Optimization of Rare Earth Leaching from Ores and Concentrates

The use of applied chemistry in the production and optimization of leach solutions from Rare Earth Element (REE) ores and concentrates was investigated. Ore and concentrate samples were characterized using scanning electron microscopy/mineral liberation analysis (SEM/MLA), X-ray Diffraction (XRD), and Inductively-coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Multiple leach tests were performed to analyze the effects of temperature, residence time, and reagent concentration on the leaching of REEs. Analysis of leach solutions was carried out using ICP-AES. Modeling and statistical analysis of extraction behavior was carried out using DesignExpert 9. Modeling data for multiple REEs indicate that extraction is strongly influenced by temperature and reagent concentration, while leaching time plays a much less important role. Experimental design techniques were able to optimize REE recovery while minimizing the extraction of gangue elements, such as iron, and a series of series of parameters were determined that were optimal for REE extraction. Differences in extraction between some of the REEs indicate that a multistage, direct leaching, operation could be implemented to effectively extract REEs from both ores and concentrates

SYNTHESIS OF CARBIDE CERAMICS VIA REDUCTION AND CARBURIZATION OF OXYANIONS ADSORBED ONTO AN ACTIVATED CARBON MATRIX

Carbide ceramics rank high among the hardest and most chemically resistant materials. Their ability to resist physical and chemical attack under conditions where more traditional materials fail make them very desirable for a number of industrial applications. Their use is limited, however, due to the expensive and energy-intensive methods required to produce them commercially. A more versatile and energy-efficient process for commercial carbide production has been developed by synthesizing micron/sub-micron carbide ceramic particles through the adsorption and subsequent carburization of anions on an activated carbon matrix. Oxyanion solutions containing sodium tungstate, sodium molybdate, or sodium metasilicate are adsorbed onto activated carbon to produce anion-loaded precursors. These precursors are carburized in the presence of a reducing atmosphere consisting of hydrogen, carbon monoxide, and methane to produce carbide crystals on the activated carbon surface. In this study, tungstate (WO42-), molybdate (MoO42-), and silicate (SiO32-) anions were evaluated. Silicon carbide (SiC) whiskers and mixed crystals of tungsten carbide (WC), tungsten semicarbide (W2C), and tungsten (W) were formed via carbothermal reduction using inert and reducing gas atmospheres at temperatures much lower than current commercial practice. Mixed crystals of WC, W2C, and W were synthesized at 950 °C under an atmosphere of 80% CH4, 10% H2, and 10% CO. Molybdenum carbide (Mo2C) was synthesized at temperatures as low as 850oC under an atmosphere consisting of 80% CH4, 10% CO, and 10% H2. Under optimal conditions, conversion to Mo2C and WC exceeded 90%. SiC was synthesized at temperatures as low as 1200 °C under H2. Separation of the WC/W2C/W crystals from the activated carbon matrix has been demonstrated using surfactant-aided density separation methods. Response surface modeling was used to determine optimal conditions for tungstate, molybdate, and silicate adsorption as well as the optimal carburization conditions for the W-loaded and Mo-loaded precursors. Results show that the carburization process is feasible and that it is possible to mathematically model and statistically optimize the production and carburization of the activated carbon precursors

Aspirin and glyceryl trinitrate effects on polyamine uptake and smooth muscle cell growth

This paper looks at aspirin and glyceryl trinitrate effects on polyamine uptake and smooth muscle cell growt

Assessment of the learning curve in health technologies: a systematic review

Objective: We reviewed and appraised the methods by which the issue of the learning curve has been addressed during health technology assessment in the past. Method: We performed a systematic review of papers in clinical databases (BIOSIS, CINAHL, Cochrane Library, EMBASE, HealthSTAR, MEDLINE, Science Citation Index, and Social Science Citation Index) using the search term "learning curve:" Results: The clinical search retrieved 4,571 abstracts for assessment, of which 559 (12%) published articles were eligible for review. Of these, 272 were judged to have formally assessed a learning curve. The procedures assessed were minimal access (51%), other surgical (41%), and diagnostic (8%). The majority of the studies were case series (95%). Some 47% of studies addressed only individual operator performance and 52% addressed institutional performance. The data were collected prospectively in 40%, retrospectively in 26%, and the method was unclear for 31%. The statistical methods used were simple graphs (44%), splitting the data chronologically and performing a t test or chi-squared test (60%), curve fitting (12%), and other model fitting (5%). Conclusions: Learning curves are rarely considered formally in health technology assessment. Where they are, the reporting of the studies and the statistical methods used are weak. As a minimum, reporting of learning should include the number and experience of the operators and a detailed description of data collection. Improved statistical methods would enhance the assessment of health technologies that require learning

