JP2009179873A - Method for recovering noble metal and combusting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering noble metals by which combustion efficiency is improved to reduce energy consumption, and further the extraction rate of noble metals can be improved, and to provide a combusting device suitable for improving combustion efficiency. <P>SOLUTION: The method for recovering noble metals includes: a combusting step where activated carbon with noble metals adsorbed therein is combusted to be ashed; and an extraction step where the noble metals are extracted from the ashed matter obtained by the combustion; wherein in the combusting step, the activated carbon is irradiated with microwaves to be combusted, and an oxygen-containing gas is fed to progress the combustion of the activated carbon. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for recovering a noble metal from a waste liquid containing a noble metal such as a plating solution, and a combustion apparatus used for the recovery method.

Precious metal plating is widely used for various decorative items, electronic device parts, and the like. In order to make effective use of precious metal resources, a method of recovering and purifying precious metal from a liquid waste such as plating waste liquid or a recovery liquid obtained by converting solid waste into a solution is used. As a conventional recovery method, there is known a method in which activated carbon adsorbed with a noble metal is burned and incinerated using a fuel such as city gas, propane gas or heavy oil, and then the noble metal is extracted from the incinerated product. . Patent Document 1 describes that a precious metal captured by incineration can be easily recovered as a precious metal recovery method using a porous carrier supporting an anthrahydroquinone compound. It is also described that a rotary incinerator or a crucible type incinerator can be adopted as an incineration method.
Japanese Patent Laid-Open No. 10-121158

  However, when activated carbon is burned using a fuel such as city gas as in the past, a large amount of energy is consumed in the combustion process. In addition, depending on the type of fuel used, combustion gas containing harmful substances such as halogen may be generated, and in order to remove the combustion gas, further secondary high-temperature heat treatment is necessary.

  In addition, the combustion method using city gas or the like is performed by heating from the outside of the combustion furnace, and it becomes difficult to make the combustion progress uniformly to the inside of the activated carbon, and the extraction rate of the noble metal may decrease. It was. Even with such a combustion method, it is possible to improve the extraction rate by repeating the combustion for a long time or by repeatedly performing the combustion and extraction, but the process becomes complicated and the consumption energy increases. It was a problem. In addition, when activated carbon is impregnated into a solution containing a noble metal, the noble metal penetrates into the pores of the activated carbon. However, in the combustion process using city gas or the like, the noble metal may cover the pore surface of the activated carbon as the combustion proceeds. there were. For this reason, it becomes difficult to supply oxygen into the pores of the activated carbon, and the progress of combustion tends to be insufficient.

  Therefore, an object of the present invention is to provide a precious metal recovery method that can improve combustion efficiency, reduce energy consumption, and improve the extraction rate of precious metals. In addition, a combustion apparatus suitable for improving combustion efficiency is provided.

  In order to solve the above-mentioned problems, the present inventors diligently studied the combustion process in the noble metal recovery method and arrived at the present invention in which activated carbon is combusted using microwaves.

  That is, the present invention provides a precious metal recovery method comprising a combustion step of burning activated carbon adsorbed with a precious metal and ashing, and an extraction step of extracting precious metal from an ash obtained by combustion. In addition, the present invention relates to a method for recovering a noble metal, in which activated carbon is burned by irradiating a microwave, and an oxygen-containing gas is supplied to advance combustion of the activated carbon.

  In the present invention, since activated carbon is burned by microwave irradiation, the heating rate is increased, and the combustion efficiency can be greatly improved. Moreover, unlike the case of using city gas or the like, the phenomenon that the noble metal adsorbed inside the activated carbon covers the pore surface by combustion hardly occurs, and the activated carbon can be incinerated efficiently. Furthermore, by supplying an oxygen-containing gas and utilizing the self-combustion of activated carbon, the combustion can be uniformly advanced to the inside of the combustion container. In addition, since air can be used as the oxygen-containing gas, generation of combustion gas containing harmful substances can be reduced.

  Hereinafter, the noble metal recovery method of the present invention will be described in detail. First, in the recovery method of the present invention, activated carbon having adsorbed noble metal is used. The noble metal source to be adsorbed on the activated carbon is not particularly limited, and a liquid waste such as a plating waste liquid or a recovered liquid obtained by dissolving a solid waste can be used. As a method for adsorbing the noble metal contained in the plating waste liquid or the recovery liquid on the activated carbon, a general method such as a method by impregnation or a method of allowing the recovery liquid to pass through the activated carbon packed in the column can be used.

