Copper is one of the most common heavy metals and an essential raw material for many industries due to its inexpensive and excellent in performance. Copper is also an essential trace element for organisms, but it can be extremely toxic when ingested in excess (Yang et al., 2020). Copper is released into the environment and society through industrial activities such as mining, metallurgy and secondary processing. (Araújo et al., 2019). Chalcopyrite (CuFeS2) is the main source of global copper reserves, and is the most abundant and widely distributed copper-bearing mineral in the earth’s crust (Sun et al., 2021; Xu et al., 2016; Zhao et al., 2019). Traditional copper extraction technologies such as pyrometallurgy and hydrometallurgy have the disadvantages of high energy consumption and large environmental pollution. In current mining industry, attention has been given to bioleaching due to the processes of it was clean (Ma et al., 2021; Sun et al., 2021). Bioleaching applies microorganisms and their secretions (mainly extracellular polymeric substances, EPS) to recover value-metals from minerals at mild conditions (Tanne & Schippers, 2019). However, the copper extraction efficiency in chalcopyrite bioleaching process is low due to some reasons: high lattice energy of chalcopyrite (Wang, 2005; Zhang et al., 2016), and easy to form passivation layers in the bioleaching process. In previous studies, by mechanochemically activated (Cao et al., 2020), regulating factors (Khoshkhoo et al., 2017; Wang et al., 2014), and introducing additives (Yang et al., 2020; Ma et al., 2017; Koleini et al., 2011) to improve copper extraction. In addition, high ore heap bioleaching and in-situ bioleaching need to solve the problem of insufficient electron acceptors inside the mine heap through aeration, which increases energy consumption (Huang et al., 2019). Therefore, the current challenge is to develop new technologies to solve these defects.

Bioelectrochemical system (BES) is unique systems that integrate microorganisms with an electrochemical method, and it shows the process of electricity generation or achieve the redox reaction with a certain potential poised by means of electron transfer between the electron acceptors and electron donors (Zhang & Angelidaki, 2015; Zheng et al., 2020). According to the direction of electron transfer and the form of energy conversion, bioelectrochemical system main can be divided into microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) (de los Ángeles Fernandez et al., 2016). In MFCs, microorganisms or enzymes as catalysts can covert the chemical energy stored in biodegradable materials to electricity. Electrons and protons released as the product of bacterial metabolism onto the anode travel towards the cathode through two paths, and electrons are finally captured and utilized by the terminal electron acceptor (TEA) of cathode (Almatouq et al., 2020; Nancharaiah et al., 2015; Pant et al., 2012; Wilberforce et al., 2021). MECs also use microorganisms or enzymes as catalysts, but the form of energy conversion and the direction of electron transfer of MECs are opposite to those of the MFCs. Recently, bioelectrochemical system as an innovative technology for the removal and recovery of heavy metal ions from wastewater have become research hotspots (Yazdi et al., 2015). In MFCs, the crude metal was deposited and recovered through reduction of heavy metal ions in the cathode chamber while organics were used as the electron donor in the anode chamber (Huang et al,.2019). However, considerable amounts of electrical energy are required in recovering heavy metal ions with MECs (Motos et al., 2015). Compared with MECs, MFCs is an environmentally friendly and sustainable way to recover heavy metal.

Bioleaching as an intersection of multiple disciplines is well suited to implement electrochemical approaches for the optimization of metal leaching and recovery (Kaksonen et al., 2020; Tanne & Schippers, 2019). The feasibility of MFCs to assist in the bioleaching of chalcopyrite concentrates has been demonstrated (Huang et al., 2019). The bioleaching of chalcopyrite involves a series of redox reactions, and the bioleaching mechanism. In the indirect mechanism, chalcopyrite is attacked by Fe3+ (Eq. (1)) and the role of bacteria is to regenerate the oxidizing agent Fe3+ and H+ (Eq. (2) and Eq. (3)) (Ma et al., 2018; Mahmoud et al., 2017; Pattanaik et al., 2020). Under acidic conditions, abiotic oxidative dissolution of chalcopyrite occurs (Eq. (4)) (Zhao et al., 2019). The direct contact mechanism was microorganisms attached to the mineral surface directly erode and oxidize metallic minerals by biological means, without any involvement of iron ions and other substances (Dong et al., 2013; Ma et al., 2018). S2−/S0 on the mineral surface loses electrons at the anaerobic anode and is reduced to higher valent sulfate ((Eq. (5) and Eq. (6)) (Ma et al., 2018). Compared to Cu2+, Fe3+ and dissolved oxygen have a higher electrode potential and act as electron acceptors for the reduction reaction, as in Eq. (7) and Eq. (8). Copper extraction along with electricity generation were achieved in the chalcopyrite bioleaching assisted by MFCs.

