Designing bioleaching reactors: challenges and innovations

International audienceBioleaching is a hydrometallurgical technique which uses the metabolic activity of lithotrophic microorganisms for the extraction of metals from sulfide ores. These microorganisms draw their energy from the oxidation of iron and/or reduced inorganic sulfur compounds, producing sulfuric acid and ferric iron. The result is a highly corrosive " bioleaching " solution that dissolves the sulfide minerals by oxidation, releasing the metals to solution. In these reactions oxygen is used as an electron acceptor. Bioleaching is a proven technology already industrially applied. Its main advantages over other processes are to be cost-effective and to provide the same duty in a simpler way in terms of operability. Bioleaching is also attractive insofar as it presents few environmental hazards. However, up to now, it remains a niche application mainly because of the limitations and the unsatisfactory performances of the reactors. One reason to explain this situation is probably the lack of research work dedicated to process development and reactor design in comparison to the great effort devoted worldwide to the biology and physiology of microorganisms. Out of the papers devoted to bioleaching published in the last decade, less than 2% deal with basic process engineering issues (such as heat and mass transfer) and bioreactor design. One of the key factors of bioleaching performances in agitated tanks is mixing. It has to be efficient in order to reach a high level of oxygen transfer rate (OTR) to comply with oxygen uptake rates of about 1500 mg L −1 h −1 , and even distribution of the various components of the slurry throughout the tank. The main costs of bioleaching operations are the investment costs of the tanks and the impellers and the operating costs of gaseous mass transfer. This presentation will give an overview of the recent advances achieved to overcome some of the limitations of bioleaching processes with a particular emphasis on the development of an alternative bioleaching reactor based on the use of floating agitators to mix and to suspend solids in the solution as well as to inject gases in the pulp. This new concept enables to decrease the costs of bioleaching processes by operating (i) in lagoons or ponds instead of tanks, (ii) at higher solid loading (> 15% w/w) than in conventional stirred tank bioreactors (STR). In these conditions of high solid load, the demand for oxygen is significantly increased and air is replaced by oxygen to provide an adequate oxygen supply The experimental testwork performed from lab to pilot scales (2 L up to 2 m 3) has confirmed that this new device operated at solid load up to 30% leads to similar leaching performances (kinetics and metal yields) than those obtained in STR at solid load below 20%. The injection of oxygen instead of air improves OTR but must be managed carefully to avoid high dissolved oxygen (DO) level in the slurry: a decrease of the activity of the bioleach microorganisms was observed when the DO concentration was above 17 ppm, which might be attributed to an oxidative stress due to the formation of toxic reactive oxygen species [1]. [1] IMLAY et al., Annual Review of Biochemistry, 77, 755–776, 2008

Extended validation of an expression to predict ORP and iron chemistry : application to complex solutions generated during the acidic leaching or bioleaching of PCBs

The present work shows that the expression developed in our previous work to predict the redox potential of the quaternary H₂SO₄-Fe₂(SO₄)₃-FeSO₄-H₂O system can still be used to predict the redox potential of the Fe³⁺/Fe²⁺ couple in more complex acidic iron sulfate solutions generated during the acidic leaching and bioleaching of Printed Circuit Boards (PCBs). This expression can also be employed to determine the ferrous and ferric concentrations based on measured redox potential, temperature and total iron by AAS, especially in ferric or ferrousdominant solutions. This equation therefore provides an alternative to the traditional colorimetric or volumetric methods for ferric and ferrous determination. The applicability of this equation in acidic iron sulfate solutions containing cupric ions was also supported by the experimental results in the literature. It is also shown that the measured redox potential is highly useful to estimate and understand the iron chemistry of industrial leaching processes.Applied Science, Faculty ofNon UBCMaterials Engineering, Department ofReviewedFacultyResearche

Co-processing of sulfidic mining wastes and metal-rich post-consumer wastes by biohydrometallurgy

International audienceThe consequence of a strong economic growth in emerging countries combined with the rise of the world population is an increase in the demand for raw materials, leading to growing concern regarding their availability and the global efficiency of the supply chain. These tensions reinforce the need to associate the development of the recycling industry to the identification of new resources which could be used for the recovery of valuable materials. The purpose of this study is to develop a novel biological co-processing approach for the recovery of strategic metals in both sulfidic mining wastes and post-consumer wastes (WEEE). The principle of this treatment is based on two steps: mine wastes are biologically oxidized, resulting in the production of a ferric iron-sulfuric acid lixiviant solution which is used to leach base and other soluble metals contained in e-scraps. Batch tests were carried out using flotation tailings wastes containing 60% of pyrite and grinded Printed Circuit Boards (PCB < 750 μm) with a solid load of 2.5%. Two series of tests were conducted in order to study the influence of the ferric iron concentration and of the bacterial activity on metals dissolution. Results showed that a higher ferric iron concentration led to an increase in the dissolution rate of copper which is the main metal contained in the PCBs. Moreover, a dissolution yield of 98.3% was reached for copper after 2 days when bacterial activity was observed, corresponding to an increase of about 20% compared to the tests without bacterial activity. Finally, this study highlights the importance of the availability of ferric iron and of the bacterial oxidation of ferrous iron for the feasibility of this bioleaching process dealing with the recycling of PCBs

