JP2016190221A - Selenate reduction catalyst, production method of selenate reduction catalyst and reduction method of selenate solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable selenium in waste water to be precipitated and efficiently separated by providing technique allowing for quick reduction of selenium present in a hexavalent form.SOLUTION: A selenate reduction catalyst related to the present invention has a carrier containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or compound oxide thereof, and one or more kind of metal particle selected from rhodium, platinum, palladium, iridium, ruthenium and a mixture thereof is carried on the carrier. It is preferable that amount of the carried metal particle is 0.5 mass% or more based on dry mass of the carrier and degree of dispersion of the metal by a CO pulse adsorption method is 20% or more. By adding sulfuric acid to a selenate solution containing hexavalent selenic acid so that sulfuric acid concentration becomes 0.005 mol/l or more and further adding the selenate reduction catalyst related to the present invention and selenate reducer, hexavalent selenium contained in the selenate solution can be precipitated and efficiently separated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a selenate reduction catalyst, a method for producing a selenate reduction catalyst, and a method for reducing a selenate solution.

Selenium is a valuable element used as a photoreceptor for photovoltaic cells and copying machines, and is contained in trace amounts in ores such as copper. In a process in which copper ore used as a general method for smelting copper is put into a furnace and melted at a high temperature, selenium volatilizes and is contained in exhaust gas, and then in the solution as selenic acid in the exhaust gas treatment process. Concentrated. The selenic acid present in the solution obtained in such an exhaust gas treatment step can be recovered by bringing it into contact with a gas such as sulfur dioxide (SO ₂ ) and reducing it to obtain simple selenium (elemental selenium).

  On the other hand, selenium is also a toxic element and needs to be separated from the wastewater so that the selenium in the wastewater is not released into the sea as it is.

For example, in Patent Document 1, suspended solids (SS), fluorine, cyanide, selenium, ammonia, etc. contained in coal gasification wastewater such as gas washing wastewater generated in the coal gasification process are efficiently removed and discharged. There has been proposed a method for obtaining treated water having good water quality that is possible or reusable. This method includes the following steps (1) to (4), and is a method for treating coal gasification wastewater in which (1) is performed before (2).
(1) Fluorine removal step for removing fluorine by coagulation precipitation (2) Cyanide decomposition step for decomposing cyanide by wet oxidation or thermal hydrolysis (3) Selenium treatment step for reducing selenate ions by metal reductant (4) Ammonia removal process to remove ammonia, etc.

  In addition, it is known that selenium in solution or waste water exists in tetravalent and hexavalent forms. In order to efficiently recover selenium from such a solution, selenic acid (VI) existing in a hexavalent form is generally reduced to a tetravalent form of selenic acid (IV) or elemental selenium and separated. Has been done.

  For example, Patent Document 2 discloses a method for reducing the cost of recovering selenium from wastewater in order to recover selenium from wastewater and enable effective use when the concentration of selenium in the wastewater is high. . Specifically, in a method for recovering selenium from selenium-containing wastewater, wastewater containing tetravalent selenium and hexavalent selenium is neutralized with acid-dissolved iron ions and precipitated as iron hydroxide sludge. At this time, tetravalent selenium is also precipitated together with iron. At this time, hexavalent selenium does not precipitate. When iron is used to precipitate hexavalent selenium and hexavalent selenium is reduced to tetravalent selenium, a lot of iron sludge is generated. By precipitating only tetravalent selenium with iron before reducing hexavalent selenium, the concentration of selenium in the iron sludge is increased, and the recovery cost is reduced.

JP 2010-221151 A JP 2014-156380 A

  However, the progress of the reduction reaction from hexavalent to tetravalent was slow, requiring contact with a large amount of iron metal. Moreover, in order to advance this reduction reaction, it is necessary to spend time under high temperature and high acid concentration, and much energy and labor are required.

  In order to properly maintain the elution of iron, it is necessary to keep the acid concentration low. However, since a large amount of iron metal is used, there is a problem that it is difficult to apply to a solution having a high acid concentration.

  In order to promote the progress of the slow reduction reaction and shorten the time, it is conceivable to use a catalyst. However, there is no catalyst suitable for rapidly reducing hexavalent selenium to the tetravalent form, and no method for efficiently treating waste water has been found.

