A method of reductive electro-bioleaching of oxide minerals

Abstract

The invention is a method of metal extraction using reductive electro-bioleaching of oxide minerals. This method of mineral treatment allows non-acidophilic soil bacterial consortia consisting of metal-reducing microorganisms growing at neutral pH to reduce the metal oxide mineral selectively, in the presence of controlled redox potentials at which the organism efficiently reduces the oxide minerals. The described reactor arrangement simultaneously allows precise anaerobic conditions and optimal agitation, enabling microbially assisted efficient electroreduction of oxide minerals. The invention is a scalable and cost-effective method of extraction of critical metals from their oxide forms and minerals.

Description

[0001] PT / 2025 / 15293

[0002] A METHOD OF REDUCTIVE ELECTRO-BIOLEACHING OF OXIDE MINERALS

[0003] FIELD OF INVENTION

[0004] The present invention pertains to the field of biohydrometallurgy, with a specific focus on the method of metal extraction from oxide minerals. The invention relates to a novel method for the reductive electro-bioleaching of oxide minerals. In particular, the present invention pertains to an improved process for the extraction of metals from oxide minerals, employing a combination of bioleaching and electrochemical techniques, which are traditionally employed for metal extraction from sulfide minerals. More specifically, the present invention utilizes a specially optimized soil bacterial consortia and controlled electrochemical conditions to enhance the efficiency and selectivity of metal recovery from various oxide minerals. The invention encompasses a method, a system, and a process for the reductive leaching of oxide minerals, providing significant advancements in metal extraction processes. The application of this invention on a commercial scale is aimed at achieving higher metal recovery rates, reduced operational costs, and lower environmental impact, thereby contributing to sustainable and economically viable metal extraction practices from low- grade oxides.

[0005] BACKGROUND OF THE INVENTION AND DESCRIPTION OF PRIOR ART

[0006] The extraction of metals from oxide minerals, such as copper, nickel, cobalt, manganese, iron, tungsten and other critical metals from the oxides, presents significant challenges. Traditional metallurgical methods for extracting metals from these ores are often costly and environmentally damaging. Bioleaching has emerged as a promising alternative due to its lower cost, simplicity, and minimal environmental impact. However, conventional bioleaching techniques have primarily focused on sulfide minerals and are limited in their application to oxide minerals. Furthermore, existing bioleaching methods suffer from slow reaction rates and lower efficiency in metal recovery.

[0007] The present invention addresses these limitations by introducing a novel method for the reductive electro-bioleaching of oxide minerals. This process employs a specially optimized soil bacterial consortia, dominated by metal-reducing bacteria, capable of sustainable metal extraction. These bacteria are capable of reducing oxide minerals under controlled electrochemical conditions. By maintaining a specific redox potential and creating an anaerobic environment using a floating mineral / organic oil film, the invention significantly enhances the efficiency and selectivity of metal recovery from oxide mineral phases.

[0008] This innovative approach not only improves the leaching rate and overall metal recovery but also reduces operational costs and environmental impact, making it a viable solution for commercial-scale metal extraction.

[0009] Reference may be made to CN103131856A which discloses a bio electrochemistry system for copper metal extraction from sulphide ores in an acidic pH of 1.8 to 2.5 using Acidithiobacillus ferrooxidans. This document specifically reveals about the complex set-up which is described to perform an electron transfer mechanism between the organism and the electrode, leading to leaching of copper metal from the sulphide ore. The setup also uses an ion exchange membrane to separate anolyte and catholyte and uses tripotassium iron hexa cyanide and phosphoric acid. This document focuses on metal extraction from sulphide mineral and does not specifically disclose about the survivability of the organism; does not address the issue of selectivity; does not address the issue of metal extraction efficiency; and does not describe how oxygen diffusion is prevented effectively in the anolyte compartment. Though this document describes about metal extraction, it does not describe about metal extraction from oxide minerals.

