Calcium adsorption at the rutile-water interface: A potentiometric study in NaCl media to 250 C

Journal Article · Fri Oct 01 04:00:00 EDT 1999 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(99)00236-7· OSTI ID:20003967

Ridley, M K; Machesky, M L; Wesolowski, D J; Palmer, D A

Calcium adsorption by rutile was studied potentiometrically from 25 to 250 C, at ionic strengths of 0.03 and 0.30 m in NaCl media, using two complementary experimental methodologies. In the first, net proton adsorption in the presence and absence of Ca{sup 2+} was monitored, and in the second, samples were periodically withdrawn during the course of a titration to determine Ca{sup 2+} adsorption directly. These experiments revealed that Ca{sup 2+} adsorption systematically increased with temperature relative to the pH of zero net proton charge in NaCl media alone (pH{sub znpc(NaCl)} - pH). That is, as temperature increased, Ca{sup 2+} adsorption commenced at progressively more positive pH{sub znpc(NaCl)} - pH values. Increasing ionic strength from 0.03 to 0.30 m NaCl suppressed Ca{sup 2+} adsorption at all temperatures as a result of either increased competition from Na{sup +} or greater complexation of Ca{sup 2+} by Cl{sup {minus}}. Finally, there was no apparent trend in the proton stoichiometric ratios (moles H{sup +} released/moles Ca{sup 2+} adsorbed) with increasing temperature. This suggests that the electrostatic and/or chemical processes involved in Ca{sup 2+} adsorption do not change greatly with increasing temperature. Favorable entropic effects, related to the increasing ease of releasing Ca{sup 2+} waters of hydration, are believed to be primarily responsible for the increase in adsorption with temperature.

• Research Organization: Illinois State Water Survey, Champaign, IL (US)
• Sponsoring Organization: National Science Foundation; Illinois State Water Survey; Illinois Department of Natural Resources; Department of Energy
• DOE Contract Number: AC05-96OR22464
• OSTI ID: 20003967
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 19-20 Vol. 63; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ADSORPTION
CALCIUM
INTERFACES
POTENTIOMETRY
RUTILE
SODIUM CHLORIDES
TEMPERATURE DEPENDENCE
WATER