THE RECOVERY OF NICKEL AND COBALT FROM THE NORTHMET DEPOSIT USING THE PLATSOL~TM PROCESS WITH PRODUCTION OF MIXED OR SEPARATE NICKEL AND COBALT HYDROXIDES

摘要

The NorthMet deposit of PolyMet Mining contains a large reserve of copper-nickel-cobalt-precious metal mineralization. Historically it has been difficult to recover separate copper and nickel concentrates of a quality broadly acceptable to custom smelters using conventional mineral processing techniques. Recently, improved flotation methods have made it possible to produce separate and saleable concentrates which will be produced during initial startup of the NorthMet deposit and construction of the PLATSOL~TM hydrometallurgical plant. After the initial transition period, it is planned that production of a bulk flotation concentrate will be followed by PLATSOL~TM hydrometallurgical treatment to produce copper, nickel/cobalt and precious metal products. The PLATSOL~TM process uses chloride-assisted total pressure oxidation treatment of a bulk concentrate to digest the base and precious metal content of the bulk concentrate into an autoclave solution. Following solid-liquid separation, the solution is then treated sequentially for precious metal recovery by reductive precipitation, copper solvent extraction and electrowinning and finally, nickel and cobalt recovery by precipitation. During the pilot plant testing of the PLATSOL~TM process for NorthMet bulk concentrate treatment, two variations on nickel and cobalt recovery were tested including mixed hydroxide precipitation with magnesia and separate nickel and cobalt hydroxide precipitation following solvent extraction separation with Cyanex 272. The results of the pilot plant testing of the nickel and cobalt recovery circuits for NorthMet are presented.