Kinetic studies of the forward extraction of trivalent Nd(III) by the commercial trioctylphosphine oxide (CYANEX 921) in kerosene from thiocyanate medium and stripping of Nd-CYANEX 921 chelate have been investigated using a Lewis cell. The different parameters affecting the extraction rate such as hydrogen ion, thiocyanate, CYANEX 921, Nd(III) concentrations in addition to temperature were separately studied and a rate equation was deduced. The experimental results demonstrated that, the rate of Nd(III) extraction is controlled by a chemical reaction at the interface rather than in the bulk phase and it is first order for CYANEX 921 concentration, while it is zero order with respect to the other investigated parameters. Kinetic studies on the stripping of Nd(III) from loaded CYANEX 921 with sulphuric acid were also carried out using the same Lewis cell. Mechanisms of both extraction and stripping processes have been proposed. (c) 2006 Elsevier B.V. All rights reserved.