Mineral Surfaces Research Articles

Quantitative study on the selective depressing effect of polysaccharides on some polar minerals

This study presents a systematic summary on the depressing effect of polysaccharides on some polar minerals, revealing that the order of their depressing strength on some polar minerals was primarily associated with the surface properties of the minerals, showing a limited correlation with the structure of polysaccharides. Subsequently, the selective depressing mechanism of polysaccharides on polar minerals was quantitatively explained from the perspective of acid–base interaction mechanism, and a criterion system for determining the depressing effect of polysaccharide on minerals was proposed. Specifically, it was found that the hydroxylation reaction of metal sites on mineral surface was a prerequisite for polysaccharide adsorption. Under the above–mentioned conditions, the selective depressing effect of polysaccharides on these minerals with different metal sites could be assessed through a parameter system in which the ion potential φ of surface metal sites served as the primary determinant, and the solubility product constant of metal hydroxides played a secondary role. In cases where minerals shared identical surface metal sites, the selective depressing effect of polysaccharides was analyzed by comparing the coordination numbers of these sites. Specifically, minerals with a higher number of coordinated surface metal sites tend to show a weaker response to depressing effect of polysaccharide. Consequently, this study theoretically elucidated the selective depressing effect of polysaccharides on polar minerals, and the criterion system proposed in this study outperforms the prediction results based on the isoelectric point (pHiep). These research findings have important guiding significance for a deeper understanding of the selective depressing mechanism of polysaccharides and the regulation of flotation.

Understanding the Role of Layered Minerals in the Emergence and Preservation of Proto-Proteins and Detection of Traces of Early Life.

ConspectusThe origin of life remains one of the most profound mysteries in science. Over millennia, theories have evolved, yet the question persists: How did life emerge from inanimate matter? At its core, the study of life's origin offers insights into our place in the universe and the nature of life itself. By delving into the chemical and geological processes that led to life's emergence, scientists gain a deeper understanding of the fundamental principles that govern living systems. This knowledge not only expands our scientific understanding but also has profound implications for fields ranging from astrobiology to synthetic biology.This research employs a multidisciplinary approach, combining a diverse array of techniques, from space missions to wet laboratory experiments to theoretical modeling. Investigations into the formation of the first proto-biomolecules are tailored to explore both the complex molecular processes that underpin life and the geological contexts in which these processes may have occurred. While laboratory experiments are aimed at mimicking the processes of early planets, not every process and sample is attainable. To this end, we demonstrate the use of molecular modeling techniques to complement experimental efforts and extraterrestrial missions. The simulations enable researchers to test hypotheses and explore scenarios that are difficult or impossible to replicate in the laboratory, bridging gaps in our understanding of prebiotic processes across vast time and space scales.Minerals, particularly layered structures like clays and hydrotalcites, play diverse and pivotal roles in the origin of life. They concentrate organic species, catalyze polymerization reactions (such as peptide formation), and provide protective environments for the molecules. Minerals have also been suggested to have acted as primitive genetic materials. Nevertheless, they may lack the ability for long-term information replication. Instead, we suggest that minerals may act as transcribers of information encoded in environmental cyclic phenomena, such as tidal or seasonal changes. We argue that extensive protection of the produced polymer will immobilize it, making it inactive for any further function. Therefore, in order to generate a functional polymer, it is essential that it remains mobile and chemically active. Furthermore, we suggest a route to the identification of pseudobiosignatures, a polymer that was polymerized on the same mineral surface and consequently retained through overprotection.This Account presents a comprehensive evaluation of the current understanding of the role of layered mineral surfaces on life's origin and biosignature preservation. It highlights the complexity of mineral-organic interactions and proposes pathways for proto-biomolecule emergence and methods for identifying and interpreting potential biosignatures. Ultimately, the quest to uncover the origin of life continues to drive scientific exploration and innovation, offering profound insights into the fundamental nature of existence and our place in the universe.

