Microbiological Redox Potential Control to Improve the Efficiency of Chalcopyrite Bioleaching

Abstract

The effect of controlling the redox potential (Eh) on chalcopyrite bioleaching kinetics was studied as a new aspect of redox control during chalcopyrite bioleaching, and its mechanism was investigated by employing the "normalized" solution redox potential (Enormal) and the reaction kinetics model. Different Eh ranges were established by use of different acidophiles (Sulfobacillus acidophilus YTF1; Sulfobacillus sibiricus N1; Acidimicrobium ferrooxidans ICP; Acidiplasma sp. Fv-AP). Cu dissolution was very susceptible to real-time change in Eh during the reaction. It was found that efficiency of bioleaching of chalcopyrite can be effectively evaluated on the basis of Enormal, since it is normalized for real-time fluctuations of concentrations of major metal solutes during bioleaching. For steady Cu solubilization during bioleaching at a maximum rate, it was important to maintain a redox potential range of 0 ≤ Enormal ≤ 1 (-0.35 mV optimal) at the mineral surface by employing a "weak" ion-oxidizer. This led to a copper recovery of > 75%. At higher Enormal levels (Enormal > 1 by "strong" microbial Fe 2+ oxidation), Cu solubilization was slowed by diffusion through the product film at the mineral surface (< 50% Cu recovery) caused by low reactivity of the chalcopyrite and by secondary passivation of the chalcopyrite surface, mainly by jarosite.

Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching

“…As dissolution of pure chalcopyrite is theoretically characterized by a 1:1 ratio of released iron to copper, this confirms the preferential oxidation of this copper mineral, or the transiently produced chalcocite, over associated copper-deficient minerals, such as pyrite, at low redox potentials. Our data independently confirms a study by Masaki et al (2018), in which microbial redox control was also attempted, likewise by members of the Sulfobacilli, i.e., S. sibiricus and S. acidophilus . Using iron-oxidizing bacteria in bioleaching processes, which raise the ORP only minimally over the threshold for the onset of leaching therefore appears possible and could benefit the performance of chalcopyrite bioleaching processes.…”

“…Consequently, ferric ions diluted in the bulk medium maintain a more homogeneous redox environment. Unfortunately, Masaki et al (2018) did not report on attachment rates and this hypothesis remains to be tested.…”

“…Many studies have investigated the optimal microbial consortia in bioleaching operations (Rawlings and Johnson, 2007), usually focusing on the need to efficiently oxidize Fe 2+ that drives the redox potential above that optimal for chalcopyrite dissolution (Hiroyoshi et al, 2013). In contrast, little attention has been paid to the possibility of controlling the redox potential of a bioleaching system by influencing the ratio of ferric to ferrous iron via suitable iron-oxidizing microbes (Masaki et al, 2018).…”

Systems biology of acidophile biofilms for efficient metal extraction

“…The problems associated with chalcopyrite bioleaching (i.e., when the target metal forms part of the mineral matrix) are slow rates and poor total recoveries often attributed to passivation of the mineral surface that has recently (2020) 7:215 | https://doi.org/10.1038/s41597-020-0519-2 www.nature.com/scientificdata www.nature.com/scientificdata/ been suggested to be by iron-oxyhydroxides 6 . One method to avoid chalcopyrite passivation is to carry out the bioleaching at low redox potentials and high temperatures 7,8 and several methods have been suggested to maintain the redox potential in the desired range including controlling the oxygen concentration 9 or utilizing a microbial community that maintains the potential in the desired range 10,11 . An additional critical factor for chalcopyrite bioleaching, especially in early stages of bioheap inoculation, is the attachment and biofilm formation on the mineral surface 12 .…”

Carbon-Assisted Bioleaching of Chalcopyrite and Three Chalcopyrite/Enargite-Bearing Complex Concentrates

“…In the case of bioleaching studies of chalcopyrite, Gericke et al [15] and Ahmadi et al [16,17] reported the advantages of E h control (via electrochemical reduction or oxygen arrest) at 600-650 mV (SHE), owing to the suppression of pyrite oxidation and thereby preventing jarosite passivation. These were followed by our E h -controlled bioleaching study using "weak" Fe 2+ -oxidizing microorganisms [18]. Masaki et al [18] reported the reaction ratelimiting step being dependent on E h and successfully clarified the chalcopyrite bioleaching efficiency by incorporating the concept of E normal : Controlling the optimal E h level to satisfy 0 ≤ E normal ≤ 1 (especially at E normal = ~0.35 at 45 • C) was critical in promoting steady Cu solubilization by a surface chemical reaction.…”