Modeling of Pu(IV) Extraction by Tri-n-butyl Phosphate from Acidic Nitrate Media Containing Acetohydroxamic Acid

The presence of acetohydroxamic acid (HAHA), proposed as a holding-back compound for the PUREX process, significantly decreases extraction of Pu by tri-n-butyl phosphate (TBP) due to the formation of strong Pu(IV)-hydroxamate complexes. From the fitting of experimental distribution ratios of Pu, two Pu(IV) species were proposed to be present in the organic phase. The contribution of Pu(NO(3))(4)(TBP)(2) species is relevant only at very low concentrations of HAHA or its absence, while under higher concentrations of HAHA, the mono- and diacetohydroxamate complexes, Pu(AHA)(NO(3))(3)(TBP)(2) and Pu(AHA)(2)(NO(3))(2)(TBP)(2), are the main extracted species. A thermodynamic model describing the speciation of tetravalent plutonium in aqueous solutions of nitric acid and acetohydroxamic acid and its distribution with 0.30 volume fraction tri-n-butyl phosphate in n-dodecane is presented.