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The reduction and dissolution of manganese(III) and (IV) oxides by organics

Citation

Stone, Alan Thomas (1983) The reduction and dissolution of manganese(III) and (IV) oxides by organics. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09112006-133416

Abstract

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Although it is known that manganese oxides are solubilized by reduction in anoxic waters, the chemical processes are poorly understood. A study of the reduction and dissolution of manganese oxide suspensions by twenty-seven organic substrates that have chemical structures similar to those of natural organics was undertaken to determine the rates and mechanisms of the solubilization reactions.

Dissolution of suspensions by hydroquinone in the pH range 6.5 < pH < 8.5 is described by the following experimental rate law: [...] where [Mn2+] is the amount of dissolved manganese, [HQ] is the hydroquinone concentration, and MnT is the initial amount of manganese oxide. The apparent activation energy of the reaction was found to be +37 kJ/mole. The Mn(III,IV) oxide suspension was prepared by oxidizing a Mn(OH)2(s.) suspension with oxygen, and has a composition characterized by [...]. Suspension particles were between 0.2 and 1.0 microns in diameter. Calcium and phosphate were found to inhibit the dissolution reaction, by adsorbing on the oxide surface.

Dihydroxybenzenes and methoxyphenols dissolved the suspensions at appreciable rates. Of the aliphatic substrates examined, only ascorbate, oxalate, and pyruvate dissolved the oxide. Dissolution by marine fulvic acid was found to be photocatalyzed.

A model was developed to explain the observed rate dependence and the relative reactivity of different organic substrates. The model assumes that complexes between substrate and surface sites form prior to electron transfer and dissolution. The pH dependence is not explained by this model; involvement of H+ in the dissolution of reduced surface sites may be responsible for the observed fractional order with respect to H+.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:catechol; hydroquinone; Infrared spectroscopy; mineral synthesis; Redox Reactions; Surface reactions
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Morgan, James J.
Thesis Committee:
  • Morgan, James J. (chair)
  • Anson, Fred C.
  • Rossman, George Robert
  • List, John A.
  • Hoffmann, Michael R.
Defense Date:4 January 1983
Record Number:CaltechETD:etd-09112006-133416
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-09112006-133416
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3462
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:27 Sep 2006
Last Modified:26 Dec 2012 03:00

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