[en] The rate constants for the interphase transfer of uranium between 3.5 M HNO₃ and tributyl phosphate (TBP) - normal hydrocarbon diluent solutions have been measured using the single drop method, Lewis cell method, and a Kenics mixer - centrifugal separator. Rate constants obtained by all methods were the same within experimental error. The variables studied that affect the rate constants include the TBP concentration, the acidity and total neutral nitrate concentrations of the aqueous phase, and temperature. Results of these tests indicate that the rate controlling mechanism is chemical reaction at the interface