Design of a fuel cell‐driven system for electricity generation and metal leaching from sulfidic mine tailings = 황화광미를 이용한 전기 생산 및 금속 침출 연료전지 시스템 설계

국문 초록 (Abstract)

본 연구에서는 황화광물 산화를 통해 자원과 에너지를 회수할 수 있는 전기화학적 연료전지 기반의 새로운 접근법을 제시하였다. 금속 광산 채광으로 발생하는 광미에는 다량의 황화광물이 포함되어 있으며, 이들이 산화될 경우 산성 광산배수(AMD)가 생성되고 구리, 아연, 납, 철 등 유용 금속이 용출되어 환경 오염과 경제적 손실을 초래한다. 기존의 화학적 산화, 생물학적 용출, 전기동력학적 처리 방법은 각각 과도한 시약 사용, 부반응 생성물에 의한 피동화, 높은 에너지 소모 등의 한계를 지니므로, 이를 극복할 수 있는 지속 가능한 처리 기술의 개발이 요구된다.
이에 본 연구에서는 연료전지 기술을 활용하여 황화광미를 산화하면서 동시에 전기를 생산할 수 있는 새로운 방법을 모색하였다. 연료전지에서 황화광미의 산화 반응은 음극에서 일어나고, 방출된 전자는 외부 회로를 거쳐 양극의 환원 반응을 구동함으로써 전기를 생성한다. 본 논문에서는 먼저 황철석(FeS2)을 연료로 하는 pyrite-fuel cell(PFC)을 구성하고, 이의 성능을 다양한 초기 pH, 온도, 용존 산소 농도 및 Acidithiobacillus ferrooxidans(철 산화 세균) 존재 유무에 따라 평가하여 최적의 산화 및 발전 조건을 규명하였다. 그 결과, 강산성 조건(pH 2.2)과 철 산화 세균의 존재가 황철석의 용해와 전기 생산을 크게 향상시켜 약 0.74 mW/m2의 최대 전력 밀도를 달성함을 확인하였다.
다음으로, 제어된 외부 회로를 통해 전자 이동을 촉진함으로써 기존의 생물학적 및 화학적 산화보다 높은 황철석 산화율과 금속 용출량을 달성할 수 있음을 실험적으로 입증하였다. 외부 회로의 저항을 최적화하여 전자 전달을 가속화한 결과, 4주 동안 용출된 철의 양이 생물학적 및 무생물학적 산화에 비해 크게 증가하였다.
더 나아가, 휘수연석(MoS2)을 연료로 사용하는 다전극 연료전지 시스템을 구축하고, 지속적인 유동 조건에서 장기 산화 실험을 수행하였다. A. ferrooxidans를 주입하여 산화-환원 반응을 촉진함으로써 Fe2+가 Fe3+로 지속적으로 재생되고 휘수연석의 산화가 효율적으로 진행되었다. 또한, 다전극 구성으로 고체 연료와 전극의 접촉 면적을 늘려 전자 회수율과 전기 출력을 향상시켰다.
결론적으로, 연료전지 기술을 활용한 황화광미 산화는 환경 정화와 유용 금속 회수를 동시에 달성할 수 있는 지속 가능한 처리 방안임이 본 연구를 통해 확인되었다. 또한 본 연구에서는 최적의 pH, 온도, 용존 산소, 외부 저항, 미생물 활용 조건을 규명함으로써 황철석과 휘수연석이 포함된 광미로부터 전기 생산과 금속 회수를 극대화할 수 있는 설계 지침을 제시하였으며, 이는 기존 처리 방법에 비해 더 친환경적인 대안이 될 수 있음을 보여주었다.

