Abstract
Extraction equilibrium formulations were established for the distribution of nickel, cobalt and sodium between n-heptane and xylene containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester ((LH)2) and 5 × 102 mol/m3 (Na, H)NO3. The composition of the organic phase species is NiL22(LH)2, CoL2(LH)2 and NaL(3/2)(LH)2, over a range of loading ratio, [M]1/[(LH)2]feed, less than 0.08 for cobalt and 0.008 for nickel. The ratio of the extraction constant for the commonly used di-(2-ethylhexyl)phosphoric acid to that using the present reagent is of the order of 10 for cobalt, copper and sodium, but increases to the order of 100 for nickel.
With increase in loading ratio, successively larger aggregated species such as (NiL2(LH)2)n(LH)2 and (CoL2)n(LH)2 (n=l, 2, 3, ...) appear. Identification of these species has been established on the assumption that the extraction constants are independent of the number of metal atoms, n, in the species.
