Removal of high level boron in aqueous solutions using continuous electrodeionization (CEDI)

The high levels of boron in nuclear power plant wastewater require removal before discharge, particularly for inland plants. Continuous electrodeionization (CEDI) is very effective at treating wastewater with low conductivity and was investigated for use in removing high levels of boric acid. Solutions containing high levels (60-400 mg/L) of boric acid were treated with a small-scale CEDI stack in a constant current mode. The removal efficiency of boron using CEDI increased from 15% to 23% as current increased from 0.5 A to 2.0 A. Boron removal ratios decreased from 45% to 16% when boron concentration in the feed solutions increased from 60 to 400 mg/L. Decreasing the feed flow rate into the diluting compartment promoted boron removal. Optimal pH was found to be at 10, at which 26% of boron was removed. The three main factors influencing boron removal of boron were as follows: borate ion speed upon entering the resin, borate ion transport rate, and ion exchange inhibition by OH−. Our results indicate that CEDI can be used to remove high levels of boron, but future modifications will be needed to enhance removal efficiency.