Nanocrystals FAU-X monoliths as highly efficient microreactors for cesium capture in continuous flow

Abstract

The performances of binderless FAU-X monoliths (0.5 × 3 cm) build of nanocrystals featuring hierarchical trimodal porosity (micro-/meso-/macroporosity) in decontamination Cs-containing effluents have been evaluated. They have been compared to those obtained with newly synthesized FAU-X particles (1 mm) build with nanocrystals. Data have been confronted to those recently reported for a benchmark reference Cs+ adsorbent Sorbmatech®, based on copper hexacyanoferrate nanoparticles (15 nm) immobilized into mesoporous silica particles (250–500 μm) (Cu-HCF@SiO2). FAU-X monoliths show high rate of adsorption in batch in less than 2 min, much faster than Cs+ adsorption in FAU-X particles (60 min). This result highlights the importance of a homogeneous macropore network in adsorbents to enhance mass transport and access to the zeolite active sites. FAU-X monoliths with 20 μm macropore diameter have been used in continuous flow experiments for sequestering Cs+ (0.5 mmol/L) in mineral drinking water containing competing cations (Ca2+, Mg2+, Na+, K+) with flow rates of 0.5–1 mL/min, corresponding to Darcy rates of 1.5–3 m/h. FAU-X monoliths are very efficient for Cs+ removal and show ideal steep breakthrough curves characteristic of fast diffusion. FAU-X monoliths are as excellent as Cu-HCF@SiO2 and could represent an alternative adsorbent for safer processes, avoiding the handling of powders or particles. Above all, this study reveals the unique hydrodynamic behavior of FAU-X monoliths and opens the route for process intensification using FAU-X in continuous flow.