Research

1439 KiB

Open AccessArticle

Dissolution and Sorption Processes on the Surface of Calcite in the Presence of High Co²⁺ Concentration

by Jorge González-López, Ángeles Fernández-González, Amalia Jiménez, Athanasios Godelitsas, Spyridon Ladas, Georgios Provatas, Anastasios Lagogiannis, Ioannis N. Pasias, Nikolaos S. Thomaidis and Manuel Prieto

Minerals 2017, 7(2), 23; https://doi.org/10.3390/min7020023 - 15 Feb 2017

Cited by 6 | Viewed by 5037

Abstract

The interaction of the calcite surface with Co²⁺-rich aqueous solutions ([Co²⁺_aq]_initial = 1000 ppm, i.e., ca. 17 mM) was investigated by means of macroscopic experiments and surface spectroscopic techniques. In the case of the macroscopic experiments, calcite [...] Read more.

The interaction of the calcite surface with Co²⁺-rich aqueous solutions ([Co²⁺_aq]_initial = 1000 ppm, i.e., ca. 17 mM) was investigated by means of macroscopic experiments and surface spectroscopic techniques. In the case of the macroscopic experiments, calcite powder and monocrystals were immersed into solutions for different time periods (from 1 min to one month). The Ca concentrations in the filtrates was measured by means of atomic absorption spectrometry (AAS) while the interacted solids were studied using a combination of X-ray photoelectron spectroscopy (XPS) and ¹²C-rutherford backscattering spectrometry (¹²C-RBS). The macroscopic data showed a characteristic surface dissolution process, in parallel to the surface sorption processes. Adsorption and co-precipitation were seen for almost the entire immersion period for both calcite powder and monocrystals. The surface study by XPS (analyzed at a depth of approximately 12 nm) suggested that adsorption takes place in the first hour of the interaction, followed by incorporation of Co²⁺ into calcite surface layers, leading to the formation of a Co²⁺-bearing surface (co)precipitate, which occurs over a period of hours and days. The ¹²C-RBS measurements on calcite {

10 \bar{1} 4

} indicated that the thickness of this surface co-precipitate was 270 nm after one day and then stabilized at 320 nm after more than a week. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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1994 KiB

Open AccessArticle

The Effect of Ca²⁺ and Mg²⁺ on the Dispersion and Flocculation Behaviors of Muscovite Particles

by Jiayan Tang, Yimin Zhang and Shenxu Bao

Minerals 2016, 6(3), 93; https://doi.org/10.3390/min6030093 - 08 Sep 2016

Cited by 19 | Viewed by 6412

Abstract

The dispersion and flocculation behavior of muscovite suspensions in the presence of Ca²⁺ and Mg²⁺ are relevant for industrial processing of pre-concentrated muscovite from stone coal, a primary source of vanadium. In this study, the dispersion and flocculation behavior were investigated [...] Read more.

The dispersion and flocculation behavior of muscovite suspensions in the presence of Ca²⁺ and Mg²⁺ are relevant for industrial processing of pre-concentrated muscovite from stone coal, a primary source of vanadium. In this study, the dispersion and flocculation behavior were investigated by means of sedimentation, zeta potential, and ion absorption experiments, as well as the force between particles and ion speciation calculations. The results indicated that the dispersion and flocculation behavior of muscovite particles without excess ions were in qualitative agreement with the classical DLVO theory. The muscovite particles aggregated mainly due to basal surface-edge interactions in acidic suspensions but were dispersed in alkaline suspension by electrostatic repulsion of the total particle surface. In acidic suspensions, the ability of muscovite to form dispersions of muscovite was increased with the decrease in the electrostatic attraction between the basal surface and the edge caused by the compression of the electric double layers withCa²⁺ and Mg²⁺. In alkaline suspension, the main adsorption form of Ca²⁺ and Mg²⁺ on muscovite surface was the ion-hydroxy complexes. The flocculation behavior of muscovite was affected by the static bridge effect of the ion-hydroxy complexes. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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2603 KiB

Open AccessArticle

The Effect of Chloride Ions on the Activity of Cerussite Surfaces

by Qicheng Feng, Shuming Wen, Qinbo Cao, Jiushuai Deng and Wenjuan Zhao

Minerals 2016, 6(3), 92; https://doi.org/10.3390/min6030092 - 06 Sep 2016

Cited by 21 | Viewed by 4454

Abstract

Chloride ions were found to potentially increase activity of cerussite surfaces. Dissolution experiments, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) studies, and density functional theory (DFT) computation were conducted in this study. Dissolution experiments showed that the lead ion concentrations in the NaCl [...] Read more.

