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Effects of Oxide Coating and Selected Cations on Nitrate Reduction by Iron Metal

^a Civil Engineering Dep., Univ. of Nebraska-Lincoln, Omaha Campus, Omaha, NE 68182-0178
^b School of Natural Resource Sciences, 309 Biochemistry, University of Nebraska-Lincoln, Lincoln, NE 68583-0728

View larger version (39K): [in a new window]   Fig. 1. Results of batch tests under differing experimental conditions (defined in Table 1). (a) Test 1; (b,c) Test 2 (note that nitrate reduction occurred in three stages, TN = NH+4+ NO-3); (d) Test 4; (e) Test 12; and (f) Test 13. Values and error bars in (a), (b), and (c) represent the average and plus or minus one standard deviation, respectively, from three replicate runs.

View larger version (19K): [in a new window]   Fig. 2. X-ray diffraction spectra analyses indicate that the black oxide coating and black precipitate generated from nitrate reduction by Fe0 under the anoxic condition are magnetite. (a) Commercial magnetite powder; (b) black coating on Fe0; and (c) black precipitate on filter paper.

View larger version (86K): [in a new window]   Fig. 3. Scanning electron microscope (SEM) image of (a) granular Fe0 before use, bare surface (x60); (b) granular iron coated with magnetite after 20 h in the reactor with the initial conditions of Test 12 (x18k); and (c) black precipitate on a filter paper, obtained after 10 h from the reactor with the initial conditions of Test 13 (x20k).

View larger version (21K): [in a new window]   Fig. 4. Results of the stoichiometric test. Transforming 1 mol of NO-3–N to NH+4–N consumed 0.75 mol of aqueous Fe2+. Results are averages of duplicates.

View larger version (22K): [in a new window]   Fig. 5. Series of tests with various initial Fe2+ concentrations (0–3.6 mM or 0–200 mg L-1) show the stoichiometry between nitrate reduction and Fe2+ depletion in the anoxic magnetite-coated Fe0–nitrate–H2O system.

View larger version (25K): [in a new window]   Fig. 6. Effect of Fe3+ or Cu2+ addition on nitrate removal. Initial conditions: 5% precoated iron + 30 mg NO-3–N L-1 + (a) 100 mg Fe3+ L-1 (FeCl3) or (b) 115 mg Cu2+ L-1 (CuCl2), without initial pH adjustment.