Cs ion exchange by a potassium nickel hexacyanoferrate loaded on a granular support

¹³⁷Cs is considered to be one of the most abundant and hazardous elements due to its presence in many effluents and wastes. We study the cesium sorption by a supported mixed K/Ni ferrocyanide on a porous Zr(OH)₄ matrix from pure water at different pH containing Cs from trace concentration (radioactive solution) to molar concentration. The material was characterized by XRD and SEM, and its chemical composition was deduced by elemental analysis. Isotherms performed at different pH demonstrated that the material had a maximum sorption capacity of 0.22 mmol/g (at pH 7) and that ion exchange was 80% driven by K/Cs exchange and 20% driven by Ni/Cs exchange. Measurement of the pH before and after sorption indicated that protons also participate in the ion exchange process. These experimental experiments allow the construction of thermodynamic database for modeling the different ionic exchanges that occur in this system using the CHESS code. The sorption of cesium from several types of effluents was then correctly modeled by a set of selectivity constants with respect to the K⁺ ion (K/Cs, K/Ni, K/Na and K/H). The present data set can be extrapolated to other K ferrocyanides and effluents. (authors)