Decontamination of very dilute Cs in seawater by a coagulation–precipitation method using a nanoparticle slurry of copper hexacyanoferrate

Abstract

We examined the highly selective Cs adsorption ability of a potassium copper hexacyanoferrate (KCuHCF) slurry ink in seawater, i.e. very low Cs concentration in the presence of Na+, K+, Mg2+, Ca2+, and Cl− ions at high concentrations. The rational synthesis of the KCuHCF nanoparticle (KCuHCF-NPs, AyCu[Fe(CN)6]1−x·zH2O) slurry ink was carried out using a Y-type micro-mixer and the composition dependence of the Cs-adsorption behavior was investigated. When a solution-to-adsorbent ratio of 10\u2006000 mL g−1 was applied, batch experiments revealed that the Cs adsorption equilibrium was achieved within 10 min, with removal efficiency reaching as high as 99% of the Cs present (initial concentration is 10 μg L−1) and a distribution coefficient (Kd) as high as 106, even in the presence of competing alkali metal cations in seawater at high concentrations. For practical use, large flocs of the KCuHCF-NPs could be immediately coagulated after Cs adsorption using a high molecular-weight ionic polymer as a coagulant, along with regular Fe2+ inorganic flocculants at the pH of seawater.