Treatment method of glass cullet with silver, manufacturing method of glass product, and treatment apparatus of glass cullet with silver

Abstract

To provide a technique capable of sufficiently removing a deposit on a surface of a glass cullet.SOLUTION: A treatment method of a glass cullet with silver includes: a silver dissolving step of dissolving silver of the glass cullet with silver with nitric acid; a glass cullet recovery step of recovering the glass cullet from which silver is removed in the silver dissolving step; and a silver recovery step of recovering silver as an insoluble salt from a silver nitric acid solution obtained in the silver dissolving step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for treating silver-coated glass cullet, a method for manufacturing a glass product, and a treatment device for silver-coated glass cullet. [Background technology]

[0002] Conventionally, in the field of automobiles and the like, methods for recycling waste glass have been considered. Since metal conductive patterns, which are components of devices such as antennas, are printed on the surface of many automobile glass, metals are often attached to the surface of glass cullet obtained by crushing the waste glass. Such metal deposits, especially deposits such as silver, corrode the melting furnace used in manufacturing glass products from the glass cullet, and have a negative effect on the quality of the melting furnace and the glass products. Therefore, various treatment techniques for removing surface deposits from glass cullet have been considered.

[0003] For example, Patent Document 1 discloses a technique for removing surface deposits such as silver prints on glass cullet by spraying an abrasive onto the glass cullet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-103336 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the technique disclosed in Patent Document 1, it is difficult to spray the abrasive evenly onto the surface of the glass cullet, and therefore, there are cases where deposits such as silver on the surface of the glass cullet cannot be sufficiently removed.

[0006] In view of the above, an object of one aspect of the present invention is to provide a technique capable of sufficiently removing deposits on the surface of glass cullet in the treatment of glass cullet. [Means for solving the problem]

[0007] One aspect of the present invention is a method for treating silver-bearing glass cullet, comprising: a silver dissolving step of dissolving silver in the silver-bearing glass cullet with nitric acid; a glass cullet recovery step of recovering the glass cullet from which the silver has been removed by the silver dissolving step; and a silver recovery step of recovering silver as an insoluble salt from the nitric acid solution of silver obtained by the silver dissolving step.

[0008] Another aspect of the present invention is a processing device for silver-bearing glass cullet, comprising a silver dissolving section that dissolves silver from the silver-bearing glass cullet with nitric acid, a glass cullet recovery section that recovers the glass cullet from which silver has been removed by dissolving the silver in the silver dissolving section, and a silver recovery section that recovers silver as an insoluble salt from the nitric acid solution of silver obtained by dissolving the silver in the silver dissolving section. Effect of the Invention

[0009] According to one aspect of the present invention, a technique can be provided that can sufficiently remove deposits on the surface of glass cullet. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows an example of a glass product from which silver-bearing glass cullet is treated according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flow diagram of a processing method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference numerals, and the description thereof may be omitted.

[0012] [Glass products and silver-plated glass cullets] First, an example of a glass product and a silver-bearing glass cullet derived from the glass product and treated in the present embodiment will be described. In this specification, "silver-bearing" refers to a state in which a substance containing silver is attached to the surface, and "substance containing silver" includes simple silver, a silver compound, and a silver alloy. The silver compound may be silver sulfide or silver chloride, and the silver alloy may be a silver-indium alloy, a silver-tin alloy, or the like.

[0013] Silver-coated glass cullet is obtained by crushing a glass product. Fig. 1 shows an automobile window glass 1 as an example of a glass product. Fig. 1(a) is a plan view of the automobile window glass 1 as seen from the inside of the vehicle, and Fig. 1(b) is a cross-sectional view taken along line II in Fig. 1(a). The automobile window glass 1 shown in Fig. 1 is a laminated glass formed by bonding glass plates 11 and 12 together with an interlayer film 20 interposed therebetween. The glass product does not necessarily have to be laminated glass, and may be a single sheet of glass.

[0014] The glass plates 11 and 12 used in the automobile window glass 1 may be made of soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, borosilicate glass, etc. The glass plates may be formed by, for example, a float method. The glass plates may be untempered or may be tempered glass that has been subjected to air-cooling tempering or chemical tempering treatment.

[0015] Examples of the intermediate film 20 include thermoplastic resins such as plasticized polyvinyl acetal resins, plasticized polyvinyl chloride resins, saturated polyester resins, plasticized saturated polyester resins, polyurethane resins, plasticized polyurethane resins, ethylene-vinyl acetate copolymer resins, ethylene-ethyl acrylate copolymer resins, cycloolefin polymer resins, and ionomer resins. In addition, a resin composition containing a modified block copolymer hydrogenated product described in Japanese Patent No. 6065221 can also be preferably used. Among these, plasticized polyvinyl acetal resins, particularly plasticized polyvinyl butyral resins, are preferably used because they have an excellent balance of various performances such as transparency, weather resistance, strength, adhesive strength, penetration resistance, impact energy absorption, moisture resistance, heat insulation, and sound insulation. The above resins may be used alone or in combination of two or more. In addition, "plasticized" means that it is plasticized by adding a plasticizer.

