Mercury determination by CV-AAS in wastewater and sewage sludge from a stabilization pond system

The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110° C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 ± 0.75 gl^–1 have been found at the entrance of the system and 0.74 ± 0.0 gl^–1 at the exit, while in sludge the results were between 0.29 ± 0.12 gkg^–1 in the facultative pond and 0.04 ± 0.02 gkg^–1 in the second maturation pond (exit).     

Determination of oxygen by deuteron-induced PIPPS

Using the 871-keV¹⁶O p/1,0/ prompt -ray, oxygen was determined with a relative precision of ±3.8% at a concentration level of 120 g g^–1. The sensitivity of the method is below 10 g g^–1. 50 nm oxide layers on silicon wafers can be determined with a relative precision of 10%. A chamber for transporting targets sensitive to atmospheric gases and humidity is described.     

NAA,GC(EC) and SRXRF study of Hg species in head hair of mothers and their newborn infants

Twenty-seven pairs of head hair from mothers and their new-born infants were collected at the time of delivery in a hospital in Beijing. The total mercury content in the hair samples was determined by INAA. The correlation between mercury content in hair of mothers and their new-born infants has been investigated. In addition, the change of Hg content in pregnant women's hair during their pregnancy was also studied by INAA and SRXRF. The results indicate a significant positive correlation between the mercury content in maternal and infant head hairs (r=+0.862, p<0.001). The average content of Hg in infant and maternal hairs was 0.66±0.31 g/g and 0.59±0.25 g/g, respectively. The infant level exceeded the maternal by 12%. The Hg content in maternal head hair gradually reduced during pregnancy. Further, the methylmercury (Me–Hg) content in 3 maternal hair samples was analyzed by GC(EC). The Me–Hg was in accordance with the total mercury content. Thus a conclusion can be drawn that damage to the infant from Hg occurred in the early stages of pregnancy.This project is funded by the International Atomic Energy Agency (Contract No. 6332/RI/RB) and the Chinese National Natural Science Foundation (Contract No. 19392100)     

Structural and thermal studies on sisal fibre

Mechanical characteristics of sisal fibre, such as UTS and Young's modulus, have been determined. The thermal degradation of sisal fibre has been observed by running its DSC and TG/DTG.

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Zusammenfassung Die mechanischen Kennwerte (UTS, Young's Modul) von Sisalfasern wurden bestimmt. Der thermische Abbau von Sisalfasern wurde mittels DSC und TG/DTG untersucht.

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The authors wish to thank Dr. R. K. Tiwari, Dr. S. V. Prasad and Dr. M. Patel for their useful suggestions.     

Acid-base strength of Cl? containing aluminate aluminas with low Na+ contamination

Aluminas with Brönsted acid sites of H_r<-–6.63, containing Cl^–, after rehydration and drying show only reduced acidity (H_R<-0.82, H_a<-–3.0). All freshly calcined catalysts give a color with phenolphthalein (Ph).

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Al₂O₃, Cl^– H_R=<-6,63, H_R<-+0,82 H_a<-–3,0. Al₃O₃ .

     

Study of reversible proton transfer from 2,2,2-trifluoronitroethane to amines by dynamic1H and19F NMR

The interaction between the weak CH-acid CF₃CH₂NO₂ and aliphatic amines has been studied by NMR in CDCl₃ and CFCl₃ solutions. It is shown that no measurable amounts of H-bonded complexes are formed. However, reversible proton transfer with the formation of ion pairs takes place. The kinetic parameters of this process have been determined.

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CH- CF₃CH₂NO₂ CDCl₃ CFCl₃. , , . .

     

Unsteady-state performance of NOx catalytic reduction by NH3

Experimental results of studying NO_x catalytic reduction by NH₃ under periodic reversals in the direction of filtration of the mixture purified in a catalyst bed are discussed.

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NO_x .

     

Kinetics and mechanism of aniline hydroxylation by cumene hydroperoxide in the presence of catalase

In a phosphate buffer with pH=7.4 at 20°C the kinetics of aniline hydroxylation to p-aminophenol by the catalase-cumene hydroperoxide system has been studied. The reaction mechanism of this system is discussed.

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20°C pH 7,4 - . .

     

Fluorinated hydrotreatment catalysts: Promotion of the catalytic activity of unsupported MoS2 by doping with F? ions

Influence of fluorination on the HDS activity of unsupported MoS₂ phase has been studied and correlated with the influence of fluoride on the CoMo and NiMo catalysts supported on -Al₂O₃.

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MoS₂ . CoMo NiMo, -Al₂O₃.

     

Application de la thermogravimetrie,de l'analyse thermique differentielle et de la spectrographie d'absorption infrarouge a l'etude de la reaction entre l'oxyde de chrome-III et les nitrates alcalins,I

Résumé On a étudié la réaction à l'état solide et fondu entre l'oxyde de chrome trivalent et les nitrates alcalins par analyse thermogravimétrique et analyse thermique différentielle. Les conditions optimales pour l'oxydation complète du chrome(III) en chrome(VI) ont été déterminées. De plus, on a établi le rendement de la réaction. La spectrophotométrie d'absorption infrarouge a permis d'identifier les phases formées aux divers stades de la réaction.

