JP2006007067A - Nitric acid reduction catalyst composition and treatment method for nitric acid solution using the same - Google Patents
Nitric acid reduction catalyst composition and treatment method for nitric acid solution using the same Download PDFInfo
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本発明は、高濃度の硝酸溶液であっても還元処理が可能な硝酸還元触媒組成物、およびこれを用いた硝酸溶液の処理方法に関するものである。 The present invention relates to a nitrate reduction catalyst composition that can be reduced even in a highly concentrated nitric acid solution, and a method for treating a nitric acid solution using the same.
硝酸性窒素は農薬肥料等に含まれ、地下水や河川に混入し得るが、硝酸イオンは生体内で亜硝酸イオンに還元され血液中のヘモグロビンと結合することによって、特に乳児にメトヘモグロビン血症を発症させる。また、成人に対しても発ガン性が疑われている。従って、水道水には硝酸イオンや亜硝酸イオンの濃度基準が設けられている。 Nitrate nitrogen is contained in agricultural fertilizers and can be mixed into groundwater and rivers, but nitrate ions are reduced to nitrite ions in the body and combined with hemoglobin in the blood, so that methemoglobinemia occurs particularly in infants. Cause it to develop. It is also suspected to be carcinogenic to adults. Therefore, the concentration standard of nitrate ion and nitrite ion is provided in tap water.
硝酸イオン等を処理する浄水方法としては、ランニングコストが安いという利点から、一般的には、微生物により処理する生物学的処理方法が採用されている。ところが、生物学的処理方法は処理能力に限界があり、多量の処理を行なうには広大な敷地を要し、また、高濃度の硝酸を処理できないという問題がある。 As a water purification method for treating nitrate ions or the like, a biological treatment method for treating with a microorganism is generally employed because of its advantage of low running cost. However, the biological treatment method has a limit in processing capability, and a large amount of processing is required to perform a large amount of treatment, and there is a problem that high concentration nitric acid cannot be treated.
生物学的処理方法の他には、イオン交換法，逆浸透法，電気透析法などの物理化学的な処理方法がある。しかし、これら方法は硝酸性窒素を単に分離するのみであって、根本的な解決にはならない。そこで、触媒の存在下に硝酸性窒素と水素等とを反応させることによって、硝酸イオン等を窒素まで還元する方法が種々検討されている。 In addition to biological treatment methods, there are physicochemical treatment methods such as ion exchange, reverse osmosis, and electrodialysis. However, these methods simply separate nitrate nitrogen and are not a fundamental solution. Therefore, various methods for reducing nitrate ions and the like to nitrogen by reacting nitrate nitrogen with hydrogen in the presence of a catalyst have been studied.
例えば特許文献１には、ヒドラジンとスポンジ銅触媒により硝酸性窒素を亜硝酸性窒素へ還元した後、更にパラジウム触媒により窒素ガスまで還元する処理方法が開示されている。また、特許文献２には、金属パラジウムと銅−パラジウム合金との混合物である触媒組成物と共に、これを用いた硝酸性窒素および亜硝酸性窒素の処理方法が開示されている。 For example, Patent Document 1 discloses a treatment method in which nitrate nitrogen is reduced to nitrite nitrogen using hydrazine and a sponge copper catalyst, and further reduced to nitrogen gas using a palladium catalyst. Patent Document 2 discloses a catalyst composition that is a mixture of metallic palladium and a copper-palladium alloy, and a method for treating nitrate nitrogen and nitrite nitrogen using the catalyst composition.
しかし、これら触媒では、高濃度の硝酸溶液、即ち低ｐＨの溶液を処理できないという問題がある。この点について、特許文献１では高濃度の硝酸性窒素を処理できると謳われているが、当該技術では排水のｐＨを８以上に調整する必要がある。実際、特許文献１の実施例では、被処理水のｐＨを１２．５と８．０に保持しつつ処理した例が開示されているが、ｐＨが８．０の場合における残存硝酸性窒素濃度等が高いことから、「ｐＨが低くなるとその反応速度が小さくなることがわかる」とされている。また、特許文献２によれば、「反応中の処理水のｐＨは４〜１１の範囲が好ましく、５〜１０の範囲がさらに好ましい」とされているが、実施例におけるｐＨは６．０に調整されている。 However, these catalysts have a problem that they cannot process a highly concentrated nitric acid solution, that is, a low pH solution. In this regard, Patent Document 1 is said to be able to treat high-concentration nitrate nitrogen, but in this technique, it is necessary to adjust the pH of the waste water to 8 or more. Actually, in the example of Patent Document 1, an example in which the pH of the water to be treated is treated while being maintained at 12.5 and 8.0 is disclosed, but the residual nitrate nitrogen concentration in the case where the pH is 8.0 is disclosed. Etc., it is said that “the reaction rate decreases with decreasing pH”. Further, according to Patent Document 2, “the pH of the treated water during the reaction is preferably in the range of 4 to 11, more preferably in the range of 5 to 10,” but the pH in the examples is 6.0. It has been adjusted.
