The prediction of multicomponent ion exchange equilibria with particular reference to the system involved in the recovery of uranium.
Loading...
Date
1976
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The problem of predicting the general ion exchange equilibria
pertaining to systems of industrial significance is generated by
the multicomponent nature of such systems and the nonidealities which
may be present in both the solution and exchanger phases.
A general framework applicable to multicomponent systems
incorporating nonideal effects in both phases is presented. For the
solution phase a well established procedure for calculating activity
coefficients is adopted. Deviations from ideal behaviour in the
exchanger phase are modelled by the Wilson equation, which expresses
the excess Gibbs free energy of mixing of the resinates as a function
of composition. A Significant advantage is afforded by this equation
in that theoretically a multicomponent system may be predicted from
the binary interaction coefficients of this equation which are
determined experimentally, thereby reducing the otherwise extensive
experimental program.
These ideas are applied to systems of increasing complexity from
simple binary characterisation experiments to the prediction of a six
component system related to that encountered in the recovery of uranium
from sulphuric acid leach liquors. Experimentation for the systems involving the ions S04 2-, Cl- and NO-3 and a strong base anion exchanger have provided a severe test for
the procedure proposed. The agreement between the predicted and experimental
resin phase composition data for this ternary system is within ± 5%.
The addition of complexing agents complicates the procedure in that
it becomes physically impossible to decompose the system into the desirable
experimental binary systems. In this case higher order systems are
characterised. Introducing a mineral acid to the ternary system
discussed previously generates the HSO-4 ion which necessitates the
characterisation of other ternary systems before the quaternary system
may be predicted. The agreement between the predicted and experimental
resin phase composition for the quaternary system is shown to be within
± 10%. The work is easily extended to include the more complex systems
generated by the complexation of metal ions with the various ligands
present. .Provided the stoichiometry of the complex species in the
exchanger phase is well defined the complexes present no difficulties
in the characterisation procedures.
Experimental studies on the acidic uranyl sulphate quaternary
system provide the desired ion exchange equilibrium constants and the
interaction coefficients.
In order that the interaction coefficients for the ion pairs such as UO2 (SO4)2-2,
Cl- and U02 (SO4)2-2, NO-3 may be estimated it is necessary
to characterise two quinary systems. Nevertheless the characteristics
of lower order systems are employed to reduce the number of unknown
parameters.
Finally it is possible to predict the resin phase composition of
the six component system which results from chloride and nitrate species
being included in the acidic uranyl sulphate system. The quantitative
effects of all the components in the solution phase on the extent of
uranium loading are predicted.
Although the ferric ion is an important component in the industrial
situation this ion has been excluded from this work because at this
stage it is not possible to identify or measure the quantity of
the various ferric complexes present in the resin phase for a
particular solution condition.
Description
Thesis (Ph.D.)-University of Natal, Durban, 1976.
Keywords
Theses--Chemical engineering.