A novel floating adsorbent for cesium based on Shirasu balloon modified with magnetite and Prussian blue

Shirasu balloon (SB) is a hollow glassy sphere produced from volcanic deposits by heating that can float up on water owing to its hollow structure. In this study, a novel adsorbent for the removal of cesium ion in water was developed by the modification of the surface of the SBs with magnetite (Mag) and Prussian blue (PB). The developed adsorbent (PB-Mag-SB) was characterized by elemental analysis, X-ray diffraction, and Fourier transform infrared spectrometry and the magnetism of the adsorbent. From these results and the change in color of the adsorbents, the successful modification of the SBs with magnetite and PB was confirmed. The developed adsorbents were added and mixed with the polluted water. After the adsorption, it could float up on the surface of water due to the buoyancy of the balloon and also be collected by a magnet due to the magnetism of the magnetite formed on the surface of the SB. Furthermore, the removal of Cs from water was achieved by binding site of PB immobilized on the Mag-SB. The PB-Mag-SB could selectively adsorb Cs even in the presence of coexisting cations at high concentrations. The adsorbent remained afloat on the water surface for at least 24 h, and approximately 99% of the adsorbent could be collected within 5 min using a magnet. The introduction of both floating and magnetism properties to the adsorbent makes it easy and selective to collect the adsorbent after the adsorption of pollutants in water. SB is a natural product with a low environmental impact; therefore, the adsorbent based on SB will contribute to the environmental remediation as a novel material for adsorption.