore, when the target is something like soil, it contains many impurities in addition to the target substance, and the presence of these impurities can reduce the accuracy of the measurement.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a pretreatment device that can effectively concentrate only the target substance to be measured from a sample containing a large amount of impurities with a simple configuration, and a pretreatment method using the same.

[0009] The configuration of the pretreatment device and pretreatment method of the present invention can be suitably applied to the concentration of heavy metals and non-metals that can be electrochemically ionized into particles, such as contaminants cadmium, lead, copper, arsenic, and mercury. [Means for solving the problem]

[0010] In order to solve the above problems, the pretreatment device and pretreatment method according to one embodiment of the present invention propose the following means. (1) A pretreatment device according to a first aspect of the present invention includes at least a liquid tank for accommodating a treatment liquid containing ions of an object to be pretreated, a working electrode, a counter electrode, and a reference electrode disposed in the liquid tank, stirring means for stirring the treatment liquid in the liquid tank, and a control unit. The control unit includes a voltage application unit for applying a voltage between the counter electrode and the working electrode, and the control unit controls the voltage application unit to apply a reduction voltage for the ions of the object to be treated between the counter electrode and the working electrode to reduce the ions of the object to be treated contained in the treatment liquid and electrodeposit them on the working electrode, and then to apply a voltage to re-ionize and dissolve impurities, excluding the object to be treated, that have been electrodeposited on the working electrode, thereby cleaning the surface of the working electrode.

[0011] (2) A second aspect of the present invention is directed to the pretreatment device of the first aspect, wherein the object to be treated contains at least one of cadmium, lead, copper, arsenic, and mercury.

[0012] (3) Aspect 3 of the present invention is a pretreatment device according to aspect 1, wherein the working electrode is a gold nanoparticle-boron-doped diamond electrode.

[0013] (4) A pretreatment method according to a fourth aspect of the present invention is a pretreatment method using the pretreatment device according to any one of the first to third aspects, and includes at least an electrodeposition step of applying a reduction voltage for ions of the object to be treated between the counter electrode and the working electrode to reduce ions of the object to be treated contained in the treatment solution and electrodeposit them on the working electrode, and an impurity dissolution step of applying a voltage to re-ionize and dissolve impurities other than the object to be treated that have been electrodeposited on the working electrode, whereby the object to be treated is concentrated and produced on the working electrode by the electrodeposition step and the impurity dissolution step.

[0014] (5) A fifth aspect of the present invention is a pretreatment method according to the fourth aspect, in which the electrodeposition step and the impurity dissolution step are repeated multiple times.

[0015] (6) A sixth aspect of the present invention is the pretreatment method of the fourth or fifth aspect, wherein the reduction voltage in the electrodeposition step is a voltage in the range of 0.1 V to 1.0 V lower than the applied voltage in the impurity dissolution step.

[0016] (7) A seventh aspect of the present invention is the pretreatment method of any one of the fourth to sixth aspects, wherein the voltage applied in the impurity dissolving step is a voltage in the range of 0.18 V to 0.4 V lower than the ionization potential of the object to be treated. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a pretreatment device and a pretreatment method using the same that can efficiently concentrate the object to be treated using a simple process, even when the concentration of the object to be treated contained in the sample is extremely small or the sample contains a large amount of impurities, thereby making it possible to create a measurement sample that is suitable for detecting the concentration of the object to be treated with high accuracy. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram showing a pre-treatment device according to an embodiment of the present invention; [Figure 2] 1 is a flowchart showing a pre-processing method according to an embodiment of the present invention in a step-by-step manner. [Figure 3] This is a graph showing peaks measured with a commercially available Au electrode using black soil containing mercury as the material to be treated. DETAILED DESCRIPTION OF THE INVENTION

[0019] A pretreatment device and a pretreatment method using the same according to one embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0020] [Pretreatment device] FIG. 1 is a schematic diagram showing the configuration of a pretreatment device according to one embodiment of the present invention. The pretreatment device 10 of this embodiment has, for example, at least a liquid tank 11, three electrodes contained in the liquid tank 11: a working electrode 12, a counter electrode 13, and a reference electrode 14, a stirring means 15 disposed in the liquid tank 11, and a control unit 16.

[0021] The liquid tank 11 may be any container that can accommodate the processing liquid W and may be made of a dielectric material such as resin or glass. In this embodiment, a circular container made of hard polyethylene and having a capacity of about 5 ml is used as the liquid tank 11.

[0022] In this embodiment, a solution in which soil eluates are dissolved in a solvent containing water is used as the treatment solution W. In such treatment solution W, trace amounts of mercury, lead, and cadmium, which are examples of the treatment target, as well as impurities other than the treatment target, are ionized and dissolved in the solvent.

