Methanol as Anti‐solvent for Recycling of Caustic Soda Solution Used in Aluminum products manufacturing

Abstract

AbstractThe recycling of caustic soda solution in aluminum processing is proposed in order to decrease the energy consumption and environmental impact. Methanol as an anti‐solvent in the caustic soda solution was found to be the most effective solvent for reducing gibbsite solubility. The gibbsite solubility in caustic soda was significantly reduced when methanol was added by more than 40 wt%. It was found that the gibbsite solubility with 55 w t% methanol was about a half of that without methanol. Methanol has low latent heat, and can be economically separated from the caustic soda solution. This recycling leads to an increase in the dissolution rate of alumina and/or aluminum, at atmospheric pressure, with a more concentrated caustic soda solution (up to 500 g/L NaOH). A more concentrated caustic soda solution can be recycled more economically, for example, that used in the die recovery process in aluminum forming plants. Optimization by the controlled addition or mixing of methanol in the caustic solution easily controls the growth rate and nucleation rate of gibbsite crystals in the crystallizer. Synergy of these advantages of the present recycling method may contribute to more cost effective operations, and minimization of environmental impacts from the disposal of spent caustic soda solution.