The interaction of cobalt, amino acids, and cobalt amino acid complexes with sediment surfaces

Organic molecules such as amino acids have long been considered the cause of some anomalous behavior of metals in the marine environment, with respect to concentration in the water and adsorption on the sediment. Many studies have investigated the adsorption of amino acids and amino acid complexes. This study investigates the adsorption of cobalt, amino acids, and cobalt amino acid complexes on both Na⁺-montmorillonite and Na⁺-birnessite (MnO₂). Amino acids were also adsorbed on Co²⁺-saturated montmorillonite and birnessite. The oxidation state and chemical nature of sorbed cobalt and the chemical nature of the amino acid amine groups were investigated using x-ray photoelectron spectroscopy (XPS). XPS enabled determination of the stoichiometry of the sorbed complexes. Electrophoresis revealed changes in the surface charge of the substrate upon interaction with cobalt, amino acids, and cobalt amino acid complexes. These changes provided insight into the reaction mechanisms and chemical species involved. Infrared and visible spectroscopy, x-ray diffraction (XRD), and quantitative analysis enabled further determination of the reactions that occurred between cobalt, amino acids, cobalt amino acid complexes and the sediment surfaces. Using XPS, it was found at pH values 4 to 7 that Co(II) adsorbed on montmorillonite as Co(II) and on birnessite as Co(III). The birnessite (MnO₂) surface was determined to be the oxidizing agent. XPS, XRD, and infrared spectroscopy indicated that amino acid adsorbed on montmorillonite by cation exchange, keying into octahedral sites, and by peptide formation. Increased adsorption was observed on Co²⁺-montmorillonite in solutions of both glycine and lysine and was attributed to coordination reactions. Both Co(gly)₃ and Co(lys)₃³⁺ complexes were observed in solution and were either formed on the clay surface and released, or desorbed cobalt was complexed in solutions. Co(lys)₃³⁺ was observed on the clay surface following interaction of Co²⁺-montmorillonite with lysine. It is proposed that dissolved oxygen oxidizes cobalt in the amino acid complexes. XPS and electrophoretic mobility measurements indicated that amino acids interact with birnessite by chelation of the surface manganese. Measurement of the Mn 3s splitting for amino acid saturated birnessite samples showed that the surface was reduced. It was inferred that the manganese dioxide surface oxidizes amino acids, but no proof of oxidized amino acids was obtained. Hydrolysis of complexes was observed on both the manganese dioxide and montmorillonite surfaces. Because these complexes are known to be relatively stable to hydrolysis in solution, it was proposed that the surface catalyzed the hydrolysis. The oxidation state and chemical nature of selected metals in Pacific manganese nodules were investigated using XPS. Analysis of binding energies, shake-up satellite features, and multiplet splittings revealed that the oxidation states for the metals in the nodules were Mn(IV), Fe(III), Co(III), Pb(II and IV), Cu(II), Ni(II), and Ti(IV).

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Department dc:contributor.department

Chemistry

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1982

Author dc:creator

• Kay, Deborah Lynne Crowther

Chair dc:contributor.committeechair

• Dillard, John G.

Committee members dc:contributor.committeemember

• Bell, Harold M.
• Graybeal, Jack D.
• Wightman, James P.
• Zelazny, L.A.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/88722

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/88722