[0023] The object to be treated in this embodiment can be any element or compound, as long as it is reduced from an ionic state and electrodeposited on an electrode by applying a reduction voltage.Specific examples include trace concentrations of substances that cause soil contamination, such as cadmium, lead, copper, arsenic, and mercury, which are difficult to measure with high accuracy in the state of a solution in which soil eluates are dissolved.

[0024] In addition, although the present embodiment has been described using soil as an example of a material containing a target substance to be treated and impurities, the material containing the target substance to be treated and concentrated by the device configuration of this embodiment is not limited to soil. For example, other than soil, examples include wastewater discharged from factories and homes, river water, various treated water, and eluate eluted from any solid.

[0025] In this embodiment, the working electrode 12 is provided with labels 12a formed by forming a boron-doped diamond (BDD) thin film on a niobium substrate or a silicon substrate, and modifying this BDD thin film with gold nanoparticles. When a reduction voltage is applied to the working electrode 12, the working electrode 12 reduces the substances to be treated contained in the treatment solution (W), such as mercury ions, lead ions, cadmium ions, and arsenic ions, as well as other impurity ions, and electrodeposits them onto the labels 12a.

[0026] The working electrode 12 does not necessarily have to include the label 12a, and may be, for example, just an electrode made of a niobium substrate or a silicon substrate. The working electrode 12 can be made of any electrode material reactive with the mercury to be detected, such as carbon, gold, or platinum, in addition to the niobium or silicon described above. The working electrode 12 may have any shape other than a plate-like shape as in this embodiment, such as nanoparticles, a mesh, a wire, or a printed electrode, and is not limited to a specific shape.

[0027] In this embodiment, the counter electrode 13 may be, for example, an electrode formed in a plate or coil shape and made of conductive diamond, silver, gold, platinum, or the like.

[0028] The reference electrode (standard electrode) 14 is an electrode that provides a reference point for potential when measuring potential, and in this embodiment, for example, a silver-silver chloride electrode (vs. Ag / AgCl) is used, which has an internal solution of potassium chloride aqueous solution and a silver wire coated with silver chloride housed in it. Note that the reference electrode (standard electrode) 14 is not limited to a silver-silver chloride electrode, and the reference electrode may be made of any material.

[0029] In this embodiment, the stirring means 15 may be a magnetic stirrer composed of a stirring bar 15a and a stirring device main body 15b. The stirring means 15 rotates the magnet of the stirring device main body 15b, which is provided below the liquid tank 11, thereby rotating the stirring bar 15a, which is magnetically attracted via the liquid tank 11, and thus stirs the treatment liquid W. As the stirring means, in addition to the magnetic stirrer described above, various stirring means such as a propeller stirrer and an ultrasonic stirrer can be used.

[0030] The control unit 16 includes a voltage application unit 22 and a current value measurement unit 23. In practice, the control unit 16 may be composed of, for example, a personal computer including a CPU and memory, a display, an external storage device, a power supply, and the like.

[0031] The control unit 16 controls the voltage application unit 22 to form a reduction voltage between the counter electrode 13 and the working electrode 12, reducing the ions of the object to be treated and the ions of impurities dissolved in the treatment liquid W and electrodepositing them onto the marker 12a of the working electrode 12.

[0032] In addition, the control unit 16 controls the voltage application unit 22 to apply voltage so that the object to be treated electrodeposited on the working electrode 12 is left on the working electrode 12 without being redissolved, and impurities other than the object to be treated are re-ionized and redissolved in the treatment liquid W.

[0033] When the concentration of the object to be treated dissolved in the treatment liquid W is predicted to be extremely small, the control unit 16 can also control the voltage application unit 22 to perform the reductive electrodeposition of ions of the object to be treated and ions of impurities and the redissolution of the impurity ions by voltage application multiple times. This allows the object to be dissolved in the treatment liquid W to be concentrated at a high concentration on the working electrode 12.

[0034] [Pretreatment method] Next, the operation of the pretreatment device 10 of the above-described embodiment and the pretreatment method of this embodiment using the pretreatment device 10 will be described. In the following description, mercury will be exemplified as the object to be concentrated. FIG. 2 is a flowchart showing a step-by-step pretreatment method according to one embodiment of the present invention.

[0035] When performing pretreatment using the pretreatment device 10 of the above-described embodiment to concentrate trace amounts of mercury dissolved in the treatment solution W, first, mercury-containing soil (sample) is prepared, which is an example of a material for preparing the treatment solution. In addition to mercury, such soil contains many types of impurities that dissolve in the solvent and become ionized.