Assessing the learning curve effect in health technologies: Lessons from the non-clinical literature

Introduction: Many health technologies exhibit some form of learning effect, and this represents a barrier to rigorous assessment. It has been shown that the statistical methods used are relatively crude. Methods to describe learning curves in fields outside medicine, for example, psychology and engineering, may be better. Methods: To systematically search non–health technology assessment literature (for example, PsycLit and Econlit databases) to identify novel statistical techniques applied to learning curves. Results: The search retrieved 9,431 abstracts for assessment, of which 18 used a statistical technique for analyzing learning effects that had not previously been identified in the clinical literature. The newly identified methods were combined with those previously used in health technology assessment, and categorized into four groups of increasing complexity: a) exploratory data analysis; b) simple data analysis; c) complex data analysis; and d) generic methods. All the complex structured data techniques for analyzing learning effects were identified in the nonclinical literature, and these emphasized the importance of estimating intra- and interindividual learning effects. Conclusion: A good dividend of more sophisticated methods was obtained by searching in nonclinical fields. These methods now require formal testing on health technology data sets

Kiss-and-Run Is a Significant Contributor to Synaptic Exocytosis and Endocytosis in Photoreceptors.

Accompanying sustained release in darkness, rod and cone photoreceptors exhibit rapid endocytosis of synaptic vesicles. Membrane capacitance measurements indicated that rapid endocytosis retrieves at least 70% of the exocytotic membrane increase. One mechanism for rapid endocytosis is kiss-and-run fusion where vesicles briefly contact the plasma membrane through a small fusion pore. Release can also occur by full-collapse in which vesicles merge completely with the plasma membrane. We assessed relative contributions of full-collapse and kiss-and-run in salamander photoreceptors using optical techniques to measure endocytosis and exocytosis of large vs. small dye molecules. Incubation with small dyes (SR101, 1 nm; 3-kDa dextran-conjugated Texas Red, 2.3 nm) loaded rod and cone synaptic terminals much more readily than larger dyes (10-kDa Texas Red, 4.6 nm; 10-kDa pHrodo, 4.6 nm; 70-kDa Texas Red, 12 nm) consistent with significant uptake through 2.3-4.6 nm fusion pores. By using total internal reflection fluorescence microscopy (TIRFM) to image individual vesicles, when rods were incubated simultaneously with Texas Red and AlexaFluor-488 dyes conjugated to either 3-kDa or 10-kDa dextran, more vesicles loaded small molecules than large molecules. Using TIRFM to detect release by the disappearance of dye-loaded vesicles, we found that SR101 and 3-kDa Texas Red were released from individual vesicles more readily than 10-kDa and 70-kDa Texas Red. Although 10-kDa pHrodo was endocytosed poorly like other large dyes, the fraction of release events was similar to SR101 and 3-kDa Texas Red. We hypothesize that while 10-kDa pHrodo may not exit through a fusion pore, release of intravesicular protons can promote detection of fusion events by rapidly quenching fluorescence of this pH-sensitive dye. Assuming that large molecules can only be released by full-collapse whereas small molecules can be released by both modes, our results indicate that 50%-70% of release from rods involves kiss-and-run with 2.3-4.6 nm fusion pores. Rapid retrieval of vesicles by kiss-and-run may limit membrane disruption of release site function during ongoing release at photoreceptor ribbon synapses

Towards the achievement of environmental standards in the South African sugar industry : the role of GIS.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.The South African Sugar Industry is a major land user in the South African provinces of KwaZulu-Natal and Mpumalanga. Although offering substantial economic benefits in these regions, monocultural sugarcane production has had a fundamental impact on the natural environment in which sugarcane is produced. Attention was focused on the growing sector of the industry after flood events during the previous decade resulted in major soil erosion of sugarcane land. Widespread intentional cane burning is attracting increasing societal and regulatory pressure. New national environmental legislation in the spirit of the United Nations Conference on Environment and Development (UNCED) Agenda 21 and various other international agreements, demand that industries - including agriculture - demonstrate sustainability in their use of environmental resources. National law now more rigorously addresses biodiversity and wetland environmental issues. New water laws will fundamentally alter the existing water-use paradigm in sugarcane production. These issues are not unique to South Africa, having much in common with those faced by other major sugar producing countries. In order to effectively manage the impacts of production processes on the environment, organisations are turning to internationally accepted environmental management standards, such as the ISO 14000 series, in order to demonstrate their environmental responsibility to government and society, whilst promoting their acceptability to consumers. The SA Sugar Industry is in the early stages of investigating appropriate environmental management systems. The natural resources required for - and impacted upon - by sugarcane production are variable in space and over time. Effective and responsible environmental management must make optimum use of appropriate technology to effectively utilise the large volumes of often complex data pertaining to these resources and associated environmental processes. Geographic Information Systems (GIS) are computer systems designed for the capture, analysis, storage and display of spatial data and attribute data related to location. Whilst not a new development, recent advances indicate that GIS has substantially matured as a decision support technology and as such is being used successfully by many organisations involved in environmental management, where its use offers unique benefits at a variety of decision levels and spatial scales. GIS is applied at many complexity levels, from simple thematic map production to complex spatial analysis. The major advantage of GIS is considered by some to be its ability to spatially model environmental scenarios, producing graphic results (usually maps). As such, GIS has considerable value in formal Decision Support Systems. The major environmental issues facing South African sugarcane producers are fundamentally spatial in nature. The development and incorporation of environmental GIS capacity into their proposed environmental management system is indispensable in addressing these issues and moving towards achieving and maintaining acceptable environmental standards in the SA sugar growing sector