[0010] Reference may be made to Kumari and Natarajan (2002 a & b) which describes a electrochemical processing of ocean manganese nodules with microbial enhancement using Acidithiobacillus thiooxidans (MCMB 41) and Acidithiobacillus ferrooxidans (TfH6). This specifically reveals the electroleaching and galvanic interactions in the manganese nodule slurry, leading to dissolution of iron and manganese along with co extraction of other nodule metals in the system. The work specifically reports the usage of metabolic extracts and spent medium of sulphur grown Acidithiobacillus thiooxidans (MCMB 41) and 9K grown (with FeSC ) Acidithiobacillus ferrooxidans (TfH6) along with IM H2SO4 at potentials -600 mV, with added pyrite for most optimal metal recovery. The work describes electrochemical or galvanically mediated dissolution of nodules but not on direct microbial growth in the system. The work describes application of pyrite at 5 times the amount of manganese nodule, to act as anode and contribute to galvanically aided dissolution of manganese for optimal recovery. The work specifically describes iron and manganese oxide dissolution in presence of pyrite and acidic bacterial spent medium and cells, and observed that direct electrobioleaching of nodules in absence of pyrite or spent medium was not feasible. It incorporates a complex three compartmental electrochemical set up. Though this work describes about electrochemical dissolution of manganese nodules, it does not address microbial reduction reactions; it does not support active growth of bacteria at applied potentials and highly acidic conditions; does not address selectivity in reduction or dissolution, as the system dissolves iron as well as manganese; reactions are conducted at highly acidic conditions (pH approx. 0.5) and high negative potentials, requiring thermostat and external cooling of the cell.

[0011] References:

[0012] 1. CN103131856A, 2013, Bio-electrochemical system used for copper sulfide ore leaching

[0013] 2. Kumari, A., & Natarajan, K. A. (2002a). Electrochemical processing of ocean manganese nodules with microbial enhancement to recover valuable metals. Mining, Metallurgy & Exploration, 19(3), 137-147. doi:10.1007 / bf03403166

[0014] 3. Kumari, A., & Natarajan, K. A. (2002b). Development of a clean bioelectrochemical process for leaching of ocean manganese nodules. Minerals Engineering 15, 103-106. doi: 10.1016 / 50892-6875(01)00209-6

[0015] Therefore, keeping in view the drawbacks of the hitherto reported prior art, the inventors of the present invention realized that none of the prior arts reveal an efficient method of metal extraction from oxide minerals using a commercially scalable arrangement for reductive electro-bio leaching, which further aids quick solubilisation and subsequent extraction of metals.

[0016] OBJECTIVES OF THE INVENTION

[0017] The main objective of the present invention is therefore to provide a method of reductive electro-bioleaching of oxide minerals which obviates the drawbacks of the hitherto reported prior art. Yet another objective of the present invention is to provide a system that allows efficient reduction of oxide minerals employing ideal electrochemical conditions enabling solubilisation and recovery of metals.

[0018] Another objective of the present invention is to utilize a unique soil bacterial consortia developed from mine soils optimized for the reduction of oxide minerals.

[0019] Another objective of the present invention is to provide a system with an improved and efficient metal oxide reduction employing a reactor arrangement which allows simultaneous growth of microorganisms in an anaerobic environment and application of electrode potential without the use of any salt bridge or membranes or separators.

[0020] Yet another objective of the present invention is to provide a system for metal extraction which reduces environmental impact by minimising the use of chemicals, lowers the operation costs and improves ease of reactions, which obviates the drawbacks of the hitherto reported prior art.

[0021] EMBODIMENTS OF THE INVENTION

[0022] In an embodiment, the present invention achieves significantly high metal recovery rates from various oxide minerals under optimised conditions.

[0023] In another embodiment, the present invention demonstrates effective oxide reduction and metal recovery with lower concentrations of chosen carbon sources, under anaerobic conditions and at neutral pH, thereby reducing the operational cost and resource requirements.

[0024] In still another embodiment, the present invention is a method to achieve reductive electrobio leaching of different oxide minerals using optimised soil bacterial consortia, with or without added pure bacterial culture.

[0025] In yet another embodiment, the present invention describes a method of applying an optimal redox potential suitable for consistent and high metal recovery rates along with active growth of the micro organisms. In still another embodiment, the present invention uses an oil layer to minimise oxygen diffusion as an inexpensive method, ensuring optimal microbial activity and improved reductive leaching performance.