  The present invention provides a catalyst capable of rapidly reducing selenium present in a hexavalent form, and by using this catalyst, selenium in waste water is precipitated and is intended to be separated efficiently.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by making both the carrier and the support material specific materials, and the present invention has been completed. It was.

  Specifically, the present invention provides the following.

  (1) The present invention provides a carrier containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof selected from rhodium, platinum, palladium, iridium, ruthenium and a mixture thereof. This is a selenate reduction catalyst carrying the above metal particles.

  (2) Moreover, this invention is a selenium reduction catalyst as described in (1) whose load of the said metal particle is 0.1 mass% or more with respect to the dry mass of the said support | carrier.

  (3) Moreover, this invention is a selenium reduction catalyst as described in (1) or (2) whose dispersibility of the said metal by a CO pulse adsorption method is 5% or more.

  (4) Further, the present invention is selected from rhodium, platinum, palladium, iridium, ruthenium and a mixture thereof as a support containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof. A method for producing a selenium reduction catalyst, wherein a metal-containing solution containing one or more metals is impregnated.

  (5) Moreover, this invention adds a sulfuric acid to the selenic acid solution containing hexavalent selenic acid so that a sulfuric acid concentration may be 0.005 mol / l or more, and it is described in any one of (1) to (3) This is a method for reducing a selenic acid solution in which a selenium reduction catalyst and a reducing agent are further added.

  According to the present invention, selenic acid existing in hexavalence can be efficiently reduced. In addition, the efficiency of the treatment of selenium contained in the waste water can be improved.

The relationship between the amount of platinum supported on the carrier of the selenium reduction catalyst, the degree of dispersion of platinum, and the reduction rate per 1% by mass of platinum is shown. Shows the relationship between the degree of dispersion of platinum supported on the carrier of the selenium reduction catalyst and the reduction rate per 1% by mass of platinum.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. Can do.

<Selenate reduction catalyst>
The selenate reduction catalyst of the present invention has a support containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof, which includes rhodium, platinum, palladium, iridium, ruthenium and One or more kinds of metal particles selected from these mixtures are supported.

[Carrier]
In general, solutions and waste water containing selenium are often acidic. Therefore, the carrier is required to be a material that can suppress dissolution in the acidic region. From this viewpoint, the carrier is titanium dioxide (TiO ₂ ), zirconium dioxide (ZrO ₂ ), dialuminum trioxide (alumina, Al ₂ O ₃ ), silicon dioxide (silica, SiO ₂ ), magnesium oxide (MgO), alkali It is necessary to be an oxide of an earth metal or a composite oxide thereof (for example, SiO ₂ —Al ₂ O ₃ (silica alumina), ZrO ₂ —MgO, etc.).

Further, the carrier is required to be a material that can prevent the supported metal particles from falling off. From this viewpoint, the carrier is titanium dioxide (TiO ₂ ), zirconium dioxide (ZrO ₂ ), dialuminum trioxide (alumina, Al ₂ O ₃ ), silicon dioxide (silica, SiO ₂ ), diboron trioxide (B _2). O ₃ ) or a composite oxide thereof (SiO ₂ —Al ₂ O ₃ (silica alumina), SiO ₂ —ZrO _2, etc.), diatomaceous earth, zeolite, phosphate, or the like.

In consideration of both acid resistance and prevention of falling off of metal particles, the support is made of titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof (for example, SiO ₂ -Al ₂ O ₃ (silica Alumina), SiO ₂ —ZrO _2, etc.).

[Supported material]
The support carries one or more kinds of metal particles selected from rhodium, platinum, palladium, iridium, ruthenium, and mixtures thereof. In general, rhodium, platinum, palladium, iridium, ruthenium, and the like are known as catalysts for promoting reduction of materials. The catalytic activity is highest for rhodium, next highest for platinum, and second highest for palladium, iridium and ruthenium. If these metals are used, the effect as a catalyst is sufficiently exhibited. However, in consideration of both catalyst activity and cost, it is preferable to use platinum as a support material.

  The amount of the metal (support material) supported is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the dry mass of the carrier, More preferably, it is 8 mass% or more. If the loading is too small, the efficiency of reducing selenic acid can be affected.

