Mineralogical Controls on Cobalt Leaching From Mixed-Oxide Ore

Abstract

In recent years, demand for cobalt—largely driven by demand for rechargeable lithium-ion batteries for electric vehicles and personal electronics—has grown faster than global cobalt production, necessitating a new look at the world’s cobalt resources and cobalt processing technologies. Oxide and oxyhydroxide ores constitute an important cobalt resource worldwide, and, if polymetallic seafloor nodules and crusts are included, make up the majority of global cobalt resources. The chief Co ore minerals in oxide ores are heterogenite (CoOOH or HCoO2) in stratiform sediment-hosted (SSH) Cu-Co ores, asbolane ((Ni, Co)xMn(O,OH)4∙nH2O) in Ni-Co laterite ores and some SSH deposits, and manganese oxide minerals such as vernadite (MnO2) in seafloor oxides, which are often also rich in Ni and Cu. Acid leaching is the cheapest and lowest-impact way to recover Co from oxide ores, but the precise mechanisms of cobalt-oxide leaching are not well characterized. In order to define major mineralogical factors in cobalt-oxide leaching performance, we leached Congolese SSH Cu-Co oxide ores and Pacific Ocean seafloor nodules in acid, then performed a comparative mineralogical study of leached and unleached samples using SEM-EDS and EPMA analyses. Both ores leached best under heat in a reducing environment, with maximum Co recoveries of 7% from our seafloor nodules and 99% from our SSH Cu-Co oxide ores. Recoveries of Ni and Cu from our seafloor nodules were as high as 40% and 33%, with a clear leaching gradient across our roughly 1 cm samples indicating that leaching was primarily limited by lixiviant access rather than by mineral leachability. We attribute the difference in Co recovery to the solubility of the host mineral’s lattice. Cobalt in SSH Cu-Co ores occurs in the relatively soluble Co-oxide lattice of heterogenite whereas Co in seafloor nodules substitutes for Mn in the relatively insoluble Mn-oxide lattice of vernadite, and consequently cannot be extracted with high recoveries without considerable, possibly prohibitive expense. Generalized to other ore types, the solubility of the mineral that hosts Co, as defined by the main structural metal, can be used as a broad guide to the leachability of Co in different oxide ores.