Review of Potential Microbial Effects on Flotation

Seasonal variation in metabolic profiles and microbial communities in a subarctic ore processing plant

The mining industry strives to reduce its water footprint by recycling water in ore processing. This leads to build-up of ions, flotation chemicals and microbial biomass, which may affect the process. The Boliden Kevitsa mine in Northern Finland is exposed to seasonal change and recycles up to 90% of the process water. We studied the variation in size, composition and putative functions of microbial communities in summer and winter in the ore processing plant. The raw water, Cu and Ni thickener overflow waters had statistically significantly higher bacterial numbers in winter compared to summer, and specific summer and winter communities were identified. Metagenomic analysis indicated that Cu and Hg resistance genes, sulphate/thiosulphate, molybdate, iron(III) and zinc ABC transporters, nitrate reduction, denitrification, thiosulphate oxidation and methylotrophy were more common in winter than in summer. Raw water drawn from the nearby river did not affect the microbial communities in the process samples, indicating that the microbial communities and metabolic capacities develop within the process over time in response to the conditions in the processing plant, water chemistry, used chemicals, ore properties and seasonal variation. We propose that the microbial community structures are unique to the Boliden Kevitsa mine and processing plant.

Graphene oxide and bacteria interactions: what is known and what should we expect?

Graphene oxide (GO) and graphene-based materials (GBMs) have gained over the last two decades considerable attention due to their intrinsic physicochemical properties and their applications. Besides, a lot of concern regarding the potential toxicity of GBMs has emerged. One of the aspects of concern is the interactions between GBMs and different environmental compartments, especially indigenous microbial and, in particular, bacterial communities. Recent research showed that GO and GBMs impacted bacterial pure culture or bacterial communities; therefore, these interactions have to be further studied to better understand and assess the fate of these materials in the environment. Here, we present our opinion and hypotheses related to possible degradation mechanisms of GO that can be used by environmental bacteria. This work is the first attempt to deduce and summarize plausible degradation pathways of GO, from structurally similar recalcitrant and toxic compounds, such as polyaromatic hydrocarbons.

Anionic nanocellulose as competing agent in microbial DNA extraction from mine process samples

Microorganisms in flotation and minerals processing may significantly affect the grade and yield of metal concentrates. However, studying the phenomena requires working techniques to detach microorganisms and their DNA from mineral particles to which they strongly adhere. We developed a new method utilizing the competitive properties of anionic nanocellulose to block sorption of DNA to and detach microbial cells from mineral particles from ore processing. In general, up to one ng DNA mL-1 sample was obtained with the custom anionic nanocellulose method (CM) compared to DNA amounts below the Qubit assay's detection limit for extractions with a commercial kit (KIT). Similarly, 0.5-4 orders of magnitude more bacterial 16S and fungal 5.8S rRNA gene copies were detected by qPCR from CM treated samples compared to KIT extractions. A clear difference in the detected microbial community structure between CM and KIT extracted samples was also observed. Commercial kits optimized for mineral soils are easy to use and time efficient but may miss a considerable part of the microbial communities. A competing agent such as anionic nanocellulose may decrease the interaction between microorganisms or their DNA and minerals and provide a comprehensive view into the microbial communities in mineral processing environments.

The microbial world in copper sulfide flotation plants (CSFP): Novel insights into bacterial communities and their application as potential pyrite bioreagents

Operations in copper sulfide flotation plants (CSFP) are complex and governed by several variables such as available technologies, reagents, and environmental conditions. However, few investigations are related to studying the microbial communities. These aspects provide a reason to compare the bacterial communities of two CSFP operated with freshwater (FwFlo) and seawater (SwFlo), and study whether indigenous bacteria could be used as pyrite bioreagents. Analyses were determined through next-generation sequencing by Illumina MiSeq System and conducted throughout the entire process: (i) minerals before and after grinding; (ii) final concentrate and concentrate thickener overflow; (iii) final tailings and tailings thickener overflow; and (iv) intake water. Bacterial strains from both plants were tested as potential bioreagents, given their tendency to adhere to pyrite after 5 min. In both CSFP, Proteobacteria (relative abundance from 45.48% to 79.22%), followed by Bacteroidetes (9.37%-44.7%), were the most abundant phyla. Regarding species, Algoriphagus olei (11.35%-43.52%) was present exclusively in FwFlo samples in contact with process water and absent in the mineral before grinding, where Cupriavidus metallidurans (16.05%) and Pseudomonas_uc (11.79%) predominated. In SwFlo samples, Marinobacter flavimaris (3.47%-41.1%), and GU061212-s (10.92%-27.63%), were the most abundant microorganisms. All of them were also detected in intake seawater. The strains with the highest adhesion rate (from 29.84% ± 0.14-100%) were phylogenetically identified as species of the genera Marinobacter, Pseudomonas, Idiomarina, Halomonas, Bacillus, Aerocuccus, and Peribacillus. Our results reveal that bacterial communities are critically dependent on process waters during mining activities, and our data depicted that indigenous bacteria could be used as potential pyrite bioreagents, evidenced by a high adhesion rate. It is thus possible to propose that different indigenous bacterial strains could be considered as new bioreagents to reduce the impact of conventional flotation reagents on health from an environment friendly perspective.

