Highly effective Cs⁺ removal by turbidity-free potassium copper hexacyanoferrate-immobilized magnetic hydrogels

Potassium copper hexacyanoferrate-immobilized magnetic hydrogel (MHPVA) has been synthesized via a facile freeze/thaw crosslinking method. The citric acid coated Fe₃O₄ is embedded into the hydrogel matrix to facilitate the dispersion of nano-sized KCuHCF particles for Cs⁺ removal, followed by the rapid recovery of the composite in a magnetic field. The Cs⁺ adsorption behavior of the MHPVA is fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The MHPVA exhibits both high Cs⁺ adsorption capacity (82.8mg/g) and distribution coefficient (K_d) of 1.18×10⁶mL/g (8.3ppm Cs⁺, V/m=1000mL/g). Sorption of above 90% Cs⁺ to the MHPVA is achieved in less than 3h of contact time. Moreover, the MHPVA reveals stable and high Cs⁺ removal efficiency across a wide pH range from 4 to 10. In terms of Cs⁺ selectivity, the MHPVA shows above 96% removal efficiency in the presence of 0.01M competing cations such as Mg²⁺, Ca²⁺, Na⁺, and K⁺ with 1ppm of Cs⁺. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.