In this paper, study of the biosorption of Cd2+ and Pb2+ by nonliving Laminaria japonica in a batch adsorption system is described. The content of acidic sites and the dissociation constant of carboxylic acid functional groups (metal-binding site) of L. japonica were experimentally determined by conductometric and potentiometric titrations and theoretically predicated by using monodentate and bidentate binding models. The models are based on the monodentate or bidentate binding reactions of bivalent metal ions to acidic sites. The acidic site content and carboxylic acid dissociation constants determined are 1.25 and 0.18 mmol L−1, respectively. The results showed that the bidentate adsorption model fits well the biosorption of bivalent metal ions onto L. japonica with the bidentate binding constants for Cd2+ and Pb2+ being 5.72 × 103 and 6.24 × 104 L mol−1, respectively. The adsorption process of L. japonica followed the pseudo-second-order kinetics.

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