Publication Date

2013

Document Type

Thesis

Committee Members

David A. Dolson (Committee Member), David A. Grossie (Committee Chair), Steven R. Higgins (Advisor), Ioana E.P. Sizemore (Committee Member), Andrew G. Stack (Committee Member)

Degree Name

Master of Science (MS)

Abstract

Mineral dissolution plays a significant role in geochemical processes such as carbon sequestration and isotope geochemistry. While factors such as temperature, pressure, and solution chemistry have been widely studied, the effects of sample history and surface morphology on dissolution rates have been studied to a lesser extent. This research focuses on the dissolution of cleaved, polished, and reacted samples of the atomically flat natural {010} cleavage plane of gypsum (CaSO4·2H2O) to further investigate upon the effect of sample history. Gypsum was chosen as the mineral of interest because of its planar crystal surface and relatively fast dissolution rate. Chemical dissolution rates as well as changes in surface morphologies were determined for cleaved, polished, and reacted crystals exposed to undersaturated solutions in continuously stirred, free-drift, batch reactors. Results from chemical rate determination showed a history effect as dissolution rate decreased in consecutive dissolution runs for polished samples. For cleaved samples, relatively slow initial dissolution rates were observed. Surface morphology development showed that cleaved samples initially dissolved through etch pit nucleation and growth, while polished samples initially dissolved through step retreat. After dissolution, both cleaved and polished surfaces only showed step bunches along the [001] direction suggesting that both cleaved and polished crystals will eventually have similar surface morphologies and dissolution rates. In conclusion, surface morphology and thus sample preparation affect the initial dissolution rates on the (010) surface of gypsum. Therefore, sample preparation is a variable that should be accounted for in laboratory experiments.

Page Count

68

Department or Program

Department of Chemistry

Year Degree Awarded

2013


Included in

Chemistry Commons

COinS