Synergistically strengthened 3D micro-scavenger cage adsorbent for selective removal of radioactive cesium

Abstract

A novel microporous three-dimensional pomegranate-like micro-scavenger cage (P-MSC) composite has been synthesized by immobilization of iron phyllosilicates clay onto a Prussian blue (PB)/alginate matrix and tested for the removal of radioactive cesium from aqueous solution. Experimental results show that the adsorption capacity increases with increasing the inactive cesium concentration from 1 ppm to 30 ppm, which may be attributed to greater number of adsorption sites and further increase in the inactive cesium concentration has no effect. The P-MSC composite exhibit maximum adsorption capacity of 108.06 mg of inactive cesium per gram of adsorbent. The adsorption isotherm is better fitted to the Freundlich model than the Langmuir model. In addition, kinetics studies show that the adsorption process is consistent with a pseudo second-order model. Furthermore, at equilibrium, the composite has an outstanding adsorption capacity of 99.24% for the radioactive cesium from aqueous solution. This may be ascribed to the fact that the AIP clay played a substantial role in protecting PB release from the P-MSC composite by cross-linking with alginate to improve the mechanical stability. Excellent adsorption capacity, easy separation, and good selectivity make the adsorbent suitable for the removal of radioactive cesium from seawater around nuclear plants and/or after nuclear accidents.

Figure 1. Schematic diagram for the fabrication of a 3D microporous PB/alginate/AIP clay composite.

Figure 2. Characterization of Ca-alginate bead and P-MSC composite.

(a) FT-IR spectra, (b) XPS spectra, and (c) the BJH N₂ adsorption/desorption isotherms for Ca-alginate bead and P-MSC composite, and (d) TGA curve of the P-MSC composite.

Figure 3

A cryo-fractured cross-section SEM images of (a,b) Ca-alginate, (c) alginate/AIP clay composite, and (d) P-MSC composite, (e) a magnified image of outer surface and inner structure of the P-MSC composite, and (f) close inspection of inner structure of the P-MSC composite.

Figure 4

(a) Mechanical properties of Ca-alginate bead and P-MSC composite and (b) release behavior of PB from the PB/Ca-alginate bead and P-MSC composite (Fig. 4b inset shows the long-term study on stability of PB in the P-MSC composite solution during 1 year).

Figure 5. Adsorption isotherms and kinetics data.

(a) Langmuir isotherm (b) Freundlich model, (c) pseudo-first-order, and (d) pseudo-second-order kinetics of the P-MSC composite.

Figure 6

(a) Adsorption capacity values of the Ca-alginate, alginate/AIP clay composite, and P-MSC composite, (b) removal efficiency of cesium ion compared to competitor cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺, and seawater (Cs concentration of 0.25 ppm or 1.88 × 10⁻³ mmol/L was initially spiked in all the samples, (c) adsorption mechanism, and (d) the removal efficiency of radioactive cesium using different adsorbents.