Aging of Pyrotechnik Compositions. The investigation of chemical changes by IR spectroscopy and x-ray diffraction

The aging of tracers, containing different amounts of Mg, Sr(NO₃)₂, KClO₄, Al-Mg alloy and organic binder, was conducted under the conditions of 50.0% and 98.5% relative humidities at 75 °C, and of 98.5% relative humidity at 25 °C. IR spectroscopy and X-ray diffraction were used for investigation of chemical changes. At the lower humidity no detectable changes were observed. Tracer of metauoxidant ratio >1 exhibits decreased stability, changing significantly under the conditions of higher humidity, even at room temperature. In the reaction sequence of aging process (Mg(OH)₂) and SrCO₃ are formed, with concomitant decrease in Mg and Sr(NO₃)₂ content. Alloy changes only slightly, and the content of KClO₄ and binder remains unchanged. Interaction between metal and nitrate is considered to be essential in the process of chemical aging.     

Influence of precursors of Li2O and MgO on surface and catalytic properties of Li‐promoted MgO in oxidative coupling of methane

The influence of the catalyst precursors (for Li₂O and MgO) used in the preparation of Li‐doped MgO (Li/Mg = 0.1) on its surface properties (viz basicity, CO₂ content and surface area) and activity/selectivity in the oxidative coupling of methane (OCM) process at 650–750 °C (CH₄/O₂ feed ratio = 3.0–8.0 and space velocity = 5140–20550 cm³ g⁻¹ h⁻¹) has been investigated. The surface and catalytic properties are found to be strongly affected by the precursor for Li₂O (viz lithium nitrate, lithium ethanoate and lithium carbonate) and MgO (viz magnesium nitrate, magnesium hydroxide prepared by different methods, magnesium carbonate, magnesium oxide and magnesium ethanoate). Among the Li–MgO (Li/MgO = 0.1) catalysts, the Li–MgO catalyst prepared using lithium carbonate and magnesium hydroxide (prepared by the precipitation from magnesium sulfate by ammonia solution) and lithium ethanoate and magnesium acetate shows high surface area and basicity, respectively. The catalysts prepared using lithium ethanoate and magnesium ethanoate, and lithium nitrate and magnesium nitrate have very high and almost no CO₂ contents, respectively. The catalysts prepared using lithium ethanoate or carbonate as precursor for Li₂O, and magnesium carbonate or ethanoate, as precursor for MgO, showed a good and comparable performance in the OCM process. The performance of the other catalysts was inferior. No direct relationship between the basicity of Li‐doped MgO or surface area and its catalytic activity/selectivity in the OCM process was, however, observed. © 2000 Society of Chemical Industry     

Denitrification in shallow groundwater in a coastal agricultural area in Japan

In a coastal agricultural area in the central part of Japan (Shizuoka), we found decreasing nitrate concentration with depth in a shallow groundwater, where the depth to water table varied between 0.6 and 1.2 m below ground surface. High nitrate concentrations (5–29 mg N L^–1) were often observed in the upper layer (0–2 m) of the groundwater, but the concentration decreased to less than 1 mg N L^–1 in the deeper layer. Ammonium was scarcely detected, and the concentration of dissolved oxygen was usually low (< 1 mgO₂ L^–1) in the groundwater. Nitrate in the groundwater often had very heavy nitrogen stable isotope ratios (>20{}). There was a negative relationship between nitrogen stable isotope ratio of nitrate and its concentration. When nitrate was injected into the groundwater with acetylene and bromide (a conservative tracer), nitrate concentration decreased to 20% of the initial level within 5 days, accompanied by the increase in nitrite and nitrous oxide concentration and a little change in bromide concentration. These results indicate that microbial denitrification plays a potential role in the decrease of nitrate in shallow groundwater at the study site.     

Electrochemical reduction of nitrates and nitrites in alkaline nuclear waste solutions

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.     

