Carbonate Adsorption to Ferrihydrite: Competitive Interaction with Phosphate for Use in Soil Systems

Juan C. Mendez; Tjisse Hiemstra

doi:10.1021/acsearthspacechem.8b00160

Carbonate Adsorption to Ferrihydrite: Competitive Interaction with Phosphate for Use in Soil Systems

Juan C. Mendez^*, Tjisse Hiemstra

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

52 Citations (Scopus)

Abstract

Carbonate (CO₃) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO₃ and PO₄ concentrations. The surface speciation of CO₃ has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO₃ occurs predominately via formation of bidentate inner-sphere complexes, either (=FeO)₂CO or (=FeO)₂CO··Na⁺. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO₄. Additionally, a minor complex is present at high CO₃ loadings. The CD model, solely parametrized by measuring the pH-dependent PO₄ adsorption as a function of the CO₃ concentration, successfully predicts the CO₃ adsorption to Fh in single-ion systems. The adsorption affinity of CO₃ to Fh is higher than to goethite, particularly at high pH and CO₃ loadings due to the enhanced formation (=FeO)₂CO··Na⁺. The PO₄ adsorption isotherm in 0.5 M NaHCO₃ can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO₃ complex formation and resolved a new species (Fe(CO₃)₂(OH)₂ ³(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.

Original language	English
Pages (from-to)	129-141
Journal	ACS Earth and Space Chemistry
Volume	3
Issue number	1
DOIs	https://doi.org/10.1021/acsearthspacechem.8b00160
Publication status	Published - 17 Jan 2019

Keywords

CD model
competition
ferrihydrite
goethite
ion adsorption
nanoparticles
solubility
surface complexation

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title = "Carbonate Adsorption to Ferrihydrite: Competitive Interaction with Phosphate for Use in Soil Systems",

abstract = "Carbonate (CO3) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO3 and PO4 concentrations. The surface speciation of CO3 has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO3 occurs predominately via formation of bidentate inner-sphere complexes, either (=FeO)2CO or (=FeO)2CO··Na+. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO4. Additionally, a minor complex is present at high CO3 loadings. The CD model, solely parametrized by measuring the pH-dependent PO4 adsorption as a function of the CO3 concentration, successfully predicts the CO3 adsorption to Fh in single-ion systems. The adsorption affinity of CO3 to Fh is higher than to goethite, particularly at high pH and CO3 loadings due to the enhanced formation (=FeO)2CO··Na+. The PO4 adsorption isotherm in 0.5 M NaHCO3 can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO3 complex formation and resolved a new species (Fe(CO3)2(OH)2 3(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.",

keywords = "CD model, competition, ferrihydrite, goethite, ion adsorption, nanoparticles, solubility, surface complexation",

author = "Mendez, {Juan C.} and Tjisse Hiemstra",

year = "2019",

month = jan,

day = "17",

doi = "10.1021/acsearthspacechem.8b00160",

language = "English",

volume = "3",

pages = "129--141",

journal = "ACS Earth and Space Chemistry",

issn = "2472-3452",

publisher = "American Chemical Society",

number = "1",

}

TY - JOUR

T1 - Carbonate Adsorption to Ferrihydrite

T2 - Competitive Interaction with Phosphate for Use in Soil Systems

AU - Mendez, Juan C.

AU - Hiemstra, Tjisse

PY - 2019/1/17

Y1 - 2019/1/17

N2 - Carbonate (CO3) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO3 and PO4 concentrations. The surface speciation of CO3 has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO3 occurs predominately via formation of bidentate inner-sphere complexes, either (=FeO)2CO or (=FeO)2CO··Na+. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO4. Additionally, a minor complex is present at high CO3 loadings. The CD model, solely parametrized by measuring the pH-dependent PO4 adsorption as a function of the CO3 concentration, successfully predicts the CO3 adsorption to Fh in single-ion systems. The adsorption affinity of CO3 to Fh is higher than to goethite, particularly at high pH and CO3 loadings due to the enhanced formation (=FeO)2CO··Na+. The PO4 adsorption isotherm in 0.5 M NaHCO3 can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO3 complex formation and resolved a new species (Fe(CO3)2(OH)2 3(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.

AB - Carbonate (CO3) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO3 and PO4 concentrations. The surface speciation of CO3 has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO3 occurs predominately via formation of bidentate inner-sphere complexes, either (=FeO)2CO or (=FeO)2CO··Na+. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO4. Additionally, a minor complex is present at high CO3 loadings. The CD model, solely parametrized by measuring the pH-dependent PO4 adsorption as a function of the CO3 concentration, successfully predicts the CO3 adsorption to Fh in single-ion systems. The adsorption affinity of CO3 to Fh is higher than to goethite, particularly at high pH and CO3 loadings due to the enhanced formation (=FeO)2CO··Na+. The PO4 adsorption isotherm in 0.5 M NaHCO3 can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO3 complex formation and resolved a new species (Fe(CO3)2(OH)2 3(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.

KW - CD model

KW - competition

KW - ferrihydrite

KW - goethite

KW - ion adsorption

KW - nanoparticles

KW - solubility

KW - surface complexation

U2 - 10.1021/acsearthspacechem.8b00160

DO - 10.1021/acsearthspacechem.8b00160

M3 - Article

AN - SCOPUS:85060143117

SN - 2472-3452

VL - 3

SP - 129

EP - 141

JO - ACS Earth and Space Chemistry

JF - ACS Earth and Space Chemistry

IS - 1

ER -

Carbonate Adsorption to Ferrihydrite: Competitive Interaction with Phosphate for Use in Soil Systems

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Keywords

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