\(\begin{array}{c}CuFe{\mathbf{S}}_{2}+4F{\mathbf{e}}^{3+}\to 5F{\mathbf{e}}^{2+}+2{\mathbf{S}}^{0}+C{\mathbf{u}}^{2+}\#\left(1\right)\end{array}\)

\(\begin{array}{c}4{\mathbf{F}\mathbf{e}}^{2+}+{\mathbf{O}}_{2}+4{\mathbf{H}}^{+}\underrightarrow{\mathbf{b}\mathbf{a}\mathbf{c}\mathbf{t}\mathbf{e}\mathbf{r}\mathbf{i}\mathbf{a}}4{\mathbf{F}\mathbf{e}}^{3+}+2{\mathbf{H}}_{2}O\#\left(2\right)\end{array}\)

\(\begin{array}{c}2{\mathbf{S}}^{0}+2{\mathbf{H}}_{2}O+3{\mathbf{O}}_{2}\underrightarrow{\mathbf{b}\mathbf{a}\mathbf{c}\mathbf{t}\mathbf{e}\mathbf{r}\mathbf{i}\mathbf{a}}2{\mathbf{S}\mathbf{O}}_{4}^{2-}+4{\mathbf{H}}^{+}\#\left(3\right)\end{array}\)

\(\begin{array}{c}{\mathbf{C}\mathbf{u}\mathbf{F}\mathbf{e}\mathbf{S}}_{2}+4{\mathbf{H}}^{+}+{\mathbf{O}}_{2}\to {\mathbf{C}\mathbf{u}}^{2+}+2{\mathbf{S}}^{0}+{\mathbf{F}\mathbf{e}}^{2+}+2{\mathbf{H}}_{2}O\# \left(4\right)\end{array}\)

Reactions of the anode:

\(\begin{array}{c}{\mathbf{S}}^{2-}-8{\mathbf{e}}^{-}+4{\mathbf{H}}_{2}O\to {\mathbf{S}\mathbf{O}}_{4}^{2-}+8{\mathbf{H}}^{+}\# \left(5\right)\end{array}\)

\(\begin{array}{c}{\mathbf{S}}^{0}-6{\mathbf{e}}^{-}+4{\mathbf{H}}_{2}O\to {\mathbf{S}\mathbf{O}}_{4}^{2-}+8{\mathbf{H}}^{+}\#\left(6\right)\end{array}\)

Reactions of the cathode:

\(\begin{array}{c}{\mathbf{O}}_{2}+4{\mathbf{e}}^{-}+4{\mathbf{H}}^{+}\to 2{\mathbf{H}}_{2}O\#\left(7\right)\end{array}\)

\(\begin{array}{c}{\mathbf{F}\mathbf{e}}^{3+}+{\mathbf{e}}^{-}\to {\mathbf{F}\mathbf{e}}^{2+}\#\left(8\right)\end{array}\)

As a high-grade ore, the chalcopyrite concentrate has been successfully bioleached with the assistance of MFCs (Huang et al., 2019). However, high-grade chalcopyrite ores in the world are becoming more and more scarce due to the consumption of copper resources and development of mine industry. In addition, low-grade ores, tailings and solid wastes contain some valuable metals, and improper disposal of these results in the waste of resources and the risk of contaminating soil or groundwater. Accordingly, the treatment and recycling of low-grade ores, tailings and solid wastes attracted much attention recently. In current study, the feasibility of low-grade chalcopyrite bioleaching assisted by MFCs was investigated. Then the mechanism for the promotion of copper extraction by MFCs was discussed.