Ultrasonic-assisted pre-concentration of iron values in bauxite residue suitable for reduction-roasting purpose

Abstract

The study aims to explore the feasibility of using low-frequency ultrasonic washing to pre-concentrate iron values in waste bauxite residue (BR) containing 32.60 wt. % iron. This novel approach involves ultrasonication followed by water-washing to pre-concentrate iron before reduction-roasting of BR. Conventional reduction-roasting of BR is more expensive compared to pre-concentrated BR, making this method potentially cost-effective. The process consists of a two-stage ultrasonic treatment procedure. In the first stage, ultrasonication at 30 degrees C, with 40% solid content (w/v) for 30 min, improves the iron grade to 41.2 wt. % with 82% recovery. However, a second stage of ultrasonication is necessary to further upgrade the iron. The study optimized the ultrasonication time, temperature, solid content (%, w/v), and water washing parameters. Under optimal conditions (ambient temperature, 30% solid content (w/v), 45 min of ultrasonication), the iron grade reached 49.1 wt. % (Fe2O3 70.2) with 66% recovery. Water-washing parameters were found to be less effective compared to ultrasonication parameters. The settling time after water washing significantly affects the grade and recovery of the product. The ultrasonic effect on the BR particle surface leads to the breakage of surface-alkali coating and the disintegration of locked particles to generate free iron and other particles. Particle size analysis supports the disintegration of BR particles into smaller pieces. The physicochemical characterizations of different products were carried out using ICP-OES, XRD, FTIR, and FESEM studies to support the experimental findings. The possible iron separation mechanism is discussed utilizing available literature, as well as experimental and characterization evidence.