Although the ion-separation results of the low-recovery ED experiments (Figure ) were encouraging, the presence of F(I) reduced the practicability of the process. High F(I) concentrations at low pH require the use of special-grade polymers and safety measures, which complicate procedures and raise the cost of membrane separation. Here we used 1 mm PP-based fluoride-resistant spacers in the ED stack, resulting in high single-cell specific electrical resistance (858-1419 Ω•cm 2 ). This high resistance was evident with low current densities (e.g., ~31 A m -2 in experiment 2; Figure ) and long durations (~25 h to reach ~50% diluate EC reduction; Figure ). Most critically, the SEC was impracticably high at 39-91 kWh m -3 for 80% SO4 2-removal in the low-recovery experiments. The limitations caused by F(I) and the high SEC prompted a modification of the stack and operational approach in high-recovery ED experiments, as follows.