Further Investigations on Simultaneous Ultrasonic Coal Flotation

This study investigates the flotation performance of a representative hard coal slime sample (d80 particle size of minus 0.2 mm) obtained from the Prosper-Haniel coal preparation plant located in Bottrop, Germany. Flotation was carried out with a newly designed flotation cell refurbished from an old ultrasonic cleaning bath (2.5 L volume) equipped with a single frequency (35 kHz) and two different power levels (80–160 W) and a sub-aeration-type flotation machine operating at a stable impeller speed (1200 rpm) and air rate (2.5 L/min). The reagent combination for conventional and simultaneous ultrasonic coal flotation tests was Ekofol-440 at variable dosages (40–300 g/t) with controlling water temperature (20–25 ◦C) at natural pH (6.5–7.0). The batch coal flotation results were analyzed by comparing the combustible recovery (%) and separation efficiency (%) values, taking mass yield and ash concentrations of the froths and tailings into account. It was found that simultaneous ultrasonic coal flotation increased yield and recovery values of the floated products with lower ash values than the conventional flotation despite using similar reagent dosages. Furthermore, particle size distribution of the ultrasonically treated and untreated coals was measured. Finely distributed coal particles seemed to be agglomerated during the ultrasonic treatment, while ash-forming slimes were removed by hydrodynamic cavitation.