Mineral weathering of iron ore tailings primed by Acidithiobacillus ferrooxidans and elemental sulfur under contrasting pH conditions

The trigger mechanisms and the gene regulatory pathways of organic acid secretion during the vanadium-titanium magnetite tailing bioleaching

The long-term mining of vanadium-titanium (V-Ti) magnetite has generated a large accumulation of tailings, which can lead to metal pollution via microbial bioleaching. Current research has focused on the bioleaching of minerals, and a few studies have explored microbial responses to metals only through limited metabolite concentrations. However, the trigger mechanisms of metal release during the V-Ti magnetite tailing bioleaching and key gene regulatory pathways for organic acid metabolism are still unclear. This study screened a bioleaching fungus from the V-Ti magnetite tailing pond groundwater. The fungus promoted tailing dissolution by secreting more organic acids (808.99 mg L-1) than without tailings (671.11 mg L-1). The released metals were responsible for the difference in organic acid metabolism. The tailing-released Fe, Zn, and V were the triggers for the organic acid secretion via up-regulating the functional genes of citric, formic, and succinic acids in the TCA cycle, Methane metabolism, and D-arginine and D-ornithine metabolisms. Fe and V also led to the accumulation of malic acid through up-regulating functional genes during the conversion of phenylalanine, tyrosine, and glycine. Ni and Cu were the inhibitors by up-regulating related functional genes and promoting the conversion of acetyl-CoA to acetoacetyl-CoA, resulting in a decrease in organic acid concentrations. This study demonstrated the triggering metals of bioleaching and fungal gene regulation pathways, which provide a novel strategy for fungi domestication by considering the up-regulating metals to improve the bioleaching efficiency.

The long-term transformation of FeIII-AsV coprecipitates at room temperature under oxic conditions: New insights for the fate and the speciation of As

The long-term stability of FeIII-AsV coprecipitates, a typically hydrometallurgical or naturally produced As-bearing wastes in tailings or in other environments, is critical to evaluating the As risk caused by them. A wide pH range, different Fe/As molar ratios, reaction media, and neutralization reagents were considered in order to find the mechanisms controlling the fate of As during the 1640 days of transformation at 25 °C. The results indicated that at pH 4 and 12, As continuously released from the solid phase. The components and their proportions determined the fate of As at pH 4. However, at pH 12, crystalline calcium carbonates (CCA) formed due to the CO2 in the air and this combined with the adsorption capacity of As on the 2-line ferrihydrite controlling the fate of As. If pH changed to 8 and 10, yukonite formed after the release of As. The CCA also appeared in the presence of Ca. Therefore, these two processes controlled the fate of As at this pH range. These findings are important for understanding and predicting the transport of As under various environmental conditions. The technology chosen for As remediation in soils and As removal from waste waters will also be benefit from these results.

Acidithiobacillus species mediated mineral weathering promotes lead immobilization in ferric-silica microstructures at sulfidic tailings

Immobilization and stabilization of heavy metals (HMs) in sulfidic and metallic tailings are critical to long-term pollution control and sustainable ecological rehabilitation. This study aims to unravel immobilization mechanisms of Pb (Ⅱ) in the neoformed hardpan structure resulting from Acidithiobacillus spp. accelerated bioweathering of sulfides in the presence of silicates. It was found that the bioweathered mineral composite exhibited an elevated Pb (Ⅱ) adsorption capacity compared to that of natural weathered mineral composite. A suit of microspectroscopic techniques such as synchrotron-based X-ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and Field-Emission Scanning Electron Microscope (FE-SEM) indicated that secondary Fe-bearing minerals, functional groups, and surface properties in the neoformed hardpan were key factors contributing to Pb (Ⅱ) adsorption and immobilization in ferric-silica microstructures. The underlying mechanisms might involve surface adsorption-complexation, dissolution-precipitation, electrostatic attraction, and ion exchange. Microbial communities within the muscovite groups undergoing bioweathering processes demonstrated distinctive survival strategies and community composition under the prevailing geochemical conditions. This proof of concept regarding Pb (Ⅱ) immobilization in microbial transformed mineral composite would provide the basis for scaling up trials for developing field-feasible methodology to management HMs pollution in sulfidic and metallic tailings in near future.

