Abstract. Graphite ore obtained from Kolaka Regency, South East Sulawesi, Indonesia have been succesfully investigated for beneficiation by froth flotation technique. Preliminary study have been done to determine the minerals types, fixed carbon content and liberation size of the graphite. Graphite is naturally floatable due to its hydrophobic property. Some suitable reagents are usually added to increase effectiveness of recovery. In this article, enrichment of graphite by froth flotation was studied by investigating the effect of reagents concentrations, rotation speed and particle size on the carbon grade and recovery of the concentrate. The carbon grade increased from 3.00% to 60.00% at the optimum flotation conditions.

The growth of Mg-doped GaN thin films by metalorganic chemical vapor deposition (MOCVD) using NH3 and Cp2Mg as a source of nitrogen and Mg, respectively, usually produces Mg–H complexes, which hinder the activation of Mg as shallow acceptor centers. Therefore, post-growth treatments are commonly required to activate these acceptor centers. The presence of Mg dopants in GaN films induces various defect-related emissions whose characteristics depend on the growth method. For this study, we prepared Mg-doped GaN thin films by plasma-assisted MOCVD. A nitrogen-plasma, instead of NH3, served as a nitrogen source to minimize the formation of Mg–H complexes, thereby eliminating the requirement for post-growth treatment. The emission characteristics were obtained by measuring the photoluminescence of the as-grown room-temperature films. Yellow, green, blue, and ultraviolet emission bands are produced by Mg-doped samples with different Mg concentrations produced by Cp2Mg flow rates of 2%, 5%, and 10% of the total flow rate. Low-Mg concentration leads to nitrogen and gallium vacancies, which results in yellow photoluminescence. At higher Mg concentration, the yellow photoluminescence is suppressed and the blue photoluminescence is enhanced because of the incorporation of vacancies by Mg atoms. The analysis of the photoluminescence spectra leads to the proposed band diagrams for Mg-doped GaN with varying Mg concentration.

Chitosan:SiO2 nanocomposite (Cs:SiO2 NCs) is synthesized via aerosol processing. Ultrasonic spray drying apparatus was used to produce smaller sized composite particles with spherical morphology. Composite from shrimp shell and water glass (Na2SiO3) as silica precursor were used for the preparation. Cs:SiO2 NCs were characterized by Fourier Transform Infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) to know about the chemical bonding and morphology of the particles, respectively. Based on the FTIR investigation the absorption peak at 1090 cm−1 represents the reaction of silanol groups of silica with carbonyl groups of polymers leading to the formation of Si-O-C bonds. The morphology of Cs:SiO2 NCs was more spherical than chitosan particles with relatively narrow size distribution. The smaller particle size of Cs:SiO2 NCs is potentially applied to engineer the material for drug delivery system.

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