Electrodialysis reversal of calcium sulphate and calcium carbonate supersaturated solution

Abstract

Electrodialysis reversal (EDR) in single-pass mode was investigated to coal-mine water desalination. Water containing (mg/L): Ca 2+ - 284, Mg 2+ - 130, SO 4 2− - 1066, Cl − - 359 and HCO 3 − - 297 was desalinated in EDR laboratory unit with 0.19 mm intermembrane distance. The electrodes polarity was changed each 17 min. 90.1 and 90.6% recoveries were achieved applying diluate velocities 8.35 and 8.14 cm/s respectively, while concentrate velocities were 0.86 and 0.90 cm/s. Mean residence time of concentrate in EDR unit was equal to 352 s. The percent of calcium sulphate saturation in EDR concentrates was equal to 368 and 362% while Langelier Saturation Index (LSI) to 1.92 and 1.60 respectively. Voltage drops vs. EDR time show no increasing tendency, which would be the result of calcium sulphate or calcium carbonate scaling in the EDR unit. It was then demonstrated that EDR in the presented mode could operate at such a high supersaturation level, which has been achieved up to now, only with chemical addition to the concentrate stream.