economically valuable metals. By day 120, the optimized Kobold B system demonstrated substantial polymetallic extraction, achieving recovery yields of 94% for nickel (Ni), 75% for copper (Cu), and 61% for iron (Fe). These results underscore the potential of this biotechnological approach for the comprehensive valorization of complex sulfidic tailings within a circular economy framework. 4. Discussion The findings of this study confirm that cobaltiferous sulfidic fresh tailings from the CS-CL scavenger fraction at the San José de Pucobre plant represent a technically viable secondary resource, with cobalt grades (950–1100 ppm) significantly exceeding the economic thresholds for mining residue valorization. The mineralogical predominance of pyrite, characterized by a high degree of surface liberation (>80%), provides an ideal substrate for microbially mediated oxidative dissolution, facilitating the release of cobalt from the mineral matrix. A critical observation of this research is that microbial inoculation serves as a decisive factor in achieving high recovery yields. The ability of inoculated systems to surpass 90% recovery by day 35 in batch assays—contrasting sharply with uninoculated controls—highlights the necessity of establishing a robust population of iron- and sulfur-oxidizing microorganisms. This strategic inoculation effectively mitigates the lag phase typically associated with the low indigenous microbial titers found in tailings, accelerating and making reproducible the onset of the biochemical processes required for sustained sulfide oxidation. The column experiments further validated these results under conditions approximating industrial percolation systems. The optimal performance of the Kobold B consortium at 45 °C and pH 1.5 suggests that thermotolerant consortia are better suited for the exothermic nature of sulfide oxidation in larger scales. The success of the "post-acid curing" inoculation strategy, combined with an 80% acid curing pre-treatment, indicates that physicochemical conditioning is essential to neutralize gangue alkalinity and create a favorable niche for microbial colonization. The taxonomical diversity within Kobold B—including Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus, and Leptospirillum ferriphilum—facilitates a synergistic metabolic network capable of maintaining high redox potentials (>600mV) while oxidizing sulfide. This environment is crucial for the indirect bioleaching mechanism, where the continuous regeneration of Fe (III) drives the dissolution of pyritic phases. Furthermore, the ability of the system to achieve high recoveries for nickel (94%) and copper (75%) underscores its potential for polymetallic valorization, strengthening the economic rationale for implementing bioleaching technologies in tailings management. Beyond metal extraction, this process contributes to environmental stewardship by transforming reactive sulfides into more stable phases, potentially reducing the long-term risk of acid mine drainage (AMD). However, scaling this technology to industrial dimensions involves challenges such as maintaining hydrodynamic uniformity and oxygen mass transfer in large-scale heaps. The 120-day timeframe observed for peak recovery opens a compelling avenue for kinetic optimization, with significant potential to enhance industrial throughput in future implementations.
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