Removal of cationic dye methyl violet 2B from water by cation exchange membranes

The removal of methyl violet 2B, a cationic dye, from water using two kinds of strong-acid cation exchange membranes, ICE 450 supported (with sulfonic acid groups and ion exchange capacity of 9.6–31 μeq/47 mm disc) and P81 (with phosphate groups and ion exchange capacity of 312 μeq/47 mm disc), was investigated in this study. In the batch process, the adsorption isotherm results show that the P81 membrane exhibited a greater maximum adsorption capacity than the ICE 450 supported membrane. However, the latter exhibited stronger and faster dye adsorption behaviors. Different desorption solutions were tested in the batch desorption process and, for both membranes, the best desorption performance (∼100%) was achieved with an aqueous solution containing 1 M NaCl in 60% methanol. In the membrane chromatography process with one piece of 47 mm membrane at a flow rate of 1 or 8 mL/min, complete dye removal and recovery from a 20 mL feed with an initial dye concentration of 0.015 g/L could be achieved for both membranes. The performance of both membranes remained practically unaltered during three successive cycles of dye adsorption and desorption. Lastly, to mimic the effluent produced by a typical dyehouse, a synthetic dye wastewater made up of 0.03 g/L methyl violet 2B and 2 g/L Na2SO4 at pH 3 and 100 °C was prepared and treated by both membranes in the membrane chromatography process. The extent of dye removal was decreased to 84–93% for the P81 membrane, which may be attributable to either salt ion competition or pH influence. By contrast, the ICE 450 supported membrane could attain nearly complete dye adsorption and desorption.