Chromium compounds are widely used in chemical, metallurgical, leather tanning and textile industries. The only chromium-bearing mineral found in nature is chromite ore. Sodium and potassium dichromate are known as raw materials of other chromium compounds among the most important chromium compounds. These two compounds could be produced from sodium and potassium chromate, respectively. In addition, sodium and potassium chromate are produced from chromite ore. The oldest method for the production of sodium chromate is on the basis of pyrometallurgy technology; moreover, scientists try to substitute this method by hydrometallurgy and more clean techniques owing to high energy consumption, low efficiency and environmental pollutions. In this thesis, the dissolving of chromite ore in potassium hydroxide solution with the injection of oxygen gas as oxidant agent to produce potassium chromate had been studied. Generally, the dissolving stage was processed in both aqueous environments and molten KOH that did not show good results in aqueous environment with maximum temperature of 200?C due to the restriction of increasing the temperature, and the maximum extraction of chromium in this condition was 30%. On the contrary, significant growth in the amount of extracted chromium was obtained by increase of temperature if molten environment. Effective factors on leaching process such as temperature, time and alkaline material / chromite ore ratio and oxygen injection pressure had been investigated. The optimum condition for dissolving of chromite ore in molten environment was temperature of 410?C, potassium hydroxide to chromite ore ratio of 2, oxygen injection pressure of 1 bar, stirring speed of 800 rpm and reaction time of 5 hr. Maximum extraction of chromium under this condition was 91%. Potassium chromate was also obtained by precipitation method from solution containing potassium chromate and potassium hydroxide by reducing the solubility of one component in order to the increase of the concentration of other component that eventually 90% of the solution containing potassium chromate was precipitated by this method. Key words: Leaching, Hydrometallurgy, Chromite ore, Potassium chromat
