The selectivity of total P over SO4 2-was estimated to be 0.1-0.17 (Table ). Only minor changes in diluate F(I) concentration were observed. Cation transport through the CEM (Figure ) was dominated by H + transport, with excellent separation between monovalent and divalent cations (experiment 2; pH ~1.5; 18 V). Diluate Ca 2+ and Mg 2+ concentrations were almost constant (increasing slightly toward the end of the experiment, likely owing to H2O osmosis toward the concentrate). In contrast, H + , (Fig. ) K + , and Na + concentrations decreased markedly (Figure ). The Na + -cation selectivities were in the range of 4.3-18.3 for Na + over Ca 2+ , 4.6-42.1 over Mg 2+ , and 0.69-1.72 over K + (Table for specific selectivity values. Increases in applied voltage promoted ion transport by increasing the current, with no significant effect on ion selectivity (Figure ). Overall, the results indicate that H + and SO4 2-are the primary solutes transfered from the diluate to the concentrate stream, enabling two practical objectives: (1) neutralization of the acidic diluate by >70%; and (2) recovery and recycling of H2SO4 without the risk of CaSO4 scaling in the concentrate (owing to negligible Ca 2+ transfer). The initial feed pH in the diluate (1.5-2.0) did not affect cation separation (Figure ) but did affect anion separation (Figure ) through acid-base equilibria. Electro-driven P transport was greater with the higher initial feed pH (2.0) due to the decreased proportion of non-ionized H3PO4 species (43% at pH 2.0 and 76% at pH 1.5, as calculated with the PHREEQC 26 sit.dat database ). Similarly, F(I) transport was negligible due to the pH-dependent species distribution, which dictated a high proportion of uncharged HF (90% at pH 2.0 and 97% at pH 1.5, as calculated with the PHREEQC phreeqc.dat database). In contrast, sulfate species (HSO4 -, SO4 2-) were completely ionized in the tested pH range and thus carried most of the current through the AEM. Acid-base equilibria at pH values typical of PAIWW thus enabled the effective separation of sulfate from phosphate and fluoride.