これら従来技術で被処理水のｐＨを比較的高くせざるを得ないのは、ｐＨが低くなると触媒が溶出し、その作用効果を発揮できなくなることによるが、場合によっては、斯かる欠点によりこれら触媒が使用できないことがある。 The reason why the pH of the water to be treated in this conventional technique has to be relatively high is that the catalyst is eluted when the pH is low, and the effect of the catalyst cannot be exhibited. The catalyst may not be used.
例えば、特許文献３には、陽電極と陰電極との間に２枚のバイポーラ膜を配し、その間の陽電極側に陰イオン交換膜を、陰電極側にナトリウムイオン選択透過膜を配置し、陰イオン交換膜とナトリウムイオン選択透過膜間で放射性廃液を処理する方法が開示されている。当該方法では、使用済核燃料等を処理した硝酸ナトリウム溶液（硝酸ナトリウムの他に、放射性核種や有機物を含む）は、電気透析によって分解されて水酸化ナトリウムと硝酸として回収されるが、ここで得られる硝酸の濃度は、地下水等に含まれるものよりもはるかに高い。従って、斯かる硝酸を従来の触媒を用いて処理しようとすると、触媒が溶液中に溶出することにより処理効率が極端に低下して、十分処理することができなかった。
上述した様に、硝酸性窒素等を還元分解するための触媒はこれまでにも存在していたが、例えばｐＨが２以下である様な高濃度の硝酸溶液を効率的に還元できる触媒はなかった。 As described above, there has been a catalyst for reducing and decomposing nitrate nitrogen and the like, but there is no catalyst that can efficiently reduce a highly concentrated nitric acid solution having a pH of 2 or less, for example. It was.
そこで、本発明が解決すべき課題は、高濃度の硝酸溶液に対しても適用可能であり、効率的に硝酸イオンや亜硝酸イオン等を還元できる硝酸還元触媒組成物と、これを用いた硝酸溶液の処理方法を提供することにある。 Therefore, the problem to be solved by the present invention can be applied to a highly concentrated nitric acid solution, and a nitrate reduction catalyst composition capable of efficiently reducing nitrate ions, nitrite ions, and the like, and nitric acid using the same. It is to provide a method for treating a solution.
本発明者らは、上記課題を解決すべく、硝酸イオンを効率的に還元できる触媒の構成につき種々検討した。その結果、一定のモル比で白金とスズとを組合わせた触媒は、高濃度の硝酸溶液にも溶出し難く、処理性能も高いことを見出して本発明を完成した。 In order to solve the above-mentioned problems, the present inventors have made various studies on the configuration of a catalyst that can efficiently reduce nitrate ions. As a result, it was found that a catalyst in which platinum and tin were combined at a fixed molar ratio was not easily eluted in a high-concentration nitric acid solution, and the processing performance was high, thereby completing the present invention.
即ち、本発明の硝酸還元触媒組成物は、白金とスズを含み、スズに対する白金のモル比（Ｐｔ/Ｓｎ）が４〜１０００であることを特徴とする。 That is, the nitrate reduction catalyst composition of the present invention contains platinum and tin, and the molar ratio of platinum to tin (Pt / Sn) is 4 to 1000.
上記硝酸還元触媒組成物では、上記モル比が２０〜５００であるものが好適である。本発明者らが実験により見出した事実であるが、モル比がこの範囲内にある触媒は、硝酸の除去率が極めて優れているからである。また、白金とスズは、担体に担持されていることが好ましい。触媒組成物の製法がより容易になったり、取扱い性も向上するからである。 In the nitric acid reduction catalyst composition, those having the molar ratio of 20 to 500 are preferable. The fact that the present inventors have found through experiments is that a catalyst having a molar ratio within this range has a very excellent nitric acid removal rate. Moreover, it is preferable that platinum and tin are supported on a carrier. This is because the production method of the catalyst composition becomes easier and the handleability is improved.
