Reagent for detecting metal, reagent for detecting bismuth and reagent for detecting lead, method for detecting metal using same, and method for manufacturing recycled material

Abstract

In this invention, selection of a coloring agent and an auxiliary material is made easy, and detection performance in a case of targeting a solid metal is thereby improved.　This reagent is used for detecting an element contained in a test object, which is a solid metal such as a copper alloy. The reagent comprises: an organic coloring agent such as xylenol orange; a keeping agent for keeping a state of adhesion to the test object; and a coloration visibility improving agent for improving visibility of coloration of the organic coloring agent with respect to a background color of the test object. The reagent also comprises a pH adjusting agent, whereby the pH is adjusted to 0 or more.

Description

Metal detection reagents, bismuth detection reagents, and lead detection reagents, metal detection methods using these, and methods for producing recycled materials

[0001] The present invention relates to a reagent for detecting metals, a reagent for detecting bismuth, and a reagent for detecting lead, a metal detection method using these reagents, and a method for producing recycled materials.

[0002] Conventionally, a method for detecting elements in solid metals has been to use a reagent such as that described in Patent Document 1. The reagent in Patent Document 1 uses potassium iodide. Specifically, a reagent consisting of a mixture of potassium iodide and nitric acid is dropped onto an alloy to be detected, and the color of the precipitate that forms in the mixture is then confirmed to determine whether the alloy contains lead or bismuth.

[0003] Japanese Patent Application Laid-Open No. 2005-024399

[0004] When detecting elements in solid metals, there is a particular need for improved detection performance. For example, LF844C, described in the examples of Patent Document 1, is an alloy with a relatively high bismuth content, about 2 to 4 mass %, which is the detection target. In contrast, there is a need to detect bismuth in an alloy with a low bismuth content, about 1 mass %. In this case, there is a need to use a substance with higher detection sensitivity as a color developer or to use an auxiliary material in combination with the color developer to improve detection performance.

[0005] On the other hand, in the examples of Patent Document 1, nitric acid with a concentration of 25% by volume is used. This results in a pH of the reagent equivalent to -1.5 to -1.0. Therefore, materials used for detection are required to be able to withstand such high acid concentrations. However, it is extremely difficult to select colorants and other auxiliary materials for improving the detection performance of the reagent that can withstand such high acid concentrations.

[0006] The object of the present invention is to provide a metal detection reagent, a bismuth detection reagent, and a lead detection reagent that make it easy to select colorants and auxiliary materials, thereby improving detection performance when targeting solid metals, a metal detection method using these, and a method for producing recycled materials.

[0007] The metal detection reagent of the first invention is a liquid reagent for detecting elements other than the main component in a solid metal, and is used by being attached to the solid metal. It contains an organic colorant that reacts with the element to produce a color, and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal, and is adjusted to a pH of 0 or higher.

[0008] According to the first aspect of the present invention, the pH of the reagent is 0 or higher, and the acid concentration is not too high, so that an organic substance that may become ineffective or decompose if the acid concentration is too high can be used as the color developer. It is easy to select an organic color developer that has high detection sensitivity under appropriate pH conditions.

[0009] Furthermore, because the acid concentration of the reagent is not too high, it is easy to select auxiliary materials to improve detection performance. In selecting such auxiliary materials, the present invention takes into consideration the following problems specific to solid metals. The first problem is that, because the reagent is liquid, it may not be possible to maintain the reagent's adherence to the solid metal. If the reagent is not sufficiently maintained on the surface of the solid metal, the color of the coloring agent may be insufficient or the color may not be fully visible. The second problem is that the original color of the solid metal surface may reduce the visibility of the reagent color. In response to these problems, the present invention employs at least one of a retention agent and a color visibility enhancer as auxiliary materials. The former material alleviates the first problem, while the latter material alleviates the second problem. As a result, the detection performance of the reagent is improved regardless of which material is used.

[0010] As described above, the first invention broadens the range of choices for colorants and auxiliary materials by using a moderate acid concentration. Accordingly, organic colorants with high detection sensitivity and materials that can mitigate the problems inherent in targeting solid metals are selected. This ensures the reagent's detection performance for solid metals. For example, the reagent can detect a target element even if its concentration in the solid metal is relatively low.

[0011] The metal detection reagent of the second invention is a liquid reagent for detecting elements other than the main component in a solid metal, and is used by impregnating a substrate and bringing the substrate into contact with the solid metal.The reagent contains an organic coloring agent that reacts with the element to produce a color, and has a pH adjusted to 0 or higher.

[0012] According to the second aspect of the present invention, the pH of the reagent is 0 or higher, and the acid concentration is not too high, so that an organic substance that may become ineffective or decompose if the acid concentration is too high can be used as the color developer. It is easy to select an organic color developer that has high detection sensitivity under appropriate pH conditions.

[0013] Furthermore, since the reagent is liquid, there is a risk that the reagent may not be able to maintain its adhesion to the solid metal. To address this issue, the reagent of the present invention is impregnated into a substrate and then brought into contact with the solid metal. This alleviates the above-mentioned problem and improves the detection performance of the reagent. The range of materials for such substrates is also wide, as the acid concentration of the reagent is not too high.

[0014] As described above, the second invention broadens the range of options for the color developer and the substrate as an auxiliary material by using a moderate acid concentration. Accordingly, an organic color developer with high detection sensitivity is selected and used by impregnating the substrate. This ensures the reagent's detection performance for solid metals. For example, even if the solid metal contains a relatively low concentration of the target element, the reagent can be used to detect it.

[0015] The reagent for bismuth detection according to the third invention is a liquid reagent for detecting bismuth in a solid metal, and is used by being attached to the solid metal. The reagent contains xylenol orange as an organic colorant that reacts with the bismuth to produce a color, and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal, and the pH is adjusted to 0 or higher.

[0016] According to the third aspect of the present invention, the pH of the reagent is 0 or higher and the acid concentration is not too high, so that xylenol orange, an organic substance that may cease to function or decompose if the acid concentration is too high, can be used as the color developer. Xylenol orange is an organic color developer that has high detection sensitivity for bismuth under appropriate pH conditions.

