Electrodialysis technology is being developed to recover salt from brines generated in the commercial process for recycling aluminum salt cake. Salt cake, a waste stream from the aluminum industry, contains aluminum metal, salt (NaCl and KCl), and nonmetallic impurities. After grinding and screening to separate out aluminum metal, salt cake solids are leached in water and filtered to recover a nonmetallic product (NMP). The filtered brine is then processed in an evaporator to separate salt and water. Researchers at Argonne National Laboratory identified electrodialysis as a promising process for salt recovery that may be less cost prohibitive than evaporation. Laboratory experiments suggested that the cost advantage of electrodialysis could be further improved through the selection of membranes to reduce power consumption and by operating with a differential pressure to reduce water transfer across the membranes. A large-scale electrodialysis pilot plant has been designed and constructed to verify laboratory results and the commercial viability of the process. Experiments are currently underway to characterize the effects of differential pressure, concentration difference, and current density on the water transfer and current efficiency of electrodialysis operations with concentrated brines.
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