Cu, Pb and Fe release from sulfide-containing tailings in seawater: Results from laboratory simulation of submarine tailings disposal.

Metal release from the deposition of sulfide-containing tailings in seawater was investigated using a batch reaction experiment inside a temperature and dissolved oxygen-controlled chamber. Two hundred grams of tailings from a porphyry Cu-Au and a sediment-hosted Cu deposit were submerged in 1.8 L synthetic seawater. The sulfides present in the porphyry Cu-Au tailings are pyrite (FeS), chalcopyrite (CuFeS) and bornite (CuFeS) while in the sediment-hosted Cu tailings are bornite, chalcocite (CuS) and covellite (CuS). Galena occurs as a minor sulfide in both tailings. Pore water and overlying seawater samples were collected and analyzed for pH, redox potential and trace metals (Cu, Pb and Fe) concentration. Results show that there is very low Cu (10-40 μg/L), Pb (1-10 μg/L) and Fe (5-50 μg/L) released into solution throughout the course of 87 days. Long-term trace metal release from tailings in seawater is therefore theorized to be low and is a slow process.