Catalytic mechanisms for As(III) oxidation by H2O2 over TiO2 surfaces, and effects of support, vacancy and photoirradiation

As(III) is much more toxic than As(V) while shows apparently lower affinity at minerals surfaces. Oxidation of As(III) to As(V) by H2O2 over anatase surface provides an attractive avenue for pollution control, and the chemocatalytic and photocatalytic mechanisms are unraveled by means of the DFT + D3 approach. Impacts of anatase as support, O2c/O3c vacancy, photoirradiation are addressed as well. As(III) oxidation under various reaction conditions leads to As(V) through dual electron transfers, while energy barriers differ substantially and decline as 1.80 (direct oxidation) > 1.35 (anatase as support) > 1.24 (O3c vacancy) > 0.50 (chemocatalysis) > 0.28 (photocatalysis) ≥ 0.26 (O2c vacancy) eV. Anatase as support promotes the reaction through bonding with H2O2/As(OH)3 and electron transfers, and its close participation during chemocatalysis produces the TiOOH active site that causes As(III) oxidation to proceed facilely under ambient circumstances. TiOOH exists in two forms (monodentate and bidentate mononuclear) and is critical for chemocatalysis, while its destruction for O3c vacancy exhibits strongly adverse effects to As(III) oxidation. Photoirradiation readily generates the OH• radicals, and corresponding mechanism is plausible while less preferred than the newly posed mechanism based on the Ti(H2O2) active site. Synergism among a number of surface atoms conduces to the superior activity for O2c vacancy and photocatalysis. Results provide a comprehensive understanding for As(III) oxidation to As(V) by H2O2, and facilitate catalysts design for As(III) oxidation that alleviates environmental pollution.

Effects of Sample Handling on Visible and Near-Infrared Soil Reflectance

Soil reflectance is a cumulative attribute determined by interactions between light (photons) and the physical, chemical, and biological properties of soil. Soil properties such as organic matter, moisture, mineral oxide contents, soil texture, and surface roughness all influence soil reflectance at unique wavelengths. Many standard sample preparation techniques are designed to alter soil properties, so as to homogenize samples to improve the consistency of reflectance data collected. This study aims to quantify the effects of one standard sample preparation activity, drying, and repeated wetting–drying cycles on visible–near-infrared soil reflectance, by collecting reflectance data from nine samples which were dried then wetted for a total of three times. This study demonstrates the major, permanent effects of a drying and wetting cycle on soil reflectance, and then presents a model which can be used to correct for these effects. These results have direct implications for remote sensing activities, soil libraries, and soil spectral libraries. These results show that without correction, data from soil spectral libraries, spectral data collected from stored samples, and spectral data transferred between studies, have limited utility for characterizing soils as they exist in the field. Soil spectral data collected in the lab requires correction before it may be used to predict soil properties in the field, as standard sample handling procedures change intrinsic soil properties and introduce systematic error into these data.

Getting to the root of the problem: Soil carbon and microbial responses to root inputs within a buried paleosol along an eroding hillslope in southwestern Nebraska, USA

Large quantities of soil carbon (C) can persist within paleosols for millennia due to burial and subsequent isolation from plant-derived inputs, atmospheric conditions, and microbial activity at the modern surface. Erosion exposes buried soils to modern root-derived C influx via root exudation and root turnover, thus stimulating microbial activity leading to SOC decomposition and accumulation through organo-mineral stabilization of modern C. With this study we aim to quantify how modern root-derived C inputs impact paleosol C decomposition and stabilization across varying degrees of isolation from modern surface conditions in southwestern Nebraska, USA, where hillslope erosion is bringing a buried Late-Pleistocene-early Holocene paleosol (the “Brady Soil”) closer to the modern surface. We collected Brady Soil samples from 0.2 m, 0.4 m, and 1.2 m below the modern surface and conducted two lab-based incubations. Soils were amended with either (1) a lab-synthesized mixture of low molecular weight compounds (12 atom% 13C), or (2) 13C enriched root residues (92 atom% 13C), in 30-day and 240-day incubation experiments, respectively. We determined microbial responses to synthetic root exudates and residues by partitioning the 13C label from Brady Soil C, including measurements of total, root, and primed C respiration, microbial biomass C (MBC), microbial C use efficiency (CUE). To assess the capacity of isolated paleosols to accrue modern plant C, we used Nano-scale Secondary Ion Mass Spectrometry imaging. We found that: (1) adding root-derived C inputs primed Brady Soil C across all depths, and was mediated by depth and composition of root additions; (2) root-derived C inputs stimulated microbial biomass C (MBC) growth similarly across depths, but the magnitude of CUE and MBC varied by chemistry of root-derived additions; (3) new particulate organic matter was incorporated into mineral-associated pools over time; (4) material from the added root residues was found in association with bacterial cells and fungal hyphae as well as with soil aggregate and mineral surfaces. Our study shows that paleosols defy expectations of C content and reactivity with depth, and changes in land cover and climate will expose buried paleosols to modern surface conditions, increasing respired C. This work highlights the importance of evaluating the role resurfacing buried soils through landscape change plays in C cycle feedbacks to the climate system.

