Performance of the vertical roller mill in a mineral processing application when coupled with internal and external classifiers

Comminution is applied in all mineral processing plants where mineral liberation is needed for separation and concentration of valuable minerals. The process is energy intensive and is predominantly carried out in tumbling mills which are known to be highly inefficient. Comminution technologies utilised in other industries, such as the vertical roller mill (VRM), a high compression dry grinding device, have the potential to contribute towards enhancing the energy efficiency of comminution and the sustainability of mineral processing. The vertical roller mill is used extensively in cement and coal grinding applications, where it is known to be more energy efficient than traditional tumbling mills. The VRM has a larger reduction ratio and greater flexibility in terms of product quality control and throughput. However, in the majority of operations where the vertical roller mill is applied, the device is coupled with an internal dynamic air classifier. These classifiers are significantly more energy intensive than other classifiers typically used in the mineral processing industry. Operating the vertical roller mill with less energy intensive classification devices could have the potential to further reduce the total comminution circuit energy. Reducing the comminution energy usage in mineral processing is important, however there are other factors which also need to be considered before the vertical roller mill can be considered as a viable alternative to tumbling mills. The effect of grinding with the vertical roller mill on product quality and mineral liberation, and their impact on downstream processing is of critical importance and has not yet been extensively investigated. This study investigates the grinding of the platinum group mineral (PGM) bearing Platreef ore, in a pilot scale vertical roller mill. The research explores the effects of milling variables and methods of classification on the mill performance, energy consumption, throughput, product characteristics and flotation response. The energy efficiency of the vertical roller mill and product flotation response is also compared with that of a traditional ball milling circuit. Vertical roller mill products of three target grinds, typical to primary, secondary and tertiary grinds in PGM circuit, were generated with the VRM operated in the standard airflow mode, with the internal dynamic air classifier, for a variety of grinding pressures (an online control used for maintaining product quality), and dam ring heights (a design variable affecting residence time on the grinding table). The specific grinding energy for the vertical roller mill was found to increase as the target grind became finer, conforming to general comminution theory. Vertical roller mill specific grinding energies were lower than those for a ball mill at all product sizes, and when estimates of classification energy and scale-up of the VRM are included, the specific energy for the vertical roller mill is up to 35% lower than for a ball mill in closed circuit. Grinding at higher pressures yielded greater throughputs and was found to generate products of less steep particle size distribution (PSD), but did not affect specific grinding energy. The effect of varying dam ring height was found to be target grind dependent. Higher dam rings yielded products with a greater proportion of fines, for higher specific grinding energies with the differences more pronounced at coarser target grinds. The grinding component of the vertical roller mill was operated in conjunction with three classification devices - the internal dynamic air classifier, external hybrid air classifier and an external vibrating screen. The external air classification circuit had a lower throughput than the internal air classification circuit, and operated with a 20 - 40% higher specific grinding energy. When including pilot scale estimations for classification energy, the external air classification circuit overall specific energy is lower at intermediate and coarse grinds, and comparable at finer target grinds, to that of the internal air classification circuit. The specific grinding energy in the VRM - external screening system was higher than both air classification circuits, however when considering the lower energy intensity of screening, this circuit may prove more efficient. The flotation response of the tumbling mill product and the vertical roller mill product prepared under different operating conditions in circuits with different classification devices was assessed using a standard reagent suite, in terms of platinum, palladium, gold (3E PGE), and copper, nickel (Cu, Ni) concentrate grades and recoveries. Both vertical roller mill and tumbling mill products yielded greater recoveries as the products became finer and valuable mineral liberation increased. The vertical roller mill products however had substantially higher recoveries, which was linked to higher froth recoveries and differences in oxidation potential within the flotation pulp. Increasing the compressive force in the VRM through the application of higher grinding pressures led to an increase in fines causing a decrease in froth stability during flotation, which corresponded with lower valuable metal recoveries. Variation in dam ring height caused small decreases in discrete PGM liberation but an increase in effective PGM liberation (considering PGMs liberated and locked in floatable base metal sulphide minerals). Flotation recoveries followed changes in froth stability with products prepared at the highest dam ring height, which had greater fines contents, yielding lower valuable metal recoveries. An optimised reagent suite for VRM products should be developed to address issues with froth stability caused by the increase in fines component at higher grinding pressure and dam ring heights. This will allow for the improvements in valuable mineral liberation with these grinding conditions to be realised as increased flotation recoveries. When operating the VRM grinding components with different classification devices, flotation performance was influenced by variation in the particle size distributions of products. External and internal air classification products with closely comparably particle size distributions yielded similar 3E PGE flotation recoveries. Flotation recoveries were however lower for the finest external air classifier product, which had a less steep PSD. A similar difference in PSD was observed for the screening vertical roller mill circuit products, which also had lower flotation recoveries than products generated with the internal dynamic air classifier. The research indicates that the vertical roller mill is able to efficiently prepare material for valuable mineral concentration through flotation. The effects that the vertical roller mill variables grinding pressure and dam ring height have on operation and the comminution product has been investigated. Furthermore the VRM has been successfully coupled with different classification devices to generate a product with flotation response better than that of tumbling mill products

