The use of a surface complexation model to describe the kinetics of ligand-promoted dissolution of anorthite

Journal Article · Wed Nov 30 23:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90146-9· OSTI ID:5077544

Amrhein, C; Suarez, D L ^[1]

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1. Salinity Laboratory, Riverside, CA (USA)

The dissolution of anorthite (CaAl{sub 2}Si{sub 2}O{sub 8}) in the presence of fluoride and oxalate was studied under controlled pH and CO{sub 2} conditions. The dissolution of anorthite in the absence of complex-forming ligands was nearly pH independent between pH 5 and 9. The presence of complex-forming ligands resulted in a dissolution rate that increased linearly with decreasing solution pH. The dissolution data were modeled using the theory that the reaction rate is proportional to the surface concentration of activated sites. Surface activated sites are formed by the adsorption of protons and complexing ligands. On anorthite, the proton-promoted activated sites are probably Si centered and the ligand-promoted activated sites Al centered. Two surface chemistry models were combined in order to describe the overall reaction. At pH values less than 4.2, the rate of the proton-promoted dissolution was linearly proportional to {Gamma}{sup 4}, where {Gamma} is the surface concentration of adsorbed protons. The rate of the ligand-promoted dissolution was found to be linearly related to the surface concentration of adsorbed protons. The rate of the ligand-promoted dissolution was found to be linearly related to the surface concentration of adsorbed ligand. These findings suggest that for most natural systems, pH and complexing ligands have a synergistic effect on feldspar dissolution. The observation in nature that Ca-rich plagioclase feldspars are less resistant to weathering than Na-rich feldspars can be attributed to the increased reactivity of organic ligands towards Ca-rich feldspars. The increased reactivity is attributed to the higher proportion of Al in the Ca-feldspars.

• OSTI ID: 5077544
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:12; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANORTHITE
BIOGEOCHEMISTRY
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHELATES
CHELATING AGENTS
CHEMICAL REACTION KINETICS
CHEMISTRY
COMPLEXES
CONCENTRATION RATIO
DISSOLUTION
FELDSPARS
GEOCHEMISTRY
KINETICS
LIGANDS
MATHEMATICAL MODELS
MINERALS
MOLECULAR MODELS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
POTENTIALS
REACTION KINETICS
SILICATE MINERALS
SOLUTES
SORPTIVE PROPERTIES
SURFACE POTENTIAL
SURFACE PROPERTIES
SYNERGISM
THERMODYNAMIC ACTIVITY
WEATHERING