Mineral Surfaces Research Articles

Temperature-Corrected Calibration of GS3 and TEROS-12 Soil Water Content Sensors

The continuous monitoring of soil water content is commonly carried out using low-frequency capacitance sensors that require a site-specific calibration to relate sensor readings to apparent dielectric bulk permittivity (Kb) and soil water content (θ). In fine-textured soils, the conversion of Kb to θ is still challenging due to temperature effects on the bound water fraction associated with clay mineral surfaces, which is disregarded in factory calibrations. Here, a multi-point calibration approach accounts for temperature effects on two soils with medium to high clay content. A calibration strategy was developed using repacked soil samples in which the Kb-θ relationship was determined for temperature (T) steps from 10 to 40 °C. This approach was tested using the GS3 and TEROS-12 sensors (METER Group, Inc. Pullman, WA, USA; formerly Decagon Devices). Kb is influenced by T in both soils with contrasting T-Kb relationships. The measured data were fitted using a linear function θ = aKb + b with temperature-dependent coefficients a and b. The slope, a(T), and intercept, b(T), of the loam soil were different from the ones of the clay soil. The consideration of a temperature correction resulted in low RMSE values, ranging from 0.007 to 0.033 cm3 cm−3, which were lower than the RMSE values obtained from factory calibration (0.046 to 0.11 cm3 cm−3). However, each experiment was replicated only twice using two different sensors. Sensor-to-sensor variability effects were thus ignored in this study and will be systematically investigated in a future study. Finally, the applicability of the proposed calibration method was tested at two experimental sites. The spatial-average θ from a network of GS3 sensors based on the new calibration fairly agreed with the independent area-wide θ from the Cosmic Ray Neutron Sensor (CRNS). This study provided a temperature-corrected calibration to increase the accuracy of commercial sensors, especially under dry conditions, at two experimental sites.

Silica Nanofluids in Low Salinity Water for Wettability Alteration of the Mineral Surface and the Effect of Surface Roughness

Silica Nanofluids in Low Salinity Water for Wettability Alteration of the Mineral Surface and the Effect of Surface Roughness

Membrane vesicles in Acidithiobacillia class extreme acidophiles: influence on collective behaviors of 'Fervidacidithiobacillus caldus'.

Membrane vesicles (MVs) are envelope-derived extracellular sacs that perform a broad diversity of physiological functions in bacteria. While considerably studied in pathogenic microorganisms, the roles, relevance, and biotechnological potential of MVs from environmental bacteria are less well established. Acidithiobacillaceae family bacteria are active players in the sulfur and iron biogeochemical cycles in extremely acidic environments and drivers of the leaching of mineral ores contributing to acid rock/mine drainage (ARD/AMD) and industrial bioleaching. One key aspect of such a role is the ability of these bacteria to tightly interact with the mineral surfaces and extract electrons and nutrients to support their chemolithotrophic metabolism. Despite recent advances in the characterization of acidithiobacilli biofilms and extracellular matrix (ECM) components, our understanding of its architectural and mechanistic aspects remains scant. Using different microscopy techniques and nano-tracking analysis we show that vesiculation is a common phenomenon in distant members of the Acidithiobacillaceae family, and further explore the role of MVs in multicellular colonization behaviors using 'Fervidacidithiobacillus caldus' as a bacterial model. Production of MVs in 'F. caldus' occurred in both planktonic cultures and biofilms formed on sulfur surfaces, where MVs appeared individually or in chains resembling tube-shaped membranous structures (TSMSs) important for microbial communication. Liquid chromatography-mass spectrometry data and bioinformatic analysis of the MV-associated proteome revealed that 'F. caldus' MVs were enriched in proteins involved in cell-cell and cell-surface processes and largely typified the MVs as outer MVs (OMVs). Finally, microbiological assays showed that amendment of 'F. caldus' MVs to cells and/or biofilms affects collective colonizing behaviors relevant to the ecophysiology and applications of these acidophiles, providing grounds for their exploitation in biomining.

