Separation of Metal Ions from Liquid Waste Streams

A unique mechanism was verified for removing uranium from continuously flowing aqueous solutions on a carbon nanofiber electrode with a bias voltage of -0.9 volts (dc versus Ag/AgC1). Uranium concentration was reduced from 100 ppm in the inlet feed to below 1 ppm in a single pass. Cell sizes of 1 cm, 2 inch and 4 inch evaluated during this program were all found to electrosorb uranium from an aqueous stream. The 4 inch cell performed well at uranium concentrations of 1000 ppm. Normally, ordinary electrolysis is not an option for removing uranyl ions because the electrodeposition potential is higher than the dissociation voltage of water. Thus, the ability to electrosorb uranium with greater than 99% effectiveness is a surprising result. In addition, the process was found to be reversible, so that the uranium can be released in a highly concentrated form. In addition to verifying the effectiveness of the system on bench top scale, a regeneration protocol was developed, consisting of passing a 0.1 M KNO{sub3}, solution at a pH of 2.0 and an applied potential of +1.0 V (dc versus Ag/AgC1) which resulted in a measured regeneration of 70% of the electrosorbed uranium. Other experiments studied the effect of pH on electrosorption and desorption, establishing a range of pH for both processes. Finally, it was found that, for an inlet solution of 100 ppm, the carbon nanofiber electrodes were able to electrosorb an amount of uranium in excess of 60% of the electrode mass