Simplification of the Acidithiobacillus ferrooxidans Culture Process for Expanding the Field of Biomachining

Biomachining is an eco-friendly metal processing method with broad application potential. Nevertheless, the bacterial culture methods that are currently involved in biomachining require the intensive use of chemical reagents, especially FeSO4, specialized equipment, and professional-level skills in the field of biology. Herein, the differences between two cultures with and without sterilization were evaluated. Acidithiobacillus ferrooxidans was cultured with iron instead of FeSO4 in the culture medium. The chemical and biochemical parameters of the culture were analyzed by studying the area of exposed iron and continuously regulating the pH. Eliminating the sterilization and sterile inoculation of the medium is feasible for culturing A. ferrooxidans. The key to achieving a high bacterial density in culture with iron was to maintain the solution pH. The possibility of mass culturing A. ferrooxidans with steel cuttings was evaluated in a custom bioreactor, and the bacterial concentration reached 9 × 107 cells/mL.

Inhibition of iron oxidation in Acidithiobacillus ferrooxidans by low-molecular-weight organic acids: Evaluation of performance and elucidation of mechanisms

The catalytic role of Acidithiobacillus ferrooxidans (A. ferrooxidans) in iron biooxidation is pivotal in the formation of Acid Mine Drainage (AMD), which poses a significant threat to the environment. To control AMD generation, treatments with low-molecular-weight organic acids are being studied, yet their exact mechanisms are unclear. In this study, AMD materials, organic acids, and molecular methods were employed to gain a deeper understanding of the inhibitory effects of low-molecular-weight organic acids on the biooxidation of iron by A. ferrooxidans. The inhibition experiments of A. ferrooxidans on the oxidation of Fe2+ showed that to attain a 90 % inhibition efficacy within 72 h, the minimum concentrations required for formic acid, acetic acid, propionic acid, and lactic acid are 0.5, 6, 4, and 10 mmol/L, respectively. Bacterial imaging illustrated the detrimental effects of these organic acids on the cell envelope structure. This includes severe damage to the outer membrane, particularly from formic and acetic acids, which also caused cell wall damage. Coupled with alterations in the types and quantities of protein, carbohydrate, and nucleic acid content in extracellular polymeric substances (EPS), indicate the mechanisms underlying these inhibitory treatments. Transcriptomic analysis revealed interference of these organic acids with crucial metabolic pathways, particularly those related to energy metabolism. These findings establish a comprehensive theoretical basis for understanding the inhibition of A. ferrooxidans' biooxidation by low-molecular-weight organic acids, offering a novel opportunity to effectively mitigate the generation of AMD at its source.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., "circular" shaped in the talc group, "fine-grained" shaped in the chlorite group, and "donut" shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Elemental Sulfur and Organic Matter Amendment Drive Alkaline pH Neutralization and Mineral Weathering in Iron Ore Tailings Through Inducing Sulfur Oxidizing Bacteria

Mineral weathering and alkaline pH neutralization are prerequisites to the ecoengineering of alkaline Fe-ore tailings into soil-like growth media (i.e., Technosols). These processes can be accelerated by the growth and physiological functions of tolerant sulfur oxidizing bacteria (SOB) in tailings. The present study characterized an indigenous SOB community enriched in the tailings, in response to the addition of elemental sulfur (S0) and organic matter (OM), as well as resultant S0oxidation, pH neutralization, and mineral weathering in a glasshouse experiment. The addition of S0 was found to have stimulated the growth of indigenous SOB, such as acidophilic Alicyclobacillaceae, Bacillaceae, and Hydrogenophilaceae in tailings. The OM amendment favored the growth of heterotrophic/mixotrophic SOB (e.g., class Alphaproteobacteria and Gammaproteobacteria). The resultant S0 oxidation neutralized the alkaline pH and enhanced the weathering of biotite-like minerals and formation of secondary minerals, such as ferrihydrite- and jarosite-like minerals. The improved physicochemical properties and secondary mineral formation facilitated organo-mineral associations that are critical to soil aggregate formation. From these findings, co-amendments of S0 and plant biomass (OM) can be applied to enhance the abundance of the indigenous SOB community in tailings and accelerate mineral weathering and geochemical changes for eco-engineered soil formation, as a sustainable option for rehabilitation of Fe ore tailings.