Evaluation of optimal size of illite adsorbent for ¹³⁷Cs removal in contaminated artificial lake

Since the Chernobyl and the Fukushima Daiichi disasters, contamination caused by radioactive accidents has attracted increasing attention. The present study evaluated immediate cleanup of ¹³⁷Cs dissolved in surface water reservoir using an illite adsorbent, simulating an event of ¹³⁷Cs contamination at Lake Paldang, South Korea. The study was conducted in two parts: (1) calculation of the residence time (t_r) of illite adsorbent, and (2) evaluation of the adsorption time (t_a) of illite adsorbent. t_r was calculated based on physical properties (e.g., density, diameter, shape, and roughness) of the illite adsorbent at designated depth of surface water. Subsequently, t_a was measured for 4 illite adsorbents (Korea01-Illite, Korea02-Illite, USA-Illite, and China-Illite) at 100 and 100,000 μg/L Cs, via kinetic adsorption experiment. Upon spraying of illite adsorbents with 50-150 μm diameter to locations where lake depth was between 6.5 m and 25.5 m, t_r ranged from 0.132 to 3.300 h t_a of 4 illite adsorbents was shorter than 0.6 and 2.5 h, for respective tests using 100 and 100,000 μg/L Cs. Based on the two characteristic times (t_r and t_a), the optimal particle diameter for the 4 illite adsorbents were evaluated at available lake depths in Lake Paldang. The study revealed that the USA-Illite is the efficient adsorbent at 100 μg/L Cs; in contrast, China-Illite could serve as the effective adsorbent at 100,000 μg/L Cs. Also, it was suggested that adsorbent efficiency had seasonal variations; t_r was 2 h longer in winter than summer. In general, the study suggests that in the event of ¹³⁷Cs contamination at Lake Paldang, Korea01-Illite is likely the best adsorbent to remove ¹³⁷Cs due to its removal efficiency and accessibility from the illite deposit in Korea.