  And the activated carbon which adsorb | sucked the noble metal is burned by a combustion process, and is ashed. Since activated carbon is a substance that easily absorbs microwaves, it can efficiently convert microwaves into heat energy. The oxygen-containing gas that promotes the combustion of activated carbon in the combustion process is supplied during at least a part of the combustion process, and when the combustion temperature at the initial stage of the combustion process is raised or near the target combustion temperature Can be supplied when reaching. Alternatively, the microwave output may be reduced or stopped after reaching a combustion temperature set as described later, and an oxygen-containing gas may be supplied at that time. Furthermore, it may be continuously supplied from the start to the end of the combustion process while monitoring the microwave output and the combustion temperature. Note that compressed air can be used as the oxygen-containing gas. According to the compressed air, the oxygen content described later can be easily adjusted. The compressed air can increase the oxygen content to about 21%, and can also increase the oxygen content to about 60% when an adsorbent such as a molecular sieve is used.

  The combustion temperature in the combustion furnace in the combustion process is preferably in the range of 500 ° C to 1100 ° C. If the combustion temperature is less than 500 ° C., the combustion is difficult to proceed and the combustion for a long time is required, so that the energy consumption increases. When the temperature exceeds 1100 ° C., the precious metal in the recovered material is melted, and the molten material may be damaged by reacting with the metal component or oxide component in the recovered material. Since the melting of the precious metal in the recovered material occurs when the melting point of the precious metal to be recovered is higher, the combustion temperature is preferably 50 to 150 ° C. lower than the melting point of the precious metal to be recovered. For example, when the collected material contains a large amount of silver, the combustion temperature is preferably 850 ° C. or lower.

  The combustion temperature is preferably adjusted by the supply amount of the oxygen-containing gas and the output for irradiating the microwave. When raising the temperature in a combustion furnace, it is preferable that the output of a microwave shall be about 50-100%. In particular, up to around 100 ° C., energy is required to evaporate the solvent in the waste liquid, so that the microwave output may be maximized. When the temperature is near 200 ° C. lower than the target combustion temperature, the microwave output may be reduced to about 10 to 50%, or the output may be stopped. That is, the combustion process can be performed so that the microwave output is reduced or stopped when the combustion temperature reaches 500 to 900 ° C. after the microwave irradiation. Even if the output of the microwave is reduced, the combustion temperature described above can be maintained by utilizing the self-combustion of activated carbon. These microwave output controls can reduce excessive energy consumption. For microwave output control, a method of automatic control by a control device, a method of on / off switching, or the like can be used.

  Further, the target combustion temperature can be maintained by adjusting the microwave output and adjusting the supply amount of the oxygen-containing gas to control the degree of self-combustion of the activated carbon. If the supply amount of the oxygen-containing gas is excessive, self-combustion may proceed excessively and the target combustion temperature may be exceeded. Conversely, if the supply amount of the oxygen-containing gas is small, a longer firing time is required. Become. The oxygen supply amount needs to be adjusted according to the amount of activated carbon to be burned, the target combustion temperature, and the oxygen content in the gas, and the required supply amount increases as the amount of activated carbon increases. For example, 1 kg of activated carbon is calcined in the absence of heat dissipation, and oxygen-containing gas is supplied at 500 L / min for a combustion temperature of 780 ° C., and oxygen-containing gas is supplied at 420 L / min for a combustion temperature of 930 ° C.

  Although the step of evaporating the solvent contained in the activated carbon adsorbing the noble metal can be performed before the combustion step, according to the present invention, the evaporation of the solvent in the combustion step can be performed without performing the evaporation step as a separate step. Can also be performed.

  After the activated carbon is incinerated by the combustion process described above, noble metal is extracted from the incinerated product. The extraction step can be performed by dissolving the ashed product with acid or alkali and extracting the noble metal from the solution. The precious metal to be extracted is preferably one or more of gold, silver, platinum, palladium, rhodium, iridium, and ruthenium. Nitric acid, aqua regia, an alkali cyanide solution, or the like can be used for dissolving the ashed product, and it is preferable to use according to the type of the precious metal to be recovered. For example, when the precious metal to be collected contains 60% or more of silver, it can be dissolved using nitric acid, and when the proportion of silver is less than 60%, aqua regia can be used. Moreover, when collect | recovering gold | metal | money and silver, it is preferable to melt | dissolve with the alkaline solution containing a cyanide. Since cyanide selectively dissolves gold and silver and hardly dissolves other metals, the recovery rate can be improved. Further, the process of separating and purifying the noble metal later becomes easy. The concentration of the solution is about 30 to 70% for nitric acid, about 50% for aqua regia, and about 50% for cyanide, and alkali cyanide is a strong alkali. Moreover, melt | dissolution can also be accelerated | stimulated by raising the liquid temperature at the time of melt | dissolution. At this time, it is preferable to adjust the reaction temperature, acid concentration, and the like so that rapid reaction or bumping does not occur.

