Intensified Bioaugmentation as a Strategy to Enhance Bioleaching of Mine Tailings with High Metal Content

Bioleaching is a technology capable of recovering metals from polluted mine tailings. However, the process is slow and time consuming. This work studies the possible enhancement of the bioleaching rate by using different bioaugmentation strategies, i.e. single and multi-step inoculation. Slurry phase batch experiments were performed using real mine tailings containing high concentrations of Fe, Pb, Zn and Mn, and low concentrations of Cd, Ni, Cr and Cu, and a mixed microbial culture of autochthonous acidophilic bacteria grown from those tailings. The effect of the inoculum concentration added at the beginning of the batch experiments was studied in the experiments with single inoculation, while the effect of different reinoculation frequencies was analysed in the multi-step inoculation tests. The results obtained showed that bioaugmentation has a high potential for enhancing the bioleaching process. For both strategies studied, metal bioleaching rates and final removal yields increased when bioaugmentation was carried out. The best results were obtained under the multi-step approach. Average bioleaching rates were multiplied at best case approximately by 2.8 (Fe), 5.0 (Zn), 7.3 (Cu), 17.0 (Mn) and 1.5 (Pb) while removal yields at best case increased approximately 122% (Fe), 31% (Cu), 9% (Cd), 19% (Zn), 17% (Mn), 33% (Ni) and 66% (Cr), compared to reference test (without bioaugmentation). The multi-step approach was able to compensate the assumed inhibitory effect of the metal dissolution during experiments, thus maintaining the active microbial population and the bioleaching rate for longer periods of time.