Adsorption Of HS Research Articles

Effect of ammonium carbamate on catalytic sulfidation and flotation of azurite

This study aimed to investigate the effectiveness of catalytic sulfidation using ammonium carbamate and sodium sulfide to achieve satisfactory flotation recovery rates of azurite. The recovery rate of 82.51 % azurite was achieved through catalytic sulfidation. The Cu(II) and S2− species on the pure azurite surface were reduced and oxidized to Cu(I) species, Sn2− or S2− species, respectively. The analyses revealed that the rougher the azurite surface, the higher the atomic concentration of S and the more CuS2 species formed, and the more xanthate adsorption led to the formation of hydrophobic surfaces, promoting the flotation of azurite. The dissociative adsorption of H2O molecules on the (011) surface of azurite hindered further adsorption of HS− species on the (011) surface of azurite. The adsorption energy of HS− species on the (011) surface of azurite was more negative with NH3, indicating that the NH3 enhanced the adsorption of HS− species. In addition, the chemical bond strength of Cu-S formed through catalytic sulfidation of azurite was stronger than the chemical bond strength of Cu-S formed through direct sulfidation. The enhancement between S and Cu bonds greatly improved the stability of sulfide layers after catalytic sulfidation.

Molecularly Reconfigurable Neuroplasticity of Layered Artificial Synapse Electronics

AbstractBrain‐inspired electronics with multimodal signal processing have been investigated as the next‐generation semiconductor platforms owing to the limitations of von Neumann architecture, which limits data processing and energy consumption efficiencies. This study demonstrates the molecular reconfiguration of plasticity of artificial synaptic devices with tunable electric conductance based on molecular dynamics at the channel surfaces for realizing chemical multimodality. Carrier transport dynamics are adjusted using the density of trapped carriers for the molecular adsorption of HS in the MoSe2 channel, and the results are consistent with the molecular simulations. In molecular dynamics‐controlled devices, enhanced hysteresis enables the engineering of artificial neuroplasticity, mimicking the neurotransmitter release of biological synapses. Owing to the molecular reconfigurability of MoSe2 devices, the synaptic weights of excitatory and inhibitory synapse modes are significantly enhanced. Thus, this study can potentially contribute to the creation of the next generation of multimodal interfaces and artificial intelligence hardware realization.

Surface activation of malachite by ammonium acetate for improved flotation separation of malachite from calcite

Flotation separation of malachite from calcite is hampered by the surface homogenization of the two mineral surfaces. Therefore, in this study, ammonium acetate (CH3COONH4) was used to improve the flotation separation of malachite from calcite. The results of micro-flotation experiments revealed that, in the presence of CH3COONH4, the recoveries of malachite and calcite were, respectively, 85.91 % and 23.73 %, which was an improvement over the experiment conducted without CH3COONH4. Analyses of the surface morphology showed that CH3COONH4 prevented the adsorption of Cu–S on calcite, leading to a significant decrease in the calcite surface roughness. CH3COONH4 also prevented the oxidation of sulfides, which facilitated the formation of highly crystalline Cu–S on malachite. Additionally, CH3COO− prevented the formation of a dense sulfide layer on calcite. The adsorption of HS− on the surface of malachite was more energetically advantageous with NH3 than without NH3. In addition, adsorbed CH3COO− sterically hindered the adsorption of Cu–S on the O site of calcite. Bonding between the carboxyl group and Cu–S adsorbed decreased calcite activation. Therefore, CH3COONH4 catalyzed the sulfidation of malachite and inhibited calcite activation by adsorbed Cu–S, leading to improved flotation separation of malachite from calcite.

