Computer Science
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58..661o&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 2, pp.661-669
Computer Science
9
Scientific paper
The dissolution kinetics of three plagioclase feldspars (An 13 , An 46 , and An 76 ) were studied in flow-through reactors over the pH range 3-7. In accordance with the surface complexation model, dissolution rate was described by the equation , where ( C h s ) is the concentration of protonated surface sites, x a is the mole fraction of these that are activated, A is the Arrhenius pre-exponential factorand E a is the activation energy for the reaction. The reaction order with respect to surface charge ( n ) at pH < 5 is a function of mineral composition, and increases with increasing anorthite content. Orders of 0.46, 1.2, and 2.0 are obtained for oligoclase, andesine, and bytownite, respectively. This indicates that the reaction intermediate is more highly protonated in feldspars of higher aluminum content. The nonintegral reaction orders obtained demonstrate the importance of several surface species in the dissolution reaction. Reaction rates increase with increasing anorthite content. In acid solution this reflects the linear dependence of E a on the number of Al-O-Si bonds involved in the rate-determining step. Under conditions of low surface protonation (in near-neutral solutions), dissolution is independent of surface charge. As reaction occurs at neutral alumina sites, the rate is approximately proportional to the anorthite (Al) content of the feldspar.
Drever James I.
Oxburgh Rachel
Sun Yan-Ting
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