Removal of period 4 transition metals by foam separation

Abstract

Anionic surfactants that form floating bubbles can adsorb metal ions and change foams at the gas–liquid interface. The final rate of ion removal by foam separation determines the selectivity or priority of adsorption of ions. Foam separation was conducted to remove multi-component chlorides of period 4 transition metals (Mn, Fe, Co, Ni, Cu, and Zn) by using sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS) as surfactants. The first-order ion-removal rate constant (k) did not completely change with an increase the atomic number of transition metals. The difference in removal rate constant (k) between the elements was not significant in multi-component chlorides of transition metals. On the other hand, the foam separation was performed in a one-component of period 4 transition metal (Mn, Fe, Co, Ni, Cu, and Zn) using SDeS (8 mmol L−1) for comparing k from alkaline earth metals having different ionic radii, respectively. The transition metal was continuously removed over time, whereas the counter ion (sodium) of the surfactant was not efficiently removed. The results also showed that the k in the one-component 4 transition metal system also slightly increased with increasing ionic radius in 5 h of foam separation. A linear relationship was observed between the first-order ion-removal rate constant (k) by foam separation and the ionic radius of the divalent metal ion. These results indicated that the selectivity of cation adsorption on the soluble monolayer is closely related to the ionic radius of the metal ion.