Quaternization of algal/PEI beads (a new sorbent): Characterization and application to scandium sorption from aqueous solutions

Algal/Polyethyleneimine beads (APEI) were successfully quaternized to prepare an efficient sorbent (Q-APEI) for Sc(III) recovery. The functionalization has been confirmed by a series of analytical procedures: titration (pH(PZC)), elemental analysis, SEM, BET, EDX, FTIR, XPS and TGA. The sorption properties for Sc(III) from mild acidic solutions have been compared for APEI and Q-APEI: the sorption capacity increases from 1.0 to 3.8 mmol Sc g(-1), at the optimum pH; (i.e., 4.5). The porous structure (specific surface area close to 34 m(2) g(-1)) of the sorbent allows reaching the equilibrium within 60-90 min. Metal desorption is highly efficient using 0.5 M HCl/CaCl2 solutions; the sorbent can be recycled for at least 5 cycles with limited decrease in sorption capacity. FTIR and XPS analysis confirm the stability of the material though some chemical changes can be observed. The sorption mechanism involves different reactive groups associated with the diversity of functional sites: carboxylate groups (from alginate) and more specifically amine groups (from PEI and quaternary amine grafted moieties) with contribution of different scandium species (free or scandium sulfate complexes), depending on the pH. The sorbent is selective from Mg(II), Sm(III), Ca(II) and Na(I) (from equimolar synthetic solutions) at pH higher than 4. The application of Q-APEI for the sorption of Sc(III) from industrial solution (derived from red mud) shows that despite a high excess of iron, titanium or aluminum, scandium sorption is highly efficient (even at low metal concentration); though the sorbent is not selective.