[0016] The automobile window glass 1 is a window glass incorporating a heat generating device such as a deicer or defogger, examples of which include a wiper deicer and a camera heater. As shown in FIG. 1(a), a silver-containing conductive pattern 40 connected to a power supply electrode (not shown) arranged in the center is arranged on the lower side of the peripheral portion of the automobile window glass 1. The silver-containing conductive pattern 40 functions as a heating stripe or the like and may be in the form of a foil or a line. Such a silver-containing conductive pattern 40 is obtained, for example, by preparing a conductive paste containing a substance containing silver and a resin, applying it to the main surface of a glass plate, and firing it during the manufacture of the automobile window glass 1.

[0017] As shown in Fig. 1(a) and (b), the silver-containing conductive pattern 40 is disposed inside the automobile window glass 1. In the example shown in Fig. 1(b), the silver-containing conductive pattern 40 is disposed on the surface of the glass plate 11 on the vehicle exterior facing the interlayer 20, but may be disposed on the surface of the glass plate 12 on the vehicle interior facing the interlayer 20, or may be disposed on a surface exposed to the vehicle exterior or interior. As shown in Fig. 1(b), when the silver-containing conductive pattern 40 is enclosed inside the automobile window glass 1, it is difficult to remove the silver without crushing the automobile window glass 1, so that the removal of silver for the reuse of glass must be performed after crushing the glass product into cullet. Therefore, the method according to the present embodiment for treating the silver-containing glass cullet can be particularly suitably used for the purpose of recycling glass products in which such a silver-containing conductive pattern is incorporated inside.

[0018] As shown in FIG. 1(a), the vehicle window glass 1 may have a shielding layer 50, also called a black ceramic layer, formed on the periphery of the glass plate 12 on the vehicle interior side. The shielding layer 50 has a function of protecting a sealant or the like for mounting and holding the vehicle window glass 1 to the vehicle body in the vehicle from ultraviolet rays or the like. The shielding layer 50 is preferably a layer formed by applying and firing a ceramic color paste, for example, black, gray, dark brown, or the like. The above-mentioned silver-containing conductive pattern 40 may be provided directly on the main surface of the glass plate 11 or 12, or may be provided on the surface of the shielding layer 50. When the silver-containing conductive pattern 40 is provided on the surface of the shielding layer 50, the glass cullet obtained by crushing the vehicle window glass 1 has the shielding layer portion attached thereto, and a substance containing silver attached to the surface of the shielding layer portion.

[0019] The silver-containing substance in the silver-containing glass cullet treated by the method according to the present embodiment is not limited to that originating from the silver-containing conductive pattern 40 in the automobile window glass 1 as described above, but may be that originating from a silver-containing substance attached to a glass product for other electronic or electrical purposes such as an antenna, or for decorative purposes. The glass product is not limited to automobile window glass, and may be any glass product having a silver-containing substance attached to its surface and for which reuse of the glass is desired. For example, it may be glass for vehicles other than automobiles, glass for architecture, glass ornaments, etc.

[0020] The thickness of silver adhering to the silver-bearing glass cullet treated by the method of this embodiment may be 3 μm or more and 10 μm or less. The amount of silver adhering to the silver-bearing glass cullet treated by the method of this embodiment is about 0.01 mass % or more and 0.1 mass % or less with respect to the total amount of the silver-bearing glass cullet.

[0021] [How to process silver-coated glass cullet] One embodiment of the present invention is a method for treating glass cullet obtained from a glass product incorporating the above-mentioned silver-containing conductive pattern or the like. FIG. 2 shows a flow diagram of the treatment method according to one embodiment of the present invention. The treatment method according to this embodiment is a method for treating silver-bearing glass cullet, and includes a silver dissolving step (S10) of dissolving silver in the silver-bearing glass cullet with nitric acid, a glass cullet recovery step (S20) of recovering the glass cullet from which silver has been removed by the silver dissolving step, and a silver recovery step (S30) of recovering silver as an insoluble salt from the nitric acid solution of silver obtained by the silver dissolving step. The treatment method according to this embodiment may include a step of crushing the glass product to obtain silver-bearing glass cullet as a pre-step of the silver dissolving step (S10). Each step will be described in more detail below.

[0022] <Pre-process> In the pre-process, the glass product is crushed to obtain silver-coated glass cullet. When obtaining silver-coated glass cullet from the above-mentioned laminated glass, that is, the window glass for an automobile, the entire laminated glass is crushed or pulverized by a crusher or the like. As a result, the glass sheets 11 and 12 are crushed into cullet. In the pre-process, the interlayer film 20 is removed, but the above-mentioned silver-containing conductive pattern 40 is crushed together with the glass sheet while remaining attached thereto, and thus becomes silver-coated glass cullet. Note that the glass cullet attached to the interlayer film may be subsequently separated by a wet process or the like.

[0023] After crushing the glass products, a process of separating the silver-bearing glass cullet from the silver-free glass cullet may be carried out prior to the silver melting process (S10). By using only the silver-bearing glass cullet obtained in this process in the silver melting process and melting the silver-free glass cullet in a melting furnace, the efficiency of recycling the glass products can be improved.

