New insights into the mechanism of cesium sorption on titanium hexacyanoferrate: Experimental findings and model development

This study aimed to provide new insights into the mechanism of Cs+ sorption on titanium hexacyanoferrate (Ti–Fe PBA) focusing on the influence of the structure and vacancies. Ti–Fe PBA was synthesized with specific vacancies using a coprecipitation synthesis method. The study successfully demonstrated the unique structure of Ti–Fe PBA and determined the ratio of vacancies within its framework through various characterization techniques, including X-ray diffraction, Fourier transform-infrared spectrometry, thermogravimetry, scanning electron microscopy, X-ray photoelectron spectroscopy and sodium hydroxide titration. The synthesized Ti–Fe PBA exhibited an impressive Cs+ sorption capacity of 3.53 mmol g−1 and demonstrated high selectivity, with a Kd value 1.5 × 106 for Cs+ sorption. In addition, Ti–Fe PBA displayed excellent stability, rapid uptake kinetics and maintained high selectivity, even in the presence of high concentrations of coexisting ions. Moreover, our new findings revealed that K–Cs ion exchange specifically occurring at the interstitial sites within the framework structure accounted for ∼35 % of the total Cs+ sorption. A sorption-surface complexation model utilizing a coupling technique that integrated PHREEQC with Python enabled in-depth analysis of titration, pH effects and sorption isotherms. The modelling results revealed that the strong ion exchange sites ≡SsOH and ≡SsONa on surfaces and vacancies contributed ∼65 % of the total Cs+ sorption.