Temperature Controls On Sorption of Humic Substances On Iron Oxides Under Dynamic Flow Conditions.

Sorption of natural organic matter (NOM) by metal hydroxides constitutes an important process through which NOM is retained and stabilized in natural environments, thereby protecting it from degradation. Due to the complex nature of the various organic carbon (OC) moieties present in NOM, it is likely that certain fractions of NOM are preferentially adsorbed over other fractions.  Climatic factors such as temperature and precipitation may also impact the equilibrium and fractionation of NOM at the water-mineral interface. Thus, in this study we investigate the influence of temperature on sorption and transport of soil humic acid (HA) and fulvic acid (FA) within a column packed with ferrihydrite-coated sand. We conducted experiments at three different temperatures (i.e., 5^o, 23^o and 40^o C) at neutral pH at a flow rate of 20.54 pore volume/day.   The results show that the amount of humic acid sorbed increases proportionally with increase in temperature while temperature changes had less influence on sorption of FA. On the other hand, the breakthrough curves clearly suggest that FA has greater sorption affinity for the Fe-oxide surface compared to HA likely due to a higher carboxylic acid content and smaller molecular size. Ongoing experiments including fluorescence, ultraviolet, and infrared spectroscopy are focused on determining the mechanisms and nature of C-functional groups that are involved in these sorption interactions. The findings of this study suggest that temperature may play a pivotal role in controlling the amount and type of NOM adsorbed to iron oxides within natural systems.