SURFACE COMPLEXATION MODELING .2. STRATEGY FOR MODELING POLYMER AND PRECIPITATION REACTIONS AT HIGH SURFACE COVERAGE

Three triple-layer model (TLM) surface complexation models that allow for the formation of multinuclear surface complexes or precipitates ar e compared, based on their ability to simulate cobalt sorption on alph a-Al2O3. These models include: (1) a surface solid solution model, (2) a surface polymer model, and (3) a surface continuum model. The solid solution model accounts for high coverage data by invoking a coprecip itation surface reaction, while the polymer model accomplishes the sam e task with multinuclear surface complexation reactions. In the contin uum model, two polymer reactions and one precipitation reaction are pr oposed. Modeling results indicate that all of the models work reasonab ly well at predicting sorption data from moderate to high surface cove rage (0.1 to 100%). Because the continuum model is the only one presen ted which is consistent with spectroscopic data throughout the range o f surface coverages examined, this model is suggested as the preferred one for modeling metal ion sorption data. Model predictions of pH-edg e and isotherm data are discussed and used in the assessment of the me rits of the three TLM models. (C) 1995 Academic Press, Inc.