Influence of Clay Particle Interactions on Leaching Percolation in Ion-adsorption-type Rare Earth Ores

Ion-adsorption-type rare earth ores (IRE-ores) are a vital source of rare earth elements globally. The percolation properties of the ore body significantly determine the ease of rare earth extraction using in situ leaching processes. This paper investigates the interactions among clay particles in ion-adsorption-type rare earth ores within aqueous solutions, utilizing methods such as mineral particle aggregation and settling and acid–base adsorption on mineral surfaces. Based on these analyses, this paper elucidates the influence of solution properties on the percolation process of ion-type rare earth ores during leaching. The results indicate that the electrostatic attraction between minerals in aqueous solutions is pronounced, enhancing the interaction and resulting in a notable instability of the aggregates. The aggregation of minerals impacts the viscous effect of water bound to the mineral surface on the solution, thereby affecting the percolation rate. Extremely low concentrations of SO42− and CH3COO− can act as surface modifiers, reducing the electrostatic attraction between particles and consequently increasing the leaching percolation rate.

Controls of Mineral Solubility on Adsorption-Induced Molecular Fractionation of Dissolved Organic Matter Revealed by 21 T FT-ICR MS.

Mineral adsorption-induced molecular fractionation of dissolved organic matter (DOM) affects the composition of both DOM and OM adsorbed and thus stabilized by minerals. However, it remains unclear what mineral properties control the magnitude of DOM fractionation. Using a combined technique approach that leverages the molecular composition identified by ultrahigh resolution 21 T Fourier transform ion cyclotron resonance mass spectrometry and adsorption isotherms, we catalogue the compositional differences that occur at the molecular level that results in fractionation due to adsorption of Suwannee River fulvic acid on aluminum (Al) and iron (Fe) oxides and a phyllosilicate (allophane) species of contrasting properties. The minerals of high solubility (i.e., amorphous Al oxide, boehmite, and allophane) exhibited much stronger DOM fractionation capabilities than the minerals of low solubility (i.e., gibbsite and Fe oxides). Specifically, the former released Al3+ to solution (0.05-0.35 mM) that formed complexes with OM and likely reduced the surface hydrophobicity of the mineral-OM assemblage, thus increasing the preference for adsorbing polar DOM molecules. The impacts of mineral solubility are exacerbated by the fact that interactions with DOM also enhance metal release from minerals. For sparsely soluble minerals, the mineral surface hydrophobicity, instead of solubility, appeared to be the primary control of their DOM fractionation power. Other chemical properties seemed less directly relevant than surface hydrophobicity and solubility in fractionating DOM.

The visible light photocatalytic performance of g-C3N4 is regulated by the Brønsted acid site on the mullite surface

Clay minerals are considered promising semiconductor carrier materials due to their unique physical and chemical properties. However, the exact mechanism by which clay minerals interact with semiconductor materials remains unknown. To this end, the present study was conducted to explore the formation of Brønsted acidic sites on the surface of mullite by modulating the cation types in mullite. It was hereby demonstrated for the first time that the presence of Brønsted acidic sites on the surface of clay minerals is conducive to the formation of N vacancies and dopant O in carbon nitride composites (CNM-30). The synergistic effect of N vacancy and doped O increases the specific surface area of CNM-30, enhances the electron-hole separation and transport efficiency, and ultimately makes CNM-30 produce more reactive oxygen species. CNM-30 possesses excellent degradation ability for gaseous phase pollutants (such as NO) and high concentration liquid phase pollutants (such as RhB and TC). Overall, this paper presents a new perspective on the design and development of semiconductor materials based on clay minerals.

Effect of seawater on flotation separation of sphalerite from pyrite

ABSTRACT There is divalent magnesium and calcium ions existed in seawater. Under alkaline conditions, magnesium and calcium ions would react with hydroxide ions to generate insoluble hydroxyl complexes or hydroxide precipitates. In flotation process, the hydrophilic substances and collectors compete for adsorption on the surface of minerals, thereby reducing the floatability of minerals. In this study, the effects of seawater on the flotation separation of sphalerite from pyrite were investigated. The results show that under strong alkaline conditions, seawater has significant adverse effects on the flotation separation. Flotation regulators such as ethylenediamine tetraacetic acid, sodium hexametaphosphate, and sodium silicate can eliminate the adverse effect to a certain extent. The mechanisms were revealed through micro-flotation experiments, contact angle measurements, zeta potential measurements, XPS analysis and FT-IR analysis.

