The excellent ion separation was retained in the high-recovery experiments, as reflected in the diluate and concentrate compositions (Figure ). Diluate solute concentrations (Figure ) were similar to those of the low-recovery experiments. The high SO4 2-flux relative to that of P and the high monovalent cation selectivity were maintained, as reflected in the evolution of the concentrate stream composition (Figure ). A marked increase in SO4 2-concentration of up to ~20 g L -1 is evident in Figure , with only a moderate rise in P content of up to ~4 g L -1 and a low ~0.6 g L -1 Cl -concentration (also low in the diluate). Na + and K + concentations increased monotonically in the concentrate, while Ca 2+ and Mg 2+ concentrations remained at <11 mg L -1 (Figure ) and the pH (Figure ) increased from 1.5 to 1.9. This pH increase was slightly lower than that recorded in the low-recovery experiments (Figure ; pH 1.5 to 2.1) due to a higher concentration gradient of H + across the CEM at higher recoveries, reducing the net H + flux. The concentrate pH (Figure ) reached a lower level (<1) because of the accumulation of H2SO4. Ion concentrations in the concentrate stream were somewhat reduced by water transfer from the diluate, with the diluate/concentrate volume ratio decreasing from 5.5 at the beginning to 4.7 at the end of the experiment. However, ion-separation performances in the highrecovery experiments enabled attainment of the treatment goals, with diluate neutralization and H2SO4 recovery while avoiding CaSO4 scaling.