[0017] Furthermore, because the acid concentration of the reagent is not too high, it is easy to select auxiliary materials to improve detection performance. In selecting such auxiliary materials, the present invention takes into consideration the following problems specific to solid metals. The first problem is that, because the reagent is liquid, it may not be possible to maintain the reagent's adherence to the solid metal. If the reagent is not sufficiently maintained on the surface of the solid metal, the color of the coloring agent may be insufficient or the color may not be fully visible. The second problem is that the original color of the solid metal surface may reduce the visibility of the reagent color. In response to these problems, the present invention employs at least one of a retention agent and a color visibility enhancer as auxiliary materials. The former material alleviates the first problem, while the latter material alleviates the second problem. As a result, the detection performance of the reagent is improved regardless of which material is used.

[0018] As described above, the third invention broadens the range of choices for coloring agents and auxiliary materials by using a moderate acid concentration. Accordingly, xylenol orange, which has high detection sensitivity, and materials that can mitigate the problems inherent in targeting solid metals are selected. This ensures the reagent's detection performance for solid metals. For example, the reagent can detect the target element even if the solid metal contains a relatively low concentration of the element.

[0019] In the third aspect of the present invention, it is preferable that the reagent contains both the retention agent and the color visibility enhancer. This can prevent the problems of the reagent attached to the solid metal not being retained on the surface of the solid metal and the original color of the surface of the solid metal reducing the visibility of the color of the reagent. This effectively improves the detection performance of the reagent.

[0020] In the third invention, the pH is preferably adjusted to 0.8 or more and 1.8 or less. This allows the coloring and selectivity of xylenol orange to bismuth to be maintained. In the third invention, the retention agent preferably contains a fixative that maintains the colored state. This allows the color of the reagent to be stable for a long period of time.

[0021] Furthermore, the lead detection reagent according to the fourth invention is a liquid reagent for detecting lead in solid metal, which is used by being attached to the solid metal, and contains xylenol orange as an organic colorant that reacts with the lead to change color, and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal, and is adjusted to a pH of 0 or higher.

[0022] According to the fourth aspect of the present invention, the pH of the reagent is 0 or higher and the acid concentration is not too high, so that xylenol orange, an organic substance that may cease to function or decompose if the acid concentration is too high, can be used as the color developer. Xylenol orange is an organic color developer that has high detection sensitivity for lead under appropriate pH conditions.

[0023] Furthermore, because the acid concentration of the reagent is not too high, it is easy to select auxiliary materials to improve detection performance. In selecting such auxiliary materials, the present invention takes into consideration the following problems specific to solid metals. The first problem is that, because the reagent is liquid, it may not be possible to maintain the reagent's adherence to the solid metal. If the reagent is not sufficiently maintained on the surface of the solid metal, the color of the coloring agent may be insufficient or the color may not be fully visible. The second problem is that the original color of the solid metal surface may reduce the visibility of the reagent color. In response to these problems, the present invention employs at least one of a retention agent and a color visibility enhancer as auxiliary materials. The former material alleviates the first problem, while the latter material alleviates the second problem. As a result, the detection performance of the reagent is improved regardless of which material is used.

[0024] As described above, the fourth invention broadens the range of choices for coloring agents and auxiliary materials by using a moderate acid concentration. Accordingly, xylenol orange, which has high detection sensitivity, and materials that can mitigate the problems inherent in targeting solid metals are selected. This ensures the reagent's detection performance for solid metals. For example, the reagent can detect the target element even if the solid metal contains a relatively low concentration of the element.

[0025] In the fourth aspect of the present invention, it is preferable that the reagent contains both the retention agent and the color visibility enhancer. This can suppress both the problem that the reagent attached to the solid metal may not be retained on the surface of the solid metal, and the problem that the original color of the surface of the solid metal may reduce the visibility of the color of the reagent. Therefore, the detection performance of the reagent is effectively improved.

[0026] In the fourth invention, the pH is preferably adjusted to 1.6 or more and 2.1 or less. This allows the color and selectivity of xylenol orange for lead to be maintained. In the fourth invention, the retention agent preferably contains a fixative that maintains the colored state. This allows the color of the reagent to be stable for a long period of time.

[0027] The metal detection method according to the fifth aspect of the present invention is carried out by attaching the reagent according to the first, third, or fourth aspect of the present invention to the surface of the solid metal. In this method, it is preferable that the reagent is attached to the surface of the solid metal by either painting or spraying the surface of the solid metal.

[0028] The metal detection method of the sixth invention is a method using the reagent of the second invention, and is carried out by rubbing the substrate against the surface of the solid metal and then observing the substrate at a position separated from the solid metal.

[0029] A metal detection method according to a seventh aspect of the present invention is a method using the reagent according to the second aspect of the present invention, and is carried out by attaching the substrate to the surface of the solid metal.

[0030] According to the fifth to seventh aspects of the present invention, metal can be detected by a simple method that can be carried out indoors or outdoors.

[0031] In the fifth aspect of the present invention, the thickness of the reagent film formed on the surface of the solid metal is preferably adjusted, which makes it easier to obtain a desired color result or to make the color appear on the surface of the reagent film.

[0032] In the fifth aspect of the present invention, it is preferable that the organic coloring agent is xylenol orange, and that the reagent is applied to the surface of the solid metal so that the thickness of the reagent film is 90 to 130 μm, thereby enabling metal detection with appropriate coloring by xylenol orange.

[0033] The metal detection method according to the eighth invention is carried out by attaching the reagent according to any one of the first to fourth inventions to the surface of the solid metal, that is, metal scrap.

[0034] According to the eighth aspect of the present invention, it is possible to easily detect various elements contained in scrap metal stored in a scrap processing plant or the like.

[0035] A ninth aspect of the present invention relates to a method for producing recycled materials, which uses solid metals separated using a metal detection method that involves attaching a reagent according to the first, third, or fourth aspect of the present invention to the surface of the solid metals. A tenth aspect of the present invention relates to a method for producing recycled materials, which uses solid metals separated using a metal detection method according to any one of the fifth to eighth aspects of the present invention.

[0036] According to the ninth or tenth aspect of the present invention, a recycled material having a desired composition can be appropriately produced by using solid metals that have been appropriately separated by the metal detection method of the present invention.

