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: Pemisahan Torium dan Uranium dari Pasir Monazit Pulau Bangka dengan Metode Destruksi dan Pengendapan
Abstrak: Thorium and uranium can be separated from monazite sand by destruction and precipitation method. Destruction was carried out using NaOH by wet and dry destruction method. Solids as the destruction result were diluted in concentrated HCl, followed by precipitation using NH4OH at pH 4 and 7. The precipitates were characterized by x-ray fluorescence. Thorium and uranium content from dry destruction were 2.40% and 0.137%, while those from wet destruction were 3.52% and 0.161%, respectively. Thorium and uranium from wet destruction had higher solubility than those from dry destruction method. By wet destruction methods the precipitates could not be obtained at pH 4, while at pH 7 the precipitates showed higher thorium content but lower uranium content than those by dry destruction. Based on thorium and uranium contents, the two methods did not give satification as separation output.
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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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