また、本発明に係る硝酸溶液の処理方法は、上記硝酸還元触媒組成物の存在下、硝酸溶液と水素ガスとを接触させることを特徴とする。 The method for treating a nitric acid solution according to the present invention is characterized in that the nitric acid solution and hydrogen gas are brought into contact with each other in the presence of the nitric acid reduction catalyst composition.
本発明の硝酸還元触媒組成物は、高濃度の硝酸溶液にも溶出し難く、硝酸イオン等を効率的に還元処理することができる。従って、本発明の硝酸還元触媒組成物とこれを用いた硝酸溶液の処理方法は、例えば、使用済核燃料の再処理において発生する高濃度硝酸溶液等の還元処理に適用することができるものとして、産業上極めて有用である。 The nitrate reduction catalyst composition of the present invention is not easily eluted even in a high-concentration nitric acid solution and can efficiently reduce nitrate ions and the like. Therefore, the nitric acid reduction catalyst composition of the present invention and the nitric acid solution treatment method using the same can be applied to a reduction treatment of a high-concentration nitric acid solution generated in the reprocessing of spent nuclear fuel, for example, It is extremely useful in industry.
本発明の硝酸還元触媒組成物は、白金とスズを含み、スズに対する白金のモル比（Ｐｔ/Ｓｎ）が４〜１０００であることを要旨とする。白金とスズとを組合わせた触媒は耐酸性に優れ、高濃度の硝酸溶液も還元処理できる。また、その組成比を検討した結果、従来触媒であるパラジウムと銅との組合わせにおいて採用されていた組成比よりも貴金属の割合を多くすることによって、活性が高くなる。斯かる組成比は、より好ましくは２０以上，５００以下である。 The nitric acid reduction catalyst composition of the present invention includes platinum and tin, and the gist is that the molar ratio of platinum to tin (Pt / Sn) is 4 to 1000. A catalyst combining platinum and tin is excellent in acid resistance and can reduce a nitric acid solution with a high concentration. Further, as a result of examining the composition ratio, the activity is increased by increasing the ratio of the noble metal compared to the composition ratio employed in the conventional combination of palladium and copper as the catalyst. Such a composition ratio is more preferably 20 or more and 500 or less.
本発明組成物の主要成分である金属（白金とスズ）の形状は特に制限されず、粉末状，箔状，スポンジ状などとすることができるが、微粒子状にすれば硝酸イオンや水素が接触すべき表面の面積が大きくなり、活性が向上するため好ましい。 The shape of the metal (platinum and tin), which is the main component of the composition of the present invention, is not particularly limited, and can be powder, foil, sponge, etc. This is preferable because the surface area to be increased is increased and the activity is improved.
本発明の硝酸還元触媒組成物としては、白金とスズが担体に担持されているものが好ましい。金属単体でも使用できるが、担体上に担持させると金属量当たりの活性が高くなり、また、取扱いが容易になるからである。ここで使用できる担体の種類は特に制限されないが、例えばアルミナ，チタニア，ジルコニア，カーボン等を挙げることができる。その形状も特に問わず、粉末，ペレット，ハニカムなどを目的に応じて適宜選択する。 The nitrate reduction catalyst composition of the present invention is preferably one in which platinum and tin are supported on a carrier. This is because a single metal can be used, but if it is supported on a carrier, the activity per metal amount becomes high and the handling becomes easy. The type of carrier that can be used here is not particularly limited, and examples thereof include alumina, titania, zirconia, and carbon. The shape is not particularly limited, and powders, pellets, honeycombs and the like are appropriately selected according to the purpose.
本発明に係る触媒の製法は従来方法を適用すればよく、特に制限はない。例えば、触媒金属（白金とスズ）の原料としては、硝酸塩や塩化物など可溶性化合物を用い、水に溶解した後に共沈させたり蒸発乾固させたりすることによって、担体上に析出させればよい。 The method for producing the catalyst according to the present invention may be a conventional method, and is not particularly limited. For example, as a raw material for catalyst metals (platinum and tin), soluble compounds such as nitrates and chlorides may be used, and may be deposited on a carrier by coprecipitation or evaporation to dryness after dissolution in water. .
金属を担体上に析出させた後は、塩を除去するために３００℃以上（好適には３５０℃程度）の空気中で加熱処理し、更に水素ガス気流中３００℃以上（好適には３５０℃程度）で還元処理を行なう。 After the metal is deposited on the support, heat treatment is performed in air at 300 ° C. or higher (preferably about 350 ° C.) to remove the salt, and further 300 ° C. or higher (preferably 350 ° C. in a hydrogen gas stream). (About)).
