Sorption of NpO2+ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength
at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase
in ionic strength from 0.20M to 1.00M (NaClO4), increased the NpO2+ sorption, which then decreased at 1.50M (NaClO4) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO2+ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate
(ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid,
ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was
observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic
acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO2+/silicate/ligand complexes. The effects of Ca(II) (1.00·10−3M) and Eu(III) (1.00·10−4 and 1.00·10−3M) ions on NpO2+ sorption to suspended silicate were also investigated.