Reversible and Efficient Sequestration of Cesium from Water by the Layered Metal Thiophosphate K0.48 Mn0.76 PS3 ⋅H2 O

Abstract

Water body contamination with radioactive species is an important issue due to significant developments in nuclear energy. Cesium (¹³⁷ Cs) radioisotope is a non-actinide fission product of uranium and plutonium that is long-lived. Hence, selective removal/capture of cesium is essential for managing radioactive waste. Herein, a detailed Cs⁺ ion-exchange study on a potassium intercalated layered metal thiophosphate, K_0.48 Mn_0.76 PS₃ ⋅H₂ O (K-MPS-1), is reported. The sorption of Cs⁺ by K-MPS-1 follows the Langmuir model with a high capacity of 337.5 mg g^-1 and high distribution coefficients in the order of about 10⁴ mL g^-1 . K-MPS-1 can sequester Cs⁺ efficiently, even from very low concentrations (ppb level). K-MPS-1 exhibits high cesium uptake over a broad pH range of 2-12 and the ion-exchange process reaches equilibrium within a short time (≈15 min), following pseudo-second-order kinetics. Moreover, K-MPS-1 demonstrates selectivity towards Cs⁺ capture in the presence of complex solutions containing excess Na⁺ , Ca²⁺ , and Mg²⁺ ions; this is due to favorable interactions between Cs (soft Lewis acid) and S (soft Lewis base). K-MPS-1 reversibly captures Cs⁺ and it can be regenerated by treating Cs-MPS-1 with a solution of KCl.

Keywords: adsorption; cesium; chalcophosphates; radiochemistry; water chemistry.