  The upper limit of the loading amount is not particularly limited, but if the loading amount is too large, the degree of dispersion of the metal that is the loading material is not sufficient, which may affect the reduction efficiency per unit mass of the loading material. Considering the high cost of the support material, it is preferable to consider not only the apparent reduction efficiency but also the reduction efficiency per unit mass of the support material. From this viewpoint, the upper limit of the loading amount is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less with respect to the dry mass of the carrier.

  In the selenate reduction catalyst according to the present invention, the dispersity of the metal (supported material) measured according to the CO pulse adsorption method in which a certain amount of carbon monoxide (CO) gas is flowed and the amount adsorbed on the catalyst surface is measured. Is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. The degree of dispersion is the ratio of the molar amount of the metal (supporting material) corresponding to the CO adsorption amount to the total molar amount of the metal (supporting material) contained in the catalyst, that is, (the metal (supporting material) corresponding to the CO adsorption amount). Mole amount) / (total amount of metal (support material) contained in catalyst) × 100. In general, the degree of dispersion has a correlation with the loading amount, and the smaller the loading amount, the larger the degree of dispersion.

  If the degree of dispersion is too low, the reduction efficiency per unit mass of the metal (support material) can be affected. In view of the high cost of the metal (support material), it is preferable to consider not only the apparent reduction efficiency but also the reduction efficiency per unit mass of the metal (support material).

<Method for Producing Selenate Reduction Catalyst>
The method for producing the selenate reducing catalyst according to the present invention is not particularly limited. For example, a support containing titanium dioxide, zirconium dioxide or a composite oxide thereof is impregnated with a solution of one or more metals selected from rhodium, platinum, palladium, iridium, ruthenium and mixtures thereof, dried, and fired. In addition to the above method, there are a method of repeatedly impregnating with a dilute solution, an incipient wetness method of impregnating at a high concentration close to the limit, a spray drying method, and the like.

  The loading amount of one or more kinds of metals selected from rhodium, platinum, palladium, iridium, ruthenium and mixtures thereof is adjusted by the platinum concentration of the platinum solution and the impregnation time of the support in the platinum solution. From this viewpoint, the platinum concentration of the platinum solution is preferably 0.5 g / l or more and 20 g / l or less, more preferably 1 g / l or more and 20 g / l or less, and 3 g / l or more and 10 g / l or less. More preferably.

  The dispersity of the metal (support material) is further determined by measuring the dispersibility of the selenate reduction catalyst in which the supported amount of the metal (support material) is within a suitable range, and the metal (support material) on the support. It is adjusted by adjusting the intensity of agitation at the time of loading.

  In the case of drying and baking to prevent the metal (supporting substance) component from eluting during the reaction, the drying is not particularly limited as long as the liquid component contained in the platinum solution can be evaporated. Also, the firing is not particularly limited as long as it can be fired on the carrier and the support material. In the catalyst preparation method in which a metal (support material) precursor is reduced using a reducing agent and deposited and immobilized on a support, drying and firing are not particularly required.

<Reduction method of selenate solution>
In the selenate solution containing hexavalent selenate, sulfuric acid is added to the selenate solution so that the sulfuric acid concentration is 0.005 mol / l or more, and the above-described selenate reduction catalyst and selenate reducer are further added. Reduced by

  The acid added to the selenic acid solution is preferably sulfuric acid. Other acids such as hydrochloric acid and nitric acid are not preferable because hydrochloric acid and nitric acid may elute the metal as the support material.

  Sulfuric acid needs to be added so that the sulfuric acid concentration is 0.005 mol / l or more, and is preferably added so that the sulfuric acid concentration is 0.005 mol / l or more, so that it becomes 0.01 mol / l or more. More preferably, it is added. The reduction reaction proceeds more easily under low pH conditions. If the sulfuric acid concentration is too low, the reaction does not proceed even if the selenate reducing catalyst and the selenate reducing agent are added, or the catalytic action is expressed. Since hexavalent selenic acid may not be reduced suitably, it is not preferable.

  The upper limit of the sulfuric acid concentration is not particularly limited as long as it does not affect the precipitation state of selenium.

  The selenate reducing agent is not particularly limited as long as it is a material capable of reducing hexavalent selenate, and examples thereof include hydrazine and hydrated hydrazine.

