Search Results (22)

The demand for strategic elements, including nickel and cobalt, increases each year due to rapid technological advancements. However, due to their scarcity and environmental concerns, the development of sustainable recycling processes supported by green-energy technologies is becoming essential. In this study, a process relying on indirect bioleaching was used to recover nickel and cobalt from three different superalloy residue powders as a second source of metals, as part of a wider study to recycle superalloys within a waste process. A comparison between the three methods was carried out to analyse the bioleaching mechanisms of the target metals. Acidolysis was selected for further study due to its set-up simplicity and superior recovery rates. Variations in agitation speed of the lixiviant processing the Ni 30167 superalloy revealed that 270 rpm achieved the optimal active metal surface–oxidising agent interaction, with 60% and 70% dissolution rates after 24 h for nickel and cobalt, respectively. For the Re 30168 superalloy, extraction rates of 60% and 50% were obtained in 48 h for nickel and cobalt, respectively. The effect of hydrogen peroxide as an additive to improve metal solubilisation and overcome passivation, are discussed together with the challenges posed by the presence of iron, the materials’ elemental complexity, and its interaction with different oxidising agents. Full article

Achieving the New World Sustainability Vision 2030 leads to enacting environmental restrictions, which aim to partially or totally reduce the negative impacts of different forms of waste and develop alternative technologies for eco-friendly and cost-effective utilization. Solid waste is a hazardous waste with many environmental and economic problems resulting from its storage and disposal. However, at the same time, these wastes contain many valuable elements. One of these solid wastes is heavy oil fly ash “HOFA” generated in power stations using heavy oil as fuel. HOFA is produced annually in massive amounts worldwide, the storage of which leads to the contamination of water resources by the contained heavy metals, resulting in many cancerogenic diseases. At the same time, these ashes contain many valuable metals in significant amounts, such as vanadium “V” and nickel “Ni” that can be extracted effectively compared to their low content and difficulty processing in their main ores. Hence, recycling these types of wastes reduces the environmental adverse effects of their storage and the harmful elements in their composition. This paper critically reviews the world resources of vanadium-bearing waste and various approaches described in the literature for recovering V, Ni, as well as other valuable metals from (HOFA) and other wastes, including pyro- and hydro-metallurgical processes or a combination. Hydro-metallurgical processes include alkaline or acidic leaching using different reagents followed by chemical precipitation, solvent extraction, and ion exchange to extract individual elements. The pyro-metallurgical processes involve the non-salt or salt roasting processes followed by acidic or alkaline leaching processes. The operational parameters and their impact on the efficiency of recovery are also discussed. The digestion mixtures of strong mineral acids used to dissolve metal ions in HOFA are also investigated. Bioleaching is a promising eco-friendly technology for recovering V and Ni through appropriate bacteria and fungi. Oxidation leaching is also a promising environmentally friendly approach and more effective. Among all these processes, the salt roasting treatment showed promising results concerning the cost, technological, and environmental effectiveness. The possibility of complex processing of HOFA has also been investigated, proposing innovative technology for completely utilizing this waste without any remaining residue. Effective zeolite for wastewater treatment has been formulated as a good alternative for conserving the available water resources. Full article

Oil sand tailings from bitumen extraction contain various contaminants, including polycyclic aromatic hydrocarbons, BTEX, and naphthenic acids, which can leak into surrounding environments, threatening aquatic ecosystems and human health. These tailings also contribute to environmental issues such as habitat disruption and greenhouse gas emissions. Despite these challenges, oil sand tailings hold significant potential for waste-to-resource recovery as they contain valuable minerals like rare earth elements (REEs), titanium, nickel, and vanadium. Traditional metal extraction methods are environmentally damaging, requiring high energy inputs and generating dust and harmful emissions. Furthermore, the coating of hydrocarbons on mineral surfaces presents an additional challenge, as it can inhibit the efficiency of metal extraction processes by blocking access to the minerals. This highlights the need for alternative, eco-friendly approaches. Bioleaching, which uses microorganisms to extract metals, emerges as a sustainable solution to unlock the valuable metals within oil sand tailings. This review discusses the minerals found in oil sand tailings, the challenges associated with their extraction, methods from hydrocarbon removal from minerals, and bioleaching as a potential metal recovery method. Full article

