Calcium alginate beads from Laminaria digitata for the removal of Cu+2 and Cd+2 from dilute aqueous metal solutions

Sodium alginate extracted from the brown algae Laminaria digitata was used to prepare metal sorbing beads. Their metal binding properties were investigated with respect to copper and cadmium ions in single and binary metal solutions. Their behaviour in batch kinetic experiments and in a flow through column for the remediation of dilute aqueous metal solutions was studied. Alginate was found to be a promising material for heavy metal sequestration while sorption was found to be following a competitive mechanism in multi-metal solutions. The obtained maximum adsorption capacities for Cu+2 and Cd+2 were 1.5 mmol/g and 2.09 mmol/g respectively. The calculated diffusion coefficients — 2.8–3.0 × 10−5 cm2/s for copper and 4.4–4.5 × 10−5 cm2/s for cadmium ions — were independent of the initial concentration. Finally, the obtained diffusion coefficients were used for the simulation of the breakthrough curves on column filtration experiments. Linear adsorption driving force model was used to provide a rough estimation of the operational and design parameters in flow column adsorption processes.