Depression Mechanism of Strontium Ions in Bastnaesite Flotation with Salicylhydroxamic Acid as Collector

Novel cytotoxicity study of strontium (Sr) doped iron oxide (Fe3O4) nanoparticles aided with ibuprofen for drug delivery applications

This work is aimed at studying the drug delivery applications of iron oxide (Fe3O4) nanoparticles with strontium (Sr) doping with varying molar ratios prepared by the co-precipitation route. The impact of increased strontium content on the particle size and magnetic properties was investigated. The impending of these nanoparticles for drug loading, drug release, and their respective cytotoxicity was also inspected.First, iron oxide nanoparticles were doped with various amounts of strontium, from 0.25, 0.50, and 0.75, to 1 mol using co-precipitation method. These synthesized nanoparticles were characterized by XRD, SEM, EDX, VSM, and FTIR for evaluating crystal structure, phase purity, morphology, composition, magnetic properties, and functional groups, respectively. Drug loading and drug release properties were determined using UV-vis spectroscopy, whereas MTT assay evaluated cytotoxicity. Colloidal stability was assessed using zeta potential in PBS solution.The findings confirmed the successful doping of iron oxide with strontium via XRD and EDX. SEM results confirmed spherical morphology for all and needle-like structure for 1 mol strontium doped sample. For VSM results, a single domain structure was established. It was also observed that the drug encapsulation efficiency increases with increased strontium content. Cytotoxicity results by MTT assay revealed increased cytotoxicity with increasing nanoparticle concentration, and ibuprofen-loaded nanoparticles showed higher cytotoxicity than un-loaded nanoparticles at the same concentration. Zeta potential results showed colloidal stability of iron oxide nanoparticles increased by the addition of strontium.This study provided predominantly comparison of the cytotoxicity of ibuprofen-loaded and non-loaded nanoparticles on Hep-2 cancer cells at similar concentrations for the first time for both Fe3O4 particles and Sr-doped Fe3O4 nanoparticles and enclosed the impact of increasing Sr doping content on Fe3O4 nanoparticles.

Surface chemistry considerations of gangue dissolved species in the bastnaesite flotation system

Inefficient flotation of bastnaesite remains a challenge in the production of rare earth elements. This study aimed to investigate the dissolution and adsorption behaviour of species that are commonly released into bastnaesite flotation pulp from Ca/Ba-bearing gangue minerals. The influence and corresponding mechanisms on the bastnaesite mineral surface and collectors, namely sodium oleate (NaOL), were evaluated experimentally based on micro-flotation, zeta potentials, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-Ray photoelectron spectroscopy (XPS) analyses. The flotation recovery of bastnaesite significantly decreased from ∼95% to ∼25%, ∼15%, ∼80%, ∼25% when exposed to calcite, fluorite, barite, and mixed dissolved species, respectively. The zeta potential of bastnaesite was pH sensitive, indicating that H+ and OH- determine the surface potential of bastnaesite. Solution chemistry analyses revealed that the presence of the dissolved species differed at various pH values. In situ ATR-FTIR demonstrated the different effects of the dissolved species from calcite, fluorite, and barite on collector adsorption. The former two dissolved species mainly depressed the chemisorption of the NaOL monomers (RCOO‒), whereas calcite also affected the physical adsorption of the oleic acid molecular dimer (RCOOH·RCOO‒). Moreover, the barite dissolved species only affected the physical adsorption of the NaOL species. The results of XPS analysis revealed that dissolved species from these three gangues could pre-adsorbed onto bastnaesite and affected the interaction with the collector. Density functional theory calculations were employed to provide further theoretical insights into the interactions between the dissolved species from calcite, fluorite, and barite and NaOL.

Improving Rare-Earth Mineral Separation with Insights from Molecular Recognition: Functionalized Hydroxamic Acid Adsorption onto Bastnäsite and Calcite

Enhancing the separation of rare-earth elements (REEs) from gangue materials in mined ores requires an understanding of the fundamental interactions driving the adsorption of collector ligands onto mineral interfaces. In this work, we examine five functionalized hydroxamic acid ligands as potential collectors for the REE-containing bastnäsite mineral in froth flotation using density functional theory calculations and a suite of surface-sensitive analytical spectroscopies. These include vibrational sum frequency generation, attenuated total reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies. Differences in the chemical makeup of these ligands on well-defined bastnäsite and calcite surfaces allow for a systematic relationship connecting the structure to adsorption activity to be framed in the context of interfacial molecular recognition. We show how the intramolecular hydrogen bonding of adsorbed ligands requires the inclusion of explicit water solvent molecules to correctly map energetic and structural trends measured by experiments. We anticipate that the results and insights from this work will motivate and inform the design of improved flotation collectors for REE ores.

A Molecular-Scale Approach to Rare-Earth Beneficiation: Thinking Small to Avoid Large Losses

Separating rare-earth-element-rich minerals from unwanted gangue in mined ores relies on selective binding of collector molecules at the interface to facilitate froth flotation. Salicylhydroxamic acid (SHA) exhibits enhanced selectivity for bastnäsite over calcite in microflotation experiments. Through a multifaceted approach, leveraging density functional theory calculations, and advanced spectroscopic methods, we provide molecular-level mechanistic insight to this selectivity. The hydroxamic acid moiety introduces strong interactions at metal-atom surface sites and hinders subsurface-cation stabilization at vacancy-defect sites, in calcite especially. Resulting from hydrogen-bond-induced interactions, SHA lies flat on the bastnäsite surface and shows a tendency for multilayer formation at high coverages. In this conformation, SHA complexation with bastnäsite metal ions is stabilized, leading to advanced flotation performance. In contrast, SHA lies perpendicular to the calcite surface due to a difference in cationic spacing. We anticipate that these insights will motivate rational design and selection of future collector molecules for enhanced ore beneficiation.

A review of reagents applied to rare-earth mineral flotation

The rare-earth elements (REE), which encompass the fifteen metallic elements of the lanthanoid series of the periodic table, yttrium and occasionally scandium, have gained enormous public, economic and scientific attention in recent years. These elements, which have been found in over 250 minerals, are of high economic and strategic importance to many high-technology industries. As such they have been designated as critical materials by several countries and many new deposits are being developed. Rare-earth mineral (REM) deposits can be broadly classified into four geological environments: carbonates, alkaline/peralkaline igneous rocks, placers and ion adsorption clays. Apart from ion adsorption clay deposits, which require no mineral processing steps, froth flotation is the most applied beneficiation technique. This paper reviews the flotation of REM, covering their surface chemical properties as well as the various flotation reagents which have been employed.