Kinetics of the Formation and Dissolution of Ni Precipitates in a Gibbsite/Amorphous Silica Mixture

There have been a number of studies that have examined metal precipitation reactions on an array of natural soil materials. While many of these investigations have focused on model single-component systems, recent research has appeared on metal precipitation on soils and clay fractions of soils. However, few studies have explored mixed model component systems, which may lead to a better understanding of metal reactions on soils and clay fractions. Furthermore, only a few studies have appeared on the stability of the metal surface precipitates. In light of this, we investigated Ni sorption and dissolution kinetics and mechanisms on a mixture of gibbsite and amorphous silica by combining macroscopic studies with X-ray absorption fine structure (XAFS) and diffuse reflectance spectroscopies (DRS), and high-resolution thermogravimetric analysis (HRTGA). Batch sorption experiments were conducted at pH 7.5 and at different reaction times to elucidate the sorption process and to study the role of residence time on metal precipitate stability. Spectroscopic and HRTGA investigations revealed alpha-Ni(OH)(2) precipitates formed on the gibbsite/silica mixture initially and over time evolved to a Ni phyllosilicate. The available Si source was derived from partial dissolution of the sorbent during Ni sorption. With increasing residence time, the precipitate phases drastically increased in stability, as shown by decreasing amounts of Ni release as effected by nitric acid (HNO(3)) and ethylenediaminetetraacetic acid (EDTA) treatments. This aging effect may be explained by the silicate-for-nitrate exchange during the first days of reaction and subsequently by silicate polymerization and partial grafting onto the hydroxide layers to form a phyllosilicate precursor phase (R. G. Ford, A. C. Scheinost, K. G. Scheckel, and D. L. Sparks, Environ. Sci. Technol. 33(18), 3140-3144, 1999). Copyright 2000 Academic Press.     

X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

帕隆藏布流域堆积体边坡的工程地质特征及稳定性评价

位于藏东南的帕隆藏布流域,处在东喜马拉雅构造结的北缘,是新构造强烈隆升区,断层、褶皱等地质构造发育。在青藏高原隆升及气候变化等内外动力作用下,研究区内堆积体分布广泛,具有独特的工程地质特征并成为该区内地质灾害的主要物源。由于河流的下切及川藏公路的修建,形成了许多高陡的堆积体边坡,以冰碛边坡最为典型。由于其特殊的物源特征及形成过程,冰碛物具有粒度分布范围广、粗粒含量多等与其他沉积物不同的粒度特征。冰碛物粒度分布范围广的特征,导致随着研究尺度的不同,其结构特征也不相同,具有明显的尺度效应。冰碛土的力学强度一般强于其他堆积体,但受不同粒径颗粒的含量及分布、形成时代的影响,其力学特征也有所差异。作者对川藏公路沿线部分典型的剖面进行了量测,所量测的剖面虽然只是整个斜坡的一部分,与经验数据相比,仍表现出高陡的特征,而且很多边坡在既高且陡的形态下仍能保持稳定。本文以极限平衡理论为基础,采用多种方法对这类边坡的稳定性进行计算分析,求出边坡的安全系数。考虑各种地震烈度下边坡的稳定性,得出这些边坡的安全系数与地震加速度具有严格的指数相关关系。     

Characterization and dissolution properties of ruthenium oxides

Ruthenium oxides (RuO(2)·1·10H(2)O and RuO(2)) have been synthesized by forced hydrolysis and oxidation of ruthenium chloride. The resulting materials were extensively characterized to determine the crystallinity, surface area, and ruthenium oxidation state. Surface charging experiments indicate a large quantity of reactive functional groups for both materials and a decrease in the acidity of the surface functional groups with crystallization of the hydrous oxide. Dissolution studies conducted in acidic and basic pH environments indicate Ru-oxides are insoluble in 0.1 M HCl and slightly soluble in 0.1 M NaOH. Oxalate and ascorbate (5 mM) promoted dissolution of RuO(2)·1·10H(2)O demonstrated an increase in dissolution rates with decreasing pH and increasing ligand surface coverage. XPS analysis of the RuO(2)·1·10H(2)O surface after ligand promoted dissolution revealed the reduction of Ru(IV) to Ru(III) indicating that both ascorbate and oxalate reductively dissolve RuO(2)·1·10H(2)O. Dissolution experiments with RuO(2) resulted in dissolution only for 5 mM oxalate at pH 3. Dissolution rates calculated for RuO(2)·1·10H(2)O and RuO(2) are compared with previously published dissolution rates for iron oxides, demonstrating an order of magnitude decrease in the oxalate and ascorbate promoted dissolution.     