[0026] In yet another embodiment, the present invention describes a scalable and cost-effective reactor with graphite electrodes, without the use of any membranes to separate metabolites or ions to participate in and perform the metal oxide reduction.

[0027] In summary, this method of treatment of low-grade oxide minerals which are otherwise unamenable for metal extraction, will greatly improve the commercial interest owing to its simplicity and ease in material handling and operation.

[0028] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0029] The invention will be explained below with reference to the exemplary embodiments depicted in the accompanying drawings;

[0030] Figure 1 illustrates the process flow chart depicting the material flow and the processes described in the invention

[0031] Figure 2 represents a schematic of the reactor and the components of the reactor that are specifically designed for an intended purpose as described in the embodiments.

[0032] Components Marked in the Drawing:

[0033] 1- Mineral / Organic Oil Layer: A layer of oil is added to the surface of the liquid medium to minimise oxygen diffusion. This creates an anaerobic environment conducive to the activity of the metal-reducing bacteria.

[0034] 2- Media, Ore and microbial consortium: The slurry typically consists of the oxide minerals suspended in a minimal salt medium (MSM) and the microbial consortium.

[0035] 3-Stirrer: Positioned at the bottom of the reactor, the stirrer ensures uniform mixing of the slurry. It helps maintain homogeneous conditions throughout the reaction medium, preventing sedimentation of the ore particles and ensuring effective contact between the bacterial consortia and the ore. 4- The reactor vessel: the reactor vessel is made of opaque or covered glass or acrylic to provide anaerobic conditions, suitable for the growth of the microorganism.

[0036] 5- Graphite Electrodes (Cathode and Anode) and voltage source (V): Cathode (Marked as The negatively charged electrode where reduction reactions occur. In this setup, bacteria interact with the cathode, facilitating the reduction of metal oxides. Anode (Marked as The positively charged electrode where oxidation reactions occur. It completes the electrical circuit within the reactor. The external power supply that applies a controlled redox potential to the electrodes. This potentiostatic control is crucial for optimising the reduction of oxide minerals by the bacterial consortia.

[0037] 6- This component is used for introducing the ore slurry into the reactor along with the microbial consortium.

[0038] Summary of the drawing:

[0039] - The reactor is designed to facilitate the reductive electro-bioleaching (REBL) of oxide minerals using a specialised bacterial consortium.

[0040] - The setup includes an inlet for introducing the ore slurry, graphite electrodes for redox reactions, a stirrer for mixing, and an oil layer to maintain anaerobic conditions.

[0041] - A voltage source provides the necessary electrical potential to drive the electrochemical reactions, microbial growth, enhancing the efficiency and selectivity of metal recovery from the ore.

[0042] Figure 3 schematically depicts the key reaction mechanism in the reductive electrobioleaching of metal oxides

[0043] Figure 4 shows the actual image of biofilm formed at cathodic and anodic interfaces at different instances of applied potential and oxide materials.

[0044] DETAILED DESCRIPTION OF THE INVENTION The invention describes a novel method for the reductive electro-bioleaching (REBL) of mixed oxide minerals, such as manganese, iron, copper, nickel, cobalt and other metal oxides and its combinations as occurring in ores. This process involves creating a slurry with ores containing these oxides in a minimal salt medium (MSM), maintaining an ore content of 0.1 to 30% by weight and incorporating 10-20% of a soil bacterial consortium, with or without added pure bacterial isolate. This consortium comprises metal-reducing bacteria, dominated by Geobacter sp., Clostridium sp., Bacillus sp., Sedimentibacter sp., Enterobacter sp., Shewanella sp. and Petrimonas sp.. The bacteria are supported by organic carbon sources like acetate, sucrose, starch, glucose, pyruvate, ethanol, glycerol, and other organic compounds. The system is maintained at a neutral pH (6.0-7.9) with a mineral / organic oil layer to minimize oxygen diffusion, creating an optimal anaerobic environment for bacterial activity.

