Ammonia Formation By The Reduction Of Nitrite/Nitrate By Fes: Ammonia Formation Under Acidic Conditions |
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Authors: | Email author" target="_blank">David?P?SummersEmail author |
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Institution: | (1) SETI Institute, NASA Ames Research Center, M/S 239-4, Moffett Field, CA, 94035-1000, U.S.A |
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Abstract: | One issue for the origin of life under a non-reducing atmosphere is the availability of the reduced nitrogen necessary for
amino acids, nucleic acids, etc. One possible source of this nitrogen is the formation of ammonia from the reduction of nitrates
and nitrites produced by the shock heating of the atmosphere and subsequent chemistry. Ferrous ions will reduce these species
to ammonium, but not under acidic conditions. We wish to report results on the reduction of nitrite and nitrate by another
source of iron (II), ferrous sulfide, FeS. FeS reduces nitrite to ammonia at lower pHs than the corresponding reduction by
aqueous Fe+ 2. The reduction follows a first order decay, in nitrite concentration, with a half-life of about 150 min (room temperature,
CO2, pH 6.25). The highest product yield of ammonia measured was 53%. Under CO2, the product yield decreases from pH 5.0 to pH 6.9. The increasing concentration of bicarbonate, at higher pH, interferes
with the reaction. Comparing experiments under N2 CO2 shows the interference of bicarbonate. The reaction proceeds well in the presence of such species as chloride, sulfate, and
phosphate, though the yield drops significantly with phosphate. FeS also reduces nitrate and, unlike with Fe+ 2, the reduction shows more reproducibility. Again, the product yield decreases with increasing pH, from 7% at pH 4.7 to 0%
at pH 6.9. It appears that nitrate is much more sensitive to the presence of added species, perhaps not competing as well
for binding sites on the FeS surface. This may be the cause of the lack of reproducibility of nitrate reduction by Fe+ 2 (which also can be sensitive to binding by certain species) |
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Keywords: | ammonia ammonium aqueous iron (II) iron sulfide FeS nitrate nitrite nitrogen fixation non-reducing atmosphere prebiotic synthesis reduction |
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