A survey of training programs for auxiliary school personnel in environmental education in New England with emphasis on the role of environmental aides.

EducationDoctor of Education (Ed.D.

Design and evaluation of a digital processing unit for satellite angular velocity estimation

A satellite's absolute attitude and angular rate are both important measurements for satellite missions that require navigation. Typically, these measurements have been made by separate sensors, with star cameras being used to determine a satellite's absolute attitude, and gyroscopes being used as the primary rate sensors. Recently, there have been multiple efforts to measure both of these quantities using only the star camera, however the work primarily involves solutions where the optical sensor and the unit that processes the images are separate integrated circuits. Operation in this modality requires the use of chip to chip communication in order to estimate angular rate from star tracker images, which can lead to an increase in system power, a degradation in performance, and increased latency. The goal of this thesis is to consolidate the sensing and processing into a single integrated circuit. The design and evaluation of a digital processing unit that estimates angular rate and facilitates the realization of image sensor and processor integration is presented. The processing unit is implemented in UMC's 130 nm process, has an area of 10 mm × 200 μm, and consumes 8.253 mW of power

Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?

We use measurements of the projected galaxy correlation function w_p and galaxy void statistics to test whether the galaxy content of halos of fixed mass is systematically different in low density environments. We present new measurements of the void probability function (VPF) and underdensity probability function (UPF) from Data Release Four of the Sloan Digital Sky Survey, as well as new measurements of the VPF from the full data release of the Two-Degree Field Galaxy Redshift Survey. We compare these measurements to predictions calculated from models of the Halo Occupation Distribution (HOD) that are constrained to match both w_p and the space density of galaxies. The standard implementation of the HOD assumes that galaxy occupation depends on halo mass only, and is independent of local environment. For luminosity-defined samples, we find that the standard HOD prediction is a good match to the observations, and the data exclude models in which galaxy formation efficiency is reduced in low-density environments. More remarkably, we find that the void statistics of red and blue galaxies (at L ~ 0.4L_*) are perfectly predicted by standard HOD models matched to the correlation function of these samples, ruling out "assembly bias" models in which galaxy color is correlated with large-scale environment at fixed halo mass. We conclude that the luminosity and color of field galaxies are determined predominantly by the mass of the halo in which they reside and have little direct dependence on the environment in which the host halo formed. In broader terms, our results show that the sizes and emptiness of voids found in the distribution of L > 0.2L_* galaxies are in excellent agreement with the predictions of a standard cosmological model with a simple connection between galaxies and dark matter halos. (abridged)Comment: 20 emulateapj pages, 9 figures. submitted to Ap

Adult bobcat (\u3ci\u3eLynx rufus\u3c/i\u3e) habitat selection in a longleaf pine savanna