[0024] <Silver melting process (S10)> In the silver dissolving step (S10), the silver adhering to the surface of the silver-bearing glass cullet is dissolved with nitric acid. That is, the silver adhering to the surface of the glass cullet is removed by utilizing a chemical reaction with a chemical. In the conventional physical removal of adhesions by spraying an abrasive, the abrasive may not reach the adhesions, resulting in some of the silver remaining. In contrast, in the silver dissolving step (S10) using nitric acid according to the present embodiment, the liquid nitric acid spreads over the entire surface of the glass cullet, so that no or almost no silver remains. In addition, even if silver has entered into minute recesses on the surface of the glass cullet, the nitric acid spreads into such recesses, so that the silver can be sufficiently removed regardless of the surface condition of the glass cullet.

[0025] The average diameter of the silver-bearing glass cullet used in the silver dissolving step (S10) according to this embodiment may be preferably 0.01 mm or more and 50 mm or less, more preferably 0.5 mm or more and 5 mm or less. Since this step (S10) utilizes a chemical as described above, it is possible to reduce or eliminate the amount of silver left behind regardless of the average diameter of the silver-bearing glass cullet. Therefore, it is possible to process silver-bearing glass cullet having a wide range of average diameters as described above. Furthermore, even silver-bearing glass cullet having a wide diameter distribution can be processed for the same reason.

[0026] The concentration of nitric acid used for dissolving silver may be preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, further preferably 20% by mass or more and 40% by mass or less, and particularly preferably 30% by mass or more and 40% by mass or less. By setting the concentration of nitric acid to 5% by mass or more, the dissolution rate of silver can be increased, and the silver dissolution step (S10) can be performed in a short time. By setting the concentration of nitric acid to 50% by mass or less, the reaction mechanism between silver and dilute nitric acid can be made dominant, and the molar amount of silver reacting with the same molar amount of nitric acid can be increased. In addition, the viscosity of nitric acid can be suppressed, so that nitric acid can easily flow on the surface of the silver-bearing glass cullet, and dissolution can be promoted. Furthermore, by setting the concentration of nitric acid to 30% by mass or more and 40% by mass or less, the heating means for the container can be omitted, and therefore costs can be reduced. Nitric acid with a concentration of 10% by mass or less is preferable from the viewpoint that it is not designated as a deleterious substance and does not need to be handled as a deleterious substance. The concentration of nitric acid can be easily adjusted by diluting concentrated nitric acid of 60 mass % or more with water.

[0027] The amount of nitric acid used in the silver dissolving step (S10) is preferably a volume that allows the entire silver-bearing glass cullet placed in the container to be immersed in the nitric acid so that the nitric acid can be in good contact with the surface of the silver-bearing glass cullet. For example, the silver-bearing glass cullet is placed in a container, and a volume of nitric acid is poured in such that the silver-bearing glass cullet is fully immersed. The volume of nitric acid depends on the degree of silver adhesion in the silver-bearing glass cullet, but is preferably 300 to 10,000 volume parts per 100 volume parts of the silver-bearing glass cullet.

[0028] In order to dissolve silver sufficiently with nitric acid, it is preferable to use nitric acid in an amount that is in excess of the molar amount of silver in the silver dissolving step (S10). For this reason, the user of the processing method according to this embodiment can estimate the total amount of silver attached to the silver-bearing glass cullet from the total amount of silver attached to the surface of the glass product before crushing, and determine the concentration and volume of nitric acid in advance.

[0029] In the silver dissolving step (S10), it is preferable to dissolve silver while flowing nitric acid. Instead of or in addition to flowing nitric acid, the silver-bearing glass cullet may be moved. Such a movement promotes the diffusion of silver ions into the nitric acid, so that silver can be dissolved in a shorter time. Even in cases where the silver on the surface of the silver-bearing glass cullet is not sufficiently exposed to nitric acid due to overlapping or adhesion between the silver-bearing glass cullet, the overlapping or adhesion between the silver-bearing glass cullet can be eliminated by moving the nitric acid and / or the silver-bearing glass cullet, so that the amount of silver remaining after removal can be reduced or eliminated.

[0030] In order to move the nitric acid and / or the silver-coated glass cullet, agitation means such as an agitation blade, an agitation ball, a magnetic stirrer, etc. can be placed inside the container to directly create movement. Alternatively, ultrasonic generation means, shaking means, etc. may be placed outside the container to impart vibrations to the container from the outside. Of these, it is preferable to use agitation means because it can smoothly flow the entire nitric acid and is easy to handle and change the conditions.

[0031] The temperature of the nitric acid in the silver dissolving step (S10) is preferably higher than room temperature, for example, higher than 15°C. When the temperature is higher than room temperature, the dissolution rate increases, so that silver can be dissolved in a shorter time. The temperature of the nitric acid in the silver dissolving step (S10) may be preferably 5°C to 70°C, more preferably 15°C to 70°C, even more preferably 30°C to 70°C, and particularly preferably 50°C to 70°C. By setting the temperature of the nitric acid in the silver dissolving step (S10) to 30°C or higher, a sufficiently high dissolution rate of silver can be obtained, and the time of the silver dissolving step (S10) can be reliably shortened. By setting the temperature to 70°C or lower, gas generation from the nitric acid can be suppressed, and the safety of the process can be improved. In order to set the temperature of the nitric acid in the silver dissolving step (S10) to 50°C or higher, it is preferable to select a material for the container to prevent elution, corrosion, and deformation of the container of the parts in the container that come into contact with the nitric acid. The material of the container is glass, stainless steel, polyethylene, or polypropylene. Glass, polyethylene or polypropylene lined metal may also be used.