Selective modification of malachite with ammonium carbamate to promote flotation separation from calcite

The malachite and calcite surfaces treated with CH6N2O2 and Na2S·9H2O featured a flotation recovery rates of 82.51% and ∼ 20%, respectively, and achieved a satisfactory selective flotation separation of malachite from calcite. CH6N2O2 could promote the formation of Cu-S on the malachite surface. A large number of Cu-S on the malachite surface resulted in increased surface roughness. However, the calcite surface remained unchanged, and S elements were not detected on its surface. CH6N2O2 could facilitate the reduction of Cu(II) on the malachite surface to Cu(I) but impeded sulfide oxidation reactions, resulting in the formation of CuS2 with higher crystallinity. The hydrated malachite surface hindered the adsorption of HS−. The activation energy of catalytic sulfidation of malachite was higher than that of direct sulfidation, indicating that NH3 can enhance the adsorption of HS−. The Cu-S chemical bond formed through the catalytic sulfidation of malachite was stronger than that formed through direct sulfidation.

Surface modification of hemimorphite via double-complexation by ammonium fluoride and copper ion to promote sulfidation

The effects of NH4F and Cu2+ ion on hemimorphite corrosion modification were studied. The recovery of hemimorphite in the presence of NH4F was 33.58% higher than that in the absence of NH4F. AFM and SEM-EDS imaging showed that the surface of hemimorphite after treatment in NH4F and Cu2+ solution than when treated with Cu2+ solution. This showed that the F− ions reacted with Si ions on the mineral surface and corroded the mineral surface. NH3 reacted with Cu2+ ions to form Cu(NH3)i2+ (i = 1, 2, 3, 4), which adsorbed onto the mineral surface. XPS analysis revealed that the −O−Si− bonds of the hemimorphite surface were damaged by NH4F, and Cu(NH3)i2+ (i = 1, 2, 3, 4) promoted CuS film formation via catalytic sulfidation to obtain hydrophobic hemimorphite. DFT calculations and ICP analysis showed that the dissociative adsorption of H2O molecule on hemimorphite surface were observed, which hindered the further adsorption of HS on the surface. The strength of the chemical bond between S−Cu−O− hemimorphite was the key to ensuring the stability of the sulfide layer after Cu(NH3)−HS adsorption. The double-complexation of NH4F and Cu2+ ensured the satisfactory sulfidation flotation separation of hemimorphite and quartz.

Influence of hydrated Ca<sup>2+</sup> and Mg<sup>2+</sup> complexes on the sulfidization of smithsonite: Density functional based tight binding (DFTB+) study

Ca<sup>2+</sup> and Mg<sup>2+</sup> are the most dominating unavoidable ions in the smithsonite flotation. In this paper, the effect of Ca<sup>2+</sup> (Mg<sup>2+</sup>) on the surface of smithsonite sulfidization in a system where water molecules are present was investigated using density functional based tight binding (DFTB+) simulations for the first time. The results indicated that the adsorption of hydrated Ca<sup>2+</sup> complexes is stronger than that of hydrated Mg<sup>2+</sup> complexes on the hydrated smithsonite (101) surface. In addition, at low concentrations of sodium sulfide, there is no adsorption of HS- on the surface pre-adsorbed with hydrated Ca<sup>2+</sup> complexes, but only on the surface pre-adsorbed with hydrated Mg<sup>2+</sup> complexes. At high concentrations of Na<sub>2</sub>S, S<sup>2-</sup> weakens the adsorption of hydrated Ca<sup>2+</sup> complexes due to competitive adsorption, but the presence of S<sup>2-</sup> could desorb hydrated Mg<sup>2+</sup> complexes from the surface. The results compared the differences in effects of Ca<sup>2+</sup> and Mg<sup>2+</sup> on smithsonite sulfidization, which could provide an atomic scale basis for researching the surface sulfidization of oxide minerals.

