Laterite deposits may contain economic grades of cobalt and nickel. Laterite ore processing is challenging, especially for iron-rich, limonitic laterites. The BMBF-funded CLIENT II project BioProLat aims to develop a biohydrometallurgical process for laterites from Brazil. Bioleaching experiments with different ore samples, addition of elemental sulfur and different cultures of acidophilic bacteria were conducted in 2L stirred tank bioreactors under aerobic or anaerobic conditions at different temperatures at low pH. Additionally, column experiments were performed to simulate heap bioleaching. Mobilisation of cobalt via bioleaching was in the range of 68-88 %, while dissolved nickel was between 17 % and 56 %. Mineralogical and geochemical analysis (XRD, SEM- MLA, DSC, LA-ICP-TOFMS, XRF) of the original ore samples as well as leaching residues was conducted to (i) identify mineral phases, which are attacked by bioleaching and (ii) estimate the portions of Co and Ni, which are released by bioleaching of different mineral phases. Cobalt was mostly hosted by Mn-rich mineral phases (e.g. asbolane), which were dissolved via bioleaching. Nickel was present in Mn-rich minerals (e.g. asbolane) and magnesium silicates (e.g. serpentine) also being dissolved via bioleaching. However, most of the nickel occurred in goethite which was almost not dissolved via bioleaching. Chemical leaching tests supported bioleaching results. For a high cobalt and nickel recovery a combined chemical leaching with bioleaching offers an option for laterite processing.