Aluminum hydroxide extraction by alkaline leaching from bauxite waste

As the fields of use of aluminum increase in the world, so the demand for alumina naturally increases. When one ton of alumina or 0.5 tons of aluminum metal is produced from bauxite ore, approximately one ton of red mud is created. This means that approximately 40% of each ton of bauxite subjected to the Bayer process turns into red mud. Red mud contains 30–60% Fe2O3, 5–20% Al2O3, 1–20% SiO2, 1–10% Na2O, and 1–10% TiO2. The fact that red mud is produced in such large quantities creates a need for studies on methods to make use of this waste, because it would be more economical to extract the iron, aluminum, and titanium compounds before it is discarded as waste. Its numerous components have varying physical properties such as magnetic sensitivity, electrical conductivity or sedimentation characteristics, and it should be possible to make use of these differences to separate the metals. The aim of this study was to obtain aluminum hydroxide from red mud. At the first stage, the red mud was subjected to classic basic leaching. The program MINITAB 17 was used to calculate estimated values of optimization and the percentage rate of solution of aluminum under optimum conditions by the Taguchi method. At the second stage microwave basic leaching of red mud was performed. In order to determine by the Taguchi statistical method the effect of the solid-liquid ratio when the sample of red mud was dissolved in a solution of sodium hydroxide, parameters of solid-liquid ratio were set at 10-60 g/L, base concentration at 2.5-10 M, and heat at 70-95⁰C; in order to determine the effect of length of time of dissolution on the sample, the time parameter was set at 1-4 hours; and in order to determine the effect of stirring speed on the dissolution of the sample, the stirring speed parameter was set at 200-800 rpm. It was found in this study that under conditions of a 10 g/L (1%) solid-liquid ratio, 10 M (40%) sodium hydroxide, a temperature of 80⁰C, four hours of dissolution and a stirring speed of 800 rpm, the dissolution ratio estimated by the MINITAB 17 program was 66.35% Al. Under the same conditions, it was found that with an increase to 2% in the solid-liquid ratio the estimated dissolution ratio was 53.76% Al.