1,721,013 research outputs found
Mineralogy Associated With Acid Mine Seepage as Determined Using Fourier Transform Infrared Spectroscopy and Relations to Acid Base Accounting
Full text linkOver 7,000 km of streams in the eastern United States are negatively affected by acid drainage from coal mines (U.S. Environmental Protection Agency, 1994). Pyrite (FeS2) is known to be the primary cause of acid formation, but analytical measurements to quickly and accurately detect trace pyrite content and predict acid drainage are lacking. This study analyzed sedimentary samples from a reclaimed east Texas lignite mine using Fourier Transform Infrared spectroscopy (FTIR) to detect the pyrite responsible for the environmental degradation of surface waters and the water table due to low (~2.5) pH. Subsequently, acid base accounting (ABA) was used to determine net acid forming potential of the mineralogy and determine FTIR utility. In conjunction with X-Ray Diffraction data, FTIR spectra and experiments and scanning electron microscopy (SEM) have semi-quantitatively detected the FeS2 which has and will release the H+ responsible for the low pH in the surface water bodies. Analytical techniques were used to develop a concept of how acid-formation from mine tailings can be predicted relatively accurately and quickly using FTIR
Aflatoxin Detoxification Method Combining Mesoamerican Nixtamalization and Clay Absorption Techniques
Full text linkAflatoxins are potent carcinogens produced by fungi Aspergillus flavus and Aspergillis parasiticus. Aflatoxins are able to contaminate different crops. Once ingested in the body, aflatoxins are able to cause harmful effects such as liver cancer. Mesoamerican cultures have used the nixtamalization food process on maize since the Aztec and Mayan civilization periods. The process has proven to be effective in reducing aflatoxin concentration within maize. Extensive research has shown the effectiveness of clays, particularly the montmorillonite-rich bentonite clays, to adsorb aflatoxins. This research is aimed to combine both techniques to evaluate their synergistic effects on aflatoxin detoxification. Montmorillonite samples that have previously shown high aflatoxin adsorption capacity will be used. The aflatoxin adsorption capacity of the montmorillonite samples will be evaluated using adsorption isotherms described in Kannewischer et al., (2006) with the modification of preparing aflatoxin solutions in lime saturated water (1.5 g/L Ca(OH)2) with a very basic pH, in order to simulate the nixtamalization process. The concentration of aflatoxin left in the solution will be analyzed using the High Performance Liquid Chromatography (HPLC) method. After sampling the aflatoxin solution at different pH���s varying from alkaline, to represent nixtamalization, to acidic, the experiments proved that there is reformation of aflatoxin within stomach pHs of 2 to 3. The aflatoxin changed chemical structure once exposed to alkaline pH, causing it to open its lactone ring structure and become more solubilized in water. Due to the change in chemical structure and conversion of the nonionic species to an anionic species, which was repelled by the negatively charged montmorilloinite, the adsorption of this new structure by the clay was minimal if any, while when in acidic conditions, the aflatoxin was adsorbed well by the montmorillonite. The preliminary results implied that combining the traditional Mexican nixtamalization food process and clay incorporation in processed corn products may further limit the bioavailability of aflatoxins compared to the individual methods along
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Pilot-Scale Demonstration of hZVI Process for Treating Flue Gas Desulfurization Wastewater at Plant Wansley, Carrollton, GA
Full text linkThe hybrid Zero Valent Iron (hZVI) process is a novel chemical treatment platform that has shown great potential in our previous bench-scale tests for removing selenium, mercury and other pollutants from Flue Gas Desulfurization (FGD) wastewater. This integrated treatment system employs new iron chemistry to create highly reactive mixture of Fe^0, iron oxides (FeOx) and various forms of Fe (II) for the chemical transformation and mineralization of various heavy metals in water. To further evaluate and develop the hZVI technology, a pilot-scale demonstration had been conducted to continuously treat 1-2 gpm of the FGD wastewater for five months at Plant Wansley, a coal-fired power plant of Georgia Power. This demonstrated that the scaled-up system was capable of reducing the total selenium (of which most was selenate) in the FGD wastewater from over 2500 ppb to below 10 ppb and total mercury from over 100 ppb to below 0.01 ppb. This hZVI system reduced other toxic metals like Arsenic (III and V), Chromium (VI), Cadmium (II), Lead (II) and Copper (II) from ppm level to ppb level in a very short reaction time. The chemical consumption was estimated to be approximately 0.2-0.4 kg of ZVI per 1 m^3 of FGD water treated, which suggested the process economics could be very competitive. The success of the pilot test shows that the system is scalable for commercial application. The operational experience and knowledge gained from this field test could provide guidance to further improvement of technology for full scale applications. The hZVI technology can be commercialized to provide a cost-effective and reliable solution to the FGD wastewater and other metal-contaminated waste streams in various industries. This technology has the potential to help industries meet the most stringent environmental regulations for heavy metals and nutrients in wastewater treatment
On the Comprehensive Optimization of the Process and Quality Control Framework in Portland Cement Production Testing Using QXRD-Based Accuracy Calibration
Full text linkThe Bogue method is the current industrial standard for the compositional analysis of anhydrous and blended cements. However, this method is disadvantageous since the formulations were developed with archaic cement chemistry knowledge. This results in phase quantity estimation errors which can be as high as 9wt.% of the total cement. Quantification of cement phases through X-ray diffraction and Rietveld refinement is an effective alternative which determines the phase quantities directly rather than through estimation. Despite having several advantages over the Bogue method, the adoption rate of Quantitative X-ray Diffraction (QXRD) in industrial quality control is quite slow. Since industrial quality control demands a reproducible technique with high precision, QXRD falls short against the Bogue method with average performance in repeatability and reproducibility. Although cement chemists recognize round robin and proficiency testing as effective solutions for this shortcoming, none of the proposed solutions remain feasible in an online testing environment.
