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The document describes a study characterizing a polymetallic concentrate from mining residuals in Portovelo, Ecuador and testing bioleaching using native microorganisms. The concentrate contained high levels of pyrite as well as gold, silver, and other metals. Native microorganisms isolated from mining sites were enriched and identified as Acidithiobacillus ferrooxidans. In bioleaching experiments, the microorganisms effectively solubilized sulfides at low pulp densities, releasing high concentrations of iron and sulfate. However, microbial activity and metal extraction decreased sharply at higher pulp densities, likely due to inhibition. The study suggests bioleaching could help process mining residuals in Portovelo but microbial adaptation to higher densities would be