[0032] When the silver-bearing glass cullet is immersed in nitric acid in the silver dissolving step (S10), the silver-bearing glass cullet can be placed in a filter bag in advance, and the filter bag can be placed in a container containing nitric acid. By using the filter bag in this way, the glass cullet can be easily removed from the nitric acid solution in which silver has been dissolved by removing the filter bag from the container after the silver dissolving step (S10) is completed. Therefore, it is not necessary to perform a separate step for separating the glass cullet from the nitric acid solution of silver. In addition, if the silver-bearing glass cullet is placed in the filter bag, when a stirring means such as a stirring blade is placed in the nitric acid in the container, it is possible to prevent the glass cullet from colliding with the stirring means, causing chipping or even breaking of the stirring means. When a filter bag is used, it is preferable to use one with a filtration accuracy of 10 μm or more and 50 μm or less.

[0033] In the treatment method according to the present embodiment, similarly to the continuous etching apparatus, the silver-coated glass cullet is placed in a nonwoven fabric tray, and while the silver-coated glass cullet is continuously fed into and taken out of the apparatus using a conveyor, the nitric acid solution is sprayed or showered from above the silver-coated glass cullet, and the liquid is recovered at the bottom of the apparatus for recycling. The nonwoven fabric tray can be reused by washing it immediately after taking out the treated glass cullet to prevent clogging.

[0034] <Glass cullet recovery process (S20)> After the silver dissolving step (S10) is completed, glass cullet from which silver has been removed and a nitric acid solution of silver are produced in the container. Therefore, after the silver dissolving step (S10), the process is divided into a glass cullet recovery step (S20) and a silver recovery step (S30) as shown in Fig. 2. Either the glass cullet recovery step (S20) or the silver recovery step (S30) may be started first, and one step may be performed first and then the other step may be performed, or both steps may be performed in parallel.

[0035] The glass cullet recovery step (S20) will be described. In the glass cullet recovery step (S20), glass cullet is removed from the silver nitric acid solution (S21). The glass cullet removal step (S21) can be performed by filtering the glass cullet using a filtering means such as a filter bag. When a filter bag is used in the silver dissolving step (S10) as described above, the glass cullet can be removed from the silver nitric acid solution by simply removing the filter bag from the silver nitric acid solution. The supernatant silver nitric acid solution may be removed by decantation or the like, and the glass cullet remaining at the bottom of the container may be removed. The filter bag can be reused by washing it immediately after removing the treated glass cullet to prevent clogging.

[0036] When filtration is used in the glass cullet removal step (S21), filtration may be performed multiple times using the same filter or by gradually increasing the mesh size of the filter. In the case of removal using a filter bag as described above, fine glass cullet may slip through the mesh of the filter bag and escape into the silver nitric acid solution, but fine glass cullet can also be removed by further filtration using a finer filter. In order to remove fine glass cullet, a flocculant can be added to the silver nitric acid solution after the silver dissolution step (S10) to promote precipitation of fine glass cullet. Examples of the flocculant include inorganic flocculants such as alum (potassium aluminum sulfate), polyaluminum chloride, ferric chloride, and polyferric sulfate, and organic flocculants such as polyacrylamide compounds and polyacrylic acid ester compounds. It is preferable to use alum because it is a salt consisting of polyvalent cations and polyvalent anions and has a high flocculation effect.

[0037] The glass cullet recovery step (S20) also includes further processing of the extracted glass cullet. For example, as shown in Fig. 2, the glass cullet is washed and neutralized (S22 to S24). This makes it possible to clean the surface of the glass cullet as much as possible and to prevent the glass cullet from being contaminated with substances that may adversely affect the quality of the melting furnace and the glass products in a melting furnace for producing glass products using the glass cullet as a raw material.

[0038] For example, the removed glass cullet is washed with a washing liquid (first washing, S22). The washing liquid may be water. The first washing step (S22) can remove nitric acid and silver nitrate remaining on the surface of the glass cullet, or solid substances that have adhered for some reason. As shown in FIG. 2, the washing liquid remaining after being used for washing in the first washing step (S22) may be added to the silver nitric acid solution in the silver chloride deposition step (S32) included in the silver recovery step (S30). In this way, the silver nitrate washed off in the first washing step (S22) can be incorporated into the silver recovery step (S30) and recovered without being discarded.

[0039] Since an acid such as nitric acid may remain on the surface of the glass cullet washed in the first washing step (S22), the surface is neutralized using an alkaline neutralizing agent in the neutralization step (S23). The neutralizing agent used in the neutralization step (S23) is not particularly limited as long as it is alkaline, but may be a carbonate or hydroxide of an alkali metal or an alkaline earth metal. Specifically, one or more of sodium bicarbonate, sodium carbonate, sodium hydroxide, etc. can be used. Among these, when gas is generated during the reaction of the acid and the neutralizing agent and the presence or absence of the reaction and the end time of the reaction are visually confirmed, it is preferable to use sodium bicarbonate, and when it is desired to suppress the generation of gas during the reaction of the acid and the neutralizing agent, it is preferable to use sodium hydroxide after installing a pH meter.