다국어 초록 (Multilingual Abstract)

Mine tailings, the byproducts of mineral processing, contain abundant sulfide minerals that pose significant environmental risks while also harboring valuable metals. This research designed a fuel cell‐driven leaching system to generate electricity while extracting metals from sulfidic tailings. In this system, oxidation of the minerals at the anode is coupled to electricity generation by separating the anodic and cathodic reactions, allowing the electrons released from sulfide oxidation to drive an external circuit. This electrochemical separation prevents electron accumulation and local reduction reactions on the mineral surface, thereby minimizing passivation and enabling continuous sulfide dissolution and stable electricity generation. This dissertation investigates a fuel cell‐based approach to sulfide oxidation for concurrent resource recovery and power generation. Specifically, a pyrite-fuel cell (PFC) system is developed and evaluated under various environmental conditions to identify optimal parameters for pyrite oxidation and electricity generation. In parallel, an electrochemical strategy is applied to enhance electron transfer from pyrite, aiming to overcome the limitations of conventional bio-oxidation and accelerate metal leaching. Furthermore, a multi-electrode fuel cell using MoS2 concentrate is designed to examine the long-term oxidation of molybdenite with the assistance of Acidithiobacillus. ferrooxidans, enabling sustained electricity generation and recovery of metals (Mo, Cu, Fe).
In Chapter 3, pyrite‐fuel cell is developed and the performance of fuel cells using pyrite‐containing mine tailings is examined under a range of initial pH, temperatures, and dissolved oxygen levels, both with and without A. ferrooxidans. The results show that strongly acidic conditions and the presence of A. ferrooxidans significantly enhance pyrite dissolution and power output, yielding a maximum power density of approximately 0.74 milliwatts per square meter. Biotic fuel cells maintained stable performance across a range of temperatures, and higher dissolved oxygen facilitated greater current generation, although excessive aeration could inhibit bacterial activity. These findings confirm that concurrent pyrite oxidation and electricity generation is feasible, and that fuel cell performance can be tuned by optimizing operating conditions.
In Chapter 4, a controlled electrochemical approach is employed to further boost pyrite oxidation beyond what is attainable through biological or direct chemical means. By optimizing the external circuit resistance, the PFC was driven to favor rapid electron extraction, thereby accelerating the anodic dissolution of pyrite. In comparative tests, the PFC achieved the highest iron release (0.84 mM Fe in 4 weeks), significantly exceeding the yields from biotic (0.56 mM) and abiotic (0.11 mM) oxidation. Importantly, although an iron-oxide layer formed on the pyrite surface, it did not passivate the reaction in the electrochemical system due to continuous electron removal through the circuit. Lowering the external resistance markedly increased the electron transport rate and thus the pyrite oxidation rate. These results demonstrate that promoting electron flow in a fuel cell not only generates power but also substantially accelerates sulfide oxidation kinetics, offering a more efficient method for metal recovery. The feasibility of the approach was confirmed using actual mine tailings: a fuel cell loaded with sulfidic lead–zinc tailings generated a stable voltage (~0.26 V of open circuit voltage) and a maximum power of 5.4 mW/m2 at current density of 43.8 mA/m2), while simultaneously leaching soluble Fe, Pb, and Zn from the waste.
In Chapter 5, the scope is extended to MoS2, a less reactive sulfide, by using a bio-augmented multi-electrode fuel cell. A molybdenite concentrate (rich in Mo with residual Cu and Fe) serves as the anodic “fuel,” and A. ferrooxidans is introduced to catalyze the oxidation process. The system is operated under continuous flow with different hydraulic retention times to evaluate mass transfer effects and long-term stability. The presence of A. ferrooxidans regenerates Fe3+ from Fe2+ in the anolyte, which in turn oxidizes MoS2 to form Mo(VI) species (e.g. MoO3) on the mineral surface. This bio-electrochemical synergy mitigates the passivation normally observed in purely chemical MoS2 leaching, allowing sustained oxidation over extended periods. Moreover, the multi-electrode design improves contact between the solid fuel and the electrodes, thereby enhancing overall electron transfer and power output.
