Bioleaching of manganese from a low-grade pyrolusite ore using Aspergillus niger: Process optimization and kinetic studies

Bioleaching of Cd from contaminated Helianthus annuus L. stalk and the safe utilization of its byproducts by Aspergillus niger

Disposal and recycling of heavy metal-enriched biomass is the key to measure the success of phytoremediation. This study employed innovative approach to use Aspergillus niger (A. niger) for the treatment of Cd-contaminated Helianthus annuus L. (sunflower) stalk after phytoremediation. Single-factor results showed that the removal of Cd at an initial pH of 3 was superior to sucrose and inoculation amount. 67.67% of Cd was removed by A. niger leaching system after 11 days based on response surface methodology optimum conditions (sucrose: 76.266 g L-1; inoculation amount: 10%; initial pH: 3), while the concentrations of nitrogen, phosphorus and potassium (N, P and K) of sunflower stalk were unaffected. While physicochemical pretreatment effectively enhanced the bioleaching efficiency, it also resulted in significant loss of P and K elements, thereby reducing the value of biomass for recycling and utilization. Therefore, the direct A. niger leaching method without pretreatment is more advantageous for the safe treatment and recycling of Cd-contaminated sunflower stalks.

Insights into metal tolerance and resistance mechanisms in Trichoderma asperellum unveiled by de novo transcriptome analysis during bioleaching

This study investigates the genetic responses of the fungus Trichoderma asperellum (T. asperellum) during bioleaching of ore and tailing samples, comparing one-step, two-step, and spent media bioleaching processes. HPLC analysis quantified oxalic acid, citric acid, and propionic acids, with oxalic acid identified as the primary organic acid involved in metal bioleaching. Metal analysis revealed differences in recovery between ore and tailing samples and among bioleaching processes. The two-step bioleaching process yielded the highest zinc (>54%) and nickel (>60%) recovery in tailings and ore, respectively. Nickel's efficient recovery in ore bioleaching was attributed to the presence of manganese, while its precipitation as nickel oxalate in tailings hindered recovery. Additional metals such as Co, Mn, Mg, Cu, and As were also successfully recovered. Transcriptomic analyses showed significant upregulation of genes associated with biological processes and cellular components, particularly those related to cell membrane structure and function, indicating T. asperellum's adaptation to environmental stresses during metal bioleaching. These findings enhance our understanding of the diverse mechanisms influencing metal recovery rates in bioleaching processes.

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact

Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.

Current overview and future perspective in fungal biorecovery of metals from secondary sources

Microorganisms are intimately involved in many biogeochemical processes that underpin the transformation of metals and cycling of related substances, such as metalloids and radionuclides. Many processes determine the mobility and bioavailability of metals, thereby influencing their transfer to the environment and living organisms. These processes are closely related to global phenomena such as soil formation and bioweathering. In addition to environmental significance, microbial metal transformations play an essential role in both in situ and ex situ bioremediation processes for solid and liquid wastes. The solubilization of heavy metals from industrial waste and soil is commonly used in bioremediation. Moreover, immobilization processes are applicable to bioremediation of metals and radionuclides from aqueous solutions. This review provides an overview of critical metal extraction and recovery from secondary sources, applied microorganisms and methods, metal-microbe interactions, as well as a detailed description of known metal recovery mechanisms.

Environmentally-friendly biorecovery of manganese from electrolytic manganese residue using a novel Penicillium oxalicum strain Z6-5-1: Kinetics and mechanism

Bioleaching is a promising route for electrolytic manganese (Mn) residue (EMR) reutilization due to being eco-friendly and cost-effective. However, microbes with high bioleaching efficiency are scarce. This work aimed to isolate, screen, and characterize a novel fungal strain with high Mn-bioleaching efficiency from EMR, and study the kinetics and mechanism. The novel Penicillium oxalicum strain Z6-5-1 was found to selectively bioleach Mn from EMR. A maximum Mn²⁺ recovery of 93.3 % was achieved after 7 days and was mainly dependent upon acidolysis of the bio-organic acids, specifically gluconic acid and oxalic acid, as well as mycelial biosorption. This efficiency was the highest reported in the literature for a fungus over such a short time. EMR strongly induced P. oxalicum to produce gluconic acid and oxalic acid. The novel transcription factor PoxCxrE of P. oxalicum controlled the production of bio-organic acids by regulating the expression of rate-limiting enzyme genes involved in the biosynthesis of bio-organic acids. Scanning electron microscopy, laser particle size analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to analyze EMR changes after bioleaching. This study provides an alternative fungal resource for Mn-bioleaching of EMR, and a novel target for metabiotic engineering to improve bio-organic acid production.

