Predicting the Breakthrough of Ternary Ca–Uranyl–Carbonate Species in Mineral Water Treated by a Fixed-Bed Granular Ferric Hydroxide Adsorbent

Abstract

A CD-MUSIC surface complexation model was set up on the basis of batch equilibrium experiments with uranyl ions and akaganéite-based granular ferric hydroxide (GFH), which is often used in water purification units around the world to remove toxic contaminants. The model considers both binary and ternary complexation of U­(VI) by carbonate and Ca ions. The CD-MUSIC model data indicated that the efficiency of U­(VI) adsorption by GFH is extremely sensitive to the carbonate concentration in water at circumneutral pH in the presence of Ca. Removal of U­(VI) from mineral water is therefore less efficient using GFH at pH >8 than at pH values close to or better below 7. The effects of the U­(VI), carbonate, and Ca concentrations on the adsorbent efficiencies achieved for different water samples were investigated using the validated CD-MUSIC model data in predictive mode. The CD-MUSIC model was used to predict the Freundlich adsorption parameters, which were in turn used to predict breakthrough curves for fixed-bed adsorbent columns using a homogeneous surface diffusion model approach. These predictions were then validated by column tests using various mineral water samples and at water treatment plants.

Comment on “Enthalpy of Uranium Adsorption onto Hematite”

“…In addition, enthalpy data for the formation of dissolved ternary Ca uranyl triscarbonato complexes strongly competing with U(VI) adsorption are necessary. 8 However, none of these thermodynamic parameters are currently available or consistent enough for an appropriate correction of Figure 1. 9 To sum up, we encourage the reader to consider cautiously the conclusions presented by Estes and Powell.…”

“…Besides, not only enthalpies for the uranyl triscarbonato surface complexes but also the carbonate oxyanion adsorption are required to comprehensively analyze the U­(VI) adsorption in the presence of DIC. In addition, enthalpy data for the formation of dissolved ternary Ca uranyl triscarbonato complexes strongly competing with U­(VI) adsorption are necessary . However, none of these thermodynamic parameters are currently available or consistent enough for an appropriate correction of Figure …”