Effective removal of cesium from wastewater via adsorptive filtration with potassium copper hexacyanoferrate-immobilized and polyethyleneimine-grafted graphene oxide.

As an attractive alternative to radioactive cesium removal, we introduced an adsorptive filtration method using a composite membrane consisting of potassium copper hexacyanoferrate (KCuHCF) and graphene-based support. Polyethyleneimine-grafted reduced graphene oxide (PEI-rGO), used as an immobilizing matrix, was effective not only in distributing KCuHCF inside the composite with the aid of abundant amino-functionality, but also in achieving high water flux by increasing the interlayer spacing of the laminar membrane structure. Due to the rapid and selective cesium adsorption properties of KCuHCF, the fabricated membrane was found to be effective in achieving complete removal of cesium ions under a high flux (over 500 L m-2 h-1), which is difficult in a conventional membrane utilizing the molecular sieving effect. This approach offers strong potential in the field of elimination of radionuclides that require rapid and complete decontamination.

Amino-functionalized magnetic chitosan beads to enhance immobilization of potassium copper hexacyanoferrate for selective Cs+ removal and facile recovery.

Potassium copper hexacyanoferrate (KCuHCF)-incorporated magnetic chitosan beads (HMC) were synthesized for both selective Cs+ removal in aqueous solutions and facile recovery of the spent adsorbent. To disperse and immobilize large amounts of the KCuHCF, methyl acrylate and diethylenetriamine were sequentially grafted onto the one-step synthesized magnetic chitosan beads. The additional introduction of amino functionality led to the enriched Cu2+ ions on the bead surface to incorporate KCuHCF into the grafting matrix. Consequently, the HMC exhibited a high Cs+ capacity calculated to be 136.47 mg g-1 from the Langmuir model, and the equilibrium was established within 4 h. Moreover, the HMC exhibited excellent stability in a wide pH range from 4 to 11 and an outstanding Cs+ selectivity (>97%) in seawater (1.11 mg L-1 Cs+). From a practical point of view, the HMC was stable during five successive adsorption cycles and easily recovered by magnets, enabling continuous operation to decontaminate a large volume of wastewater.

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 (Kd) 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.