Abstract
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.
Highlights
Available literature stated that the separate phases of the froth flotation process might be influenced by mechanical vibrations, by the acoustic wave process, or by a joint manifestation of these two physical phenomena
Previous researchers [2,3] indicated that modifying solid surfaces, especially physical surface cleaning by help of a cavitation process created by power ultrasound at certain frequency and time intervals before and during froth flotation might cause significant changes in the adsorption of collectors on mineral surfaces and in their flotation responses
While previous researchers [4,5,6,7,8] investigated the effects of ultrasonics before the flotation process for removal of adsorbed layers of reagents from mineral surfaces or emulsification of the reagents, recent studies [9,10,11,12,13,14,15,16,17,18] have concentrated on the effect of ultrasonic treatment during the flotation process, which is called simultaneous ultrasonic treatment
Summary
Available literature stated that the separate phases of the froth flotation process might be influenced by mechanical vibrations, by the acoustic wave process, or by a joint manifestation of these two physical phenomena. Previous researchers [2,3] indicated that modifying solid surfaces, especially physical surface cleaning by help of a cavitation process created by power ultrasound at certain frequency and time intervals before and during froth flotation might cause significant changes in the adsorption of collectors on mineral surfaces and in their flotation responses. While previous researchers [4,5,6,7,8] investigated the effects of ultrasonics before the flotation process for removal of adsorbed layers of reagents from mineral surfaces or emulsification of the reagents, recent studies [9,10,11,12,13,14,15,16,17,18] have concentrated on the effect of ultrasonic treatment during the flotation process, which is called simultaneous ultrasonic treatment.
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