Date of Award

Spring 1993

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Robert D Harter

Abstract

Reaction of nickel with soil B horizons under various ionic strengths, pH and temperature conditions was conducted using a batch kinetics method. The forward and reverse apparent rate constants were determined using computer simulation techniques. Thermodynamic parameters were calculated from the rate constants. Increase in soil pH and temperature increased the sorption of nickel, while increase in ionic strength decreased nickel sorption. The reactions were all spontaneous with negative standard free energies ($\Delta$G$\sp\circ$); soils having higher nickel sorption capacity were more negative. The free energy decreased with increase in pH. The enthalpy ($\Delta$H$\sp\circ$) and entropy ($\Delta$S$\sp\circ$) for the reactions were positive and higher for higher nickel sorbing soils, both $\Delta$H$\sp\circ$ and $\Delta$S$\sp\circ$ increased with increase in surface coverage. The large positive $\Delta$S$\sp\circ$ indicated a certain degree of nickel dehydration when sorbed by soils particles, greater dehydration is observed with increase in surface coverage.

Nickel sorption sites on soil surfaces were evaluated using nickel sorption isotherms and Wavelength Dispersive Spectroscopy (WDS). No specific soil component explained the relative nickel sorption capacities of the soils. WDS indicated that nickel sorption is related to iron in soils, but neither total, citrate-dithionite-bicarbonate (CDB) nor ammonium oxalate (NH$\sb4$OX) extractable iron were able to explain this trend.

The reaction of nickel at the goethite/water interface was studied using kinetics by means of pressure-jump (p-jump) relaxation. Two step relaxations were observed for nickel adsorption at 25$\sp\circ$C. The fast and slow relaxations decreased with decrease in pH. Both relaxations were attributed to simultaneous adsorption/desorption of Ni$\sp{2+}$ on sites with different bonding energies. A modified triple layer model (TLM) was used to analyze the effect of ionic strength on nickel adsorption at the goethite/water interface. An inner-sphere complexation model fitted the experimental data well. Results of zeta potential also supported the specific adsorption of nickel at the interface.

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