The Extraction of Selected Transplutonium(III) and Lanthanide(III) Ions by Dihexyl-<i>N, N</i>-diethylcarbamoylmethylphosphonate from Aqueous Nitrate Media

Abstract

Abstract The extraction behavior of selected transplutonium(III) and lanthanide(III) ions fromnitrate solution was studied using relatively pure dihexyl-N, N-diethyl-carbamoylmethylphosphonate (DHDECMP). The data obtained for Am(III) and Eu(III) using DHDECMP were compared with analogous measurements obtained with dibutyl butylphosphonate (DB[BP]) and in certain cases with dihexyl-N, N-diethylcarbamoylethylphosphonate (DHDECEP). It was found that both the nitrate and extractant concentration dependencies were third power. The Kd 's for Am(III) and for Eu(III) measured from low acid LiNO3 solutions were similar for DHDECMP, DHDECEP, and DB[BP], thus giving no evidence for any significant chelation effect for DHDECMP. Significant differences among DHDECMP, DHDECEP, and DB[BP] are found for the extraction of Am(III) and Eu(III) from 1 to 5 M HNO3. These differences are explained by the ability of DHDECMP (and to a lesser extent, DHDECEP) to buffer itself against HNO3 by protonation of the amide group. The Kd 's for Am(III) through Fm(III) and for La(III) through Lu(III) measured from LiNO3 and HNO3 using DHDECMP show a definite tetrad effect when plotted as a function of Z. The Kd 's for the lanthanides generally decrease with Z whereas the Kd 's for the transplutonium elements change very little with Z.