本発明に係る硝酸溶液の処理方法では、本発明の硝酸還元触媒組成物を、処理すべき硝酸溶液に懸濁した後、水素ガスを吹き込むことによって、硝酸イオンや亜硝酸イオンを還元する。本発明の触媒組成物は、高濃度の硝酸溶液を還元処理できるという特性を有するが、勿論、低濃度の硝酸溶液にも適用することができる。 In the nitric acid solution treatment method according to the present invention, the nitric acid reduction catalyst composition of the present invention is suspended in the nitric acid solution to be treated, and then hydrogen gas is blown to reduce nitrate ions and nitrite ions. The catalyst composition of the present invention has a characteristic that a highly concentrated nitric acid solution can be reduced, but of course can also be applied to a low concentration nitric acid solution.
硝酸還元触媒組成物の添加量は、処理すべき硝酸溶液の濃度等により適宜調整すればよいが、例えば、硝酸溶液１Ｌに対して０．０１〜１ｇ程度の範囲で適宜調整する。特に高濃度の硝酸溶液を処理する場合は、触媒の量よりも水素との接触効率の影響が大きく、水素ガスが硝酸溶液に吹き込まれ更に触媒表面へ如何に拡散するかが重要であるため、攪拌したり水素ガスの気泡を小さくするなど、気液の接触効率の向上を図ることが望ましい。また、反応温度は特に問わず、室温の温度域でも十分な処理を行なうことができる。 The addition amount of the nitric acid reduction catalyst composition may be appropriately adjusted depending on the concentration of the nitric acid solution to be treated and the like. For example, it is appropriately adjusted within a range of about 0.01 to 1 g with respect to 1 L of the nitric acid solution. Especially when treating highly concentrated nitric acid solutions, the effect of contact efficiency with hydrogen is greater than the amount of catalyst, and it is important how hydrogen gas is blown into the nitric acid solution and further diffuses to the catalyst surface. It is desirable to improve the gas-liquid contact efficiency, for example, by stirring or reducing the bubbles of hydrogen gas. Further, the reaction temperature is not particularly limited, and sufficient treatment can be performed even in a temperature range of room temperature.
本発明方法で用いる反応装置としては特に制限はなく、例えば、流動床や固定床などの形式の装置を適宜選択することができる。流動床を用いる場合には、触媒を懸濁させた被処理液中に、散気管やエジェクタ等のガス分散機構を用いて水素ガスを吹き込めばよい。この際、被処理水は、連続で供給してもよいし、回分で供給してもよい。 There is no restriction | limiting in particular as a reactor used by the method of this invention, For example, apparatuses, such as a fluid bed and a fixed bed, can be selected suitably. In the case of using a fluidized bed, hydrogen gas may be blown into the liquid to be treated in which the catalyst is suspended using a gas dispersion mechanism such as an air diffuser or an ejector. At this time, the water to be treated may be supplied continuously or in batches.
固定床を用いる場合には、ペレットやハニカムなどモノリス構造の形状の触媒を反応塔に充填し、被処理液と水素を向流若しくは並流で供給して反応させればよい。被処理液や水素ガスは反応塔を１回のみ通過させるだけでもよいが、繰り返し循環させることで、触媒の充填量や未反応の水素を削減することができる。 In the case of using a fixed bed, a catalyst having a monolithic structure such as a pellet or a honeycomb may be packed in a reaction tower, and the liquid to be treated and hydrogen may be supplied in a countercurrent or a parallel flow to cause a reaction. The liquid to be treated and hydrogen gas may be passed only once through the reaction tower, but by repeatedly circulating, the amount of catalyst filling and unreacted hydrogen can be reduced.
以下に、実施例を示すことにより本発明を更に詳細に説明するが、本発明の範囲はこれらに限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited thereto.