Study on the role of microbial metabolites in in-situ noncontact bioleaching of ion-adsorption rare earth ore

Ion adsorption rare earth ore nearly satisfy global market demand for heavy rare earth elements (HREEs). Bio-leaching has important potential for the clean and efficient extraction of ion-adsorption rare earth ore. However, the complexities of in-situ mining restrict the use of contact/direct bio-leaching, and non-contact/indirect bio-leaching would be the best choice. This study explore the potential of fermentation broths prepared by Yarrowia lipolytica (ATCC 30162) for the bio-leaching of ion-adsorption rare earth ore, and three typical metabolites (potassium citrate (K3Cit), sodium citrate (Na3Cit) and ammonium citrate ((NH4)3Cit) of Yarrowia lipolytica were further evaluated in simulated bioleaching (non-contact bioleaching) of ion-adsorption rare earth ore, including leaching behavior, seepage rule and rare earth elements (REEs) morphological transformation. The column leaching experiments shown that direct leaching of REEs using fermentation broths results in incomplete leaching of REEs due to the influence of impurities. Using the purified and prepared metabolites as lixiviant, REEs can be effectively extracted (leaching efficiency >90%) at cation concentration was only 10 % of the commonly used ammonium sulfate concentration (45 mM). Cation type had less effect on leaching efficiency. During the ion-adsorption rare earth ore leaching process, rare earth ions form a variety of complex chelates with citrate, thus transferring rare earth elements from the mineral surface to the leachate. Experimental results showed that pH and concentration together determined the type and form of rare earth chelates, which in turn affect the leaching behavior of REEs and solution seepage rule. This study helps to provide a theoretical basis for the regulation and enhancement of ion-adsorption rare earth ore non-contact bioleaching process.

Adsorption behavior of helium in quartz slit by molecular simulation

Due to the multiple influences of unique physicochemical properties of helium, petrographic characteristics and temperature and pressure conditions, little is known about the helium adsorption behaviors in minerals and rocks at geological conditions. Based on the grand canonical Monte Carlo simulations, this study revealed the adsorption characteristics of pure helium and the competitive adsorption of binary mixtures with different proportions of methane and helium under geological temperature and pressure conditions in quartz slit model. Molecular simulation of pure helium shows that physical adsorption of helium exists in mineral surfaces, which indicates a preservation mechanism of helium in helium source rocks. Binary mixtures simulations indicate that the adsorption capacity of methane in quartz is stronger than that of helium, and the competitive adsorption of methane increases with decreasing burial depth. This means that during the upwards migration processes of natural gas, the adsorbed helium that distributed in the migration pathway will be gradually displaced by methane, then concentrate in the hydrocarbon gases and subsequently accumulate together in favorable traps to form helium-rich natural gas reservoirs. Our results provide a molecular-scale insight into the preservation and accumulation of helium in helium source rocks and are significant for assessing the helium resource potential.

Spatial variability of mineral surface area and carbon sequestration potential at the farm scale – a case study

Spatial variability of mineral surface area and carbon sequestration potential at the farm scale – a case study

Effect of dissolved metal ions from mineral surfaces on the surface wettability of phosphate ore by flotation

The dissolved metal ions have a significant effect on the wettability of mineral surface in flotation slurry. In this work, the composition and characteristic of phosphate ore raw (R), flotation concentrate (FC), and flotation tailing (FT), the dissolution of metal ions from mineral surface and its effect on mineral surface wettability were investigated. The results of the dissolution test indicated that the concentrations of Ca2+ and Mg2+ are high (FT > R > FC), while Fe3+ and Al3+ were low in the slurry. H3PO4, as the slurry pH regulator, has the weakest dissolved ability of metal ions from mineral surface compared with HCl, HNO3 and H2SO4. The surface tension tests revealed that metal ions will combine with NaOL in the slurry, causing the consumption of NaOL. The contact Angle tests performed that some of NaOL adsorption sites on the FC and FT surface were covered the hydrolysates of Fe3+ and Al3+, which inhibited the hydrophobicity of the FC and FT surfaces. Ca2+ and Mg2+ consumed part of NaOL in the slurry, inhibiting the hydrophobicity of the FT surface. However, the adsorption of Ca2+ and Mg2+ on the FC surface increased the adsorption of NaOL, which enhanced the hydrophobicity of the FC surface.

