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    Dissolution of thermally dehydrated ulexite in ammonium acetate solutions
    (Elsevier, 2013) Demirkiran, Nizamettin; Bayrakci, Nazli; Asin, Celal
    Ulexite, a boron mineral, contains a substantial amount of hydration water. Using calcination method, some part of water in the composition of solid can be removed from the solid matrix, and a porous structure can be obtained to increase the reaction rate. The dissolution of the calcined ulexite samples at various temperatures was investigated. Ammonium acetate was used as a leach reagent. The effects of some reaction parameters on the dissolution of the calcined ulexite were examined. It is found that the dissolution rate of calcined samples is higher than that of the uncalcined sample. The dissolution rate of the calcined ulexite is enhanced with increasing calcination temperature up to 150 degrees C. It is determined that the reaction rate conforms to the chemical reaction model. The activation energy of the dissolution process was calculated to be 41.5 kJ/mol.
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    Reductive leaching of pyrolusite ore by using sawdust for production of manganese sulfate
    (Pleiades Publishing Inc, 2012) Ekmekyapar, Ahmet; Asin, Celal; Demirkiran, Nizamettin; Kunkul, Asim; Baysar, Ahmet; Ceylan, Kadim
    Manganese compounds, such as manganese sulfate, can be obtained from pyrolusite, a manganese ore. Low-grade manganese ores is usually treated by hydrometallurgical methods. In this study, the leaching and recovery of manganese from pyrolusite ore in sulfuric acid solutions containing sawdust as reducing agent was investigated. The effects of experimental parameters, such as sulfuric acid concentration, sawdust amount, solid-to-liquid ratio, stirring speed, particle size, reaction temperature, and leaching time, on the manganese extraction from ore were examined. The results showed that the leaching rate of pyrolusite ore increased with an increasing sulfuric acid concentration, sawdust amount, stirring speed, reaction temperature and leaching time, and decreasing in solid to liquid ratio and particle size. The kinetic analysis of leaching process was carried out, and it was determined that the reaction rate was controlled by diffusion through the product layer under the experimental conditions in this work. The activation energy was found to be 22.35 kJ mol(-1). Manganese can be recovered as manganese sulfate by the evaporative crystallization of the purified leach liquor.