Sargassum seaweed as biosorbent for heavy metals

Six different species of non-living Sargassum biomass were compared on the basis of their equilibrium Cd and Cu uptake in order to evaluate potential variability in the sorption performance of different Sargassum species. Biosorption uptakes for Cd at the optimal pH of 4.5 ranged from q(max) = 0.90 mmol/g for Sargassum sp. 1 to 0.66 mmol/g for S. filipendula I representing a 36% difference. Three species were evaluated for their Cu uptake where q(max) = 0.93 mmol/g for S. vulgare; 0.89 mmol/g for S. filipendula I, and 0.80 for S. fluitans, representing a 16% difference between the lowest and highest values. Potentiometric titrations were carried out on S. vulgare, S. fluitans and S. filipendula I and yielded the similar results of 1.5 mmol/g weakly acidic sites for S. vulgare and S. fluitans, and 1.6 mmol/g for S. filipendula I. Estimates of 0.3 mmol/g of strongly acidic sites for S. fluitans and S. filipendula I and 0.5 mmol/g for S. vulgare were obtained. The total number of active sites averaged 1.9 +/- 0.1 mmol/g. The elution efficiency for Cu-desorption from S. filipendula was determined for CaCl2, Ca(NO3)(2), and HCl at various concentrations and solid:liquid ratios (S/L). The highest elution efficiency was >95% for Cu for all elutants at S/L = 1 g/l and decreased for both calcium salts with increasing S/L to less than 50% at S/L = 10 g/l as a new batch sorption equilibrium was reached quickly. CaCl2 was chosen to be the most suitable metal-cation desorbing agent. (C) 2000 Elsevier Science Ltd. All rights reserved.