1,720,984 research outputs found
Elemental iron (Fe0) for better drinking water in rural areas of developing countries
No full textMany of the reasons behind the anthropogenic contamination problems in rural environments of developing countries lie in changes in the traditional way of life and the ignorance on the toxic potential of introduced manufactured products. A generalization trend exists within the international community suggesting that water in developing countries is of poor quality. However, the water quality is rarely analytically determined. Existing potabilization solutions may be prohibitively expensive for the rural populations. Therefore, efficient and affordable technologies are still needed to ameliorate the water quality. In the recent two decades,elemental iron has shown the capacity to remove all possible contaminants (including viruses) from the groundwater. This paper presents a concept to scale down the conventional iron barrier technology to meet the requirements of small communities and households in rural environments worldwide
Investigating the mechanism of Uranium removal by zerovalent iron
Get PDFZerovalent iron (ZVI) has been proposed as a reactive material in permeable in situ walls for groundwater contaminated by metal pollutants. For such pollutants that interact with corrosion products, the determination of the actual mechanism of their removal is very important to predict their stability in the long term. From a study of the effects of pyrite (FeS2) and manganese nodules (MnO2) on the uranium removal potential of a selected ZVI material, a test methodology (FeS2MnO2 method) is suggested to follow the pathway of contaminant removal by ZVI materials. An interpretation of the removal potential of ZVI for uranium in the presence of both additives corroborates coprecipitation with iron corrosion products as the initial removal mechanism for uranium.Keywords: iron, redox reactions, uranium, water treatmentresearc
Characterizing As, Cu, Fe and U solubilization by natural waters
Get PDFThe effects of carbonate concentration and the presence of in-situ generated iron oxide and hydroxide phases (iron oxyhydroxides) on arsenic (As), copper (Cu), and uranium (U) release from natural rocks were investigated under oxic conditions and in the pH range from 6 to 9. For this purpose non-disturbed batch experiments were conducted with a constant amount of each contaminant bearing rock/mineral and different types of water (deionised, mineral, spring, and tap water). For comparison parallel experiments were conducted with 0.1 M Na2CO3 and 0.1 M H2SO4. The favourable role of carbonate bearing minerals for U and Cu transport could not be confirmed by using dolomite. The presence of elemental iron and pyrite retards As, Cu and U solubilization. This study shows that using natural materials in laboratory investigations is a practical tool to investigate natural processes.researc
Surface complexation of U(VI) by Fe and Mn (hydr)oxides
No full textSorption of U(VI) to iron and manganese (hydr)oxides is a fundamental control on the mobility of uranium in oxic soil and groundwater. Surface complexation models for these sorption reactions are needed to enable reactive transport simulations of U in the environment. We have been investigating the sorption of U(VI) to iron and manganese (hydr)oxide minerals using classical batch sorption experiments, EXAFS spectroscopy and first-principles (quantum mechanical) calculations of the structures and energetics of U surface complexes. EXAFS spectra of U surface complexes are complicated by multiple scattering and the poor resolution of U-carbonate complexes. We argue that previous models for surface complexation need to be reassessed. Instead, we show that on goethite (α-FeOOH) and ferrihydrite (Fe10O14(OH)2), we can model both our EXAFS and our sorption experiments using three surface complexes, (>FeOH)2UO2(H2O)3, >FeOCO2UO2, and (>FeOH)2UO2CO3. Using these complexes, we fit our batch sorption experiments to a surface complexation models for U on goethite and ferrihydrite with a 1pK model for surface protonation, an extended Stern model for surface electrostatics and inclusion of all known UO2-OH-CO3 aqueous complexes in the current thermodynamic database. The models give an excellent fit to our sorption experiments done in both ambient and reduced CO2 environments at surface loadings of 0.02-2.0 wt. % U. We find that we can model the EXAFS and batch sorption experiments of U(VI) on birnessite as an inner-sphere (>Mn2O)3UO2++ and (>Mn2O)3UO2CO3 complexes over vacancy sites. In the environment, U(VI) and its carbonate complexes will be preferentially sorbed by iron(III) (hydr)oxides over manganese(IV) oxide
Assessment of rehabilitated uranium mine sites, Australia
No full textRecent research on rehabilitated uranium mine sites located in wet climates has revealed the varied success of the applied rehabilitation efforts. In comparison, there is little knowledge of the status and environmental impacts of rehabilitated uranium mines in dry climates. Mary Kathleen and Radium Hill represent first generation Australian uranium mines, which are located in semi-arid regions. The aim of this communication is to report on the current environmental status and potential hazards of these former uranium mine sites
Particle swarm optimization for the estimation of surface complexation constants with the geochemical model PHREEQC-3.1.2
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
