SOLVENT-EXTRACTION INVESTIGATION OF MOLYBDENUM(VI) EQUILIBRIA

The extraction of molybdenum(VI) by tri-n-butyl phosphate (TBP) or a 50% TBP-cyclohexane mixture from 1.0 M NaClO4 medium has been investigated as a function of molybdenum concentration at various approximately constant pH values in the.range 1.0-2.0. A satisfactory description of the extraction system could be obtained by computer treatment of the data when all the relevant protonation and condensation equilibria in both phases were taken into account. In the pH range investigated the existence of two large polyanions in the aqueous phase has been confirmed, i.e. [Mo36O112(OH2)16]8- and most probably [MO18O56]4-. Formation constants have been calculated for these ions and also for some other species which agree well with values previously determined by other methods.