Abstract
Biofilm formation within the process of bioleaching of copper sulfides is a relevant aspect of iron- and sulfur-oxidizing acidophilic microorganisms as it represents their lifestyle in the actual heap/dump mining industry. Here, we used biofilm flow cell chambers to establish laminar regimes and compare them with turbulent conditions to evaluate biofilm formation and mineralogic dynamics through QEMSCAN and SEM-EDS during bioleaching of primary copper sulfide minerals at 30°C. We found that laminar regimes triggered the buildup of biofilm using Leptospirillum spp. and Acidithiobacillus thiooxidans (inoculation ratio 3:1) at a cell concentration of 106 cells/g mineral on bornite (Cu5FeS4) but not for chalcopyrite (CuFeS2). Conversely, biofilm did not occur on any of the tested minerals under turbulent conditions. Inoculating the bacterial community with ferric iron (Fe3+) under shaking conditions resulted in rapid copper recovery from bornite, leaching 40% of the Cu content after 10 days of cultivation. The addition of ferrous iron (Fe2+) instead promoted Cu recovery of 30% at day 48, clearly delaying the leaching process. More efficiently, the biofilm-forming laminar regime almost doubled the leached copper amount (54%) after 32 days. In-depth inspection of the microbiologic dynamics showed that bacteria developing biofilm on the surface of bornite corresponded mainly to At. Thiooxidans, while Leptospirillum spp. were detected in planktonic form, highlighting the role of biofilm buildup as a means for the bioleaching of primary sulfides. We finally propose a mechanism for bornite bioleaching during biofilm formation where sulfur regeneration to sulfuric acid by the sulfur-oxidizing microorganisms is crucial to prevent iron precipitation for efficient copper recovery.
Highlights
One of the most important challenges that face the copper industry is the development of sustainable technologies to leach complex ores composed of mixed copper mineral species in low grades, with a prevalence of primary copper sulfides
We investigated the capabilities of Leptospirillum spp. and At. thiooxidans to form biofilm on primary copper sulfides utilizing a standardized and reproducible flow cell approach that resembles heap/dump bioleaching conditions
We found that the bubble trap is essential for attaining a homogeneous flow and proper propagation of acidophilic microorganisms (Crusz et al, 2012)
Summary
One of the most important challenges that face the copper industry is the development of sustainable technologies to leach complex ores composed of mixed copper mineral species in low grades, with a prevalence of primary copper sulfides. The major component of these materials is usually chalcopyrite (CuFeS2), followed by bornite (Cu5FeS4) (Panda et al, 2015). To this end, bioleaching has emerged as an efficient technology to leach secondary sulfides under mesophilic conditions (ambient temperature) (Bustos et al, 1993) and primary sulfides mostly under thermophilic conditions above 60◦C (Duarte et al, 1993) or at moderate thermophilic (45–50◦C) in stirred tank bioreactors (Cancho et al, 2007; Hedrich et al, 2018). Acidophilic bacterial consortia recovered 43% of copper from chalcopyrite using shake flasks at room temperature (25–30◦C) (Ma et al, 2018). Inoculation of the moderate thermophilic Leptospirillum ferriphilum and Acidithiobacillus caldus in shaking flasks at 45◦C enabled the conversion of bornite into several intermediates including covellite (CuS) and isocubanite (CuFe2S3) through the bioleaching process, with a final copper extraction of 70% (Hong et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
