Boehmite (γ-AlOOH) and gibbsite (α-Al(OH) 3 ) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications. Developing the ability to understand and predict the properties and characteristics of these materials, on the basis of their natural growth or synthesis pathways, is an important 1 fundamental science enterprise with wide ranging impacts. The present study describes bulk and surface characteristics of these novel materials in comprehensive detail, using a collectively-sophisticated set of experimental capabilities, including a range of conventional laboratory solids analyses and national user facility analyses such as synchrotron X-ray absorption and scattering spectroscopies, as well as small angle neutron scattering. Their thermal stability is investigated using in situ temperature-dependent Raman spectroscopy. These pure and effectively defect-free materials are ideal for synthesis of advanced alumina products.
X-ray absorption near-edge structure (XANES) has been applied to the quantitative analysis of chromate (CrO«* 12 3') content in oxides, silicate glasses, and simulated cementitous waste forms. The method uses the normalized area of a pre-edge peak (bound-state transition) in XANES spectra acquired with the synchrotron X-ray microprobe on beam line X26A at the National Synchrotron Light Source. The estimated accuracy of the technique is ± 5% in terms of Cr6+/total Cr. The minimum detection limit approaches 10 ppm Cr64" using a 150-µ synchrotron X-ray beam. These results demonstrate the value of synchrotron-based mi-croXANES for the nondestructive quantification of the first-row transition metal species present as tetrahedral oxyanions.
The chemistry of technetium in cement waste forms has been studied with x-ray absorption fine structure (XAFS) spectroscopy. Using the Tc K-edge x-ray absorption near-edge structure (XANES) as a probe of the technetium speciation, our results show that partial reduction of the pertechnetate ion, Tc04-, takes place in the presence of the cement additive, blast furnace slag (BFS). The addition of the reducing agents FeS, Na2S, and NaH2P02 produces more extensive reduction of Tc04-, while the compounds FeO, Fe304, and Mn304 are observed to be unreactive. The extended x-ray absorption fine structure (EXAFS) data for the BFS, Na2S, and FeS treated cements indicate the presence of Tc clusters possessing first shell S coordination. For the Na2S and FeS additives, Te-Te interactions are detected in the EXAFS demonstrating an extended structure similar to that ofTcS2. The EXAFS spectrum of the NaH2P02 treated cement reveals Te-O and Te-Te interactions that resemble those found in the structure ofTc02.
Humic substances are ubiquitous in the environment, occurring in all soils, waters, and sediments of the ecosphere. Humic substances arise from the decomposition of plant and animal tissues yet are more stable than their precursors. Their size, molecular weight, elemental composition, structure, and the number and position of functional groups vary, depending on the origin and age of the material. Humic and fulvic substances have been studied extensively for more than 200 years; however, much remains unknown regarding their structure and properties.Humic substances are those organic compounds found in the environment that cannot be classified as any other chemical class of compounds (e.g., polysaccharides, proteins, etc.). They are traditionally defined according to their solubilities. Fulvic acids are those organic materials that are soluble in water at all pH values. Humic acids are those materials that are insoluble at acidic pH values (pH < 2) but are soluble at higher pH values. Humin is the fraction of natural organic materials that is insoluble in water at all pH values. These definitions reflect the traditional methods for separating the different fractions from the original mixture.The humic content of soils varies from 0 to almost 10%. In surface waters, the humic content, expressed as dissolved organic carbon (DOC), varies from 0.1 to 50 ppm in dark-water swamps. In ocean waters, the DOC varies from 0.5 to 1.2 ppm at the surface, and the DOC in samples from deep groundwaters varies from 0.1 to 10 ppm (1). In addition, about 10% of the DOC in surface waters is found in suspended matter, either as organic or organically coated inorganic particulates. Structure and CompositionHumic materials have a wide range of molecular weights and sizes, ranging from a few hundred to as much as several hundred thousand atomic mass units. In general, fulvic acids are of lower molecular weight than humic acids, and soil-derived materials are larger than aquatic materials (1,2). Humic materials vary in composition depending on their source, location, and method of extraction; however, their similarities are more
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