三元硝酸熔盐高温热稳定性实验研究与机理分析

通过熔盐质量损失率和试样中NO2-含量变化状况,以及熔盐材料的热重(TG)曲线,研究了三元硝酸熔盐(53%KNO3-40%NaNO2-7%NaNO3)在空气和氮气气氛中高温条件下的热稳定性性能。结果表明,三元硝酸熔盐空气中的上限使用温度为773K,高温时存在劣化现象;而在氮气气氛中三元熔盐的热分解温度为723K。同时,从热力学和动力学角度分析得到,三元硝酸熔盐在773K以下空气中发生的反应为亚硝酸钠的分解和氧化;而在氮气气氛中三元熔盐723K以下时主要发生的是亚硝酸钠的分解反应。在氧气含量一定的情况下,氧气的扩散和亚硝酸盐的分解反应符合一级反应动力学模型。     

Comparison of different synthesis routes for Mg–Al layered double hydroxides (LDH): Characterization of the structural phases and anion exchange properties

Nitrate forms of layered double hydroxides (LDHs) were synthesized based on the co-precipitation method under different synthesis conditions (aqueous ammonia solution or potassium hydroxide to control the pH of the solution; magnesium to aluminium ratios of 2:1 and 5:1). In a second step the lab procedure was up-scaled to pilot plant scale. The effects of the synthesis conditions on the structural and textural properties as well as on the anion exchange of the LDH products were investigated using different methods to evaluate the suitability as a soil conditioner. Using a Mg:Al ratio of 2:1 resulted in higher basal spacings compared to a Mg:Al ratio of 5:1, while the type of pH-controlling solution had no effect. Based on nitrogen adsorption isotherms the specific surface area of pores was calculated. The highest values for specific surface areas were found for LDHs synthesized using KOH at a Mg:Al ratio of 5:1. These products had a lower total nitrate adsorption capacity compared to LDHs synthesized at a lower Mg:Al ratio. However, nitrate exchangeability by counter anions for LDHs synthesized using KOH at a Mg:Al ratio 5:1 differed significantly (HCO₃⁻ > Cl⁻ > SO₄²⁻) indicating that these LDHs are preferable under a multi-anionic environment like the soil solution.     

好氧反硝化菌BN5降解苯酚的特性研究

研究了异养硝化-好氧反硝化菌Pseudomonas sp.BN5去除硝态氮同时降解苯酚的特性。研究表明,当pH=7,转速为180 r/min时,该菌株对420 mg/L苯酚的降解率达100%,对40 mg/L硝态氮的降解率达93.31%。随培养基内苯酚浓度的升高,最终细胞浓度上升,硝酸还原酶和亚硝酸还原酶酶活逐渐降低,且亚硝酸还原酶受抑制较大。氮平衡分析显示,消耗的硝态氮中有54.6%转化为胞内氮,39.4%以含氮气体的形式被去除,表明菌株主要通过好氧反硝化作用和细胞同化作用脱氮。     

Effect of the new nitrification inhibitor DMPP in comparison to DCD on nitrous oxide (N2O) emissions and methane (CH4) oxidation during 3 years of repeated applications in field experiments

In a 3-year field experiment the effect of the new nitrification inhibitor DMPP (3,4-dimethyl pyrazole phosphate, trade name ENTEC) on the release of N₂O and on methane oxidation was examined in comparison to dicyandiamide (DCD). Soil samples were analysed for the concentrations of ammonium, nitrite, nitrate and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N₂O by 41% (1997), 47% (1998) and 53% (1999) (with an average of 49%) while DCD reduced N₂O emissions by 30% (1997), 22% (1998) and 29% (1999) (with an average of 26%), respectively. Both nitrification inhibitors (NI) failed to affect methane oxidation negatively. The plots that received DCD or DMPP, respectively, even seem to function as enhanced sinks for atmospheric methane. DMPP apparently stimulated methane oxidation by ca. 28% in comparison to the control. The concentrations of ammonium remained unaffected by nitrification inhibitors whereas the amounts of nitrite diminished in the plots treated with DCD by 25% and with DMPP by 20%, respectively. Nitrate concentrations in soil were in both NI treatments 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. Dicyandiamide was mineralized more rapidly than DMPP (data for the cropping season in 1997 as an example). This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of Yttria Nanopowders by Two Precipitation Methods and Investigation of Synthesis Conditions

