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

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.

Stability of Eu(III)-silicate colloids: Effect of Eu content, pH, electrolyte and fulvic acid.

Dissolved silicic acid in the environment has strong affinity for actinides (An), but An(III)-silicate colloids have been scarcely investigated. In this study, Eu(III)-silicate colloids, an analogue to An(III)-silicate, were prepared and the aggregation kinetics of the colloids was investigated as a function of Eu content (Si/Eu molar ratio), pH, background electrolyte (NaCl, NaNO3, NaClO4, KCl and CsCl) and fulvic acid (FA). Results indicated that the colloids with higher Si/Eu molar ratio exhibited higher stability under the same conditions. The stability of the colloids increased with increasing aqueous pH (7.1-9.4) and decreasing ionic strength, and the inhibition effect of monovalent electrolytes on the colloid stability followed the order of Na+ < K+ < Cs+ and Cl- < NO3- < ClO4-. In addition, the presence of FA significantly increased the stability of the colloids. The dependence of the stability on the chemical conditions in all cases could be illustrated by DLVO theory. Disaggregation kinetics showed that the aggregation process of the colloids was not fully reversible, because a time-dependent size memory effect led to a bigger mean size of disaggregated colloids as compared to the initial ones. The present work provides detailed insight in the formation and stability of An(III)-silicate colloids under the alkaline conditions relevant to geological disposal of radioactive waste, which is critical for understanding the behavior of this type of colloids in the environment.