[0045] The reactor used in this method is custom-made from glass or acrylic and designed to accommodate the specific needs of the process. Graphite electrodes serve as both anode and cathode materials. The suspension within the reactor is subjected to controlled potentiostatic conditions, with an applied redox potential ranging from 100 mV to -900 mV over a period of 24 hours to 8 days. The design of the reactor includes features to ensure efficient anaerobic mixing, such as a stirrer shaft that penetrates the floating mineral / organic oil film and agitates at low RPM without disturbing the film's surface tension. This innovative design helps maintain the necessary conditions for the reductive bioleaching process to occur effectively at a lower operational cost.

[0046] The process described in this invention significantly enhances the recovery of metals from oxide ores compared to traditional methods while providing several operational advantages. The use of a specially optimized soil bacterial consortium, combined with controlled electrochemical conditions and the innovative use of a mineral / organic oil film, results in high efficiency and selectivity in metal leaching. The reactor's simple and effective design, coupled with the low requirement for carbon sources, contributes to the method's commercial viability and scalability. In essence, this invention offers a promising solution forthe extraction of valuable metals from oxide ores, with potential environmental and economic benefits.

[0047] Significance of the invention and the key reaction mechanisms: The significance of this invention lies in the rapid kinetics of bioleaching achieved through the synergistic effects of microbial activity and the application of an external redox potential. The process accelerates the reduction of oxide ores, largely due to the development of thick biofilms on both the ore and electrode surfaces. The anaerobic environment within the reactor, maintained by the mineral / organic oil layer, and the controlled electrochemical potential promote favourable conditions for biofilm formation, allowing metal-reducing bacteria to efficiently transfer electrons between the electrodes and the ore particles.

[0048] The biofilm serves as a critical interface for external electron transfer (EET), where bacteria, including species like Geobacter sp., Shewanella sp., Clostridium sp., Bacillus sp. etc, facilitate electron flow through two primary pathways. At the anode, bacteria oxidize the supplied organic carbon (e.g., glucose or acetate) and transfer the resulting electrons to the anode, forming a current. This electron transfer from the bacterial metabolic processes is vital for maintaining the overall redox balance. At the cathode, the bacteria mediate electron transfer from the cathode to the ore particles, either directly or through interspecies electron transfer (IET), where one bacteria transfers electron to another via biofilm. This results in the reduction of metal oxides, into more soluble forms, which can then be easily extracted from the ore.

[0049] This system is highly efficient due to the simultaneous bio-electrochemical and biochemical pathways, which drastically enhance the rate of bioleaching compared to traditional methods. The applied potential creates a favourable electron transfer mechanism, driving faster metal recovery and higher selectivity, as observed with recovery rates of up to 95% for a particular metal. A schematic representation of the reaction mechanism and different instances of biofilm formation is provided in figure 3 and figure 4 respectively.

[0050] Key Reaction Mechanism:

[0051] 1. Anodic Reaction (at the anode surface):

[0052] Bacteria + Organic carbon CO2 + e + H+

[0053] Bacteria oxidize organic carbon, transferring electrons to the anode and releasing protons and carbon dioxide. 2. Cathodic Reaction (at the cathode media interface):

[0054] Bacteria

[0055] The metal oxide (MOx) receives electrons from cathode mediated through bacteria, resulting in the formation of soluble Mx+ions, which can be easily solubilized by pH adjustment.

[0056] This integrated microbial-electrochemical system enhances the rate of bioleaching by creating a highly conductive biofilm that supports efficient metal oxide reduction and recovery. The unique combination of the microbial consortia, applied redox potential, and anaerobic conditions distinguishes this method from traditional bioleaching and chemical processes, with significant operational convenience for commercial exploitation leading to economic benefits. The simple electro-biochemical reactor design with active biofilm is advantageous over conventional membrane based set up enabling scale up through fed batch operation of this system.

[0057] EXAMPLES

[0058] The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention in any manner.

[0059] Example 1

[0060] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide, iron oxide and silica is crushed to less than 300 microns, preferably less than 180 microns particle size, and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% preferably 10% ore content, with about 5-20% soil bacteria consortia, preferably 10% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 5000 mg of glucose, preferably 2000 mg was added as the carbon source, followed by a few millilitres of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential of 100mV to -900mV, preferably 100 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 5 days and the pH of 6.5 was maintained with intermittent observation. After 5 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 36% for manganese and 41% iron.

