Abstract: Since the tailings reservoir of Fengshan Copper Mine completes its closure，there is no place to discharge the generated fine-grained tailings，which restricts the production progress. In order to use unclassified tailings for backfilling，the original vertical sand silo is abandoned，instead，a deep cone thickener is adopted to thicken the unclassified tailings before backfilling the underground stopes. The parti⁃ cle size characteristics and sedimentation properties of unclassified tailings aggregates are among the key factors affecting unclassified tailings backfilling. To investigate the flocculation and sedimentation properties of the unclassified tailings from Fengshan Copper Mine，first，a laser particle size analyzer is used to con⁃ duct particle size analysis on the unclassified tailings. Second，through static thickening and sedimentation tests of the unclassified tailings，a selection test is carried out on 11 types of flocculants from 5 manufactur⁃ ers. The optimal feed concentration of the deep cone thickener and its consumption per unit is determined. The results show that the content of -20 μm ( -625 mesh ) ultrafine particles in the whole tailings sample of Fengshan Copper Mine is more than 35 %，with a median particle size d50 of 38.98 μm，so it belongs to fine�grained tailings. The optimal flocculant selected is Flocculant B1，with an optimal consumption per unit of 20 g/t，and the optimal feed concentration of the deep cone thickener is 15%~20%. These results can pro⁃ vide data support for the thickening of unclassified tailings in Fengshan Copper Mine.

Key words: tailings pond, unclassified tailings, stope backfilling, flocculation and sedimentation