Mechanisms of N2 molecule adsorption and accumulation on surfactant-modified substrates: A molecular dynamics simulation

In flotation processes, gas molecules adhere to and accumulate on the target mineral surface, forming micro-nanobubbles, which can significantly enhance the efficiency of particle-bubble adhesion. Surfactants are commonly employed as auxiliary agents and play pivotal roles in flotation. However, the effect of surfactant pre-adsorption at the solid–liquid interface on the microscopic process of gas molecule adsorption and accumulation remains unclear. In this study, varying degrees of roughness surface in carbon substrates, the fatty alcohol polyoxyethylene ether (C12EO15), nitrogen molecules (N2), and water molecules (H2O) were employed to construct a gas–liquid–solid model for molecular dynamics simulations aimed at elucidating the underlying mechanisms of N2 molecule adsorption and accumulation on surfactant-modified substrates at the molecular level. The research findings revealed that N2 molecules preferred adsorption in close proximity to carbon atoms along the alkyl chain of the C12EO15 molecule. C12EO15 molecules exhibit a bending and intertwining behaviour on the hydrophobic carbon substrate surface, thereby forming a “network” adsorption layer. An increase in the quantity of surfactants provides abundant adsorption sites for N2 molecules at the solid–liquid interface, consequently augmenting the adsorption capacity of N2 molecules. Nonetheless, the presence of interstitial gaps between the surfactant-formed adsorption sites impedes the diffusion of the N2 molecules at each adsorption locus. This hindrance may obstruct the subsequent generation of micro-nano bubbles at the solid–liquid interface.

Electrochemistry and DFT study of galvanic interaction on the surface of monoclinic pyrrhotite (0 0 1) and galena (1 0 0)

The electrochemical interaction between galena and monoclinic pyrrhotite was investigated to examine its impact on the physical and chemical properties of the mineral micro-surface. This investigation employed techniques such as electrochemistry, metal ion stripping, X-ray photoelectron spectroscopy, and quantum chemistry. The electrochemical test results demonstrate that the galena surface in the electro-couple system exhibits a lower electrostatic potential and higher electrochemical activity compared to the monoclinic pyrrhotite surface, rendering it more susceptible to oxidation dissolution. Monoclinic pyrrhotite significantly amplifies the corrosion rate of the galena surface. Mulliken charge population calculations indicate that electrons are consistently transferred from galena to monoclinic pyrrhotite, with the number of electron transfers on the mineral surface increasing as the interaction distance decreases. The analysis of state density revealed a shift in the surface state density of galena towards lower energy levels, resulting in decreased reactivity and increased difficulty for the reagent to adsorb onto the mineral surface. Conversely, monoclinic pyrrhotite exhibited an opposite trend. The XPS test results indicate that galvanic interaction leads to the formation of hydrophilic substances, PbSxOy and Pb(OH)2, on the surface of galena. Additionally, the surface of monoclinic pyrrhotite not only adsorbs Pb2+ but also undergoes S0 formation, thereby augmenting its hydrophobic nature.

Towards an ecosystem capacity to stabilise organic carbon in soils.

