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Adsorption study on PGM elements by AlHCF from nitric acid solution

AlHCFによる硝酸溶液からのPGM元素吸着の研究

三島 理愛 ; 立岡 壮太郎*; 稲葉 優介*; 針貝 美樹*; 松村 達郎  ; 渡邊 真太*; 尾上 順*; 中瀬 正彦*; 竹下 健二*

Mishima, Ria; Tachioka, Sotaro*; Inaba, Yusuke*; Harigai, Miki*; Matsumura, Tatsuro; Watanabe, Shinta*; Onoe, Jun*; Nakase, Masahiko*; Takeshita, Kenji*

日本では高レベル放射性廃液(HLLW)をガラス固化し地下深部に最終処分する方針であるが、ガラス固化処理中に発生する、HLLW中の白金族元素の析出とMoのイエローフェーズ形成が問題になっており、さらにそれら解決のための洗浄運転による発生ガラス固化体量と必要な最終処分場面積の増大も問題となる。本研究では吸着材としてフェロシアン化アルミニウム(AlHCF)に着目し、AlHCFの各種金属イオンに対する吸着挙動を解明し溶出と吸着の関係を理解することを目的に、AlHCFの合成と処理条件による吸着性能への影響と、金属イオンの吸着とAlHCFの溶出との関係を調査した。合成したAlHCFは模擬HLLWにおいて白金族元素とMoに対し吸着性能を示すことが分かった。各元素に対する吸着機構を調べるためPd単成分溶液での吸着試験を行った結果、Pd吸着過程で溶出したFeとAlの元素比は1:4となり、本来のAlHCF内のFeとAlの元素比3:4と異なることから、Pdの吸着だけでなく再吸着と安定化のメカニズムの存在が示唆された。

In Japan, the final disposal of high level liquid waste (HLLW) will be done after vitrification into borosilicate glass and then disposed into deep underground. In this vitrification process, there are some concerns. The first concern is precipitation of platinum group metals (PGMs) in the melter due to their low solubility into borosilicate glass. The second concern is the formation of yellow phase caused by Mo content. The final concern is the generation of huge number of vitrified glasses and the requirement of wide space needed for final disposal. Among many kinds of extractants and adsorbents for separation of such metal ions, metal hexacyanoferrate (HCFs) were reported to have an ability to adsorb PGMs. The objective of this study is to elucidate the adsorption behavior of aluminum hexacyanoferrate (AlHCF) for various metal ions and understand the relation between elution and adsorption. The effect of synthetic and workup conditions on PGM and Mo adsorption from simulated HLLW (sHLLW) was surveyed. Also, the relationship between adsorption of metal ions and elution of the AlHCF was studied. The synthesized AlHCF showed adsorption performance for PGMs and Mo in simulated HLLW. As a result of an adsorption test with a Pd single component solution to investigate the adsorption mechanism, the eluted element ratio was Fe:Al = 1:4 in the Pd adsorption test. However, the element ratio was Fe:Al = 3:4 in the original AlHCF. Therefore, it was suggested the existence of not only Pd adsorption, but also resorption and stabilization mechanisms.

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