Determining the Effects of Abiotic Reduction and Crystallization of Ferric Hydroxides Associated with Organic Matter.

The presence of organic matter has been found to either enhance or inhibit crystallization of ferrihydrite under both aerobic and anaerobic conditions. The primary objective of this study was to determine the effect of co-precipitated organic matter on the crystalinity and stability of ferrihydrite. This phenomenon may have significant implications, as the minerology of iron hydroxides affects a wetland sediment’s redox status, sorptive capacity, and pH, which in turn affects the availability, cycling, and transport of nutrients, organic matter, and metals. Precipitate characteristics were monitored during a two-week incubation using an iron-based coagulant and dissolved organic matter (DOM) from an agricultural drain. Results indicate the presence of co-precipitated organic matter strongly inhibited the reductive crystallization of iron hydroxide materials. The DOM- iron hydroxide interaction produced a stable floc material that inhibited the release of DOM back into solution regardless of pH, Fe:DOM ratio, and type of reductant added. This implies that unlike simple organic compounds used in past studies, co-precipitated natural organic matter stabilize iron hydroxides in aquatic environments controlling the reductive potential of wetland sediments.