  And, as a combustion apparatus used in the recovery method of the present invention, a combustion container having an oxygen-containing gas inlet and injecting activated carbon for combustion, a microwave oscillator for oscillating microwaves for heating the activated carbon, And a temperature sensor that measures the combustion temperature in the combustion container. The combustion apparatus of the present invention is suitable for burning activated carbon by microwaves, and can supply oxygen-containing gas to advance internal combustion of activated carbon.

  The combustion container is preferably made of a material having a dielectric loss coefficient of 5 or less. The dielectric loss coefficient is a value that serves as an index representing the ease of heat generation of a substance heated by microwaves. The larger the dielectric loss coefficient, the larger the heat generation amount, and the more selectively heated. For this reason, if the material has a dielectric loss coefficient of 5 or less, microwaves can be selectively used for combustion of activated carbon. The dielectric loss coefficient (ε ′ × tan δ) measured by free space method measurement for graphite and the like is 22.6 for carbon plate, 17.7 for graphite (extruded product), 3.52 for silicon carbide, and alumina for alumina. 0.0624, cordierite is 0.046 or less.

Further, the combustion container is preferably made of a material having a thermal expansion coefficient of 5.0 × 10 ⁻⁶ K ⁻¹ or less. This is because even when a partial temperature difference occurs in the combustion container during combustion, the container is hardly damaged due to the generation of thermal stress. The values of coefficient of thermal expansion are 4.5 × 10 ⁻⁶ K ⁻¹ for cordierite-mullite, 3.0 × 10 ⁻⁶ K ^{−1 for} cordierite, and 1.5 × 10 ⁻⁶ K ^{−1 for} fused silica. Quartz is 1.2 × 10 ⁻⁶ K ⁻¹ .

  From the above, it is preferable to use a ceramic material such as silicon carbide, alumina, cordierite, etc. as the combustion container. These materials are excellent in heat resistance in addition to having a small dielectric loss coefficient and thermal expansion coefficient. Further, according to the present inventors, it has been found that when silicon carbide and cordierite are each used as a combustion container, the use of cordierite having a smaller dielectric loss coefficient can shorten the combustion time.

  It is preferable that the combustion apparatus further includes control means for controlling the output of the microwave oscillator in accordance with the combustion temperature. After the combustion temperature is sufficiently increased by the microwave output, the energy consumption can be reduced by reducing or stopping the output and allowing combustion to proceed by internal combustion of the activated carbon.

  The combustion apparatus preferably further includes a gas flow rate adjusting means connected to the oxygen-containing gas inlet and supplying an oxygen-containing gas having a flow rate corresponding to the combustion temperature. The oxygen-containing gas is supplied to maintain the internal combustion of the activated carbon after the combustion temperature rises, and the combustion temperature can be adjusted by the supply amount of the oxygen-containing gas.

  Regarding the above-described microwave output and oxygen-containing gas supply amount adjusting means, as an example, a description will be given of a case where the combustion apparatus includes a temperature adjusting means. The temperature adjusting means is connected to a thermocouple for measuring the combustion temperature in the combustion vessel and receives a temperature signal from the thermocouple. It is preferable to set a suitable combustion temperature range in advance in the temperature adjusting means. Then, after the combustion is started by the microwave output, when the combustion temperature received by the temperature signal from the thermocouple reaches a preset suitable combustion temperature, the temperature adjusting means outputs to the microwave oscillator By transmitting the control signal, the output of the microwave can be controlled. Also, the flow rate control signal can be transmitted to the flow rate adjusting means for the oxygen-containing gas to adjust the gas supply amount.

  The combustion container preferably further includes one or more filters. The filter prevents the activated carbon ash from being scattered after combustion, and the filter can be installed on an exhaust path for exhausting the combustion gas in the combustion container to prevent a reduction in the recovery rate of the noble metal. Although the filter can obtain the scattering prevention effect even with one stage, it is more preferable to install a plurality of stages in order to improve the scattering prevention effect. The material can be made of alumina, cordierite, mullite, silicon carbide or the like, and can be in the shape of a honeycomb or the like. The filter hole is preferably smaller than the size of the ash to prevent scattering of the ash, but considering the recovery of clogged ash, multiple holes with relatively large holes are used. It can also be installed.

