SURFACE CHEMISTY STUDY OF MONAZITE FLOTATION IN COAL REFUSE SYSTEMS

Rare earth mineral recovery from alternative resources such as coal and coal byproducts is increasingly important to provide an opportunity for economic recovery from U.S. sources. Currently, China produces the majority of the 149,000 tons of rare earth elements used annually worldwide of which the U.S. imports 11% or around 16,000 tons. There are no significant mining operations producing rare earth elements in the U.S. However, there are many U.S. sources containing rare earth minerals such as monazite including heavy mineral sand and phosphate operations. Monazite mineral particles of a few microns have also been detected in Fire Clay seam coal. Preliminary attempts to concentrate the rare earth mineral using flotation test results indicated that monazite was floated together with carbonate minerals. The flotation chemistry of a monazite-carbonate mineral system has received limited attention by researchers. As such, a systematic study of monazite flotation chemistry was conducted and the results reported in this dissertation. The surface charging mechanisms of monazite in aqueous systems were studied using electrokinetic tests, solution equilibrium calculation, crystal structure analysis, and electrostatic model prediction. The surface charge of monazite was found to be developed by protonation/deprotonation reactions. In other words, the hydrogen and hydroxyl ions were potential determining ions instead of the lattice ions of monazite. Electrokinetic tests of natural monazite mineral showed that the isoelectric point (IEP) occurred at pH 6.0. Solution equilibrium calculation and electrostatic model predictions of cerium monazite (CePO4) yielded an IEP of pH 7.2. The discrepancy between the two IEP values may be due to the different REE composition and/or the amount of carbon dioxide dissolved in solution. A common collector used to produce a hydrophobic monazite surface is octanohydroxamic acid. Adsorption studies found multilayer formation of octanohydroxamic acid on monazite surfaces at pH values of 3.0, 6.0, and 9.0. A kinetic study showed that the maximum adsorption density and rate for below monolayer coverage occurred at a solution pH value of 9.0, which was attributed to the chemical reaction between octanohydroxamate species and surface active sites (e.g., REE(OH)2+). For beyond multilayer adsorption, maximum adsorption occurred at pH 11.0 due to the abundance of hydroxyl ions in solution. The contributing effect of hydroxyl ions was proven by titration tests and FTIR analyses. When calcium ions existed in solution, specific adsorption of Ca(OH)+ on monazite surfaces occurred in both neutral and basic environments as indicated by the electrokinetic results. At low concentrations, Ca(OH)+ competed with octanohydroxamic acid for P-OH sites. However, higher dosages of Ca(OH)+ served as active sites for octanohydroxamic acid. The monazite floatability was negatively affected by the hydration of the adsorbed calcium species. The calcium ion dissolved from calcite mineral surfaces, which exist in the coal sources, provided an explanation for the depression of monazite in the combined systems. Single mineral flotation of monazite and calcite showed that sodium silicate and sodium hexametaphosphate efficiently depressed calcite while providing minimal effects on monazite recovery. However, in the monazite-calcite combined system, both monazite and calcite were depressed using the two regulators. Electrokinetic data and solution equilibrium calculations indicated that hydrolyzed species of calcium such as Ca(OH)+ interacted with silicates and formed a compact hydrophilic layer on monazite surfaces by hydrogen bonding and surface reaction. The compact layer decreased collector adsorption due to steric hindrance. Using 6×10-5 M EDTA together with 2.5×10-4 M octanohydroxamic acid and 0.05 g/L sodium silicate, monazite recovery of more than 90% was achieved while only recovering 20% of calcite. Based on the fundamental study, rare earth concentrates with 4700 ppm of REEs were produced from the Fire Clay fine coal refuse using column flotation

The Effect of Conditioning on the Flotation of Pyrrhotite in the Presence of Chlorite

