Ion-exchange properties of potassium nickel hexacyanoferrate(II) compounds

A series of nonstoichiometric compounds K_2-xNi_x/2[NiFe(CN)₆]nH₂O was prepared by varying Ni/Fe molar ratio from 0.1 to 100. The products had a face-centered cubic (fee) structure, and the lattice parameter slightly increased with decreasing K/Fe ratio. The uptake rate of Cs⁺ was enhanced at lower K/Fe ratio below 1.32 and reached equilibrium within 8 h for the products with K/Fe below 0.86. The distribution coefficients of Cs⁺ on the products were above 10⁴ cm³/g in the presence of 1 mol/dm³ Na⁺, K⁺ or H⁺, while those of other nuclides were less than 10², indicating high selectivity of the product to Cs⁺. The uptake of Cs⁺ followed a Langmuir-type isotherm and the maximum amount of Cs⁺ adsorbed was evaluated to be 1.0 to 1.5 mmol/g. Cesium nuclides were efficiently removed from a simulated high-level liquid waste.