An integrated nanofiltration-membrane crystallization (NF-MC) system has been tested for the removal of sodium sulfate from aqueous wastes originated by the production process of base raw materials (Ni-H) for special rechargeable batteries. Nanofiltration experiments on NF90-2540 FilmTec(TM) modules showed high rejection values to sodium sulfate (>99%) when operated at pressure of 3.45 x 10(6) Pa; it was possible to achieve a maximum permeate recovery factor of 50% when starting from 60 g l(-1) Na(2)SO(4) feed solution. The membrane crystallizer, operated downstream to the pre-concentration NF unit, was able to produce thenardite crystals (the anhydrous form of sodium sulfate) grown from slurry with density up to 21 kg m(-3); the solid product exhibited narrow size distribution (coefficient of variation similar to 30%). Polypropylene hollow-fibre membranes showed a hydrophobic character stable over 2 days of continuous operation. (C) 2010 Elsevier B.V. All rights reserved.