D2EHPA based strontium removal from strongly alkaline nuclear waste Original Research Article

A method for Sr removal from strong alkaline solutions in the presence of 1M NaOH and 3M NaNO3 has been developed. The method is based on Di-2-ethyl hexyl phosphoric acid (D2EHPA) acting as a carrier in liquid membrane or as an extractant in simultaneous extraction-reextraction. After removal, Sr can be precipitated as SrSO4 if H2SO4 is used as the stripping phase, thus giving the possibility to concentrate radioactive Sr in a small volume of solid phase within one technological step. Using this method in a bulk liquid membrane process without EDTA, a rate of Sr removal near 10−6 mol-m−2-s−1 could be achieved, which is typical for liquid membranes. The hindrance effect of EDTA on the Sr removal has been demonstrated and a simple method to reduce this effect by addition of Ca2+ is suggested. In the case of the extraction-reextraction process with the membrane based demulsification, 98% of Sr was removed at a rate of 4.5×10−9 mol-s−1-L−1. The process is simple and should allow removal of all radioactive Sr from radioactive waste at the Hanford site, USA, in one to two years, depending on the plant scale.