Recovery of entrained CSSX solvent from caustic aqueous raffinate using coalescers.

摘要

A solvent was developed at Oak Ridge National laboratory (ORNL) for a caustic-side solvent extraction (CSSX) process that removes cesium from Savannah River Site (SRS) tank waste. After treatment, a small fraction of the solvent is entrained in the caustic raffinate at a level of 100-300 ppm, well above the solubilities for the various solvent components. Recovery of this solvent can produce a potential cost saving in excess of $5M per annum based on a processing rate of 20 gpm. In this study we examined the issues associated with the use of a coalescer for solvent recovery and measured the physical properties of the solvent and simulant. The density, surface, and interfacial tension, and viscosity of the optimized solvent and a full-component SRS waste simulant were determined as a function of temperature. The entrainment of the solvent components in the SRS waste simulant during the operation of a four-stage 4-cm contactor unit was quantified based on chemical and volumetric analysis. The chemical stabilities of several candidate commercial coalescing media in the caustic simulant were examined. Stainless steel media showed little degradation over a 30-day test; polymer media tended to be coated by the organic. A laboratory-scale coalescer was operated in tandem with a four stage 4-cm contactor unit. Results indicate that a 90% recovery of the entrained solvent can be achieved using a commercial coalescer equipped with appropriate media and at appropriate operating conditions. Finally, several commercial coalescer options are discussed.