Biosorption of toxic metal ions by alkali-extracted biomass of a marine cyanobacterium,Phormidium valderianum BDU 30501

Alkali-extracted biomass of Phormidium valderianum BDU 30501, a marine filamentous, non-heterocystous cyanobacterium adsorbed more than 90% of cadmium ions from solutions containing 0.1–40mM. Cadmium binding accounted up to 18% of biomass weight (w/w). The algal biosorbent was also efficient is sequestering metal ions (Cd²+, Co²+, Cu²+, Ni²+) from a mixture. Biosorbent placed in dialysis tubing could concentrate Cd2+ (50–65%) from 1l solution (10 and 100ppm) at equilibrium. Biosorbent immobilized in polyvinyl foam also removed cadmium and cobalt efficiently, but required longer contact times (24h). Most of the bound metal ions (> 80%) could be desorbed with 0.1M HCl or EDTA, while other reagents were less efficient in the order: H2SO4 > NH4Cl > CaCl2 > Na_{2SO 4} > KSCN > KCl > NH_4OH > NaHCO₃. The regenerated biosorbent retained 80% of the initial binding capacity for Cd2+ and 50% binding capacity for Co2+ up to three cycles of reuse. Infrared spectra of the biosorbent preparation suggested carboxyl groups to be the primary sites for metal binding.