Bacterial leaching is a well-known green technology proposed for the extraction of valuable metals into solution. However, this biotechnology has some “bottle neck” problems too. Arsenopyrite, a gold-bearing ore, is a refractory mineral material that is hardly soluble and contains toxic arsenic compounds which decrease any bioleaching production. The most common biotechnology used for this process is provided with the species Acidithiobacillus ferrooxidans: autotrophic and acidophilic bacterial strains including ones resistant to inorganic arsenic compounds. Common attempts to dissolve arsenopyrite with increasing volumes of sulfuric acid provoke acidification of the environment and its pollution with toxic compounds. In our research, we compared two A. ferrooxidans strains of different origin: TFBk isolated from arsenopyrite ore (pre-adopted to arsenic), the Republic of Kazakhstan, and ShA-GNK isolated from silicate nickel-ferrous ore (laterite, without arsenic), the Russian Federation. The studied genomes of both strains showed the presence of the same genes providing defense against arsenic compounds, but the resistance to toxic compounds was higher in the strain that had never been exposed to any high As concentration under the natural conditions. Both strains showed a weak oxidation of the arsenopyrite flotation concentrate (AFC). In accordance with the published data, supplementation of the medium with formate stimulated bacterial growth in the culturing medium. However, this supplementation to the leaching solution decreased the arsenopyrite oxidation during the first stage of the AFC leaching because formate was used as an alternative energy substrate, but subsequently gave a higher iron yield later. Full article

The goal of the present work was to study the recovery of copper, nickel, and platinum group metals (PGMs) (Pt and Pd) from low-grade copper–nickel ore containing pyrrhotite, pentlandite, and chalcopyrite by column bioleaching followed by cyanidation. The ore sample contained the following: Ni—0.74%, Cu—0.23%, Fe—14.8%, S_total—8.1%, and S_sulfide—7.8%. The Pt and Pd contents in the ore sample were 0.2535 and 0.515 g/t, respectively. Biological leaching in columns was carried out at 25, 35, and 45 °C for 140 days. A mixed culture of acidophilic microorganisms was used as an inoculum. Cu and Ni extraction depended on temperature, and at 45 °C, copper and nickel recovery was the highest, being 2.1 and 1.8 times higher than that at 25 °C, respectively. As a result, up to 35% of nickel and up to 10% of copper were recovered by bioleaching within 140 days. Bioleaching resulted in an increase in Pt and Pd recovery by cyanidation, but the effect on Pd recovery was insignificant. Pt recovery varied in the range of 3–40% depending on process conditions; Pd recovery was 44–55%. Full article

To date, electronic waste (e-waste) is the fastest-growing waste stream worldwide due to technological advancement and the advent of the Fourth Industrial Revolution. Although e-waste is an environmental hazard, these materials are considered good secondary sources of metals. This study examined the bioleaching of metals from printed circuit boards, where a two-step bioleaching approach was used with iron–sulfur-oxidizing microorganisms at different e-waste particle sizes. The metal analysis from the different particle sizes (PSs) showed that copper (Cu), tin (Sn), and lead (Pb) were predominantly deposited in the coarser fraction, ranging from 500 to 710 µm at 28.7, 20.5, and 11.1 wt.%, respectively. On the other hand, metals such as iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), and aluminum (Al) were mostly deposited in the finer fraction, which ranged from 38 to 150 µm at 37.3, 5.9, 8.8, 1.3, and 4.2 wt.%, respectively. After the bioleaching process, it was observed that higher metal extraction occurred at a PS ranging from 38 to 150 µm, which achieved recovery efficiency rates of 62.9%, 68.2%, 95.3%, 86.1%, 61.9%, 47.2%, 21.2%, and 63.6% for Al, Cu, Fe, Mn, Ni, Pb, Sn, and Zn, respectively, over 10 days. Full article

The aim of the present research was to examine the process of bioleaching and the application of a combined process for the recovery of copper and nickel from industrial sand deposits. The investigated sample of sands finer than 0.1 mm in size contained 0.32% Ni and 0.22% Cu. Industrial sands were processed by bioleaching in flasks on a thermostatically controlled shaker. In addition, sand roasting experiments were carried out with ammonium sulfate. An attempt was also made to use a combined process, including low-temperature roasting of the sands mixed with ammonium sulfate, water-leaching of the roasted mixture, and subsequent biological after-leaching of the residue. In the process of roasting the industrial sands in a mixture including ammonium sulfate at a temperature of 400 °C, more than 70% of the non-ferrous metals were recovered. We examined the possibility of recovering non-ferrous metals using a combined process including low-temperature roasting of industrial sands and the additional recovery of non-ferrous metals by bioleaching using the Acidithiobacillus ferrivorans bacterial strain, which was found to increase the recovery of non-ferrous metals to up to 90%. Full article

