Toxic metal biosorption by macrocolonies of cyanobacterium Nostoc sphaeroides Kutzing

The cyanobacterium Nostoc sphaeroides Kutzing is expected to be effective in toxic metal adsorption as it produces abundant exopolysaccharides with functional groups. Therefore, the adsorption properties of Cu2+, Cd2+, Cr3+, Pb2+, Ni2+, and Mn2+ on fresh macrocolonies and algal powder of N. sphaeroides were compared at pH 5 and 25 degrees C. The adsorption capacity of fresh biomass for Pb2+ and of algal powder for Pb2+ and Cr3+ were highest in single metal solutions. Compared to the fresh biomass, the metal adsorption capacities of algal powder were similar for Ni2+, Cd2+, and Pb2+ and slightly greater for Cr3+, but they were markedly smaller for Mn2+ and Cu2+. Coexisting ions ( in tap water or in multiple solutions) significantly decreased the metal adsorption capacity, except for Cr3+ in tap water. The Pb2+ and Cr3+ adsorption dynamic process fitted the pseudo- secondorder model well, showing fast adsorption at the first stage in 10 and 20 min, respectively. Higher pH in acidic ranges favored the adsorption greatly. The Langmuir isotherm model was suitable for explaining the adsorption, and the maximum adsorption capacities were 116.28 and 22.37 mg g- 1 for Pb2+ and Cr3+, respectively. The adsorption process was endothermic, confirmed by the significantly higher adsorption capability at higher temperature. Hydroxyl, amino, and carboxyl groups were the main functional groups based on Fourier transform infrared spectroscopy analysis, and they bind to metal ions via ion exchange. The results suggest that fresh macrocolonies of N. sphaeroides can be used as an effective biosorbent for metal ion removal, especially for Pb2+ and Cr3+.