Biosorption has been considered a promising technology for the treatment of industrial effluents containing heavy metals. However, the development of a cost-effective technique for biomass ...immobilization is essential for successful application of biosorption in industrial processes. In this study, a new method of reversible encapsulation of the highly pigmented biomass from Aspergillus nidulans mutant using semipermeable cellulose membrane was developed and the efficiency of the encapsulated biosorbent in the removal and recovery of copper ions was evaluated. Data analysis showed that the pseudo-second-order model better described copper adsorption by encapsulated biosorbent and a good correlation (r2 > 0.96) to the Langmuir isotherm was obtained. The maximum biosorption capacities for the encapsulated biosorbents were higher (333.5 and 116.1 mg g-1 for EB10 and EB30, respectively) than that for free biomass (92.0 mg g-1). SEM-EDXS and FT-IR analysis revealed that several functional groups on fungal biomass were involved in copper adsorption through ion-exchange mechanism. Sorption/desorption experiments showed that the metal recovery efficiency by encapsulated biosorbent remained constant at approximately 70% during five biosorption/desorption cycles. Therefore, this study demonstrated that the new encapsulation method of the fungal biomass using a semipermeable cellulose membrane is efficient for heavy metal ion removal and recovery from aqueous solutions in multiple adsorption-desorption cycles. In addition, this reversible encapsulation method has great potential for application in the treatment of heavy metal contaminated industrial effluents due to its low cost, the possibility of recovering adsorbed ions and the reuse of biosorbent in consecutive biosorption/desorption cycles with high efficiency of metal removal and recovery.
In order to find a sustainable and low-cost alternative route to the traditional recovery of aluminum, the filamentous fungus
Penicillium simplicissimum
was evaluated for aluminum recovery from ...low-grade bauxite ore. The oat-agar medium was carefully chosen as the foremost solid medium for fungal sporulation due to lower cost, ease in preparation, and high spore production in a short incubation time. To examine the acid production capability in submerged fermentation,
P. simplicissimum
was inoculated in a medium augmented with glucose and molasses as an energy source. High-performance liquid chromatography (HPLC) technique was used for the determination of the produced organic acids. Three different bioleaching approaches were evaluated using 1% bauxite pulp density. The culture containing
P. simplicissimum
spores grown in a medium supplemented with molasses leached 86.6% Al in the direct two steps on the fifth day, 56.5% in the direct one step on the fourth day, and 71.7% in the indirect bioleaching on the fourth day, while in the controlled sterile flasks, Al leaching was almost negligible. A maximal amount of Al was leached by the fungal strains using low-cost molasses as a substrate.
Fertilization is essential to provide suitable conditions for plant development and crop productivity, but the environmental cost of fertilizers is a drawback for achieving a sustainable agriculture. ...A potential alternative is the use of unprocessed (raw) nutrient sources such as elemental sulfur (S
0
) and mineral oxides (ZnO, MnO, CuO) as fertilizers. However, these low reactive sources are not readily available to plants. Here, we developed a bioactive coating material containing microorganisms that allowed different nutrients to be made available from unprocessed nutrient sources. For that, the coating material composed of maize starch, elemental sulfur (S
0
), mineral oxides (ZnO, MnO, CuO), and a microbial source (
Aspergillus niger
or
Acidithiobacillus thiooxidans
) was applied on monoammonium phosphate (MAP) granules, as a model fertilizer. Our results revealed that the bioactive coating did not affect the phosphorus (P) release, since it did not impose a physical barrier. However, the acidifying capacity of both microorganisms significantly enhanced the oxide solubilization and elemental sulfur oxidation. The presence of
Aspergillus niger
or
Acidithiobacillus thiooxidans
promoted local acidification, achieving sulfate release of up to 76.4 and 83.8% in 42 days of soil incubation. Furthermore, the bioactive coating material with
Aspergillus niger
reached Cu, Zn and Mn solubilization up to 10.9, 14.6 and 34.3% in 42 days of soil incubation. This phenomenon suggested that the organic acids produced by
Aspergillus niger
chelate the cations, reducing precipitation and, therefore, increasing their solubilization. This innovative system can effectively supply nutrients to plants using cheap and low reactivity nutrient sources with the advantage that it can be co-applied on currently used fertilizer granules in a single delivery, making easier the adoption by producers.
Graphical Abstract
The packing material selection for a bioreactor is an important factor to consider, since the characteristics of this material can directly affect the performance of the bioprocess, as well as the ...investment costs. Different types of low cost packing materials were studied in columns to reduce the initial and operational costs of biogas biodesulfurization. The most prominent (PVC pieces from construction pipes) was applied in a bench-scale biotrickling filter to remove the H2S of the biogas from a real sewage treatment plant in Brazil, responsible for 90 thousand inhabitants. At the optimal experimental condition, the reactor presented a Removal Efficiency (RE) of up to 95.72% and Elimination Capacity (EC) of 98 gS·m−3·h−1, similar to open pore polyurethane foam, the traditional material widely used for H2S removal. These results demonstrated the high potential of application of this packing material in a full scale considering the robustness of the system filled with this support, even when submitted to high sulfide concentration, fluctuations in H2S content in biogas, and temperature variations.
