Kinetic analysis of the reactive liquid–liquid test system ZnSO 4 /D2EHPA/n-heptane M.B. Mansur a, * , M.J. Slater b , E.C. Biscaia Jr. c a Departamento de Engenharia Quı ´mica, Universidade Federal de Minas Gerais, Rua Espı ´rito Santo 35-6° andar, 30160-030 Belo Horizonte, MG, Brazil b Department of Chemical Engineering, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK c Programa de Engenharia Quı ´mica, COPPE, Universidade Federal do Rio de Janeiro, Caixa Postal 68502, 21945-970 Rio de Janeiro, RJ, Brazil Received 13 February 2001; received in revised form 19 June 2001; accepted 23 July 2001 Abstract The kinetics of zinc extraction and stripping have been investigated for the ZnSO 4 /D2EHPA/diluent system (D2EHPA = di(2-ethylhexyl) phosphoric acid), which is under consideration as a proposed reactive extraction liquid –liquid test system by the European Federation of Chemical Engineering. Data in low and high concentration domains have been fitted to chemical kinetic and kinetic – diffusive models in order to discern the mechanism of zinc extraction and stripping for practical operational conditions. The existence of the correlation between the estimated parameters and the contributions to the overall flux of the reactive species through the interface has been determined by statistical analysis. The study has concluded that both extraction and stripping rate processes are described by the same reaction mechanism scheme as suggested by Ajawin et al. [Chem. Eng. Res. Des. 61 (1983) 62] but with the stoichiometry and complexes proposed by Mansur et al. [Hydrometallurgy (2002)]. Flux equations lead to the calculation of the individual resistance terms for mass transfer and chemical reaction using simple equations with activity coefficients equal to unity. The extraction process shows mixed controlled kinetics, whereas the mass transfer of the zinc complex was found to be rate-determining for stripping conditions. The model satisfactorily explains the data with a relative error lower than 10%. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Zn/H 2 SO 4 /D2EHPA system; Extraction and stripping kinetics; Reactive test system 1. Introduction The adoption of test systems for liquid–liquid extraction studies enables the evaluation of the mass transfer rates and the hydrodynamic features of differ- ent types of equipment based on reliable description of equilibrium and kinetics. Three ternary physical extraction systems have been recommended by the European Federation of Chemical Engineering (Misek, 1978). As a proposed reactive extraction test system, i.e. extraction with simultaneous chemical reaction and diffusive effects, the ZnSO 4 /D2EHPA/dodecane sys- tem (D2EHPA= di(2-ethylhexyl) phosphoric acid) ap- pears to meet most of the requirements. Other aliphatic diluents (n-heptane for example) have been suggested 0304-386X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0304-386X(01)00210-9 * Corresponding author. E-mail address: mansur@deq.ufmg.br (M.B. Mansur). www.elsevier.com/locate/hydromet Hydrometallurgy 63 (2002) 107– 116