海水中有用金属捕集材実海域特性試験

Characteristics tests for recovery of rare metals from real sea with adsorbents

片貝 秋雄; 笠井 昇; 玉田 正男; 長谷川 伸; 瀬古 典明; 川端 幸哉*; 大沼 謙二*; 武田 隼人*; 須郷 高信

Katakai, Akio; Kasai, Noboru; Tamada, Masao; Hasegawa, Shin; Seko, Noriaki; Kawabata, Yukiya*; Onuma, Kenji*; Takeda, Hayato*; Sugo, Takanobu

放射線グラフト重合法により作製した有用金属捕集材の性能を実海域で評価するため設置した有用金属捕集材実海域試験装置における捕集工程,溶離工程,捕集及び装置の特性試験結果について記載した。捕集工程では、捕集材カセットを吸着床に充填し、実海域試験装置から20mの深さに係留し、一定期間の係留後、引き上げる。捕集材カセットは、ウラン吸着分布分析を行うため吸着床中のアドレスを明確にした。係留期間中の海水温度,流速,波高を測定した。溶離工程では、係留中に付着した海洋生物を除去した捕集材カセットを溶離ユニットに充填し、分別溶離装置を使用してアルカリ金属と有用金属とを2段階で溶離した。溶離後の捕集材カセットは同装置で再生処理した。溶離した有用金属は分離精製施設へ輸送するため、市販のキレート樹脂に再吸着させた。捕集特性試験では吸着床内のアドレスの違いによる捕集材カセット毎の吸着量の差はほとんど認められなかった。また、捕集材カセット内のウランの層及び面分布は、ほぼ均一であることから、海水のカセット内への流入についてはほぼ一様な特性であることがわかった。また、捕集工程から溶離工程までの一連の特性試験を行った結果、有用金属捕集材実海域試験装置はすべての工程で正常に動作することを確認した。

The present report dealt with experimental methods of adsorbents synthesis, recovery, elution, analysis in experimental equipment for recovery of rare metals from seawater to evaluate performance of the adsorbent synthesized by radiation-induced graft-polymerization. In the adsorbent synthesis, monomers of acrylonitrile and methacryl acid were continuously co-grafted into polymer nonwoven fabric irradiated with electron beam. The grafted nonwoven fabric was amidoximated and treated with alkaline solution in batch processing. The obtained adsorbent fabrics which were cut into 116 sheets of the square, 160 mm 290 mm, were alternatively stacked with spacers to make an adsorbent cassette. In recovery process, a large-sized cage packing 144 pieces of the adsorbent cassette was dipped into sea in the depth of 20 m by using an experimental marine equipment. In the case of a small-sized cage, there are 36 adsorbent cassettes in it. In elution step, first, marine animals which were adhered on the adsorbent cassette were washed out immediately after the adsorbent cassettes were recovered from sea. From every 72 adsorbent cassettes packed into elution unit, second, alkaline and rare metals were fractionally eluted by changing acid concentration in fractional elution equipment. The eluted metals were adsorbed onto a commercial chelate resin to transport them to purificatory factory. Concentrations of metals in eluent and waste solution were analyzed with inducticely coupled plasma atomic emission and mass spectrometry (ICP-AES and ICP-MS). The rare metal distribution in the adsorbent was evaluated by using the same analytical methods.