Synergistic adsorptions of Na2CO3 and Na2SiO3 on calcium minerals revealed by spectroscopic and ab initio molecular dynamics studies

Synthesis, structure, and superconductivity of La7+2x Sr1-4x K x Na x Cu4O16-δ

Sodium and potassium have been doped into La7SrCu4O16-δ to form La7+2x Sr1-4x K x Na x Cu4O16-δ solid solutions by a solid-state reaction, which crystallizes in the I4/mmm space group when 0 ≤ x < 0.16 and Fmmm when 0.16 < x ≤ 0.25. With the equivalent replacement of four Sr2+ by one Na+, one K+ and two La3+, it is very interesting to find that T zero c (the definition is presented in the introduction part) of La7+2x Sr1-4x K x Na x Cu4O16-δ does not remain constant with an increase in x but first increases from 14.8 K for x = 0.00 to 33.9 K for x = 0.10 and then decreases to 18.5 K for x = 0.175.

Hybrid organic-inorganic structures trigger the formation of primitive cell-like compartments

Alkaline hydrothermal vents have become a candidate setting for the origins of life on Earth and beyond. This is due to several key features including the presence of gradients of temperature, redox potential, pH, the availability of inorganic minerals, and the existence of a network of inorganic pore spaces that could have served as primitive compartments. Chemical gardens have long been used as experimental proxies for hydrothermal vents. This paper investigates-10pc]Please note that the spelling of the following author name in the manuscript differs from the spelling provided in the article metadata: Richard J. G. Löffler. The spelling provided in the manuscript has been retained; please confirm. a set of prebiotic interactions between such inorganic structures and fatty alcohols. The integration of a medium-chain fatty alcohol, decanol, within these inorganic minerals, produced a range of emergent 3 dimensions structures at both macroscopic and microscopic scales. Fatty alcohols can be considered plausible prebiotic amphiphiles that might have assisted the formation of protocellular structures such as vesicles. The experiments presented herein show that neither chemical gardens nor decanol alone promote vesicle formation, but chemical gardens grown in the presence of decanol, which is then integrated into inorganic mineral structures, support vesicle formation. These observations suggest that the interaction of fatty alcohols and inorganic mineral structures could have played an important role in the emergence of protocells, yielding support for the evolution of living cells.

Cation Adsorption in TiO2 Nanotubes: Implication for Water Decontamination

TiO2 nanotubes constitute very promising nanomaterials for water decontamination by the removal of cations. We combined a range of experimental techniques from structural analyses to measurements of the properties of aqueous suspensions of nanotubes, with (i) continuous solvent modeling and (ii) quantum DFT-based simulations to assess the adsorption of Cs+ on TiO2 nanotubes and to predict the separation of metal ions. The methodology is set to be operable under realistic conditions, which, in this case, include the presence of CO2 that needs to be treated as a substantial contaminant, both in experiments and in models. The mesoscopic model, based on the Poisson-Boltzmann equation and surface adsorption equilibrium, predicts that H+ ions are the charge-determining species, while Cs+ ions are in the diffuse layer of the outer surface with a significant contribution only at high concentrations and high pH. The effect of the size of nanotubes in terms of the polydispersity and the distribution of the inner and outer radii is shown to be a third-order effect that is very small when the nanotube layer is not very thick (ranging from 1 to 2 nm). Besides, DFT-based molecular dynamics simulations demonstrate that, for protonation, the one-site and successive association assumption is correct, while, for Cs+ adsorption, the size of the cation is important and the adsorption sites should be carefully defined.

Electronic, mechanical and piezoelectric properties of glass-like complex Na2Si1-x Ge x O3 (x = 0.0, 0.25, 0.50, 0.75, 1.0)

Motivated by our previous work on pristine Na2SiO3, we proceeded with calculations on the structural, electronic, mechanical and piezoelectric properties of complex glass-like Na2Si1-x Ge x O3 (x = 0.0, 0.25, 0.50, 0.75, 1.0) by using density functional theory (DFT). Interestingly, the optimized bond lengths and bond angles of Na2SiO3 and Na2GeO3 resemble each other with high similarity. On doping we report the negative formation energy and feasibility of transition of Na2SiO3 → Na2GeO3 while the structural symmetry is preserved. Analyzing the electronic profile, we have observed a reduced band gap on increasing x = Ge concentration at Si-sites. All the systems are indirect band gap (Z-Γ) semiconductors. The studied systems have shown mechanical stabilities by satisfying the Born criteria for mechanical stability. The calculated results have shown highly anisotropic behaviour and high melting temperature, which are a signature of glass materials. The piezoelectric tensor (both direct and converse) is computed. The results thus obtained predict that the systems under investigation are potential piezoelectric materials for energy harvesting.

