The combined use of a sand screw, hydrocyclones, and gel-logs to treat placer mine process water

Abstract

This study describes a low-maintenance tailings treatment system for placer mines. A sand screw and two 20 inch hydrocyclones were used to remove gravel, sand and silt from a sluice box discharge. Gel-logs were introduced subsequent to the main settling pond to reduce the suspended solids. Results drawn from a two year study at a placer mine in interior Alaska indicated that: (1) Most of the plus 50 mm particles can be removed from the sluice tailings by the combination of a sand screw and 20 inch hydrocyclones, (2) When using the hydrocyclone overflow, without further cleaning, in recycle operation, the performance of the sand screw and hydrocyclones change due to the build up of fine particles. (3) In laboratory testing cationic type gel-logs proved to be effective in reducing the turbidity of settling pond water from 4,000 NTU to 80 NTU. However, at the mine this test result could not be duplicated even though 14 logs were applied to treat 25% (c 500gpm) of the pond overflow. The cost of installation and operation of the sand screw and hydrocyclone system was about 11% of the total operational cost of the mine in 1986.