Experiences with HPTN 067/ADAPT Study-Provided Open-Label PrEP Among Women in Cape Town: Facilitators and Barriers Within a Mutuality Framework.

Placebo-controlled trials of pre-exposure prophylaxis (PrEP) have reported challenges with study-product uptake and use, with the greatest challenges reported in studies with young women in sub-Saharan Africa. We conducted a qualitative sub-study to explore experiences with open-label PrEP among young women in Cape Town, South Africa participating in HTPN 067/Alternative Dosing to Augment Pre-Exposure Prophylaxis Pill Taking (ADAPT). HPTN 067/ADAPT provided open label oral FTC/TDF PrEP to young women in Cape Town, South Africa who were randomized to daily and non-daily PrEP regimens. Following completion of study participation, women were invited into a qualitative sub-study including focus groups and in-depth interviews. Interviews and groups followed a semi-structured guide, were recorded, transcribed, and translated to English from isiXhosa, and coded using framework analysis. Sixty of the 179 women enrolled in HPTN 067/ADAPT participated in either a focus group (six groups for a total of 42 participants) or an in-depth interview (n = 18). This sample of mostly young, unmarried women identified facilitators of and barriers to PrEP use, as well as factors influencing study participation. Cross-cutting themes characterizing discourse suggested that women placed high value on contributing to the well-being of one's community (Ubuntu), experienced a degree of skepticism towards PrEP and the study more generally, and reported a wide range of approaches towards PrEP (ranging from active avoidance to high levels of persistence and adherence). A Mutuality Framework is proposed that identifies four dynamics (distrust, uncertainty, alignment, and mutuality) that represent distinct interactions between self, community and study and serve to contextualize women's experiences. Implications for better understanding PrEP use, and non-use, and intervention opportunities are discussed. In this sample of women, PrEP use in the context of an open-label research trial was heavily influenced by underlying beliefs about safety, reciprocity of contributions to community, and trust in transparency and integrity of the research. Greater attention to factors positioning women in the different dynamics of the proposed Mutuality Framework could direct intervention approaches in clinical trials, as well as open-label PrEP scale-up

Geologic context of geodetic data across a Basin and Range normal fault, Crescent Valley, Nevada

Geodetic strain and late Quaternary faulting in the Basin and Range province is distributed over a region much wider than historic seismicity, which is localized near the margins of the province. In the relatively aseismic interior, both the magnitude and direction of geodetic strain may be inconsistent with the Holocene faulting record. We document the best example of such a disagreement across the NE striking, ~55° NW dipping Crescent normal fault, where a NW oriented, 70 km geodetic baseline records contemporary shortening of ~2 mm/yr orthogonal to the fault trace. In contrast, our geomorphic, paleoseismic, and geochronologic analyses of the Crescent fault suggest that a large extensional rupture occurred during the late Holocene epoch. An excavation across the fault at Fourmile Canyon reveals that the most recent event occurred at 2.8 ± 0.1 ka, with net vertical tectonic displacement of 4.6 ± 0.4 m at this location, corresponding to the release of ~3 m of accumulated NW-SE extension. Measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event, implying a moment magnitude M_w of at least 6.6. No prior event occurred between ~2.8 ka and ~6.4 ± 0.1 ka, the ^(14)C calender age of strata near the base of the exposed section. Assuming typical slip rates for Basin and Range faults (~0.3 mm/yr), these results imply that up to one third, or ~1 m, of the extensional strain released in the previous earthquake could have reaccumulated across the fault since ~2.8 ka. However, the contemporary shortening implies that the fault is unloading due to a transient process, whose duration is limited to between 6 years (geodetic recording time) and 2.8 ka (the age of the most recent event). These results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements