Radiation-induced reduction process of hazardous chromium(VI) ion to non-hazardous chromium oxide with the lower oxidation state in aqueous solution - oxide system

水溶液-酸化物共存の非均質系での有害な6価クロムイオンの放射線誘起還元処理

永石 隆二 ; 山田 禮司; 籏野 嘉彦; 吉田 善行

Nagaishi, Ryuji; Yamada, Reiji; Hatano, Yoshihiko; Yoshida, Zenko

水溶液-酸化物共存の非均質系で有害な6価クロムイオンの線誘起還元を研究した。中性からアルカリ性の水溶液中では、酸化物を添加しない場合、6価クロムはほとんど還元しない。これは水の分解生成物の還元種が6価クロムを還元する一方、酸化種が低酸化状態のクロムを等量あるいはそれ以上酸化するためである。その溶液に酸化物を添加すると、溶液中の6価クロムを0.05ppm未満(日本の環境への排出基準値)まで顕著に低減することに成功した。これはクロムが酸化物へ吸着すること,酸化物によって6価クロムの還元が促進することによる。本発表では、放射線源として放射性廃棄物を利用した6価クロム還元処理の可能性についても議論した。

Radiation-induced reduction of chromium(VI) ion in aqueous solution was investigated in the presence of small amount of insoluble oxide particle such as TiO, AlO and SiO by using Co -ray. Solution at pH 1.0, simulating industrial liquid waste, became neutral or basic by adding the oxide particle: the positive shift of pH of solution was dependent on the kind and particle size of oxide. The chromium(VI) ion was successfully reduced in the radiolysis of the neutral or basic solution in the presence of oxide, while not in the absence. These indicate that amount of chromium(VI) reduced by reducing radicals of water radiolysis is almost equal to that of chromium with the lower oxidation state oxidized by the oxidizing radicals in the solution, and that adsorption of chromium to oxide and enhancement in the reduction of chromium(VI) take place in the presence of oxide. The insoluble chromium(III) oxide formed in the reduction of chromium(VI) was also responsible for the reduction. The radiation-induced reduction process of hazardous chromium(VI) with utilizing high-level radioactive wastes as radiation resources was further discussed.