This review paper explores the potential of bioleaching as a sustainable alternative for recovering metals from solid matrices. With over 12 billion tons of solid waste annually worldwide, bioleaching provides a promising opportunity to extract metals from solid waste, avoiding harmful chemical processes. It explains bacterial and fungal bioleaching techniques that extract copper, gold, zinc, and other metals from solid matrices. Fungal bioleaching effectively extracts a wide range of valuable metals, including nickel, vanadium, aluminium, molybdenum, cobalt, iron, manganese, silver, platinum, and palladium. The review highlights different solid matrices with metal contents that have the potential to be recovered by bioleaching, presenting promising bioprocess alternatives to current industrially available technologies for metal recovery. The optimal conditions for bioleaching, including pH, temperature, agitation–aeration, and pulp density are also discussed. The review shows that bioleaching has the potential to play a crucial role in the transition to a more sustainable and circular economy by providing an efficient, cost-effective, and environmentally friendly method for metal recovery from solid matrices. Full article

Bacterial isolates assigned to the species Alicyclobacillus tolerans, which occupies an intermediate position between an organotrophic genus Alicyclobacillus and mixotrophic genus Sulfobacillus, were revealed as members of the acidophilic chemolithotrophic community during stirred-tank bioleaching of violarite–pentlandite–chalcopyrite concentrate at 40 °C. Surprisingly, this species succeeded more common iron-oxidizing community members after a series of bioleaching processes in bioreactors. The possibility of mixotrophic and organoheterotrophic growth of Al. tolerans, tolerance to low pH values (1.0–1.15), as well as preservation of cells via sporulation under unfavorable conditions, may explain its key role in the bioleaching of the copper–nickel bulk concentrate. Isolation of two other sulfur-oxidizing pure cultures dominating the microbial community, together with their phylogenetic characterization, allowed the assignment of these isolates to the species Acidithiobacillus caldus. This and other studies of acidophilic microbial communities are important for the development and intensification of the bioleaching processes, including a biobeneficiation approach previously proposed by us. Full article

The aim of the present work was to perform copper, nickel, and platinum group metals (PGMs) recovery from low-grade copper–nickel concentrate containing pyrrhotite, pentlandite, and chalcopyrite by bioleaching in stirred tank reactors in batch mode and subsequent cyanidation. The concentrate contained (%) Fe 32.7, Cu 0.7, Ni 2.3, S_total 20.9, S_sulfide 17, 0.1 g/t Pt, and 1.35 g/t Pd. The bioleaching was performed at 30 and 40 °C using two different microbial consortia. At 30 °C, bioleaching was performed using mixed culture including Acidithiobacillus ferrivorans strains isolated from the sample of acid mine drainage from copper–nickel deposit. At 40 °C, bioleaching was performed using microbial population formed during long-term bioleaching of copper-zinc concentrate at 40 °C. Bioleaching was performed for 40 days at pulp density of 10% (solid to liquid ratio 1:10). At 30 °C, 70% Ni and 14% Cu were leached, while 72% Ni and 34% Cu were recovered in the solution at 40 °C. PGM were extracted from the concentrate and bioleaching residue obtained at 40 °C by cyanidation. Cyanidation made it possible to extract 5.5% Pt and 17.3% Pd from the concentrate and 37.8% Pt and 87.8% Pd from the bioleaching residue. Thus, it was shown that the concentrate studied might be processed using bioleaching and subsequent cyanidation to extract both non-ferrous metals and PGM. Full article

Bioleaching of the bulk copper–nickel sulfide concentrate was proposed as a method to remove nickel from it and to obtain a concentrate containing copper as chalcopyrite. This approach is based on the different refractoriness of sulfide minerals in ferric sulfate solutions and oxidation by acidophilic microorganisms. The bulk concentrate contained 10.8% copper in the form of chalcopyrite (CuFeS₂) and 7.2% nickel that occurred in pentlandite ((Ni,Fe)₉S₈) and violarite (FeNi₂S₄). Three microbial communities grown at 35, 40, and 50 °C were used for bioleaching. The microbial community at 40 °C was the most diverse in the genus and species composition. At all temperatures of the process, the key roles in bioleaching belonged to mixotrophic and heterotrophic acidophiles. The highest levels of nickel leaching of 97.2 and 96.3% were observed in the case of communities growing at 40 and 50 °C, respectively. At the same time, the bioleach residue, which could be characterized as a marketable high-grade copper (chalcopyrite) concentrate, was obtained only at 40 °C. This solid contained 15.6% copper and 0.54% nickel. Thus, the biobeneficiation of bulk sulfide concentrates can be a promising field of biohydrometallurgy. Full article