Sustainable Downstream Separation of Itaconic Acid Using Carbon-Based Adsorbents

Separation of itaconic acid from aqueous solution has been explored using various carbon-based adsorbents obtained from the pyrolysis and KOH activation of coconut shell biomass. The best preparation conditions to obtain a tailored adsorbent for itaconic acid purification were identified via a Taguchi experimental design, where its adsorption properties were maximized. The best activated carbon was obtained via coconut shell pyrolysis at 750 °C for 4 h plus an activation with 0.1 KOH and a final treatment at 800 °C for 2 h. This adsorbent showed an adsorption capacity of 4.31 mmol/g at 20 °C and pH 3 with a surface area of 466 m2/g. Itaconic acid separation was exothermic and pH-dependent where electrostatic forces and hydrogen bonding were the main adsorption interactions. Calculated adsorption rate constants for itaconic acid adsorption were 0.44–1.20 h-1. Results of adsorbent characterization analysis indicated the presence of a crystallization of itaconic acid molecules onto the activated carbon surface where 3–4 molecules could interact to form the clusters. This organic acid was recovered from the adsorbent surface via desorption with water or ethanol, thus facilitating its final purification. The best activated carbon obtained in this study is a promising alternative to perform sustainable and energy-efficient downstream separation and purification of itaconic acid produced via fermentation.

Unveiling Sodium Ion Pollution in Spray-Dried Precursors and Its Implications for the Green Upcycling of Spent Lithium-Ion Batteries

Unclear impurity pollution is one of the key scientific problems that limit the large-scale production of new lithium-ion batteries (LIBs) from spent LIBs. This work is the first to report the pollution path, pollution degree, and solution method of sodium ions in the recycling process of spent LIBs in the real world. The results show that sodium ions can intrude into the precursor particles to form crystalline salts with the anion of the leaching acid that cover the transition metal elements, thereby resulting in a failed precursor. Specifically, the intrusion of sodium ions will produce a variety of pollutants containing metal oxide bonds, such as Na-O, NaO₂, and Na⁺-O₂, on the precursor surface. These active lattice oxygen will further adsorb or react to form organic oxygen, chemical oxygen, and free oxygen, which will highly deteriorate the surface cleanliness. Strictly controlling the consumption of sodium salt in each step and using ammonia instead of NaOH for pH regulation can effectively solve sodium ion pollution to prepare high-quality battery precursors. It reveals that for the green upcycling of spent LIBs, we should strengthen the design of the recycling process to reduce the consumption of chemical reagents, which will produce unexpected secondary pollution.

Effect of Fluoride Ion on the Separation of Fluorite from Calcite Using Flotation with Acidified Water Glass

As a common depressant, acidified water glass (AWG) has strong inhibitory effects on fluorite and calcite. The inhibited fluorite is difficult to be recovered, thus resulting in the waste of resources and low flotation efficiency. In this study, the interaction of fluoride ions with fluorite and calcite surfaces was investigated, and its effects of AWG adsorption on mineral surfaces were evaluated. Micro-flotation experiments indicated that the flotation recovery of fluorite is 88.72% after fluoride ion treatment, that is, approximately fourfold with respect to that without fluoride ion modification. The results of solution chemical calculations showed that SiO(OH)3− is the main component to inhibit fluorite, and Si(OH)4 is the main component to inhibit calcite in AWG solution. XPS and ICP-MS results showed that fluoride ions can improve the floatability of fluorite by converting CaSiO3 on the surface of fluorite into CaF2, but the conversion ability of Si(OH)4 on the surface of calcite is weak, which increases the difference in floatability between fluorite and calcite. The above results were further verified by the analysis of flotation foam image and contact angle measurement. After fluorine ion treatment, the contact angle of fluorite increased, and it was more easily adsorbed on the foam. Therefore, the interaction of the fluoride ion with the fluorite surfaces eliminated the adsorption of AWG on fluorite, thereby resulting in the enhanced hydrophobicity of fluorite. Different from the traditional metal ions modification, the idea of anion modification in this paper is expected to be further studied.

Adsorption mechanisms of fatty acids on fluorite unraveled by infrared spectroscopy and first-principles calculations

HYPOTHESIS

The adsorption mechanisms of fatty acids on minerals are largely debated from years, and their understanding is now required to improve flotation processing in the critical context of raw materials. Three wavenumbers have been observed in the literature for the asymmetric stretching vibration of COO^- after the adsorption of fatty acids on mineral surfaces. They have been interpreted as different adsorbed forms, such as a precipitate formation, an adsorption of sole or bridged carboxylates, an anion exchange, or adsorbed modes, such as monodentate or bidentate configurations.

