Bioleaching Research Articles

Multi-Scale and Trans-Disciplinary Research and Technology Developments of Heap Bioleaching

Multi-Scale and Trans-Disciplinary Research and Technology Developments of Heap Bioleaching

Coupling of bioleaching and electrokinetic soil flushing for the in-situ removal of impurity from Pb-Zn mine tailings

This study combines bioleaching and electrokinetics (EK) for the in-situ removal of metals from polluted mine tailings collected from an abandoned Pb-Zn mine. The proposed treatment strategy consisted in the external production of an acid bioleaching (BL) medium in a bioreactor by means of autochthonous acidophilic microorganisms incubated from real mine tailings; next, the BL medium was subsequently used as anolyte and placed in contact in situ with the polluted soil, taking advantage of EK mechanisms r for dissolution and transport of metals to the cathode compartment. After obtaining a microbial culture capable of producing the bioleaching medium, lab-scale EK experiments were performed, and the influence of the voltage dosage (0.5, 1.0 and 1.5 V cm−1) was assessed. The results obtained showed that the BL medium improved the metal removal efficiency, and that the applied voltage gradient had a clear influence. Specifically, the combination of an electric current under 1.5 V cm−1 and the BL medium increased the metal removal rates by 17 % (Fe), 4 % (Cu), 2 % (Zn), 12 % (Mn), 12 % (Ni), 1 % (Cr) and 7 % (Co), as compared to those without using BL. With this novel treatment, it was also possible to comply with the local regulatory requirements for most of the metals studied. This technology offers several advantages over other EK-bioleaching configurations previously reported. It was found that the limiting factor in the process was the voltage gradient applied, as higher voltages increased metal removal yields but also producing higher soil heating with the consequent energy losses.

Bioleaching of a lateritic ore (Piauí, Brazil) in percolators

Heap leaching of laterites for extraction of nickel and cobalt is an attractive alternative to capital and energy intensive high pressure acid leaching, the dominant hydrometallurgical processing technology for limonitic laterites. Conventional approach for heap leaching of laterites is leaching with sulfuric acid. Consumption of sulfuric acid during heap leaching is substantial and industrial-scale operations require construction of a sulfuric acid production plant on site. In this study, heap bioleaching of laterites was simulated in laboratory scale column percolators and bioleaching of nickel and cobalt from lateritic material was successfully demonstrated for the first time. The process is based on biooxidation of the bacterially modified “wet sulfur” inside column percolators by sulfur-oxidizing acidophilic bacteria Acidithiobacillus thiooxidans. The “wet sulfur“ was generated in a bioreactor with the bacterial culture, harvested, and mixed with lateritic ore before forming agglomerates to be filled in the percolator columns. Liquid was circulated with a flow rate of 8 mL/min. Maximum metal extraction was 66% nickel, 95% cobalt, 10% iron, 55% magnesium and 89% manganese from the Piauí lateritic ore after one month bioleaching. For comparison, chemical leaching with 1 M sulfuric acid with or without addition of 10 g/L of ferrous sulfate heptahydrate as reductant resulted in extraction of approximately 80% nickel, 86% cobalt, 33% iron, 50% magnesium and 81% manganese. With bioleaching a higher cobalt but lower nickel and iron extraction was achieved, i.e. a better selectivity of nickel over iron extraction, as well as a relatively higher pH of the pregnant leach solution requiring less limestone and, consequently, lower CO2 emission and generation of iron cake waste in case of laterite bioleaching. Overall, the results are promising and show potential of laterite heap bioleaching to be further developed to application on industrial scale.

