Chromium and cobalt sequestration using exopolysaccharides produced by freshwater cyanobacterium Nostoc linckia

This study investigated biosorption of chromium(VI) and cobalt(II) by exopolysaccharides (EPS) of a freshwater cyanobacterium, Nostoc linckia HA-46 from aqueous solution. Experiments were performed in batch mode to determine the adsorption dynamics of the cyanobacterial EPS. The adsorption capacity for Cr(VI) and Co(II) ions by EPS is found to be dependent on pH, contact time and initial metal ion concentration. The uptake kinetics of the metal ions follow pseudo-second order model. The maximum adsorption coefficient of determination (0.993Cr and 0.997Co) for Langmuir model indicates best fitness of this model in explaining the sorption as a multilayer process. The maximum adsorption capacities of the EPS were 14.3 mg Cr g−1 (at pH 2.0) and 17.9 mg Co g−1 (at pH 4.0) at an initial concentration of 20 mg L−1. The EPS of Nostoc linckia shows better biosorption capacity for Co(II) than Cr(IV) metal ion.