Thallium(I) sorption using Prussian blue immobilized in alginate capsules

Prussian blue (PB) was immobilized in alginate capsules. The composite sorbent was used for the recovery of Tl(1) ions from slightly acidic solutions: optimum pH being close to 4. The sorption isotherm can be described by the bi-site Langmuir sorption isotherm. This means that the metal ion can be bound through two different sorption sites: one having a strong affinity for Tl(1) (probably PB), the other having a lower affinity (probably the encapsulating material). The kinetics are described by either the pseudo-second order rate equation or the Crank's equation (resistance to intraparticle diffusion). The ionic strength (increased by addition of NaCl, KCl or CaCl2) slightly decreased sorption capacity. The SEM-EDX analysis of PB-alginate capsules (before and after Tl(1) sorption) shows that the PB is homogeneously distributed in the capsules and that all reactive groups remain available for metal binding.