The influence of conditioning on the flotation of pyrrhotite in the presence of chlorite was investigated through flotation tests, sedimentation tests, and X-ray photoelectron spectroscopy (XPS) analysis. The flotation results show that chlorite slimes dramatically impair the flotation of pyrrhotite. Sedimentation and flotation tests reveal that conditioning can effectively remove chlorite slimes from pyrrhotite surfaces, resulting in an enhanced flotation recovery of pyrrhotite. When mixed minerals were conditioned under the natural atmosphere, a faster conditioning speed and longer conditioning time decreased the flotation recovery of pyrrhotite. However, when mixed minerals were conditioned under a nitrogen atmosphere, a more intensive conditioning process provided better flotation results. XPS analyses illustrate that a faster conditioning speed and longer conditioning time under the natural atmosphere accelerates the oxidation of pyrrhotite, leading to a decrease in the flotation recovery of pyrrhotite

Design And Experiment of Axial Air-Suction Drum Seed-Metering Device

This study developed an axial air-suction drum seed-metering device without a special vacuum pump and associated pipeline facilities, greatly simplifying the structure of the air-suction drum seed-metering device, which aimed to solve the problems of complex structure and difficult maintenance of traditional air suction drum seed-metering device. The geometric model of the seed-metering device was established by SOLIDWORKS. In addition, numerical simulation tests were carried out on the seed-metering device based on CFD to verify the feasibility of the theoretical operation of the seed-metering device. The seed-metering device was processed and a test bench was built for physical testing, which verified the feasibility of the actual operation of the seed-metering device. The bench test results showed that when the fan speed reached 2100 rpm, the adsorption rate of the seed-metering device on tomato seeds, pepper seeds, and eggplant seeds reached more than 86.39%,87.22%, and 93.06%, respectively. Besides, when the fan speed reached 2400 rpm, the adsorption rate of the seed-metering device on tomato seeds, hot pepper seeds, and eggplant seeds all reached more than 95%, which demonstrated that the seed-metering device has good seed suction performance despite its straightforward design

ODSum: New Benchmarks for Open Domain Multi-Document Summarization

Open-domain Multi-Document Summarization (ODMDS) is a critical tool for condensing vast arrays of documents into coherent, concise summaries. With a more inter-related document set, there does not necessarily exist a correct answer for the retrieval, making it hard to measure the retrieving performance. We propose a rule-based method to process query-based document summarization datasets into ODMDS datasets. Based on this method, we introduce a novel dataset, ODSum, a sophisticated case with its document index interdependent and often interrelated. We tackle ODMDS with the \textit{retrieve-then-summarize} method, and the performance of a list of retrievers and summarizers is investigated. Through extensive experiments, we identify variances in evaluation metrics and provide insights into their reliability. We also found that LLMs suffer great performance loss from retrieving errors. We further experimented methods to improve the performance as well as investigate their robustness against imperfect retrieval. We will release our data and code at https://github.com/yale-nlp/ODSum

Remote Sensing Evidence for Significant Variations in the Global Gross Domestic Product during the COVID-19 Epidemic

Coronavirus disease 2019 (COVID-19) has been spreading rapidly and is still threatening human health currently. A series of measures for restraining epidemic spreading has been adopted throughout the world, which seriously impacted the gross domestic product (GDP) globally. However, details of the changes in the GDP and its spatial heterogeneity characteristics on a fine scale worldwide during the pandemic are still uncertain. We designed a novel scheme to simulate a 0.1° × 0.1° resolution grid global GDP map during the COVID-19 pandemic. Simulated nighttime-light remotely sensed data (SNTL) was forecasted via a GM(1, 1) model under the assumption that there was no COVID-19 epidemic in 2020. We constructed a geographically weighted regression (GWR) model to determine the quantitative relationship between the variation of nighttime light (ΔNTL) and the variation of GDP (ΔGDP). The scheme can detect and explain the spatial heterogeneity of ΔGDP at the grid scale. It is found that a series of policies played an obvious role in affecting GDP. This work demonstrated that the global GDP, except for in a few countries, represented a remarkably decreasing trend, whereas the ΔGDP exhibited significant differences

