SURFACE COMPLEXATION MODELING .1. STRATEGY FOR MODELING MONOMER COMPLEX-FORMATION AT MODERATE SURFACE COVERAGE

Surface complexation models (SCMs) have previously been shown to be ca pable of predicting metal ion sorption behavior onto mineral surfaces. Application of SCMs, however, requires a self-consistent approach for determining model parameter values. In this paper, titration data for alpha-Al2O3 and metal ion sorption data for Co(II) are used to determ ine the metal ion sorption parameters for the triple-layer model (TLM) version of the SCM, This was accomplished by calibrating the TLM para meters to a moderate-coverage (0.1%) data set and then using these val ues to predict data over a wide range of surface coverages (0.05 to 10 %), pH(5 to 9), and ionic strength (0.001 to 0.1 M as NaNO3). The resu lts of the analysis showed that a range of TLM parameter values could fit the calibration data set equally well. However, when metal ion sor ption data covering a range of ionic strength and surface coverages we re considered, an optimal set of TLM parameter values could be identif ied. For high surface coverage data (>10%), the model was shown to und erpredict the data, presumably due to the formation of multinuclear sp ecies. In order to extend the model predictions range to high surface coverage, polymer or surface precipitation TLM reactions are needed. ( C) 1995 Academic Press, Inc.