Showing papers on "Ammonia published in 1996"

Abiotic Nitrate Reduction to Ammonium: Key Role of Green Rust

Abstract: Leaching of nitrate from soils and sediments can be reduced in anoxic environments due to denitrification to N2O/N2 or reduction of nitrate to ammonium. While microbial dissimilatory reduction of nitrate to ammonia is well known, it is shown here that this conversion can also proceed at appreciable rates in abiotic systems in the presence of green rust compounds [FeII4FeIII2(OH)12SO4·yH2O]. In the reaction nitrate is stoichiometrically reduced to ammonium, and magnetite (Fe3O4) is the sole Fe-containing product. At a constant pH of approximately 8.25 and 25 °C, the rate expression is given as: d[NH4+]/dt = k[Fe(II)]GR[NO3-],where k = 4.93 × 10-5 ± 0.39 × 10-5 L mol-1 s-1. In anoxic soils and sediments, this reaction may also lead to a nitrate to ammonium reduction, at rates of similar magnitude or even higher than microbial reduction rates. Hence green rust should be considered a possible important reductant for nitrate reduction to ammonium in subsoils, sediments, or aquifers where microbially mediated ...

NOx-Reduction in Diesel Exhaust Gas with Urea and Selective Catalytic Reduction

Abstract: High values of NOx reduction may be obtained with urea as a reducing agent and a standard SCR catalyst based on TiO2-WO3-V2O5. The process was carefully investigated for possible secondary emissions and it could be shown that urea-SCR does not lead to relevant emissions of nitrogen dioxide, nitrous oxide, hydrogen cyanide and isocyanic acid. Further investigations using a HPLC method have also proved that addition compounds of higher molecular mass than urea (and urea itself) are not emitted in appreciable amounts as long as the process is properly managed, i.e., as long as the emission of ammonia is kept low. The limiting secondary emission is ammonia slip, the major problem when ammonia is used directly as a reducing agent.

The Principles and Applications of Ammonia Leaching of Metals—A Review

Abstract: An extensive literature survey on the principles and applications of ammonia leaching processes in hydrometallurgy is presented in this paper. The combination of ammonia anal ammonium salts is known to be a powerful lixiviant used in hydrometallurgical processes. Many metals can be extracted using the mixture of ammonia/ammonium. The thermodynamics and kinetics of the dissolution of various metals in ammonia/ammonium salts have been reviewed. The solubility, volatility, and complexation ability of various metals with ammonia have been reviewed and discussed. Eh-pH diagrams of various metal-ammonia-water systems are presented. Also presented is a comprehensive literature survey on the leaching behavior of metals in ammoniacal solutions. The metals considered in this paper are copper, cobalt, nickel, zinc, cadmium, silver, gold and palladium.

Electrochemical reduction of nitrates and nitrites in alkaline nuclear waste solutions

Abstract: Sodium nitrate and nitrite are major components of alkaline nuclear waste streams and contribute to environmental release hazards. The electrochemical reduction of these materials to gaseous products has been studied in a synthetic waste mixture. The effects of electrode materials, cell design, and other experimental parameters have been investigated. Lead was found to be the best cathode material in terms of current efficiency for the reduction of nitrate and nitrite in the synthetic mix. The current efficiency for nitrite and nitrate removal is improved in divided cells due to the elimination of anodic oxidation of nitrite. Operation of the divided cells at high current densities (300–600 mA cm−2) and high temperatures (80°C) provides more efficient reduction of nitrite and nitrate. Nearly complete reduction of nitrite and nitrate to nitrogen, ammonia, or nitrous oxide was demonstrated in 1000 h tests in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane, and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm−2 and a temperature of 70° C. Greater than 99% of the nitrite and nitrate was removed from the synthetic waste mix batch in the 1000 h tests at an overall destruction efficiency of 55%. The process developed shows promise for treating large volumes of waste.

Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2

Abstract: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2. The optimum metal content varies depending on the nature of the metal. A correlation between the ammonia yield and the intermediary MH bond strength is established (low bond strength gives rise to low ammonia yield).

