The rate of sulfide oxidation by [sigma]MnO[sub 2] in seawater

Conference · Thu Jul 01 00:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:5975650

Yao, W; Millero, F J ^[1]

---

1. Univ. of Miami, FL (United States)

The rate of oxidation of hydrogen sulfide by manganese dioxide in seawater was determined as a function of pH (2.0-9.0), temperature (5-45[degrees]C), and ionic strength (0.4M). The overall rate constant, k, in seawater at pH = 8.17 was found to be first order with respect to both sulfide and manganese dioxide: [minus]d[H[sub 2]S][sub t]/dt = k[H[sub 2]S][sub t][MnO[sub 2]]. The rate constant, k, for seawater (S = 35.8, pH = 8.17) at 25[degrees]C was found to be 436 M[sup [minus]1] min[sup [minus]1], or 0.0244 m[sup [minus]2] 1 min[sup [minus]1] when [MnO[sub 2]] is expressed in surface area (m[sup 2]/L). The energies of activation were found to be 14 [+-] 1 KJ mol[sup [minus]1] and 10 [+-] 1 KJ mol[sup [minus]1], respectively, for pH = 8.2 and pH = 5.0 in seawater (S = 35). The rate increased from pH 2.0 to a maximum at a pH of about 5.0 and decreased at higher pH. This pH dependence was attributed to formation of a surface complex between >MnO[sup [minus]] and H[sub 2]S. As the concentrations of HS[sup [minus]] increases above pH = 5 the rate of the reaction decreases. The rate of sulfide oxidation by MnO[sub 2] is not strongly dependent on ionic strength. The rates in 0.57 M NaCl were found to be slightly higher than the rates in seawater. Measurements made in solutions of the major sea salts indicated that Ca[sup 2+] and Mg[sup 2+] caused the rates to decrease, apparently by absorbing on the surface of manganese dioxide. Measurements made in artificial seawater (Na[sup +], Mg[sup 2+], Ca[sup 2+], Cl[sup [minus]], and SO[sub 4][sup 2[minus]]) were found to be in good agreement with the measurements in actual seawater. Phosphate was found to inhibit the reaction significantly.

• OSTI ID: 5975650
• Report Number(s): CONF-911017-; CODEN: GCACAK
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 57:14; Conference: Annual meeting and exhibition of the Geological Society of America (GSA), San Diego, CA (United States), 21-23 Oct 1991; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROGEN SULFIDES
OXIDATION
MANGANESE OXIDES
CHEMICAL REACTIONS
CHEMICAL REACTION KINETICS
IONIC COMPOSITION
PH VALUE
SEAWATER
SULFUR CYCLE
TEMPERATURE DEPENDENCE
CHALCOGENIDES
HYDROGEN COMPOUNDS
KINETICS
MANGANESE COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
WATER
540310* - Environment
Aquatic- Basic Studies- (1990-)
400201 - Chemical & Physicochemical Properties