توصيفگر ها :
آلونيت , تشويه , فروشويي , سينتيك , آلومينا
چكيده انگليسي :
The extraction of aluminum, sulfur, and potassium from an alunite ore (Ghazvin, Iran) was studied by roasting followed by two-stage alkaline leaching. In the roasting stage, the effects of several key parameters including temperature (520 to 620 °C), reaction time (30-150 min), particle size (0.075 to 10 mm), and furnace medium (with and without diesel fuel and with charcoal) were investigated on the leachability of sulfur and potassium by sodium carbonate and of aluminum by sodium hydroxide. The first leaching stage was carried out with sodium carbonate at a pulp density of 20% (w/w), a reaction time of 4 hours, a particle size of less than 75 µm, a temperature of 95 °C and a ratio of sodium carbonate to alunite of 1.5:1. The highest extractions of sulfur and potassium (99.9 % for both elements) were obtained with the ore roasted at 620 °C, a particle size of 3 mm, and a roasting time of 90 min. The extractions were significantly increased by increasing the temperature and roasting time. The second stage of leaching was conducted at the temperature of 95 °C, leaching time of 6 hours and the sodium hydroxide concentration of 5 M at 15 % pulp density. The highest aluminum extraction (95.3 %) was obtained by reductive roasting with charcoal at a temperature of 570 °C, a roasting time of 30 min, and a particle size of less than 3 mm. For potassium and sulfur extraction, increasing the roasting temperature, reaction time and diesel fuel addition (above 3%) resulted in a decrease in aluminum extraction, which was attributed to the conversion of the alumina phase to a stable phase.
In this study, the dissolution kinetics of aluminum from alunite, and then the alumina production were investigated. The effects of several critical parameters including particle size, temperature, reaction time, and concentration of sodium hydroxide were investigated in the leaching process. The results showed that increasing temperature, reaction time, and decreasing the particle size increased the extraction of aluminum. The maximum aluminum extraction (92.3 %) was at 95 °C, stirring speed of 500 rpm, particle size below 38 µm, reaction time of 6 h, pulp density of 5% (w/w), and sodium hydroxide concentration of 5 M. The dissolution kinetics of aluminum were investigated at 27-95 °C and described by the shrinking core model controlled by the mixed. The activation energy of the alunite leaching was determined to be 27.96 kJ/mol. To produce alumina, the leachate went through three stages of desilication, precipitation, and calcination. The effects of precipitation time (15-45 h), and seed addition (50 and 100 g/L) were investigated. The maximum grade of alumina (99.15 %) was gained in the precipitation time of 45 h, temperature of 70°C, seed content of 100 g/L, and calcination temperature of 1100 °C in a period of 3 h.
In order to investigate the leaching of alunite using the column method, the effect parameters of particle size and concentration of sodium carbonate and sodium hydroxide were carried out in two stages in order to extract sulfur and potassium in the first stage and aluminum in the second stage. The maximum extraction rate of sulfur, potassium and aluminum is 52.7, 58.7 and 47.68%, respectively, in the conditions of 2 mm particle size and in the first stage with the concentration ratio of sodium carbonate to alunite equal to 1:1.5 and in the second step was with 5 M sodium hydroxide. The dissolution rate was better in stirred leaching than in column leaching. In general, the results of this study show that due to the atmospheric conditions of leaching, the possibility of producing by-products and the processing of alunite resources, especially in countries with low-quality bauxite resources, alunite can be a suitable alternative for alumina production.
