Biosorption of Cadmium Ions from Aqueous Solution Onto Non-living Lichen Ramalina fraxinea Biomass

Living lichens are known to accumulate metals across their surface. in this study, the biosorption of cadmium ions (Cd(2+)) by the lichen Ramalina fraxinea was investigated in aqueous solution in a batch system with respect to pH, contact time, temperature, initial cadmium ion concentration and size of biomass. The adsorption data appear to fit both the Langmuir and Freundlich adsorption models. The maximum adsorption capacity of the lichen R. fraxinea was found to be 7.00 mg/g at pH 6. The kinetic data were analyzed using the pseudo-first-order and pseudo-second-order equations. Kinetic parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients for each kinetic model were calculated and discussed. The adsorption process of cadmium ions onto the R. fraxinea biomass fitted well the pseudo-second-order kinetic model. It appears that R. fraxinea adsorbs cadmium ions moderately compared to some biosorbents.