Yttrium oxide nanopowder was successfully synthesized by two precipitation methods, through which Y₂O₃ nanopowder was prepared by ammonium hydroxide and ammonium hydrogen carbonate as precipitants. Hydroxide and carbonate precursors of Y₂O₃ with approximate composition of Y(OH)₃ and Y₂(CO₃)₃, respectively, were synthesized using yttrium nitrate as the starting salt. XRD results show cubic yttrium oxide phase for annealed samples. SEM and TEM images show that samples are composed of agglomerated and nonagglomerated nanoparticles with different shapes and sizes. Optimal conditions for synthesis of nanoparticles were defined as 3‐h aging time, ammonium hydrogen carbonate as precipitant, and calcination temperature of 1000°C.     

Disposal of Energetic Materials by Alkaline Pressure Hydrolysis and combined techniques

Due to the reduction of armament and especially due to the German reunification we are met by the objective of the disposal of energetic materials. Environmentally friendly disposal methods available for the different propellants, explosives and pyrotechnics are urgently needed. The main component of gun and rocket propellants is the energetic polymer nitrocellulose. One method to dispose nitrocellulose containing propellants is the combination of rapid chemical destruction by pressure hydrolysis and the biological degradation of the reaction mixture. The study describes the results of pressure hydrolysis of different gun and rocket propellants. Under alkaline conditions (propellant to NaOH ratio 2.3:1; reaction temperature 150 °C; pressure below 30 bar) biological degradable reaction products were formed. The main products in the liquid phase were simple mono- and dicarboxylic acids. Dependent on the reaction conditions 30–50 % of the nitrogen content of the propellants was transformed to nitrite and nitrate. The gaseous nitrogen containing products were N₂ (16–46 %), N₂O (2–23 %), NO_x (0–5 %). Overall 40%–60% of the propellant nitrogen was transformed to gaseous products. In the solid residues a nitrogen content between 2 % and 9 % was found. The residues were mostly due to additives used in propellant manufacturing. In the case of nitrocellulose pressure hydrolysis below 30 bar and reaction temperature about 150 °C are sufficient.     

Preparation of GdBa2Cu3O6+x (GdBCO) precursor powder by spray-drying a nitrate solution containing PEG

Several precursor powders, obtained after precipitation from metal nitrate solution containing polyethylene glycol (PEG) (inside a Pyrex glass reactor or by spray-drying), and their thermal evolution to GdBa₂Cu₃O_6+x (GdBCO) were analyzed by thermogravimetry, differential thermal analysis, Fourier-transform infrared spectroscopy, and X-ray diffraction. The amount of PEG had a crucial role in the BaCO₃ content of the “Kjeldahl precursors,” but a minor effect on the degree of transformation to GdBCO at 900°C, which did not reach completion after 1 hour. In contrast, a low-PEG spray-dried powder led to almost 100% GdBCO in only 5 minutes. The high degree of cation dispersion reached by spray-drying and the coexistence with a liquid phase can explain this short reaction time. The spray-dried powder compares favorably with the mechanical mix of metal oxides and Ba carbonate that is commonly used as precursor powder for the synthesis following a solid-state reaction.     

Mg-Al hydrotalcite coating on zeolites for improved carbon dioxide adsorption

Hydrotalcite was synthesized by co-precipitation using metal nitrate precursor and potassium carbonate with Mg:Al ratio of 3:1. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and nitrogen adsorption/desorption. The surface morphology and chemical composition were characterized by scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Characterization of hydrotalcite reveals that hydrotalcite prepared in this work exhibited a type II isotherm which is typical of mesoporous and slit shape pore materials. The hydrotalcite structures demonstrated higher degree of crystallinity when thermally treated at 700 °C. Carbon dioxide adsorption was conducted using adsorption unit and the result showed an increase of CO₂ adsorption when hydrotalcite was coated on commercial zeolites.     