Assessment of the visible light effect on one-step bacterial leaching of metals from spent lithium-ion batteries cathode pretreated by a bio-chemical lixiviant

Over the years, the extensive generation of spent lithium-ion battery cathodes (SLIBCs) and the absence of a practical recycling criterion for these hazardous yet metal-rich urban resources have posed a severe environmental threat. To address this issue, we propose an innovative hybrid strategy based on the characterization of SLIBCs, which includes pretreatment and an evaluation of the effect of visible light on one-step bacterial leaching of SLIBCs. This research presents, for the first time, an evaluation of the impact of visible light on the semiconducting properties of SLIBC and its potential to enhance extracellular electron transfer (EET) between the heterotrophic bacterium Bacillus foraminis and the waste. This increased electron transfer leads to more efficient metal bioleaching. In this strategy, we applied a novel bio-chemical pretreatment to modify the powder structure, considering the high metal content in the waste. This novel approach utilized metabolites from the spent medium of Bacillus foraminis cultures at pH∼5.4 and H2O2 (15% (v/v)). A pulp density of 10 g/L, a duration of 48 h, and a temperature of 60 °C resulted in the extraction of 98% of the manganese content. Subsequently, we assessed the bioleaching of pretreated SLIBC under both visible light and darkness conditions. Results indicate that, under 15,000 lux for 6 days, we achieved acceptable extraction rates: 68% Cu, 41% Li, 25% Co, and 16% Ni. In contrast, in darkness, extraction rates were notably lower, at 23% Cu, 9.9% Li, 3.9% Co, and 2.6% Ni. The increased extraction efficiency under visible light can be attributed to the proposed mechanism of light's effect on enhancing extracellular electron transfer between bacteria and SLIBC with semiconducting properties. FTIR, XRD, and FE-SEM analyses were also instrumental in understanding the effectiveness of the proposed strategy.

Comparison of bioleaching of a sulfidic copper ore (chalcopyrite) in column percolators and in stirred-tank bioreactors including microbial community analysis

Chalcopyrite is the most abundant Cu-sulfide and economically the most important copper mineral in the world. It is known to be recalcitrant in hydrometallurgical processing and therefore chalcopyrite bioleaching has been thoroughly studied for improvement of processing. In this study, the microbial diversity in 22 samples from the Sarcheshmeh copper mine in Iran was investigated via 16S rRNA gene sequencing. In total, 1063 species were recognized after metagenomic analysis including the ferrous iron- and sulfur-oxidizing acidophilic genera Acidithiobacillus, Leptospirillum, Sulfobacillus and Ferroplasma. Mesophilic as well as moderately thermophilic acidophilic ferrous iron- and sulfur-oxidizing microorganisms were enriched from these samples and bioleaching was studied in shake flask experiments using a chalcopyrite-containing ore sample from the same mine. These enrichment cultures were further used as inoculum for bioleaching experiments in percolation columns for simulating heap bioleaching. Addition of 100 mM NaCl to the bioleaching medium was assessed to improve the dissolution rate of chalcopyrite. For comparison, bioleaching in stirred tank reactors with a defined microbial consortium was carried out as well. While just maximal 32% copper could be extracted in the flask bioleaching experiments, 73% and 76% of copper recovery was recorded after 30 and 10 days bioleaching in columns and bioreactors, respectively. Based on the results, both, the application of moderately thermophilic acidophilic bacteria in stirred tank bioreactors, and natural enrichment cultures of mesoacidophiles, with addition of 100 mM NaCl in column percolators with agglomerated ore allowed for a robust chalcopyrite dissolution and copper recovery from Sarcheshmeh copper ore via bioleaching.

Draft genome sequence of Acidiplasma cupricumulans strain BH2T, isolated from a pregnant leachate solution of heap bioleaching.

We report the draft genome sequence of a type strain Acidiplasma cupricumulans Strain BH2T, isolated from a pregnant leachate solution of industrial-scale chalcocite bioleach heap (Monywa, Myanmar). The genome is 1.7 Mbp long with a GC content of 34.2%.

