SOLVENT EXTRACTION EQUIPMENT DESIGN AND OPERATION: FUTURE DIRECTIONS FROM AN ENGINEERING PERSPECTIVE

The operation of solvent extraction plants involves optimisation of conditions to minimise loss of solvent and maximise recovery. Because of these competing goals there are a number of different geometries of contactors that have evolved for different services; in the future, lower feed concentration and higher recoveries will lead to a consideration of new ways of contacting the two phases. The potential of some of the newer devices is compared with more traditional contactors. The current methods used for design and scale up of column-type solvent extraction devices are reviewed. This covers both the hydrodynamic factors which determine column cross-section and throughput, and mass transfer performance through the influence of drop size, holdup, mass transfer coefficient, axial dispersion, and drop interactions (coalescence and breakage). The current techniques for scale up are limited and rely on extensive pilot testing before final designs can be confidently achieved. A discussion of the potential for more sophisticated models for performance evaluation is also included.