DESIGN AND SCALEUP OF MIXER-SETTLERS FOR THE DAPEX SOLVENT EXTRACTION PROCESS

The basis for design and scale-up of mixer-settlers for the Dapex solvent extraction process was determined by a unit operaiions study in scale model units. Rate constants for uranium extraction involving stage efficiency, phase ratio, and residence time are directly propcrtional to the cube root of power input in the mixer. Typical mixing requirements for 90% stage efficiency are 30 hp/1000 gal and 2 min residence for extraction and 0.7 hp/1000 gal and 1.5 min for stripping. The scale-up of geometrically similar mixers is based on constant specific pcwer input. The flow capacity of gravity settlors is limited by a dispersion band, which increases exponentially with flow rate. The scale-up of settlers is based on constant flow rate of dispersed min for stripping. The scale-up of geometrically similar mixers is based on constant specific pcwer input. The fiow capacity of gravity settlers is limited by a dispersion band, which increases exponentially with flow rate. The scale-up of settlers is based on constant flow rate of dispersed phase per unit settler area and constant band thickness. The nominal flow capacity (50% of flooding) of the dispersed phase is approximately I gpm/-sq ft of settler area. Emulsions and solvent entrainment are minimized by control of mixing to form solvent-continuous dispersions. Operating data from two uranium mills confirm the scale-up relations over a range of flow rates of 200-fold for mixers and 1000-fold for settlers. (auth