  The supply amount of the selenate reducing agent is not particularly limited, but considering both the ability to efficiently reduce hexavalent selenate and the prevention of the remaining selenate reducing agent, The supply amount of the reducing agent is preferably 3 to 10 times the molar amount of hexavalent selenic acid.

  As the reduction reaction proceeds, Se (VI) in the liquid is reduced to settle as Se elements. Therefore, when the selenate reducing catalyst according to the present invention is used, selenium present in a hexavalent form can be rapidly reduced, and selenium in the waste water can be precipitated and efficiently separated.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention does not receive a restriction | limiting at all in these description.

<Preparation of selenate reduction catalyst>
[Example 1]
10 g of TiO ₂ (product name: P25, manufactured by Nippon Aerosil Co., Ltd.) is added to 10 ml of a dinitroammineplatinum (IV) aqueous solution containing 0.05 g of Pt, and maintained at 75 ° C. with stirring with a stirrer over 2 hours. Water was evaporated. Then, the selenate reduction catalyst which concerns on Example 1 was obtained by vacuum-drying further at the temperature of 80 degreeC, and then baking for 2 hours, maintaining at 500 degreeC in air | atmosphere. When the platinum quality of this selenate reducing catalyst was analyzed, the amount of platinum supported was 10% by mass relative to the dry mass of the carrier.

[Example 2]
A selenate reduction catalyst according to Example 2 was obtained by the same method as Example 1 except that TiO ₂ was changed to ZrO ₂ (product name: JRC-ZRO-3, manufactured by the Japan Society for Catalysis). The amount of platinum supported was 10% by mass relative to the dry mass of the carrier.

Example 3
A selenate reduction catalyst according to Example 3 was obtained in the same manner as in Example 1 except that the supported amount of platinum was 0.8% by mass with respect to the dry mass of the carrier.

Example 4
A selenate reduction catalyst according to Example 4 was obtained in the same manner as in Example 1 except that the amount of platinum supported was 5% by mass with respect to the dry mass of the carrier.

Example 5
A selenate reduction catalyst according to Example 5 was obtained in the same manner as in Example 1 except that the amount of platinum supported was 20% by mass with respect to the dry mass of the support.

[Comparative Example]
The same TiO ₂ as in Example 1 was vacuum-dried at a temperature of 80 ° C. without being brought into contact with a dinitroammineplatinum (IV) aqueous solution, and then calcined for 2 hours while maintaining at 500 ° C. in the atmosphere. The selenate reduction catalyst according to the example was obtained.

<Evaluation> Reduction of selenate solution [Evaluation 1: Comparison of selenate reduction catalyst]
200 ml of an aqueous solution having a sulfuric acid concentration of 0.01 M / l and 0.1 M / l was added to each of the selenate reduction catalysts according to Examples 1 and 2 and the comparative example, and further Na ₂ SeO ₄ was added at 0.1 mM / l. Then, the mixture was heated to 80 ° C. while bubbling with nitrogen, and when the temperature reached 80 ° C., the temperature was maintained and held for 30 minutes with stirring. After 30 minutes, the Se concentration in the liquid was measured with an ICP analyzer and found to be 0.7 mM / l.

  The molar concentration of Se contained in the liquid at this time was 100%, and hydrazine hydrate (hydrazine monohydrate) corresponding to 10 times the molar amount of Se was added to the selenic acid solution after stirring. And after adding 2 hours after adding hydrazine hydrate, the liquid was sampled and the Se concentration was measured.

  As the reduction reaction proceeds, Se (VI) in the liquid is reduced to settle as Se elements. Therefore, the amount of reduced Se can be calculated by subtracting the Se concentration after 2 hours from the addition of hydrazine hydrate from the Se concentration before adding hydrazine hydrate.

Therefore, ((Se concentration before adding hydrazine hydrate) − (Se concentration after 2 hours from adding hydrazine hydrate)) / (Se concentration before adding hydrazine hydrate) × 100 The reduction rate of selenic acid. The results are shown in Table 1.

  When the selenate reduction catalyst according to the example is used, hexavalent selenate can be reduced with an extremely high efficiency of 34% in a short time of 2 hours.

  On the other hand, when the selenate reducing catalyst according to the comparative example is used, hexavalent selenate can hardly be reduced even if the sulfuric acid concentration in the starting solution is within a suitable range.