好氧聚磷污泥反硝化除磷特性研究

以培养成功的好氧聚磷污泥为研究对象,考察其在硝酸盐或亚硝酸盐存在下的反硝化除磷特性。结果表明,好氧聚磷污泥在在未经厌氧/缺氧驯化条件下已具有良好反硝化聚磷特性。好氧聚磷污泥可利用硝酸盐作为电子受体进行脱氮除磷,在硝酸盐耗尽后停止聚磷,在一定的浓度范围内聚磷量与硝酸盐消耗量具有线性关系。在以亚硝酸盐作为电子受体的条件下,好氧聚磷污泥与反硝化聚磷污泥具有相似特点:在初始亚硝酸盐浓度较低情况下可少量聚磷,在其浓度较高时聚磷受到抑制。亚硝酸盐有可能为解偶联剂,在其还原的过程中并不耦合发生聚磷。反硝化速率随着其硝酸盐或亚硝酸盐初始浓度的升高而降低。     

Basic magnesium carbonate flame retardants for polypropylene

Magnesium hydroxide and magnesium carbonates have attracted attention as endothermic flame retardants that are sufficiently stable to be incorporated into thermoplastics without decomposition. In this survey, a basic form of magnesium carbonate, magnesium carbonate hydroxide pentahydrate [(MgCO₃)₄ · Mg(OH)₂ · 5H₂O] was evaluated as a flame retardant for polypropylene. This filler (MCHP) has a thermal stability intermediate between that of alumina trihydrate (ATH) and magnesium hydroxide, which is sufficient to allow incorporation into polypropylene without decomposition. The MCHP is most effective at high filler concentrations near 60% where it was found to impart a Limiting Oxygen Index of 28.2 with a V-O rating (no dripping). This is slightly more effective than the flammability ratings for ATH and Mg(OH)₂ under the same conditions. The effectiveness of MCHP was attributed to the large endothermic loss of water of hydration, which also dilutes the combustion gases. This action was further aided by the formation of an intumescent char on the burning surface, which eventually extinguished the flame. Various combinations of magnesium oxide, magnesium hydroxide, magnesium carbonate, and MCHP were evaluated in order to clarify the mechanism of the flame retardant and improve the efficiency of the protective action. However, no synergism was evident, and the flame retardant results were found to be additive. The mechanical properties and processabilities of these highly filled compounds are very sensitive to the type of surface treatment. The method of Savides was employed to compare the burning temperature of the test specimens and to measure the rates of combustion.     

The effect of nitrogenous fertilizers on the nitrification of forest soils

The effect of fertilization with urea and ammonium nitrate on nitrogen mineralization was studied in a series of laboratory incubation experiments. The samples (humus layer) were collected from field experiments with different applications of fertilizers during a period of 11–14 years. The nitrogen fertilization influenced some chemical properties of the humus layer such as pH, N-Kjeldahl content and the content of inorganic nitrogen, especially in the samples from North Sweden. Nitrate nitrogen was formed in humus samples classified as non-nitrifying in several cases, usually after urea fertilization.     

Efficient electrochemical reduction of nitrate to nitrogen on tin cathode at very high cathodic potentials

The electrochemical reduction of nitrate on tin cathode at very high cathodic potentials was studied in 0.1 M K₂SO₄, 0.05 M KNO₃ electrolyte. A high rate of nitrate reduction (0.206 mmol min⁻¹ cm⁻²) and a high selectivity (%S) of nitrogen (92%) was obtained at −2.9 V versus Ag/AgCl. The main by-products were ammonia (8%) and nitrite (<0.02%). Small amounts of N₂O and traces of NO were also detected.As the cathodic potential increases, the %S of nitrogen increases, while that of ammonia displays a maximum at −2.2 V. The %S of nitrite decreases from 65% at −1.8 V to <0.02% at −2.4 V. The kinetic analysis indicated that the formation of nitrogen and ammonia proceeds through the intermediate nitrite.The reduction follows first order kinetics for both nitrate and nitrite at more cathodic potentials than −2.4 V, while at less negative potentials the kinetics is more complicated.The %Faradaic efficiency (%FE) of the reduction at −2.9 V was about 60% initially and decreased to 22% at 40 min.A cathodic corrosion of tin was observed, which was more intensive in the absence of nitrate. At potentials more negative than −2.4 V, small amounts of tin hydride were detected.     

