Upcycling of steel slag for manufacture of Prussian-blue-encapsulated pectin beads and its use for efficient removal of aqueous cesium

Development of innovative technology for solid waste disposal, particularly the synthesis of novel energy and environmental materials via upcycling of solid wastes, is essential for boosting sustainable development in urban areas. In this study, we developed a novel synthesis method for Prussian-blue-encapsulated pectin beads (PB@PD) using Fe and Ca sources in steel slag (SS) and demonstrated its feasibility for the removal of Cs⁺ via batch and fixed-bed column reactors. Hydrochloric acid (HCl) was used for Fe and Ca dissolution in the SS suspension, and the extracted Fe and Ca were then used for the synthesis of Prussian blue and pectin polymer beads, respectively. The surface characteristics of PB@PD were determined through advanced microscopy and surface analyses, which confirmed the successful formation of a PB crystal structure and well-distributed PB particles in the cross-linked pectin structure. Batch isotherm adsorption experiments conducted using PB@PD revealed that the maximum adsorption capacity of Cs⁺ was 54.34 mg/g. PB@PD could be recycled up to four times and was very effective for Cs⁺ adsorption in artificial seawater. Furthermore, we successfully applied PB@PD as a filling material in a fixed-bed column reactor and obtained an effective adsorption capacity (41.75–43.9 mg/g) without any clogging problem during the continuous Cs⁺ treatment.