In this study, primary focus is allotted to promoting a viable solution to address the repeatability and reproducibility issue in QXRD. Improved QXRD protocols were developed, tested, and, optimized to be applicable in a manual as well as an automated testing environment. Techniques such as multispectral image analysis, point counting, heat of hydration measurements, and, phase decomposition tracing were harnessed to validate the resulting QXRD results with improved repeatability and reproducibility. Furthermore, a mathematical relationship between the Bogue method and the improved QXRD quantification was generated to qualify the improvements from a familiar perspective
Detection and Quantification of Expansive Clay Minerals in Geologically-Diverse Texas Aggregate Fines
No full textExpansive clay mineral contamination of road aggregate materials in Texas is a persistent problem. Hydrous layer silicate minerals - particularly smectites - in concretes are associated with decreased strength and durability in Portland cement and asphalt concretes. The Texas Department of Transportation (TXDOT) and Texas A&M Transportation Institute (TTI) evaluated the methylene blue adsorption test for its potential to identify and estimate quantities of expansive clays in aggregate stockpiles.
Clay mineral quantification was completed for 27 geologically-diverse aggregate materials from Texas, Oklahoma, and Arkansas. X-ray diffraction analysis (XRD) of separated clays on glass was conducted, and NEWMOD was utilized to model the resulting diffraction patterns. Methylene blue adsorption (MBA) and cation exchange capacity (CEC) of clay fractions (< 2��m) and -40 mesh screenings (< 400 ��m) were determined for most aggregates.
Many of the aggregates exhibited significant quantities of expansive clay minerals such as smectite, which are linked to deleterious performance properties in concretes. While the majority of aggregates were derived from crushed limestone or calcareous river gravel parent materials, severalexhibited uncommon origins and unusual clay mineralogy. Due to the relatively low number of aggregates tested and diverse geological origins of the different aggregates,it proved difficult to formalize any conclusions abouttrendsbetweenthedifferent aggregate performance properties
Mineralogy and Geochemistry of Pb, Zn and Ag Mine Tailings Originating From Carbonate-Rich Deposits
Full text linkMining for silver, lead, zinc, and copper in Zimapan, Hidalgo State, Mexico has been ongoing since 1576. Unsecured tailings heaps and associated acid mine drainage have presented problems related to soil quality, water quality, and dust emission control in the Zimapan area. Objectives of the study of the mine tailings are (1) to determine mineralogy of the tailings in order to identify acid-producing minerals and heavy metals at risk for release in acidic conditions, and (2) to quantify carbonate minerals and (3) to determine heavy metal content that may be released by the products of sulfide mineral weathering. Representative mine tailings have been sampled from a site located north of Zimapan. Mineralogical characterization has been conducted with X-ray diffraction (XRD), and scanning and transmission electron microscopes (SEM and TEM). Total carbonates have been determined the Chittick procedure. X-Ray Fluorescence (XRF) has been utilized to determine total elemental composition. XRD and SEM analyses have confirmed the presence of pyrite and arsenopyrite indicating a potential for acid mine drainage. Calcite has been confirmed to have a significant presence in the unweathered samples by XRD and the Chittick procedure, with some samples containing an average of 19.4% calcite. NAA and XRF have revealed significant concentrations of toxic elements such as As, Pb and Zn in both the oxidized and unoxidized samples
Variations on the Author
Full text link“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
PHYTOREMEDIATION OF ARSENIC AND THE IMMOBILIZATION OF LEAD IN SOIL: THE IMPACTS OF APATITE PARTICLE SIZE
Full text linkApatite was added to a soil highly contaminated with As and Pb to enhance As uptake by the hyperaccumulating fern, Pteris cretica. Arsenic and lead co-contamination is common in smelter soils and can be a major source of environmental harm. In situ chemical stabilization of contaminants can be an acceptable remediation option, but simultaneous immobilization of Pb and As faces serious obstacles. The two contaminants have antagonistic immobilization chemistries: the effective use of P to immobilize Pb greatly mobilizes As. However, this effect can be exploited if the mobilized As is assimilated by As hyperaccumulating plants, such as members of the Pteris species. Apatite is an effective source of phosphorus when used with Pteris arsenic hyperaccumulators but the effect of particle size has not been studied. Changes in soil and plant chemistry were studied for two concentrations of total soil As (750 mg/kg and 1,500 mg As /kg soil); three particle sizes of added apatite (500 ��m-250 ��m, 250 ��m-105 ��m, <105 ��m); and three molar ratios of P:As (1:1, 1:2, 1:5). The treatments were found to have a significant impact on both the arsenic concentrations in the plants and plant biomass. In addition, IVBA analysis of the soil showed a reduction in the amount of arsenic found to be bioaccessible. Plant phosphorus concentrations and plant arsenic concentrations were correlated with indications that phosphorus is promoting arsenic uptake and plant growth
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