Silica-Reinforced AMP-Calcium Alginate Beads for Efficient and Selective Removal of Cesium from a Strong Acidic Medium

Abstract

Due to the significant selectivity for Cs⁺, ammonium molybdophosphate (AMP) possesses potential to uptake radiocesium from high-level liquid waste (HLLW), whereas its micro-crystalline structure and fine powder morphology limit its industrial application. Although the granulation method with alginate is prospective for the preparation of an AMP exchanger, the mechanical strength of obtained beads may be insufficient for application. In this context, we prepared silica-reinforced AMP-calcium alginate (ACS) beads and evaluated their performance for Cs⁺ removal from strong acidic solutions. It was found that the addition of silica in the fabrication significantly improved the mechanical strength of the beads in comparison to those without silica. Notably, the beads with an AMP/silica mass ratio of 1.0 exhibited an exceptional mechanical strength, surpassing that of ACS beads composed of other components. The batch experiment results indicated that the Cs⁺ adsorption follows a non-linear pseudo-second-order rate equation. The distribution coefficient of Cs⁺ was high even in extreme acidic conditions (∼1.6 × 10² mL/g in 8.0 mol/L HNO₃ solution). The Cs⁺ adsorption can be well fitted with the Langmuir model, and the estimated maximum exchange capacity in 3.0 mol/L HNO₃ could reach 23.9 mg/g. More importantly, ACS beads showed excellent selectivity toward Cs⁺ uptake over eight co-existing metal ions in simulated HLLW, with separation factor values all above 145. The column experiment exhibited that the beads can serve as the stationary phase in columns to effectively remove Cs⁺. The findings of this study are significant as they provide insights into the development of efficient materials for radiocesium removal from high-level liquid waste. The results demonstrate the potential of silica-reinforced ACS beads for Cs⁺ adsorption, with promising applications in industrial settings.

Figure 1

Fabrication process of the composite. In the figure, some images are sourced from https://mp.weixin.qq.com/s/_jBXVGvgJa8OCSHgGDxUoQ and free domain.

Figure 2

Mechanical strengths of ACS beads with different AMP/silica mass ratios.

Figure 3

Photographic image (a), SEM images (b,c), and the corresponding EDX analysis (d) of the synthesized adsorbent.

Figure 4

XRD pattern (a), FT-IR spectra (b), N₂ adsorption–desorption isotherms, (c) and corresponding pore-size distribution curve (d) of ACS-1.0 beads.

Figure 5

Kinetics of Cs⁺ removal by ACS-1.0 beads. [Cs⁺] = 3.75 × 10^–4 mol/L, m/V = 10 g/L, and [HNO₃] = 3.0 mol/L.

Figure 6

Effect of HNO₃ concentration on the adsorption of Cs⁺ on ACS-1.0 beads. m/V = 10 g/L.

Figure 7

Experimental data and simulated curve for the adsorption isotherm of Cs⁺ on ACS-1.0 beads. m/V = 10 g/L, [HNO₃] = 3.0 mol/L.

Figure 8

K_d value of metal ions (a) and the separation factor SF of Cs⁺ from interfering metals (b) in simulated HLLW. m/V = 10 g/L, [HNO₃] = 3.0 mol/L.

Figure 9

XPS survey spectra of ACS-1.0 beads before and after Cs⁺ adsorption.

Figure 10

Effect of NH₄NO₃ concentration and desorption times on the desorption efficiency of ACS-1.0 beads. [Cs⁺] = 3.75 × 10^–4 mol/L, m/V = 10 g/L, and [HNO₃] = 3.0 mol/L.

Figure 11

Breakthrough curves involving in simulated HLLW. [HNO₃] = 3.0 mol/L.