[0040] After the neutralization step (S23), the glass cullet is washed again in a second washing step (S24). The washing agent used in this step may be water. This makes it possible to remove the neutralizing agent and substances generated by neutralization, and therefore prevents the neutralizing agent from being mixed into the melting furnace for manufacturing glass products using the glass cullet as a raw material, thereby preventing the manufacture of glass products from being hindered.

[0041] In the above-mentioned first washing step (S22), neutralization step (S23) and second washing step (S24), the tools used, the presence or absence of vibration and the conditions therefor, etc. may be those of a known washing method for glass cullet or inorganic granular material.

[0042] It is also possible to omit the first washing step (S22), that is, to neutralize (S23) the glass cullet obtained from the glass cullet removal step (S21) and then wash (S24). However, in the first washing step (S22), it is preferable to wash off to some extent the acid such as nitric acid adhering to the surface of the glass cullet immediately after the glass cullet removal step (S21), so that the amount of alkali required for neutralization in the neutralization step (S23) can be reduced.

[0043] After the second washing step (S24), the glass cullet may be dried. For drying, a known drying method for glass cullet or inorganic particulates can be used. For example, the glass cullet may be dried naturally, or may be dried under heating, for example, using hot air, or in the absence of air. Drying under heating is preferred because dried glass cullet can be obtained in a short time.

[0044] In this way, in the glass cullet recovery step (S20), by going through the above-mentioned washing and neutralization (S22 to S24), purified glass cullet can finally be recovered (S25). Here, the average diameter of the glass cullet finally recovered can be smaller than the average diameter of the silver-coated glass cullet used in the above-mentioned silver melting step (S10). This is because the glass cullet is subjected to force by going through each step, and the glass cullet is crushed or part of the glass cullet is chipped. The average diameter of the glass cullet finally recovered in the glass cullet recovery step (S20) can be preferably 0.01 mm or more and 50 mm or less, more preferably 0.5 mm or more and 5 mm or less.

[0045] In the glass cullet recovery step (S20), the average diameter and diameter distribution of the recovered glass cullet will vary depending on the removal method in the glass cullet removal step (S21). For example, by using an absolute filter capable of filtering out fine particles, fine glass cullet of 10 μm or less can be recovered. Fine glass cullet can be used for ceramic glazes, expanding the range of applications for the reuse of glass cullet.

[0046] The glass cullet obtained in the glass cullet recovery step (S20) can be used as a raw material for manufacturing glass products such as glass plates. In this case, the recovered glass cullet may be mixed with glass raw materials such as silica sand. Since silver has been sufficiently removed from the surface of the glass cullet recovered in the processing method of this embodiment, even if the glass cullet is melted in a melting furnace during reuse of the glass cullet, there is no or almost no possibility that the silver will corrode the melting furnace. Therefore, the processing method of this embodiment can be used to promote the recycling of automotive window glass, which has not been reused due to concerns about the quality of the melting furnace and glass products.

[0047] <Silver recovery process (S30)> The above-mentioned glass cullet recovery step (S20) is a step for recovering glass cullet and leading to reuse, while the silver recovery step (S30) is a step for recovering silver and leading to reuse. In other words, according to the treatment method of the present embodiment, not only can the glass cullet be separated from the silver-bearing glass cullet and reused for the manufacture of glass products, but the silver removed from the silver-bearing glass cullet can also be reused without being discarded. Silver may be reused in automobile window glass as a conductive pattern included in an antenna, an electric heating device, etc., incorporated in automobile window glass. It can also be used for conductive patterns in electric and electronic devices in products other than automobile window glass, medical products, jewelry, tableware, etc.

[0048] The silver recovery step (S30) is a step of recovering silver as an insoluble salt (precipitate) from the silver nitric acid solution obtained by the silver dissolving step (S10). Specifically, first, the silver nitric acid solution is taken out (S31). The silver nitric acid solution taking out step (S31) can be carried out simultaneously with the glass cullet taking out (S21) as described above. The silver nitric acid solution obtained after the silver dissolving step (S10) is a silver nitrate aqueous solution, or in other words, an aqueous solution containing silver ions and nitrate ions.

[0049] After the silver nitric acid solution extraction step (S31), a metal chloride is added to the silver nitric acid solution to precipitate poorly soluble silver chloride (S32). The metal chloride may be an alkali metal or alkaline earth metal chloride, and specific examples include potassium chloride, sodium chloride, magnesium chloride, calcium chloride, etc. Among these, potassium chloride or sodium chloride is preferred because of its low cost and ease of reuse of the recovered material. In addition, the metal chloride is preferably added to the silver nitric acid solution in the form of an aqueous solution.

[0050] In the silver chloride precipitating step (S32), in order to recover silver sufficiently, a metal chloride in an excess molar amount relative to the molar amount of silver may be added to the silver nitric acid solution. On the other hand, when the liquid portion after precipitating silver chloride in the silver chloride precipitating step (S32), i.e., the residual precipitated liquid, is reused in the silver dissolving step (S10), a metal chloride in an amount equal to or less than the molar amount of silver may be added to the silver nitric acid solution. The user of the processing method according to this embodiment can estimate the total amount of silver attached to the silver-bearing glass cullet from the total amount of silver attached to the surface of the glass product before crushing, and can determine the amount of metal chloride to be added in advance. In addition, when selecting the material of the container to prevent the elution and corrosion of the parts in contact with the nitric acid in the container and the deformation of the container, the range of the concentration of nitric acid, temperature, and residence time of the silver-bearing glass cullet in the silver chloride precipitating step (S32) can be determined.

