Following the batch assays, five bioleaching campaigns were conducted using 30-cm-high minicolumns to evaluate cobalt recovery under varying operational parameters. This experimental phase aimed to simulate percolation conditions while assessing the influence of key variables on leaching performance. The following parameters were systematically evaluated: - Microbial Consortia: Performance comparison between the Kobold A and Kobold B consortia. - Operating pH and Temperature: Systems were maintained at pH levels of 1.0 or 1.5, and temperatures of 30 °C or 45 °C. - Acid Curing: The mineral was subjected to chemical pre-treatment at 60% and 80% acid curing levels to neutralize gangue and promote initial metal mobilization. - Inoculation Dynamics: Inoculum concentrations ranging from 1×10⁶ to 1×10⁸ cells·g⁻¹ of total solids were tested. - Inoculation Methodology: Two inoculation modes were compared: delivery via irrigation and application immediately following the acid-curing resting period. Physicochemical variables, including pH, Eh, and dissolved metal concentrations (cobalt, nickel, copper, and iron), were monitored periodically to characterize the kinetic behavior and overall recovery efficiency of the system. 3. Results 3.1.Microbial consortia To isolate an optimal microbial consortium for the bioleaching process, a comprehensive scouting was performed at the San José de Pucobre flotation plant. Samples were retrieved from diverse operational points within the flotation circuit and subsequently cultivated in batch systems at 30 °C, 45 °C, and 55 °C. Microbial growth was confirmed at 30 °C and 45 °C (Table 1), whereas no growth was observed at 55 °C. Of the 11 samples evaluated, six exhibited robust iron and/or sulfur oxidation activity. Based on these results, two distinct cultures were established: Kobold A (30 °C) and Kobold B (45 °C). Table 1 – Growth of microorganisms according to sampling areas Mine Samples 30 °C 45 °C Raw material Concentrate Sulfated pool solids Cpy pool solids Scavenger tailing Columns tailing Rougher feed Column feed Cell viability assays revealed that the Kobold B consortium maintained 100% viability under optimal growth conditions and over 90% viability when exposed to the "Cola Scavenger". Genomic characterization via 16S rRNA sequencing (Oxford Nanopore Technologies) identified a diverse microbial population. Kobold A was primarily composed of Acidithiobacillus caldus, Sulfobacillus sp., Acidithiobacillus sp., Acidithiobacillus ferrooxidans, and Leptospirillum sp. In
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