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A Study on the Effects of Ultrasonic Irradiation as Pretreatment Method on High-Ash Coal Flotation and Kinetics

ABSTRACT This research work was undertaken to assess effect of ultrasonic irradiation as a pretreatment method for high-ash coal flotation and its kinetics. Ultrasonic treatment was applied prior to flotation at different ultrasonic power levels and periods. Feed samples containing 50.29% ash and 1.10% sulfur were acquired from the Tabas coal mine located in Yazd province, Iran. Flotation experiments were conducted based on a two-level fractional factorial design with six variables: ultrasound intensity, collector dosage, conditioning time, pH, rotor speed, and solid content. The collected data were analyzed by DX7.0 software to evaluate the effect of each parameter on the optimization criteria. Considering the highest combustible recovery and the lowest ash and sulfur contents, value of optimized parameters were as follows: ultrasound intensity, 30 W/cm2; 1500 g/t collector, 11 min of conditioning time, pH = 7.5, 800 rev/min of rotor speed, and 10% solid content. Under these conditions, 56.9% combustible recovery and 9.21% ash content of product were obtained. Finally, the kinetic flotation experiments were conducted using the optimized level of parameters in first stage. It was observed that coal flotation on an average was 10% faster using ultrasonic conditioning in comparison with the conventional conditioning. Flotation of high-ash coal with ultrasound pretreatment could be described almost with the fully mixed, second-order models.