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Recovery of Rare Earth Elements from Apatite Ores by Hydrometallurgical Prosess
Get PDF秋田大学博士（工学）The demand for rare earth elements has increased in recent years due to uncertainty of supply and the high technological applications associated with their electronic, optical and magnetic properties. Currently, China has provided over 90% of the world's total output of rare earths. Commercially operating mines around the world mainly extract bastnasite, monazite and xenotime ores. Due to fast depletion of REEs reserves, the another rare earth sources need to be found. Apatite is one of the important REEs host minerals and can be a potential source for the REEs. Separation of REEs from apatite has not been studied extensively compared with other main minerals such as monazite, bastnasite and xenotime. The experimental trials for the selective leaching of REEs from apatite were still unsuccessful with sulphuric acid because calcium and most REEs contained in apatite were precipitated as a phosphogypsum. Therefore, it was essential to develop an effective method for extraction of REEs from apatite ores. This rsearch intended to cultivate REEs recovery process from apatite ores by leaching, solvent extraction, stripping, precipitation and calcination. This PhD thesis composes of (5) chapters: introduction, main (3) chapters, where an advanced hydrometallurgical process of REOs production from apatite were discussed, and the conclusion
Develoment of Metal Supply Risk Assessment Method
Get PDF秋田大学博士（資源学）Measuring the supply risk of metals is of great importance for corporations to control market risks, for nations to make strategical investments or trading plans, and for humanity to achieve sustainability in the long run. Academically, supply risk of metals was discussed in metals’criticality studies, where,“supply risk”represented one aspect of criticality together with“importance to economy”and“environmental implication”. In these studies,“supply risk”was mainly measured by the weighted average of a series of arbitrarily selected risk indicators. Due to the subjective selection of the risk indicators and invalid weighting methods used in the studies, the results of those studies are too ambiguous to obtain practical significance. In view of these shortages, this doctoral study is aimed at finding solutions to evaluate supply risk of metals at different periods, and thereby, help relevant stakeholders take informed decisions.
The sources of supply risk of metals vary according to the time periods. In the short term (one year or lesser), market risk should be considered a priority. It could come from the price volatility of metal commodities, which dominates the profitability of a project. In the medium term (one to five years), risks related to international investments should be considered a priority. This is because no country can stand alone in terms of natural resources; countries heavily depend on each other. For foreign direct investments, institutional conditions of countries with resource sovereignty are the primary consideration, especially in an era where mining is increasingly concentrated in developing countries. In the long term (ten years or more), human society, as a community with a shared future, will have to face physical depletion of natural resources, since resources buried in the earth's crust are limited, and recycling rates had hardly reached 100%. Moreover, long before encountering the physical depletion of ores, increased prices of resources may compel some minerals unavailable economically, leading to economic depletion.
This dissertation mainly contains three parallel but independent studies regarding three periods, and an aggregated assessment based on the results of each period's study. Specifically, in the short term, the objects are copper, nickel, zinc, lead, tin, silver, gold, platinum, and palladium. A new method called Spline-Generalized Autoregressive Conditional Heteroskedasticity was applied to generate the low frequency price volatility series from the original price volatility series. Using this low frequency price volatility, empirical evidence of the impact of macroeconomic variables on price volatility was confirmed. Also, the impact of world unemployment rate; inflation rate of the U.S. dollar; Treasury-EuroDollar spread; Standard & Poor's 500 index; residential property prices in the USA; and exchange rate of the South African rand, the Russian ruble, and the Canadian dollar to the U.S. dollar were found to be significant. Moreover, based on world economic performance in 2017, we found that the riskiest metal in 2018 would be copper with a volatility of 48%, followed by lead (36%) and silver (33%).
