Towards Bioleaching of a Vanadium Containing Magnetite for Metal Recovery

Vanadium – a transition metal – is found in the ferrous-ferric mineral, magnetite. Vanadium has many industrial applications, such as in the production of high-strength low-alloy steels, and its increasing global industrial consumption requires new primary sources. Bioleaching is a biotechnological process for microbially catalyzed dissolution of minerals and wastes for metal recovery such as biogenic organic acid dissolution of bauxite residues. In this study, 16S rRNA gene amplicon sequencing was used to identify microorganisms in Nordic mining environments influenced by vanadium containing sources. These data identified gene sequences that aligned to the Gluconobacter genus that produce gluconic acid. Several strategies for magnetite dissolution were tested including oxidative and reductive bioleaching by acidophilic microbes along with dissimilatory reduction by Shewanella spp. that did not yield significant metal release. In addition, abiotic dissolution of the magnetite was tested with gluconic and oxalic acids, and yielded 3.99 and 81.31% iron release as a proxy for vanadium release, respectively. As a proof of principle, leaching via gluconic acid production by Gluconobacter oxydans resulted in a maximum yield of 9.8% of the available iron and 3.3% of the vanadium. Addition of an increased concentration of glucose as electron donor for gluconic acid production alone, or in combination with calcium carbonate to buffer the pH, increased the rate of iron dissolution and final vanadium recoveries. These data suggest a strategy of biogenic organic acid mediated vanadium recovery from magnetite and point the way to testing additional microbial species to optimize the recovery.

Influence of Pd:Bi ratio on Pd-Bi/Al2O3 catalysts: structure, surface and activity in glucose oxidation

Pd-Bi nanoparticles show high efficiency in catalyzing gluconic acid production by glucose oxidation reaction. Although this type of catalysts was studied for some time, the correlation between bismuth content and...

Identification of Heterotrophic Zinc Mobilization Processes among Bacterial Strains Isolated from Wheat Rhizosphere (Triticum aestivum L.)

ABSTRACTSoil and plant inoculation with heterotrophic zinc-solubilizing bacteria (ZSB) is considered a promising approach for increasing zinc (Zn) phytoavailability and enhancing crop growth and nutritional quality. Nevertheless, it is necessary to understand the underlying bacterial solubilization processes to predict their repeatability in inoculation strategies. Acidification via gluconic acid production remains the most reported process. In this study, wheat rhizosphere soil serial dilutions were plated on several solid microbiological media supplemented with scarcely soluble Zn oxide (ZnO), and 115 putative Zn-solubilizing isolates were directly detected based on the formation of solubilization halos around the colonies. Eight strains were selected based on their Zn solubilization efficiency and siderophore production capacity. These included one strain ofCurtobacterium, two ofPlantibacter, three strains ofPseudomonas, one ofStenotrophomonas, and one strain ofStreptomyces. In ZnO liquid solubilization assays, the presence of glucose clearly stimulated organic acid production, leading to medium acidification and ZnO solubilization. While solubilization byStreptomycesandCurtobacteriumwas attributed to the accumulated production of six and seven different organic acids, respectively, the other strains solubilized Zn via gluconic, malonic, and oxalic acids exclusively. In contrast, in the absence of glucose, ZnO dissolution resulted from proton extrusion (e.g., via ammonia consumption byPlantibacterstrains) and complexation processes (i.e., complexation with glutamic acid in cultures ofCurtobacterium). Therefore, while gluconic acid production was described as a major Zn solubilization mechanism in the literature, this study goes beyond and shows that solubilization mechanisms vary among ZSB and are strongly affected by growth conditions.IMPORTANCEBarriers toward a better understanding of the mechanisms underlying zinc (Zn) solubilization by bacteria include the lack of methodological tools for isolation, discrimination, and identification of such organisms. Our study proposes a direct bacterial isolation procedure, which prevents the need to screen numerous bacterial candidates (for which the ability to solubilize Zn is unknown) for recovering Zn-solubilizing bacteria (ZSB). Moreover, we confirm the potential of matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) as a quick and accurate tool for the identification and discrimination of environmental bacterial isolates. This work also describes various Zn solubilization processes used by wheat rhizosphere bacteria, including proton extrusion and the production of different organic acids among bacterial strains. These processes were also clearly affected by growth conditions (i.e., solid versus liquid cultures and the presence and absence of glucose). Although highlighted mechanisms may have significant effects at the soil-plant interface, these should only be transposed cautiously to real ecological situations.