skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies

Abstract

Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe{sub 2}O{sub 3}{center_dot}nH{sub 2}O, n=1-3) and HMO (MnO{sub 2}) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO{sub 6} (MnO{sub 6}) octahedra with Pb{single_bond}O distance of 2.25-2.35 Angstroms and Pb{single_bond}Fe(Mn) distances of 3.29-3.36 (3.65-3.76) Angstroms. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8x10{sup -3} to 1.5x10{sup -2}, loading 2.03x10{sup -4} to 9.1 x 10{sup -3} mol Pb/g, and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits short-range order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake ({approx}77%) followed by a slow intraparticle diffusion step ({approx}23%) resulting in a surface diffusivity of 2.5x10{sup -15} cm{sup 2}/s. Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
914129
Report Number(s):
BNL-78697-2007-JA
Journal ID: ISSN 0021-9797; JCISA5; TRN: US0801562
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Colloid Interface Sci.; Journal Volume: 299; Journal Issue: 1-3
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ADSORPTION; CRYSTALLIZATION; DIFFUSION; HEAVY METALS; IRON OXIDES; MANGANESE OXIDES; OXIDES; SORPTION; TRANSPORT; NSLS; national synchrotron light source

Citation Formats

Xu,Y., Boonfueng, T., Axe, L., Maeng, S., and Tyson, T. Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies. United States: N. p., 2006. Web. doi:10.1016/j.jcis.2006.01.041.
Xu,Y., Boonfueng, T., Axe, L., Maeng, S., & Tyson, T. Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies. United States. doi:10.1016/j.jcis.2006.01.041.
Xu,Y., Boonfueng, T., Axe, L., Maeng, S., and Tyson, T. Sun . "Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies". United States. doi:10.1016/j.jcis.2006.01.041.
@article{osti_914129,
title = {Surface Complexation of Pb(II) on Amorphous Iron Oxide and Manganese Oxide: Spectroscopic and Time Studies},
author = {Xu,Y. and Boonfueng, T. and Axe, L. and Maeng, S. and Tyson, T.},
abstractNote = {Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe{sub 2}O{sub 3}{center_dot}nH{sub 2}O, n=1-3) and HMO (MnO{sub 2}) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO{sub 6} (MnO{sub 6}) octahedra with Pb{single_bond}O distance of 2.25-2.35 Angstroms and Pb{single_bond}Fe(Mn) distances of 3.29-3.36 (3.65-3.76) Angstroms. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8x10{sup -3} to 1.5x10{sup -2}, loading 2.03x10{sup -4} to 9.1 x 10{sup -3} mol Pb/g, and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits short-range order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake ({approx}77%) followed by a slow intraparticle diffusion step ({approx}23%) resulting in a surface diffusivity of 2.5x10{sup -15} cm{sup 2}/s. Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction.},
doi = {10.1016/j.jcis.2006.01.041},
journal = {J. Colloid Interface Sci.},
number = 1-3,
volume = 299,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Pb(II) sorption on goethite and hematite powders was studied at room temperature as a function of pH (6-8), sorption density (2-10 {mu}moles/m{sup 2} ), and [Pb]{sub eq} (0.2 {mu}M - 1.2 mM) in 0.1 M NaNO{sub 3} electrolyte using XAFS spectroscopy. Pb(II) ions were found to be hydrolyzed and adsorbed as mononuclear bidentate complexes to edges of FeO{sub 6} octahedra on both goethite and hematite under all conditions. Hydrolysis of Pb(II) appears to be a primary source of proton release associated with surface complexation of Pb(II). A bond-valence model was used to relate the relative stabilities of iron-oxide surface functionalmore » groups and Pb(II) adsorption complexes to their structures and compositions. This combined approach suggests that Pb(II) adsorption occurs primarily at unprotonated [Fe {sub Fe}{sup Fe}(>)O{sup -{1/2}}] sites and at [Fe-OH{sub 2}{sup +}{sup +{1/2}}] sites. Several adsorption reactions are proposed. Comparison to EXAFS results from Pb(II) adsorption on aluminum oxides suggests that the edge lengths of surface AlO{sub 6} or FeO{sub 6} octahedra partially determine the reactivities and densities of available surface sites. The results of this study provide a basis for constructing chemically realistic descriptions of Pb(II) surface complexation reactions on Fe hydroxides. 46 refs., 7 figs., 4 tabs.« less