製造例１ 本発明に係る触媒の製造
塩化スズ １３５ｍｇ（０．３２ｍｍｏｌ）を水 ２００ｍＬに溶解し、当該溶液へ貴金属触媒であるＰｔ/Ａｌ2Ｏ3（和光純薬工業製，Ｐｔ：５％） ５ｇ（Ｐｔ：１．２８ｍｍｏｌ）を懸濁させた後、ロータリーエバポレーターを用いて蒸発乾固させた。この触媒を空気中３５０℃で３時間熱処理した後、更に５％水素中３５０℃で３時間処理した。得られたＰｔ/Ｓｎ触媒（製造Ｎｏ．１）の各金属の含有率を、ＩＣＰ発光分光分析装置（島津製作所製，ICPS-8000）を用いてＩＣＰ発光分光分析法により測定した。結果を表１に示す。
Production Example 1 Production of Catalyst According to the Present Invention 135 mg (0.32 mmol) of tin chloride was dissolved in 200 mL of water, and Pt / Al 2 O 3 as a noble metal catalyst (Pt: 5%, manufactured by Wako Pure Chemical Industries) was added to the solution. After 5 g (Pt: 1.28 mmol) was suspended, it was evaporated to dryness using a rotary evaporator. This catalyst was heat-treated in air at 350 ° C. for 3 hours, and further treated in 5% hydrogen at 350 ° C. for 3 hours. The content of each metal of the obtained Pt / Sn catalyst (Production No. 1) was measured by ICP emission spectroscopy using an ICP emission spectrometer (ICPS-8000, manufactured by Shimadzu Corporation). The results are shown in Table 1.
製造例２ 従来触媒の製造
上記製造例１において、塩化スズの代わりに硝酸銅 ７７ｍｇ（０．３２ｍｍｏｌ）を用いた以外は同様の処理を行なって、Ｐｔ/Ｃｕ触媒（製造Ｎｏ．２）を製造した。また、塩化スズの代わりに硝酸銅 １４２ｍｇ（０．６ｍｍｏｌ）を、Ｐｔ/Ａｌ2Ｏ3の代わりにＰｄ／Ｃ（和光純薬工業製，Ｐｄ：５％） ５ｇ（Ｐｄ：２．４ｍｍｏｌ）を用いて、Ｐｄ/Ｃｕ触媒（製造Ｎｏ．３）を製造した。各触媒について、各金属の含有率を製造例１と同様に求めた。
Production Example 2 Production of Conventional Catalyst A Pt / Cu catalyst (Production No. 2) was produced in the same manner as in Production Example 1 except that 77 mg (0.32 mmol) of copper nitrate was used instead of tin chloride. did. In addition, 142 mg (0.6 mmol) of copper nitrate instead of tin chloride, 5 g of Pd / C (manufactured by Wako Pure Chemical Industries, Pd: 5%) instead of Pt / Al 2 O 3 (Pd: 2.4 mmol) Using this, a Pd / Cu catalyst (Production No. 3) was produced. About each catalyst, the content rate of each metal was calculated | required similarly to manufacture example 1.
試験例１ 触媒の耐酸性評価
濃度１０００ｐｐｍに調整した硝酸溶液（ｐＨ １．７）に、上記製造例１と２で製造したＰｔ/Ｓｎ触媒（製造Ｎｏ．１），Ｐｔ/Ｃｕ触媒（製造Ｎｏ．２）およびＰｄ/Ｃｕ触媒（製造Ｎｏ．３）それぞれを懸濁し、２４時間攪拌した。その後、当該混合液をろ過し、ＩＣＰ発光分光分析装置（島津製作所製，ICPS-8000）を用いたＩＣＰ発光分光分析法によって、ろ液に含まれる各金属の濃度を測定してろ液中の金属量を求め、更に下記式に基づいて溶出率を計算した。
溶出率＝（ろ液中の金属量(ｍｇ)／触媒に当初含まれる金属量(ｍｇ)）×１００
結果を表１に示す。
Test Example 1 Acid Resistance Evaluation of Catalyst Pt / Sn catalyst (Production No. 1), Pt / Cu catalyst (Production No.) produced in Production Examples 1 and 2 were added to a nitric acid solution (pH 1.7) adjusted to a concentration of 1000 ppm. .2) and Pd / Cu catalyst (Production No. 3) were suspended and stirred for 24 hours. Thereafter, the mixed solution is filtered, and the concentration of each metal contained in the filtrate is measured by ICP emission spectroscopy using an ICP emission spectrometer (ICPS-8000, manufactured by Shimadzu Corporation). The amount was determined, and the dissolution rate was calculated based on the following formula.
Elution rate = (Amount of metal in filtrate (mg) / Amount of metal initially contained in catalyst (mg)) × 100
The results are shown in Table 1.