An update on possibilities of metals recovery from Polish copper ores by biotechnology. Project Ecometals

The possibilities of metals recovery from copper ores with the biotechnological methods are widely known. The methods consist in bioleaching of copper ores, copper concentrates and byproducts of their production, as well as metals recovery from leaching solutions. Biohydrometallurgical methods were tested for years to be applied at KGHM Polska Miedź S.A., in order to improve efficiency of copper production. Several different research units worked on the topic, and the most significant and wide range initiatives in this area are mentioned in this article. One of the initiatives is an ongoing German and French Ecometals project. KGHM Polska Miedź S.A. and KGHM Cuprum Ltd. Research and Development Centre are this project Partners. In the frame of the project different metals bearing materials (ores, concentrates and tailings) are tested. Among them three lithological types of the copper ore from Rudna mine and the copper concentrate from Lubin concentrator are used for studies. The article gives a general overview of these activities, with the main focus on results of bioleaching studies of selected materials, conducted by KGHM Cuprum. In these studies sandstone and shale, as well as so called “shale concentrate” (containing 39% of the shale) were used for experiments, and possibilities of their bioleaching were evaluated

An update on possibilities of metals recovery from Polish copper ores by biotechnology. Project Ecometals

The possibilities of metals recovery from copper ores with the biotechnological methods are widely known. The methods consist in bioleaching of copper ores, copper concentrates and byproducts of their production, as well as metals recovery from leaching solutions. Biohydrometallurgical methods were tested for years to be applied at KGHM Polska Miedź S.A., in order to improve efficiency of copper production. Several different research units worked on the topic, and the most significant and wide range initiatives in this area are mentioned in this article. One of the initiatives is an ongoing German and French Ecometals project. KGHM Polska Miedź S.A. and KGHM Cuprum Ltd. Research and Development Centre are this project Partners. In the frame of the project different metals bearing materials (ores, concentrates and tailings) are tested. Among them three lithological types of the copper ore from Rudna mine and the copper concentrate from Lubin concentrator are used for studies. The article gives a general overview of these activities, with the main focus on results of bioleaching studies of selected materials, conducted by KGHM Cuprum. In these studies sandstone and shale, as well as so called “shale concentrate” (containing 39% of the shale) were used for experiments, and possibilities of their bioleaching were evaluated

Data_Sheet_1_Fe(III) bioreduction kinetics in anaerobic batch and continuous stirred tank reactors with acidophilic bacteria relevant for bioleaching of limonitic laterites.docx

In the framework of the H2020 project CROCODILE, the recovery of Co from oxidized ores by reductive bioleaching has been studied. The objective was to reduce Fe(III) to Fe(II) to enhance the dissolution of Co from New-Caledonian limonitic laterites, mainly composed of goethite and Mn oxides. This study focused on the Fe(III) bioreduction which is a relevant reaction of this process. In the first step, biomass growth was sustained by aerobic bio-oxidation of elemental sulfur. In the second step, the biomass anaerobically reduced Fe(III) to Fe(II). The last step, which is not in the scope of this study, was the reduction of limonites and the dissolution of metals. This study aimed at assessing the Fe(III) bioreduction rate at 35°C with a microbial consortium composed predominantly of Sulfobacillus (Sb.) species as the iron reducers and Acidithiobacillus (At.) caldus. It evaluated the influence of the biomass concentration on the Fe(III) bioreduction rate and yield, both in batch and continuous mode. The influence of the composition of the growth medium on the bioreduction rate was assessed in continuous mode. A mean Fe(III) bioreduction rate of 1.7 mg·L−1·h−1 was measured in batch mode, i.e., 13 times faster than the abiotic control (0.13 mg·L−1·h−1). An increase in biomass concentrations in the liquid phase from 4 × 108 cells·mL−1 to 3 × 109 cells·mL−1 resulted in an increase of the mean Fe(III) bioreduction rate from 1.7 to 10 mg·L−1·h−1. A test in continuous stirred tank reactors at 35°C resulted in further optimization of the Fe(III) bioreduction rate which reached 20 mg·L−1·h−1. A large excess of nutrients enables to obtain higher kinetics. The determination of this kinetics is essential for the design of a reductive bioleaching process.</p