The sedimentation characteristics of the reactive standard test system zinc + D2EHPA are investigated in this work. Experiments with single droplets rising in a stagnant continuous phase have been carried out. The concentration of D2EHPA, zinc, and sulfuric acid as well as the diameter of the droplets are varied. The velocity of droplets is observed to be transient for several seconds. High mass-transfer rates increase the velocity of single droplets for the case of reactive extraction whereas for physical systems contrary behavior is observed. Therefore, droplets seem to behave principally different in reactive and physical extraction. This is explained by the inter-facially active properties of D2EHPA. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 160-167, 2010