Judul: Pemurnian Trinatrium Fosfat Hasil Samping Pengolahan Monasit dengan Metode Rekristalisasi dan Adsorpsi.
Abstrak: Proses pengolahan monasit menjadi rare earth element (REE) dengan metode basa menghasilkan produk samping berupa garam trinatrium fosfat (Na3PO4). Garam tersebut masih mengandung pengotor yang bersifat radioaktif, yaitu 125.25 ppm uranium (U) dan 702 ppm torium (Th). Tujuan penelitian ini adalah memurnikan Na3PO4 dengan metode rekristalisasi dan adsorpsi. Kondisi optimum rekristalisasi yang didapatkan ialah konsentrasi awal larutan Na3PO4 77.34 g/100 mL dengan waktu pengadukan 30 menit. Rasio adsorben optimum yang didapatkan adalah 10% dengan campuran adsorben karbon aktif dan bentonit (7:3). Rendemen Na3PO4 hasil rekristalisasi mencapai 90% dengan kemurnian fosfat 97%. Kadar uranium pada kristal menurun dari 125.25 hingga 54.41 ppm dan kadar Th tidak terdeteksi. Analisa termogravimetrik (TGA) kristal hasil rekristalisasi membuktikan terdapat 12 molekul H2O pada kisi kristal. Spektra fourier transform infrared (FTIR) Na3PO4 menunjukkan vibrasi ulur PO43- pada bilangan gelombang 993 cm-1, vibrasi asimetri dan simetri H2O pada bilangan gelombang 3585 cm-1 dan 2910−3585 cm-1, dan vibrasi tekuk H2O pada bilangan gelombang 1651 cm-1. Titik leleh kristal yang didapatkan memiliki rentang yang sempit sesuai dengan standar, yaitu 73−78.3 °C.
Keyword: adsorpsi, monasit, rekristalisasi, trinatrium fosfat

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: Construction of Strongly Optimal Binary Linear Code with Minimum Distance 9 and 11
Abstrak: A binary linear code of length n over q F is a subspace of n q F . A code has three parameters that attached to it, namely length, dimension, and minimum distance. A code with length n, dimension k and minimum distance d is often called [n, k, d ]-code. Usually, when two parameters are given, then we want to find a code that has the best value for the last parameter. Based on Gilbert- Varshamov bound, if a [n, k, d ]-code exists and can not be expanded, we call it a strongly optimal code. In this paper, we construct strongly optimal code with minimum distance 9 and 11. In constructing the code, we created a theorem and algorithm based on Gilbert-Varshamov bound before we implement the algorithm to MAPLE programming language. Because of computational limitations, the program can only construct up to k = 10 for d = 9 and k = 12 for d = 11.
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