Rate of cobalt extraction by D2EHPA from aqueous forming drops : cobalt extraction from aqueous forming drops by di-2-ethylhexylphosphoric acid is studied by flow injection analysis and a computer program is used to calculate mass transfer coefficients. F
A study of the extraction of cobalt II ions from an aqueous
growing drop into a continuous medium of di-2-ethylhexylphosphoric
acid (D2EHPA) is made. The apparatus for this technique is
described and a flow injection analysis method for measuring the
cobalt remaining in the aqueous phase has been developed.
In this study the feed concentration of cobalt has varied
between 8.48 x 10-3 and 16.97 x 10-3 mole 9-1. The D2EHPA held in
n-heptane, has been altered between 0.143 and 2.41 mole
pH has been adjusted between 3.10 and 4.44. The principal
temperature applied to this study was 25 ±0.5*C. Acetate buffers
have been used, but it is shown by calculation that about 70% of the
cobaltous ion is in an uncomplexed form.
The kinetics of the extraction have been modelled using a method
based upon reaction in an aqueous zone near to the liquid-liquid
interface with diffusion of species towards and away from the
interface. This model provided a fundamental parameter 01 which
incorporates the chemical rate constant kR, the D2EHPA partition
coefficient PHR, the acid dissociation constnat KD for D2EHPA and
the metal ion diffusivity in the interface diffusion region.
The results have been compared with those of other workers who
studied the transfer of cobalt into an organic drop from an aqueous
The diffusion controlling film is the aqueous one. The rate
constant for, the extraction reaction equation is, from this work, kR
- 106.34 M3 kmol-1 sec-1 which can be compared with that found by
another worker using the reverse transfer system, i. e. kR - 106.18
m3 kmol-I sec-i.
. Finally, the mass transfer coefficients were found to change
with varying feed concentrations and pH, this is also in agreement
with other workers who have studied different liquid-liquid systems.