In the medium term, the objects are the same nine metals as that studied in the short term. Considering the lack of a quantitative analysis on the common causes of resource nationalism due to data limitation, this study started with a data survey in which the occurrence of resource nationalism in 83 metal-supplying countries from 2000 to 2013 was summarized into a binary panel. Then, an empirical analysis was conducted using the binary choice logit method. As a result, several factors such as high technology export, ores and metals exports, rule of law, natural resource rent, and trade openness were found to be dominating the risk of resource nationalism in high-and-upper-middle-income countries. In lower-middle-and-low-income-countries, changes in mineral rent, government effectiveness, high technology export, and policy perception index were determined to be relevant. Finally, a prediction of the risk of resource nationalism of countries and commodities was made. In 2015, North Korea (100%), Panama (100%), Lao PDR (92%), Mongolia (87%), Kazakhstan (84%), Vietnam (81%), Cuba (78%), Guatemala (72%), Peru (71%), Iran (68%), Venezuela (68%), Papua New Guinea (67%), Russian Federation (63%), Chile (60%), Suriname (54%), Congo (DRC) (54%), and Sierra Leone (51%) were predicted to be risky. The top three risky metals were found to be copper (49%), tin (48%), and silver (46%).
In the long term, to estimate the supply shortage of silver, technological progress in the crystalline silicone (c-Si) photovoltaic (PV) industry was investigated using scenarios including PV lifetime prolongation, technology shift, efficiency improvement, silver demand rate reduction, PV recycling, and total effects. Classic curve fittings and theories (logistic curve, Weibull distribution, intensity of use) were introduced to complete the task. Mining supply was estimated based on parent metal sources, such as copper, zinc, lead, gold and silver. Recycling supply was estimated using a product of silver weighted life-time and end-of-recycling-rate. Demand for silver was divided according to usage, including those for jewelry and silverware, electronics and batteries, photography, c-Si PV, and others. The result shows that silver supply shortage for manufacturing demand will occur from 2030. Technology improvements in the PV industry could delay when the shortage begins, but they will not prevent it. Silver supply shortage for c-Si PV could be eliminated under the total effects scenario.
Finally, we aggregated the results of the three periods into four risk ratings: low, marginal, risky, and crucial. For price volatility, the market Volatility Index (VIX) published by the Chicago Board Options Exchange was used as the risk scale because this index represents implied volatility of the options market. For resource nationalism, Value at Risk was used to divide relative risk levels among countries. For supply shortage, historical supply deficit (real-time balance of supply and demand) was considered as a measurement. As a result, a route map of the supply risk of metals was produced. Taking silver as an example, the result shows that the supply risk of silver would reduce from risky to marginal but rebound to crucial in the long term
Orexin/hypocretin levels in the cerebrospinal fluid and characteristics of myotonic dystrophy type 1 with excessive daytime sleepiness
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Impact of Oxygen Status on 10B-BPA Uptake into Human Glioblastoma Cells, referring to Significance in Boron Neutron Capture Therapy
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Bedside assessment of regional cerebral perfusion using near-infrared spectroscopy and indocyanine green in patients with atherosclerotic occlusive disease.
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Late Pliocene Paleoceanography in the Subpolar North Atlantic (IODP site U1314) deduced from Calcareous Nannofossil Observation
Get PDF秋田大学博士（工学）Calcareous nannofossils were observed to reconstruct surface water conditions during the late Pliocene sediments (2.55 to 2.88 Ma) from the southern Gardar Drift, in the subpolar North Atlantic IODP Site U1314 (56°21.9’1N, 27°53.3’W) at an average resolution of 3 kyr. Based on quantitative analyses twenty-four species belonging to fourteen genera are identified and are rare to very abundant with moderate to good preservation. One calcareous nannofossil datum event is found within the samples interval, which is the Last Occurrence (LO) of Discoaster tamalis in sample B28H-2A, B at 272.81 mcd. It correlates with Datum A discussed by Sato et al. (2004) which is considered strongly related to the heavy glaciation in the Northern Hemisphere. The datum event dates to an age 2.756 Ma, situated within upper Gauss Chron or just below MIS G7. Based on the nannofossil event that is found at IODP Site U1314, the studied interval belongs to Zone NN16 (Martini, 1971). However, referring to Okada and Bukry (1980) the studied interval is included within two Subzones, which are Subzones CN12b and CN12a as defined by the LO of D. tamalis. In general, the coccolith assemblages are dominated by species belonging to genus Reticulofenestra with different (sized-defined) morphotype. Thus the significant changes in paleoceanographic condition are mainly shown by the ratio of Reticulofenstra morphometry.
