Year of Award

2007

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Inorganic Option)

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Edward Rosenberg

Commitee Members

Mike DeGrandpre, Alexander Ross, John Gerdes, Jesse Johnson

Keywords

Acid mine drainage, Chelating materials, EDTA, Metal removal, Silica Polyamine Composites

Abstract

The goals of this thesis were to improve the performance of silica polyamine composites by manipulating the surface structure and to understand the relationship between, polymer structure and ligand modification of the grafted polyamine. Improvements in silica polyamine composite performance resulted from modifying silica gel with methyltrichlorosilane (MTCS) substituted for a molar fraction of reagent chloropropyltrichlorosilane (CPTCS), which has been traditionally employed. MTCS does not possess a terminal chloride group thus preventing the subsequent attachment of a polyamine to this moiety. MTCS has a smaller molecular volume than CPTCS and as a consequence greater coverage of the silica gel surface by silanes was determined by elemental analysis and NMR. An increase in the fraction of amines not attached to the surface (free amines) allowed improved mass transfer kinetics and in some cases improvements in metal ion sorption capacities of the polymer modified materials. Further, MTCS is cheaper than CPTCS thus allowing a more economically sound synthesis. As a result of an increase in free amines, silica gel polyamine composites were modified with sodium chloroacetate and other metal selective ligands in higher yield, resulting in a material with substantially improved copper ion capacities. Silica polyamine composites have also been modified with a novel series of amino acid chelating ligands for the purpose of selective extraction of heavy metals from aqueous media. The presence of the functional groups was confirmed by 13C NMR and elemental analysis. The adsorption properties of modified composites have been determined for divalent and trivalent metal ions. Cycle testing was performed to measure longevity. Selective extraction and recovery of a single metal ion from media containing multiple metal ions has been demonstrated. The structure of the polyamine used has been shown to have a significant impact on the specific selectivity of modified silica polyamine composites even when modified with the same ligand. Potential areas of application have been tested and appear promising. These include an acid mine drainage polluted stream near Helena, MT, as well as synthetic high pressure leach laterite solutions.

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© Copyright 2007 Mark Anthony Hughes