Complexation of Europium(III) with Carbonate Ions in Groundwater

Abstract

ABSTRACTThe equilibrium extraction behavior of Eu(III) studied in chloroform solutions containing l-nitroso-2-naphthol (HA), either alone or combined with 2, 2'-dipyridyl, 1, 10-phenanthroline (phen), or trioctylphosphine oxide (TOPO) shows that the metal ion is extracted as either EuA, EuA3.2, 2'-dipyridyl, EuA3·phen, or EuA3·2TOPO, respectively. The synergic effect of phen or TOPO on the extraction of Eu(III) with l-nitroso-2-naphthol is more pronounced over that of 2, 2'-dipyridyl. The carbonate complexation of Eu(III) has been studied in 1.0 M ionic strength solutions at pH 8.0–9.0 and 25 °C using the synergic extraction system of 1-nitrşso-2-naphthol and pheo. The following complexes have been identified: EuCO34, Eu(CO3)2-, Eu(CO3)33-, and Eu(CO3)45- the results suggest that the first two species predominate at carbonate concentrations and pH similar to those found in most groundwaters. The formation constants of these species have been calculated at zero ionic strength using both SIT and ion pairing models.