Three Component raoultian behavior in relation to metal refining by crystallization and reflux

Abstract

A form of ternary solution behavior is derived, and used to predict the movement of elements between solid and liquid phases during metal refining by crystallization and reflux. This behavior is termed “Raoultian ternary behavior” because it refers to composition regions in which the solvent metal predominates,i.e. the impurities are present at dilute concentrations. Raoultian ternary solution behavior is limited to the solvent side of eutectic systems, for sufficiently high solvent concentrations; it is independent of the behavior of the system in the hypereutectic regions. It is shown, firstly, that the extent of solid solubility of an impurity in a dilute binary system may be predicted from latent heat of fusion and melting point data and the location of the liquidus line and, secondly, that by combining such data for two impurity-solvent binary systems it is possible to calculate the behavior of the corresponding dilute ternary system. It is also shown that Raoultian ternary behavior requires that the solidus and liquidus curves, on an isothermal composition diagram, be straight lines. The application of Raoultian solution behavior is discussed in relation to the prediction of the number of theoretical steps obtained during the operation of a crystallization and reflux column, and the practical results obtained.