Influence of bioaugmentation with Ferroplasma thermophilum on chalcopyrite bioleaching and microbial community structure

• Bioaugmentation with F. thermophilum for chalcopyrite bioleaching
• Bioaugmentation at the early leaching stage accelerated copper extraction.
• Bioaugmentation at the early stage enhanced the growth of microorganisms.
• Bioaugmentation at the advanced stage was detrimental to chalcopyrite dissolution.

Ferroplasma spp. are cell wall-deficient, extremely acidophilic and iron-oxidising archaea that have considerable biotechnological potential for bioleaching processes. The current study focuses on investigating the ecological importance of mixotrophic Ferroplasma thermophilum L1 during chalcopyrite bioleaching and the feasibility of bioaugmentation with this archaeon to improve the extraction of copper from chalcopyrite. Bioaugmentation consisted of the addition of highly concentrated F. thermophilum (with different inoculum concentrations) into the two defined bioleaching systems that represented the early and advanced chalcopyrite bioleaching stages. The evolution of bioleaching performance, microbial community structure and leached solid residues after bioaugmentation were compared with those in the conventional (control) bioleaching experiment. The results of bioaugmentation undertaken at the early stage showed that the growth of Leptospirillum ferriphilum and Acidithiobacillus caldus were promoted after bioaugmentation, which, in turn, assisted F. thermophilum in surviving under the same conditions. Concurrently, the mineral dissolving and copper extraction rates were significantly accelerated, especially in the ‘Fer-1/1’ test that was bioaugmented with the highest addition amount. After 24 days, 90.2% of the total copper was leached out, which was higher than the value (83.4%) obtained in the control. The untimely formation of a ‘Jarosite’ passivation layer decreased the rate of copper release at the later stage of the ‘Fer-1/1’ test. The bioaugmentation of the advanced leaching stage was detrimental to the chalcopyrite dissolution; the number of added F. thermophilum cells negatively correlated with the copper recovery. The poor bioleaching was also primarily associated with the formation of iron precipitation due to the increased cell numbers of iron oxidisers. These findings indicate that different bioaugmented treatments with F. thermophilum clearly influenced chalcopyrite leaching and the microbial community. Bioaugmentation could be a useful remedy to accelerate chalcopyrite dissolution.