Sorption of Eu(III) on Attapulgite Studied by Batch, XPS and EXAFS Techniques

TL;DR

This study investigates how pH, ionic strength, temperature, and organic acids influence Eu(III) sorption on attapulgite, revealing complexation mechanisms and environmental implications through batch, XPS, and EXAFS analyses.

Contribution

It provides new insights into Eu(III) sorption mechanisms on attapulgite, especially in the presence of fulvic and humic acids, using advanced spectroscopic techniques.

Findings

Sorption depends strongly on pH and ionic strength.

Humic substances modulate Eu(III) sorption behavior.

EXAFS reveals changes in Eu-O distances and coordination with pH.

Abstract

The effects of pH, ionic strength and temperature on sorption of Eu(III) on attapulgite were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The results indicated that the sorption of Eu(III) on attapulgite was strongly dependent on pH and ionic strength, and independent of temperature. In the presence of FA/HA, Eu(III) sorption was enhanced at pH < 4, decreased at pH range of 4 - 6, and then increased again at pH > 7. The X-ray photoelectron spectroscopy (XPS) analysis suggested that the sorption of Eu(III) might be expressed as ?X3Eu0 ?SwOHEu3+ and ?SOEu-OOC-/HA in the ternary Eu/HA/attapulgite system. The extended X-ray absorption fine structure (EXAFS) analysis of Eu-HA complexes indicated that the distances of d(Eu-O) decreased from 2.451 to 2.360 {\AA} with increasing pH from 1.76 to 9.50, whereas the coordination number (N) decreased from ~9.94 to ~8.56. Different complexation species were also found for the different addition sequences of HA and Eu(III) to attapulgite suspension. The results are important to understand the influence of humic substances on Eu(III) behavior in the natural environment.