Background: Pine savannas are primarily managed with frequent prescribed fire (≤ 3 years) to promote diversity of flora and fauna, and to maintain open, park-like conditions needed by species such as the endangered red-cockaded woodpecker (Picoides borealis). However, a knowledge gap exists in our understanding of bobcat (Lynx rufus) habitat selection in longleaf pine savannas and research is warranted to direct our future management decisions. Methods: We examined bobcat habitat selection in a pine savanna managed with frequent fires at two spatial scales (i.e., study area boundary [hereafter, landscape scale]) and annual area of use [95% kernel density; local scale]), and assessed effects of prescribed fire on bobcat habitat selection. Specifically, we monitored 45 bobcats (16 males and 29 females) during 2001–2007. Results: We found differential habitat selection by sex. At the landscape scale, female bobcats were closer to mixed pine-hardwoods, young pine, and secondary roads, but farther from mature pine and hardwoods stands relative to males. We found no difference in selection of agriculture, shrub-scrub, and primary roads between sexes. At the annual area of use scale, female bobcats were closer to secondary roads, but farther from agriculture and shrub-scrub relative to males. We found no difference in selection of mature pine, mixed pine-hardwoods, hardwoods, young pine, and primary roads between sexes. Bobcats primarily selected for stands burned ≤ 1.1 years post-fire. Conclusions: Our results show that bobcats exploit a broad range of habitat types in pine landscapes managed with frequent fire and commonly use recently burned stands (≤ 1.1 year post-fire), suggesting prey in many areas of this system are at risk of bobcat predation. Additionally, we suggest land managers consider scale of selection by bobcats when developing habitat management strategies

Habitat Characteristics of Eastern Wild Turkey Nest and Ground-roost Sites in 2 Longleaf Pine Forests

Managing and restoring longleaf pine forests throughout the Southeast is a conservation priority. Prescribed fire is an integral part of these activities, as it is the primary means of controlling hardwood encroachment and maintaining native groundcover. Nest site and preflight brood groundroost site selection of eastern wild turkeys (Meleagris gallopavo silvestris) has not been well studied in longleaf pine systems. Therefore, we determined habitat characteristics associated with wild turkey nests and ground-roosts in 2 longleaf pine forests in southwestern Georgia. We radio-tagged 45 female turkeys and evaluated habitat characteristics associated with 84 nests and 51 ground-roosts during the 2011–2013 nesting seasons. Nests were located farther from mature pine and mature pine-hardwood stands and closer to shrub/scrub habitats than expected. Nests were also negatively associated with percent canopy closure and positively associated with percent woody ground cover and vegetation height. Ground-roosts were closer to mature pine-hardwood stands and open water than were random sites. We suggest that management of longleaf pine forests should focus on maintaining open-canopied forests with adequate understory vegetation to serve as nesting and brood-rearing cover. Our findings suggest that frequent prescribed fire (≤ 2 years), when the management goal is to optimize restoration of longleaf ecosystems, is conducive to maintaining wild turkey populations

Survival and cause-specific mortality of female eastern wild turkeys in two frequently-burned longleaf pine savannas

Longleaf pine savannas have declined throughout the southeastern United States due to land-use change. Fortunately, natural resource professionals are currently restoring these ecologically and economically important savannas. Although efforts are underway to restore longleaf pine savannas, little information exists on female eastern wild turkey Meleagris gallopavo silvestris population dynamics in these systems. Therefore, we evaluated survival and cause-specific mortality of female eastern wild turkeys in two longleaf pine savannas in southwestern Georgia. We radio-marked 126 female wild turkeys during 2010–2013 and monitored their survival; 66 (52.4%) radio-marked females died during the study. We estimated causes of death for 37 mortality events with predation serving as the leading known cause of mortality, with 35.1% of mortalities attributed to mesocarnivore predation (e.g., bobcat Lynx rufus, coyote Canis latrans, and gray fox Urocyon cinereoargenteus) and 18.9% to great-horned owl Bubo virginianus predation. One female (2.7%) was hit by a vehicle. Seasonal survival estimates varied from a high during fall (Ŝ = 0.94; 95% CI: 0.86–1.00) to a low during spring (Ŝ = 0.76; 95% CI: 0.68–0.87). Survival of incubating females was 0.82 (95% CI: 0.71–0.93) and survival of nonincubating females was 0.67 (95% CI: 0.52–0.87). Annual survival was 0.55 (95% CI: 0.44–0.67). To ensure sustainable wild turkey populations in longleaf pine savannas, we suggest managers monitor relationships between survival and population productivity

