Immobilization of metal hexacyanoferrates in chitin beads for cesium sorption: synthesis and characterization

Abstract

Five metal-potassium hexacyanoferrate/chitin composites (based on Cu, Ni, Zn, Co or Fe co-metal) have been prepared and characterized, using SEM-EDX, TEM, X-ray diffraction and FT-IR, before being compared for Cs(I) and ¹³⁷Cs(I) sorption. The Zn-ion exchanger was characterized by a much larger crystal size of about 250 nm compared with a few tens of nm for other ion-exchangers. The ion-exchangers are well distributed in the whole mass of the composite and they are fully accessible to Cs(I), as evidenced by Cs(I) distribution after metal sorption. Uptake kinetics can be modeled using both the pseudo-second order rate equation and the Crank equation (resistance to intraparticle diffusion coefficient). Sorption isotherms showed substantial differences in the sorbents that can be ranked as Cu > Ni > Zn > Co > Fe. However, based on ¹³⁷Cs K_d values, the sorbents can be ranked as Co ≫ Fe ≫ Cu ≫ Ni > Zn. Taking into account the cost and toxicity of metals (both in terms of manufacturing and potential metal release) a Prussian Blue based sorbent (i.e., iron-potassium hexacyanoferrate/chitin composite) sounds to be a good composite for Cs(I) recovery from radionuclide-containing effluents.