The growing demand for rare earth elements (REEs) confronted with a parallel supply risk, draws major interest to utilize secondary resources bearing higher REE content than the primary resources. ...The European Commission has recently identified bauxite as a Critical Raw Material (CRM). In particular, unexploited bauxite residues have invited due attention owing to their abundance (worldwide generation at 120 – 150 million tons/yr) and presence of REEs (0.5 - 1.7 kg/ton) and scandium (Sc) in particular, with Fe: 14–45%, Al: 5–14%, Si: 1–9%, Na: 1–6% and Ti: 2–12%. Nevertheless, it has also to be taken into consideration that higher amassing of this waste is turning into a global concern due to its hazardous impacts and disposal issues owing to its high alkalinity, fine particle size and metal content. Industrial valorization of REEs from stockpiled bauxite residues could possibly unlock approximately a 4.3 trillion-dollar economy globally. This review foresees bauxite as a potential resource for REEs and identifies the problems associated with disposal of bauxite residues. Considering the recycling potential of bauxite residues for supplying valuable metals for technology, biotechnology is seen as a promising alternative to the conventional methods. Comprehensive details including role and challenges of biotechnology in green recovery of REEs from bauxite residues, their scale-up and environmental issues are critically discussed. Furthermore, w.r.t. the bauxite residues, the REE market potential is presented with discussions into future prospects, following the current impact of COVID-19 pandemic on the demand and supply of REE to industrial sectors.
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•Acidithiobacillus thiooxidans presented better acid production than thermophilic archeas.•Two-step bioleaching prevents possible inhibition caused by acid consumption.•Two step ...bioleaching reached 98% neodymium extraction.•Two step bioleaching extracted 60% of all rare earth from phosphogypsum.•Biogenic acid showed an extraction yield similar to commercial acid.
Industrial production of sulfuric acid requires a high amount of energy and in remote regions such as mineral extraction pits, in situ production becomes unfeasible. This work proposes an alternative for the production of H2SO4 that uses sulfur-oxidizing microorganisms. The production capacity of this acid in a mesophilic (30 °C) and a thermophilic (65 °C) condition was studied by three collected consortia from acid mine drainage and compared with Acidithiobacillus thiooxidans. It was found that At. thiooxidans presented higher sulfuric acid production than the consortia collected and, therefore, it was selected for the bioleaching of rare earths elements (REEs) from phosphogypsum (PG). Due to the acid consumption of phosphogypsum, the two-step bioleaching condition resulted in higher REEs extraction (98% Nd, 60% Ce, 58% La, and 62% Y) when compared to one-step bioleaching (28% Nd, 17% Ce, 18% La, and 30% Y). The process was performed on a reactor scale and it was possible to extract 55.0% of the REEs contained in 300 g of waste and concentrate them into 0.922 g of rare earth oxalates, with a final yield of 52.5%, showing that the proposed bioprocess has potential application even in remote areas due to its low energy consumption when compared to traditional processes.
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•Hydrometallurgy from the perspective of semiconductor electrochemistry.•Charge transfer at the interface chalcopyrite/electrolyte solution.•New sustainable and less expensive ...strategies for metal recovery.•Electronic structure of minerals can provide new ideas for an effective lixiviation.
The purpose of this article is to explore potential solutions for hydrometallurgical processes using semiconductor electrochemistry as an approach, that has received limited attention from the scientific community. Hydrometallurgy involves more sustainable methods for obtaining metallic resources through dissolution, offering the possibility to leach low-grade ores and recycle waste with low metal concentrations. Several minerals of interest are semiconductors, such as stibnite (Sb2S3), chalcopyrite (CuFeS2), chalcocite (Cu2S), bornite (Cu5FeS4), and sphalerite (ZnS). Thus, understanding the nature of these minerals in contact with an electrolyte solution is crucial for promoting efficiency and scalability of hydrometallurgy, as the efficiency of the reactions involved in the process is dictated by the charge transfer at the interface between the semiconductor and the electrolyte solution containing the redox pairs. Furthermore, this article proposes new models and cost-effective strategies for solubilizing ores from the perspective of semiconductor electrochemistry.
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•Chalcopyrite dissolution followed different routes on concentrated and low-grade ores.•A new bioleaching route based on chemoorganotrophs metabolic activity was assessed.•A new ...two-step model for ferrous-promoted chalcopyrite leaching was proposed.•The solution potential (ES) is decisive and allows to predict the prevailing route.
Chalcopyrite is highly recalcitrant to bioleaching and its dissolution mechanisms are still debatable. In this study, both concentrated and low-grade chalcopyrite were subjected to bioleaching using three microbial consortia under thermophilic conditions. Copper extraction efficiency from concentrated chalcopyrite was assessed in Erlenmeyer flasks and reached nearly 90 % in all consortia, whereas it was limited to 30 % in the abiotic control. Results indicate the prevalence of the chalcocite mechanism, in which chalcopyrite is initially reduced to chalcocite followed by its dissolution. This mechanism was enabled by maintaining the solution potential (ES) lower than the Nernst potential (E1), with microbial activity playing an essential role in lowering ES. The most abundant microorganisms were affiliated with primary producers (such as Cyanobacteria) and chemoorganotrophs (such as Bradyrhizobium), contributing to chalcopyrite dissolution indirectly. Microorganisms kept pH within 1.9–2.1, which led to higher Fe3+ precipitation and lower ES. Copper extraction in low-grade ore reactors was assessed in batch system with closed circulation between a five-liter jacketed packed bed reactor and a five-liter buffer vessel, simulating a (bio)leaching heap. Differently from the observed in concentrated ore, copper extraction efficiency from low-grade chalcopyrite was higher in the abiotic control (60 % compared to 40–47 % under biotic conditions). Based on thermodynamic calculations, a new two-step model for ferrous-promoted chalcopyrite leaching was proposed, whereby chalcopyrite is reduced to bornite followed by its fast oxidation. Understanding copper extraction through different routes is crucial for achieving efficient (bio)leaching of chalcopyrite.
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