Altered Gray Matter Volume and Its Correlation With PTSD Severity in Chinese Earthquake Survivors

Objective: To detect the changes of gray matter volume (GMV) and their correlation with severity of symptom in patients with post-traumatic stress disorder (PTSD) who were defined with updated DSM-5 diagnostic criteria.Method: 71 participants were assigned into PTSD group (n = 35) or trauma-exposed control (TEC) group (n = 36) with the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Voxel-based morphometry analysis was used to detect alterations in GMV in the PTSD group.Results: We found that the PTSD group had larger GMV in the left middle temporal gyrus (MTG) and in the right dorsal medial prefrontal cortex (dmPFC), and smaller GMV in the region of the right temporal pole (TP) than the TEC group. We also found that PTSD Checklist for DSM-5 (PCL-5) scores correlated positively with the left MTG and right dmPFC GMV, and negatively with left TP GMV. These correlations were consistent with the findings of the between-group comparisons.Conclusions: GMV alterations in the MTG, dmPFC, and TP are detected in the group comparisons and correlated with symptom severity when classifying PTSD individuals according to DSM-5 diagnostic criteria within an earthquake-exposed population

Bis{tris­[3-(2-pyrid­yl)-1H-pyrazole]iron(II)} tetra­deca­molybdo(V,VI)silicate

The asymmetric unit of the title compound, [Fe(C8H7N3)3]2[SiMo14O44], consists of a complex [Fe(C8H7N3)3]2+ cation and half of a derivative of an α-Keggin-type anion, [SiMo14O44]4−. In the mixed-valent MoV/VI anion, the α-Keggin type core is capped on two oppositely disposed tetra­gonal faces by additional (MoO2) units. The [SiMo14O44]4− anion shows disorder. Two O atoms of the central SiO4 group ( symmetry) are equally disordered about an inversion centre. Moreover, two of the outer bridging O atoms and the O atoms of the capping (MoO2) unit are likewise disordered. The Fe2+ cation is surrounded in a slightly distorted octa­hedral coordination by six N atoms from three 3-(2-pyrid­yl)-1H-pyrazole ligands. N—H⋯O hydrogen bonding between the cations and anions leads to a consolidation of the structure

Identifying Population Hollowing Out Regions and Their Dynamic Characteristics across Central China

Continuous urbanization and industrialization lead to plenty of rural residents migrating to cities for a living, which seriously accelerated the population hollowing issues. This generated series of social issues, including residential estate idle and numerous vigorous laborers migrating from undeveloped rural areas to wealthy cities and towns. Quantitatively determining the population hollowing characteristic is the priority task of realizing rural revitalization. However, the traditional field investigation methods have obvious deficiencies in describing socio-economic phenomena, especially population hollowing, due to weak efficiency and low accuracy. Here, this paper conceives a novel scheme for representing population hollowing levels and exploring the spatiotemporal dynamic of population hollowing. The nighttime light images were introduced to identify the potential hollowing areas by using the nightlight decreasing trend analysis. In addition, the entropy weight approach was adopted to construct an index for evaluating the population hollowing level based on statistical datasets at the political boundary scale. Moreover, we comprehensively incorporated physical and anthropic factors to simulate the population hollowing level via random forest (RF) at a grid-scale, and the validation was conducted to evaluate the simulation results. Some findings were achieved. The population hollowing phenomenon decreasing gradually was mainly distributed in rural areas, especially in the north of the study area. The RF model demonstrated the best accuracy with relatively higher R2 (Mean = 0.615) compared with the multiple linear regression (MLR) and the geographically weighted regression (GWR). The population hollowing degree of the grid-scale was consistent with the results of the township scale. The population hollowing degree represented an obvious trend that decreased in the north but increased in the south during 2016–2020 and exhibited a significant reduction trend across the entire study area during 2019–2020. The present study supplies a novel perspective for detecting population hollowing and provides scientific support and a first-hand dataset for rural revitalization