Biosorption Mechanism of Cadmium, Lead and Zinc Metals by Green and Red Macroalgae

摘要

The mechanisms of biosorption of certain cationic metals (Cd2+, Pb2+, and Zn2+) on to non-living green (Monostroma nitidum) and red (Gloiopeltis furcata, Gracilaria sp.) algae were studied using different experimental methodologies. Techniques such as FTIR, SEM, potentiometric titration, analytic quantification with an ICP and chemical blockage were used to characterize the biomass structure and determine their adsorption capacity. The adsorption capacities of the different metals according to the Langmuir model are between the 0.20 to 0.90 mmol metal/g of dry biomass. Carboxyl and hydroxyl functional groups were identified as important components of the biomass involved in the biosorption process. When comparing the FTIR spectra of the raw biomass against the one of metal loaded, no shift in the frequencies was observed between them, indicating a lack of complexation. The releasing of earth alkaline metals (Ca2+, K+, Mg2+) after the biosorption process indicates an ion exchange process. This is believed to be the main mechanism of biosorption by the three algae.