Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces

Nelson, Joey; Wasylenki, Laura E.; Bargar, John R.; Brown, Gordon E.; Maher, Kate

doi:10.1016/j.gca.2017.08.003

Cited by 45 publications

(72 citation statements)

References 54 publications

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“…These trends, similar but less strong compared to the impacts on the kinetics, again show that siliceous composition—which enhances the formation of high-surface-area three-dimensional geopolymer gel—is vital for enhanced Pb sorption performance. 57 , 58 Also, high Na content is expected to enhance the formation of the three-dimensional geopolymer gel, 59 and on the account of the high exchangeability of Na, thought to also improve the ion-exchange properties of the resulting geopolymer sorbent.…”

Section: Results and Discussionmentioning

confidence: 99%

Structure–Property Relationship of Geopolymers for Aqueous Pb Removal

et al. 2020

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The geopolymer—an inorganic polymeric material synthesized from the reaction of aluminosilicate precursors and alkaline activating solutions—has gained wide research attention in recent decades as a promising adsorbent for the removal of aqueous heavy metals. However, the high variability of the material and several unanswered questions have limited its development and general adoption in the industry. This study evaluates the impacts of composition and microstructure on the performance of geopolymers for aqueous lead (Pb) removal to elucidate the composition–structure–property relationship. The Pb sorption kinetics and efficiency of four geopolymers, prepared using different fly ash precursors and activating solutions, were investigated. Although all the four geopolymer compositions studied displayed a high Pb removal efficiency of over 99.5%, with a slight decrease in efficiency with increasing Ca/(Si + Al) and Al/Si contents, the results show that the sorption kinetics decreases exponentially with increasing Ca/(Si + Al) and Al/Si molar ratios. The performance of the geopolymers also shows strong correlation to the microstructure, wherein the sorption kinetics increases exponentially, while the efficiency increases slightly, with increasing mass fraction of the amorphous phase in the geopolymer’s phase assemblage. The results of this research indicate that using appropriate precursor formulation and curing conditions to evoke the best microstructures, geopolymer materials can be optimized for high performance in removing heavy metals, thereby improving the chances of the material’s general acceptability in the adsorbent industry.

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Section: Results and Discussionmentioning

confidence: 99%

Structure–Property Relationship of Geopolymers for Aqueous Pb Removal

et al. 2020

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Section: Methodsmentioning

confidence: 99%

“…The Zn-bearing mineral standards presented here were previously characterized by EXAFS and X-ray diffraction analysis to establish purity and homogeneity of the phases as detailed by Nelson et al (2017). The adsorption samples of Zn on silica presented here were also previously characterized by EXAFS analysis to establish the coordination environment as detailed by Nelson et al (2017). The specific silica substrates were purchased as 0.5-10 mm conchoidally fractured quartz particles and 74-125 mm conchoidally fractured SiO 2(am) particles with measured specific surface areas of 5.92 AE 0.06 m 2 g À1 (2) and 9.76 AE 0.29 m 2 g À1 (2), respectively (Nelson et al, 2017).…”

Section: Methodsmentioning

confidence: 99%

“…The adsorption samples of Zn on silica presented here were also previously characterized by EXAFS analysis to establish the coordination environment as detailed by Nelson et al (2017). The specific silica substrates were purchased as 0.5-10 mm conchoidally fractured quartz particles and 74-125 mm conchoidally fractured SiO 2(am) particles with measured specific surface areas of 5.92 AE 0.06 m 2 g À1 (2) and 9.76 AE 0.29 m 2 g À1 (2), respectively (Nelson et al, 2017). Adsorption experiments were conducted in ambient laboratory atmosphere at room temperature (22 C).…”

Section: Methodsmentioning

confidence: 99%

“…The propensity for transition metals, including Zn, to reside in multiple coordination environments makes aqueous, sorbed and mineral speciation complex and identification in unknown specimens challenging. Such variations in the Zn coordination environment have been documented at several mineral surfaces, including silica (Nelson et al, 2017(Nelson et al, , 2018Roberts et al, 2003), kaolinite (Guinoiseau et al, 2016;Nachtegaal & Sparks, 2004), alumina (Trainor et al, 2000;Roberts et al, 2003), montmorillonite (Lee et al, 2004), birnessite (Qin et al, 2018;Manceau et al, 2002), hematite (Ha et al, 2009), goethite (Nachtegaal & Sparks, 2004;Hamilton et al, 2016) and ferrihydrite (Waychunas et al, 2002). The precise bonding environment of Zn on mineral surfaces has implications for mobility and toxicity because different sorbed species may be differentially labile, such as octahedral versus tetrahedral Zn complexes on birnessite (Qin et al, 2018) and inner-sphere versus outer-sphere Zn complexes on hematite (Ha et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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XANES reflects coordination change and underlying surface disorder of zinc adsorbed to silica

Nelson

2021

J Synchrotron Rad

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Zinc K-edge X-ray absorption near-edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn-bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Znads) on quartz and amorphous silica [SiO2(am)] are presented from the Zn–water–silica surface system: outer-sphere octahedral Znads on quartz, inner-sphere octahedral Znads on quartz, inner-sphere tetrahedral Znads on quartz, inner-sphere octahedral Znads on SiO2(am) and inner-sphere tetrahedral Znads on SiO2(am). XANES spectral analysis of these complexes on quartz versus SiO2(am) reveals that normalized peak absorbance and K-edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption-edge energy of Znads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO2(am), the absorption-edge energy of Znads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Znads presents a single K-edge peak feature, whereas tetrahedral Znads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K-edge of tetrahedral Znads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO2(am). Linear combination fitting of samples with a mixture of Znads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Znads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Znads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X-ray absorption fine structure (EXAFS) derived coordination environments for these Znads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis.

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Adsorption characteristics of copper ion on nanoporous silica

Niu

Qin

et al. 2019

Acta Geochim

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Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces

Cited by 45 publications

References 54 publications

Structure–Property Relationship of Geopolymers for Aqueous Pb Removal

Structure–Property Relationship of Geopolymers for Aqueous Pb Removal

XANES reflects coordination change and underlying surface disorder of zinc adsorbed to silica

Adsorption characteristics of copper ion on nanoporous silica

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