Filtration and retention of mineral processing slurries with pumice and common clay: low-cost materials for environmental applications in the small-scale mining industry

The sixth region of Chile hosts the giant El Teniente porphyry copper deposit and several polymetallic districts exploited in small mine works; the latter are situated and processed in a predominantly agricultural area. This mining activity has a potential for environmental damage caused by infiltration of mineral processing slurries. As possible low-cost material for environmental applications, a local common clay and pumice were tested in 1:1 mixtures for the retention of Cu, As, Mo and Fe in mine waste waters and mineral processing slurries (pH range 3–6). In batch filtrations, simulating a single spillage of slurry, copper levels were reduced from >1100 to <0.05 ppm, Mo from 0.7 to <0.3 ppm, Fe from 400 to <0.1 ppm and As from 174 to <5×10−4 ppm. The filtered solutions increased K levels due to cation exchange in smectite; leaching of Cl and SO4 from pumice was observed. Retention of oil and grease by pure pumice was excellent (reduction of 13600 to <10 mg/l). The volume of slurry filtered should not exceed the volume of the filtration medium; a rapid saturation of Cu and SO4 was observed in the filtration medium. The basic filtration tests indicate this filtration mixture may be a cheap option for short- to medium-term retention of slurry spillage in small mines and mineral processing plants during maintenance works.