Eastern wild turkey nest site selection in two frequently burned pine savannas

Introduction: Reproductive success is a critical factor affecting avian demographics and can be influenced by many factors including nesting chronology, predation risk, and fine-scale nest site selection. Methods: We modeled the relative influences of habitat-related covariates at six spatial scales (nest site: 15-, 40-, 80-, 120-, 160-, and 200-m radii) on Eastern wild turkey (Meleagris gallopavo silvestris) nest site selection in two pine savannas managed by frequent prescribed fire (≤3 years) in southwestern Georgia during 2011–2013. Results: Nest site (15-m scale) habitat metrics (mean visual obstruction [cm] and canopy closure [%]) had the greatest influence on nest site selection relative to covariates measured at larger spatial scales. Scaled odds ratios suggested that nests were 26.8 % more likely to occur for every 10 cm increase in mean vegetation height with a range of 7.5 to 150.0 cm and 18.5 % less likely to occur for every 10 % increase in canopy closure with a range from 0.0 to 97.8 %. Total ground cover, canopy closure, edge density, and percent land cover type (e.g., mature pine, mixed pine/hardwood, shrub/scrub) had minimal influence on nest site selection. Conclusions: Management of pine savannas for turkey nest sites should focus on creating early-successional vegetation to conceal nests from potential predators. Additionally, we suggest that future studies consider evaluating the influence of spatial scale on turkey nest site selection

Survival and cause-specific mortality of female eastern wild turkeys in two frequently-burned longleaf pine savannas

Longleaf pine savannas have declined throughout the southeastern United States due to land-use change. Fortunately, natural resource professionals are currently restoring these ecologically and economically important savannas. Although efforts are underway to restore longleaf pine savannas, little information exists on female eastern wild turkey Meleagris gallopavo silvestris population dynamics in these systems. Therefore, we evaluated survival and cause-specific mortality of female eastern wild turkeys in two longleaf pine savannas in southwestern Georgia. We radio-marked 126 female wild turkeys during 2010–2013 and monitored their survival; 66 (52.4%) radio-marked females died during the study. We estimated causes of death for 37 mortality events with predation serving as the leading known cause of mortality, with 35.1% of mortalities attributed to mesocarnivore predation (e.g., bobcat Lynx rufus, coyote Canis latrans, and gray fox Urocyon cinereoargenteus) and 18.9% to great-horned owl Bubo virginianus predation. One female (2.7%) was hit by a vehicle. Seasonal survival estimates varied from a high during fall (Ŝ = 0.94; 95% CI: 0.86–1.00) to a low during spring (Ŝ = 0.76; 95% CI: 0.68–0.87). Survival of incubating females was 0.82 (95% CI: 0.71–0.93) and survival of nonincubating females was 0.67 (95% CI: 0.52–0.87). Annual survival was 0.55 (95% CI: 0.44–0.67). To ensure sustainable wild turkey populations in longleaf pine savannas, we suggest managers monitor relationships between survival and population productivity

Lifting the Anterior Midcheek and Nasolabial Fold:Introduction to the Melo Fat Pad Anatomy and Its Role in Longevity and Recurrence

BACKGROUND: A limitation of current facelift techniques is the early postoperative reappearance of anterior midcheek laxity associated with recurrence of the nasolabial fold (NLF).OBJECTIVES: This study was undertaken to examine the regional anatomy of the anterior midcheek and NLF with a focus on explaining the early recurrence phenomenon and to explore the possibility of alternative surgical methods that prolong NLF correction.METHODS: Fifty cadaver heads were studied (16 embalmed, 34 fresh, mean age 75 years). Following preliminary dissections and macro-sectioning, a series of standardized layered dissections were performed, complemented by histology, sheet plastination and micro-CT. Mechanical testing of the melo fat pad (MFP) and skin was performed to gain insight on which structure is responsible for transmission of the lifting tension in a composite facelift procedure.RESULTS: Anatomical dissections, sheet plastination and micro-CT demonstrated the three-dimensional architecture and borders of the MFP. Histology of a lifted midcheek demonstrated that a composite MFP lift causes a change in connective tissue organization from a hanging-down pattern into a pulled upward pattern suggesting traction on the skin. Mechanical testing confirmed that, in a composite lift, despite the sutures being placed directly into the deep aspect of the MFP, the lifting tension distal to the suture is transmitted through the skin and not through the MFP.CONCLUSIONS: As a composite midcheek lift is usually performed, it is the skin and not the MFP itself, that bears the load of the non-dissected tissues distal to the lifting suture. For this reason, early recurrence of the NLF occurs following skin relaxation in the postoperative period. Accordingly, specific surgical procedures for remodeling the MFP should be explored, possibly in combination with volume restoration of the fat and bone, for more lasting improvement of the NLF.</p