Reaction of hydroquinine with hematite II. Calculated electron-transfer rates and comparison to the reductive dissolution rate.

Journal Article · Thu Jan 01 04:00:00 EST 2004 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1016/j.jcis.2004.01.001· OSTI ID:1007856

Stack, Andrew G ^[1]; Rosso, Kevin M ^[1]; Smith, Dayle ^[2]; Eggleston, Carrick M ^[1]

---

1. ORNL
2. Whitman College

The rate of reaction of hematite with quinones and the quinone moieties of larger molecules may be an important factor in limiting the rate of reductive dissolution of hematite, especially by iron-reducing bacteria. It is possible that the rate of reductive dissolution of hematite in the presence of excess hydroquinone at pH 2.5 may be limited by the electron-transfer rate. Here, a reductive dissolution rate was measured and compared to electron-transfer rates calculated using Marcus theory. An experimental rate constant was measured at 9.5 x 10{sup -6} s{sup -1} and the reaction order with respect to the hematite concentration was found to be 1.1. Both the dissolution rate and the reaction order of hematite concentration compare well with previous measurements. Of the Marcus theory calculations, the inner-sphere part of the reorganization energy and the electronic coupling matrix element for hydroquinone self-exchange electron transfer are calculated using ab initio methods. The second order self-exchange rate constant was calculated to be 1.3 x 10{sup 7} M{sup -1} s{sup -1}, which compares well with experimental measurements. Using previously published data calculated for hexaquairon(III)/(II), the calculated electron-transfer rate for the cross reaction with hydroquinone also compares well to experimental measurements. A hypothetical reductive dissolution rate is calculated using the first-order electron-transfer rate constant and the concentration of total adsorbed quinone. Three different models of the hematite surface are used as well as multiple estimates for the reduction potential, the surface charge, and the adsorption density of hydroquinone. No calculated dissolution rate is less than five orders of magnitude faster than the experimentally measured one.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1007856
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 274; ISSN 0021-9797
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ADSORPTION
BACTERIA
BIODEGRADATION
DISSOLUTION
ELECTRON TRANSFER
HEMATITE
KINETIC EQUATIONS
QUINONES
REACTION KINETICS
REDUCTION