Study on U collection method from seawater for simplifying the usage of ultra-trace anthropogenic radioactive U as oceanic circulation tracer

Abstract

Our aim of this study is to make seawater anthropogenic radioactive U isotopes widely and conveniently available as ocean circulation tracers. We attempted to optimize the adsorption and desorption process of seawater U isotopes using an ”amidoxime adsorbent” for simple U collection. The results of adsorption experiments showed that the optimum conditions for U adsorption were seawater pH 4 and 0.40 mmol of adsorbed functional group per 1 kg of seawater using a glass beaker, and seawater pH 8 using a closed polyethylene container with a similar ratio of functional group additive for experiments on-board. The results of desorption experiments showed that U recovery (based on seawater) was more than 80 % with 2 mol/dm³ hydrochloric acid. Therefore, the amidoxime adsorbent can be used for simple U collection not only in the laboratory but also on-board ships, which is a great step forward toward the simple use of seawater anthropogenic radioactive U isotopes as tracers for ocean circulation.