[0037] 1 is a graph showing measurement results according to one embodiment of the present invention; 2 is a photograph obtained in another embodiment of the present invention; 3 is a photograph obtained in yet another embodiment of the present invention; 4 is a schematic diagram showing a reagent application mode according to one embodiment of the present invention; 5 is a schematic diagram on the left side showing a state in which the reagent is spread more thinly along the surface of the specimen than the schematic diagram on the right side;

[0038] [First embodiment]

[0039] A metal detection reagent and a metal detection method according to a first embodiment of the present invention are described. These reagents and methods are used to detect relatively small amounts of metal elements (hereinafter referred to as "target elements") other than the main component contained in a solid metal (hereinafter referred to as "analyte"). The main component refers to the component with the highest concentration among the components contained in the alloy. The analyte is a copper alloy, its raw material, and other metals. Copper alloys include brass and bronze. Specific examples of brass include bismuth-based brass (e.g., JIS C6803), lead-based brass (e.g., JIS C3604, C3771, C3531), silicon-based brass (e.g., JIS C6932), and high-strength brass (e.g., JIS C6782). Specific examples of bronze include lead-based bronze (e.g., JIS CAC406C), bismuth-based bronze (e.g., JIS CAC902C), and phosphor bronze (JIS C5212).

[0040] The reagent and method according to the present embodiment are used, for example, in a process for separating scrap metal into different materials at indoor or outdoor sites such as scrap processing plants, as a pre-process for recycling scrap metal. For this purpose, the reagent is prepared in a liquid form and applied to the surface of the scrap metal to be inspected by applying it with a brush or paintbrush, spraying it with a spraying device such as a spray gun, or by using a substrate in the form of a sheet or sticker, or a substrate in the form of a cotton swab.

[0041] The reagent according to this embodiment is an aqueous solution containing an organic colorant, a pH adjuster, and an additive. The pH values ​​described herein are based on measurements using a pH meter that employs the glass electrode method. Specifically, the pH measurements were performed using a pH meter, LAQUAtwin-pH-33B (manufactured by Horiba).

[0042] Organic colorants are materials that utilize organic compounds and change color by forming bonds such as complexes with metal ions. Examples include xylenol orange (hereinafter referred to as "XO," primarily used for detecting bismuth and lead). Other examples of organic complexes include rhodizonic acid (for detecting lead) and o-phenanthroline (for detecting nickel, etc.), and organic precipitations include dimethylglyoxime (for detecting nickel, etc.). One or a combination of two or more of these compounds is used. Compared to colorants using inorganic compounds, organic colorants have higher selectivity and sensitivity for the metal ions of the target metal, resulting in higher detection sensitivity. Examples of XO analogs include semixylenol orange and methylthymol blue, which, like XO, can be used to detect bismuth and lead.

[0043] For example, XO can be used as an organic coloring agent for bismuth as the target element. When bismuth-containing brass is used as the test object, the recommended concentration of XO is 0.05 to 0.20 mass%. It is preferable to use different concentrations of the organic coloring agent depending on the purpose, such as 0.05 mass% when the test speed is important, or 0.20 mass% (when the maximum bismuth concentration of the test object is 3 mass%) when it is desired to grasp the bismuth concentration of the test object (see the Examples described later).

[0044] The pH adjuster is a material used to adjust the pH of the reagent to a range suitable for the organic colorant. Organic colorants may cease to function or decompose if the acid concentration is too high. Therefore, in this embodiment, the pH adjuster is adjusted so that the pH of the reagent is 0 or higher. This prevents the acid concentration of the reagent from being too high, suppressing decomposition and malfunction of the organic colorant, and enabling the appropriate use of highly sensitive organic colorants.

[0045] Furthermore, the pH adjuster is adjusted to a concentration such that the pH of the reagent allows the organic coloring agent to react appropriately with the target element. As an example, XO exhibits a yellow color at a pH of 6 or less, and when it binds with various metal ions, it changes color to red or purple depending on the type of binding entity. XO can bind with many types of metal ions, but the metal ions that bind are limited depending on the pH range. For example, by setting the pH to approximately 1 to 2, the metal ions that bind can be limited to a limited number of ions, including bismuth.

[0046] The pH adjuster is contained in the reagent under conditions such that the pH of the reagent is adjusted to a range appropriate for each of the organic colorant and the target element. The appropriate pH range refers to a pH range in which the organic colorant contained in the reagent and the target element form a bond after the solid metal reacts with the acid contained in the reagent and the acid is consumed to dissolve the solid metal surface.

[0047] For example, when bismuth-containing brass or bronze is used as the analyte and XO is used as the organic coloring agent for the reagent targeting bismuth as the target element, the pH is set to approximately 1 to 2 using a pH adjuster. This corresponds to the range in which the red coloration and selectivity of XO relative to bismuth are ensured to a certain extent. In other words, this corresponds to the range in which elements other than bismuth, such as copper, zinc (brass), or copper, tin (bronze), are not detected in brass or bronze because they do not colorate or, if they do colorate, are a color other than red, and only bismuth is properly detected. From this perspective, a suitable range is pH 0.8 to 1.8. Furthermore, a suitable range for detecting only bismuth, excluding the suitable range for a combined bismuth and lead test reagent described below, is pH 0.8 to 1.4.

[0048] Furthermore, when XO is used as an organic coloring agent in a reagent for analyte-based lead brass or bronze and targeting lead, the pH is set to a range of 1.6 to 2.1 using a pH adjuster. Of this range, a pH of 1.6 to 1.8 corresponds to the range in which bismuth exhibits a red coloration, while lead exhibits a purple coloration, as described above, making it possible to clearly distinguish between bismuth and lead. Therefore, this range can be used as a composite reagent for bismuth and lead. In contrast, at a pH of around 2, only lead exhibits a deep purple coloration. Therefore, a pH of around 2 is suitable for a reagent containing lead alone. The upper limit of this range, pH 2.1, avoids the range in which high-strength brass exhibits coloration. Depending on the coexisting substances in the reagent, the usage environment, and the elements contained in the analyte, a pH greater than 2.1 can be used.

