We live in a time with a growing global demand for critical raw materials, as well as increasing environmental and geopolitical concerns. This context has intensified the need for more sustainable resource strategies. Among these, the secondary recovery of industrial by-products has gained traction. It is seen as a promising alternative to traditional mining. Despite their known residual metal content and reactive silicate matrix, ferro-nickel slags (FNS), generated during nickel smelting, represent a largely underexplored secondary resource. This Master’s thesis addresses this gap, by investigating the secondary recovery and repurposing potential of FNS. Case studies are performed with slags originating from two sites: Cerro Matoso (Colombia) and Loma de Níquel (Venezuela). The study aims to assess whether these industrial byproducts can be used as alternative resources within a circular economy framework. This can either be by recovering residual metallic elements or by repurposing the bulk slag material. The research is based on a multi-method approach combining field sampling, chemical analysis (pXRF and ICP-OES), and mineralogical and reflectance assessment (XRD, ASD). The compositions of the slags were examined with a focus on their residual nickel content and its hosting mineral phases. Their suitability was tested for repurposing as cement alternatives, fertilizers, carbon mineralization, mineral wool and asphalt. Success criteria were set up, and evaluated based on physical, chemical, and economic feasibility. Results showed that both Cerro Matoso’s and Loma de Níquel’s slags contain valuable metals (e.g.
Ni, Co, Fe) and exhibit favorable characteristics for multiple re-use pathways. However, feasibility is largely influenced by mineralogical entrapment, as well as economical and regulatory constraints. This study explores the untapped value of FNS and emphasizes the importance of further investigating secondary recovery strategies. It contributes to the broader discourse on sustainable resource management by demonstrating how industrial waste can transition from liability to asset when viewed through a circular economy lens.