[0061] Example 2

[0062] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide, iron oxide and silica is crushed to less than 300 microns, preferably less than 180 microns particle size, and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% ore preferably 5% ore content, with about 5-20% soil bacteria consortia, preferably 10% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 5000 mg of glucose, preferably 2500 mg was added as the carbon source, followed by a few millilitres of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential of 100mV to -900mV, preferably - 200 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 2 days and the pH of 6.5 was maintained with intermittent observation. After 2 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 38% for manganese and 12% iron.

[0063] Example 3

[0064] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide, iron oxide and copper oxide is crushed to less than 300 microns, preferably less than 150 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% preferably 5% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 5500 mg of glucose, preferably 4500 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential lOOmV to -900mV, preferably -400 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 6 days and the pH of 6.9 was maintained with intermittent observation. After 6 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 82% for manganese, 61% Cu and 17% iron.

[0065] Example 4

[0066] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide, iron oxide and silica is crushed to less than 300 microns, preferably less than 150 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% preferably 4% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 5500 mg of glucose, preferably 4500 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential 100mV to -900mV, preferably -400 mV is applied across the electrodes using an external power source. Reaction was performed without stirring for a period of 8 days and the pH of 6.8 was maintained with intermittent observation. After 8 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 76% for manganese and 21% iron.

[0067] Example 5

[0068] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide, iron oxide and silica is crushed to less than 300 microns, preferably less than 150 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% ore preferably 4% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 5000mg of sodium acetate, preferably 2000 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential lOOmV to -900mV, preferably -300 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 5 days and the pH of 6.8 was maintained with intermittent observation. After 5 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 34% for manganese and 9% iron.

[0069] Example 6

[0070] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade ore comprising but not limited to manganese oxide and iron oxide encompassing minor amounts of nickel, cobalt and copper oxides is crushed to less than 300 microns, preferably less than 120 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30%, preferably 4% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria and introduced in the reactor. About 500 to 6500 mg of glucose, preferably 4500 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential 100mV to -900mV, preferably -400 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 8 days and the pH of 6.7 was maintained with intermittent observation. After 8 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 94% for manganese and 25% iron.

[0071] Example 7

[0072] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade lateritic ore comprising but not limited to chromium oxide, iron oxide, iron oxyhydroxide containing nickel and cobalt is crushed to less than 300 microns, preferably less than 180 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% ore preferably 4% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria MCC 0288, and introduced in the reactor. About 500 to 5000mg of glucose, preferably 2000 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential lOOmV to -900mV, preferably -500 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 7 days and the pH of 6.5 was maintained with intermittent observation. After 7 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 95% for nickel, 80% chromium and 85% iron.

[0073] Example 8

[0074] Minimal salt solution medium (MSM) was prepared, sterilized by standard autoclaving procedure and kept aside for further processing. A low grade lateritic ore comprising but not limited to chromium oxide, iron oxide, iron oxyhydroxide containing nickel and cobalt is crushed to less than 300 microns, preferably less than 150 microns particle size and suspended in the prepared minimal salt medium in a slurry form with about 0.1 to 30% ore preferably 4% ore content, with about 5-20% soil bacteria consortia, preferably 15% bacterial inoculum containing metal reducing bacteria MCC 0288 and added bacterial isolate ATCC BAA 1096, and introduced in the reactor. About 500 to 5000mg of glucose, preferably 2500 mg was added as the carbon source, followed by a few ml of mineral oil to cover the reaction mixture to prevent oxygen diffusion. A controlled redox potential 100mV to -900mV, preferably -400 mV is applied across the electrodes using an external power source. Stirring was performed for a period of 7 days with intermittent pH observation. After 7 days, the pH of the reduced ore slurry is adjusted to solubilise the reduced metal at a recovery rate of 89% for nickel, 83% chromium and 80% iron.

[0075] ADVANTAGES OF THE INVENTION

[0076] Enhanced Bacterial Efficiency: Utilization of a specifically optimized soil bacterial consortia with or without addition of a pure bacterial culture, which are highly effective in reductive leaching under controlled conditions.

[0077] Optimized Redox Potential Control: Maintaining a controlled redox potentials at neutral pH range, critical for optimizing bacterial reduction of oxide ores.