Diving into micro- and macroscopic properties of egg-tempera paint based on Sienna pigment

Egg-tempera painting was a pictorial technique widespread in the Middle Ages. In this work, Sienna earth and yolk have been used to formulate tempera paints according to historical recipes. Micro- and macroscopic properties were investigated to understand the interactions between the pigment and the binder. The pigment, inorganic part of the paint, was characterized by X-Ray Diffraction (XRD), thermal analysis (TG-DTA), Fourier Transform Infrared (FT-IR) Spectroscopy, granulometry, as well as Scanning Electron Microscopy (SEM). Then lecithin adsorption onto pigment particles was probed to understand yolk interaction with Sienna earth, pure kaolinite and goethite particles. NMR-Relaxometry was used to investigate the behavior and accessibility of the mineral surfaces to yolk and water. Macroscopic rheological properties of the paint systems were finally investigated.

The application of synthetic antibacterial minerals to combat topical infections: exploring a mouse model of MRSA infection

The development of new antibiotics has stalled, and novel strategies are needed as we enter the age of antibiotic resistance. Certain naturally occurring clays have been shown to be effective in killing antibiotic resistant bacteria. However, these natural clays are too variable to be used in clinical settings. Our study shows that synthetic antibacterial minerals exhibit potent antibacterial activity against topical MRSA infections and increase the rate of wound closure relative to controls. The antibacterial minerals maintain a redox cycle between Fe2+/Fe3+ and the surfaces of pyrite minerals, which act as a semiconductor and produce reactive oxygen species (ROS), while smectite minerals act as a cation exchange reservoir. Acidic conditions are maintained throughout the application of the hydrated minerals and can mitigate the alkaline pH conditions observed in chronic non-healing wounds. These results provide evidence for the strategy of ‘iron overload’ to combat antibiotic resistant infections through the maintained release of Fe2+ and generation of ROS via distinct geochemical reactions that can break the chronic wound damage cycle.

Exploring wettability variations on minerals surfaces: Insights from spreading coefficient and interaction energy analysis

The wettability of minerals plays a pivotal role in determining the distribution of residual oil and devising effective flooding strategies for enhanced oil recovery. Utilizing molecular dynamics simulations, we investigated the surface wettability of various typical minerals. The simulation results illustrate that the modeled crude oil spreads completely on most mineral surfaces. We proposed an efficient approach to calculate the spreading coefficient of the modeled crude oil on mineral surfaces, yielding accurate predictions of the spreading state — whether it is completely spread or not. Compared with the conventional spreading simulation method, our approach offers significant time savings in the calculations. Additionally, our findings underscore the influence of various crude oil components on mineral surface wettability, emphasizing the crucial role of microscopic interactions between these components and the mineral. These insights contribute to a refined understanding of mineral surface wettability and its correlation with crude oil composition, offering valuable guidance for optimizing reservoir management and production strategies.

FLOT-ART: An integrated plant optimization tool for the flotation of copper and copper–gold ores

Conventional flotation plant optimization procedures for copper and copper–gold ores have served the industry well over decades. But with the present trend in declining ore grades along with increase in metallurgical complexity, many flotation operations are experiencing significant challenges in sustaining design or operational budgeted recovery and concentrate quality targets. The need to use non-conventional water sources like brackish, sea water, and recycled process water has exacerbated the problem. Also with the emergence of various large mechanical cells and new non-mechanical flotation technologies, the ongoing use of traditional plant operational strategies is further adding to the challenges.This paper discusses an integrated plant optimization tool for the flotation of complex copper and copper–gold ores in addressing the present challenges, branded as FLOT-ART (Flotation Advanced Recovery Technology). This includes a cohesive flotation plant optimization approach starting with a mineral surface preparation step in grinding followed by advanced mineral-specific electrochemistry and cell hydrodynamics based circuit operation. This approach then allows an ore-specific grade-recovery control strategy for optimum flotation performance. This development is based on extensive greenfield projects, brownfield plant expansion studies along with operational optimization programs involving bench and plant campaigns. Principles of the FLOT-ART optimization system will be presented in this paper along with some commercial applications in the flotation of copper and copper–gold ores.

