Showing papers on "Chemical state published in 1976"

In situ experiments on the dissolved and colloidal state of iron in an acid bog lake1

Abstract: A sampler and an anaJytica1 and characterization scheme were developed to investigate the chemical and physical state of iron in a highly stained acid bog lake (North Gate Lake), Iron fractions were chemically separated by reactivity to bathophenanthroline (BPN) after specific digestion procedures. Physical separation by anaerobic in situ filtration (450 nm) and in situ dialysis (4.8 nm) resulted in three size classes: particulate, colloidal, and dissolved. Inorganic, nonreactive species of iron [e.g. Fe( OH)a] reprcscnt minor amomlts of the total iron in North Gate Lake, in contrast to lakes of pH 6-8. In situ radiochemical analyses revealed that colloidal reactive ferric iron predominates in the oxygenated epilimnion, while dialyzable or dissolved ferrous iron increases with depth. Unlike iron, organic matter is prcscnt in a nontransicnt colloidal state. In acid (pH 4-5) bog lakes ferric iron may be colloidal not as an inorganic complex (OH-) but as reactive Fe”’ by complexation with the colloidal organic acids. After thermally induced mixing with anaerobic waters, ferric iron is reduced and dissolved; however some of the BPN reactive iron remains colloidal, suggesting the presence of a residual ferrous organic complex. Inorganic iron may be present in the epilimnion of oxygenated lakes of pH 6-8 as Fe ( III) hydroxides in the form of tither a precipitate or a sol (Hutchinson 1957; Shapiro 1964). Shapiro (1964) showed that organic acids could hold iron in apparent solution above pH 5 as peptized ~01s. IIowever, at lower pH, ionization of organic acids decreases, the rate of oxidation of iron becomes indepedent of pH, and the solubility of all ionic forms of iron increases. Low pH, combined with low oxygen tensions and a reducing environment containing colloidal organic matter (COM), may permit large amounts of ionic iron to be present without inorganic (hydroxyl ion) complexation in bog lakes. In addition, the low ionic strength of bog lake water, as indicated by the low conductivity (20-30 pmhos cm-l at lS’C>, reduces the coagulation formation of particulate forms of iron. Under these conditions, solution size, oxidation state, and organic acid complexation of ferrous and ferric iron may be ’ Supported by U.S. Atomic Energy Commission contract AT( ll-l)-1771. a Present address: Environ. Sci. and Eng., Univ. North Carolina, Chapel IIill 27514. LIMNOLOGY AND OCEANOGlbWFIY 674 quite different from those in lakes of neutral or basic pI1. Low dissolved oxygen, high C02, low pH, and the presence of reducing organic and inorganic compounds all favor formation of ferrous iron. Decomposing organic residues ( including “humic acid”) can reduce ferric to ferrous iron or form ferrousorganic complexes ( Bloomfield 1952). Shapiro (1966) showed that colored organic acids could reduce ferric iron from natural waters, and IIem (1960) showed that tannic acid reduced ferric iron in artificial laboratory systems. Divalent sulfur compounds ( e.g. I12S) in lake waters can also reduce ferric iron ( Stumm and Morgan 1970). All the above are encountered in highly colored acid bog water (pI1 4-5) and tend to increase the solubility of iron by favoring the ferrous state. Bog lakes therefore present complex systems for measurement of the physical and chemical states of iron. Sampling and analytic al difficulties have created some uncertainties regarding the iron species at specific depths in the water column. My purpose here is to define more precisely the states of iron in acid bog lakes and to determine SEFTEMBEI2 1976, V. 21(5) Dissolved and colloidal iron 675 the in situ relationship of iron to COM in differentially oxygenated lake waters. I thank F. F. Hooper, J. Shapiro, J. W. McMahon, P. Kilham, and J. Elder for reviewing the manuscript. I also thank R. E. Gordon for use of the Notre Dame tract, and E. Baker for help in the iron analysis. Study area and methods The experiments were done in North Gate Lake, a small, highly colored, meromictic lake in Section 37 of T45N, R42W, Gogebic County, Michigan. It is one of many bog lakes on a 2,225 ha reserve owned by the University of Notre Dame, has a surface area of about 0.4 ha, and a maximum depth of 8 m. The open water is surrounded by a Sphagnum mat which extends into a black spruce forest. Measurements of the oxidation state and speciation of iron in lakes are difficult. The two oxidation states of iron and their various complexes may occur simultaneously at a given depth, both the oxidation state and coordination are very sensitive to dissolved oxygen, and the oxygen content of samples is easily altered during handling. Bathophenanthroline (BPN) was used to measure ferrous iron; it does not react with any other metal ion (including Fe3+). BPN gives a colored complex that can be extracted by n-hexyl alcohol at pH 4.0 to isolate the colored complex from its aqueous solution, increase sensitivity, and extend the specificity to the point where there is no known interference by either metal cations or common anions (Smith et al. 1952). The analytical scheme is shown in Fig. 1. All samples were duplicated and each digestion procedure contained a blank. Solutions were read in a Klett-Summerson calorimeter using the 4-cm cell. Standards were run with each experiment. Since Fe( II) is unstable in the presence of oxygen, samples are usually preserved at the time of collection. Preservation with acid accelerates the reduction of Fe( III) to Fe( II), releases iron from organic complexes, and dissolves inorganic ferrous salts (McMahon 1967; O’Connor et al. 1965). Thus, only total ferrous iron is measurable. Chemical characterization of iron (II) and (III)