Soil organic carbon (SOC) accrual, and particularly the formation of fine fraction carbon (OCfine), has a large potential to act as sink for atmospheric CO2. For reliable estimates of this potential and efficient policy advice, the major limiting factors for OCfine accrual need to be understood. The upper boundary of the correlation between fine mineral particles (silt + clay) and OCfine is widely used to estimate the maximum mineralogical capacity of soils to store OCfine, suggesting that mineral surfaces get C saturated. Using a dataset covering the temperate zone and partly other climates on OCfine contents and a SOC turnover model, we provide two independent lines of evidence, that this empirical upper boundary does not indicate C saturation. Firstly, the C loading of the silt + clay fraction was found to strongly exceed previous saturation estimates in coarse-textured soils, which raises the question of why this is not observed in fine-textured soils. Secondly, a subsequent modelling exercise revealed, that for 74% of all investigated soils, local net primary production (NPP) would not be sufficient to reach a C loading of 80 g C kg-1 silt + clay, which was previously assumed to be a general C saturation point. The proportion of soils with potentially enough NPP to reach that point decreased strongly with increasing silt + clay content. High C loadings can thus hardly be reached in more fine-textured soils, even if all NPP would be available as C input. As a pragmatic approach, we introduced texture-dependent, empirical maximum C loadings of the fine fraction, that decreased from 160 g kg-1 in coarse to 75 g kg-1 in most fine-textured soils. We conclude that OCfine accrual in soils is mainly limited by C inputs and is strongly modulated by texture, mineralogy, climate and other site properties, which could be formulated as an ecosystem capacity to stabilise SOC.

Adsorption pathways of boron on clay and their implications for boron cycling on land and in the ocean

Reversible adsorption and isotope fractionation of boron on the surface of clay minerals is a key process that impacts boron isotope cycling in porewater, rivers and the ocean. However, the differences in boron isotope fractionation factors between various clay minerals and their dependence on fluid chemistry are not well known. We performed two sets of experiments, using solutions of pure water with added boron and seawater, to explore the isotope behavior during adsorption of boron onto kaolinite, smectite and illite. We found that the amount of sorbed boron increases with ionic strength of solutions and is proportional to the cation exchange capacity of a given clay mineral. Maximum adsorption is observed in alkaline seawater, which we attribute to the efficient fixation of magnesium-borate ion pairs onto negatively charged surface sites. Isotopic fractionation is modestly different between clays and demonstrates that clay surfaces preferentially sorb borate, even when the concentration of borate in solution is low. In both pure water and seawater, adsorbed complexes retain the isotopic composition of their dissolved precursors (borate or boric acid) with minimal isotopic fractionation. In other words, isotopic composition of adsorbed boron is set by the ability of clays to adsorb boron from an already fractionated boron pool rather than specific fractionation associated with the complexation reaction. Our experimental results allow us to provide revised constraints on the adsorbed boron being transported in terrestrial fluids and the ocean.

Experimental constraints on barium isotope fractionation during adsorption–desorption reactions: Implications for weathering and erosion tracer applications

Constraining the processes that fractionate barium isotopes is essential for utilising barium isotope ratios as environmental tracers. Barium concentration measurements from soils, rivers, and estuaries demonstrate that adsorption–desorption reactions significantly influence the distribution of fluid–mobile barium at the Earth’s surface, potentially driving isotopic fractionation. To quantify the direction and magnitude of isotopic fractionation resulting from these reactions, a riverine and an estuarine series of batch experiments were conducted using environmentally important adsorbent minerals and surface waters. Himalayan river sediment and water samples were used to validate the experimental results.Adsorption–desorption reactions were found to be rapid, relative to the average transit time of sediment and water in catchments, and largely reversible. The direction and magnitude of isotopic fractionation in the riverine experiment series were consistent with the riverine field samples (preferential adsorption of the lighter isotopes). The reaction rate, reversibility, and magnitude of isotopic fractionation were found to depend primarily on the mineral. Experiments performed with iron oxyhydroxides (goethite and ferrihydrite) resulted in a greater degree of fractionation compared to clay minerals (kaolinite and montmorillonite). Estuarine experiments, designed to simulate sediment passage through a salinity gradient, demonstrated a high degree of reversibility, with 77% to 94% of adsorbed barium desorbed upon the addition of seawater to freshwater-equilibrated clay minerals.The results of the estuarine experiments suggest that barium isotope ratios measured in marine paleo-archives (e.g., corals) will reflect both the adsorbed and dissolved freshwater barium inputs to the ocean. The combined findings of this study indicate that the chemical and isotopic behaviour of barium differs from more conventional group 1 and 2 metal isotope systems due to a significant proportion of barium released from bedrock dissolution partitioning to mineral surfaces, rapid reaction rates between fluid–mobile phases, and a high degree of reaction reversibility. Consequently, riverine barium isotope ratios are likely to provide unique insights into the complex array of terrestrial weathering and erosion processes that sustain life on Earth.

