Submitted to: Geochimica et Cosmochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2001
Publication Date: N/A
Interpretive Summary: The reddish-orange iron oxide sediments that occur naturally in the upland streams of northwest Mississippi can potentially be used as an amendment to improve soil resistance to erosion and to remove contaminants such as heavy metals and phosphorous from water supplies. However, the extent to which in particular iron oxide performs such functions depends on its chemical and mineralogical characteristics. We conducted a laboratory analysis of iron oxides from several streams and determined that these materials were primarily composed of two mineral forms known as ferrihydrite and lepidocrocite. These are the two most chemically reactive iron oxide minerals that occur in abundant quantities in nature. Based on these findings, we suggest that their use as an amendment to prove soil and water properties would be successful.
Technical Abstract: Iron oxide precipitates are abundant in small stream systems of northwest Mississippi, USA, especially during the wet winter months. The properties of these specific materials are unknown even though they have the potential to influence soil physical properties and absorb chemical pollutants in sediment environments. Streamwater and associated precipitates were collected from four streams at Cedar Creek (CC), Lee's Creek (LC), Spring Creek (SP), and Toby Creek (TC) during winter flow periods. Specimens were characterized for mineralogy, color, and solubility in oxalate (o), dithionite (d), and HNO3. Water chemistry was dominated by Ca, Na, Mg, and K, with an average pH of 7.0. X-ray diffraction (XRD) and differential scanning colorimeter (DSC) data indicated that the precipitates were primarily poorly ordered ferrihydrite (CC, TC) and lepidocrocite (LC, SC). The Feo/Fed ratios were 0.40 (CC), 0.68 (LC), 0.66 (SC), and 0.67 (TC). Organic C contents were 80.6, 38.0, 63.0, and 51.3 g/kg**-1 for the same samples. Precipitate color was uniform among sites, averaging 6.7 YR 4.8/6.2. After oxalate extraction, redness increased slightly in the CC and SC specimens, and decreased in the others. Extraction with dithionite depleted the red color in all specimens, but had less effect on the CC and SC samples which retained hues at 7.9 and 7.3 YR, respectively. Dithionite extractable P equaled 1.02 (CC), 0.72 (LC), 0.56 (SC), and 0.99 (TC) g kg**-1. This study indicated that the precipitates are either primarily poorly ordered ferrihydrite or lepidocrocite, and that the redder, ferrihydrite specimens contain the greatest P concentrations.