Insights into the EPS production and distribution of planktonic and attached Sulfobacillus thermosulfidooxidans cells during bioleaching

Bacterial leaching can effectively promote the bioleaching of chalcopyrite by secreting extracellular polymeric substances (EPS). In this study, the production and distribution of EPS on the surface of planktonic and attached cells of Sulfobacillus thermosulfidooxidans (S. thermosulfidooxidans) during the process of chalcopyrite concentrate bioleaching were observed in situ using Field emission scanning electron microscope (FE-SEM) and Confocal laser scanning microscope (CLSM). The TOC content and key components of EPS were extracted during the chalcopyrite bioleaching process. Moreover, the main functional groups of extracellular polymorphs were identified through Fourier transmission-infrared spectroscopy (FT-IR). The results showed a similar trend in the evolution of EPS content in planktonic and attached cells. However, the EPS content secreted by the cells attached was more than that of planktonic cells during the entire process of bioleaching. Furthermore, the results of FE-SEM indicated that the EPS secreted by the attached cells is thicker and stickier, with better adsorption performance. The FT-IR spectrum analysis revealed that the O–H, C–H, and CO bonds are the main functional groups of EPS. This work further clarifies the role of EPS in the bioleaching process.

A mining industry overview of cobalt in Finland: exploration, deposits and utilization

Finland has a significant role in the European Union cobalt supply, with the largest known cobalt resources and only cobalt-producing mines in Europe. In addition, Finland is a globally significant producer of refined cobalt. However, Finland, along with the rest of Europe, is strongly dependent on cobalt imports. Recycled cobalt covers a small fraction of the country's demand, as well as that of the rest of Europe. Most of the cobalt deposits in Finland can be grouped into five genetic types (± subtypes). The orthomagmatic and Outokumpu types have been among the most important sources of cobalt in Finland. The Talvivaara type hosts the largest known cobalt resource in Europe, mostly in the Terrafame Sotkamo deposit. The most common cobalt minerals in the Finnish deposits are sulfides, and to a lesser extent sulfarsenides. These are concentrated by froth flotation, and the concentrates treated in Finnish cobalt refineries. An exception to this is the Terrafame Sotkamo mine, where bio-heap leaching technology is utilized for metal recovery, and metalliferous liquid is processed to battery-grade chemicals. Assessment of undiscovered mineral resources, prospectivity modelling, the exploration history and recent discoveries highlight the exploration potential for several types of Co-enriched mineral deposits in Finland. Thematic collection: This article is part of the energy-critical metals for a low carbon transition collection available at: https://www.lyellcollection.org/topic/collections/critical-metals

Underground Development of Mineral Subsoil Using Microorganisms: A Mini-Review

This mini-review is devoted to the analysis of the current state of the relatively rarely used underground bio-mining of natural minerals. On the basis of this analysis, it is substantiated that bacterial leaching technology has no alternative for environmentally safe and economically break-even mining of ore-bearing rocks and off -balance metal-bearing formations that are difficult to access, or unprofitable for traditional methods. It is emphasized that the efficiency of biotechnology depends on the accuracy of modeling and operational control of the working parameters of the process of biological extraction of metals, for which it is necessary to develop a new combined hydro-technical system with the possibility of the reverse technological influence on the regimes of leaching. Such controlled modes of the process are the intensity of forced aeration, pH level of the bacterial solution, amount of nutrient medium, and duration of leaching. To improve the accuracy of prediction and control of underground microbiological development, the use of a control method based on an adaptive-network-based fuzzy inference system (ANFIS) is recommended.

