EFFECTS OF FULVIC ACID ON URANIUM VI SORPTION AND TRANSPORT BEHAVIOR: THE ROLE OF FULVIC ACID CONCENTRATIONS AND SYSTEM KINETICS

A detailed understanding of the effects of natural organic matter (NOM) on metal transport behavior is needed for the successful remediation of many metal-contaminated groundwater systems. While numerous studies have shown that NOM can enhance metal-ion transport relative to NOM-free systems, others indicate that, under certain circumstances, NOM may also retard metal transport. These contradictory observations may be the result of several factors, including: 1) the binding of NOM to different mineral phases; 2) the NOM/metal ratio; and 3) sorption kinetics and transport rates.

In this study, we investigate the effects of fulvic acid (FA) on the mobility of uranium (VI) in saturated groundwater systems. Batch sorption experiments are used to determine FA effects on uranium (VI) sorption to a silica sand (pHpzc = 6.3) over a wide range of pH values and FA concentrations and as a function of time. Furthermore, column transport experiments allow us to study these effects under advective flow conditions.

Based on preliminary results, we conclude that the presence of FA has the potential to decrease uranium (VI) sorption to the silica sand after short system equilibration times, leading to enhanced uranium mobility under advective flow conditions. This enhancement is observed over a pH range from 5 to 8 and even at fairly low FA concentration levels characteristic of deep groundwater systems. However, system kinetics also play an important role, with significantly slower uranium sorption rates in the presence of FA compared to NOM-free systems. Under long term conditions and full equilibration of both types of systems, this could potentially lead to either similar or even enhanced uranium sorption in the presence of NOM in the same mineralogical system. As a consequence, groundwater velocities and local retention times in saturated groundwater systems could represent important factors in determining the fate of metal contaminants in the presence of NOM.