Cesium removal by foam separation involving anionic polymer and surfactant

Foam separation is a method that utilizes the adsorption of surfactants at the gas–liquid interface. Foam separation has the disadvantage of a slow removal rate owing to the limited number of metal adsorption sites (anionic sites) on the bubble surface. This study was conducted to increase the cesium removal rate using ionic polymers with anionic surfactants. Two types of surfactants were used for foam separation: disodium lauryl sulfosuccinate (diSLSS) and sodium dodecyl sulfate (SDS). DiSLSS can form vesicles 200 nm in size in an aqueous solution. An ionic polymer with varying molecular weight made from acrylic acid acted as an adsorbent.

The first-order of removal rate (k) of Cs increased from 7.0 × 10⁻⁴ min⁻¹ to 2.0 × 10⁻³ min⁻¹ by adding polyacrylic acid (molecular weight: 1800 g mol⁻¹, initial concentration: 0.08 %) to the diSLSS surfactant system. In addition, the molecular weight of polyacrylic acid did not significantly affect the Cs removal rate in the diSLSS system. In contrast, the addition of polyacrylic acid decreased the Cs removal rate in the SDS aqueous solution.

Spectroscopic measurements revealed that the amount of polyacrylic acid gradually decreased in the aqueous solution of diSLSS during foam separation. However, polyacrylic acid does not effectively adsorb at the gas–liquid interface and remains primarily in the SDS solution after foam separation.

Additionally, in the diSLSS aqueous solution, the addition of polyacrylic acid further reduced the surface tension value (γ), whereas in the SDS system, the γ of aqueous solution exhibited a slight increase. These results indicate that the addition of polyacrylic acid is advantageous for adsorption onto the bubble interface in the diSLSS system. Furthermore, the addition of polyacrylic acid increased the size of the diSLSS vesicles in the aqueous solution and decreased the zeta potential. This implied that polyacrylic acid was adsorbed onto the vesicle surface or incorporated into the membrane and removed along with the foam. These results indicate that the addition of polyacrylic acid favors the removal of Cs in aqueous solutions containing hydrophilic particles such as vesicles.