From understanding the rate limitations of bioleaching mechanisms to improved bioleach process design

While bioleaching has become established technology for the leaching of refractory gold concentrates and in the heap leaching of copper sulfide minerals, many other applications, although demonstrated at the laboratory scale, have not found significant uptake in industrial biomining. The reasons for this are manifold, but generally relate back to engineering constraints in operating processes at large scale while remaining economically viable.The paper unpacks acidophile sulfide bioleaching mechanisms within bioreactors into various sub-processes and analyses them in terms of their rate limitations, such as gas-liquid mass transfer of oxygen and CO2, diffusion constraints between and within mineral particles, competing side reactions etc. It becomes clear that microbial metabolic reactions are generally not what limits the kinetics of bioleaching reactions overall but rather the reaction environment. Improved process design to enhance the economic performance of bioleaching therefore needs to target the slowest sub-process in the bioleaching mechanism, which is rarely the biological one.Conventional tank and heap bioleaching processes are discussed in this context and routes taken towards their improvement discussed. Further, various promising novel concepts in biomining, such as leaching with biogenic lixiviants, phytomining and tailings leaching are evaluated within this framework, in each case identifying the potentially limiting sub-processes. It becomes clear that the relative ‘slowness’ of these sub-processes prohibits exploitation through designed active industrial processes; they can, however, still be facilitated through suitably designed ‘passive’ processes in which the time taken for slow processes is less of an economic constraint. While this is an obvious approach in bioremediation, it can also be employed for the economic recovery of value from otherwise sub-economic mineral deposits and waste materials through heap bioleaching. This way it can also play a role in the drive towards a circular economy.

Recovery of non-ferrous metals from sulfide ores by bioleaching on the example of the Allarechensk technogenic deposit

The possibility of processing sulfide copper-nickel raw materials by heap bioleaching due to the environmental attractiveness of this approach is becoming an increasingly relevant topic for mining and processing. On the example of the Allarechensk technogenic deposit ore, the effectiveness of the bioleaching method for the copper and nickel recovery has been considered. The content of metals in the original ore sample: nickel – 2.42 % and copper – 0.75 %. The ore grinded to the size of –5+3 mm has been irrigated with a solution containing a strain of Acidithiobacillus ferrivorans. The S : L ratio is 4 : 1, the flow rate is equal to 0.1 mL/min. In pregnant solutions, the pH and redox potential values have been controlled, and the concentrations of ferrous and ferric iron, copper, and nickel ions have also been measured. The experiment duration is 11 months, 8.9 % nickel and 6.1 % copper have been recovered. Copper has been extracted from pregnant solutions by cementation on iron, the maximum recovery is 97.3 %. Thus, it has been shown that the proposed scheme for the recovery of metals is promising for the processing of sulfide raw materials, in particular, low-grade ores and enrichment waste.

Recovery of valuable metals from spent lithium-ion batteries using microbial agents for bioleaching: a review.

Spent lithium-ion batteries (LIBs) are increasingly generated due to their widespread use for various energy-related applications. Spent LIBs contain several valuable metals including cobalt (Co) and lithium (Li) whose supply cannot be sustained in the long-term in view of their increased demand. To avoid environmental pollution and recover valuable metals, recycling of spent LIBs is widely explored using different methods. Bioleaching (biohydrometallurgy), an environmentally benign process, is receiving increased attention in recent years since it utilizes suitable microorganisms for selective leaching of Co and Li from spent LIBs and is cost-effective. A comprehensive and critical analysis of recent studies on the performance of various microbial agents for the extraction of Co and Li from the solid matrix of spent LIBs would help for development of novel and practical strategies for effective extraction of precious metals from spent LIBs. Specifically, this review focuses on the current advancements in the application of microbial agents namely bacteria (e.g., Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans) and fungi (e.g., Aspergillus niger) for the recovery of Co and Li from spent LIBs. Both bacterial and fungal leaching are effective for metal dissolution from spent LIBs. Among the two valuable metals, the dissolution rate of Li is higher than Co. The key metabolites which drive the bacterial leaching include sulfuric acid, while citric acid, gluconic acid and oxalic acid are the dominant metabolites in fungal leaching. The bioleaching performance depends on both biotic (microbial agents) and abiotic factors (pH, pulp density, dissolved oxygen level and temperature). The major biochemical mechanisms which contribute to metal dissolution include acidolysis, redoxolysis and complexolysis. In most cases, the shrinking core model is suitable to describe the bioleaching kinetics. Biological-based methods (e.g., bioprecipitation) can be applied for metal recovery from the bioleaching solution. There are several potential operational challenges and knowledge gaps which should be addressed in future studies to scale-up the bioleaching process. Overall, this review is of importance from the perspective of development of highly efficient and sustainable bioleaching processes for optimum resource recovery of Co and Li from spent LIBs, and conservation of natural resources to achieve circular economy.