Unveiling the role of Ca ion in the sulfidation of smithsonite: A density functional theory study

In this paper, density functional theory calculations were innovatively used to study the experimentally observed depression of Ca ion and its mechanism on the sulfidation of smithsonite. The calculation results indicated that the reactivity of smithsonite surface after Ca ion adsorption was remarkably decreased, and the adsorption energies for HS on smithsonite surface in the presence of Ca ion were far larger than those in the absence of Ca ion. For one thing, the analysis results of Mulliken bond population, electron density, and partial density of states showed that the generated Ca-S bonds for HS adsorption on smithsonite surface after Ca ion adsorption were weaker and more unstable compared with Zn-S bonds for HS adsorption on the surface before Ca ion adsorption. For another, the hydration shell on smithsonite surface after Ca ion adsorption was found to be more difficult to be broken through by HS. These two factors lead to the inhibition of Ca ion on the adsorption of HS on the surface of smithsonite. This work reveals inhibition of Ca ion and its atomic-level mechanism on the sulfidation of smithsonite, which is helpful to the understanding of the negative effect of Ca ion on the sulfidation of smithsonite.

A DFT-based method to determine the ammonium-induced activation and sulfidation pathway of tenorite

BackgroundThe ammonia modification of minerals surfaces has been successfully applied to obtain a successful flotation performance and plays an important role in the sulfidation flotation of copper oxides. First principle calculations based on density functional theory (DFT) are able to provide information on the electronic structures, properties, adsorption energies, and electron transfer of the mineral surface and floatation reagents, thus helping to understand the interaction mechanisms of reagents with copper oxides. MethodsThe DFT was explored to discuss the mechanisms underlying the HS– species and NH3 direct and activated sulfidation of tenorite (1 1 1) surfaces. The relationship between Cu–S–NH3 species distribution and pH value in the solution was simulated by visual MINTEQ. Significant findingsThe Cu 3d orbital peak was observed to be stronger at the Fermi level than that of the O 2p orbit on the tenorite (1 1 1) surface, and the negative adsorption energy and adsorption effect of HS– get better results through calculations, while the Cu 3d and 4 s peaks overlapped the corresponding S 3 s and 3p peaks at the HS– adsorption on tenorite (1 1 1) surface. The maximum adsorption energy of NH3 and HS– on the tenorite (1 1 1) surface was determined as –19.63 eV, which is more negative than that with just the adsorption of HS– on the tenorite (1 1 1) surface. Herein, we combined Visual MINTEQ and DMOL3 models to indicate that the addition of NH3 ions catalyzes the formation of CuS(s), ie., NH3 mainly catalyzes the interaction between HS– species and Me(OH)2 on the hydroxylated oxidized ore surface or solution, that is, Me(OH)2 first dehydroxylates to metal ions, and then forms sulfide species with HS–. The flotation experiment was consistent with the DFT calculation results.

DFT insights into the sulfidation mechanism of Fe-impurity smithsonite

The sulfidation-flotation of Fe-bearing smithsonite is still a challenge in practice. Currently, theoretical understandings on reagents adsorption on impurity-bearing mineral surface are still lacking. Here we first systematically investigated the adsorption of HS on perfect and Fe-impurity smithsonite (101) surfaces in the absence and presence of H2O by density-functional theory (DFT). We found Fe-impurity dramatically changed the structure and electronic properties of smithsonite surface. In the absence and presence of H2O, the adsorption energies of HS on Fe-bearing smithsonite surface were all lower than those of perfect surface. The Mulliken bond populations and DOS analysis results showed that the formed Fe-S bonds on Fe-impurity smithsonite surface were less stable than the Zn-S bonds formed on the perfect surface. Meanwhile, the competitive adsorption capacity of H2O and HS on perfect and Fe-impurity surfaces was different. The interaction of H2O and HS to TZn site on perfect surface was in the order of HS > H2O while that to TFe site on TFe-impurity surface was H2O > HS, and the adsorption of HS was depressed. Furthermore, S-OH was contained in the sulfidation product of BFe-impurity surface, and the hydrophobicity of the formed sulfidation film greatly decreased, which was also not conducive to the sulfidation-flotation.