[0078] Lower Carbon Source Requirement: Demonstration of effective metal recovery with lower carbon source concentrations, for example about 500 to 6000 mg of glucose or sodium acetate, significantly reducing operational costs. Reduced Oxygen Interference: Employing a method of introducing a floating mineral / organic oil layer to minimize oxygen diffusion, ensuring anaerobic conditions for effective bacterial activity.

[0079] Higher Metal Recovery Rates: Achieving significantly higher metal recovery rates, for example, of up to 94% for manganese, 95% nickel under optimized conditions exhibiting superior performance.

[0080] Simple and Effective Reactor Design: Utilizing a custom-made glass or acrylic reactor with graphite electrodes without the use of any membranes, simplifying the setup and making the process commercially viable and scalable. Environmental and Economic Benefits: Reduces environmental impact by minimizing the use of chemicals and lowers operational costs through efficient use of resources and simplified reactor design.

Claims

WE CLAIM:

1. A method for reductive electro -bioleaching of oxide minerals, the method comprising:1.1 preparing an aqueous slurry of oxide mineral particles in a minimal salt medium (MSM), the slurry containing 1-20% (w / v) oxide minerals;1.2 inoculating the slurry with a bacterial consortium comprising one or more metal-reducing microorganisms consisting of Geobacter sp., Shewanella sp. , Clostridium sp., Bacillus sp., Sedimentibacter sp., Enterobacter sp., Petrimonas sp., and functional analogues thereof;1.3 adding to the slurry an organic carbon source selected from the group consisting of glucose, acetate, glycerol, ethanol, pyruvate, sucrose, starch, formate, lactic acid, and combinations thereof;1.4 covering the slurry with a floating layer of oil selected from the group consisting of paraffin oil, silicone oil, mineral oil, vegetable-derived oil, and combinations thereof to restrict oxygen diffusion;1.5 immersing in the slurry a pair of graphite electrodes serving as anode and cathode, and applying a controlled redox potential between +100 mV and -900 mV under potentiostatic conditions;1.6 maintaining the slurry at pH 6.0-7.9 and temperature 20-50 °C for 24 h to 8 days to permit microbial biofilm formation and extracellular electron transfer; and1.7 subsequently adjusting the pH of the treated slurry to solubilize and recover metal ions from reduced oxide minerals.

2. The method of claim 1, wherein the oxide minerals comprise one or more selected from the group consisting of manganese oxide, iron oxide, copper oxide, nickel oxide, cobalt oxide, and mixtures, variants of oxides thereof.

3. The method of claim 1 , wherein the organic carbon source is present at 500pg -6000 mg L1and is selected from the group consisting of glucose, acetate, glycerol, ethanol, pyruvate, sucrose, starch, formate, lactic acid, and combinations thereof.

4. The method of claim 1, wherein the bacterial consortium is derived from mine-impacted soils or sediment samples enriched under anaerobic conditions.

5. The method of claim 1, wherein the floating oil layer has a thickness of 0.5-5 cm and is selected to provide an oxygen permeability < 1 x 109cm3 / cm2s ' Pa6. The method of claim 1, wherein the electrodes are graphite rods of 90-100% carbon purity, and the reactor comprises a sealed glass or inert-polymer vessel with a magnetically coupled stirrer shaft configured to penetrate the oil layer without disruption.

7. The method of claim 1, wherein the redox potential is maintained at -100 mV to -900 mV, the pH is maintained at 6.5-7.5, and the temperature is maintained at 30-40 °C.

8. The method of claim 1, wherein microbial-mediated electron transfer comprises direct electron transfer (DET) from electrode to ore via conductive biofilms and / or interspecies electron transfer (IET) among consortium members.

9. The method of claim 1, wherein metal recovery efficiency is > 90% for manganese, > 25% for iron, and > 90% for Nickel under optimized conditions.

10. A metal-ion-containing solution produced by the method of any one of claims 1-10, wherein the solution comprises dissolved Mn2+, Fe2+, Co2+, Cr3+, Cu2+and / or Ni2+ions at concentrations reflecting the recovery of oxide minerals into the aqueous phase.

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