Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents—A Mini-Review

Abstract

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.

Preparation, characterization and application in cobalt ion adsorption using nanoparticle films of hybrid copper–nickel hexacyanoferrate

“…The high adsorption capacity can be interpreted by the large lattice size of CuHCF. This is consistent with the fact that the sorption capacity of CuHCF is larger than that of NiHCF, as mentioned by Thierry et al 54 It is remarkable that the equilibrium removal efficiency of Cu 1 Ni 2 HCF lms is higher than that of NiHCF lms, and slightly lower than that of CuHCF lms, which may due to the well-ordered porous structures of CuHCF lms. The redox peaks of CuHCF lm in Co 2+ solutions are sharper than those of Cu 1 Ni 2 HCF lm, indicating a faster dynamic process.…”

Solvent-assisted synthesis of potassium copper hexacyanoferrate embedded 3D-interconnected porous hydrogel for highly selective and rapid cesium ion removal

“…Assuming that Cs + adsorption is mainly accompanied by the ion exchange with K + as reported in previous studies [3,35,47], the theoretical ion exchange capacity (TEC) is calculated from the amount of K + in KCuHCF ( Table 2). The HPC shows much higher theoretical adsorption capacity than the bulk KCuHCF, which will be discussed later with the adsorption isotherm study.…”

Adsorption kinetics, equilibrium and radiation effect studies of radioactive cesium by polymer‐based adsorbent

“…Exposure of organic materials such as polymers to energetic radiations like gamma may cause chemical decomposition and affect their physico-chemical properties [43]. This may not only affect the adsorption affinity but also the long-term stability of radionuclide-loaded polymer adsorbent.…”