Understanding a Core Pilin of the Type IVa Pili of Acidithiobacillus thiooxidans, PilV.

Pilins are protein subunits of pili. The pilins of type IV pili (T4P) in pathogenic bacteria are well characterized, but anything is known about the T4P proteins in acidophilic chemolithoautotrophic microorganisms such as the genus Acidithiobacillus. The interest in T4P of A. thiooxidans is because of their possible role in cell recruitment and bacterial aggregation on the surface of minerals during biooxidation of sulfide minerals. In this study we present a successful ad hoc methodology for the heterologous expression and purification of extracellular proteins such as the minor pilin PilV of the T4P of A. thiooxidans, a pilin exposed to extreme conditions of acidity and high oxidation-reduction potentials, and that interact with metal sulfides in an environment rich in dissolved minerals. Once obtained, the model structure of A. thiooxidans PilV revealed the core basic architecture of T4P pilins. Because of the acidophilic condition, we carried out in silico characterization of the protonation status of acidic and basic residues of PilV in order to calculate the ionization state at specific pH values and evaluated their pH stability. Further biophysical characterization was done using UV-visible and fluorescence spectroscopy and the results showed that PilV remains soluble and stable even after exposure to significant changes of pH. PilV has a unique amino acid composition that exhibits acid stability, with significant biotechnology implications such as biooxidation of sulfide minerals. The biophysics profiles of PilV open new paradigms about resilient proteins and stimulate the study of other pilins from extremophiles.

Irreversible Trace Metal Binding to Goethite Controlled by the Ion Size.

The dynamics of trace metals at mineral surfaces influence their fate and bioaccessibility in the environment. Trace metals on iron (oxyhydr)oxide surfaces display adsorption-desorption hysteresis, suggesting entrapment after aging. However, desorption experiments may perturb the coordination environment of adsorbed metals, the distribution of labile Fe(III), and mineral aggregation properties, influencing the interpretation of labile metal fractions. In this study, we investigated irreversible binding of nickel, zinc, and cadmium to goethite after aging times of 2-120 days using isotope exchange. Dissolved and adsorbed metal pools exchange rapidly, with half times <90 min, but all metals display a solid-associated fraction inaccessible to isotope exchange. The size of this nonlabile pool is the largest for nickel, with the smallest ionic radius, and the smallest for cadmium, with the largest ionic radius. Spectroscopy and extractions suggest that the irreversibly bound metals are incorporated in the goethite structure. Rapid exchange of labile solid-associated metals with solution demonstrates that adsorbed metals can sustain the dissolved pool in response to biological uptake or fluid flow. Trace metal fractions that irreversibly bind following adsorption provide a contaminant sequestration pathway, limit the availability of micronutrients, and record metal isotope signatures of environmental processes.

New insights into the influence of mineral surface transformation on the flotation behavior of anhydrite/apatite

Apatite is generally associated with calcium-containing minerals such as anhydrite, which are difficult to separate due to their similar surface characteristics. In this study, the influence of anhydrite on the flotation behavior of apatite in a fatty acid system was systematically investigated using micro-flotation tests, solution chemical calculations, and surface chemical analyses based on the theory of flotation solution chemistry. The single and mixed mineral flotation experiments revealed that an increasing concentration of anhydrite in the mixed ore system rises, apatite flotation is inhibited while anhydrite flotation is activated. The solution chemical calculation results demonstrated that in the mixed system of anhydrite/apatite, the surface dissolution of anhydrite in the pulp will change the solution chemistry environment, resulting in a drastic decrease in the number of surfaces located ions on the apatite surface and inhibiting its flotation. Furthermore, when the pH of the solution exceeds 4.3, the surface of anhydrite transformed to apatite, promoting anhydrite flotation. The results of the X-ray photoelectron spectroscopy (XPS) analysis further confirmed that the phosphate ions dissolved by apatite were adsorbed on the anhydrite surface at pH= 9, forming calcium phosphate films. Based on the above test results, a novel flotation process was designed to realize the selective flotation of apatite from anhydrite-rich phosphate ores. This study can serve as a theoretical foundation and a practical reference for the separation of calcium-containing minerals.

