Reinforced silica monoliths functionalised with metal hexacyanoferrates for cesium decontamination: a combination of a one-pot procedure and skeleton calcination

Abstract

The nuclear plant accident of Fukushima Daiichi occurred following a tsunami on March 11th 2011 and gave rise to the production of large volume aqueous outflows containing radioactive cesium and seawater. This problem urged researchers to develop materials suitable for high flux continuous sorption processes able to promote the selective entrapment of cesium while sodium is widely present in the contaminated outflows. This work is focused on the achievement of silica monoliths with hierarchical porosity (meso- and macropores) combining on one hand enhanced mechanical strength thanks to a calcination step and on the other hand a one-pot functionalisation procedure in order to insert metal hexacyanoferrate (MHCF) particles inside the pores. This combination is generally difficult to achieve due to the MHCF alteration for temperatures above 200 °C. However, these problems can be avoided following the procedure described in this paper. Finally synthetic routes for meso/macroporous silica monoliths functionalised with sorbent particles highly selective towards cesium, CoHCF, CuHCF and ZnHCF are described. The weight ratio of MHCF reaches 7.1% wt with a total cesium sorption capacity of 24.1 mg g⁻¹ in the case of monoliths functionalised with ZnHCF. This value is not altered by the presence of sodium in the aqueous solution. MHCF particles are located mainly inside the macropores while the mesopore network allows for a high exchange surface between the aqueous outflows and MHCF particles embedded in the monoliths.