Improving thickener bed density by ultrasonic treatment

•Effect of ultrasonics on thickener bed density and aggregate structure.•Ultrasonication in transition zone can improve bed density by 3.76 wt.%.•Cryo-SEM shows aggregates change from mainly E-E to F-F by ultrasonics and raking.

We report here the effect of 28 k Hz ultrasonic on dewatering of mineral tailings in conjunction with a mechanic rake. It is found that when a moderate level of ultrasonic energy (2.01 W/L), which will not disperse the settled bed in thickener but enough to open the closed network structure, is delivered to the transition settling zone for 2.5 min, the bed density in a lab bench top thickener improves from 33.72 wt.% to 37.48 wt.%, which is an 11% improvement on bed density. Cryo-SEM is used to image and analyse settled bed aggregates structure changes which clearly demonstrates a denser settled bed after ultrasonic treatment. The combination effects of ultrasonics and rake in the transition zone rearrange the settled bed structure from mainly E-E to mainly F-F clearly shown by the cryo-SEM images. This indicates that the ultrasonication in the transition zone could break up the E-E and E-F associations, which allow loose aggregates to be compacted into much denser F-F aggregates. In situ shear stress measurement also confirms these findings. This technology will be beneficial for tailings' management where the improvement in thickener bed density is environmentally and economically crucial.

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