ELECTRICALLY AUGMENTED SETTLERS AND COALESCERS FOR SOLVENT-EXTRACTION

The rate of phase separation of water-in-oil dispersions can be dramatically improved by using an applied electric field to promote coalescence of the dispersed phase. The electrical properties of many solvent systems for metals extraction are such that this technology is an appropriate means of improving the performance of conventional settlers (presently used in numerous hydrometallurgical processes) and as a basis for the design of novel, low inventory, coalescers for the future. In this context, new technology involving the use of pulsed DC with insulation coated electrodes is of particular interest, since it permits the treatment of dispersions in which the proportion of aqueous phase is 50% or higher. The development of the pulsed DC method is described with reference to some hitherto unpublished results on the effect of electrode coating material and the inter-relationship between electrode separation and optimum pulsation frequency. Performance data are presented to illustrate the possibilities for up-rating conventional settlers. Measurements of dispersion band depth and entrainment are given as a function of specific throughput for a laboratory settler operated with and without an applied electric field. Two new forms of electrical coalescer are described and experimental results that validate the designs are reported.