[Evaluation 2: Comparison of sulfuric acid concentration in the starting solution]
For the selenate reduction catalyst according to Example 1, except that four types of aqueous solutions having sulfuric acid concentrations of 0.001 M / l, 0.01 M / l, 0.1 M / l, and 0.5 M / l were added, [Evaluation 1: Comparison of selenate reduction catalyst] The reduction rate of hexavalent selenate was determined by the same method. The results are shown in Table 2.

  When the selenate reducing catalyst according to the example is used, when the sulfuric acid concentration in the starting solution is in the range of 0.01 mol / l or more and 0.5 mol / l or less, hexavalent selenate is reduced to 20% in a short time of 2 hours. It can reduce at the above ratio. In particular, when the sulfuric acid concentration in the starting solution is 0.01 mol / l or more and 0.1 mol / l or less, hexavalent selenic acid can be more efficiently reduced, and the sulfuric acid concentration in the starting solution is about 0.01 mol / l. And can be reduced more efficiently.

  On the other hand, if the sulfuric acid concentration in the starting solution is too low, hexavalent selenate cannot be reduced even if the selenate reduction catalyst according to the example is used. This reaction is more likely to proceed as the pH is lower, and it is considered that the reaction did not proceed even when the catalytic action was exhibited at a sulfuric acid concentration as low as 0.001 mol / l.

[Evaluation 3: Comparison of platinum particle loading]
The reduction rate of hexavalent selenate was determined by the same method as [Evaluation 1: Comparison of selenate reduction catalyst] except that the selenate reduction catalyst was changed to the four types of Examples 1 and 3-5. The reduction rate per 1% by mass of platinum particles was also determined. The results are shown in Table 3.

  It is sufficient that the supported amount of platinum particles is 0.8% by mass or more with respect to the dry mass of the carrier, and it can be said that hexavalent selenic acid can be efficiently reduced if the supported amount is 0.8% by mass or more. The greater the amount of platinum particles supported, the higher the apparent reduction rate. However, it can be seen from Table 3 that if the loading amount is too large, the reduction efficiency per unit mass of the platinum particles can be affected. In view of the high cost of the platinum particles, it is preferable to consider not only the apparent reduction efficiency but also the reduction efficiency per unit mass of the platinum particles. From this viewpoint, the upper limit of the loading amount is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less with respect to the dry mass of the carrier.

In order to consider the influence of too much loading, the dispersity of the selenate reduction catalyst according to Examples 1 and 3 to 5 was measured according to a CO pulse adsorption method which is a known method. Table 4 and FIG. 1 show the relationship between the supported amount, the degree of dispersion, and the reduction rate per 1% by mass of platinum particles. FIG. 2 shows the relationship between the degree of dispersion and the reduction rate per 1% by mass of the platinum particles.

  From Table 4 and FIGS. 1 and 2, it can be said that the reduction efficiency per unit mass of the platinum particles has a correlation with the degree of dispersion of platinum. If the degree of dispersion is too low, the reduction efficiency per unit mass of the platinum particles can be affected. In view of the high cost of the platinum particles, it is preferable to consider not only the apparent reduction efficiency but also the reduction efficiency per unit mass of the platinum particles.

Claims (5)

  One or more kinds of metal particles selected from rhodium, platinum, palladium, iridium, ruthenium and a mixture thereof are supported on a support containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof. Selenate reduction catalyst.   2. The selenate reduction catalyst according to claim 1, wherein the supported amount of the metal particles is 0.1% by mass or more based on the dry mass of the carrier.   The selenate reduction catalyst according to claim 1 or 2, wherein a degree of dispersion of the metal by a CO pulse adsorption method is 5% or more.   A metal containing one or more kinds of metals selected from rhodium, platinum, palladium, iridium, ruthenium, and mixtures thereof on a carrier containing titanium dioxide, zirconium dioxide, dialuminum trioxide, silicon dioxide or a composite oxide thereof. A method for producing a selenate-reducing catalyst, wherein the containing solution is impregnated.   A sulfuric acid is added to a selenic acid solution containing hexavalent selenic acid so that the sulfuric acid concentration becomes 0.005 mol / l or more, and the selenate reducing catalyst and the selenate reducing agent according to claim 1, A method for reducing a selenic acid solution.

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