A combination of physiology, metabolomics, and genetics reveals the two-component system ResS/ResR-mediated Fe and Al release from biotite by Pseudomonas pergaminensis F77

Understanding of the mechanisms on bacteria-regulated mineral dissolution functions is important for further insight into mineral-microbe interactions. The functions of the two-component system have been studied. However, the molecular mechanisms involved in bacterial two-component system-mediated mineral dissolution are poorly understood. Here, the two-component regulatory system ResS/ResR in the mineral-solubilizing bacterium Pseudomonas pergaminensis F77 was characterized for its involvement in biotite dissolution. Strain F77 and the F77ΔresS, F77ΔresR, and F77ΔresS/R mutants were constructed and compared for the ResS/ResR system-mediated Fe and Al release from biotite in the medium and the mechanisms involved. After 3 days of incubation, the F77ΔresS, F77ΔresR, and F77ΔresS/R mutants significantly decreased the Fe and Al concentrations in the medium compared with F77. The F77ΔresS/R mutant had a greater impact on Fe and Al release from biotite than did the F77ΔresS or F77ΔresR mutant. The F77∆resS/R mutant exhibited significantly reduced Fe and Al concentrations by 21–61 % between 12 h and 48 h of incubation compared with F77. Significantly increased pH values and decreased cell counts on the mineral surfaces were found in the presence of the F77∆resS/R mutant compared with those in the presence of F77 between 12 h and 48 h of incubation. Metabolomic analysis revealed that the extracellular metabolites associated with biotite dissolution were downregulated in the F77ΔresS/R mutant. These downregulated metabolites included GDP-fucose, 20-carboxyleukotriene B4, PGP (16:1(9Z)/16:0), 3′,5′-cyclic AMP, and a variety of acidic metabolites involved in carbohydrate, amino acid, and lipid metabolisms, glycan biosynthesis, and cellular community function. Furthermore, the expression levels of the genes involved in the production of these metabolites were downregulated in the F77ΔresS/R mutant compared with those in F77. Our findings suggested that the ResS/ResR system in F77 contributed to mineral dissolution by mediating the production of mineral-solubilizing related extracellular metabolites and bacterial adsorption on mineral surface.

Thermodynamic conditions for the presence of physically sorbed collectors on a mineral surface in an elementary act of flotation

Thermodynamic conditions for the presence of physically sorbed collectors on a mineral surface in an elementary act of flotation

Sorption of 32Si and 45Ca by isotopic exchange during recrystallisation of cement phases

The uptake kinetics of 32Si and 45Ca on cement minerals including C-S-H phases, portlandite, AFm phases, ettringite, and aged hardened cement paste were determined through batch sorption experiments. A two-step uptake kinetics was observed, with a fast initial step during ∼1 day followed by a much slower second step, not yet completed after one year. The working hypothesis that the fast uptake is caused by exchange of the radioisotopes with stable isotopes adsorbed on the mineral surface, whereas the slow uptake step is due to uptake in the crystal lattice during recrystallisation, was tested with the help of phenomenological models that combine surface adsorption and homogeneous recrystallisation. The experimental data could be reproduced satisfactorily using a refined version of the formerly published continuous homogeneous recrystallisation (CHOR) model, supporting the working hypothesis and allowing equilibrium sorption coefficients (Rd; L kg−1) for these radionuclides to be calculated on a mechanistic basis. This provides insight into the intrinsic rates and mechanisms of interaction between cementitious materials and their pore fluids which contain dissolved calcium and silicon.

The carbon activation of electric furnace ferronickel slag and its utilization in cement-based materials

The high annual emissions and low utilization rate of electric furnace ferronickel slag (EFS) have brought enormous impacts on environment. This work intends to propose a methodology for the carbon activation of EFS to improve its resource utilization. To this end, the exfoliation-carbonation (i.e., hybrid aqueous carbonation) was developed and compared with CO2 bubbling carbonation (i.e., direct aqueous carbonation). The carbonation process of EFS and the hydration and mechanical strength of activated EFS blended cement-based materials was evaluated. Experimental results indicated that mechanical pre-treatment could disorder forsterite crystal and promote the dissolution of Mg to form Si enriched mineral surface. The direct aqueous carbonation led to the formation of passivation layer which could be striped by hybrid aqueous carbonation to facilitate further carbon mineralization. Increase in temperature significantly improved the decomposition of forsterite and accelerated the carbon mineralization kinetics. The activated EFS could accelerate the hydration and promote the mechanical strength of cement-based materials. Carbon mineralization is an effective method to strengthening the activity of EFS.