Bioleaching of zinc, copper and antimony from a tetrahedrite concentrate using acidophilic microorganisms

In this study, bacterial leaching of zinc, copper and antimony from tetrahedrite concentrate was investigated with mixed mesophilic and mixed moderately thermophilic microorganisms. The mineralogical studies showed that tetrahedrite ((Cu,Fe)12Sb4S13), ankerite (Ca(Fe,Mg)(CO3)2) and quartz (SiO2) are the main mineral phases. During bioleaching experiments, the effects of different chemicals and factors such as graphite, silver nitrate, L-cysteine, pyrite, and mechanical activation were studied for the first time. It was found that the removal of toxic antimony from tetrahedrite concentrate by alkaline Na2S-NaOH facilitates the growth of microorganisms and extraction rates of metals. The maximum extraction of zinc, copper and antimony was 99.7%, >99.9% and 92.8% with ORP, cell counts and Fe(III) concentration of 666 mV, 108 cells/ml and 9.58 g/l, respectively, using the moderately thermophilic culture with the tetrahedrite residue obtained after alkaline leaching (low-Sb). Under the same control leaching conditions with H2SO4, the maximum extraction of zinc, copper and antimony was 26.2%, 46.1% and 10.7% with low ORP and Fe(III) concentration of 464 mV and 5.18 g/l, respectively. The results showed that bacterial leaching of tetrahedrite concentrate significantly improves the extraction of metals compared to control test. As an important result, mechanical activation by planetary mill played a significant role during tetrahedrite bioleaching. Residual analysis proved the formation of antimony sulfide (Sb2S5) and jarosite (K3Fe9S6O42H18) phase as dissolution inhibitors and acanthite phase (Ag2S) as accelerator for dissolution kinetics.

Alteration of sulfide ore of the Samolazovskoe deposit, Aldan shield, in an experimental bioleaching heap

The article contains the results of a mineralogical study of sulfide ores of the Samolazovskoe deposit (Aldan Shield) and the products of their experimental bacterial oxidation in a heap. Pyrite and marcasite are the major minerals of primary ores. They form fine-grained crystalline and micrometer-grained to cryptocrystalline aggregates. Sphalerite, galena, chalcopyrite, pyrrhotite, fahlore, luzonite, bournonite and other Sb sulfosalts, antimonite, arsenopyrite are minor minerals. Tiemannite, coloradoite, calaverite, hessite, petzite and native gold are rare. The ores in the experimental biooxidation heap are mostly altered in its upper parts. The secondary products of the alteration of ores include fine-grained Mg- and S-bearing calcite, smectites after feldspars, and films of Fe3+oxyhydroxides on the surface and in fractures of ore. In the lower part of the heap, technogenic processes are weak and mainly include the formation of gypsum . The sulfides are preserved throughout the heap vertical profile including very fine crystalline, colloform and botryoidal aggregates with a nonstoichiometric ratio of cations and anions and the presence of As, Ni and Cu. The botryoidal aggregates of the Fe disulfides contain galena, which forms a “microseptary” structure, which was not found in primary ores. The high-fineness native gold was found in assemblage with coloradoite and calaverite as inclusions in fine-grained aggregates of Fe disulfides. The conclusion is made on an insufficient impact of the bioleaching of refractory ores in the irrigation regime used, and forming of the secondary minerals that prevent the extraction of gold. Keywords: Samolazovskoe deposit, Aldan Shield, coloradoite, calaverite, native gold, refractory ores, bio-oxidation.

