Thermodynamics of the system lead sulfide and thiol collector

The thermodynamics of the systems between lead sulfide and two thiol collectors, potassium ethyl xanthate and sodium diethyl dithiophosphate, have been examined in this work. It was found that the experimental data cannot be explained using the thermodynamics of bulk phases. Therefore, a mixed phase model was developed in which the concentrations of the components PbS and (PbX)₂S in the surface phase are taken into account. When the experimental results are compared with the theoretical ones it could be found that the system of ethyl xanthate and lead sulfide behaves as an ideal mixed phase, whereas the system of diethyl dithiophosphate behaves non-ideally, i.e. the activity coefficients of the components in the surface phase are unity in the former system but differ from unity in the latter case.
This difference is probably due to the different sizes of the two thiol collector molecules.