Surface Complexation Model for the Heavy Metal Adsorption on Natural Sediment

Abstract

Surface complexation models (SCMs) have been successfully used to describe metal ion adsorption on pure mineral materials. However, such models have rarely been applied to model adsorption on natural materials. In this study, the surface complexation model approach was used to describe the surface properties and adsorption behavior of natural aquatic sediment. Three typical versions of the surface complexation model were used: constant capacitance model (CCM), diffuse layer model (DLM), and triple layer model (TLM). All the model parameters were determined on the basis of the experimental data of the potentiometric titration and the metal adsorption isotherm using LeAn River (China) sediment. The experimental data of the adsorption edges were used to verify the performance of the models. This work indicated that all three models can simulate the experimental results very well. In predicting the adsorption behavior of the sediment sample, the relative errors of these three models were quite close. The results illustrate that SCMs can be used to successfully model natural materials. IntroductionThe behavior, transport, and ultimate fate of heavy metals in aquatic environment depend largely on their sorption reactions with sediment particles (1-4). Thus, it is very important to investigate such reactions. Different empirical approaches, in particular the measurement of adsorption isotherms and the corresponding partitioning parameters, have commonly been used in the studies of the adsorption behavior of natural sediments or soils (5-10). However, limitations of these empirical ways have been observed (1,(11)(12)(13). Extensive studies have been made on surface complexation models (SCMs) to describe the adsorption of heavy metals on pure mineral surfaces, especially on pure hydrous oxide solid surfaces; the results are quite promising (14)(15)(16)(17)(18)(19)(20)(21)(22)(23). It has also been hoped that SCMs can be used with natural materials, but unfortunately, there have been very few studies that apply SCMs to natural materials and to sediments in particular. Mouvet and Bourg (24) were the first to use the chemical equilibrium models to quantitatively describe the adsorption data of metals to river sediment. They reported that the adsorption constants of the metals are directly proportional to their first hydrolysis constants. They concluded that to a certain degree the chemical equilibrium program can be used to predict the speciation of Cu, Ni, Pb, and Zn in a river. Fu and Allen (25) studied the Cd adsorption on an oxic sediment sample by carrying out both acid-base titration experiments and Cd adsorption experiments with the sediment sample. They used a multisite binding model that contained the effect of pH by considering the titration data against their adsorption data. The results derived from the model were close to that from the experiment. They suggested that the adsorption behavior of natural sediment can be modeled via one or two surface reactions. Charlet (26) and Osaki et al. (27,28) used the conce...

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