Dose–Response Relationship of Photobiomodulation Therapy on Matrix Metalloproteinase in Healing Dynamics of Diabetic Neuropathic Ulcers—An in vivo Study

Individuals with diabetic foot ulcers have overlapped the inflammatory, proliferative and remodeling phase, making the tissue vulnerable to delayed healing responses. We aimed to establish the dose–response relationship of photobiomodulation therapy of different doses and matrix metalloproteinases in the healing dynamics of diabetic neuropathic ulcers. Diabetes was induced in 126 Albino Wistar rats, and neuropathy was induced to the hind paw by a sciatic nerve injury method. An excisional wound was created on the neuropathy-induced leg. Photobiomodulation therapy of dosages 4, 6, 8, 10, 12 and 15 J cm⁻² and wavelength 655 nm and 808 nm was irradiated. Photobiomodulation therapy of dosages 4, 6 and 8 J cm⁻² showed better wound healing properties with optimized levels of matrix metalloproteinases-1 and 8. We observed a strong dose response in the experimental group treated with 6 and 8 J cm⁻². The findings from the present study conclude that photobiomodulation therapy of dosages 4, 6 and 8 J cm⁻² is suggestive of usefulness in diabetic neuropathic ulcer healing. Markers like matrix metalloproteinases may give a clear direction on response to the therapy. Based on the findings from the present study, we recommend to validate the findings for safety and efficacy in future through human prospective randomized controlled clinical trials.     

W1{infty}-convergence of the discrete free boundary for obstacle problems

We examine the discrete free boundaries arising from a finiteelement discretization of a variational inequality. We giveL error bounds for the Hausdorff distance of the discrete andtrue free boundary, as well as for the normals. The theoreticalresults are confirmed by numerical experiments in two and threedimensions.     

Analytical characterisation of nanoscale zero-valent iron: A methodological review

Zero-valent iron nanoparticles (nZVI) have been widely tested as they are showing significant promise for environmental remediation. However, many recent studies have demonstrated that their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Both the mobility and reactivity of nZVI mainly depends on properties such as particle size, surface chemistry and bulk composition. In order to ensure efficient remediation, it is crucial to accurately assess and understand the implications of these properties before deploying these materials into contaminated environments. Many analytical techniques are now available to determine these parameters and this paper provides a critical review of their usefulness and limitations for nZVI characterisation. These analytical techniques include microscopy and light scattering techniques for the determination of particle size, size distribution and aggregation state, and X-ray techniques for the characterisation of surface chemistry and bulk composition. Example characterisation data derived from commercial nZVI materials is used to further illustrate method strengths and limitations. Finally, some important challenges with respect to the characterisation of nZVI in groundwater samples are discussed.     

Arsenate adsorption on ruthenium oxides: A spectroscopic and kinetic investigation

Arsenate adsorption on amorphous (RuO(2)1.1H(2)O) and crystalline (RuO(2)) ruthenium oxides was evaluated using spectroscopic and kinetic methods to elucidate the adsorption mechanism. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local coordination environment of adsorbed arsenate. Additionally, pressure-jump (p-jump) relaxation spectroscopy was used to investigate the kinetics of arsenate adsorption/desorption on ruthenium oxides. Chemical relaxations resulting from the induced pressure change were monitored via electrical conductivity detection. EXAFS data were collected for two initial arsenate solution concentrations, 3 and 33 mM at pH 5. The collected spectra indicated a similar coordination environment for arsenate adsorbed to RuO(2)1.1H(2)O for both arsenate concentrations. In contrast the EXAFS spectra of RuO(2) indicated differences in the local coordination environments for the crystalline material with increasing arsenate concentration. Data analysis indicated that both mono- and bidentate surfaces complexes were present on both RuO(2)1.1H(2)O and RuO(2). Relaxation spectra from the pressure-jump experiments of both ruthenium oxides resulted in a double relaxation event. Based on the relaxation spectra, a two step reaction mechanism for arsenate adsorption is proposed resulting in the formation of a bidentate surface complex. Analysis of the kinetic and spectroscopic data suggested that while there were two relaxation events, arsenate adsorbed to ruthenium oxide surfaces through both mono- and bidentate surface complexes.