The effect of surface vacancy on adsorption of HS on smithsonite (101) surface: A DFT study

In this paper, the effect of Zn-vacancy defect on adsorption of HS on smithsonite (101) surface was studied by density-functional theory (DFT). The results showed that Zn-vacancy defect made the peaks of the VB and VT defect surfaces both move to left, and the peaks of them around the Fermi energy both decreased. Hence, the reactivity of VB and VT defect surfaces were both lower than that of the perfect smithsonite surface. The presence of Zn-vacancy on the smithsonite surface not only inhibited the adsorption of HS on the site of Zn-vacancy (VT-V and VB-V) but also depressed its adsorption on the Zn site nearby the Zn-vacancy (VT-BZn and VB-TZn). When HS was on the VT-BZn site on the smithsonite surface, the adsorption site of HS was the bridge between S atom the two Zn atoms, and when on the VT-V and VB-TZn sites, the adsorption site of HS was the Zn atom on the smithsonite surface. While on the VB-V site, the adsorption site of HS was the C atom on the smithsonite surface, and the bonding of S‒C was formed. Meanwhile, electron transfers among the bonding atoms on smithsonite surface were observed. The results can provide insights into the sulphidization of smithsonite containing defects.

The effect of sodium hydrosulfide on molybdenite flotation in seawater and diluted seawater

Seawater is used in copper-molybdenum flotation plants when fresh water resources are limited. To minimize the negative effect of process seawater on molybdenite flotation, diluting process seawater with fresh water is a common practice. This study was designed to identify whether the dilution of process seawater in copper-molybdenum flotation plants benefits molybdenite flotation where NaHS is added to depress chalcopyrite. Seawater was prepared based on the concentrations of salts in the process seawater used in a copper-molybdenum flotation plant, and diluted with different proportions of de-ionized water. The concentrations of NaHS chosen to test in molybdenite flotation were determined by conducting chalcopyrite flotation to depress chalcopyrite. It was found that the concentration of NaHS which maximumly depressed chalcopyrite also depressed molybdenite to some extent in both seawater and diluted seawater. Water chemical equilibrium calculation, Cryo-XPS analysis and SEM measurement indicated that the depression mechanisms of NaHS on molybdenite were different in seawater and diluted seawater. Significant dilution of seawater weakened the buffer effect of seawater on pH and raised the pH in flotation significantly after the addition of NaHS so that Mg(OH)2 and CaCO3 precipitates formed to depress molybdenite. Insignificant dilution of seawater had little effect on flotation pH after the addition of NaHS, but the adsorption of HS− and the formation of SO42− on micro-edges of basal plane surfaces of molybdenite at a high NaHS concentration decreased the hydrophobicity of the basal plane surfaces, leading to reduced molybdenite flotation recovery.

Effect of Chloride Concentration on Stress Corrosion Behavior and Mechanism of SA516Gr70N Steel in Alkaline NaCl/Na2S Solution

The effects of chloride on the electrochemical process and susceptibility to stress corrosion cracking (SCC) of SA516Gr70N steel in alkaline NaCl/Na2S solution were investigated by using electrochemical techniques (impedance spectroscopy and polarization curve measurement) and slow strain rate tensile (SSRT) tests. SA516Gr70N steel exhibited SCC susceptibility to a certain extent in alkaline NaCl/Na2S solution. The susceptibility to SCC decreased with increasing chloride concentrations in solutions with pH values of 9 and 11, while susceptibility was not apparent in higher pH solutions. Electrochemical analysis showed that the corrosion potential became more negative, and the anodic corrosion rate decreased with increasing chloride concentration due to the competitive adsorption of HS− and Cl−. The mechanism of SCC is mainly controlled by anodic dissolution with the addition of chloride.

