The purification of materials by zone refining has been analyzed theoretically and investigated experimentally with a view to establishing operational parameters and optimum processing conditions. A numerical model capable of predicting the solute redistribution at any stage of a multi-pass zone refining is proposed. Experimental work was carried out using tin of commercial grade purity as the starting material. Axial impurity profiles have been determined experimentally for equilibrium distribution coefficients less, as well as higher, than unity. These results are compared with theoretical results furnished by the proposed model in order to validate its predictions. A reasonably good agreement was observed in all cases examined. The efficiency of zone refining as a function of the number of passes and zone length has been modelled. Analysis of solute profiles after a significant number of molten zone passes shows that the model can establish an optimum combination of initial long zones followed by shorter ones, providing improvement in purification efficiency without the technical difficulties which arise with the process that allows a continuous variation of zone size. (C) 2000 Elsevier Science S.A. All rights reserved.29841671299305