Kinetics of selenate and selenite adsorption/desorption at the goethite/water interface

Journal Article · Sat Dec 01 04:00:00 EST 1990 · Environmental Science and Technology; (USA)

DOI:https://doi.org/10.1021/es00082a010· OSTI ID:5928736

Zhang, Pengchu; Sparks, D L ^[1]

---

1. Univ. of Delaware, Newark (USA)

Kinetics and mechanisms of selenate and selenite adsorption/desorption at the goethite/water interface were studied by using pressure-jump (p-jump) relaxation with conductivity detection at 298.15 K. A single relaxation was ascribed to SeO{sub 4}{sup 2{minus}} on a surface site through electrostatic attraction accompanied simultaneously by a protonation process. The intrinsic rate constant for adsorption (log k{sub 1}{sup int} = 8.55) was much larger than that for desorption (log k{sub 1{minus}}{sup int} = 0.52). The intrinsic equilibrium constant obtained from the kinetic study (log K{sub kinetic}{sup int} = 8.02) was of the same order of magnitude as that obtained from the equilibrium study (log K{sub model}{sup int} = 8.65). Unlike SeO{sub 4}{sup 2{minus}}, selenite adsorption on goethite produced two types of complexes, XHSeO{sub 3}{sup 0} and XSeO{sub 3}{sup {minus}}, via a ligand-exchange mechanism. Double relaxations were attributed to two reaction steps. The first step was the formation of an outer-sphere surface complex through electrostatic attraction. In the second step, the adsorbed selenite ion replaced a H{sub 2}O from the protonated surface hydroxyl group and formed an inner-sphere surface complex.

• OSTI ID: 5928736
• Journal Information: Environmental Science and Technology; (USA), Journal Name: Environmental Science and Technology; (USA) Vol. 24:12; ISSN ESTHA; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
540320 -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (1990-)
ADSORPTION
CHROMATOGRAPHY
DATA
DESORPTION
EXPERIMENTAL DATA
GOETHITE
HYDROGEN COMPOUNDS
INFORMATION
ION EXCHANGE CHROMATOGRAPHY
KINETICS
MEASURING METHODS
MINERALS
NUMERICAL DATA
OXIDE MINERALS
OXYGEN COMPOUNDS
REACTION KINETICS
SELENATES
SELENITES
SELENIUM COMPOUNDS
SEPARATION PROCESSES
SORPTION
WATER