Overall this work demonstrates that integrating fuel cell technology with sulfide oxidation is a viable strategy for simultaneous environmental remediation and resource recovery. It eliminates the need for external power or harsh chemicals by electrically harnessing the sulfide oxidation energy inherent in the tailings. The research shows that operating parameters can be optimized to maximize both power generation and metal leaching efficiency, through measures such as maintaining low pH, incorporating multiple electrodes, and utilizing microbial catalysts to sustain rapid oxidation. This coupled approach is expected to enable effective metal leaching, with nearly complete extraction of copper and iron within one year and substantial molybdenum recovery, while producing power densities in the range of mW/m2. The findings present a novel and sustainable method for mine waste remediation. The fuel cell‐driven system provides a means to transform an environmental burden into a source of electricity and valuable metals. The insights gained offer a foundation for scaling up to field applications, where such systems could mitigate long-term pollution from sulfidic mine tailings while contributing to clean energy generation and circular resource use.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• 1.1. Background 1
• 1.2. Objective and scope 5
• 1.3. Organization of dissertation 6
• References 8
• CHAPTER 2. Literature review 11
• 2.1. Valuable metals in mine waste 11
• 2.2. Aqueous sulfide mineral oxidation 14
• 2.3. Mass transfer characteristics of the fuel cell technology 20
• 2.4. Role of Acidithiobacillus ferrooxidans 23
• References 28
• CHAPTER 3. Development of pyrite‐fuel cell and environmental effect for electricity generation 36
• 3.1. Introduction 36
• 3.2. Materials and methods 40
• 3.2.1. Preparation of pyrite and bacterial culture 40
• 3.2.2. PFCs construction 40
• 3.2.3. PFCs operation 41
• 3.2.4. Efficiency of PFCs 42
• 3.2.5. Analyses 44
• 3.2.6. Fe mine tailings fuel cell setup and operation 45
• 3.3. Results 50
• 3.3.1. Effect of initial pH on fuel cell performance of PFCs 50
• 3.3.2. Effect of temperature on fuel cell performance of PFCs 52
• 3.3.3. Effect of gas purging on fuel cell performance of PFCs 57
• 3.3.4. Electricity generation from Fe mine tailings fuel cell 59
• 3.4. Discussion 61
• 3.4.1. Voltage decrease in PFCs with time 61
• 3.4.2. Effect of initial pH, bacteria, and temperature on performance of PFCs 62
• 3.4.3. Effect of gas purging on the electrical performance of PFCs 65
• 3.4.4. Electricity generation from sulfide mineral containing mine tailings 65
• 3.5. Summary 66
• References 67
• CHAPTER 4. Facilitation of pyrite dissolution through enhanced electron transfer in pyrite-fuel cells 71
• 4.1. Introduction 71
• 4.2. Materials and methods 76
• 4.2.1. Preparation of pyrite and pyrite fuel cell 76
• 4.2.2. Experimental setup and operation 77
• 4.2.3. Analyses 79
• 4.2.4. Fuel cell-driven metal leaching using Pb-Zn mine tailings 79
• 4.3. Results 81
• 4.3.1. Comparison of aqueous pyrite oxidation by different methods 81
• 4.3.2. Electricity generation performance and electron transfer rate of pyrite-fuel cells 83
• 4.3.3. Effect of external resistance on pyrite dissolution in pyrite-fuel cells 84
• 4.3.4. Effect of initial pH and Eh of electrolyte in pyrite-fuel cells 85
• 4.3.5. Enhanced electron transfer with continuous-flow-type pyrite-fuel cells 93
• 4.3.6. Pb and Zn leaching from Pb-Zn mine tailings using the fuel cell system 96
• 4.4. Discussion 97
• 4.5. Environmental implications 100
• 4.6. Summary 102
• References 103
• CHAPTER 5. Multi-electrode molybdenite‐fuel cell: Enhanced electricity generation and molybdenum leaching 107
• 5.1. Introduction 107
• 5.2. Materials and methods 112
• 5.2.1. Reactor design 112
• 5.2.2. Anode substrate (MoS2 concentrate) 113
• 5.2.3. Acidithiobacillus ferrooxidans and media 114
• 5.2.4. Operating conditions and HRT control 115
• 5.2.5. Electrochemical measurements 115
• 5.2.6. Material characterization 116
• 5.3. Results and discussion 119
• 5.3.1. Abiotic MoS2 oxidation of the MoS2 fuel cell 119
• 5.3.2. Effects of Acidithiobacillus ferrooxidans: Performance under Biotic vs. Abiotic conditions 127
• 5.4. Discussion 134
• 5.4.1. Electrode configuration and flow regime: Impact on performance 134
• 5.4.2. Role of Acidithiobacillus ferrooxidans in preventing passivation 135
• 5.4.3. Leaching efficiency 137
• 5.5. Summary 139
• References 140
• CHAPTER 6. Conclusions, applications, and further study 146
• 6.1. Conclusions 146
• 6.2. Applications 154
• 6.3. Further study 158
• 국문 초록 161