Calcareous nannofossil assemblage, magnetic susceptibility (MS) and natural gamma radiation (NGR) records in the IODP Site U1314 indicate that the surface ocean condition was very stable with a warm and oligotrophic condition prior to ~2.76 Ma. It is characterized by the dominance of medium and large Reticulofenestra with low detrital input to the site area (low NGR values). The size variations of Reticulofenestra are uni-modal indicated by coccolith size of 3 to 4μm. This suggests an extension of Mid-Pliocene warm influence and the final closure of Central American Seaway (CAS) was incomplete. The warm current originates in eastern equatorial Atlantic flowed to the Pacific Ocean and the northward surface currents were weak with no ice sheets covered the northern hemisphere when the CAS was still opened. The main source of sediment in the Gardar Drift is pelagic sediment that has been eroded and redeposited by the southward flowing Iceland‐Scotland Overflow Water (ISOW) and Northeast Atlantic Deep Water (NEADW) (Grützner and Higgins, 2010). It is reflected with variations of MS values compare with the isotope oxygen stratigraphy. Before ~2.76 Ma, no climatic changes are found in the Arctic Ocean. Therefore the changes of oxygen isotope were only controlled by Antartic ice sheet volume changes. The increased sea ice extent in Antarctic or the Southern Ocean resulted in increased northward influx of Antarctic Bottom Water (AABW) formation and intensified Lower Deep Water (LDW).
At around 2.76 Ma the studied site was marked by the collapse of sea surface stability with strong mixing condition and increased non-magnetic minerals (possibly IRD; Hayashi et al., 2010). It reflects the intensification of Northern Hemisphere Glaciation (NHG) and correlates with the final closure of CAS. This condition is characterized by an abrupt decrease of the maximum coccolith of Reticulofenestra specimens and short-term decrease and increase of MS and NGR values (Hayashi et al., 2010). Afterward as the Quaternary climate style established, the relative abundance of Reticulofenestra coccolith, especially specimens with coccolith size <2 μm and 3-4 μm show a positive and negative correlation to the isotope stratigraphy of Lisiecki and Raymo (2005). The small Reticulofenestra specimens (<2 μm) seem to increase in several colder phases or glacial stages (positive correlation), whereas the Reticulofenestra group of 3-4 μm shows decreasing in abundance during the glacial stages (negative correlation). The orrespondence between those two types of specimens is might be having different preference ecology or different species. The size variations of Reticulofenestra during this period are cyclic changes from uni-modal to bimodal. During interglacial stages, larger Reticulofenestra specimens characterize late Pliocene of subpolar North Atlantic Ocean with warmer and stable ocean condition. It ends with shifting dominance larger Reticulofenestra specimens to smaller size during glacial stages. It is represented by unstable sea surface and mixing condition. The smaller specimens of Reticulofenestra specimens are likely more adaptable to unfavorable conditions, relative to larger specimens, in exploiting limited resources. In the study area, the mixing condition or higher nutrient input might be due to increase of ice sheets that lead to higher velocity of sea surface circulation causes a collapse of sea surface waters, IRD transport and deposition that are triggering eutrophic conditions, the southward migration of the subpolar front, or combination of all factors. Some delays are observed in the peak of smaller Reticulofenestra (<2 μm) compared with the δ18O record of Lisiecki and Raymo (2005), mainly about 10 kyr, relatively. The delays might represent an adaptation of some taxa, which is benefited from oligotrophic environments before ecological collapse occurred
