Improving thickener bed density by ultrasonic treatment

Abstract

We report here the effect of 28kHz ultrasonic on dewatering of mineral tailings in conjunction with a mechanic rake. It is found that when a moderate level of ultrasonic energy (2.01W/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 2.5min, the bed density in a lab bench top thickener improves from 33.72wt.% to 37.48wt.%, 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.