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Title: Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength

Abstract

The sorption of divalent strontium, Sr{sup 2+}, and divalent lead, Pb{sup 2+}, on zeolitized tuffs from the Nevada Test Site (NTS) was investigated using macroscopic batch sorption experiments and x-ray absorption spectroscopy (XAS) as a function of geochemical parameters, including pH, ionic strength, and type of background electrolyte. The sorption of Sr{sup 2+} is dependent on the ionic strength of the medium and independent of pH, suggesting that Sr{sup 2+} sorption is controlled by ion exchange at permanent charge sites. At higher ionic strengths, background electrolyte cations compete effectively with Sr{sup 2+} for cation exchange sites and Sr{sup 2+} sorption is suppressed. At the two lower ionic strengths (0.01 and 0.1 M), Pb{sup 2+} sorption is also consistent with adsorption by cation exchange. At the highest ionic strength (1.0 M), however, exclusion of Pb{sup 2+} from cation exchange sites resulted in pH dependent adsorption, consistent with sorption on amphoteric surface hydroxyl sites or formation of surface precipitates. XAS was used to test these hypotheses. Based on XAS data, Sr{sup 2+} formed hydrated surface complexes coordinated with approximately eight oxygen atoms at an average distance of 2.60 ({+-}0.02) {angstrom}, regardless of conditions, consistent with the formation of mononuclear, outer-sphere surface complexesmore » at the Ca2 site in the B channel of clinoptilolite. The coordination environment of sorbed Pb{sup 2+} was more complex and a function of pH and ionic strength. The first shell consisted of two to three oxygen atoms at an average distance of 2.20 ({+-}0.02) {angstrom}. At low pH and ionic strength, XAS data were consistent with Pb{sup 2+} adsorption at the Na1 and Ca2 cation exchange sites in channels A and B of clinoptilolite, respectively. At the highest ionic strength (1.0 M) and low pH, XAS provides evidence for formation of Pb{sup 2+} monodentate, corner-sharing inner-sphere complexes, while at higher pH, XAS analysis is consistent with formation of edge-sharing bidentate inner-sphere complexes. As surface coverage increased, appearance of a second Pb{sup 2+} peak suggests the formation of polynuclear, inner-sphere surface complexes. These results have significant implications for the transport of radionuclides and other contaminants at the NTS and other nuclear test sites and the modeling of these processes.« less

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Lab., Richland, WA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15006236
Report Number(s):
PNWD-SA-6288
Journal ID: ISSN 0003-004X; AMMIAY; TRN: US200503%%270
DOE Contract Number:  
AC06-76RL01830
Resource Type:
Journal Article
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 88; Journal Issue: 11-12 Pt.2; Other Information: PBD: 1 Nov 2003; Journal ID: ISSN 0003-004X
Country of Publication:
United States
Language:
English
Subject:
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; ABSORPTION SPECTROSCOPY; ADSORPTION; ATOMS; CATIONS; CLINOPTILOLITE; ELECTROLYTES; ION EXCHANGE; NEVADA TEST SITE; NUCLEAR TEST SITES; OXYGEN; RADIOISOTOPES; SIMULATION; SORPTION; STRONTIUM; TRANSPORT; XAS, SR, PB, SORPTION, NTS

Citation Formats

Um, Wooyong, and Papelis, Charalambos. Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength. United States: N. p., 2003. Web. doi:10.2138/am-2003-11-1247.
Um, Wooyong, & Papelis, Charalambos. Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength. United States. doi:10.2138/am-2003-11-1247.
Um, Wooyong, and Papelis, Charalambos. Sat . "Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength". United States. doi:10.2138/am-2003-11-1247.
@article{osti_15006236,
title = {Sorption mechanisms of Sr and Pb on zeolitized tuffs from the Nevada test site as a function of pH and ionic strength},
author = {Um, Wooyong and Papelis, Charalambos},
abstractNote = {The sorption of divalent strontium, Sr{sup 2+}, and divalent lead, Pb{sup 2+}, on zeolitized tuffs from the Nevada Test Site (NTS) was investigated using macroscopic batch sorption experiments and x-ray absorption spectroscopy (XAS) as a function of geochemical parameters, including pH, ionic strength, and type of background electrolyte. The sorption of Sr{sup 2+} is dependent on the ionic strength of the medium and independent of pH, suggesting that Sr{sup 2+} sorption is controlled by ion exchange at permanent charge sites. At higher ionic strengths, background electrolyte cations compete effectively with Sr{sup 2+} for cation exchange sites and Sr{sup 2+} sorption is suppressed. At the two lower ionic strengths (0.01 and 0.1 M), Pb{sup 2+} sorption is also consistent with adsorption by cation exchange. At the highest ionic strength (1.0 M), however, exclusion of Pb{sup 2+} from cation exchange sites resulted in pH dependent adsorption, consistent with sorption on amphoteric surface hydroxyl sites or formation of surface precipitates. XAS was used to test these hypotheses. Based on XAS data, Sr{sup 2+} formed hydrated surface complexes coordinated with approximately eight oxygen atoms at an average distance of 2.60 ({+-}0.02) {angstrom}, regardless of conditions, consistent with the formation of mononuclear, outer-sphere surface complexes at the Ca2 site in the B channel of clinoptilolite. The coordination environment of sorbed Pb{sup 2+} was more complex and a function of pH and ionic strength. The first shell consisted of two to three oxygen atoms at an average distance of 2.20 ({+-}0.02) {angstrom}. At low pH and ionic strength, XAS data were consistent with Pb{sup 2+} adsorption at the Na1 and Ca2 cation exchange sites in channels A and B of clinoptilolite, respectively. At the highest ionic strength (1.0 M) and low pH, XAS provides evidence for formation of Pb{sup 2+} monodentate, corner-sharing inner-sphere complexes, while at higher pH, XAS analysis is consistent with formation of edge-sharing bidentate inner-sphere complexes. As surface coverage increased, appearance of a second Pb{sup 2+} peak suggests the formation of polynuclear, inner-sphere surface complexes. These results have significant implications for the transport of radionuclides and other contaminants at the NTS and other nuclear test sites and the modeling of these processes.},
doi = {10.2138/am-2003-11-1247},
journal = {American Mineralogist},
issn = {0003-004X},
number = 11-12 Pt.2,
volume = 88,
place = {United States},
year = {2003},
month = {11}
}