Synergistic adsorption of ethyl xanthate and butyl xanthate on pyrite surfaces: A DFT study

AbstractPyrite is the most widely distributed sulfide mineral with a wide range of uses, and pyrite is mainly recovered by means of flotation in practical production, and the commonly used flotation collectors are mainly xanthates with good flotation performance. The adsorption behavior of commonly used collectors ethyl xanthate and butyl xanthate on the surface of pyrite is investigated by using the density functional tight bounding theory (DFTB). The results show that when a single reagent acts on the pyrite surface, butyl xanthate has a stronger effect than ethyl xanthate, and the adsorbed mineral surface shows obvious hydrophobicity. The interaction between ethyl xanthate and butyl xanthate had a stronger effect than that of a single reagent, and the simulation of the flotation environment at ordinary temperature using molecular dynamics revealed that the synergistic adsorption of the two different reagents on the surface of pyrite was more hydrophobic, that is, the synergistic adsorption of the combined collector of ethyl xanthate and butyl xanthate on the surface of pyrite was stronger. The results of the study are of great significance for the synergistic effect between the combined collector and the mineral.

Geochemical drivers of manganese removal in drinking water reservoirs under hypolimnetic oxygenation

Manganese (Mn) is a naturally occurring contaminant commonly found in drinking water supplies. In lakes and reservoirs, water authorities increasingly use in situ treatment by hypolimnetic oxygenation (HOx) systems to remove metals such as Mn from the water column. HOx systems introduce dissolved oxygen (DO) to the bottom waters (hypolimnion) to promote oxidation and subsequent removal of metals from the water column. Previous laboratory studies have shown the importance of individual geochemical drivers (pH, alkalinity, mineral surfaces) on Mn oxidation, but few studies have examined the influence of these drivers of Mn removal in concert. In this study, we conducted field monitoring and laboratory experiments to examine how pH, alkalinity and the presence of mineral particles influence Mn removal at two drinking water reservoirs in southwest Virginia, both with HOx systems: Falling Creek Reservoir (FCR) and Carvins Cove Reservoir (CCR). Both reservoirs have had historical issues with elevated (>0.05 mg/L) Mn concentrations during seasonal stratification (May–October). Watershed geology contributes to differences in pH and alkalinity between the reservoirs, with FCR having lower historical medians of hypolimnetic pH and alkalinity (6.6 and 18 mg/L CaCO3, respectively) than CCR (7.2 and 62 mg/L CaCO3, respectively).Results of laboratory experiments examining the influence of pH on Mn removal showed substantial Mn loss within 14 days only under high pH (10) conditions. Mn removal did not occur at pH 6 or 8 over the same 14-day period. In experiments with pH 10 and alkalinity >70 mg/L CaCO3, near-total Mn removal occurred within 2 h. Mn removal occurred concurrently with precipitation of microscopic (<5 μm) particles, followed by formation of macroscopic (>100 μm) particles. Particles of both size classes were identified as Mn oxides (MnOx). These observations suggest that increasing pH and alkalinity promotes Mn oxidation and subsequent removal from solution. Results of experiments with pH 10 and alkalinity >70 mg/L CaCO3 suggest that heterogeneous oxidation by MnOx partially drives rapid Mn removal. Thus, initial formation of MnOx creates a positive feedback loop that can enhance additional Mn loss. In experiments using water collected from FCR and CCR, we observed rapid Mn removal in unfiltered water (0.002–0.05 d−1) but no significant removal of Mn in filtered water. These results, in combination with results of analysis of particles collected from reservoir water, suggest that minerals present in the water column likely catalyze MnOx formation. Together, our experimental results suggest that heterogenous oxidation is an important process of Mn removal, while pH and alkalinity variations of the range expected in natural freshwaters contribute less to differential Mn removal. The formation of MnOx particles during in situ oxygenation, as well as the presence of suspended minerals that occur naturally in water columns, play an important role in promoting Mn oxidation and should be accounted for in Mn removal treatment strategies.