Studies of MoO3–Al2O3 Catalyst in Ethylene Polymerization. III. The Nature of Mo(V) and Its Relation with Activity

Abstract: In order to determine the active center of ethylene polymerization over MoO3–Al2O3, the g-tensor and the amount of molybdenum(V) in each chemical state were determined by means of ESR measurement. The anisotropy of the g-tensor revealed the strength of the crystal field in the state; the decreasing order of the strengths was as follows: state(S)>state(M)>state(W)>MoO3–SiO2\fallingdotseqfree MoO3. In the state(S) molybdenum oxide is insoluble in aq.10M–NH3, in the state(M) it is soluble in aq. NH3 but insoluble in water, and in the state(W) it is soluble in water. The amount of molybdenum(V) in the state(W) was studied in connection with the activity, because only the state(W) was suitable for polymerization. The behavior of the activity was in fair agreement with that of the molybdenum(V) content in the state(W) and this content depedned on the amount of supported MoO3 and on the extent of reduction. The amount of molybdenum(V) in the state(W) corresponded to the amount of chemisorbed hydrogen, which was ...

Abstract: AES characterization of oxidized films of Mg, Al, and Si

Abstract: Chemical effects on Auger spectra have been studied for some time. Only recently, however, has it been shown that these effects can be used to study the ’’chemical structure’’ of interfaces by observing the rate of appearance of one chemical state and the rate of disappearance of another chemical state of an element during depth profiling.1–3 In this way, the simultaneous existence of different states of the same element can be observed. Percentages of the atoms in these different chemical states present at any position in the interface can be determined. Also, the chemical state of various elements present can be identified and changes mapped out through interfaces.Studies of the chemical structure of interfaces offer important information in the attempt to understand the behavior of interfaces in semiconductor devices. The characterization of these interfaces in Si and Al is of critical importance to LSI technology, particularly for MOS devices. The system which is of greatest interest in actual device ...

The chemical nature of the interface Ge-ZnSe heterojunctions: a study with molecular beam techniques

Abstract: The chemical interaction occurring between zinc selenide vapour and a (100) germanium surface has been investigated by a molecular beam technique. Two different chemical states of the germanium surface have been employed in the study of this interaction. In one state the germanium was prepared so as to produce a clean, restructured (100) germanium surface; in the other, the clean, restructured surface was covered with an adsorbed monolayer of oxygen. The method by which these surfaces were achieved is discussed and mass spectrometry is used to observe the reaction products by the interaction between the zinc selenide and the germanium surface.

Application of Electronic Spectroscopy to the Chemical Characterization of Iridium and Palladium Catalysts

Abstract: Publisher Summary This chapter presents results from an electronic (optical) spectroscopic study concerning the different stages of preparation of supported iridium and palladium catalysts obtained by either the exchange or the impregnation method. It deals with (1) the chemical state of the active element in the precursor solution, (2) the interaction between support and solution, (3) the nature of surface complexes after impregnation (or exchange) and drying, and (4) the chemical state of the active element after reduction. The interaction between support and solution may be considered from two points of view. According to some authors, an interaction is involved when the metal ion concentration in the solution decreases while immersing the carrier. The interaction is also effective if the chemical state and local environment of the metal ion on the carrier are different from those in the solid layer obtained after evaporation of the precursor solution on some definite inert surface.