Mass transfer kinetics of reactive multi-cation co-extraction into bis(2-ethylhexyl) phosphoric acid

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 linear increase of initial extraction rate with stirring speed. Mass transfer coefficients of individual species are determined at experimental conditions that maintain mass transfer resistance in the donor phase. With known individual mass transfer coefficients and measured equilibrium data (stoichiometric coefficients and equilibrium constants), concentration courses in the stirred cell can be calculated for multi-cation co-extraction. Experimental and calculated results show good agreement, confirming the basic assumption that the chemical reaction is located at the liquid/liquid interface.