Kinetics and mechanisms of sulfate adsorption/desorption on goethite using pressure-jump relaxation

Journal Article · · Soil Science Society of America Journal; (United States)

DOI:https://doi.org/10.2136/sssaj1990.03615995005400050011x· OSTI ID:5466911

Zhang, Peng Chu; Sparks, D L ^[1]

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1. Univ. of Delaware, Newark (USA)

Sulfate adsorption/desorption on goethite (FeOOH) in aqueous suspension was investigated thermodynamically and kinetically. The SO{sub 4}-adsorption isotherm indicated that adsorption decreased with increased pH of the goethite suspension. The triple-layer model fit the experimental data well when adsorbed SO{sub 4} was assumed to be located at the {beta} plane and held via outer-sphere complexation. Pressure-jump relaxation was used to determine the kinetics of SO{sub 4} adsorption/desorption processes. Based on the equilibrium and kinetic studies, the authors hypothesized and tested two reaction mechanisms for SO{sub 4} retention. The first postulated mechanism (Reaction 1) assumed that SO{sub 4} was adsorbed on a positively charged surface site through electrostatic attraction. This mechanism was rejected because of the poor conformity between the intrinsic equilibrium constant (K{sub eq}{sup int}) determined from the static studies and that found from the ratio of forward (k{sub 1}{sup int}) and backward (k{sub {minus}1}{sup int}) rate constants, i.e., K{sub 1}{sup int} = k{sub 1}{sup int}/k{sub {minus}1}{sup int}. It was found that the adsorption of SO{sub 4} on goethite occurred simultaneously with the protonation of a neutral surface site, as assumed in the second hypothesized mechanism (Reaction 2). Based on this mechanism, a linear relationship between the reciprocal relaxation time ({tau}{sup {minus}1}) and various concentration terms was observed. From this relationship, k{sub 2}{sup int} and k{sub {minus}2}{sup int} were calculated and were 2.02 {times} 10{sup 8} mol{sup {minus}2}L{sup 2}s{sup {minus}1} and 0.144 s{sup {minus}1}, respectively. The intrinsic equilibrium constant from kinetic measurements (K{sub 2}{sup int}) was 10{sup 9.14} mol{sup {minus}2}L{sup 2}, which was similar to the intrinsic equilibrium constant from the equilibrium studies, 10{sup 9.60}.

• OSTI ID: 5466911
• Journal Information: Soil Science Society of America Journal; (United States), Journal Name: Soil Science Society of America Journal; (United States) Vol. 54:5; ISSN SSSJD; ISSN 0361-5995
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
ADSORPTION
ADSORPTION ISOTHERMS
DESORPTION
DISSOLUTION
GOETHITE
ISOTHERMS
LEACHING
MATHEMATICAL MODELS
MINERALS
OXIDE MINERALS
OXYGEN COMPOUNDS
SEPARATION PROCESSES
SORPTION
SORPTIVE PROPERTIES
SULFATES
SULFUR COMPOUNDS
SURFACE PROPERTIES
THERMODYNAMICS