Bioleaching of Mine Tailings by Mesophilic: Acidithiobacillus spp., Leptospirillum ferrooxidans, and Thermophilic: Sulfobacillus thermosulfidooxidans Cultures with the Addition of Ag+ Additive

Abstract

This research focused on applying and comparing the performance of microorganisms with different temperature preferences, assessing the overall percentage recovery of elements (copper, zinc, arsenic, and iron) from mine tailings in the Staré Ransko region (Czech Republic). The study examined the solubilisation process using a mesophilic mixed bacterial culture, including Acidithiobacillus ferrooxidans (AF), Acidithiobacillus thiooxidans (AT), Leptospirillum ferrooxidans (LF), and the thermophilic species Sulfobacillus thermosulfidooxidans (ST). Under biotic conditions, constant process parameters were maintained, including a particle size of 71–100 µm, a pH value of 1.8, agitation at 150 rpm, and a pulp density of 10% (w/v). The only exception was the temperature, which varied for optimal multiplication of cultures (30 °C/50 °C). Additionally, the research examined the impact of AgNO3 additive at a concentration of Ag+ ions of 5 mg·L−1. The research focused on the solubilisation of Cu, Zn, Fe, and As and the results demonstrated that the application of microorganisms ST, combined with the action of Ag+ ions, enhanced the kinetics of the extraction process, leading to the highest final recovery of all elements (Cu 91.93%, Zn 85.67%, As 69.16%, and Fe 71.72%) under the specified conditions. The study observed that the most significant increase in solubilisation can be attributed to the additive cation in the case of copper (AF, AT, LF/Ag+ by 40.33%; ST/Ag+ by 44.39%) and arsenic (AF, AT, LF/Ag+ by 23.79%; ST/Ag+ by 26.08%). Notably, the intensification of leaching using thermophilic bacteria at a constant suspension temperature of 50 °C was primarily determined for Zn (ST by 18.36%, ST/Ag+ by 14.24%). After 24 days of extraction, the emergence of secondary minerals, namely CaSO4·2H2O and KFe3(SO4)2(OH)6, was identified. The study highlighted a significant increase in the extraction mechanism kinetics due to the influence of microorganisms, contrasting with the low solubilities observed under abiotic conditions (Cu 9.00%, Zn 14.17%, As 4.28%, Fe 6.23%).