  • Pb(II) sorption on Al{sub 2}-O{sub 3} powders was studied as functions of sorption density (from 0.5 to 5.2 {mu}moles/m{sup 2}) and [Pb]{sub eq} (0.03-1.4 mM) in 0.1 M NaNO{sub 3} electrolyte solution using XAFS spectroscopy. At pH 6 and 7, Pb(II) ions were found to be fully hydrolyzed and adsorbed preferentially as mononuclear bidentate complexes to edges of AlO{sub 6} octahedra. At higher sorption densities ({Gamma} {ge}3.4 {mu}moles - m{sup -2}), XAFS results suggest the presence of dimeric Pb(II) surface complexes. A bond-valence model was used in conjunction with these results to constrain the compositions and reaction stoichiometries of adsorptionmore » complexes. We conclude that Pb(II) adsorption on alumina is attributable to complexation by [Al{sub Al}{sup Al}(>)O{sup -{1/2}}] and [Al-OH{sup -{1/2}}] surface functional groups. Several plausible Pb(II) adsorption reactions are proposed, based on these results, which provide a basis for chemically realistic descriptions of surface complexation of Pb(II) on aluminum oxides. 46 refs., 7 figs., 4 tabs.« less
  • Efficient sewage purification, flotation of minerals, etching of deposited scale, coprecipitation of hydroxides, and many other important problems require a detailed investigation of adsorption phenomena at the hydroxide-solution interface. Corrosion and protection of oxide phases and electrolysis with metal oxides used as the electrode can be added to the list of problems mentioned above. A large body of data on the adsorption of ions and chelating agents on oxides has been accumulated to date. In connection with the development of ideas on the structure of the ionic part of the electrical double layer at the oxide-solution interface, we deem itmore » important to consider and systematize the data on adsorption of the ions.« less
  • Carburization studies of a series of reduced iron-manganese catalysts were done under synthesis gas (H/sub 2//CO) conditions. Evidence was obtained for three types of carbon - carbidic, partially hydrogenated, and graphitic (coke-like carbon). These carbon types could be removed slowly with hydrogen; however, a relatively high temperature (500/sup 0/C) was needed to remove all carbon. The low manganese oxide-containing catalysts showed greater specific activity for carbon monoxide and hexene hydrogenation than iron. The high manganese catalysts exhibited significantly increased hexene hydrogenation activity, possibly due to the presence of very small iron crystallites. Incorporation of manganese appears to chemically or electronicallymore » promote the active iron surface. In particular, it appears to alter the CO hydrogen reaction path by suppressing the direct formation of paraffins from the reactive intermediate, leading to higher olefins. 30 refs., 5 figs., 3 tabs.« less
  • The triple-layer model of the oxide/water interface can be used to calculate the partitioning of metals among solid and aqueous phases. The defensible use of the triple-layer model in groundwater/sediment systems requires an adequate and consistent set of intrinsic adsorption constants. In the present study, published values of p{sup *}K{sup int} for cation adsorption on iron and manganese oxides have been used to calculate values for surface complexation constants (log K{sup SC}) via log K{sub M(OH)n}{sup SC} = pK{sub a2}{sup int} - p{sup *}K{sub M(OH)n}{sup int} - log {beta}{sub 1n} where pK{sub a2}{sup int} is the intrinsic acidity constant andmore » {beta}{sub 1n} is the nth cation hydrolysis constant. This transformation reduced the variation between log K{sup SC} values determined by different investigators. Uncertainties in acidity constants and variations in site loading with adsorbing metal are the major sources of variation in the values of p{sup *}K{sup int}. In addition, ionic strength can affect the values of p{sup *}K{sup int} for strongly adsorbed cations. Predictive equations based on ion size and hydrolysis behavior have been derived and missing values of p{sup *}K{sup int} for important pollutant metals predicted. Although these equations do not explicitly account for variations in ionic strength and surface loading, they are useful for predicting values of p{sup *}K{sup int} with uncertainties of 0.5-0.8 ({alpha}-FeOOH) and 0.4-1.5 log units ({delta}-MnO{sub 2}). Recently published K{sup SC} values validate the predictive equation developed for the first and second hydrolysis products of thorium. A data base of p{sup *}K{sup int} values is presented in which the variability in pK{sub a2}{sup int} values are removed and missing values estimated.« less