[0036] This sample (unit: g) is mixed with a solvent (pure water to which hydrochloric acid has been added to give a hydrogen ion concentration index of 5.8 to 6.3) at a ratio of 10% by mass, and the volume of the mixture is adjusted to 1000 mL to obtain a sample solution. Note that it is preferable to use a solvent with a pH of 4 to 9 that can dissolve a sufficient amount of electrolytes.

[0037] Next, the prepared sample solution is shaken by hand for about 1 minute at room temperature (20°C) and atmospheric pressure (1 atmosphere). The sample solution may be shaken using a shaker, and the shaker settings may be, for example, 6 hours, approximately 200 shakes per minute, and a shaking width of about 4 to 5 cm.

[0038] The shaken solution is filtered, for example, through a membrane filter, and the filtrate is used as a treatment solution (treatment solution formation step S1). The pore size of the membrane filter used may be, for example, about 0.45 μm (average pore size).

[0039] The treatment liquid M thus obtained contains mercury ions resulting from the dissolution of mercury contained in the soil and ions of impurities resulting from the dissolution of impurities other than mercury. Then, for example, about 5 milliliters of this treatment liquid M is placed in the liquid tank 11 of the pretreatment device 10. Then, a stirrer 15a is placed in the bottom of the liquid tank 11, and the stirrer body 15b is operated to stir the treatment liquid M in the liquid tank 11 (stirring step S2). The treatment liquid is constantly stirred during measurement to prevent sediment from forming at the bottom of the liquid tank 11.

[0040] Next, the working electrode 12, the counter electrode 13, and the reference electrode 14 are arranged at a predetermined distance from one another in the liquid tank 11. Then, the control unit 16 is operated to concentrate mercury, which is an example of a substance to be treated, contained in the treatment liquid M in a predetermined operation mode.

[0041] First, a reduction voltage for mercury ions, which are the object to be treated, is applied between the counter electrode 13 and the working electrode 12 to reduce the mercury ions contained in the treatment solution W and electrodeposit them onto the working electrode 12 (electrodeposition step S3). At this time, impurity ions having a reduction voltage close to that of the mercury ions are also reduced and electrodeposited onto the working electrode 12 together with the mercury.

[0042] The voltage (reduction voltage) applied in the electrodeposition step S3 may be set, for example, in the range of 0.1 V to 1.0 V. As an example, when the object to be treated is mercury, the reduction voltage is preferably in the range of −0.9 V or more and −0.6 V or less. The voltage application time in the electrodeposition step S3 may be, for example, in the range of 500 seconds or more and less than 700 seconds.

[0043] Next, a voltage sweep (voltage application) is performed from the electrodeposition potential of mercury to a predetermined sweep voltage, and the impurities electrodeposited together with mercury on the working electrode 12 are re-ionized and dissolved in the treatment solution W (impurity dissolving step S4). The voltage applied in the impurity dissolving step S4 may be a voltage lower than the ionization potential of the treatment object by a range of -0.4 V to -0.18 V. When the treatment object is mercury, the voltage is preferably lower than the ionization potential of mercury by a range of -0.3 V to -0.18 V.

[0044] By performing the impurity dissolving step S4, only the impurities are dissolved on the working electrode 12, and only the mercury, which is the object to be treated, remains electrodeposited on the label 12a of the working electrode 12. This makes it possible to concentrate and produce the object to be treated, mercury in this embodiment, on the label 12a of the working electrode 12.

[0045] The electrodeposition step S3 and the impurity dissolving step S4 may be repeated multiple times. For example, if the mercury concentration of the object to be treated is up to 10 ppb, the electrodeposition step S3 and the impurity dissolving step S4 may be performed, for example, once or twice. If the mercury concentration is less than 10 ppb, for example, about 0.3 ppb, the electrodeposition step S3 and the impurity dissolving step S4 may be performed, for example, six or seven times. If the mercury concentration of the object to be treated is about 0.5 ppb, which is the environmental standard value, the electrodeposition step S3 and the impurity dissolving step S4 may be performed, for example, five or six times. This allows the substance to be treated to be concentrated and produced at the working electrode 12 even if the concentration is low, for example, less than 1 ppb.

[0046] As described above, according to the pretreatment method using the pretreatment device of the present invention, even if the concentration of the treatment target contained in the treatment solution is extremely small, the treatment target can be electrodeposited so as to be concentrated on the working electrode, and impurities contained in the treatment solution can be separated. By concentrating the treatment target by the pretreatment method using such a pretreatment device, it becomes possible to accurately determine the concentration of the treatment target contained in the treatment solution in a subsequent process, for example.

