TY - JOUR
T1 - Cu(II) adsorption at the calcite-water interface in the presence of natural organic matter
T2 - Kinetic studies and molecular-scale characterization
AU - Lee, Young J.
AU - Elzinga, Evert J.
AU - Reeder, Richard J.
N1 - Funding Information:
Support for this research was provided by NSF grants CHE0221934 (Center for Environmental Molecular Science) and EAR0207756. We thank the beamline personnel at X11A (NSLS), X18B (NSLS), and 12-BM (BESSRC, APS) where EXAFS data were collected for this research. We also thank David Hirschberg at Marine Sciences Research Center, SUNY-Stony Brook, for TOC analysis. We thank two anonymous reviewers, whose comments improved the final version of this manuscript.
PY - 2005/1/1
Y1 - 2005/1/1
N2 - We have characterized the adsorption of Suwannee River humic acid (SRHA) and Cu(II) on calcite from preequilibrated solutions at pH 8.25. Sorption isotherms of SRHA on calcite follow Langmuir-type behavior at SRHA concentrations less than 15 mg C L-1, whereas non-Langmuirian uptake becomes evident at concentrations greater than 15 mg C L-1. The adsorption of SRHA on calcite is rapid and mostly irreversible, with corresponding changes in electrostatic properties. At pH 8.25, Cu(II) uptake by calcite in the presence of dissolved SRHA decreases with increasing dissolved SRHA concentration, suggesting that formation of Cu-SRHA aqueous complexes is the primary factor controlling Cu(II) sorption at the calcite surface under the conditions of our experiments. We also observed that surface-bound SRHA has little influence on Cu(II) uptake by calcite, suggesting that Cu(II) coordinates to calcite surface sites rather than to surface-bound SRHA. Cu K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopic results show that the local coordination of Cu adsorbed at the calcite surface is very similar in the presence and absence of SRHA. Ca backscatterers at ∼3.90 Å indicate that Cu(II) forms tetragonally distorted inner-sphere adsorption complexes in both binary and ternary systems. Subtle differences in the XANES and EXAFS between binary sorption samples and ternary sorption samples, however, prevent us from ruling out the formation of ternary Cu-SRHA surface complexes. Our findings demonstrate that SRHA plays an important role in controlling the fate and transport of Cu(II) in calcite-bearing systems.
AB - We have characterized the adsorption of Suwannee River humic acid (SRHA) and Cu(II) on calcite from preequilibrated solutions at pH 8.25. Sorption isotherms of SRHA on calcite follow Langmuir-type behavior at SRHA concentrations less than 15 mg C L-1, whereas non-Langmuirian uptake becomes evident at concentrations greater than 15 mg C L-1. The adsorption of SRHA on calcite is rapid and mostly irreversible, with corresponding changes in electrostatic properties. At pH 8.25, Cu(II) uptake by calcite in the presence of dissolved SRHA decreases with increasing dissolved SRHA concentration, suggesting that formation of Cu-SRHA aqueous complexes is the primary factor controlling Cu(II) sorption at the calcite surface under the conditions of our experiments. We also observed that surface-bound SRHA has little influence on Cu(II) uptake by calcite, suggesting that Cu(II) coordinates to calcite surface sites rather than to surface-bound SRHA. Cu K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopic results show that the local coordination of Cu adsorbed at the calcite surface is very similar in the presence and absence of SRHA. Ca backscatterers at ∼3.90 Å indicate that Cu(II) forms tetragonally distorted inner-sphere adsorption complexes in both binary and ternary systems. Subtle differences in the XANES and EXAFS between binary sorption samples and ternary sorption samples, however, prevent us from ruling out the formation of ternary Cu-SRHA surface complexes. Our findings demonstrate that SRHA plays an important role in controlling the fate and transport of Cu(II) in calcite-bearing systems.
UR - http://www.scopus.com/inward/record.url?scp=11244318434&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2004.06.015
DO - 10.1016/j.gca.2004.06.015
M3 - Article
AN - SCOPUS:11244318434
SN - 0016-7037
VL - 69
SP - 49
EP - 61
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
IS - 1
ER -