Mechanism study of the impact of Escherichia coli on coal flotation

Escherichia coli as water-borne bacteria exists in the recirculation water of coal flotation and affects the recovery of coal flotation. In order to study the effect of Escherichia coli on coal flotation, we changed the concentration of Escherichia coli and pH in the coal flotation system and found that Escherichia coli had an adverse effect on coal flotation. The concentration of Escherichia coli was negatively correlated with the recovery of coal. When the concentration of Escherichia coli reached 5.0 × 109 cells/ml, the recovery of coal flotation was 50.25%, and the change of pH basically did not affect the adverse effect of Escherichia coli on coal flotation. The mechanism was studied through Zeta potential, Fourier transform infrared spectroscopy, Scanning electron microscopy and Contact angle measurements. The results revealed that Escherichia coli could be adsorbed to the coal surface by hydrogen bonding, which changed the hydrophobicity of the coal surface and then reduced the recovery of coal flotation.

Long-amplicon MinION-based sequencing study in a salt-contaminated twelfth century granite-built chapel

Abstract

The irregular damp dark staining on the stonework of a salt-contaminated twelfth century granite-built chapel is thought to be related to a non-homogeneous distribution of salts and microbial communities. To enhance understanding of the role of microorganisms in the presence of salt and damp stains, we determined the salt content and identified the microbial ecosystem in several paving slabs and inner wall slabs (untreated and previously bio-desalinated) and in the exterior surrounding soil. Soluble salt analysis and culture-dependent approaches combined with archaeal and bacterial 16S rRNA and fungal ITS fragment as well as with the functional genes nirK, dsr, and soxB long-amplicon MinION-based sequencing were performed. State-of-the-art technology was used for microbial identification, providing information about the microbial diversity and phylogenetic groups present and enabling us to gain some insight into the biological cycles occurring in the community key genes involved in the different geomicrobiological cycles. A well-defined relationship between microbial data and soluble salts was identified, suggesting that poorly soluble salts (CaSO₄) could fill the pores in the stone and lead to condensation and dissolution of highly soluble salts (Ca(NO₃)₂ and Mg(NO₃)₂) in the thin layer of water formed on the stonework. By contrast, no direct relationship between the damp staining and the salt content or related microbiota was established. Further analysis regarding organic matter and recalcitrant elements in the stonework should be carried out.

Key points

• Poorly (CaSO₄) and highly (Ca(NO₃)₂, Mg(NO₃)₂) soluble salts were detected

• Halophilic and mineral weathering microorganisms reveal ecological impacts of salts

• Microbial communities involved in nitrate and sulfate cycles were detected

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11961-8.

Editorial for Special Issue “Water within Minerals Processing”

The products of mining are key to the technology development of the future [...]

Identification and Metabolism of Naturally Prevailing Microorganisms in Zinc and Copper Mineral Processing

It has only recently been discovered that naturally prevailing microorganisms have a notable role in flotation in addition to chemical process parameters and overall water quality. This study’s aim was to assess the prevailing microbial communities in relation to process chemistry in a zinc and copper mineral flotation plant. Due to the limitations of cultivation-based microbial methods that detect only a fraction of the total microbial diversity, DNA-based methods were utilised. However, it was discovered that the DNA extraction methods need to be improved for these environments with high mineral particle content. Microbial communities and metabolism were studied with quantitative PCR and amplicon sequencing of bacterial, archaeal and fungal marker genes and shotgun sequencing. Bacteria dominated the microbial communities, but in addition, both archaea and fungi were present. The predominant bacterial metabolism included versatile sulfur compound oxidation. Putative Thiovirga sp. dominated in the zinc plant and the water circuit samples, whereas Thiobacillus spp. dominated the copper plant. Halothiobacillus spp. were also an apparent part of the community in all samples. Nitrogen metabolism was more related to assimilatory than dissimilatory nitrate and nitrite oxidation/reduction reactions. Abundance of heavy metal resistance genes emphasized the adaptation and competitive edge of the core microbiome in these extreme conditions compared to microorganisms freshly entering the process.

Challenges in the Assessment of Mining Process Water Quality

The changes in water quality owing to recirculation of water in mineral processing plants can compromise the plant performance as well as maintenance needs. Therefore, mining process water quality assessment is becoming critical. Nevertheless, very few studies have investigated the suitability of the current analysis methodology practiced in certified laboratories for evaluating mining process water quality. This article presents two case studies to highlight the major issues encountered when performing sampling for physicochemical and chemical parameters in process water at two European mine sites using procedures from two certified laboratories. In addition, microorganisms were shown to be abundant in process waters and likely affect the mining water chemistries. However, the protocols used for microbial studies are not optimal for mining process samples, and need to be improved. The results showed difficulties in providing satisfactory results when analyzing control samples. Additionally, the analysis results presented a strong imbalance in TDS and sulfur compounds. Several potential causes associated with the poor quality of the analysis results have been outlined with a specific focus on the preservation methods. A literature review on the degradation of thiosalts suggested that the current preservation procedures are not suitable for preserving sulfur compounds. Moreover, the results indicated that the water matrix strongly influenced the validity of the chosen analysis method. In conclusion, the analysis methods should be customized for the different mining water matrix types in order to ensure the accuracy and reproducibility of the results.