Combined effect of cathodic potential and sulfur species on calcareous deposition, hydrogen permeation, and hydrogen embrittlement of a low carbon bainite steel in artificial seawater

Calcareous deposition, hydrogen permeation, and hydrogen embrittlement of E690 steel in thiosulfate-containing artificial seawater (ASW) under cathodic polarization are investigated. Sulfur species in acidic ASW eliminate the aragonite precipitation, attributed to the variation of cathodic reaction, favorable adsorption of HS− and enhanced hydrogen evolution. The maximum permeation current was achieved at −850 mVSCE due to the change of interfacial pH and promotion ability of sulfur species. Hydrogen embrittlement susceptibility increases linearly with logarithm increase of hydrogen concentration, while the preferential cracking pathway evolves from lath boundary separation at low hydrogen concentration to prior austenite grain boundary failure at high concentrations.

DFT insights into the electronic properties and adsorption mechanism of HS− on smithsonite (1 0 1) surface

Sulfidization flotation is commonly used to recover zinc oxide minerals from ores, and sulfidization is a critical stage. However, few studies on the microscopic mechanism of smithsonite sulfidization have been performed. In this work, density functional theory calculations are conducted to investigate the electronic properties and adsorption mechanism of sulfide ion species on smithsonite (1 0 1) surface. Results indicate that the ZnO bond breaks when smithsonite crystal is crushed and ground, and that zinc atoms are the dominant reactive sites for the subsequent adsorption of flotation reagents onto smithsonite surface. HS− ions can spontaneously react with Zn atoms at the top, bottom, and bridge sites of the mineral-surface layer, thereby forming a newly stable structure of ZnS on smithsonite (1 0 1) surface. The adsorption of HS− ion on this smithsonite surface greatly influences the structural and electronic properties of smithsonite (1 0 1) surface, changing the structure of ZnO and CO at the surface layer of smithsonite. We observe an obvious electron transfer between Zn and S atoms after HS− ion adsorption, as well as a significant difference in charge transfer when HS− ion adsorbs at different Zn sites on mineral surface. Besides, it proves that a slight oxidation occurs in the sulfidization process of smithsonite at the atomic level.

Combined DFT and XPS investigation of enhanced adsorption of sulfide species onto cerussite by surface modification with chloride

This study systematically investigates the enhanced adsorption of sulfide species onto cerussite by surface modification with chloride through density functional theory calculations and X-ray photoelectron spectroscopy (XPS) measurements. Calculation results demonstrate obvious differences in the surface structures and electronic properties of cerussite after HS− adsorption in the absence and presence of chloride species. Surface modification with chloride promotes the stable adsorption of HS− onto the cerussite surface, and the hybridization of Pb 6p orbital at the surface layer and S 3p orbital from HS− is enhanced. Moreover, the reactivity of cerussite surfaces is enhanced by the occurrence of new DOS peaks of Pb 6p and S 3p near the Fermi level and by the transfer of additional electrons between the bonding atoms in the presence of chloride. Meanwhile, Mulliken population and XPS analysis results indicate that a slight oxidation is involved in the interaction between sulfide species and cerussite surfaces because of the presence of disulfide and polysulfide in the sulfidization products. In addition, a higher proportion of disulfide and polysulfide relative to the overall S is exhibited in the presence of chloride, facilitating the sulfidization flotation of cerussite.

Corrosion behavior of 316L stainless steel anode in alkaline sulfide solutions and the consequent influence on Ga electrowinning

During Ga enrichment by ion exchange, sodium sulfide is an indispensable compound to elute Ga (III) from resin. The effects of residual S2− ions on the corrosion behavior of stainless steel anode and Ga electrodeposition are studied. It is found that 316L stainless steel anode is corroded seriously and Ga is hardly electrodeposited in the presence of 2.17g/L S2−. The adsorption of HS− ions damages the passive film of anode surface, which leads to the formation of soluble and colloidal (NaFeS2)n. After 48h electrowinning, the weight loss of stainless steel anode (7.38mg/cm2) in Ga solution with 2.17g/L S2− is much larger than that (0.23mg/cm2) in solution without S2−. Green-black precipitates are found in Ga (III) solution due to the degradation of colloidal (NaFeS2)n. Meanwhile, the corrosion of stainless steel anode brings iron ions into Ga (III) solution. Iron species are deposited or absorbed on the cathode, which is unfavorable to Ga electrodeposition. At lower S2− concentration, both Fe and O are detected in Ga coatings. When S2− concentration is up to 2.17g/L S2−, Ga electrodeposition is completely inhibited.

