Computer Science
Scientific paper
Nov 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52.2609c&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 52, Issue 11, pp.2609-2623
Computer Science
15
Scientific paper
Comparison of experimental and theoretical potentiometric titrations of kaolinite at 25°C indicates that the adsorption of H + and OH - ions to the mineral surface are metal cation specific and that the net adsorption can be modeled in terms of the constituent oxide components. We conclude, from the potentiometric, electrophoretic, and dissolution rate data presented in this paper, that the pH-dependence of the dissolution rates of slightly soluble oxide and silicate minerals is controlled by the adsorption of H + and OH - ions to specific metal cation surface reaction sites. The dissolution kinetics of corundum and -Al 2 O 3 at 2 °C and of kaolinite at 25°C and 60°C were studied as functions of solution pH. Corundum dissolution rates decrease from pH l to 8, are pH-independent from pH 8 to 9, and increase from pH 9 to 11. The dissolution rates are directly proportional to the adsorption of H + and OH - ions to the oxide surface. The rate equations are: k = 10 -12.75 C H s and K = 10 +24.50 ¦ C H s ¦ 4 at pH < pK a 1 (intr) and pH > pK a 2 (intr) respectively, where pK a 1 (intr) and pK a 2 (intr) are the -Al 2 O 3 intrinsic acidity constants. Three consecutive periods of dissolution are observed for kaolinite at 25°C and 60°C: an initial period of incongruent dissolution where A1 is preferentially removed over Si at pH < 6.0 and pH > 9.3 at 25°C and at pH < 4.5 and pH > 12 at 60°C, and the reverse occurs at pH > 6.0 and pH < 9.3 at 25°C, and at pH > 4.5 and pH < 12.0 at 60°C, a short-term high dissolution period, and a long-term steady-state period. At 25°C, the long-term dissolution is slightly incongruent up to 1000 hours, such that the Al dissolves at a faster rate than Si from pH 2 to 9. However, both the Al and Si rates decrease with increasing pH to pH 4, show little pH-dependence from pH 4-9, and increase with increasing pH in the alkaline pH region. At 60°C, the long-term steady-state dissolution is congruent. The rates decrease with increasing pH to pH 5, are pH-independent from pH 5-8, and increase with increasing pH at pH > 8. Kaolinite dissolution is a complex function of H + and OH - ion adsorption to > AlOH and > SiOH surface reaction sites.
Carroll-Webb Susan A.
Walther John V.
No associations
LandOfFree
A surface complex reaction model for the pH-dependence of corundum and kaolinite dissolution rates does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A surface complex reaction model for the pH-dependence of corundum and kaolinite dissolution rates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A surface complex reaction model for the pH-dependence of corundum and kaolinite dissolution rates will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1826031