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 elec-tron 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 x 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.