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Competitive surface complexation of o-phthalate and phosphate on goethite (alpha-FeOOH) particles

Nilsson, N.; Persson, Per LU ; Lovgren, L. and Sjoberg, S. (1996) In Geochimica et Cosmochimica Acta 60. p.4385-4395
Abstract
Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate and phthalate at the goethite-water interface have been studied in 0.1 M Na(NO3) media at 298.2 K within the range 3.0 < -log [H+] < 8.5. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate and phthalate analyses. The binary and ternary chemical subsystems H+-goethite and H+-goethite-H2PO4- have been investigated earlier and described according to the constant capacitance model. The adsorption of phthalate showed a strong ionic strength dependence which indicated that phthalate is adsorbed as outer-sphere complexes. The experimental data in the subsystem H+-goethite-phthalate... (More)
Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate and phthalate at the goethite-water interface have been studied in 0.1 M Na(NO3) media at 298.2 K within the range 3.0 < -log [H+] < 8.5. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate and phthalate analyses. The binary and ternary chemical subsystems H+-goethite and H+-goethite-H2PO4- have been investigated earlier and described according to the constant capacitance model. The adsorption of phthalate showed a strong ionic strength dependence which indicated that phthalate is adsorbed as outer-sphere complexes. The experimental data in the subsystem H+-goethite-phthalate were evaluated on the basis of an extended constant capacitance model with the aid of the computer program FITEQL, version 2.0. One plane for inner sphere complexation and one plane for outer-sphere complexation, each with an associated constant capacitance, were included in the extended constant capacitance model. Surface complexation of phthalate is described by two outer-sphere complexes, =FeOH(2)(+)L(2-) and =FeOH(2)(+)HL(-). In the experiments with simultaneous complexation of phosphate and phthalate, the complexation of phosphate was not influenced by the presence of phthalate. On the other hand, the complexation of phthalate was decreased even at low phosphate concentrations. The equilibrium models determined for the subsystems were used to predict the adsorption of phosphate and phthalate in the quaternary system. It was found that these predictions were in good agreement with experimental titration and phosphate/phthalate adsorption data. Diffuse reflectance IR-spectra were recorded to obtain structural information of the phthalate complexes. The spectroscopic data did not contradict the outer-sphere model. However, because of the complexity of the phthalate molecule conclusive structural assignment could not be made. (Less)
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Contribution to journal
publication status
published
subject
in
Geochimica et Cosmochimica Acta
volume
60
pages
4385 - 4395
publisher
Elsevier
external identifiers
  • scopus:0030441606
ISSN
0016-7037
DOI
10.1016/S0016-7037(96)00258-X
language
English
LU publication?
no
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5484c7a2-eb6f-4456-b560-2af0526c94dd (old id 4332680)
date added to LUP
2014-03-04 09:44:05
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2017-06-25 03:27:32
@article{5484c7a2-eb6f-4456-b560-2af0526c94dd,
  abstract     = {Complexation of o-phthalate (1,2-benzenedicarboxylate) and competitive complexation of phosphate and phthalate at the goethite-water interface have been studied in 0.1 M Na(NO3) media at 298.2 K within the range 3.0 &lt; -log [H+] &lt; 8.5. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate and phthalate analyses. The binary and ternary chemical subsystems H+-goethite and H+-goethite-H2PO4- have been investigated earlier and described according to the constant capacitance model. The adsorption of phthalate showed a strong ionic strength dependence which indicated that phthalate is adsorbed as outer-sphere complexes. The experimental data in the subsystem H+-goethite-phthalate were evaluated on the basis of an extended constant capacitance model with the aid of the computer program FITEQL, version 2.0. One plane for inner sphere complexation and one plane for outer-sphere complexation, each with an associated constant capacitance, were included in the extended constant capacitance model. Surface complexation of phthalate is described by two outer-sphere complexes, =FeOH(2)(+)L(2-) and =FeOH(2)(+)HL(-). In the experiments with simultaneous complexation of phosphate and phthalate, the complexation of phosphate was not influenced by the presence of phthalate. On the other hand, the complexation of phthalate was decreased even at low phosphate concentrations. The equilibrium models determined for the subsystems were used to predict the adsorption of phosphate and phthalate in the quaternary system. It was found that these predictions were in good agreement with experimental titration and phosphate/phthalate adsorption data. Diffuse reflectance IR-spectra were recorded to obtain structural information of the phthalate complexes. The spectroscopic data did not contradict the outer-sphere model. However, because of the complexity of the phthalate molecule conclusive structural assignment could not be made.},
  author       = {Nilsson, N. and Persson, Per and Lovgren, L. and Sjoberg, S.},
  issn         = {0016-7037},
  language     = {eng},
  pages        = {4385--4395},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {Competitive surface complexation of o-phthalate and phosphate on goethite (alpha-FeOOH) particles},
  url          = {http://dx.doi.org/10.1016/S0016-7037(96)00258-X},
  volume       = {60},
  year         = {1996},
}