Ionic strength effects in biosorption of metals by marine algae

Biosorption, the passive accumulation of metals by biomass, can be used as a cost-effective process for the treatment of metal polluted industrial eff luents. The green alga Ulva fascia and the brown seaweeds Sargassum hemiphy llum, Petalonia fascia, and Colpomenia sinuosa were characterized in terms of their number of binding sites, their charge density and intrinsic proton binding constant (pK(a),) using pH titrations at different ionic strengths . The determined number of binding sites decreased in the order Petalonia g reater than or equal to Sargassum > Colpomenia > Ulva. Due to their high nu mber of binding sites Sargassum and Petalonia are most promising for biosor ption applications. The decrease of proton binding with increasing ionic st rength and pH as well as the increase of Cu and Ni binding with increasing pH and decreasing ionic strength could be described by the Donnan model in conjunction with an ion exchange biosorption isotherm. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.