  The combustion container preferably includes means for diffusing oxygen-containing gas. As the diffusing means, for example, a baffle can be installed on the inside of the combustion container of the oxygen-containing gas inlet, and the introduced oxygen-containing gas can be diffused into the apparatus. It is also preferable to install a honeycomb-like plate for charging activated carbon in the combustion container, and the oxygen-containing gas diffused by the baffle can be uniformly supplied to the activated carbon on the plate. The same material and shape as the filter can be used for the baffle.

  As described above, according to the noble metal recovery method of the present invention, by improving the combustion efficiency, it is possible to reduce the energy consumption required for combustion and to improve the extraction rate of the noble metal. Moreover, according to the combustion apparatus of this invention, activated carbon can be burned more efficiently.

  Hereinafter, the best embodiment of the present invention will be described.

[First embodiment]
FIG. 1 is a schematic front sectional view of a microwave combustion apparatus in an embodiment of the present invention. As shown in the figure, a combustion chamber made of fused silica and having a diameter of 400 mm and a height of 400 mm was placed in a metallic chamber, and a microwave oscillator was connected via a waveguide. Four microwave oscillators with a frequency of 2.45 GHz and an output of 1.5 kW were connected, and the chamber was made of titanium steel. In this microwave combustion apparatus, when the control output is 100%, the microwave output is 6.0 kW, and when the control output is 50%, the microwave output is 3.0 kW. In addition, an oxygen-containing gas inlet having a diameter of 35 mm was provided at the bottom of the combustion container, and connected to a blower and a gas flow controller. In addition, a thermocouple was inserted inside the combustion container, and the combustion temperature inside the activated carbon was measured. As the microwave oscillator used in the present invention, an output (rated output) corresponding to the processing amount can be used, but one with a frequency of 2 to 3 GHz and an output of 0.1 to 50 kW is usually used. It is done.

  A baffle for diffusing the introduced gas was installed in the combustion container, and the activated carbon was put on a honeycomb plate installed inside the apparatus. By diffusing the oxygen-containing gas supplied from the blower with the baffle, the oxygen-containing gas can be uniformly supplied to the activated carbon on the honeycomb plate. The baffle is made of mullite with a square plate with a side of 70 mm and four legs with a side of 10 mm and a height of 20 mm. A honeycomb with a 1 mm diameter hole occupies 15% of the total plane area. A light quality one was used.

  In addition, a filter is installed in the exhaust path for exhausting the combustion gas generated by the combustion in the combustion container so that the burned ash is prevented from scattering. In this example, four stages of filters made of an alumina honeycomb in which a square hole with a side of 1 mm occupies 70% of the total plane area were installed.

Example 1 : Using the above-mentioned combustion apparatus, the precious metal was recovered by supplying compressed air having an oxygen content of 21% as an oxygen-containing gas from activated carbon that had adsorbed Ag and Pd. Activated carbon was burned by introducing 12250 g of activated carbon adsorbing Ag and Pd onto a honeycomb plate in a combustion vessel and making microwaves enter the chamber through a waveguide from a microwave oscillator. The output of the microwave when raising the combustion temperature was 80%. After the combustion temperature rose to 750 ° C., air was supplied as an oxygen-containing gas at 400 L / min, and the combustion temperature was adjusted to be constant at 750 ° C. After burning for 8 hours, the activated carbon could be incinerated. From the obtained ashed product, Ag and Pd were extracted using concentrated nitric acid. The extraction rate of Ag was 98%, and the extraction rate of Pd was 95.5%. The recovery rate of the precious metal with respect to the amount of the precious metal adsorbed on the activated carbon was 99%. Moreover, the energy consumption required for combustion per kg of activated carbon was about 500 kJ.

Example 2 : Noble metal was recovered from activated carbon adsorbed with Pt. When activated carbon was burned at a combustion temperature of 850 ° C. using the same apparatus as in Example 1, activated carbon could be ashed in 7.5 hours. When Pt was extracted from the obtained ashed product using aqua regia, the Pt extraction rate was 97.5%. The recovery rate of the noble metal relative to the amount of the noble metal adsorbed on the activated carbon was 98%. Electric energy consumption required for combustion per kg of activated carbon was about 520 kJ.

Comparative example 1 : The activated carbon which adsorb | sucked Ag and Pd was burned using the gas furnace, and the noble metal was collect | recovered. 8520 g of activated carbon on which Ag and Pd were adsorbed was put into a stainless steel combustion vessel, and the activated carbon was burned in a gas furnace so that the combustion temperature was constant at 750 ° C. When burned for 15 hours, some unburned activated carbon remained. From the obtained ashed product, Ag and Pd were extracted using concentrated nitric acid. The extraction rate of Ag was 94.5%, and the extraction rate of Pd was 62.2%. The recovery rate of the noble metal with respect to the amount of the noble metal adsorbed on the activated carbon was 96%. The energy consumed for combustion per kg of activated carbon was about 4000 kJ.