[0049] The pH adjuster may be any one or a combination of two or more of perchloric acid, hydrochloric acid, nitric acid, sulfuric acid, citric acid, tartaric acid, sodium hydroxide, potassium hydroxide, sodium carbonate, aqueous ammonia, etc. For example, when XO is used as an organic coloring agent, perchloric acid is used for clear coloring, while nitric acid is used when it is desired to impart oxidizing power to the reagent and control the valence of elements that are eluted. Acids with stronger oxidizing power or smaller acid dissociation constants will develop color more quickly, but they tend to deteriorate more easily when the reagent is stored for a long period of time.

[0050] The additives include materials for improving the performance of the reagent. As described above, the pH adjuster is adjusted so that the pH of the reagent is 0 or higher. This prevents the acid concentration of the reagent from being too high, and allows for the appropriate selection of materials for improving the performance of the reagent, as described below.

[0051] When selecting the additive material, the following problems specific to the analyte being a solid metal were taken into consideration. The first problem is that, because the reagent is in liquid form, there is a risk that the reagent may not be able to maintain its adhesion to the analyte. If the reagent cannot be sufficiently retained on the surface of the analyte, the color of the organic coloring agent may not develop sufficiently, or the color may not be clearly visible. The second problem is that the original color of the analyte surface may reduce the visibility of the color of the reagent.

[0052] The additive to the reagent according to this embodiment includes a fixative (an example of a "retention agent" in the present invention) to address the first problem. The fixative solidifies the reagent (increasing its viscosity and preventing fluidization, thereby maintaining its adhesion to the analyte). For example, the fixative may consist of one or a combination of two or more of a resin emulsion in water, a water-soluble thickener, a gelling agent, etc. The resins mentioned above include both synthetic and natural resins. The coloring behavior of organic colorants is highly dependent on the pH of the reagent. Therefore, if the reagent attached to the analyte dries or reacts excessively with the analyte, causing a change in the pH of the reagent, the bond (e.g., complex) between the organic colorant and the target element may decompose and fade, or elements other than the target element may bond to the organic colorant, potentially rendering the reagent unable to detect the target element. In contrast, the fixative dries and retains the bond between the organic colorant and the target element on the solid metal surface. This allows the bonded body to maintain its state for a long period of time, so the color formed by the bond between the organic coloring agent and the target element is maintained regardless of the ambient pH. Furthermore, excess coloring agent, such as unbound coloring agent, is trapped inside the reagent, preventing it from coming into contact with elements other than the target element. Therefore, regardless of the ambient pH, the risk of the organic coloring agent bonding with elements other than the target element and causing coloration is reduced.

[0053] To address this issue, the inventors applied a reagent containing XO, a fixing agent, and a background color blocking agent, with a pH adjusted for bismuth detection, to bismuth-containing brass. The reagent reacted with the bismuth in the brass, turning red, and then dried, remaining on the solid metal surface. The reagent was left for two weeks and then vigorously scrubbed under running water. As a result, the red color of the reagent was not lost. Such color stability and robustness are particularly useful when separating large quantities of analytes, such as when processing scrap metal at a scrap processing plant.

[0054] A first specific example of a fixing agent is an emulsion of vinyl acetate resin, vinyl chloride resin, acrylic resin, etc. (including modified or copolymerized versions of these) dispersed in water. A second specific example of a fixing agent is a polyether polymer compound such as polyethylene glycol, a cellulose derivative such as hydroxyethyl cellulose, or a water-soluble thickener or gelling agent such as propylene glycol alginate. The first specific example is preferably used when high fixing stability is required for the reagent that has been dried and held on the solid metal surface. The second specific example is preferably used when high fixing stability is not required for the reagent that has been dried and held on the solid metal surface.

[0055] The amount of fixative added to the reagent is preferably adjusted using the viscosity of the reagent as an indicator. For example, when applying or spraying the reagent using a commercially available brush or spray gun, adjusting the viscosity to approximately 500 mPa·s makes it easier to obtain a liquid that can be used for both application and spraying. The liquid temperature during viscosity adjustment should be matched to the temperature at which the reagent will be used. If the viscosity of the reagent is too low, the amount of reagent adhering to the analyte will be reduced, the color of the reagent will be weak, and the reagent will be more likely to be repelled from the surface of the analyte and run off. If the viscosity of the reagent is too high, the amount of reagent adhering to the analyte will increase, and the diffusion of ions of the target element eluted from the analyte will also be slowed, which may significantly slow the color of the reagent. Furthermore, when spraying the reagent, a special spray gun that can handle high viscosities may be required, or spraying may not be possible at all.

[0056] In addition, additives that maintain the reagent's adhesion to the analyte may include one or a combination of two or more of the following (which correspond to examples of the "retention agent" of the present invention): a dispersant (to prevent the background color-blocking agent from settling, as described below), a surfactant (to prevent the reagent from being repelled when the analyte is covered with an oil film), a viscosity modifier, a thixotropic agent (to prevent dripping, maintaining a constant reagent film thickness and achieving stable color development), and a protective colloid (to prevent the hydrophobic colloid from condensing and ensuring a constant solidification time). As a result, when the reagent is attached to the analyte, as shown in the schematic diagrams A(1) and A(2) on the left side of Figure 4, the reagent 2a spreads thinly over the surface of the analyte 1, making it less likely to spill. The thin spread of the reagent 2a provides a wide area of ​​contact between the target element contained in the analyte 1 and the reagent, accelerating color development. Photograph A(3) of Figure 4 shows the uniform color development of the reagent. Furthermore, the amount of reagent used can be reduced, making this reagent easier to use when large amounts of analyte are required. Furthermore, if the reagent is less likely to spill from the specimen, the specimen can be moved with the reagent still attached, improving work efficiency when testing a large number of specimens. The schematic diagrams B(1) and B(2) on the right side of Figure 4 show a state in which such measures are not taken, with the reagent 2b rising high above the surface of the specimen 1. Photograph B(3) of Figure 4 shows a situation in which the reagent is colored only at the edges. In Figure 4, the area surrounded by the dashed line indicates that the surface of the specimen 1 has dissolved over the entire area 1a and 1b where the reagent is applied. This allows the target element in the specimen 1 to elute into the reagent. Figure 4 shows the elution of lead as an example of a target element in the specimen 1. Not limited to lead, various target elements will elute into the reagents 2a and 2b. Surfactants for purposes other than those described above for preventing oil films include antifoaming agents and leveling agents (additives that reduce the surface tension of the coating surface and level the film thickness, i.e., flatten it).

