Abstract:It becomes more and more common to use ultrafine unclassified tailings with the extensive application of paste backfilling. In this paper, deep cone thickening test was carried out in laboratory by the use of unclassified tailings from Qiandongshang mine. As the test tailings ,its density was 2.879g/cm3, the permeability coefficient was 0.167cm/h, the content of -20μm particles was 46.76% and the maximum particle size was less than 1000μm.Thereby, it is a kind of ultrafine unclassified tailings with poor dewatering. Flocculation sedimentation test shows that it could reach the maximum underflow concentration after the completion of feeding for 1 hour with three kinds of slurry feeding concentration. The underflow concentration didn’t increased significantly as the increase of feeding concentration. The result shows that the underflow mass concentration of the unclassified tailing slurry was about 67%. It provides significant evidence for the process design of backfilling and deep cone selection of ultrafine unclassified tailings.