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 (82.8 mg/g) and distribution coefficient (Kd) of 1.18 × 10⁶ mL/g (8.3 ppm Cs+, V/m = 1000 mL/g). Sorption of above 90% Cs+ to the MHPVA is achieved in less than 3 h 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 0.01 M competing cations such as Mg²+, Ca²+, Na+, and K+ with 1 ppm of Cs+. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5 days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.