Structural study of lanthanides(III) in aqueous nitrate and chloride solutions by EXAFS

Abstract

Structural studies of lanthanide ions (Nd3+≈Lu3+: about 1 mol/l) in the aqueous chloride (HCl: 0≈6 mol/l) and nitrate (HNO3: 0−13 mol/l) solutions were carried out by extended X-ray absorption fine structure (EXAFS). The radial structural functions appeared to be mainly characterized by hydration in both chloride and nitrate systems and coordination of nitrate ion in nitrate systems. These results indicated that nitrate ion forms inner-sphere complex with lanthanide but chloride ion hardly forms one. The quantitative analyses of EXAFS data have revealed that the total coordination numbers of lanthanide ranged from about 9 for light lanthanides to about 8 for heavy lanthanides in all the samples. The bond distances of Ln−O were from about 2.3 to 2.5 A for Ln−OH2 and from about 2.4 to 2.6 A for Ln−O2NO. Nitrate ion locates at 0.1 A longer position than water, it suggested that nitrate ion ligates more weakly than water.