Application of Desalination Membranes to Nuclide (Cs, Sr, and Co) Separation

Desalination and nuclide separation, with cesium (Cs), strontium (Sr), and cobalt (Co), using commercial polymeric membranes are investigated under room temperature (298 K) to elucidate the permeation mechanism and possibility of applying commercial membranes to the separation of radioactive nuclides. The physicochemical properties of membranes are characterized by multiple techniques. The thickness of the selective layer and the boundary between the layers of membranes are observed by scanning electron microscopy. The chemical structure of selective and support layers is assessed by direct Fourier transform infrared/attenuated total reflection measurements on membrane samples. Thermogravimetric analysis demonstrates the composition comparison between membranes, which describes the relative amount of selective layers consisting of polyamide. The separation performance of polyamide-based commercial membranes is tested on simulated seawater (35,000 ppm of NaCl) and single- and multi-component aqueous nuclide solutions (10 ppm). Nanofiltration (NF) membranes exhibit a high flux of 160-210 L m^-2 h^-1 with low 31-64% rejection on the permeation of simulated seawater, while reverse osmosis (RO) membranes display a low flux of 13-22 L m^-2 h^-1 with nearly 80% rejection. This reveals RO membranes to be more effective for the rejecting nuclides (Cs, Sr, and Co) in dilute aqueous solutions, and NF membranes have advantage on high throughput. RO membranes reject above 93% for single components and even higher for mixed nuclide separation (>98%), and NF membranes permeate high flux above 230 L m^-2 h^-1. This study indicates that the desalination membranes (NF and RO) can be potential candidates for nuclide separation with combination.