BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 illustrates a flowchart of the steps of the preferred embodiment; Figs 2A and 2B illustrate various plan views of alternative crucible designs; Fig. 3 is a sectional view of the electrolytic concentrator; Figs 4 and 5