Recovery of non-ferrous metals from sulfide ores by the method of heap bioleaching on the example of Allarechensk technogenic deposit

On the example of the Allarechensk technogenic deposit ore, the heap bioleaching method feasibility for the copper-nickel ores processing and non-ferrous metals recovery was considered. The content of metals in the initial ore sample was following: nickel – 2.42 %, copper – 0.75 %. The ore grinded to a size of -5+3 mm was irrigated with a solution containing a strain of Acidithiobacillus ferrivorans. The S:L ratio was 4:1, the flow rate was 0.1 mL/min. In pregnant solutions, the pH and ORP values were controlled, and the concentrations of ferrous and ferric iron, copper, and nickel ions were also measured. The experiment duration was 330 days, 8.9 % nickel and 6.1 % copper were recovered. The pathways for the metals extraction from pregnant solutions, as well as the utilization of bioleaching residue were considered.

BACTERIAL LEACHING OF BALANCED ORES OF ALBITITE DEPOSITS OF THE UKRAINIAN SHIELD

Prospects for increasing the raw materials resources of uranium ore deposits of the albite formation of the Ingul megablock of the Ukrainian Shield and the possibility of reducing the impact of harmful waste due to the method of bacterial leaching of metals were considered. Mineral-forming systems of uranium-bearing albitites of the Ukrainian Shield have always been considered as monoelement, exclusively uranium objects. However, their out-of-balance ores and tailings contain elevated, up to industrial, concentrations of other metals, which, under conditions of hypergenic processes, pose a potential threat of environmental pollution. In order to determine the possibility of expanding raw materials resources of albite deposits of the Ukrainian Shield due to the use of the method of bacterial leaching of metals, the composition of industrial ores and host rocks was considered. In particular, our data from their mineralogical and geochemical research showed that uranium and five of its companion elements: thorium, vanadium, beryllium, zirconium and lead reach industrial content. At the same time, cobalt, nickel and zinc are characterized by an increased content close to the minimum industrial values. The most promising for bacterial leaching are rocks that contain sulfides. The rocks of the uranium ore albitite formation contain sulfur-containing compounds and, in particular, pyrite, as well as bi- and trivalent iron. We found the highest content of sulfides in albitized rocks (up to 0.82%), ore-free albitites (up to 0.81%), low-ore albitites (up to 0.61%), that is, in rocks accumulated in industrial waste. It is assumed that the use of bacterial leaching methods with the participation of chemolithotrophic microorganisms can be promising for the processing of off-balance ores and will contribute to the expansion of the raw material base of albite deposits of the Ukrainian Shield, due not only to uranium, but also to nickel, cobalt and zinc.

Simulated heap bioleaching of sulfide copper-nickel technogenic waste in the Arctic

A laboratory scale study was conducted, aimed at finding an effective method for processing copper-nickel technogenic raw materials. The heap bioleaching effectiveness for the processing of low-grade copper-nickel raw materials in the climatic conditions of the Arctic was considered. The intensity of copper and nickel leaching was studied at various ambient temperatures. The role of aeration on the recovery level of metals into solution was considered. By the end of the experiment without aeration, 8.43% copper and 16.26% nickel were recovered, while the use of aeration for 100 days made it possible to recover 8.47% copper and 16.78% nickel.

Iron Removal from Kaolin Waste Dumps by Chemical (Oxalic and Citric Acids) and Biological (Bacillus Strain) Leaching

Kaolin waste dumps contain a huge volume of material that cannot be commercialized due to the presence of variable amounts of iron minerals, which impart a yellowish color to the kaolin. Elimination of iron from kaolin using either a chemical or a biological method was the aim of this study. The chemical leaching of iron from kaolin was carried out using response surface methodology to optimize the reaction conditions. Time was found to be the most influential variable, although oxalic acid must be present to leach 32% of the iron. Biological leaching was also assayed for 14 days using a Bacillus strain. The results of bacterial leaching of iron from kaolin showed <1% iron elimination.