Effect of Hydrogen Sulfide Ions on the Passive Behavior of Type 316L Stainless Steel

The effect of hydrogen sulfide ions (HS−) on the passivity of type 316L stainless steel was investigated in pH 8.4 boric acid-borate buffer solution. Galvanostatic polarization of a silver microelectrode covered with Ag2S generated both OH− and HS− above the stainless steel surface. During potentiostatic polarization of the stainless steel, the passivity-maintaining current density increased with increase in the concentration of HS− in the vicinity of the surface. The impedance of the stainless steel at a constant frequency decreased during polarization in the presence of HS−, while it was sustained after dilution of HS−. Electrochemical impedance spectroscopy (EIS), Mott-Schottky (M-S) analysis and scanning electrochemical microscopy (SECM) showed that a defective and n-type semiconductive passive film was formed in the solution containing HS−. Auger electron spectroscopy (AES) revealed that metal cations and oxygen vacancies in the passive film on the stainless steel increased when it was formed in a HS−-containing solution. The series of changes in passive film properties is thought to be due to adsorption of HS– on the film surface during the polarization.

Characterization of AISI 1005 corrosion films grown under cyclic voltammetry of low sulfide ion concentrations

The mechanism of AISI 1005 corrosion in sulfide ion solutions has been investigated using cyclic voltammetry, electrochemical impedance spectroscopy, X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The proposed mechanism occurs with the initial formation of oxygenated ferrous species followed by adsorption of HS− species, precipitation of iron monosulfides and their partial conversion to bisulfide iron. This mechanism was demonstrated by XRD results that revealed Fe-O and Fe-S phases and by MS results that detected pyrite as the major proportion (94%) of the iron species in the corrosion product.

Adsorption of H2S, HS, S, and H on a stepped Fe(310) surface

Using periodic density functional theory we studied adsorption of H2S, HS, S and H on the Fe(310) stepped surface, comparing our results with those on Fe(100). H2S is predicted to weakly adsorb on all high-symmetry sites, with the bridge site at the step edge as preferred one, oriented perpendicularly to the (100) terraces with the two H atoms pointing out of the surface. Adsorption of HS, S, and H is more stable on the bridge, four-fold hollow, and three-fold hollow sites, respectively. The detailed analysis of the computed local density of states show common trends with the behavior of adsorption energies and is able to account for energy differences of all species adsorbed on Fe(100) and Fe(310).

Passivation at semiconductor/electrolyte interface: Role of adsorbate solvation and reactivity in surface atomic and electronic structure modification of III–V semiconductor

These studies are focused on understanding the role played by a solvent in chemical and electronic processes occurred in the course of semiconductor surface passivation at semiconductor/electrolyte interface. It is shown that the chemical reactivity of the ionic adsorbate at a semiconductor/electrolyte interface can be changed considerably through interaction with solvent molecules. The reactivity of anions depends essentially on the solvating solvent: hydrated ions could be either slightly electrophilic or slightly nucleophilic, whereas the ions solvated by alcohol molecules are always strongly nucleophilic. Mechanism of interaction of such solvated ions with the semiconductor surface atoms depends on the solvent, as is demonstrated by the example of processes occurred at GaAs(1 0 0)/sulfide solution interfaces. It is found that on adsorption of HS − ions from different solvents the As S bonds with solvent-dependent ionic character are formed on a GaAs(1 0 0) surface. The surface obtained in such a way possesses different ionization energy and exhibit different electronic properties dependent on the solvent.