[0051] In the silver chloride precipitation step (S32), the liquid may be made to flow in order to make the precipitation reaction faster. In that case, the same means as those for moving the nitric acid in the silver dissolution step (S10), such as a stirring means, can be used.

[0052] Furthermore, a flocculant can be added in the silver chloride precipitation step (S32). The size of the precipitate obtained can be increased by the flocculant. In addition, since the precipitation rate of the precipitate also increases, when recovery is performed using decantation in the subsequent silver chloride recovery step (S33), the time required for the recovery step can be shortened. In addition, when filtration is performed using a filter, if the size of the precipitate is large, it is possible to prevent the precipitated silver chloride from slipping through the filter, depending on the coarseness of the filter. Examples of the flocculant include inorganic flocculants such as alum (potassium aluminum sulfate), polyaluminum chloride, ferric chloride, and polyferric sulfate, and organic flocculants such as polyacrylamide compounds and polyacrylic acid ester compounds. It is preferable to use alum because it is a salt consisting of polyvalent cations and polyvalent anions and has a high flocculation effect.

[0053] Regardless of whether or not a flocculant is used, it is preferable to leave the silver chloride to stand for a predetermined time or more after it is precipitated. This allows even precipitates with small particle sizes to be sufficiently precipitated. The time for leaving the silver chloride to stand may be about 10 minutes to 24 hours.

[0054] After such a silver chloride precipitation step (S32), the precipitated silver chloride is recovered (S33). As described above, silver chloride can be recovered by filtration. For the filtration, a filtering means such as a filter bag or an absolute filter can be used. When a filter bag is used, silver chloride can be recovered in a state where it is attached to the filter bag. Moreover, regardless of whether a flocculant is used or not, silver chloride may be recovered by taking out the residual precipitation liquid by decantation or the like.

[0055] In the silver recovery step (S30), silver is recovered in the form of silver chloride. However, depending on the purpose for which the silver is to be reused, silver may be recovered as an element or in the form of another compound.

[0056] The precipitation residual liquid is a liquid that mainly contains nitric acid, although it contains metal ions derived from the metal chloride used for precipitation. In the treatment method of this embodiment, such a precipitation residual liquid containing nitric acid can also be reused. For example, the precipitation residual liquid can be returned to the silver dissolving step (S10) and used to dissolve silver in the silver-bearing glass cullet. In this case, the precipitation residual liquid may be used as it is, or may be used after performing treatments such as removing foreign matter, adjusting the concentration and adjusting the pH. In addition, the precipitation residual liquid can be mixed with newly prepared nitric acid and used. In this way, according to the treatment method of this embodiment, a flow including a route for circulating nitric acid is also possible.

[0057] <Nitrate recovery process (S40)> Furthermore, according to this embodiment, nitrate can also be recovered (S40) from the precipitation residual liquid generated in the silver chloride precipitation step (S32). In the nitrate recovery step (S40), the precipitation residual liquid is taken out (S41), neutralized (S42), and nitrate can be recovered (S43). That is, the method for treating silver-bearing glass cullet according to this embodiment may further include recovering nitrate from the residual liquid generated in the process of recovering silver as an insoluble salt in the silver recovery step (S30).

[0058] The deposition residual liquid removal step (S41) can be carried out simultaneously with the above-mentioned silver chloride recovery step (S33) in the silver recovery step (S30). The removed deposition residual liquid is neutralized with an alkaline neutralizing agent using a pH meter in the neutralization step (S42). An aqueous nitrate solution is obtained by neutralization. The neutralizing agent used in the neutralization step (S42) is not particularly limited as long as it is alkaline. The neutralizing agent may be a carbonate or hydroxide of an alkali metal or an alkaline earth metal, and among these, one or more of potassium hydroxide and sodium hydroxide are preferred. When sodium hydroxide is used as the neutralizing agent, an aqueous sodium nitrate solution is obtained. Also, when potassium hydroxide is used as the neutralizing agent, an aqueous potassium nitrate solution is obtained.

[0059] In the nitrate recovery step (S43), the nitrate aqueous solution obtained in the neutralization step (S42) can be recovered in the form of an aqueous solution without treatment. In addition, the nitrate aqueous solution can be recovered as a solid nitrate by drying or the like. Nitrate is used as a raw material for, for example, gunpowder, fertilizer, etc. When potassium hydroxide or sodium hydroxide is used as a neutralizing agent, potassium nitrate or sodium nitrate is obtained as the nitrate. Potassium nitrate and sodium nitrate are particularly preferred when used as raw materials for fertilizer.

[0060] The silver recovery step (S30) and the nitrate recovery step (S40) may be carried out after transferring the liquid to a container other than the container used in the silver dissolving step (S10) using a liquid transfer pump or the like.

[0061] As described above, according to the processing method of this embodiment, glass cullet, silver, and nitrate can be regenerated from silver-bearing glass cullet that has conventionally been disposed of by landfilling, etc., and can be reused in the same field or in other fields.

[0062] [Glass product manufacturing method] In a method for producing a glass product according to an embodiment of the present invention, glass cullet recovered using the above-mentioned method for treating silver-bearing glass cullet is melted and molded to produce a glass product.