[0047] In the above-described embodiment, mercury is used as an example of the object to be treated, and soil is used as an example of the pretreatment object containing this mercury. However, the object to be treated may be any object, such as various metals and their compounds, or non-metallic elements, and the object containing these objects to be treated is not limited to soil, but may be anything.

[0048] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0049] (Verification example 1) Using mercury-containing soil (black soil, Arakida soil, river sand, and Fuji sand) as the treatment object, the reaction of mercury was investigated in samples that had been concentrated using the pretreatment method of this embodiment (example of the present invention) and in samples that had not been concentrated (conventional example). The results are shown in Table 1.

[0050] [Table 1]

[0051] According to the results shown in Table 1, the samples (invention examples) in which mercury was concentrated using the pretreatment method of this embodiment, except for Arakida clay, successfully obtained mercury detection signals at both 1 ppb and 10 ppb concentrations.

[0052] On the other hand, in samples where mercury was not concentrated (comparative examples), no mercury detection signal was obtained or the detection signal was low for Arakida soil and river sand, and even for Fuji sand and black soil, the detection signal intensity was lower than that of the present invention example at a concentration of 10 ppb.

[0053] Therefore, it was confirmed that the pretreatment method of this embodiment can electrochemically concentrate the concentration of the substance to be treated, thereby producing a sample (treatment liquid) whose concentration can be detected even at extremely low concentrations.

[0054] (Verification example 2) The peaks measured using a commercially available Au electrode for black soil containing mercury as the treatment target are shown in Figure 3. The results shown in Figure 3 confirm that the sample in which mercury was concentrated using the pretreatment method of this embodiment showed a reduction in the peaks of unknown components, i.e., impurities (see arrows in Figure 3), and a clearer mercury peak, compared to the sample that was not pretreated for concentration.

[0055] In the above-described embodiment, a gold nanoparticle-boron-doped diamond electrode is given as an example of a working electrode, but the working electrode can be made of an electrode material that is reactive with any object to be processed, and the material of the working electrode is not limited. [Industrial Applicability]

[0056] The pretreatment device and pretreatment method of the present invention can concentrate and increase the concentration of trace amounts of substances to be treated, for example, 1 ppb or less, thereby producing samples whose concentrations can be measured with high accuracy, and thus have industrial applicability. [Explanation of symbols]

[0057] 10...Pretreatment device 11...Liquid tank 12...Working electrode 12a...Sign 13...opposite 14...Reference electrode 15...Stirring means 16...Control unit 22...Voltage application section

Claims

1. The apparatus includes at least a liquid tank that contains a treatment liquid containing ions of a treatment target to be pretreated, a working electrode, a counter electrode, and a reference electrode that are disposed in the liquid tank, a stirring means that stirs the treatment liquid in the liquid tank, and a control unit; the control unit has a voltage application unit that applies a voltage between the counter electrode and the working electrode, The control unit controls the voltage application unit to apply a reduction voltage for ions of the object to be treated between the counter electrode and the working electrode to reduce ions of the object to be treated contained in the treatment solution and electrodeposit them on the working electrode, and then further apply a voltage to re-ionize and dissolve impurities, excluding the object to be treated, that have been electrodeposited on the working electrode, thereby cleaning the surface of the working electrode.

2. The pretreatment device according to claim 1 , wherein the object to be treated contains at least one of cadmium, lead, copper, arsenic, and mercury.

3. 3. The pretreatment device according to claim 1, wherein the working electrode is a gold nanoparticle-boron-doped diamond electrode.

4. A pretreatment method using the pretreatment device according to claim 1 or 2, an electrodeposition step of applying a reduction voltage for ions of the object to be treated between the counter electrode and the working electrode to reduce ions of the object to be treated contained in the treatment solution and electrodeposit them onto the working electrode; and an impurity dissolving step of applying a voltage to re-ionize and dissolve impurities, excluding the object to be treated, electrodeposited on the working electrode, A pretreatment method in which the substance to be treated is concentrated and generated on the working electrode by the electrodeposition step and the impurity dissolution step.

5. The pretreatment method according to claim 4 , wherein the electrodeposition step and the impurity dissolution step are repeated multiple times.

6. 5. The pretreatment method according to claim 4, wherein the reduction voltage in the electrodeposition step is a voltage in the range of 0.1 V to 1.0 V lower than the applied voltage in the impurity dissolution step.

7. The pretreatment method according to claim 4 , wherein the voltage applied in the impurity dissolving step is a voltage in a range of 0.18 V to 0.4 V lower than the ionization potential of the object to be treated.

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