[0057] To address the second problem, the additive to the reagent according to this embodiment contains a background color shielding agent (an example of a "color visibility enhancer" according to the present invention). The background color shielding agent is a material that shields the background color when the reagent is attached to a specimen, that is, makes the color of the specimen's surface less visible through the reagent. This improves the visibility of the color of the organic colorant against the background color (the color of the specimen's surface).

[0058] Examples of background color blocking agents include fluororesins, cellulose fibers, filter paper, minerals, ceramics, hollow resin powders, oils, and other substances that render the reagent opaque when added to the reagent. The amount of background color blocking agent added to the reagent is preferably kept to a minimum so that the color of the specimen surface is not visible through the reagent. Adding an excessive amount of background color blocking agent may block the color of the organic coloring agent, potentially reducing the visibility of the test. The color of the background color blocking agent itself is preferably a color that clearly distinguishes the color of the organic coloring agent, such as white. The vinyl acetate resin used as the background color blocking agent also functions as a thickener, providing fixation when the reagent dries on a metal surface. Other useful thickeners include cellulose derivatives and polymers of quaternary or tertiary ammonium salts.

[0059] In addition, whether a fixing agent, background color blocking agent, or other additive is added, a substance that is unlikely to lose its properties in the vicinity of the pH range adjusted by the pH adjuster and that does not interfere with the reaction mechanism of the reagent is selected.

[0060] As described above, the reagent according to this embodiment contains a pH adjuster that adjusts the pH to 0 or higher, thereby dissolving the surface of the solid metal being the specimen and diffusing the elements contained in this solid metal into the reagent. The organic coloring agent contained in the reagent then binds to the target element, causing the surface of the dissolved solid metal to develop a color.

[0061] In this way, by reducing the amount of pH adjuster and adjusting the pH to 0 or above, the acid concentration is not too high and the reagent is not classified as a poisonous substance, thereby improving safety and preserving the working environment. In addition, because the acid concentration is not too high, various organic coloring agents can be blended.

[0062] Furthermore, the reagent according to this embodiment is a liquid, and fixing agents such as vinyl acetate resin emulsions, which are examples of retention agents added to maintain the reagent adhered to the surface of solid metal, are prone to deterioration at high acid concentrations. However, the reagent according to this embodiment has a pH adjusted to 0 or above, making the retention agent less likely to deteriorate. This means that the reagent can be used as a one-component, all-in-one liquid reagent that does not need to be mixed immediately before use, and can also be stored for a long period of time.

[0063] Furthermore, the reagent according to this embodiment contains a resin such as a vinyl acetate resin emulsion as a fixing agent, so that the reagent dries and is held on the solid metal surface in a state where a complex (color former) consisting of the target element and the color former is embedded in the mesh structure of the resin, thereby maintaining color stability that can withstand impact, friction, wind and rain, etc. Furthermore, the inclusion of the resin can prevent the reagent from scattering, prevent contamination of the working environment, and improve work safety.

[0064] However, reducing the amount of pH adjuster reduces the amount of dissolved analyte, which may result in a decrease in color visibility. Therefore, the reagent according to this embodiment contains a background color shielding agent, e.g., an organic substance such as a resin, as an example of a color visibility enhancer, thereby improving color visibility on the surface of the solid metal and enabling surface inspection. Furthermore, because the organic substance decomposes at high temperatures into harmless gas, there is no need to remove the reagent after inspection. The scrap can be cast and melted with the reagent still applied, thereby achieving the casting suitability of the reagent.

[0065] As described above, the reagent according to this embodiment is a one-component, i.e., all-in-one, liquid reagent that does not need to be mixed immediately before use, while at the same time improving color development on the surface of solid metals, providing good color development stability, ensuring a good working environment and safety during testing, and having the notable features of being able to recycle scrap coated with the reagent by casting and melting it without having to remove the reagent after testing.

[0066] (Method of applying reagent)

[0067] The reagent is applied to the specimen in a flat manner using an application tool such as a paintbrush, spatula, sprayer, or dispenser, thereby controlling the thickness of the reagent film formed on the specimen surface (i.e., film thickness) to fall within an appropriate range. If the film thickness falls below the lower limit of this range, the pH of the reagent is likely to change when the reagent reacts with the solid metal specimen and the acid in the reagent is consumed. This may result in the failure to obtain the desired coloration results. On the other hand, if the film thickness exceeds the upper limit of this range, the target element eluted from the specimen is less likely to diffuse to the coating surface, resulting in a dull coloration. By controlling the film thickness within an appropriate range, these problems are less likely to occur. According to the examples described below, the appropriate film thickness range was 90 to 130 μm. Note that this film thickness range may vary depending on the coexisting substances in the reagent and the usage environment.

[0068] (First Example)

[0069] As an example of this embodiment, an experiment was conducted to determine the appropriate range of the concentration of the organic coloring agent. This experiment was based on the following considerations: There is a limit to the amount of target element that can be eluted from the surface of the specimen. Therefore, even if the concentration of the organic coloring agent in the reagent is increased, the color intensity saturates at a certain value. Furthermore, the remaining organic coloring agent that has not bound to the target element remains on the surface of the specimen, retaining its original color. Therefore, the original color of the organic coloring agent that has not bound to the target element may interfere with the color of the organic coloring agent that has bound to the target element, potentially reducing its visibility.

[0070] Therefore, in this example, a reagent was prepared using bismuth-based brass as the test specimen and XO as the organic coloring agent. Perchloric acid was used as the pH adjuster, and a vinyl acetate resin emulsion was used as the additive (fixing agent, etc.). The pH of the reagent was adjusted to 1.1. In this manner, three types of reagents with different XO concentrations were prepared. These three types of reagents were then sprayed onto bismuth-based brass with a common component composition, and the color development of the reagents was repeatedly measured while measuring the elapsed time from spraying.

