Abstract
At Vale’s Copper Cliff Nickel Refinery (CCNR), a solid residue is produced through the INCO Pressure Carbonyl (IPC) process, which typically contains 50 to 60% Cu, 5 to 10% Ni, 4 to 8% Co, 5 to 10% Fe, 0.5 to 1.5% As and trace amounts of Se, Te, PGM and Au. The IPC residue is treated in the 1st stage pressure leach autoclaves at 150oC to extract 80 to 95% Ni, Co and Fe, as well as 30 to 40% As. The 1st stage leach residue is then subjected to the Total Oxidative Leach (TOL) process to produce a Cu electrolyte to be treated by Cu electrowinning and a PGM/Au residue to be further treated at Vale’s Precious Metals Refinery at Port Colborne. Hence most of the As, Ni, Co and Fe remained in the 1st stage leach residue are dissolved in the TOL process and reported to the Cu electrolyte.
With the increase of As in the feed concentrate to the Smelter at Sudbury in recent years, the As in the IPC residue, as well as the As in the Cu electrolyte and in the TOC residue, have been significantly increased. To better understand and improve the extractions of As and other elements in the 1st stage pressure leach autoclaves, a test program was conducted at the Vale Technology Centre in Mississauga. The results from bench scale testing confirmed that increasing the operating temperature in the 1st stage leach autoclave from 150 to 180oC would significantly improve the extractions of As, Ni, Co and Fe. Based on the results obtained in this test program, one of three 1st stage autoclaves at CCNR was reconstructed in 2022 to increase its operating temperature from 150 to 180oC. Commissioning of this reconstructed 1st stage autoclave has been scheduled in 2023. This paper presents the results obtained in the lab tests and process development.