Judul: Pengayaan Unsur Tanah Jarang Secara Destruksi dan Pengendapan dari Pasir Monasit Bangka
Abstrak: Rare earth elements (REEs) are lanthanide elements widely used in high-tech electronic equipment. In this study, REEs from earth minerals were enriched through several stages, namely destruction, extraction by microwave oven, and precipitation. The dry and wet destruction phases by using NaOH produced a total of 25.56% and 44.30% REEs, respectively. At the extraction by microwaves stage with HCl 37% as solvent, REEs were successfully dissolved in 30 minutes at high energy. Total amount of REEs which contained in the liquid phase from wet and dry destruction were 35.72% and 29.97%, respectively. Precipitation of REEs started when the pH value was higher than 7, reached by using NH4OH 2 N. Total precipitated REEs in wet and dry feed destruction at pH 10 was 2.76% and 1.18%, respectively. Precipitation at pH 10 gave the highest total REEs. Dry feed destruction produced precipitate that effectively enrich REEs by decreasing impurity elements, such as Si and P, and there was no Th element found. It is also contained low U element which was only 12 ppm. This is consistent with the value of percent recovery and the non-radioactive REEs which was smaller than the wet feed destruction, but contains elements of U in the amount of not less than 0.00006 g and without Th element.
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Judul: Destruksi Hasil Samping Penambangan Timah Belitung Menggunakan Microwave untuk Ekstraksi Unsur Tanah Jarang
Abstrak: Rare earth elements (REE) in pure state are widely used for high-tech electronic equipment. Rare earth elements are contained in by-product of tin mining process. This study attempted to use microwave to destruct sample from by-product of tin mining in Belitung as an effort to obtain pure REE. Parameter of destruction is the ratio sample with NaOH, time, and energy. Preliminary test using X-ray fluorescence shows that the sample contains 377 ppm of lantanum (La) and 125 ppm of yttrium (Y). The best destruction condition occured in ratio sample:NaOH, 35:65 with percentage of destruction 19.96% and 4.48% for La and Y; the best destruction time is 30 minutes by the acquirement of 27.95% La and 4.61% Y; best energy at 450 watt by the acquirement of 38.52% La and 13.86% Y. To get La, destruction uses microwave better than oven, but contrary with Y.
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Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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