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The reaction between trivalent chromium and alkali nitrates in the solid and molten phase was studied by thermogravimetry and differential thermal analysis. The optimum conditions for the oxidation Cr(III) Cr(IV) as well as the yield were determined. The phases existing at various reaction stages were identified by infrared spectroscopy.

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Zusammenfassung Die Reaktion in fester sowie in geschmolzener Phase zwischen dreiwertigem Chrom und Alkalinitraten wurde thermogravimetrisch und differential-thermoanalytisch geprüft. Die optimalen Umstände der Oxydation Cr(III) Cr(VI) sowie die Reaktionsausbeute wurden bestimmt. Durch infrarote Spektroskopie wurden die in verschiedenen Reaktionszeitpunkten vorliegenden Phasen identifiziert.

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() () . Cr(III) Cr(IV) . .

     

Kinetics of thermal decomposition of MCO3 to MO (M=Ca,Sr and Ba)

The kinetics of the thermal decompositions of CaCO₃, SrCO₃ and BaCO₃ into their oxides were studied by thermogravimetry at constant and linearly increasing temperatures. The kinetics of the isothermal decompositions of calcium and strontium carbonates were described by the lawR _n =1–(1–)^1/n , wheren=1.8 and 1.2, respectively. The kinetics of the non-isothermal decompositions of the two carbonates, analysed by the Ozawa and Coats-Redfern methods, were in keeping with the isothermal kinetics. True kinetic compensation laws were established for each decomposition of the two carbonates, including the data under both isothermal and non-isothermal conditions.As concerns the decompositions of BaCO₃, however, there was some difference between the kinetic features relating the isothermal and non-isothermal conditions. A true kinetic compensation law was not established in this case.

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Zusammenfassung Die Kinetik der thermischen Zersetzung von CaCO₃, SrCO₃ und BaCO₃ zu den Oxiden wurden durch Thermogravimetrie bei konstanter und linear ansteigender Temperatur untersucht. Die Kinetik der isothermen Zersetzung von Calcium- und Strontium-carbonat folgt dem GesetzR _n =1–(1 –)^1/n, won=1,8 bzw. 1,2. Die Kinetik der nichtisothermen nach den Methoden von Ozawa und Coats-Redfern analysierten Zersetzung der zwei Carbonate ist in Übereinstimmung mit der isothermen Zersetzung. Wahre kinetische Kompensationsgesetze wurden für die Zersetzung der beiden Carbonate erhalten, einschließlich der sich sowohl auf isotherme als auch auf nichtisotherme Bedingungen beziehenden Daten. Was die Zersetzung von Bariumcarbonat betrifft, so wurden einige Unterschiede im kinetischen Verhalten bei der Zersetzung unter isothermen und nichtisothermen Bedingungen festgestellt. Ein wahres kinetisches Kompensationsgesetz konnte in diesem Falle nicht ermittelt werden.

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, . R _n =1–(1–)^1/n , , , 1,8 1,2. , -, . « » , . , , . - «» .

     

Thermal decomposition of Y,La and light lanthanide ferulates

The conditions of thermal decomposition of Y, La and light lanthanide ferulates have been studied. On heating, these complexes decomposed in various ways; lanthanum ferulate in four stages, Ce(III) ferulate in three stages, and the ferulates of Y, Pr(III), Nd, Sm, Eu(III) and Gd in two stages, the oxides finally being formed. The complexes lose crystallization water to form anhydrous or hydrated salts, and are then decomposed directly to oxides. Only lanthanum ferulate decomposes to the oxide with intermediate formation of La₂O₂CO₃. The temperatures of oxide formation change periodically with the decrease in the ionic potential in the lanthanide series.

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Zusammenfassung Es wurden die Bedingungen der Zersetzung der Y-, La- und leichten Lanthanidferulate untersucht. Die erhaltenen Komplexe werden beim Erhitzen auf verschiedene Weise zersetzt. Lanthanferulat wird über vier, Ce(III)-Ferulat über drei und die Ferulate von Y, Pr(III), Nd, Sm, Eu(III) und Gd über zwei Zwischenstufen in das entsprechende Oxid überführt. Aus den Komplexen entstehen zunächst unter Verlust von Kristallwasser wasserfreie oder hydratisierte Salze, die dann direkt zu den Oxiden abgebaut werden. Nur Lanthanferulat wird über eine intermediäre Verbindung des Typs M₂O₂CO₃ zum Oxid abgebaut. Die Bildungstemperaturen der Oxide ändern sich periodisch mit abnehmenden Ionenpotential in der Lanthanidenreihe.

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Y, La . . , — , Y, (III) Nd, Sm,Eu(III) Gd — . , , . L₂₂₃. .

     

FTIR investigation of the structure of vanadium oxides on ZrO2 and oxidation of toluene on it

The oxidation of toluene has been studied on V₂O₅/ZrO₂ by both FTIR spectroscopy and pulse method. The results suggest that Lewis-acidic sites play a significant role in the formation of benzaldehyde from toluene.

