Design of a Modular Annular Centrifugal Contactor for Lab-Scale Counter-Current Multistage Solvent Extraction

ABSTRACT Annular centrifugal contactors (ACCs) have appealing properties as counter-current multistage solvent extraction (SX) equipment, allowing high throughput at short residence times, small liquid hold-up, and small footprint. The number of commercial suppliers of laboratory-scale ACCs is limited, and their designs have restricted flexibility. Commercial 25 mm diameter ACCs were customized with transparent PMMA surroundings of the mixing zones, allowing visual process monitoring and identification of operational malfunctions. The separation zone of several rotors was lengthened compared to the factory design, which allows longer average residence times in the modified contactors, while keeping the organic flow rate constant in the bank of interconnected contactors. The Couette gap could be increased or decreased without affecting the mixing performance. A 3D-printed stator allows for more efficient draining of the light and heavy phases, and reduces liquid hold-up and volumes required to efficiently achieve steady-state conditions in the process. The hydrodynamic performance of the modified equipment was demonstrated by a SX process of uranium with TBP. First a literature data set of distribution ratios for uranium in HNO3 and 30% TBP diluted in dodecane was utilized to create an empirical model in SX Process simulation software. A flowsheet was designed to validate the model, and it provides an example of the methodology to progress from batch to multistage process. Online density measurements were used to monitor and control the uranium concentrations, and to achieve the desired high metal loading steady-state conditions. It was demonstrated that ruthenium decontamination from uranium could be improved in modified ACCs with longer residence time in the mixing zones of the scrubbing section.