Improvement in Nickel, Cobalt, Iron, and Arsenic Extractions in the First-Stage Autoclaves at Copper Cliff Nickel Refinery

At Vale’s Copper Cliff Nickel Refinery (CCNR), a solid residue is produced through the INCO pressure carbonyl (IPC) process, which typically contains 50–60% Cu, 5–10% Ni, 4–8% Co, 5–10% Fe, 0.5–1.5% As, and trace amounts of Pb, Bi, Sb, Sn, Se, Te, PGM, Ag, and Au. The IPC residue is treated in the first-stage pressure leach autoclaves at 150 °C to extract 80–95% Ni, Co, and Fe, as well as 30–40% As. As arsenic in the feed concentrate to the Smelter at Sudbury has increased in recent years, the arsenic in the IPC residue, as well as the arsenic in the copper electrolyte and in the leach residue, has been significantly increased. To better understand and improve the extractions of arsenic and other elements in the first-stage pressure leach autoclaves, a test program was conducted at the Vale’s Technology Centre in Mississauga. The results from bench scale testing confirmed that increasing the operating temperature in the first-stage leach autoclave from 150 to 180 °C would significantly improve the extractions of arsenic, nickel, cobalt, and iron. Based on the results obtained in this test program, one of three first-stage autoclaves at CCNR was reconstructed in 2022 to increase its operating temperature from 150 to 180 °C. Commissioning of this reconstructed first-stage autoclave has been scheduled in 2023. This paper presents the results obtained in the lab tests and process development.