The influence of a fulvic acid on the adsorption of europium and strontium by alumina and quartz: effects of pH and ionic strength

A batch method has been employed to study the adsorption of trace quantities of Eu and Sr on α-Al2O3 and SiO2 as a function of pH (3-9), ionic strength (0.10 and 0.01 M NaClO4) and the presence of a well-characterized aquatic fulvic acid (FA). A comparison of Eu and Sr adsorption by alumina showed that FA could both reduce and enhance metal ion adsorption. In the absence of FA the adsorption of the metal ions onto alumina was a function of both pH and ionic strength. In the presence of FA the ionic strength effect on the Eu adsorption vanished, while the Sr adsorption showed a clear dependence on ionic strength. The adsorption of Eu and Sr on quartz was lower than the adsorption of the metals on alumina. Additionally, the adsorption of Eu and Sr on quartz was apparently lower than the adsorption on alumina in the presence of Fa. For both metal ions the adsorption on quartz was higher at 0.10 M than at 0.01 M NaClO4 - an observation that was reversed in the case of alumina. Increasing concentrations of FA lowered the pH at which Eu adsorption on alumina would be reduced. (orig.)