[0063] [Processing equipment for silver-coated glass cullet] Another embodiment of the present invention is an apparatus for carrying out the above-mentioned method for treating silver-bearing glass cullet. That is, another embodiment is an apparatus for treating silver-bearing glass cullet, comprising a silver dissolving section for dissolving silver in the silver-bearing glass cullet with nitric acid, a glass cullet recovery section for recovering the glass cullet from which silver has been removed by the silver dissolving step, and a silver recovery section for recovering silver as an insoluble salt from the nitric acid solution of silver obtained by the silver dissolving step.

[0064] The silver-coated glass cullet may be fed to the processing device in a batch manner and removed in a batch manner, or may be fed and removed continuously in a continuous manner. The continuous manner can increase the amount of silver-coated glass cullet processed per unit time. The container in the processing device is made of glass, stainless steel, polyethylene, or polypropylene. Metal lined with glass, polyethylene, or polypropylene may also be used. EXAMPLES

[0065] Hereinafter, the embodiment of the present invention will be further described based on experimental examples.

[0066] (Example 1) =Pre-process= A single-panel tempered rear glass having a silver print pattern on one side was crushed with a glass-breaking hammer to obtain silver-coated glass cullets with an average diameter of 10 mm. The average diameter of the silver-coated glass cullets was the average diameter measured by image processing of an optical microscope. Meanwhile, 3.8 kg of dilution water was added to 3.2 kg of 60% by mass nitric acid to prepare 7 kg of 30% by mass nitric acid.

[0067] =Silver melting process= A filter bag (polypropylene nonwoven fabric manufactured by 3M, nominal filtration accuracy 10 μm) containing 5 kg of silver-tagged glass cullet was placed in a 5 L glass container and immersed in 7 kg of 30% by mass nitric acid. Without heating, the filter bag containing the silver-tagged glass cullet was oscillated back and forth in the rotation direction in nitric acid with a rotation width of 30° and a frequency of 0.5 Hz. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 10 minutes after the start of the silver dissolving process.

[0068] =Silver recovery process= After the filter bag containing the glass cullet was removed from the container, a silver nitric acid solution remained in the container. 10 g of potassium chloride was dissolved in ion-exchanged water to obtain a 10% by mass potassium chloride aqueous solution, and 10 g of this was added to the container. When the mixture was stirred for 5 minutes using a mechanical stirrer (Three-One Motor, manufactured by Shinto Scientific Co., Ltd.) with four pitched paddle blades at 100 rpm, a precipitate of silver chloride was observed at the bottom of the container. Furthermore, the contents of the container were filtered using a separately prepared filter bag (polypropylene nonwoven fabric, manufactured by 3M, nominal filtration accuracy 10 μm) to filter out the precipitate. The amount of precipitate filtered out was about 3 g.

[0069] =Nitrate recovery process= The pH of the filtrate (residual liquid) that had passed through a filter bag contained in a separate container was checked and found to be acidic. A 50% by mass aqueous solution of potassium hydroxide was gradually added to the filtrate while suppressing the rise in liquid temperature due to heat of neutralization by adding ice until the filtrate became neutral. At that time, stirring was performed under the same conditions using the mechanical stirrer. As a result, 10 kg of an aqueous solution of potassium nitrate was obtained.

[0070] (Example 2) The experiment was carried out in the same manner as in Example 1, except that the concentration of nitric acid used in the silver dissolving step was 10 mass% and the temperature of the nitric acid was maintained at 50°C. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 2 hours after the start of the silver dissolving step. In addition, the precipitate filtered out after the silver recovery step was about 2 g, and the potassium nitrate aqueous solution obtained in the nitrate recovery step was 6.3 kg.

[0071] (Example 3) Except for changing the concentration of nitric acid used in the silver dissolving step to 20 mass%, an experiment was performed in the same manner as in Example 1. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 45 minutes after the start of the silver dissolving step.

[0072] (Example 4) An experiment was carried out in the same manner as in Example 1, except that the concentration of nitric acid used in the silver dissolving step was 20 mass % and the temperature of the nitric acid was maintained at 50° C. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 1 minute after the start of the silver dissolving step.

[0073] (Example 5) The experiment was carried out in the same manner as in Example 1, except that the concentration of nitric acid used in the silver dissolving step was 40 mass%. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 1 minute after the start of the silver dissolving step. In addition, the precipitate filtered out after the silver recovery step was about 3 g, and the potassium nitrate aqueous solution obtained in the nitrate recovery step was 12 kg.

[0074] (Example 6) A laminated glass having a silver print pattern attached to the periphery of one side was used. The laminated glass was made by sandwiching an interlayer film containing polyvinyl butyral as a main component between two glass sheets, and the silver print pattern was arranged on the surface of the glass sheet in contact with the interlayer film. The laminated glass was previously cut and separated to remove the terminals and solder-containing parts connected to the silver print pattern, and then crushed by sandwiching between two bladed rolls, and further swung in a surfactant aqueous solution to separate silver-covered glass cullets with an average diameter of 1 mm from the interlayer film. Thereafter, the experiment was carried out in the same manner as in Example 1. The glass cullet surface was visually observed, and it was confirmed that the silver had almost disappeared from the glass cullet surface 5 minutes after the start of the silver dissolving process.

