Potentiometric titrations of rutile suspensions to 250 C

Journal Article · Wed Apr 15 00:00:00 EDT 1998 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1997.5401· OSTI ID:616334

Machesky, M L ^[1]; Wesolowski, D J; Palmer, D A ^[2]; Ichiro-Hayashi, Ken ^[3]

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1. Illinois State Water Survey, Champaign, IL (United States)
2. Oak Ridge National Lab., TN (United States). Chemical and Analytical Sciences Div.
3. Tohoku Univ., Sendai (Japan). Inst. of Mineralogy, Petrology and Economic Geology

A stirred hydrogen electrode concentration cell was used to conduct potentiometric titrations of rutile suspensions from 25 to 250 C in NaCl and tetramethylammonium chloride media (0.03 to 1.1 m). Hydrothermal pretreatment of the rutile improved titration reproducibility, decreased titration hysteresis, and facilitated determination of the point of zero net proton charge (pHznpc). These pHznpc values are 5.4, 5.1, 4.7, 4.4, 4.3 ({+-} 0.2 pH units), and 4.2 ({+-} 0.3 pH units) at 25, 50, 100, 150, 200, and 250 C, respectively. The difference between these pHznpc values and 1/2 pK{sub w} (the neutral pH of water) is rather constant between 25 and 250 C ({minus} 1.45 {+-} 0.2). This constancy is useful for predictive purposes and, more fundamentally, may reflect similarities between the hydration behavior of surface hydroxyl groups and water. A three-layer, 1pKa surface complexation model with three adjustable parameters (two capacitance values and one counterion binding constant) adequately described all titration data. The most apparent trend in these data for pH values greater than the pHznpc was the increase in proton release (negative surface charge) with increasing temperature. This reflects more efficient screening by Na{sup +} relative to Cl{sup {minus}}. Replacing Na{sup +} with the larger tetramethylammonium cation for some conditions resulted in decreased proton release due to the less efficient screening of negative surface charge by this larger cation.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-96OR22464
• OSTI ID: 616334
• Journal Information: Journal of Colloid and Interface Science, Vol. 200, Issue 2; Other Information: PBD: 15 Apr 1998
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
RUTILE
POTENTIOMETRY
SODIUM CHLORIDES
AMMONIUM CHLORIDES
EXPERIMENTAL DATA
ADSORPTION
SORPTIVE PROPERTIES