Hydrometallurgical production of valuable and non-ferrous metals is traditionally accompanied with acid waste effluents/acid mine drainage leading to acidification of the mining areas. The traditional cause of this pollution is the well-known technology based on the recovery of metals with acid solutions and the application of strong acidophilic leaching bacteria for the oxidation of sulfide ores. In our experiments, we used neutrophilic autotrophic bacteria (NAB) stimulated with formic acid or coupled with acidophilic bacteria. The first approach was based on using formic acid as an energetic substrate by autotrophic bacteria. In the second case, the NAB provided initial biogenic acidification for the following growth of the inoculated acidophilic bacteria. Our experiments resulted in increased nickel recovery from the low-grade sulfide ores, which was provided by the NAB in a medium supplemented with formic acid. Bioleaching resulted in 1116 mg Ni/L (69.75%) in the medium with formate and only 35.4 mg Ni/L without formate in 43 days. As a whole, our bench scale experiments showed that the stimulated NAB can be effective at pH 7–5. Partially replacing sulfuric acid with formic acid could also give benefits via the following natural degradation of acid wastes. As a whole, this approach is more environmentally friendly than conventional bioleaching techniques. Full article

Bearing in mind the metal rich composition of printed circuit boards (PCBs), this material represents a secondary source of valuable metals and offers an entrepreneurial opportunity in the metal sales market. Based on the ability of microorganisms to regenerate and produce the chemical oxidants that are responsible for metal leaching, bioleaching has become an efficient and affordable alternative to conventional metal recycling technologies, although further research is still necessary before industrial implementation. This study focuses on the recovery of metals contained in mobile phone PCBs through a combined process. Two different PCB pre-treatments were evaluated: grinding the whole piece and removing the epoxy cover from the piece without grinding. The benefit of A. ferrooxidans activity on the metal solubilization rate was analyzed. Additional chemical leaching assays were also conducted for comparison purposes and the reagents ferric iron (Fe³⁺) and sulfuric acid (H₂SO₄) were selected for these experiments. The copper extraction results obtained in Fe³⁺ experiments with and without bacteria (A. ferrooxidans) were similar after 260 h of operation, indicating the need for alternative strategies to ensure a controlled and continuous metal biodissolution rate. The contribution of H₂SO₄ to the leaching processes for copper and nickel was almost negligible during the first 50 h, and more significant thereafter. The recovered metals were precipitated from a synthetic solution simulating a real ferric leaching by adding sodium hydroxide (NaOH) and sodium sulfide (Na₂S). The combination of both precipitants allowed an effective removal of metals from the leachate. Full article

The feasibility of processing low-grade copper-nickel ores by heap bioleaching was investigated. It was found that an iron-oxidizing strain of acidophilic microorganisms, Acidithiobacillus ferrivorans, is effective in the leaching of sulfide ores from the deposits in Russia’s Murmansk region. Sulfide mineralization of the studied mineral feeds was described using the methods of X-ray phase analysis and optical microscopy. In the process of leaching, the pH and Eh values and the concentrations of ferric and ferrous iron, nickel, and copper ions were monitored. By the end of the experiment, 16.5% of nickel and 7.5% of copper was recovered from the ore of the Allarechensk technogenic deposit, while 22.5% of nickel and 12.7% copper were recovered from the ore of the Nud II deposit. By silicate analysis of the solid phase, patterns of ore chemistry change were described during the process of bioleaching. Full article

Acid bioleaching of a low-grade and polymetallic sulfide concentrate was studied, in order to determine suitable feed material particle size and pH for efficient leaching of valuable metals. The sulfide concentrate consisted of pyrite (50 wt %), pyrrhotite (31 wt %), quartz (10 wt %) and lower amounts of cobalt, nickel, zinc and copper (each <1 wt %). After adaptation of microorganisms in shake flasks, stirred tank tests were conducted at different pH levels and supplementing feed material at different particle sizes (milled to d80 < 150 µm, <50 µm, <28 µm, <19 µm). The operation at pH 1.8 was seen prone to iron precipitation, while this was not observed at a pH between 1.3 and 1.5. Additional milling to decrease particle size from the initial d80 < 150 µm had a major positive effect on cobalt- and nickel-leaching yields, proposing that at least d80 < 28 µm should be targeted. The best leaching yields for the main economic elements, cobalt and nickel, were 98% and 94%, respectively, reached with d80 < 19 µm at pH 1.3. However, it was considered that at pH 1.5, similar results could be obtained. This research sets the basis for continuing the experiments at a continuous pilot scale. Full article