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

Author:
  • N. Nilsson
  • Per Persson
  • L. Lovgren
  • S. Sjoberg
Publishing year: 1996
Language: English
Pages: 4385-4395
Publication/Series: Geochimica et Cosmochimica Acta
Volume: 60
Document type: Journal article
Publisher: Elsevier
Additional info: 22

Abstract english

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.

Keywords

  • Earth and Related Environmental Sciences

Other

Published
  • ISSN: 0016-7037
Per Persson
E-mail: per [dot] persson [at] biol [dot] lu [dot] se

Professor

MEMEG

+46 46 222 17 96

+46 70 266 38 79

E-C350

50

Professor

Centre for Environmental and Climate Research (CEC)

+46 46 222 17 96

+46 70 266 38 79

D350

Ekologihuset, Sölvegatan 37, Lund

50