Title

Electrochemical treatment of metal-bearing aqueous wastes based on novel forms of carbon

Semester

Spring

Date of Graduation

1999

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

John W. Zondlo.

Abstract

Electrochemical remediation is an economic approach for long-term clean-up of metal-bearing aqueous wastes because it provides a means of continuous, selective removal of metal contaminants and offers terminal processes for recovery of the metals. In this study, three forms of novel carbon material were tested as electrodes for the removal of heavy metals and radionuclides from aqueous wastes by electrodeposition and/or electrosorption.;Copper and lead ions in aqueous solution were effectively removed by electrodeposition on two of the carbon electrodes. The continuous, single-pass deposition through a small laboratory-scale cell removed 99% of copper and 83-88% of lead, respectively. On the other hand, deposition of nickel was difficult even at high negative potentials. The efficiency of nickel removal was greatly improved by pre-plating a small amount of copper on the carbon electrode.;Selective removal of lead from lead-nickel mixed wastes by electrodeposition was difficult. Nickel was removed even at potentials less negative than its formal reduction potential probably by its electrosorption on the active sites created by lead deposition. The lead-nickel separation was improved at more acidic conditions; lead deposition was enhanced by increasing the quantity of the working-electrode carbon. A combination of the two factors led to effective separation of lead from the lead-nickel mixture.;The removal of lead from aqueous solution by deposition using a "scaled-up" 1.5-inch diameter cell was studied as a function of operating parameters including current density, pH, flow rate, initial lead concentration and electrolyte composition. It was found that the deposition was not greatly affected by solution pH in the range of 3.5 to 5.3. Increase in the solution flow rate up to 20 mL/min improved the current efficiency while increase of the current density from 0.394 to 0.789 mA/m2 resulted in significant decrease in the current efficiency, indicating the process was mainly controlled by mass transport under these conditions. A model was developed to simulate the continuous, single-pass deposition process and the mass transport coefficient of the carbon electrode was determined by correlating the normalized lead concentration with the reciprocal of the volumetric flow rate operated at the limiting current.;Uranyl ions in aqueous solution were effectively removed by electrosorption onto an electrode made of oxidized vapor-grown carbon fibers. Under suitable potentials (e.g., -0.45 to -0.9V), up to 99.9% of uranium was removed from a 100 mg/L feed solution by a single pass through the cell. The adsorbed uranium was easy to strip and recover in solid form by filtration. A sorption capacity over 1.20 g U/g carbon fiber was reached. Such superior performance of uranium electrosorption was believed a result of negative charge enhanced ion-exchange sorption combined with surface-induced precipitation of uranyl hydroxide.

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