Bioleaching Without Alkali Addition: A More Sustainable Approach for the Management and Valorization of Mining Waste with High Pyrite Content

Bioleaching has been postulated as a promising technology for the management and valorization of mining waste while reducing environmental risks associated with acid mine drainage. However, when mining waste has a high net acid-producing potential, bioleaching in stirred-tank bioreactors may require alkali addition for pH control, in order to avoid inhibitory biological effects due to excessive acidity, which promotes iron and sulfate precipitation. For such cases, this work proposes a more sustainable bioleaching strategy based on the operation without alkali addition for pH correction. Two pyritic mining wastes with net acid-producing potentials > 850 kg H2SO4/t were bioleached in 5 L stirred-tank reactors at initial pulp densities of 5, 10, and 15%. Without pH correction, pyrite conversions > 95% and weight losses of about 80% were achieved at pH < 0.6. By contrast, when pH was controlled by adding CaCO3 or K2CO3, similar pyrite conversions were obtained, but weight losses remained below 40% due to Fe and gypsum precipitation. The highest bioleaching rates without pH correction (> 700 g mining waste m−3 h−1) were obtained at an initial pulp density of 10%, 30 °C, a final ORP of ~0.7 V, and a final pH < 0.8. Under these conditions, Co extractions > 95% were achieved, while Cu and Sb extractions reached up to 87% and 77%, respectively. Operating without alkali addition reduced mining-waste volume by about 70% and decreased acid-generation potential by more than 90%, thereby facilitating storage, reducing visual impact, and mitigating the risk of acid mine drainage generation. Graphical Abstract