Comparative example 2 : The activated carbon which adsorb | sucked Pt was burned using the gas furnace, and the noble metal was collect | recovered. The combustion conditions were the same as in Comparative Example 1. When burned for 15 hours, some unburned activated carbon remained. Pt was extracted from the obtained ashed product using aqua regia. The extraction rate of Pt was 75.3%. The recovery rate of the precious metal with respect to the amount of the precious metal adsorbed on the activated carbon was 85%. The energy consumption required for combustion per kg of activated carbon was about 4500 kJ.

Reference Example : Activated carbon not adsorbing noble metal was burned by the same combustion apparatus as in the example. 10000 g of activated carbon not adsorbing noble metal was burned for 9 hours at a constant combustion temperature of 850 ° C. Before and after combustion, the weight decreased by 92%, and 8% of unburned activated carbon remained.

  From the above, according to the recovery method of the example using the microwave, compared with the recovery method of the comparative example using the gas furnace, the activated carbon can be ashed in a short time, and the combustion progressed uniformly. . Moreover, the recovery rate of precious metals was also good, and the energy consumption required for combustion could be reduced. Further, according to the reference example, it was found that the activated carbon that adsorbed the noble metal was easily ashed compared to the activated carbon that did not adsorb the noble metal. This is because the noble metal is uniformly adsorbed in the activated carbon, so that when it is irradiated with microwaves, discharge energy is generated between the particles of the noble metal, and an oxidation catalytic effect between the noble metal and the activated carbon occurs. Conceivable.

[Second Embodiment]
In the same method as in Example 1 of the first embodiment, the precious metal was recovered by changing the combustion temperature as shown in Table 1.

  From Table 1, it was found that when the combustion temperature was 500 to 1100 ° C., the recovery rate was high and the energy consumption was small. On the other hand, when the combustion temperature is less than 500 ° C., a large amount of energy consumption tends to be required, and when it exceeds 1100 ° C., it becomes difficult to recover the noble metal.

Schematic cross section of microwave combustion device

Claims (14)

In a method for recovering a noble metal having a combustion step of burning activated carbon adsorbed with a noble metal and ashing, and an extraction step of extracting noble metal from an ash obtained by combustion,
The combustion process is a method for recovering a noble metal, in which activated carbon is burned by irradiating microwaves, and combustion of activated carbon is advanced by supplying an oxygen-containing gas. The precious metal recovery method according to claim 1, wherein the combustion step is performed at a combustion temperature in a range of 500 to 1100 ° C. The precious metal recovery method according to claim 1 or 2, wherein the combustion step is performed by adjusting an output for irradiating microwaves and a supply amount of the oxygen-containing gas in accordance with a combustion temperature in the combustion container. The precious metal recovery according to any one of claims 1 to 3, wherein, in the combustion step, the microwave output is reduced or stopped when the combustion temperature reaches 500 to 900 ° C after the microwave irradiation. Method. The extraction step is a method for recovering a noble metal according to any one of claims 1 to 4, wherein the ash is dissolved with an acid or an alkali, and the noble metal is extracted from the solution. The method for recovering a noble metal according to any one of claims 1 to 5, wherein the noble metal is at least one of gold, silver, platinum, palladium, rhodium, iridium, and ruthenium. A combustion device for burning activated carbon adsorbing precious metals to ash,
A combustion vessel having an oxygen-containing gas inlet and burning activated carbon, a microwave oscillator for oscillating microwaves for heating the activated carbon, a temperature sensor for measuring the combustion temperature in the combustion vessel, A combustion apparatus comprising: The combustion apparatus according to claim 7, wherein the combustion container is made of a material having a dielectric loss coefficient of 5 or less. 9. The combustion apparatus according to claim 7, wherein the combustion container is made of a material having a thermal expansion coefficient of 5.0 × 10 ⁻⁶ K ⁻¹ or less. The combustion apparatus according to any one of claims 7 to 9, wherein the combustion container is made of any one of cordierite, cordierite-mullite, fused silica, and quartz. The combustion apparatus according to any one of claims 7 to 10, further comprising control means for controlling the output of the microwave oscillator in accordance with the combustion temperature. The combustion apparatus according to any one of claims 7 to 11, further comprising a gas flow rate adjusting means connected to the oxygen-containing gas inlet and supplying a gas having a flow rate corresponding to the combustion temperature. The combustion apparatus according to any one of claims 7 to 12, wherein the combustion container further includes one or more filters. The combustion apparatus according to any one of claims 7 to 13, wherein the combustion container includes means for diffusing oxygen-containing gas.