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V₂O₅/ZrO₂ - , . .

     

Changes in iron oxidation state and surface composition of iron-chromium catalyst reduced by hydrogen

X-ray photoelectron spectroscopic studies of the reduction of iron-chromium catalysts have been carried out to determine changes in the relative surface concentrations of iron(II) and (III) oxides and metallic iron and in its surface composition at 100–500°C.

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(II), (III) 100–500°C. .

     

Methods for characterization and their influence on the structure of silicon-rich zeolites

H, Li, Na, Cs, NH₄, Mg and Al-ZSM 5 zeolites and H and NH₄-mordenites were studied by DTA, X-ray diffraction, TPD and adsorption measurements. The stability relating to dealumination and structure destruction depends on the nature of the cation.H and NH₄-ZSM 5 were strongly dealuminated to silicalitelike phases in the temperature range 973–1273 K during the course of the DTA measurement. NH₄-mordenite was dealuminated below 873 K in the TPD experiment on the deammonization.The thermal destruction of ZSM 5 containing Na⁺, Mg²⁺, Al³⁺ and Cs⁺ ions begins at about 1400 K. Excess sodium ions present in the original Na-ZSM 5 decreased the thermal stability. For H and NH₄-mordenites, complete amorphization was found at 1270 K.

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Zusammenfassung H-, Li-, Na-, Cs-, NH₄-, Mg- und Al-Zeolithe ZSM 5 sowie H- und NH₄-Mordenit wurden durch DTA, Röntgenbeugung, temperaturprogrammierte Desorption (TPD) und Adsorptionsmessungen untersucht. Die Stabilität gegenüber Dealuminierung und Strukturzusammenbruch hängt von der Art des Kations ab. H- und NH₄-ZS_M 5 werden im Verlauf der DTA-Messungen im Bereich 973–1273 K zu Silicalit-ähnlichen Phasen dealuminiert. NH4-Mordenit wird unterhalb 873 K bei der Ammoniakabspaltung im TPD-Experiment dealuminiert. Der thermische Zusammenbruch von Na-, Mg-, Al- und Cs-ZSM 5 beginnt um 1400 K. Im ursprünglichen NaZSM 5 vorhandene überschüssige Natriumionen verringern seine thermische Stabilität. Für H- und NH4-Mordenit wird bei 1270 K vollständige Amorphisierung gefunden.

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,. H, Li, Na, Cs, NH4, Mg, Al ZSM 5 -, N4- . . , - NH4-ZSM 5 973–1273 . , NH4 873 . ZSM 5 , , , , 1400 . NaZSM 5 . /N4- 1270 .

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Critical parameters affecting dynamic mechanical analysis using a du Pont 981 analyser

The parameters affecting Young's modulus and the glass transition temperature have been investigated. Sample dimensions as well as the sample clamping have been shown to be critical. For analysis at non-ambient temperatures the gas flow rate as well as the position of the sample thermocouple, are also important.

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Zusammenfassung Es wurden die den Young Modulus und die Glasübergangstemperatur beeinflussenden Parameter untersucht. Die Probengröße und die Packungsdichte der Probe erwiesen sich als kritisch. Für Analysen oberhalb der Raumtemperatur sind die Geschwindigkeit der Gasströmung und die Lage des Thermoelements in der Probe besonders wichtig.

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We wish to thank the South African C. S. I. R. for financial assistance.     

Calculation of rates for the various routes of complex reactions

Methods of the numerical calculation of rates for the routes of complex reactions have been investigated.

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Transverse photothermal deflection spectroscopy (PDS) applied to thermal diffusiyity measurements

Transverse photothermal deflection spectroscopy(PDS) is applied for the determination of thermal diffusivities of solid surfaces. The theory of PDS is briefly recalled and some approximated analytical formulae concerning the transverse configuration are derived. In materials where the thermal diffusivity is smaller than that of the air, the dependence of the deflection angle on the displacement between pump and probe beams is shown to have a minimum that relates to the thermal diffusivity, thereby allowing its straightforward measurement. Measurements carried out on Al₂O₃ samples with different porosities at room temperature show a good agreement between experiment and theory.

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Zusammenfassung Die transverse photothermische Reflektionsspektroskopie (PDS) wird zur Bestimmung der thermischen Diffusivität von festen Oberflächen herangezogen. Die Theorie der PDS wird kurz dargelegt und einige sich auf die transverse Konfiguration beziehenden analytischen Näherungsgleichungen abgeleitet. Es wird gezeigt, daß bei Materialien mit kleinerer thermischer Diffusivität als Luft die Abhängigkeit des Deflektionswinkels von der Ablenkung zwischen Pumpen- und Probenstrahl ein Minimum aufweist, das mit der thermischen Diffusivität im Zusammenhang steht und somit deren zuverlässige Messung ermöglicht. An Al₂O₃-Proben unterschiedlicher Porosität bei Raumtemperatur ausgeführte Messungen zeigen gute Übereinstimmung von Experiment und Theorie.

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. , . , , , , . , , .