Organically modified clay with potassium copper hexacyanoferrate for enhanced Cs+ adsorption capacity and selective recovery by flotation

Abstract

The selective capture of mobile radioactive nuclides, such as ¹³⁷Cs⁺, is crucial to the clean-up and remediation of contaminated environments. While remediation remains a challenging task, the current study considers novel organo-clay composites containing potassium copper hexacyanoferrate (KCuHCF) as a viable option for large-scale clean-up. A three-step synthesis has been demonstrated whereby pristine montmorillonite clay was readily modified to incorporate KCuHCF nanoparticles for enhanced and selective Cs⁺ removal from aqueous environments. Alkyldiamine (DT) was used as an organic modifier to intercalate the clay and provided chelating sites to anchor copper onto the clay matrix, from which KCuHCF nanoparticles were subsequently grown in situ via the coordination of hexacyanoferrate precursors with the immobilized copper ions. The organo-clay–HCF composite particles exhibited a superior Cs⁺ adsorption capacity (q_m = 206 mg g⁻¹), twice that of the pristine clay. The enhanced performance also extended to high Cs⁺ selectivity in seawater, with the organo-clay–HCF composites demonstrating Cs⁺ selectivity values in excess of 10⁵ mL g⁻¹, two orders of magnitude greater than the pristine clay. Organo modification of the clay particles reduced the particle wettability, thus facilitating the separation of Cs-loaded composite particles from aqueous environments by collector-less flotation. Batch flotation experiments showed recovery efficiencies of the Cs-loaded composite particles of up to 90%, which was in great contrast to the low recovery of less than 15% for the Cs-loaded pristine montmorillonite. The current study provides a new concept for the treatment of contaminated aqueous environments.