[0071] Figure 1 is a graph showing the measurement results. In the graph of Figure 1, the color difference ΔE00 on the vertical axis is based on the color of XO before bismuth is bonded. ΔE00 is a color difference calculated based on the CIE DE2000 color difference formula. This is the same as CIE LAB (L * a * b * The color difference based on the color space) is adjusted according to the actual color discrimination range of humans. Lower limit A represents the lower limit of the color difference at which the color of the reagent can be accurately discriminated even outdoors. Lower limit B represents the color difference below lower limit A, which may cause the color of the reagent to be misidentified outdoors, but represents the lower limit of the color difference at which the color of the reagent can be accurately discriminated indoors.

[0072] "XO equivalent" corresponds to a reagent in which the concentration of XO is adjusted so that the reagent contains an amount of XO that is completely combined with the upper limit amount of bismuth eluted into the reagent attached to the analyte, with no excess. "XO equivalent x α" corresponds to a reagent in which the concentration of XO is adjusted so that the reagent attached to the analyte contains an amount of XO that is α times the amount of "XO equivalent" reagent.

[0073] As shown in the graph in Figure 1, of the three types of reagents, the "XO equivalent x 0.75" reagent reached the timing when the color difference exceeded the lower limits A and B the earliest, and the color difference saturated the earliest. The higher the XO concentration, the longer it took to reach these timings.

[0074] As described above, when prioritizing the speed, work efficiency, and cost of the test, it has been found that it is best to limit the concentration of the organic coloring agent to be mixed into the reagent to a concentration that provides the minimum necessary color difference and color intensity. In this example, this corresponds to the reagent "XO equivalent x 0.75".

[0075] (Second Example)

[0076] A reagent was prepared by adding perchloric acid to a 65% vinyl acetate resin emulsion (water content: 60% by weight) to adjust the pH to 1.1, and then adding 0.07% by weight of XO to adjust the viscosity to 500 mPa·s. This reagent was applied to brass JIS C3604 (59% by weight copper, 38% by weight zinc, 3% by weight lead) and brass JIS C6803 (60% by weight copper, 38% by weight zinc, 1% by weight bismuth, 1% by weight tin), and the results were observed for two weeks. No discoloration was observed for the reagent applied to brass C3604, and the applied reagent dried to near transparency after approximately 10 minutes. No change in appearance was observed even after two weeks. For the reagent applied to brass C6803, coloration began within a few seconds of application, and the color stabilized to red-pink after approximately three minutes. After about 10 minutes, the applied reagent had stably turned red even after drying. There was no change in appearance even after two weeks, maintaining the red color after drying. Figure 2 is a photograph showing the reagent approximately 3 minutes after application to C3604 and C6803. Note that this sample maintained a clear color even after one year. This is because the reagent dries with the target element bonded to the resin network structure of the vinyl acetate resin emulsion, which serves as a retention agent (fixer), and is then held on the solid metal surface. When resin is used as a retention agent (fixer), the target element bonded to the resin network structure is held on the solid metal surface as the reagent dries, thereby maintaining color stability.

[0077] (Third Example)

[0078] A reagent was prepared by adding 65% by weight of vinyl acetate resin emulsion (water content: 60% by weight) as an additive to a 0.05% by weight XO aqueous solution adjusted to pH 1.1 with perchloric acid. This reagent was applied to brass C6803 with the same composition as in Example 2, and the test was observed for 10 minutes. The results showed that the reagent began to discolor within a few seconds of application, and the color stabilized at red to pink after about one minute. Figure 3 shows photographs of the brass coated with the reagent taken multiple times from application to one minute after application, showing the color change of the reagent.

[0079] (Fourth Example)

[0080] Several types of reagents were prepared by adding a 65% by weight vinyl acetate resin emulsion (water content: 60% by weight) as an additive to a 0.05% by weight XO aqueous solution and adjusting the pH to different values ​​with perchloric acid. Five types of brass, Samples 4-1 to 4-5, were also prepared as test specimens. Sample 4-1 was a lead-based brass (JIS C3604), Sample 4-2 was a low-lead brass (CDA C46750), Sample 4-3 was a bismuth-based brass (JIS C6803), Sample 4-4 was a high-strength brass (JIS C6782), and Sample 4-5 was a silicon-based brass (JIS C6932). The specific compositions of these samples are shown in Table 1 below. In Table 1, "-" indicates that the component is not included, and "balance" indicates the remainder.

[0081]

[0082] Each of the above multiple types of reagents, each with a different pH value, was applied to these samples using a bar coater. The bar coaters were used to control the thickness of the reagent film on the sample surface; for pH 0.8 to 1.4, an OSP-120T (manufactured by OSG System Products) was used, and for pH 0.5 and pH 2.1 to 3.8, an OSP-150T (manufactured by OSG System Products) was used. For pH 1.5 to pH 1.8, both bar coaters were used. The film thickness of the reagent using the OSP-150T was greater than that of the reagent using the OSP-120T. The changes in the reagent on the sample surface over time were then observed. The results are shown in Table 2 below.

[0083]

[0084] In Table 2, "- -" indicates that data was acquired, but the target element was not included, so theoretically coloration would not occur, and therefore the test results also showed no coloration. Furthermore, double circles (◎) indicate strong coloration, open circles (◯) indicate coloration, and crosses (×) indicate no coloration. Black circles (●) indicate a range in which coloration occurs but requires a larger film thickness. This is demonstrated by the following results. When a reagent with a pH of 1.5 to 1.8 was applied to sample 4-3 using OSP-120T, the reagent developed coloration, but then premature fading occurred. When a reagent with a pH of 1.5 to 1.8 was applied to sample 4-3 using OSP-150T, the premature fading was less likely to occur. When a reagent with a pH of 1.8 was applied to sample 4-3 using OSP-120T, the reagent film thickness on the surface of sample 4-3 was approximately 100 μm. When a reagent of pH 1.8 was applied to sample 4-3 using OSP-150T, the thickness of the reagent film on the surface of sample 4-3 was about 130 μm.