Application of Machine Learning in a Mineral Leaching Process-Taking Pyrolusite Leaching as an Example

In this study, several machine learning models were used to analyze the process variables of electric-field-enhanced pyrolusite leaching and predict the leaching rate of manganese, and the applicability of those models in the leaching process of hydrometallurgy was compared. It showed that there was no correlation between the six leaching conditions; in addition to the leaching time, the concentrations of sulfuric acid and ferrous sulfate had great influences on the leaching of pyrolusite. The results of the prediction models showed that the support vector regression model has the best prediction performance, with regression index (R ²) = 0.92 and mean square error = 25.04, followed by the gradient boosting regression model (R ² > 0.85). In this research, machine learning models were applied to the optimization of the manganese leaching process, and the research process and methods were also applicable to other hydrometallurgical processes for majorization and result prediction.

Potential and current practices of recycling waste printed circuit boards: A review of the recent progress in pyrometallurgy

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated.

Thermal activation significantly improves the organic pollutant removal rate of low-grade manganese ore in a peroxymonosulfate system

Low-cost, eco-friendly and effective catalysts are essential for activating peroxymonosulfate (PMS) to purify water. Hence, we investigated using thermal activation natural low-grade manganese ore (CNMO) as an effective catalyst to activate PMS for the removal of Acid Orange 7 (AO7), a harmful azo dye. CNMO exhibited a more effective activation ability than either the pure component substances alone or natural manganese ore (NMO), owing to its increased charge transfer, pore size and acidic sites. The activation mechanism of PMS was elucidated, and the degradation of AO7 was noted to have been caused by singlet oxygen (¹O₂), and increased electron transfer. Moreover, the outstanding degradation of AO7 in actual water indicated that the CNMO/PMS system was highly resistant to surrounding organic and inorganic compounds, and the CNMO exhibited extraordinarily high stability and recyclability. Thus, this study provides not only a new choice of PMS activator that offers low cost, and excellent and stable performance, but also a novel direction for the efficient utilization of low-grade manganese ore.

Thermally activated natural low-grade manganese ore was used as an efficient and stable catalyst for enhancing the activation of PMS through increased charge transfer, pore size and acidic sites.

Bioleaching of Manganese Oxides at Different Oxidation States by Filamentous Fungus Aspergillus niger

This work aimed to examine the bioleaching of manganese oxides at various oxidation states (MnO, MnO·Mn₂O₃, Mn₂O₃ and MnO₂) by a strain of the filamentous fungus Aspergillus niger, a frequent soil representative. Our results showed that the fungus effectively disintegrated the crystal structure of selected mineral manganese phases. Thereby, during a 31-day static incubation of oxides in the presence of fungus, manganese was bioextracted into the culture medium and, in some cases, transformed into a new biogenic mineral. The latter resulted from the precipitation of extracted manganese with biogenic oxalate. The Mn(II,III)-oxide was the most susceptible to fungal biodeterioration, and up to 26% of the manganese content in oxide was extracted by the fungus into the medium. The detected variabilities in biogenic oxalate and gluconate accumulation in the medium are also discussed regarding the fungal sensitivity to manganese. These suggest an alternative pathway of manganese oxides’ biodeterioration via a reductive dissolution. There, the oxalate metabolites are consumed as the reductive agents. Our results highlight the significance of fungal activity in manganese mobilization and transformation. The soil fungi should be considered an important geoactive agent that affects the stability of natural geochemical barriers.

An Old Technique with A Promising Future: Recent Advances in the Use of Electrodeposition for Metal Recovery

Although the first published works on electrodeposition dates from more than one century ago (1905), the uses of this technique in the recovery of metals are attracting an increasing interest from the scientific community in the recent years. Moreover, the intense use of metals in electronics and the necessity to assure a second life of these devices in a context of circular economy, have increased the interest of the scientific community on electrodeposition, with almost 3000 works published per year nowadays. In this review, we aim to revise the most relevant and recent publications in the application of electrodeposition for metal recovery. These contributions have been classified into four main groups of approaches: (1) treatment and reuse of wastewater; (2) use of ionic liquids; (3) use of bio-electrochemical processes (microbial fuel cells and microbial electrolysis cells) and (4) integration of electrodeposition with other processes (bioleaching, adsorption, membrane processes, etc.). This would increase the awareness about the importance of the technology and would serve as a starting point for anyone that aims to start working in the field.