Abstract
SXFIT is the latest in a series of programs developed in our group to model solvent extraction
systems of increasing complexity. SXFIT permits the user complete freedom to define the
constituents from which the composition of each phase is to be specified in the data and from
which all species of a model for a system are assumed to be formed. Activity coefficients in the
nonaqueous and aqueous phases, water activity, apparent molar volumes of aqueous species,
and solution density needed for the conversion of concentration from the molarity to the
molality scale are all taken into account by the program. Several extraction systems relevant to
nuclear-waste treatment were modeled successfully using this program. As an example, the
cesium extraction efficiency of the CSSX process chosen by the USDOE for cesium removal
from high-level waste stored at the Savannah River Site can be predicted correctly for varying
feed composition.
