Experimental investigation of cell design for the electrolysis of iron oxide suspensions in alkaline electrolyte

Following feasibility studies of iron production by electrolytic reduction of hematite particles suspended in a strong alkaline medium, this article concerns the use of engineering methods to investigate the performance of various cell configurations, in view to designing larger processes: a horizontal flow cell with parallel electrodes and two rotating cylindrical electrodes were used for this purpose. The performance was analyzed in terms of current efficiency at 0.1 A cm(-2) and deposit morphology. The results reveal a negligible role of the mass transfer of Fe (+III) ions from the bulk electrolyte on the process efficiency, as formerly suggested in reaction mechanism studies. Conventional ion-mass transfer theory is therefore not applicable and another approach is proposed. Dispersed phase transport processes, more precisely the mechanical forces acting on both the 10 mu m ore particles and the evolved oxygen bubbles, can quantitatively and qualitatively explain the cells performance. The configuration with the external rotating cathode allows both efficient contacts of the particles with the cathode and rapid removal of the produced gas phase; however the two rotating electrode devices are subject to appreciable ohmic losses due to the current lead system. The parallel plate configuration, with the cathode at the bottom appears as the best configuration for the deposition which can be achieved with low energy consumption.