Iron nitrate reduction

Thus, it was observed that the first-order rate constants (/q) for nitrate reduction by untreated Fe° increase due to the pretreatment of iron metal with HC1 however, observed increases in the rate constant for nitrite reduction have been relatively small under similar acid pretreatment conditions. During the first 12 hr, the rate constant for nitrate reduction showed a gradual decline, and this decline seems to have been clearly influenced by the presence of chloride. The reaction rate constants for nitrate and nitrite reduction by untreated Fe° turnings are directly dependent on the concentration of Fe° used, ranging between 69.4 and 208.2 g/L thus /c, and k, increase linearly with increases in the surface area of the untreated iron. Table 13.8 demonstrates that acid-treated Fe° is more reactive than its untreated counterpart. 

Following consumption of dissolved O2, the thermodynamically favored electron acceptor is nitrate (N03-). Nitrate reduction can be coupled to anaerobic oxidation of metal sulfides (Appelo and Postma, 1999), which may include arsenic-rich phases. The release of sorbed arsenic may also be coupled to the reduction of Mn(IV) (oxy)(hydr)oxides, such as birnessite CS-MnCb) (Scott and Morgan, 1995). The electrostatic bond between the sorbed arsenic and the host mineral is dramatically weakened by an overall decrease of net positive charge so that surface-complexed arsenic could dissolve. However, arsenic liberated by these redox reactions may reprecipitate as a mixed As(III)-Mn(II) solid phase (Toumassat et al., 2002) or resorb as surface complexes by iron (oxy)(hydr)oxides (McArthur et al., 2004). The most widespread arsenic occurrence in natural waters probably results from reduction of iron (oxy)(hydr)oxides under anoxic conditions, which are commonly associated with rapid sediment accumulation and burial (Smedley and Kinniburgh, 2002). In anoxic alluvial aquifers, iron is commonly the dominant redox-sensitive solute with concentrations as high as 30 mg L-1 (Smedley and Kinniburgh, 2002). However, the reduction of As(V) to As(III) may lag behind Fe(III) reduction (Islam et al., 2004). 

Oxidation of arsenic-bearing pyrite with adsorption onto iron oxides and/or other metal (oxy)(hydr)oxides Nitrate reduction by pyrite oxidation (note that Appelo and Postma, 1999 referred to pure rather than arsenian pyrite) Manganese oxide reduction and release of sorbed arsenic Fe(lll) reduction on oxide surfaces changes net charge leading to arsenic desorption Iron oxide reductive dissolution and release of sorbed arsenic catalyzed by NOM degradation... 

NADH, reduced nicotinamide-adenine dinueleotide Q, coenzyme Q FNR, fumarate nitrate reduction SoxR, superoxide activated regulatory protein IRP, iron regulatory protein NIFU, nitrogen fixation gene U product. 

Relatively recently Fe/S proteins have been found to function in the regulation of biosynthesis. This can be by promoting deoxyribonucleic acid (DNA) transcription, e.g. the [2Fe-2S] containing Escherichia coli superoxide-activated (SoxR) transcription activator [10-12], or the presumably [4Fe-4S]-containing E. coli transcription factor fumarate nitrate reduction (FNR) [13,14], Alternatively, the Fe/S protein can act by interference with messenger ribonucleic acid (mRNA) translation, i.e., the iron regulatory proteins (IRPs) [15,16], These interactions are stoichiometric, therefore not catalytic. Presumably, they are also a form of sensoring, namely, of oxidants and/or iron [17],... 

Sprensen, J. (1987) Nitrate reduction in marine sediment pathways and interactions with iron and sulfur cycling. Geomicrobiol. J. 5, 401 -21. 

The reaction of Mo(H20)63+ and nitrate in aqueous solutions results in the formation of Mo2Oi(H20)62+ and nitrite. Mo(III) coordinated to oxygen and nitrogen donor atoms of EDTA also reduces nitrate in aqueous solutions. The reduction of nitrate by a Mo(III)-EDTA complex results in the formation of nitrite and a Mo(V)-EDTA complex, as determined by chemical and spectrophotometric techniques. These reactions serve as models for biological nitrate reduction. In addition, molybdate coordinates to naturally produced phenolates. The molybdenum-coordinating phenolates also coordinate tungstate and ferric iron. Two of these phenolates contain threonine, glycine, alanine, and 2,3-dihydroxybenzoic acid. 

However, information is still rare regarding the effects of ultraviolet fight on the zero-valent iron system. In the case of nitrate reduction by Fe(0), a detrimental effect of 254-nm irradiation on ferrous ion dissolution and ni-... 

Ottley C. J., Davison W., and Edmunds W. M. (1997) Chemical catalysis of nitrate reduction by iron(ll). Geochim. Cosmochim. Acta 61, 1819-1828. 

Iron can be said to be the most chemically versatile of all the elements used by nature. It is essential for dioxygen uptake and transport in the vast majority of living systems, is ubiquitous in electron transfer relays and oxygen metabolism, is used widely as the catalytic center in enzymes catalyzing chemical changes as diverse as dinitrogen fixation, nitrate reduction, and isopenicillin-N-synthase, and is vital for DNA... 

Nitration of an aromatic ring is a particularly important reaction 5 the nitro-substituted product can be reduced by reagents such as iron metal or SnCl2 to yield an arylamine, ArNHg. Attachment of a nitrogen to an aromatic rii by the two-step nitration/reduction sequence is a key part of the industrial synthesis of dyes and many pharmaceutica agents. We ll discuss this and other reactions of aromatic nitrogen compounds in Chapter 24. 

TPR and TPO patterns of silica-supported rhodium, iron, and iron-rhodium catalysts are shown in Fig. 11.5 [14]. These catalysts were prepared by pore volume impregnation from aqueous solutions of iron nitrate and rhodium chloride. Note the difference in reduction temperature between the noble metal rhodium and the non-noble metal iron. The bimetallic combination reduces largely in the same temperature range as the rhodium catalyst does, indicating that rhodium catalyzes the reduction of the iron. This forms evidence that rhodium and iron are well mixed in the fresh catalyst. The TPR patterns of the freshly prepared catalysts consist of two peaks, one coincides with that of the TPR pattern of the fully oxidized catalyst (right panel of Fig. 11.5) and can thus be... 

Derivation From naphthalene-a-sulfonic acid by nitration, reduction with iron, and separation from the l-naphthylamine-8-sulfonic acid also formed. 

When pore waters in both marine and continental sediments become significantly depleted in dissolved oxygen (< 0.5 ml/1), three geochemical subzones successively prevail (Fig. 1) (i) nitrate reduction into nitrogen (NR) (ii) manganese reduction to Mn aq. (MnR) and, subsequently, (iii) iron reduction to Fe " aq. (FeR). The type and elemental composition of carbonate cement formed are hence strongly controlled by the amount of Fe-and Mn-oxides/oxyhydroxides. 

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