EXPERIMENTS/THEORY

Diffuse reflectance infrared Fourier transform spectroscopy was combined with ab initio molecular dynamics simulations and simulation of infrared spectra. Fluorite and sodium octanoate - or longer-chain fatty acids - were used as prototypical materials for all the investigations.

FINDINGS

At low fatty acids concentration, the asymmetric stretching vibration of COO^- peaks at 1560 cm^-1 while, at higher concentration, this infrared band converts into a doublet peaking at 1535 and 1575 cm^-1. Using simulations, we assign the band at 1560 cm^-1 to the adsorption of a carboxylate molecule bridged on a sodium counter-cation and the doublet at 1535 and 1575 cm^-1 to the adsorption of the sole carboxylate anion under a monodentate or a bidentate binuclear configuration, respectively. The formation of an adsorbed layer on the mineral surface is initiated by the adsorption of a sodium carboxylate and followed by the adsorption of mixed sole anionic forms. The role of the carboxylate counter-cation is highlighted for the first time, which was totally ignored in the literature beforehand. This particularly opens the path to the development of innovative strategies to enhance the separation contrast between minerals, which is of uttermost importance for the recovery of critical raw materials.

Structure-Elasticity Relationship of Potassium Silicate Glasses from Brillouin Light Scattering Spectroscopy and Molecular Dynamics Simulations

Brillouin light scattering (BLS) spectroscopy and molecular dynamic (MD) simulations allowed the identification of a relationship between the elastic properties and the structure of K-containing glasses of formula (K₂O)_x-(SiO₂)_1-x, having different K₂O concentrations. Excellent agreement was observed between experimental data and simulations. The peculiar elastic properties observed for these potassium silicate glasses have been extensively discussed in terms of structural and energetic features of the materials. Elastic properties were shown to be strongly dependent on the asymmetry of potential energy in the K-BO interactions and the K-NBO interactions. A low K₂O content (below 10-15% K₂O) appeared to be in favor of K⁺-BO interactions and high asymmetry of potential energy, whereas a high K₂O content (from 10 to 15% K₂O) was in favor of K⁺-NBO interactions with lower asymmetry. Our results suggest a possible explanation to the observed anomalous dependence of elastic properties of potassium silicate glasses with K₂O amount.

The Challenge of Tungsten Skarn Processing by Froth Flotation: A Review

Recently, tungsten has drawn worldwide attention considering its high supply risk and economic importance in the modern society. Skarns represent one of the most important types of tungsten deposits in terms of reserves. They contain fine-grained scheelite (CaWO₄) associated with complex gangue minerals, i.e., minerals that display similar properties, particularly surface properties, compared to scheelite. Consistently, the froth flotation of scheelite still remains, in the twenty first century, a strong scientific, industrial, and technical challenge. Various reagents suitable for scheelite flotation (collectors and depressants, mostly) are reviewed in the present work, with a strong focus on the separation of scheelite from calcium salts, namely, fluorite, apatite, and calcite, which generally represent significant amounts in tungsten skarns. Albeit some reagents allow increasing significantly the selectivity regarding a mineral, most reagents fail in providing a good global selectivity in favor of scheelite. Overall, the greenest, most efficient, and cheapest method for scheelite flotation is to use fatty acids as collectors with sodium silicate as depressant, although this solution suffers from a crucial lack of selectivity regarding the above-mentioned calcium salts. Therefore, the use of reagent combinations, commonly displaying synergistic effects, is highly recommended to achieve a selective flotation of scheelite from the calcium salts as well as from calcium silicates.

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Sulfidization is required in the amine flotation of smithsonite; however, the sulfidization mechanism of smithsonite is still not fully understood. In this work, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were used to characterize sulfidized and unsulfidized smithsonite. The XPS and UV–vis DRS analyses showed that smithsonite sulfidization is a transformation of ZnCO3 to ZnS on the smithsonite surfaces. However, this transformation is localized, resulting in the coexistence of ZnCO3 and ZnS or in the formation of ZnS island structures on the sulfidized smithsonite surfaces. AFM height imaging showed that sulfidization can substantially change the surface morphology of smithsonite; in addition, AFM phase imaging demonstrated that sulfidization occurs locally on the smithsonite surfaces. Based on our findings, it can be concluded that smithsonite sulfidization is clearly a heterogeneous solid–liquid reaction in which the solid product attaches at the surfaces of unreacted smithsonite. Smithsonite sulfidization involves heterogeneous nucleation and growth of ZnS nuclei. Moreover, the ZnS might nucleate and grow preferentially in the regions with high reactivity, which might account for the formation of ZnS island structures. In addition, sphalerite-structured ZnS is more likely to be the sulfidization product of smithsonite under flotation-relevantconditions, as also demonstrated by the results of our UV–vis DRS analyses. The results of this study can provide deeper insights into the sulfidization mechanism of smithsonite.