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Preliminary studies of lithium recovery technology from seawater by electrodialysis using ionic liquid membrane

イオン液体を用いた電気透析法による海水からのリチウム回収技術の予備的試験

星野 毅

Hoshino, Tsuyoshi

近年、地球温暖化緩和に向けた低炭素化社会実現のため、電気自動車,家庭用蓄電池等の大型リチウムイオン電池開発が進み、原料となるリチウム資源の需要は急増している。また、核融合炉の燃料トリチウム製造に必要なリチウムは、リチウムの中でも約7.6%しか存在しない、希少なリチウム6($$^{6}$$Li)を多量に使用する。リチウムは、全元素112種のうち、特に希少なレアメタル31元素の一つであり、レメタルの確保は世界各国の国策課題となっている。そこで、海水からリチウムを効率的に回収する革新的資源回収技術の実用化を目指し、リチウムイオンを選択的に透過可能なイオン液体を用いた電気透析法により、リチウム資源を回収する技術に関する試験を行った。実際の海水を用い、2Vの定電位にて2時間のLi資源回収試験を行ったところ、海水中に高濃度に含まれるNa等のイオンはイオン液体を透過せず、Liイオンのみを透過させ、Li回収液におけるLi回収率は5.94%と低電位測定にもかかわらず高い回収率となり、本技術によりLiイオンのみが選択的に回収できる見通しを得た。

Lithium (Li), one of the 31 rare metal elements among the 112 known elements, is fast becoming a valuable commodity. As a means of addressing global warming, the world is increasingly turning to the use of Li-ion batteries in electric vehicles and as storage batteries in the home; therefore, there is a growing need for Li. Li is primarily recovered from salt lakes in South America but is also present in seawater. Thus, I propose a new method for recovering Li from seawater by electrodialysis, wherein Li selectively permeates from the anode side to the cathode side through an ionic liquid. Hoshino developed a novel Li-isotope separation technique that uses an ionic liquid. This technique could also be used to recover Li from seawater. Measurements of the ion concentration at the cathode side as a function of dialysis duration showed that the Li concentration increased to 5.94% after 2 h with an applied electric voltage of 2 V. Moreover, the other ions in the seawater did not permeate an ionic liquid. With both ends of an ionic liquid covered with a MEA (Membrane Electrode Assembly) to prevent outflow of the ionic liquid, the Li concentration increased. This new recovery method shows good energy efficiency and is easily scalable and thus is suitable for use in seawater desalination plants.

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パーセンタイル:96.6

分野:Engineering, Chemical

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