[0075] (Example 7) The parts containing the terminals and solder cut and separated in Example 6, i.e., the tin-plated brass terminals with polyethylene-coated copper wires and the pieces containing lead-free solder containing tin and silver, were used together with the silver-coated glass cullet in an experiment conducted in the same manner as in Example 6. It was confirmed by visual inspection that the copper wires, brass terminals and solder had almost disappeared within 2 hours from the start of the melting process. The polyethylene coating, however, remained unmelted.

[0076] (Example 8) As in Example 6, the silver in the silver-attached glass cullet derived from the laminated glass was dissolved, and the filter bag containing the glass cullet was taken out of the container, and the nitric acid solution of silver in the container was left to stand for 24 hours. The precipitation of fine glass cullet was confirmed at the bottom of the container. The precipitate was then separated by multiple decantations. Specifically, the process of removing the supernatant of the nitric acid solution after standing, adding water, stirring, and standing for 10 minutes was repeated twice, and the process of removing the supernatant of the water suspension after standing, adding denatured alcohol (Mixed Ethanol NP manufactured by Yamaichi Chemical Industry Co., Ltd., 85.5% ethanol; 9.6% isopropyl alcohol; 4.9% methanol), stirring, and standing for 10 minutes was repeated twice. After standing in the final decantation, the supernatant was removed and the resulting precipitate was collected and dried, and the collected amount was 14 g.

[0077] (Example 9) In Example 8, the silver nitric acid solution (supernatant) after separating the precipitate by decantation was subjected to the same procedure as in the silver recovery process in Example 1 to precipitate silver chloride, and the precipitate of silver chloride was filtered off using a filter bag, and the remaining nitric acid solution was allowed to stand for 24 hours. The precipitation of fine silver chloride particles was confirmed at the bottom of the container. Then, decantation was performed multiple times in the same manner as in Example 8. After leaving the solution in the final decantation, the supernatant was removed, and the resulting precipitate was collected and dried, yielding a recovery amount of 0.3 g.

[0078] (Example 10) In Example 9, 10 g of 5 mass% alum aqueous solution was added dropwise to the nitric acid solution obtained after filtering off the silver chloride precipitate with a filter bag, and the solution was stirred and allowed to stand for 10 minutes, whereupon the precipitation of fine silver chloride particles was confirmed at the bottom of the container. Then, decantation was performed multiple times in the same manner as in Example 8. After leaving the solution to stand in the final decantation, the supernatant liquid was removed, and the resulting precipitate was collected and dried, yielding a recovery amount of 0.3 g.

[0079] Thus, it was found that by using nitric acid with a concentration of 10% by mass or more and 40% by mass or less in the silver dissolving step, the silver dissolving rate can be increased and the time required for the silver dissolving step, and in turn the entire processing method for silver-bearing glass cullet, can be shortened. It was found that the silver dissolving rate can be further increased by maintaining the temperature of the nitric acid at 50°C. In order to reduce the volume and installation area of ​​the processing equipment, the silver dissolving time is preferably 2 hours or less, and more preferably 10 minutes or less. [Explanation of symbols]

[0080] 1. Automotive window glass 11, 12 Glass plate 20 Interlayer 40 Silver-containing conductive pattern 50 shielding layer

Claims

1. A silver dissolving process in which the silver in the silver-coated glass cullet is dissolved with nitric acid; a glass cullet recovery step of recovering the glass cullet from which silver has been removed by the silver dissolving step; A silver recovery step of recovering silver as an insoluble salt from the nitric acid solution of silver obtained in the silver dissolution step.

2. 2. The method for treating silver-coated glass cullet according to claim 1, wherein a concentration of the nitric acid in the silver dissolving step is 10% by mass or more and 40% by mass or less.

3. 3. The method for treating silver-coated glass cullet according to claim 1, wherein the glass cullet recovery step includes washing the glass cullet.

4. 3. The method for treating silver-bearing glass cullet according to claim 1, wherein the silver recovery step includes adding a metal chloride to the nitric acid solution of silver to precipitate silver chloride.

5. 5. The method for treating silver-bearing glass cullet according to claim 4, wherein the silver recovery step recovers the silver chloride by filtration.

6. 5. The method for treating silver-bearing glass cullet according to claim 4, wherein the silver recovery step includes adding a coagulant to the nitric acid solution of silver.

7. 3. The method for treating silver-bearing glass cullet according to claim 1, further comprising a nitrate recovery step of recovering nitrate from a residual liquid produced in the process of recovering the silver as an insoluble salt.

8. The silver-coated glass cullet is obtained from a laminated glass formed by laminating a plurality of glass plates with an interlayer interposed therebetween, 3. The method for treating silver-coated glass cullet according to claim 1, wherein a substance containing silver is disposed on a surface of the glass plate facing the interlayer film.

9. 3. A method for manufacturing a glass product, comprising melting and molding the glass cullet recovered by the method for treating silver-coated glass cullet according to claim 1 or 2 to manufacture a glass product.

10. A silver dissolving section dissolves the silver in the silver-coated glass cullet with nitric acid; a glass cullet recovery section for recovering glass cullet from which silver has been removed by dissolving silver in the silver melting section; and a silver recovery section for recovering silver as an insoluble salt from the nitric acid solution of silver obtained by dissolving silver in the silver dissolution section.

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