Chloride ions were found to potentially increase activity of cerussite surfaces. Dissolution experiments, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) studies, and density functional theory (DFT) computation were conducted in this study. Dissolution experiments showed that the lead ion concentrations in the NaCl solution system were lower than those in the deionized water system and that the lead ion concentrations in NaCl + Na₂S aqueous systems decreased by approximately one order of magnitude compared with that in the Na₂S system alone. Results of zeta potential measurements revealed that the pretreatment with chloride ions of cerussite caused a more positive zeta potential than that without chloride ions. XPS analysis results indicated that the number of lead ions on the mineral surface increased after cerussite was treated with chloride ions. Results of DFT computation implied that the number of lead atoms on the mineral surface increased and that the activity improved after PbCl⁺ was adsorbed onto the cerussite surface. The contribution of chloride ions to the activity on the mineral surface is attributed to the increase in the number of active sites and enhancement in the activity of these sites, resulting in improved sulfidization and flotation performance. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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3369 KiB

Open AccessArticle

The Influence of Impurity Monovalent Cations Adsorption on Reconstructed Chalcopyrite (001)-S Surface in Leaching Process

by Zhenlun Wei, Yubiao Li, Qing Xiao and Shaoxian Song

Minerals 2016, 6(3), 89; https://doi.org/10.3390/min6030089 - 29 Aug 2016

Cited by 10 | Viewed by 4092

Abstract

Hydrometallurgical processing of chalcopyrite is hindered predominantly due to the passivation layers formed on the chalcopyrite surface. However, the effects of impurity cations released from the gangue are not yet well understood. Density functional theory (DFT) calculations were carried out to investigate monovalent [...] Read more.

Hydrometallurgical processing of chalcopyrite is hindered predominantly due to the passivation layers formed on the chalcopyrite surface. However, the effects of impurity cations released from the gangue are not yet well understood. Density functional theory (DFT) calculations were carried out to investigate monovalent cations of Na⁺ and K⁺ on chalcopyrite (001)-S surface using Materials Studio. The results show that the 3d orbital of Fe and 3p orbital of S predominantly contribute to their activities during chalcopyrite oxidation and dissolution processes. In addition, SO₄²⁻ is more likely to be adsorbed on one Fe site in the presence of Na⁺, while it is preferentially adsorbed on two Fe sites in the presence of K⁺. However, the adsorption of both Na₂SO₄ and K₂SO₄ on the chalcopyrite (001)-S surface contributes to the breakage of S–S bonds, indicating that the impurity cations of Na⁺ and K⁺ are beneficial to chalcopyrite leaching in a sulfuric environment. The adsorption energy and partial density of states (PDOS) analyses further indicate that the adsorption of Na₂SO₄ on chalcopyrite (001)-S surface is favored in both -BB (bidentate binuclear ) and -BM (bidentate mononuclear) modes, compared to the adsorption of K₂SO₄. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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2346 KiB

Open AccessArticle

Restraining Na-Montmorillonite Delamination in Water by Adsorption of Sodium Dodecyl Sulfate or Octadecyl Trimethyl Ammonium Chloride on the Edges

by Hongliang Li, Yunliang Zhao, Tianxing Chen, Yuri Nahmad and Shaoxian Song

Minerals 2016, 6(3), 87; https://doi.org/10.3390/min6030087 - 23 Aug 2016

Cited by 3 | Viewed by 5155

Abstract

The delamination of montmorillonite in water leads to sliming in ore slurry, which is detrimental to mineral flotation and solid/water separation. In this work, the delamination of Na-montmorillonite (Na-MMT) has been restrained by sodium dodecyl sulfate (SDS) or octadecyl trimethyl ammonium chloride (1831) [...] Read more.

