Tailings are remaining processing waste streams from mines, disposed after valuable minerals extraction from the mined ore. Tailings contain varying concentrations of residual valuable metals that are currently lost due to lack of economical treatment possibilities. With sulfide containing tailings there is also a risk of acid rock drainage. In this study, iron- and sulfur-oxidizing microorganisms were utilized in bioleaching to treat pyrite-rich tailings to liberate mainly cobalt, alongside with other valuable metals. After adaptation of the microbial culture and batch bioleaching tests, the continuous-batch mode mini-pilot protocol was applied in 10 L stirred tank reactors (30 °C, 100 g/L solid content), reaching high leaching yields for the target metals (Co 87%, Zn 100%, Ni 67%, Cu 43%) in approximately 10 days retention time. The results show potential to turn challenging tailing streams into secondary resource for valuable metals.