Low-grade chalcopyrite ore, heap leaching or smelting recovery route?

Chalcopyrite, the major mineral source of copper, is commonly treated pyrometallurgically, using froth flotation, smelting, converting and electrorefining processes. The ore treatment however is limited to the cut-off grade concentration below which the extraction is not economically viable. In this study a comparison of feasibility of the pyrometallurgical and hydrometallurgical treatment of low grade (0.23%–0.35% Cu), high content chalcopyrite (>90% CuFeS2) ore were studied from both technical and economic viewpoints. On a technical stance, the results of a pilot test on froth flotation of 100 t of low-grade ore are presented. The pilot test results confirm the generation of a Cu concentrate of a grade range 23.3–19.6% Cu with a copper recovery in the range 90.9–78.1%. For the hydrometallurgical treatment, bio heap leaching of 40,000 t of low-grade ore using agglomeration and aeration was proven to achieve a copper recovery of 32.6% for the chalcopyrite portion of the ore over 326 days of operation.On the economic side, the operating cost of the process per tonne of copper cathode for both processes were reported. The operating cost for the pyrometallurgical (PM) processing plant was calculated to be 1.4 times less than the hydrometallurgical (HM) processing plant. The sales revenue of the PM route was also higher than that of the HM route due to the byproducts credit. Capital cost estimates were made assuming that the current solvent extraction/electrowinning (SX/EW) facilities in a HM route and the current smelting and electrorefining plants in the PM route have enough free capacity to absorb the upstream outputs. Applying the copper extraction efficiencies of the pilot plants, the profitability indicators for both routes in treatment of 3000,000 t ore/year was studied. The impact of the interest rate was found significant in economic preference of the HM route over the PM route. This is due to the high capital cost of the mineral processing plant despite of the higher operating cost of the HM plant. The capital cost of the mineral processing plant can make the HM route feasible at interest rates higher than 27.5%. At discount rates lower than 27.5%, the PM route process is viable over the HM route at copper market price of US$9500/t. A drop in copper selling price to US$6000/t acts in favor of the HM route, making it feasible at interest rates higher than 22.4%. For a general scenario where the construction of SX/EW and smelter/refinery plants are required, the discount rate at which the net present value (NPV) of the two routes are equal has decreased from 27.5% to 17%. In this scenario, for discount rates higher than 17%, the HM route with 31% total copper recovery is more feasible than the PM route with 79% recovery.

Optimized biogenic sulfuric acid production and application in the treatment of waste incineration residues

The biological leaching of metals from different waste streams by bacteria is intensively investigated to address metal recycling and circular economy goals. However, usually external addition of sulfuric acid is required to maintain the low pH optimum of the bacteria to ensure efficient leaching. Extremely acidophilic Acidithiobacillus spp. producing sulfuric acid and ferric iron have been investigated for several decades in the bioleaching of metal-containing ores. Their application has now been extended to the extraction of metals from artificial ores and other secondary sources. In this study, an optimized process for producing biogenic sulfuric acid from elemental sulfur by two sulfur-oxidizing species, A. thiooxidans and A. caldus and their combinations, was investigated in batch and stirred tank experiments. Using a combined culture of both species, 1.05 M and 1.4 M biogenic sulfuric acid was produced at 30 °C and 6% elemental sulfur in batch and semi continuous modes, respectively. The acid produced was then used to control the pH in a heap bioleaching system in which iron- and sulfur-oxidizing A. ferrooxidans was applied to biologically leach metals from waste incineration residuals. Metals like Cu, Ni, Al, Mn, and Zn were successfully recovered by 99, 93, 84, 77 and 68%, respectively within three weeks of heap bioleaching. Overall, a potential value recovery of incorporated metals >70% could be achieved. This highlights the potential and novelty of applying extremely acidophilic sulfur-oxidizing bacteria for cheap and efficient production of biogenic sulfuric acid and its use in pH control.