[0085] (Fifth Example)

[0086] A reagent was prepared by adding 65% by mass of vinyl acetate resin emulsion (water content: 60% by mass) as an additive to a 0.05% by mass XO aqueous solution adjusted to pH 1.1 with perchloric acid. Samples 5-1 to 5-4 were also prepared as test specimens. Sample 5-1 consisted of lead-based brass (JIS C3604), sample 5-2 consisted of lead-based bronze (JIS CAC406C), sample 5-3 consisted of bismuth-based brass (JIS C6803), and sample 5-4 consisted of bismuth-based bronze (JIS CAC902C). The specific compositions of these samples are shown in Table 3 below. In Table 3, "-" indicates that the component is not included, and "balance" indicates the remainder.

[0087]

[0088] The above-mentioned reagent was applied to these samples using six types of bar coaters. When the film thickness of the reagent was measured, the measured values ​​were 50, 75, 90, 130, 160, and 210 μm, depending on the six types of bar coaters. The color of the reagent on the sample surface was as shown in Table 4 below. The six types of bar coaters, in order from thinnest to thickest, were OSP-52T, OSP-80T, OSP-100T, OSP-150T, OSP-200T, and OSP-300T.

[0089]

[0090] In Table 4, a cross (x) indicates that there was no or almost no coloring, a white triangle (△) indicates that light coloring occurred, and a white circle (◯) indicates that coloring occurred well. A black triangle (▲) indicates that coloring occurred, but not well. More specifically, in the ▲, coloring occurred only on the outer edge of the area where the reagent was applied, and the coloring was light inside. Note that "- -" indicates that the measurement was not yet performed.

[0091] As in the case above, a reagent was prepared with only the pH adjusted for lead detection, and when it was applied to a sample made of lead-based brass, good coloring appeared on the surface of the film at a film thickness of 90 to 130 μm. Outside the above range, coloring was poor or did not appear properly on the surface of the film.

[0092] (Sixth Example)

[0093] Multiple reagents containing 0.05% by mass of XO, perchloric acid as a pH adjuster, and a vinyl acetate resin emulsion as an additive were prepared, varying the concentration of the pH adjuster. These reagents were left undisturbed in a container, and the number of days from the day of preparation until discoloration began was measured. As a result, a linear relationship was found between the reciprocal x of the pH adjuster concentration (mol / L) and the number of days y. Specifically, the regression line y = 1.0396 * x - 0.1699 (R = 0.9973) was obtained.

[0094] (Other conditions related to the concentration of organic coloring agents)

[0095] When the amount of organic coloring agent contained in the reagent is sufficient relative to the amount of target element eluted from the analyte into the reagent, the color difference and color intensity of the color produced by the organic coloring agent due to the reaction with the target element are proportional to the amount of target element eluted from the analyte into the reagent. Therefore, when a group of analytes with various target element blend ratios are to be detected, the analytes can be separated by blend ratio by adjusting the concentration of the organic coloring agent to match the maximum blend ratio of the analyte group.

[0096] For example, in a reagent for use with a group of analytes made of bismuth-containing brass with a bismuth content of 1 to 3% by mass, the concentration of the organic coloring agent may be adjusted to a content of 3% by mass. Specifically, the concentration of XO may be adjusted so that the reagent contains an amount of XO sufficient to bind to the upper limit of the amount of bismuth eluted into the reagent from a 3% by mass analyte. For example, by applying a predetermined amount of reagent to the analyte and measuring the color difference or color intensity of the color of the reagent after a sufficient amount of time has passed, the amount of target element eluted into the reagent can be determined based on the measurement results. The amount of target element eluted into the reagent increases depending on the content of the target element in the analyte. Therefore, the content of the target element in the analyte can be determined based on the measurement results.

[0097] If a test sample group containing multiple test samples with different compounding ratios were not separated by compounding ratio, but instead separated solely by the presence or absence of a target element, the separated test sample group would contain test samples with various compounding ratios. Therefore, for example, when a recycled material is obtained from a test sample group separated in this manner, the resulting recycled material would have an intermediate composition of the target element mixture in the raw test sample group. Test samples with different compounding ratios of one metal element often also differ in the types and compounding ratios of other elements. Therefore, a recycled material with an intermediate composition, such as the one described above, would have a different composition from any of the original test samples, making it difficult to reuse. Therefore, by separating a test sample group by compounding ratio as described above, such problems can be alleviated.

[0098] (Effects of this embodiment)

[0099] According to the first embodiment described above, the reagent has a pH of 0 or higher and a moderate acid concentration. This allows the use of organic colorants that may cease functioning or decompose if the acid concentration is too high. It is easy to select organic colorants with high detection sensitivity under appropriate pH conditions. Furthermore, because the reagent's acid concentration is not too high, it is easy to select auxiliary materials to improve detection performance. In selecting such auxiliary materials, this embodiment takes into account the first and second problems inherent to targeting solid metals. In response to these issues, the reagent of this embodiment contains a fixative, surfactant, etc., and a background color blocking agent. The fixative, surfactant, etc., mitigate the first problem, while the background color blocking agent mitigate the second problem. This improves the detection performance of the reagent. For example, the reagent enables detection even when the target element has a relatively low content. Specifically, when brass, which has a bismuth content of approximately 1% by mass, is used as the target element, bismuth can be detected.

[0100] Second Embodiment

[0101] A metal detection reagent and metal detection method according to a second embodiment, which is another preferred embodiment of the present invention, will be described. The specimen according to the second embodiment is the same as the specimen according to the first embodiment. Furthermore, the reagent according to the second embodiment uses the same organic coloring agent and pH adjuster as in the first embodiment. Descriptions of elements common to the first embodiment will be omitted where appropriate.

[0102] The reagent according to the second embodiment is an aqueous solution containing at least an organic coloring agent and a pH adjuster. This reagent is used by impregnating a liquid-impregnable substrate and bringing the substrate into contact with the surface of a test specimen. The substrate is, for example, a member made of paper, cotton, synthetic fiber, glass fiber, or the like, and may be in the form of a sheet or a cotton swab.

[0103] When the substrate is in the form of a sheet, the substrate impregnated with the reagent is attached to the surface of the specimen, thereby attaching the reagent to the specimen. This causes the target element to elute from the specimen into the reagent on the substrate. The examiner then checks the color of the reagent on the substrate.

[0104] When the substrate is in the form of a cotton swab, the substrate impregnated with the reagent is rubbed against the surface of the specimen, causing the target element to elute from the specimen into the reagent on the substrate.The substrate is then removed from the specimen and brought in front of the examiner, who then checks the color of the reagent on the substrate.