Electrochemical reduction of nitrogen oxyanions in 1 M sodium hydroxide solutions at silver,copper and CuInSe2 electrodes

The reduction of nitrate and nitrite ions was studied in 1m NaOH supporting electrolyte. Voltammetric investigations show that, on silver cathodes, nitrate reduction begins at potentials about 500 mV more positive than nitrite reduction, the latter being superimposed on hydrogen evolution. Electrolyses of nitrate solutions at –1.4V/sce give nitrite with good selectivity. On copper cathodes, nitrate and nitrite reductions occur in the same region of potentials and show similar voltammetric profiles. The dominant product of nitrite reduction is ammonia, whereas nitrate may be reduced to nitrite at –1.1 V/sce and to ammonia with high yields at –1.4 V/sce. Reduction of nitrogen oxyanions may also be performed on CuInSe₂ (photo)cathodes. Photoassisted reductions of nitrate performed on p-CuInSe₂ at –1.4 V/sce gave mixtures of ammonia, nitrite and hydrogen.     

Phase structure and electrochemical properties of Ml1?xMgxNi2.78Co0.50Mn0.11Al0.11 hydrogen storage alloys

The effect of magnesium content on the phase structure and electrochemical properties of Ml_1−x Mg _x Ni_2.78Co_0.50Mn_0.11Al_0.11 (x = 0.05, 0.10, 0.20, 0.30) hydrogen storage alloys was investigated. The results of X-ray diffraction reveal that all the alloys consist of the major phase (La, Mg)Ni₃ and the secondary phase LaNi₅. With increase in x, the relative content of the (La, Mg)Ni₃ phase increases gradually, and the maximum capacity and low temperature dischargeability of the alloy electrodes first increase and then decrease. When x is 0.20, the discharge capacity of the alloy electrode reaches 363 mAh g⁻¹ at 293 K and 216 mAh g⁻¹ at 233 K, respectively. The high rate dischargeability of the alloy electrodes increases with increase in x. When the discharge current density is 1200 mA g⁻¹, the high rate dischargeability of the alloy electrodes increases from 22.0% to 50.4% with x increasing from 0.05 to 0.30. The cycling stability of the electrodes decreases gradually with increase in magnesium content.     

Catalytic denitrification of water with palladium-based catalysts supported on activated carbons

The performance of carbon-supported, Pd bimetallic catalysts for nitrate reduction has been investigated. Pd–In and Pd–Sn catalysts have been tested for a range of nitrate concentration up to 1000 ppm in acidic and close to neutral pH. Pd–Cu was also studied at pH 5 for reference. Nitrate reduction was inhibited strongly by nitrite and moderately by sulphate. Activated carbon catalysts are shown to display an activity similar to metal oxide supported catalysts.     

Ammonia,Nitrite and Nitrate Nitrogen Removal from Polluted Source Water with Ozonation and BAC Processes

Studies on the removal of ammonia-, nitrite-, and nitrate nitrogen with ozonation (O₃), sand filtration (SF), biological activated carbon (BAC), SF-BAC, and/or O₃-BAC processes were carried out in two pilot plants and a full scale plant, respectively. The results showed that all of the tested processes exhibited certain nitrogen removal efficiencies, of which both the O₃-SF-BAC and O₃-BAC processes were most effective and efficient in removing ammonia nitrogen, with mean removal efficiencies of some 90 and 80 percent, respectively.

Ozonation was found able to oxidize some organic nitrogen into ammonia, and nitrite ion into nitrate ion. It was also found out, with interest, that the O₃-BAC process can carry the nitrification process to the end under sufficient DO content, as well as more hydrocarbon substrates through ozonation that are more easily assimilated by some strains of nitrobacter that can multiply heterotrophically in its carbon beds. In the BAC process, both the DO and easily assimilated substrate contents were too low in its carbon beds due to no ozonation to sustain nitrobacter growth; but the nitrite conversion bacteria, like nitrosornas, can survive under such conditions. As a result, nitrite or nitrate ion content increased multiply in the effluents from BAC or O₃-BAC processes over their influents. respectively.

The removal mechanisms of various processes for the three forms of nitrogen were studied and discussed, and the optimum design parameters were determined as well.