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Environmental fate & pathways

Adsorption / desorption

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adsorption / desorption
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study

Data source

Reference Type:
Silicate and Phosphate Adsorption on Gibbsite Studied by X-ray Photoelectron Spectroscopy Angular Distributions
Alvarez, Robustiano., Charles S. Fadley, and James A. Silva
Bibliographic source:
Soil Sci Soc Am J 1980 44: 422-425.

Materials and methods

Test guideline
no guideline followed
Type of method:
batch equilibrium method
other: synthetic gibbsite

Test material

Constituent 1
Reference substance name:
EC Number:
EC Name:
Cas Number:
orthosilicic acid

Study design

Batch equilibrium or other method

Analytical monitoring:
not required
Details on test conditions:
The adsorbent chosen for this study was solid A1(OH)3 powder with a surface area of 9.7 m2/g as measured by the BET method. The adsorbates were aqueous solutions of Si(OH)4 (75 ppm Si) CaSiO3 (75 ppm Si), , Ca(NO3)2 (0.005M), and Ca(H2PO4)2 (0.01M). The gibbsite was
shaken with unbuffered solutions of the adsorbates for three hours and allowed to equilibrate for 8 hours then was separated by filtration through a Buchner funnel, and the remaining solid leached with a relatively large volume of water [solid to water ratio = 1:50]. Most of the more
weakly bonded adsorbate species would be removed from the gibbsite surface by this leaching. The solid samples were then dried for eight hours at 55°C at atmospheric pressure and subsequently pressed into small wafers. Examination of the surfaces of these wafers was carried out with a
Hewlett Packard 5950A ESCA spectrometer capable of an instrumental resolution of —0.5 eV. The pressure in the spectrometer chamber during these measurements was ~10"8 torr.
Duration of adsorption equilibration
11 h

Results and discussion

Applicant's summary and conclusion

Executive summary:

Summary of observations:

1) No Si was detected on the A1(OH)3 surface in the Si(OH)4 treatment which suggests weak adsorption of Si on gibbsite in the absence of Ca.

2) When CaSiO3 was the adsorbate, both Ca and Si were detected on the adsorbent surface with an approximate Ca/Si ratio of 1/8.

3) Ca and P were both present on the adsorbent after Ca(H2PO4)2 treatment.

4) Atomic concentration ratio estimates calculated from peak intensities, kinetic energies, and photoelectron cross-sections, showed that Ca/Si exceeds Ca/P on the alumina surface.