Effect of pH, temperature, amount of litter and storage density on ammonia emissions from stable manure

Abstract: In laboratory tests using stable manure consisting of wheat straw and slurry, ammonia emission was found to have two peaks corresponding to the population dynamics of proteolytic bacteria and amino acid-degrading bacteria respectively. Cumulative ammonia emissions over 14 days were 0.8-23.2 % of the initial total nitrogen (N t ) and were both abiotically and biotically induced. Changes in pH had the most significant effect on the abiotically induced ammonia emissions. After 14 days of decomposition, at pH values of 6.0 and 7.5, abiotically induced emissions remained close to the limit of detectability, whereas at pH 9.0 as much as 9.8 % of the initial N t was lost. An increase in storage pressure from 0 to 400 and 800 kp/m 2 generally decreased the biotic emissions to 9.6, 2.8 and 2.3 %; while increasing the amounts of litter (2.5, 5.0 and 15.0 kg straw/LAU per day) led to a decline not only in the biotic (17.1, 12.8, 3.5 %) but also in the abiotic emissions (6.1, 5.5, 1.6%). Varying the temperature (20, 30 and 40 °C) resulted in biotically induced emissions of 7.9, 11.7 and 11.6%, respectively, and abiotically induced emissions of 1.1, 1.4 and 2.2 % of the initial N t . At temperatures of 30 and 40 °C, the amount of microbially digested sources of carbon available was obviously sufficient to permit almost total reincorporation of NH 4 + from 4 days onwards.

Inhibiting and deactivating effects of water on the selective catalytic reduction of Nitric Oxide with ammonia over MnOx/Al2O3

Abstract: The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnOx-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water.

Helicobacter pylori utilises urea for amino acid synthesis

Abstract: Helicobacter pylori has one of the highest urease activities of all known bacteria. Its enzymatic production of ammonia protects the organism from acid damage by gastric juice. The possibility that the urease activity allows the bacterium to utilise urea as a nitrogen source for the synthesis of amino acids was investigated. H. pylori (NCTC 11638) was incubated with 50 mM urea, enriched to 5 atom% excess 15N, that is the excess enrichment of 15N above the normal background, in the presence of either NaCl pH 6.0, or 0.2M citrate pH 6.0. E. coli (NCTC 9001) was used as a urease-negative control. 15N enrichment was detected by isotope ratio mass spectrometry. H. pylori showed intracellular incorporation of 15N in the presence of citrate buffer pH 6.0 but there was no significant incorporation of 15N in unbuffered saline or by E. coli in either pH 6.0 citrate buffer or unbuffered saline. The intracellular fate of the urea-nitrogen was determined by means of gas chromatography/mass spectrometry following incubation with 15N enriched 5 mM urea in the presence of either 0.2 M citrate buffer pH 6.0 or 0.2 M acetate buffer pH 6.0. After 5 min incubation in either buffer the 15N label appeared in glutamate, glutamine, phenylalanine, aspartate and alanine. It appears, therefore, that at pH and urea concentrations typical of the gastric mucosal surface, H. pylori utilises exogenous urea as a nitrogen source for amino acid synthesis. The ammonia produced by H. pylori urease activity thus facilitates the organism's nitrogen metabolism at neutral pH as well as protecting it from acid damage at low pH.

Ammonia emission from young barley plants: influence of N source, light/dark cycles and inhibition of glutamine synthetase

Abstract: Barley (Hordeum vulgare L cv Golf) plants were grown at two different relative addition rates ; 01 and 02 d -1 of nitrate Three to five days before measurements started the plants were transferred to a nutrient solution with 2 mM nitrate or ammonium The ammonium-grown plants showed increased ammonium levels in both shoots and roots and also increased ammonium concentrations in xylem sap Ammonia emission measured in cuvettes connected to an automatic NH 3 monitor was close to zero for nitrate-grown plants but increased to 059 and 088 nmol NH 3 m -2 s -1 for plants transferred to ammonium after growing at RA = 02 and 01 d -1 , respectively In darkness, NH 3 emission decreased together with photosynthesis and transpiration, but increased rapidly when the light was turned on again Addition of 05 mM methionine sulphoximine (MSO) to the plants caused an almost complete inhibition of both root and shoot glutamine synthetase (GS) activity after 24 h Ammonia emission increased dramatically and photosynthesis and transpiration decreased in both nitrate- and ammonium-grown plants as a result of the GS inhibition At the same time plant tissue and xylem sap ammonium concentrations increased, indicating the importance of GS in controlling plant ammonium levels and thereby NH 3 emission from the leaves

Process for producing 4-trifluoromethylnicotinic acid

Abstract: A process for producing 4-trifluoromethylnicotinic acid of the formula (VIII) or its salt: (VIII) which comprises (i) a first step of reacting a halide of the formula (I): CF3COHal (I) wherein Hal is a halogen atom, with a compound of the formula (II): CH2=CHOR1 (II) wherein R1 is an alkyl group, in the presence of a base to obtain a 4-alkoxy-1,1,1-trifluoro-3-buten-2-one of the formula (III): CF3CO-CH=CH-OR1 (III) wherein R1 is as defined above, and reacting this compound with ammonia to obtain 4-amino-1,1,1-trifluoro-3-buten-2-one of the formula (IV): (IV) and (ii) a second step of subjecting the 4-amino-1,1,1-trifluoro-3-buten-2-one obtained in the first step and a compound of the formula (V): ACO2R2 (V) wherein R2 is an ester-forming residue, and A is (R3O)CH=CH- or (R3O)2CHCH2-, wherein R3 is an alkyl group, to a condensation reaction to obtain a compound of the formula (VI) (inclusive of its salt): (VI) wherein R2 is as defined above, and/or a compound of the formula (VII) (inclusive of its salt): (VII) wherein R2 and R3 are as defined above, as the reaction product, and then subjecting the reaction product to ring closure and hydrolysis.

