چكيده به لاتين
The processing of pyrolusite ore (MnO2) by the conventional smelting method is associated with problems such as high carbon footprint, high energy consumption and various accidents, and therefore the interest for hydrometallurgical processing has been increased. The dissolution of pyrolusite requires the conversion of Mn(IV) to Mn(II) This is not possible without using a suitable reductant, which is one of the challenges of pyrolusite hydrometallurgy. In recent years, a thermal pretreatment aiming at solid state decomposition or reduction of pyrolusite to its lower oxides has attracted the attention of researchers. Calcination using microwave heating are far better than conventional heating, as higher efficiency can be achieved in a very short period of time and at a lower calcination temperature. In the present research, the carbothermal processing of a pyrolusite concentrate with the help of microwave heating has been investigated in order to facilitate the dissolution of the concentrate in sulfuric acid media. From the preliminary experiments, it was found that microwave heating of a mixture of the concentrate and carbon black for a few minutes has a very favorable result in reducing MnO2 to MnO and subsequently, dissolution in sulfuric acid with high efficiency. The main experiments were designed and implemented using a two-level factorial design and a stepwise approach. In the first step, the influence of the parameters of C:Mn molar ratio, microwave heating time and microwave power on the efficiency of manganese dissolution in a fixed leaching conditions were investigated. In the second step, the effect of C:Mn molar ratio, leaching time and leaching temperature on the dissolution efficiency of manganese were examined and the dissolution efficiency of manganses was modeled by statistical analysis of the results. Based on the obtained results, the molar ratio of C:Mn of 0.7, heating time of 254 seconds, microwave power of 850 watts, leaching time of 90 minutes and leaching temperature of 80 ℃ with a dissolution efficiency of 75% was determined as the best conditions. Also, in additional leaching tests to investigate the effect of time, a 90% recovery of manganese were obtained by taking the molar ratio of C:Mn of 0.8, heating time of 254 seconds, microwave power of 850 W, leaching time of 20 minutes and leaching temperature of 85°C. In the investigation of two types of domestic ores from Sabzevar and Vunarach, manganese recoveries of 63% and 85% were obtained, respectively, under the following conditions: molar ratio C:Mn of 2, heating time of 254 seconds, microwave power of 850 W, leaching time of 60 minutes and leaching temperature of 85°C.
