Immobilization of inorganic ion-exchanger into biopolymer foams – Application to cesium sorption

• Highly porous composites are prepared for immobilizing nickel potassium ferrocyanide.
• The composite material is very efficient for removing Cs(I) in the range pH 2–8.
• The process is selective for Cs(I) even in presence of large excess of Na(I), K(I).
• Kinetics are controlled by the pseudo-second order rate equation.
• The discs can be used for dynamic and reactive filtration of radionuclide solutions.

Nickel–potassium ferrocyanide (along with other ferrocyanide sub-products, as shown by mineralization, SEM–EDX and XRD analyses) has been immobilized in highly porous discs of chitin for the sorption of Cs(I) from near neutral solutions. The immobilization process allows synthesizing stable materials that can bind up to 80 mg Cs g−1 (i.e., 240 mg Cs g−1 ion-exchanger). Cesium sorption is hardly affected by the pH between pH 2 and 8. The sorbent is selective to Cs(I) even in the presence of high concentrations of Na(I), K(I), Rb(I) or NH4+. The pseudo-second order rate equation fits well kinetic profiles: the rate coefficient increases with the flow rate of recirculation (to force the access to potentially non-interconnected pores), as an evidence of the control of uptake kinetics by diffusion properties. In fixed-bed columns, the breakthrough curve is accurately described by the Clark model and the sorption capacity (at sorbent saturation) is consistent with the values obtained in sorption isotherms. Preliminary tests performed on 137Cs spiked solutions confirm the efficiency of the material for the treatment of effluents bearing radionuclides.

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