Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Robert J. Gale

Abstract

Electrokinetic soil processing is an emerging remediation technique with the capability to decontaminate low permeability soils containing heavy metals and some organics. The process consists on applying small current densities between electrodes immersed in the soil mass; the electrochemistry developed across the system causes desorption and transport of the contaminants to the electrodes where, depending on their chemistry, they precipitate, electrodeposit, or elute with the electroosmotic flow. Its potential to remove selected radionuclides (uranium-238, thorium-232, and radium-226) is assessed in the present studies. The process removed 85 to 95% uranium-238 at 1000 pCi/g activity from kaolinite. Complicating features arise (i.e. precipitation of insoluble hydroxides, high electrical gradient profiles, high energy expenditure). The energy consumed during the process ranged between 81 to 315 kW-hr/m$\sp3$ of processed soil. Due to precipitation of uranium hydroxide, the removal rate decreased close to the cathode, but enhanced tests (acetic acid depolarization, adipic acid-molded sections tests) showed it is possible to improve removal rates near the cathode at lower energy expenditure. Between 80 to 90% of thorium-232 at different activities was removed using an acid-molded enhancement technique. Thorium was strongly adsorbed onto the soil surface and also showed a strong tendency to precipitate as insoluble and gelatinous hydroxides, complicating its transport and increasing the energy expenditure during the process. Radium-226 at 1000 pCi/g precipitated as insoluble radium sulfate, preventing its transport. Use of complexing agents may be needed to achieve radium removal. The efficiency of the process proved to be dependant on the chemistry of the specific radioactive contaminants, but its usefulness as a remediation technique was demonstrated in this work.

Pages

242

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