Effect of calcium lignosulfonate on the interaction forces between fine calcite and fluorite

The separation of fluorite and calcite during flotation is challenging due to the complex interfacial forces that cause capping of fine-grained calcite on coarse-grained fluorite. In this paper, the micro flotation test, Zeta potential test, contact Angle test, scanning electron microscope and E-DLVO theoretical calculation were used to investigate the combination of sodium hexametaphosphate (SHMP) and calcium lignosulphonate (CLS) to disperse calcite on fluorite surface. The test results show that SHMP and CLS alone cannot effectively remove the cover, but the combination of the two can achieve good dispersion effect. In addition, Zeta potential shows that SHMP can significantly enhance the electrical properties of mineral surface, while CLS has a negligible effect on it. The contact Angle test proved that CLS adsorbed on the surface of mineral enhanced the hydrophilicity and hydration force of mineral. E-DLVO theoretical calculation further proves that CLS can not only enhance the hydration force between minerals, but also generate steric hindrance effect. When the distance between minerals is less than 1.8 nm, the steric hindrance force is greater than the repulsion force of hydration, and the steric hindrance force plays a dominant role.

Impact of Variable Water Chemistry on PFOS-Goethite Interactions: Experimental Evidence and Surface Complexation Modeling.

Perfluorooctanesulfonate (PFOS) has become a major concern due to its widespread occurrence in the environment and severe toxic effects. In this study, we investigate PFOS sorption on goethite surfaces under different water chemistry conditions to understand the impact of variable groundwater chemistry. Our investigation is based on multiple lines of evidence, including (i) a series of sorption experiments with varying pH, ionic strength, and PFOS initial concentration, (ii) IR spectroscopy analysis, and (iii) surface complexation modeling. PFOS was found to bind to goethite through a strong hydrogen-bonded (HB) complex and a weaker outer-sphere complex involving Na+ coadsorption (OS-Na+). The pH and ionic strength of the solution had a nontrivial impact on the speciation and coexistence of these surface complexes. Acidic conditions and low ionic strength promoted hydrogen bonding between the sulfonate headgroup and protonated hydroxo surface sites. Higher electrolyte concentrations and pH values hindered the formation of strong hydrogen bonds upon the formation of a ternary PFOS-Na+-goethite outer-sphere complex. The findings of this study illuminate the key control of variable solution chemistry on PFOS adsorption to mineral surfaces and the importance to develop surface complexation models integrating mechanistic insights for the accurate prediction of PFOS mobility and environmental fate.

Soil texture, fertilization, cover crop species and management affect nitrous oxide emissions from no-till cropland

Cover crops reduce nitrate leached, but effects on nitrous oxide (N2O) emissions are mixed. Cover crops can reduce N2O emissions by reducing levels of mineral nitrogen (N) and surface soil moisture during spring. Cover crops can also increase N2O emissions by adding organic substrates, releasing N during decomposition, or increasing summer soil water content. Winter-killed cover crops can increase soluble organic C and N during periods of typically low microbial activity. We hypothesized that planting a cover crop mix of radish (Raphanus sativus)-crimson clover (Trifolium incarnatum)-rye (Secale cereale) would increase direct N2O emissions relative to no cover crop, and result in lower direct and indirect N2O emissions than planting radish alone. We also hypothesized that extending the cover crop growing season, by planting earlier and killing later, would increase direct N2O emissions during winter, decrease direct N2O emissions during summer, and decrease indirect N2O emissions. To address these hypotheses, we conducted two field experiments (on sandy and silty soils) over four site-years. We measured cover crop biomass and N content, soil mineral N concentrations, soil moisture, green canopy cover, soil porewater nitrate, direct N2O emissions, and estimated indirect N2O emissions. Nitrous oxide emissions were ~ 7.8 times greater at the silty than the sandy sites due to greater soil moisture retention. Site-years with high radish biomass exhibited greater direct N2O emissions than sites with low radish biomass following winter-kill. Indirect N2O emissions were decreased ~7 % by planting cover crops and by ~70 % by planting cover crops early. Fertilizer induced emission peaks were 8.2 times greater than all previous N2O emissions combined at a silty site. Our results suggested that soil texture and fertilization played an important role in direct N2O emissions, while cover crop species, biomass, and timing played a more important role in NO3 leached, and thus, indirect N2O emissions.

