Separation of cobalt-60, strontium-90, and cesium-137 radioisotopes by competitive transport across polymer inclusion membranes with organophosphorous acids

The removal and separation of Co-60, Sr-90, and Cs-137 radioisotopes from nitrate aqueous solutions were studied by competitive transport across cellulose triacetate plasticized membranes using organophosphorous acids compounds (D2EHPA, Cyanex 272, Cyanex 301 and Cyanex 302). Competitive transport of trace radionuclides ions from 0.10 M NaNO3 aqueous solutions across polymer inclusion membranes containing cellulose triacetate as the support, D2EHPA as the ion carrier and o-nitrophenyl pentyl ether as the plasticizer provide the selectivity order: Co(II) > Cs(I) > Sr(II). The affinities of the radioisotopes investigated for Cyanex 272 and Cyanex 302 follow the order Cs(I) > Sr(II) > Co(II). The influence of ion carrier acidity on cation transport selectivity and effectiveness was explored. The results show a linear decrease of permeability coefficient values for Co(II) with an increase of pKa values of ion carriers. A long-term transport experiment was carried out to demonstrate the durability of polymer inclusion membranes.

The competitive transport of Cs-137, Sr-90 and Co-60 ions with organophosphorous acids such as D2EHPA and Cyanex 301 give high selectivity coefficients for Co(II) over other metal ions, i.e., 17.6 and 79.3 for Co(II)/Cs(I) and Co(II)/Sr(II) with Cyanex 301 and 9.2 and 41.3 with D2EHPA for Co(II)/Cs(I) and Co(II)/Sr(II), respectively. On the other hand, the selectivity coefficients for Cyanex 272 and Cyanex 301 were low. The correlation between permeability metal ions and pKa of ion carriers is linear and with pKa increase the permeability coefficients of Co(II) decreases. Preconcentration of Cs-137, Sr-90 and Co-60 with a volume ratio of aqueous source phase and receiving phase equal to 10 is high for Co-60 (CF = 8.43) and lower for Cs-137 (CF = 0.55) and Sr-90 (CF = 0.22). On the other hand, values of recovery factors were high for Co-60 (RF = 84.1%) and low for other isotopes (RFSr = 2.1%, RFCs = 5.5%). The polymer inclusion membranes were very stable during seven sequential experiments, which indicates PIM applicability in longterm experiments.