上記結果によれば、従来の硝酸還元触媒である製造Ｎｏ．２の触媒ではＰｔの溶出がみられ、製造Ｎｏ．３ではＰｄとＣｕの両方が溶出していた。一方、本発明に係る触媒（製造Ｎｏ．１）では、１０００ｐｐｍという廃液としては高濃度の硝酸溶液中で２４時間攪拌しても、金属の溶出は認められなかった。従って、本発明の硝酸還元触媒は、高濃度の硝酸溶液中でも活性は低下しないことが実証された。 According to the above results, the production number of the conventional nitrate reduction catalyst is as follows. In the catalyst No. 2, elution of Pt was observed. In No. 3, both Pd and Cu were eluted. On the other hand, in the catalyst according to the present invention (Production No. 1), no metal elution was observed even when the waste solution of 1000 ppm was stirred in a highly concentrated nitric acid solution for 24 hours. Therefore, it was demonstrated that the activity of the nitrate reduction catalyst of the present invention does not decrease even in a highly concentrated nitric acid solution.
製造例３
上記製造例１において、Ｓｎに対するＰｔのモル比を変えて種々の触媒を製造した。斯かる触媒中の金属割合（Ｐｔ/Ｓｎ）は、上記製造例１と同様にＩＣＰ発光分光分析法により確認した。
Production Example 3
In Production Example 1, various catalysts were produced by changing the molar ratio of Pt to Sn. The metal ratio (Pt / Sn) in the catalyst was confirmed by ICP emission spectroscopic analysis as in Production Example 1.
試験例２ 硝酸還元性能評価
上記製造例３で製造したＳｎに対するＰｔのモル比（Ｐｔ/Ｓｎ）が１００である触媒を用いて、硝酸の還元処理を行なった。具体的には、１０００ｐｐｍの硝酸溶液 ２Ｌ中に触媒 １ｇを懸濁し、室温で攪拌しながら、溶液中に水素ガスを１Ｌ／分で散気した。１０分毎に溶液を分取し、３０分後にガス吹き込みを停止した。分取した試料は、触媒をろ過により分離した後、ろ液中の硝酸性窒素の濃度を測定した。結果を図１に示す。
Test Example 2 Nitric Acid Reduction Performance Evaluation Using a catalyst having a molar ratio of Pt to Sn (Pt / Sn) of 100 produced in Production Example 3 above, reduction treatment of nitric acid was performed. Specifically, 1 g of the catalyst was suspended in 2 L of a 1000 ppm nitric acid solution, and hydrogen gas was diffused into the solution at 1 L / min while stirring at room temperature. The solution was collected every 10 minutes, and gas blowing was stopped after 30 minutes. From the sample collected, the catalyst was separated by filtration, and then the concentration of nitrate nitrogen in the filtrate was measured. The results are shown in FIG.
図１の結果より、本発明の硝酸還元触媒は、１０００ｐｐｍという高濃度の硝酸であっても活性が低下せず、処理時間に比例して硝酸を還元処理できることが明らかとなった。 From the results shown in FIG. 1, it has been clarified that the nitric acid reduction catalyst of the present invention does not decrease the activity even at a high concentration of 1000 ppm nitric acid and can reduce nitric acid in proportion to the treatment time.
試験例３
モル比（Ｐｔ/Ｓｎ）を変えて製造した触媒を用いて、上記試験例２と同様の手法で硝酸性窒素の還元処理性能の評価を行なった。また、比較のために、Ｐｔのみの触媒でも評価した。結果を表２に示す。
Test example 3
Using the catalyst produced by changing the molar ratio (Pt / Sn), the reduction performance of nitrate nitrogen was evaluated in the same manner as in Test Example 2. For comparison, a catalyst containing only Pt was also evaluated. The results are shown in Table 2.
当該結果によれば、Ｐｔのみでは高濃度の硝酸溶液を処理することができず、ＰｔとＳｎとを組合わせる必要があるが、Ｓｎに対するＰｔのモル比（Ｐｔ/Ｓｎ）が低過ぎても高過ぎても処理効率は低下することが明らかとなった。また、Ｐｔ/Ｓｎが４〜１０００の範囲にあれば高濃度硝酸を処理することができ、２０〜５００の範囲であれば特に効果に優れることが実証された。 According to the result, it is not possible to treat a high-concentration nitric acid solution with Pt alone, and it is necessary to combine Pt and Sn. It became clear that the processing efficiency was lowered even if it was too high. Further, it was proved that high concentration nitric acid can be treated if Pt / Sn is in the range of 4 to 1000, and that the effect is particularly excellent in the range of 20 to 500.
Claims (4)
A nitric acid solution treatment method comprising contacting a nitric acid solution with hydrogen gas in the presence of the nitric acid reduction catalyst composition according to claim 1.
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