[0105] The reagent of this embodiment is adjusted to a pH of 0 or higher using a pH adjuster, as in the first embodiment. This prevents the reagent from having an excessively high acid concentration, allowing for the appropriate selection of a substrate material and the appropriate use of the reagent by impregnating the substrate. The substrate is then brought into contact with the test specimen, allowing the reagent to adhere to the test specimen. Therefore, the first problem described above is less likely to occur compared to the first embodiment, in which the reagent is directly adhered to the test specimen surface. Therefore, the reagent of the second embodiment does not require the addition of a fixing agent, surfactant, etc. (materials corresponding to the "retention agent" of the present invention). Furthermore, the color of the organic colorant is displayed on the substrate. Therefore, by selecting a substrate color that is unlikely to reduce the visibility of the reagent color, the second problem described above is less likely to occur. Therefore, the reagent of the second embodiment does not necessarily require the addition of a background color shielding agent (materials corresponding to the "color visibility enhancer" of the present invention). Depending on the characteristics of the substrate and the test environment, a fixing agent, background color shielding agent, etc. may be appropriately added to the reagent.

[0106] As described above, the reagent of the second embodiment has a moderate acid concentration, thereby broadening the range of choices for coloring agents and substrates. Accordingly, an organic coloring agent with high detection sensitivity is selected, and the agent is impregnated into a substrate for use. This ensures the detection performance of the reagent for the analyte. For example, even if the analyte contains a relatively low content of the target element, the reagent can be used to detect it. Specifically, when brass containing approximately 1% bismuth by mass is used as the analyte, bismuth can be detected as the target element.

[0107] [Another embodiment of pre-processing for metal detection]

[0108] For example, if the test object is scrap metal and oil, such as cutting oil or anti-rust oil, is attached to the surface of the test object, the oil on the test object surface may repel the reagent when used. Therefore, pretreatment, such as degreasing the test object surface, may be required. In contrast, the water-soluble reagent according to this embodiment adjusts the pH of the reagent to 0 to 14. Therefore, the aforementioned surfactant can be added to deal with the oil. This prevents the reagent from being repelled, allowing metal detection to be performed without degreasing as a pretreatment. For example, if the test object is scrap metal and has an oxide film on its surface, it is desirable to remove the oxide film by polishing or pickling as a pretreatment.

[0109] <Modification>

[0110] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configurations should not be considered to be limited to these embodiments. The scope of the present invention is defined by the claims rather than the above description of the embodiments, and further includes all modifications within the meaning and scope of the claims.

[0111] For example, in the first embodiment described above, both a material that maintains adhesion to the analyte, such as a fixing agent, and a background color blocking agent are contained as additives in the reagent. Alternatively, the reagent may contain only one of the material that maintains adhesion to the analyte, such as a fixing agent, and the background color blocking agent. The presence of either of these improves the detection performance of the reagent compared to a case in which neither is contained.

Claims

1. A liquid reagent for detecting elements other than the main component in a solid metal, the reagent comprising: an organic colorant that is used by being attached to the solid metal and reacts with the element to produce a color; and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal; and the metal detection reagent is characterized by having a pH adjusted to 0 or higher.

2. A liquid reagent for detecting elements other than the main components in solid metals, which is used by impregnating a substrate and bringing the substrate into contact with the solid metal, and which contains an organic coloring agent that reacts with the element to produce a color, and which has a pH adjusted to 0 or higher.

3. A liquid reagent for detecting bismuth in solid metal, which is used by being attached to the solid metal and contains xylenol orange as an organic colorant that reacts with the bismuth to produce a color, and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal, and which has a pH adjusted to 0 or higher.

4. A reagent for detecting bismuth according to claim 3, characterized in that it contains both the retention agent and the color visibility enhancer.

5. A reagent for detecting bismuth according to claim 3, characterized in that the pH is adjusted to 0.8 or more and 1.8 or less.

6. A reagent for detecting bismuth according to claim 3, characterized in that the retention agent contains a fixing agent that maintains the colored state.

7. A liquid reagent for detecting lead in solid metal, the reagent comprising: xylenol orange as an organic colorant that reacts with the lead to produce a color when attached to the solid metal; and at least one of a retention agent that maintains the state of attachment to the solid metal and a color visibility enhancer that improves the visibility of the color of the organic colorant relative to the color of the surface of the solid metal; and the lead detection reagent is characterized by having a pH adjusted to 0 or higher.

8. A reagent for detecting lead according to claim 7, characterized in that it contains both the retention agent and the color visibility enhancer.

9. A reagent for detecting lead according to claim 7, characterized in that the pH is adjusted to 1.6 or more and 2.1 or less.

10. A reagent for detecting lead according to claim 7, characterized in that the retention agent contains a fixing agent that maintains the colored state.

11. A method for detecting metals, comprising attaching the reagent according to any one of claims 1 and 3 to 10 to the surface of said solid metal.

12. A metal detection method according to claim 11, wherein the reagent is attached to the surface of the solid metal by either painting or spraying the surface of the solid metal.

13. The metal detection method according to claim 12, wherein the thickness of the film of the reagent formed on the surface of the solid metal is adjusted.

14. The metal detection method according to claim 13, wherein the organic coloring agent is xylenol orange, and the reagent is applied to the surface of the solid metal so that the thickness of the reagent film is 90 to 130 μm.

15. A metal detection method using the reagent described in claim 2, characterized in that after rubbing the substrate against the surface of the solid metal, the substrate is observed at a position spaced apart from the solid metal.

16. A metal detection method using the reagent according to claim 2, characterized in that the substrate is attached to the surface of the solid metal.

17. A metal detection method comprising attaching the reagent according to claim 1, 2, 3 or 7 to the surface of the solid metal, which is scrap metal.

18. A method for producing a recycled material, characterized in that the recycled material is produced using the solid metal that has been separated using a metal detection method in which the reagent described in any one of claims 1 and 3 to 10 is attached to the surface of the solid metal.

19. A method for producing recycled materials, comprising producing recycled materials using the solid metals separated using the metal detection method described in claim 15 or 16.

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