Cobalt is critical to the renewable energy sector due to its use as the raw material for rechargeable batteries. The rapidly growing battery industry consumes more than 80% of the worlds Co, which is creating concern about future supply. There are three main primary cobalt deposit types: sediment-hosted Cu deposits, Ni sulfide deposits, and Ni laterite deposits, where cobalt is recovered as a by-product along with Cu and Ni. In the future, Co may be sourced from polymetallic ocean nodules. Co recoveries from conventional metallurgical processes have typically been low. It is therefore an opportune time to consider how unconventional resources such as metallurgical waste can be reprocessed to help meet the demand for Co. In this paper, we review the characteristics and process options for Co in Caron process residue, pyrite tailings, and metallurgical slags. While these materials contain Co, cost-effective recovery of Co from these streams remains a challenge. For example, the Co concentration is typically low (< 0.5 wt.%), and the Co is largely unliberated, requiring a chemical reaction to facilitate effective extraction. In this article, we will review these opportunities considering the previous literature as the basis of a discussion to develop future pathways to reprocess these metallurgical process wastes.