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lmenite (FeO.TiO2) ore from Bangka island-Indonesia is a potential raw material for synthesizing titanium dioxide (TiO2), which can be used further as pigmen and photocatalyst. The fabrication of TiO2 particles from ilmenite can be carried out through the solvent extraction using sulfuric acid route. Therefore, the solubility of the ilmenite ore in sulfuric acid environment is one of the key factors to obtain the desired TiO2 particles. The current research is aimed at comparing the solubility of pristine Bangka ilmenite ore with that of precedingly decomposed by sodium hidroxide (NaOH) in pressurized and atmospheric reflux reactors. The dissolution of both precursors was carried out in those reactors under various temperatures of 75, 100, 125, 150 and 175°C. The results showed that the optimum dilution was achieved at 150°C. The obtained recovery of ilmenite was 88.8 % for the pressurized reactor and 75.5% for the atmospheric reflux reactor. The solubility of titanium (Ti) element increased steadily to reach a recovery of 68% at 150°C and decreased significantly afterwards. It was also found that the increase of iron (Fe) element solubility was proportional to the increase of processing temperatures.

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ABSTRAKProses pelindian mangan dari bijih mangan dioksida dalam larutan asam sulfat telah berhasil dilakukan. Tujuan penelitian untuk mempelajari pengaruh dari kecepatan pengadukan, konsentrasi asam sulfat dan perbandingan massa padatan/larutan terhadap mangan yang terekstrak. Dalam penelitian ini, bijih mangan dipreparasi melalui proses reduksi menggunakan arang pada 700 o C selama 120 menit selanjutnya dilindi menggunakan larutan asam sulfat. Pada setiap percobaan, sebanyak 75 gram sampel dimasukkan dan dilindi dengan 750 ml larutan H 2 SO 4 dalam gelas reaktor.Setelah proses pelindian, kemudian disaring dan dianalisa dengan menggunakan Atomic Absorption Spectrometer. Hasil percobaan menunjukkan bahwa laju pelindian meningkat dengan naiknya kecepatan pengadukan dan konsentrasi asam serta menurunnya rasio perbandingan persen padatan. Kondisi optimum diperoleh pada kecepatan pengadukan 400 rpm, konsentrasi asam sulfat 12% pada 75 o C selama 180 menit dengan mangan terekstrak sebesar 84,61%.Kata kunci : asam sulfat, bijih mangan, pelindian, mangan sulfat ABSTRACTThe leaching of manganese from manganese dioxide ores in sulfuric acid solution was investigated. The effects of agitation, sulfuric acid concentration and solid/liquid mass ratio on the leaching efficiency of manganese were studied. In this study, manganese dioxide ores were treated by reduction roasting using charcoal as a reductant at 700 o C for 120 min. Then, roasted samples were subjected to extract manganese by sulfuric acid leaching. in each leaching test, 75 g of sample was put and leached in a glass reactor with 750 mL sulfuric acid solution. At the end of each leaching experiment, the slurry was filtered and the filtrate was analyzed by Atomic Absorption Spectrometer. The experimental results indicated that the leaching rate increases with the increases of the agitation, sulfuric acid concentration and with the decreases of solid/liquid mass ratio. The optimal condition for leaching manganese from manganese dioxide ores was determined as the agitation of 400 rpm and sulfuric acid concentration of 12%for 180 minat 75 o C. Under the optimal condition, the leaching efficiency of manganese can reach 84.61%.

Nickel is obtained from laterite ores by a metallurgical process to produces ferronickel. Nickel metal is present in a carrier mineral, a nickel magnesium silicate hydrate compound called garnierite. Garnierite is the common name of magnesium silicate hydrate minerals including chlorite, clay and serpentine. This study to investigate the phase formed when the nickel ore is roasted from a temperature of 600°C to a temperature of 1000°C under atmospheric enviromental. Microscopic analysis of roasted samples was analyzed by SEM-EDX and the dehydroxylation and recrystallization was studied using DTA-TGA. The endothermic peak was appear at 78.8°C, 293.7°C and 638.0°C, this corresponds to the release of free water and the release of crystalline water. While the exothermic peak occurs at 828.0°C. The exothermic temperatures associated with structural changes due to dihydroxylation of serpentine into a forsterite phase. Based on the XRD graph it is known that the sample of the roasting will produce the olivine and forsterite phases.

Ferronickel slag is a by-product of the nickel smelting process. Recycling of ferronickel slag is required since it contains valuable elements besides its potency to pollute the environment. In order to take advantage of the valuable materials and reducing the potential hazard, beneficiation of ferronickel slag is essential. Alkali fusion of ferronickel slag using Na2CO3 in the roasting process was carried out. This study aims to determine the decomposition of the mixture of ferronickel slag-Na2CO3 in the roasting process. Roasting temperature and time were 800–1,000 °C and 60‒240 minutes, respectively. Characterizations of the ferronickel slag were conducted by XRF, ICP-OES, XRD and SEM-EDS. Meanwhile, roasted products were characterized using ICP-OES, XRD and SEM-EDS. Characterization of the ferronickel slag indicates that Mg and Si are the main elements followed by Fe, Al and Cr. Moreover, olivine is detected as the main phase. The roasting process caused percent weight loss of the roasted products, which indicates decomposition occurred and affected the elements content, phases and morphology. The roasting process at about 900 °C for 60 minutes is a preferable decomposition base on the process conditions applied and the change of elements content. Aluminum (Al) and chromium (Cr) content in the roasted products upgraded significantly compared to iron (Fe) and magnesium (Mg) content. Olivine phase transforms to some phases, which were bounded with the sodium compound such as Na2MgSiO4, Na4SiO4 and Na2CrO4. The rough layer is observed on the surface of the roasted product as a result of the decomposition process. It indicates that liquid-solid mass transfer is initiated from the surface