MEAN MOLAL ACTIVITY-COEFFICIENTS OF AQUEOUS RARE-EARTH BROMIDE SOLUTIONS AT 25-DEGREES-C

Mean molal activity coefficients and water activities of aqueous solutions of 15 rare earth elements were determined at 25.0-degrees-C from dilute to saturated concentrations. Conductance and isopiestic measurements were carried out to obtain osmotic coefficients, from which mean molal activity coefficients and water activities were computed by fitting the values to the semi-empirical least-squares equations. The mean molal activity coefficients and water activities of the bromides were in between those of chlorides and perchlorates, showing the outer-sphere coordination of bromide to trivalent rare earth ions. The trends in the coefficients and activities are discussed in terms of ionic interactions, ionic radii and the numbers of coordination and hydration.