Selective adsorption analysis of BAPTA depressants on the surface of carbonate minerals: Insights into flotation behavior and adsorption mechanism

Flotation separation of magnesite and calcite, two carbonate minerals, poses a significant challenge due to their intrinsic surface similarities. In this study, 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) was employed as a depressant to selectively regulate the mineral surface property in magnesite-calcite flotation. Micro-flotation experiments demonstrated that successful separation of magnesite-calcite mixtures could be achieved with 40 mg/L BAPTA and 100 mg/L sodium oleate (NaOL). Contact angle measurements and Ultraviolet-Visible absorption spectrum analysis revealed that pre-adsorption of BAPTA selectively hindered the adsorption of sodium oleate onto calcite surface, effectively eliminating the surface hydrophobicity of calcite induced by sodium oleate. The Extended-Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory further indicated a reduced attractive interaction energy between magnesite and calcite particles in the presence of BAPTA. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulation elucidated the stronger binding affinity of BAPTA towards calcium ions. Finally, a model was established for the selective formation of cage-like chelating structures on the calcite surface by BAPTA.

SBSNet: selective branch segmentation network of coal flotation froth images

ABSTRACT Flotation is a physical and chemical process that uses the difference between mineral surface properties to separate valuable minerals from worthless minerals through the attachment of bubbles. The visual information of the flotation foam surface can reflect the flotation effect and will be closely related to the flotation conditions, directly indicating the degree of mineralization of the foam layer. Considering the problem that coal slurry foam images are difficult to segment due to the mutual adhesion of bubbles and fuzzy boundaries, in this work, we proposed a new and effective segmentation algorithm for extracting coal slurry flotation foam edge information. Based on the encoder and decoder structure, a selective multi-branch input segmentation deep neural network model was designed. We evaluated the proposed method and model using a self-built coal slurry foam image segmentation dataset. The intersection over union, mean intersection over union, and PA evaluation indicators of this method increased by 12.8376%, 7.2716%, and 1.457%, respectively, compared with those of the U-Net model. The experimental results showed that the selective branch segmentation network model had high accuracy and robustness in extracting coal slurry bubble edge information, and it could effectively solve the problem of difficult segmentation of coal slurry foam images. This study provided a foundation for optimizing flotation process parameters and realizing intelligent flotation site parameters.

Effect of Interfacial Action on the Generation and Transformation of Reactive Oxygen Species in Tripolyphosphate-Enhanced Heterogeneous Fe3O4/O2 Systems.

It has been reported that tripolyphosphate (TPP) can enhance the oxygenation of natural Fe(II)-containing minerals to produce reactive oxygen species (ROS). However, the molecular structure of the TPP-Fe(II) mineral surface complex and the role of this complex in the generation and transformation of ROS have not been fully characterized. In the present study, a heterogeneous magnetite (Fe3O4)/O2/TPP system was developed for the degradation of p-nitrophenol (PNP). The results showed that the addition of TPP significantly accelerated the removal of PNP in the Fe3O4/O2 system and extended the range of effective pH to neutral. Experiments combined with density functional theory calculations revealed that the activation of O2 mainly occurs on the surface of Fe3O4 induced by a structural Fe(II)-TPP complex, where the generated O2•- (intermediate active species) can be rapidly converted into H2O2, and then the •OH generated by the Fenton reaction is released into the solution. This increases the concentration of •OH produced and the efficiency of •OH produced relative to Fe(II) consumed, compared with the homogeneous system. Furthermore, the binding of TPP to the surface of Fe3O4 led to stretching and even cleavage of the Fe-O bonds. Consequently, more Fe(II)/(III) atoms are exposed to the solvation environment and are available for the binding of active O2 and O2•-. This study demonstrates how common iron minerals and O2 in the natural environment can be combined to yield a green remediation technology.