Title

The rates of oxidation of reduced sulfur compounds in seawater

Date of Award

1991

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine and Atmospheric Chemistry

First Committee Member

Frank J. Millero, Committee Chair

Abstract

This dissertation is focused on the thermodynamics and kinetics of the sulfite and sulfide system in seawater. Both laboratory and field studies were made on the effect of ionic interactions between metal and sulfur species on the rate of oxidation.The first study was the effect of metals (Na, Mg, Ni, Co, Mn and Cd) on the ionization of H$\sb2$SO$\sb3$. The results have been treated using both the ion pairing and Pitzer specific interaction models.The second study was the determination of stability constants for metal sulfide complexes using square wave voltammetry technique. The stability constants for Cu, Pb, Zn, Fe, Co, Ni and Mn with HS$\sp-$ represent the first detailed studies on these complexes in seawater.In the kinetic studies the oxidation of sulfite in seawater were measured as a function of pH, temperature and salinity. The rate is second and half order with respect to sulfite and oxygen, respectively. The effect of pH on the rates was attributed to the rate determining step involving the combination of HSO$\sb3\sp-$ and SO$\sb3\sp{2-}$. Mn$\sp{2+}$ was found to increase the rates. Additions of Fe$\sp{3+}$ and Fe$\sp{2+}$ have a catalytic effect only before they hydrolyze.The effect of metals on the oxidation of H$\sb2$S has been studied in seawater. Below 100 nM, none of the metals except Fe$\sp{2+}$ affect the rate of oxidation. At higher concentrations the rates increase for all the metals except Zn$\sp{2+}$.The major products formed from the oxidation of H$\sb2$S were SO$\sb3\sp{2-}$, S$\sb2$O$\sb3\sp{2-}$ and SO$\sb4\sp{2-}$. Product distribution predicted by a overall model agree with the measured concentrations.Field measurements were made in the Cariaco Trench. In the anoxic waters of the Trench, SO$\sb3\sp{2-}$ and S$\sb2$O$\sb3\sp{2-}$ were found at $\mu$M levels. The ratio of C:N:P:S in the waters was close to the theoretical ratio of 106:16:1:53. The rates of sulfide oxidation were ten times faster than that in surface water and agree with the rates predicted due to the level of Fe$\sp{2+}$ and Mn$\sp{2+}$ in the waters.

Keywords

Physical Oceanography; Chemistry, Physical; Geochemistry

Link to Full Text

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