The delamination of montmorillonite in water leads to sliming in ore slurry, which is detrimental to mineral flotation and solid/water separation. In this work, the delamination of Na-montmorillonite (Na-MMT) has been restrained by sodium dodecyl sulfate (SDS) or octadecyl trimethyl ammonium chloride (1831) through the adsorption on the edge of the mineral. The experimental results have shown that the pretreatment by adding SDS and 1831 could greatly reduce the Stokes size percentage of −1.1 µm particles in the aqueous Na-MMT suspension. From the X-ray diffractometer (XRD) results, the interlayer spacing of the MMT pre-treated by SDS and 1831 is smaller than that of original MMT particles. Adsorption position of SDS and 1831 on MMT surfaces was analyzed by the measurements of adsorption capacity of SDS and 1831, inductively-coupled plasma spectra, and zeta potential before and after the plane surface of MMT was covered with tetraethylenepentaminecopper ([Cu(tetren)]²⁺). The results indicated that SDS and 1831 are adsorbed on the edge and the whole surface of Na-MMT, respectively. Delamination of MMT could be well restrained by the adsorption of SDS and 1831 on the edges of MMT. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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2638 KiB

Open AccessArticle

Molecularly-Limited Fractal Surface Area of Mineral Powders

by Petr Jandacka, Jaromir Pistora, Jan Valicek and Vilem Madr

Minerals 2016, 6(2), 44; https://doi.org/10.3390/min6020044 - 13 May 2016

Viewed by 4054

Abstract

The topic of the specific surface area (SSA) of powders is not sufficiently described in the literature in spite of its nontrivial contribution to adsorption and dissolution processes. Fractal geometry provides a way to determine this parameter via relation SSA ~ x⁽ [...] Read more.

The topic of the specific surface area (SSA) of powders is not sufficiently described in the literature in spite of its nontrivial contribution to adsorption and dissolution processes. Fractal geometry provides a way to determine this parameter via relation SSA ~ x^{(D − 3)}s^{(2 − D)}, where x (m) is the particle size and s (m) is a scale. Such a relation respects nano-, micro-, or macro-topography on the surface. Within this theory, the fractal dimension 2 ≤ D < 3 and scale parameter s plays a significant role. The parameter D may be determined from BET or dissolution measurements on several samples, changing the powder particle sizes or sizes of adsorbate molecules. If the fractality of the surface is high, the SSA does not depend on the particle size distribution and vice versa. In this paper, the SSA parameter is analyzed from the point of view of adsorption and dissolution processes. In the case of adsorption, a new equation for the SSA, depending on the term (2 − D)∙(s₂ − s_BET)/s_BET, is derived, where s_BET and s₂ are effective cross-sectional diameters for BET and new adsorbates. Determination of the SSA for the dissolution process appears to be very complicated, since the fractality of the surface may change in the process. Nevertheless, the presented equations have good application potential. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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3463 KiB

Open AccessArticle

Edge Structure of Montmorillonite from Atomistic Simulations

by Aric G. Newton, Kideok D. Kwon and Dae-Kyo Cheong

Minerals 2016, 6(2), 25; https://doi.org/10.3390/min6020025 - 25 Mar 2016

Cited by 30 | Viewed by 7482

Abstract

Classical molecular dynamics (MD) simulations have been performed to investigate the effects of substitutions in the octahedral sheet (Mg for Al) and layer charge on an atomistic model of the montmorillonite edge. The edge models considered substitutions in both the solvent accessible and [...] Read more.

Classical molecular dynamics (MD) simulations have been performed to investigate the effects of substitutions in the octahedral sheet (Mg for Al) and layer charge on an atomistic model of the montmorillonite edge. The edge models considered substitutions in both the solvent accessible and inaccessible octahedral positions of the edge bond chain for a representative edge surface. The MD simulations based on CLAYFF, a fully-flexible forcefield widely used in the MD simulations of bulk clay minerals, predicted Mg–O bond distances at the edge and in bulk that agreed with those of the density functional theory (DFT) geometry optimizations and available experimental data. The DFT results for the edge surfaces indicated that substitutions in the solvent inaccessible positions of the edge bond chain are energetically favorable and an increase in layer charge and local substitution density coincided with the occurrence of five-coordinate, square pyramidal Mg and Al edge structures. Both computational methods predicted these square pyramidal structures, which are stabilized by water bridging H-bonds between the unsaturated bridging oxygen [(Al or Mg)–O–Si] and other surface O atoms. The MD simulations predict that the presence of Mg substitutions in the edge bond chain results in increased disorder of the edge Al polyhedra relative to the unsubstituted edge. In addition to the square pyramidal Al, these disordered structures include trigonal bipyramidal and tetrahedral Al at the edge and inverted Si tetrahedra. These simulation results represent the first test of the fully-flexible CLAYFF forcefield for classical MD simulations of the Na-monmorillonite edge and demonstrate the potential of combined classical MD simulations and DFT geometry-optimizations to elucidate the edge structure of 2:1 phyllosilicate minerals. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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5267 KiB

