RIGOROUS ANALYSIS OF S2L-TYPE PHASE SOLUBILITY DIAGRAMS TO OBTAIN INDIVIDUAL FORMATION AND SOLUBILITY PRODUCT CONSTANTS OF BOTH SL-TYPE ANDS2L-TYPE COMPLEXES

A rigorous simple model has been developed for the analysis of S2L-typ e phase solubility diagrams. The model utilizes the inherent informati on built into all segments of the phase diagram to obtain individual f ormation (K-11 and K-21) and solubility product constants, either K-S1 1 or K-S21, depending on which of the two SL or S2L complexes reaches saturation first. The model uses the measured solubility S-eq against solubiliser concentration L-t, in addition to the corresponding values at the onset and end of the plateau. This is used to analyze the enti re phase diagram including the descending portion. Nonlinear least squ are fitting of the entire data sets proved quite efficient in convergi ng to a unique fit, especially because the model includes only one sin gle floating parameter to estimate. The model offers a simple vehicle to distinguish between the two types of S2L phase solubility profiles: those involving an S2L-complex precipitate, and others having an S2L- complex precipitate instead. The limits of precision required to obtai n reasonable estimates of formation constants were investigated throug h computer simulation of experimental data. (C) 1997 Elsevier Science B.V.