Nanomorphology effects on the bioactivity and chemical activity of metal oxides, sulphides, and silicates

Project Presentation The mining industry faces challenges linked to the sustainable production of steadily more complex and poorer ores. This requires knowledge of how very small mineral particles will react during ore processing. This is particularly important during flotation. Available models do not completely explain what is occurring on the interface between the mineral phase and the flotation liquids during flotation and bioflotation. This project responded to these challenges by developing a better fundamental knowledge and predictive model of the interactions of submicron and nanoparticles (NPs) with biosurfactants, biopolymers, and bacteria relevant to ore processing. A primary objective was to understand how and why nanoscale morphological features (nanoparticle/nanopore size and shape, surface porosity, and nanoroughness) of metal oxides, sulfides and silicates influence their separation using flotation and bioflotation. We sought to provide answers to the two main fundamental questions: How does nanomorphology (size, shape, nanoporosity) of nanoparticles affect their adsorption, dissolution-reprecipitation, and acid-base properties and fate (aggregation, deposition, dissolution, growth/modification) in aqueous solutions under the flotation conditions and why? How do these properties affect the interaction of nanoparticles with bacteria and why? Our focus has been on the separation of Cu oxide and rare earth minerals, as Cu and rare earth elements (REE) are critical for the green energy transition. REE present a significant strategic value to Norway due to development of large scale REE deposits such as the Fen Complex. Answers to the above questions will help us develop economically more effective environmentally benign schemes for the recovery of critical elements by flotation and bioflotation. This knowledge will be of value for understanding nanotoxicology and employment of NPs for environmental remediation. Results We found microbial biosurfactants (glycolipids) hold great potential as flotation reagents. In particular, they can separate copper sulfides from ores, as well as ultrafine particles of hematite, malachite and quartz from their artificial mixtures. Spectroscopic and macroscopic methods, gave insight into adsorption mechanisms of biosurfactants on ultrafine metal sulfide, oxide particles, as well as quartz. We found conditions under which glycolipids can separate CeO2 ultrafine particles and hematite (Fe2O3) by flotation. These biosurfactants are not only selectively adsorbed on ultrafine particles but also selectively flocculate them. We are the first to demonstrate that selectivity can be enhanced by controlling the redox state of the CeO2 particles. We have also shown that anionic polymer alginate in the presence of cations can be used to precipitate Fe2O3 and CeO2 nanoparticles, and how this effect depends on the composition of alginate and on the valency of the cation. Our results have been published in 5 academic articles in international, high impact journals and one manuscript has been submitted for publication (its revised version (minor revision) is currently under review). The project’s scope and the results of its mineral processing part were disseminated through one book chapter, one conference paper, a YouTube video, and multiple presentations at international, high-impact conferences. The Ph.D. Thesis was successfully defended on the 15th of January 2024. Our research results have been made openly available. It has been shown that Rhodococcus opacus bacteria can adapt to nanoparticles of iron and copper oxides. The adapted bacteria bound better to the particles, resulting in an increased rate of precipitation of the NPs from solution. For Cu-adapted bacteria, the phenotype was stable, and several proteins were found to be overexpressed. In the biotechnological part of the project, a PhD thesis was defended, and one paper was published. Results were disseminated through one book chapter and a conference presentation. Outcomes and Impact This study advances fundamental understanding of the parameters that govern (bio)chemical activity of ultrafine mineral particles. The acquired knowledge can be useful in designing selective interactions of ultrafine sulfide, oxide, and silicate minerals with biomolecules. It will help develop new environmentally sound and cost-effective (bio)chemical schemes of flotation, contributing to the ongoing effort to reduce the carbon footprint of mineral processing by replacing potentially toxic petroleum-based reagents with eco-friendly alternatives produced from biomass. The project’s results are also of interest for environment remediation/detoxification, where microbe biosurfactants are used to remove toxic heavy metals. The discovered dependence of the flotation of ultrafine ceria (cerium(IV)oxide) on the oxidation state of surface Ce ions is an innovative approach to enhanced separation of redox-active rare-earth minerals.

This study advances fundamental understanding of the parameters that govern (bio)chemical activity of ultrafine mineral particles. The acquired knowledge can be useful in designing selective interactions of ultrafine sulfide, oxide, and silicate minerals with biomolecules. It will help develop new environmentally sound and cost-effective (bio)chemical schemes of flotation, thereby contributing to the ongoing effort to reduce carbon footprint of mineral processing by replasing toxic petroleum-based reagents by eco-freendly alternative produced from biomass. The project’s results are also of interest for the environment remediation/detoxification, where biosurfactants are microbes are used for the removal of toxic heavy metals. The discovered dependence of the flotation of ultrafine ceria on the oxidation state of surface Ce ions is an innovative approach to enhanced separation of redox-active rare-earth minerals. The fundamental insight into the flocculation properties of alginate biopolymers with respect to ceria and hematite nanoparticles can widen the application of alginate as bioflocculants. The biotechnological part provides new knowlewdge about the growth of Rhodococcus opacus, a biotechnologically important bacterium with metabolic capability for bioremediation and metal recovery.

Processes at nano-biointerfaces are at the cutting edge of research towards innovations in many society-formative technologies ranging from nanomedicine to ore processing, recycling, and the environment protection. The proposed research program is the first attempt to carry out a systematic fundamental study to determine the effect of changing the physical (particle size, shape, surface roughness/porosity) and chemical properties (surface energy, crystallinity, surface charge, structure of adsorption sites, hydrophobicity) of nanoparticles (NPs) on adsorption of selected surfactants, exopolysaccharides and proteins as well as on interaction of bacteria based on direct molecular-level in situ spectroscopic data about reactivity of NPs. Results of this study will advance fundamental understanding of the parameters that govern (bio)chemical activity and the environmental impact of nanostructured materials. The acquired knowledge is the key to designing selective interactions of minerals with reagents and will ultimately end in developing new environmentally sound and cost-effective (bio)chemical schemes of flotation and the environment remediation/ detoxification. We are aiming at establishing correlation between nanomorphology (nanosize, shape, and nanoporosity) of NPs and their adsorption properties and their interaction with different classes of surfactants, biomolecules, and bacteria from a perspective to overcome the problem of changed floatability of minerals when their size is submicron and/or their surface has nanoirregularities (pits, hills, and nanopores) or even employ this effect as a novel source of enhanced and selective reactivity of minerals. The project will promote innovations in adapting existing research methods and developing new characterization tools for probing the amount, binding mode, and packing of molecules adsorbed on nanoheterogeneous substrates, especially using in situ spectroscopic techniques.