Magnetic zeolite for Cs$^+$ and Sr$^{2+}$ to clean up radioactively contaminated water from the Fukushima Daiichi Nuclear Power Plant

Abstract

Magnetic zeolite hybrid systems have been developed for decontaminating radioactive wastewater from the reactors at Fukushima Daiichi Nuclear Power Plant. Superparamagnetic Fe$_3$O$_4$ and CoFe$_2$O$_4$ (M$_x$O$_y$) nanoparticles were used to make core-shell M$_x$O$_y$/SiO$_2$/zeolite (MSZ) systems. The MSZ were synthesised by 3 steps; preparing M$_x$O$_y$ particles by the solgel method firstly, the M$_x$O$_y$ particles were coated by SiO$_2$ by the Stöber method, then the M$_x$O$_y$/SiO$_2$ particles were mixed with zeolite seeds of zeolite A, zeolite X or CHA-Na. In addition, M$_x$O$_y$/Chabazite-Na (CHA-Na) was synthesised by a one-pot synthesis using an autoclave by crystallising the nanoparticles on preformed zeolite particles. The products were characterised by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy. The elemental compositions of the cobalt ferrite, the M$_x$O$_y$/CHA-Na and the MSZ were characterised by X-ray fluorescence. The magnetic properties of all products were measured by a magnetic property measurement system or vibrating sample magnetometer. The M$_x$O$_y$ particle diameters were calculated from the full width at half maximum of the X-ray peaks, observing by the TEM images, or measured by dynamic light scattering. The Cs or Sr adsorption capacities of the M$_x$O$_y$/CHA-Na and the MSZ were characterised by inductively coupled plasma mass spectrometry