Open AccessArticle

The Growth of Gypsum in the Presence of Hexavalent Chromium: A Multiscale Study

by Juan Morales, José Manuel Astilleros, Emilio Matesanz and Lurdes Fernández-Díaz

Minerals 2016, 6(1), 22; https://doi.org/10.3390/min6010022 - 15 Mar 2016

Cited by 10 | Viewed by 5177

Abstract

The sorption of dissolved inorganic pollutants into the structure of minerals is an important process that controls the mobility and fate of these pollutants in the Earth’s crust. It also modifies the surface structure and composition of the host mineral, affecting its crystallization [...] Read more.

The sorption of dissolved inorganic pollutants into the structure of minerals is an important process that controls the mobility and fate of these pollutants in the Earth’s crust. It also modifies the surface structure and composition of the host mineral, affecting its crystallization kinetics. Here, we investigate the effect of hexavalent chromium, Cr(VI), on the nucleation and growth of gypsum by conducting two types of experiments: (i) in situ atomic force microscopy (AFM) observations of the growth of gypsum {010} surfaces in the presence of Cr(VI) and (ii) gypsum precipitation experiments by mixing aqueous solutions containing variable amounts of Cr(VI). Gypsum precipitation is progressively delayed when occurring from solutions bearing increasing Cr(VI) concentrations. Chemical analyses of gypsum precipitates show that gypsum incorporates small Cr(VI) amounts that correlate with the content of this ion in the aqueous solution. Gypsum cell parameters variation reflects this incorporation. At the molecular scale, Cr(VI) induces a slowdown of step advance rates on gypsum {010} surfaces accompanied by the roughening of nanostep edges and the so-called “template effect”. This effect involves the reproduction of the original nanotopography after the completion of individual advancing monolayers and appears as a general nanoscale phenomenon occurring during growth of solid solutions from aqueous solutions even in the case of compositionally-restricted solid solutions. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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7115 KiB

Open AccessArticle

Ab initio Studies of O₂Adsorption on (110) Nickel-Rich Pentlandite (Fe₄Ni₅S₈) Mineral Surface

by Peace P. Mkhonto, Hasani R. Chauke and Phuti E. Ngoepe

Minerals 2015, 5(4), 665-678; https://doi.org/10.3390/min5040516 - 12 Oct 2015

Cited by 27 | Viewed by 6553

Abstract

Ab initio density functional theory was used to investigate the adsorption of oxygen molecule on the nickel-rich pentlandite (110) surface, which is important for mineral extraction. The three most reactive adsorption sites: Fe-top, Ni-top, and fcc-hollow have been considered. Firstly, the non-adsorbed pentlandite [...] Read more.

Ab initio density functional theory was used to investigate the adsorption of oxygen molecule on the nickel-rich pentlandite (110) surface, which is important for mineral extraction. The three most reactive adsorption sites: Fe-top, Ni-top, and fcc-hollow have been considered. Firstly, the non-adsorbed pentlandite surface reflects the Ni atoms relaxing inwards. Consequently, their electronic structure showed high Fe 3d-orbital contribution than the Ni 3d-orbitals at the EF (indicating that the Fe atoms are more reactive than Ni). Secondly, the O2-adsorbed surface predicted lowest adsorption energy for Fe-top (-1.902 eV), as a more spontaneous reaction is likely to occur than on fcc-hollow (-1.891 eV) and Ni-top (-0.040 eV) sites, suggesting Fe preferential oxidation. The density of states indicates that the O₂ show prevalence of electrons in the ^πp* antibonding orbitals, and are reduced to zero states at the valence band on metal-bonded oxygen (O₁). The ^πp* orbital is observed to reside just above the EF for Fe-top and fcc-hollow site, while on Ni-top is half-occupied for both metal-bonded oxygen (O₁) and terminal oxygen (O₂). Finally, the isosurface charge density difference showed electron (charge) depletion on Ni/Fe metals and accumulation on the O₂ molecule. Bader analysis indicated that the oxidized Fe and Ni atoms adopt more positive charge, while O₂ on Fe-top atoms possesses more negative charge than on Ni-top, resulting with O₁ possessing a smaller charge than O₂ atom. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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