Removal of Ammonia from Air by a Peat Biofilter

Abstract: Peat was studied as a filter material for removing ammonia from air. Since the peat itself contained no nitrifiers and had no nitrification potential, it was inoculated with nitrifying bacteria from nitrifying activated sludge. To achieve good nitrifying activity, the acid filter material had to be neutralized by Ca(OH)2. The addition of nutrients (P, K, Mg+ and micronutrients) increased the capacity of the filter to oxidize ammonia to nitrate. The removal of ammonia was effective (mean removal rate 95 %) when initial concentrations were less than 14 mg NH3 m−3 (1.8 g NH3 m−3 peat per hour). The biofilter became overloaded at a concentration of 45 mg NH3 m−3 (7.9 g NH3 m−3 peat per hour), which caused an accumulation of ammonium and nitrite, as the ammonium inhibited oxidation of the nitrite. The biofilter operated properly down to a temperature of 5°C, and the amounts of bacteria and fungi released from biofilter into the filtered air were low.

Studies on kinetics of ammonia synthesis over ruthenium catalyst supported on active carbon

Abstract: The rate of ammonia synthesis was measured for ruthenium and iron catalysts under high (100 bar) and under atmospheric pressures. The effect of ammonia concentration in the gas phase on reaction rate was measured at 400, 430, and 470°C for p = 100bar at 370 and 400°C for p = 1bar . It was found that ruthenium is less sensitive than iron to the increase of ammonia pressure in the gas phase. It is also much less sensitive to changes in the total pressure (for p H 2 :p N 2 =const. ). At relatively high conversion degrees the ruthenium catalyst used was several times more active than the fused iron catalyst at 100 bar and 25–40 times more active under atmospheric pressure.

A historical record of ammonium concentrations from a glacier in the Alps

Abstract: Ammonia is the primary gaseous alkaline species in the atmosphere over Europe, neutralising up to 70% of the original acidity in precipitation [Buijsman et al., 1987]. It is directly involved in the conversion of sulphur dioxide and nitrogen oxides into the aerosol phase. Furthermore, ammonium contributes considerably to the nitrogen deposition and soil acidification which causes extensive changes in plant communities in many ecosystems [Moore, 1995; Rohde et al., 1995]. However, in Europe continuous long-term measurements of atmospheric ammonia or ammonium in precipitation are lacking. Here, we present a continuous, high-resolution record of ammonium in precipitation for the time period 1780 to 1980 deduced from an ice core recovered from a high-altitude glacier in the Alps. The ammonium level remained constant from 1780 to 1870 and increased afterwards by a factor of three. This trend shows that ammonia emissions in Europe have substantially increased in the last 100 years.

Effect of the clay mineral zeolite on ammonia inhibition of anaerobic thermophilic reactors treating cattle manure

Abstract: Addition of zeolite counteracted to some extent the inhibitory effect of ammonia during thermophilic anaerobic digestion of cattle manure. In continuously‐fed reactor experiments, addition of zeolite delayed the onset of the inhibition and aided process recovery after initial inhibition. The effect was observed mainly when the ammonia concentration was increased gradually, indicating that the major effect of zeolite was not through a direct antagonistic effect towards ammonia but through an increased process resistance to toxic compounds. In batch experiments zeolite had a similar stimulatory effect leading to a decreased lag phase and increased methane production rate in ammonia inhibited reactors.

Optical ammonia sensing films based on an immobilized metalloporphyrin

Abstract: Optical sensing films for ammonia gas have been developed by immobilizing zinc 5,10,15,20-tetraphenylporphine (ZnTPP) in silicone rubber. The detection of ammonia can be achieved using both absorbance and fluorescence emission measurements. Spectral changes were observed due to the coordination of NH3 molecules to the ZnII ion in the immobilized metalloporphyrin. Effects of other immobilization matrices on sensor properties were investigated. ZnTPP-silicone films were found to show a reasonably high sensitivity to ammonia, with a linear range of 0–6 mg m–3(0–8.5 ppm). The detection limit for ammonia in nitrogen was 0.5 mg m–3(0.7 ppm). The equilibrium response time of the films was approximately 4 min and the reaction with ammonia was reversible. ZnTPP films were also found to be sensitive to triethylamine.