Kinetic evaluation for 137Cs desorption from riverine particles in seawater, and exploration of sorbent agents for fixation of the desorbed fraction

In this study, we evaluated 1) the potential ability of sorbents to adsorb ¹³⁷Cs desorbed from contaminated riverine particles that had been introduced into seawater, and 2) the rates of desorption of ¹³⁷Cs from weak and strong sorption sites. We performed particle–seawater desorption experiments to simulate the mixing of riverine particles with seawater and used a kinetic model to simulate results. We tested two sorbent agents: beach sand collected from less contaminated coast and zeolite. Neither of the two sorbents sorbed the ¹³⁷Cs that desorbed from the contaminated river sediment particles because of competition for sorption sites from cations abundant in seawater. Rates of desorption from strong sorption sites, which accounted for 77–99% of the ¹³⁷Cs carried by the particles, were 3–4 orders of magnitude slower than the rates of desorption from weak sorption sites. The implication was that most ¹³⁷Cs can be tightly sorbed onto particles. Desorption of ¹³⁷Cs from weak sorption sites was estimated to be almost complete within 30 min, but ¹³⁷Cs sorbed onto weak sorption sites was a minor component (1–23% of total ¹³⁷Cs) of ¹³⁷Cs on riverine particles.