A. Geist et al., Mass transfer kinetics of reactive multi-cation co-extraction into bis(2-ethylhexyl) phosphoric acid, SOLVENT EXT, 18(3), 2000, pp. 493-515
The kinetics of mass transfer for the chemical extraction of various metal
cations with bis(2-ethylhexyl) phosphoric acid (D2EHPA) has been studied in
a stirred cell. With all cations investigated (Cd2+, Cu2+, Ni2+, Pb2+, Zn2
+), mass transfer is found to be limited by diffusion as indicated by a lin
ear increase of initial extraction rate with stirring speed. Mass transfer
coefficients of individual species are determined at experimental condition
s that maintain mass transfer resistance in the donor phase. With known ind
ividual mass transfer coefficients and measured equilibrium data (stoichiom
etric coefficients and equilibrium constants), concentration courses in the
stirred cell can be calculated for multi-cation co-extraction. Experimenta
l and calculated results show good agreement, confirming the basic assumpti
on that the chemical reaction is located at the liquid/liquid interface.