Chromium (VI) Separation from Aqueous Solution Using Anion Exchange Membrane

The preparation is reported of a chemically modified crosslinked poly(methyl methacrylate–ethylene glycol dimethacrylate) (PMMA–EGDM) copolymer anion exchange ultrafiltration membrane on a macroporous clay support. This is obtained by nitrating a PMMA–EGDM membrane using NOx (a mixture of NO and NO2), which is further reduced to an amine group using hydrazine hydrate to form an anion-exchange membrane (AEM). The membrane thus formed is characterized for its properties such as ion-exchange capacity, membrane swelling, contact angle measurements, and membrane morphologies. The results show that the membrane becomes highly hydrophilic on the introduction of a charge and the separation experiments on the chromium (VI) salt solution show that the permeate flux (keeping the same rejection level of 90%) is considerably increased (by 100-fold). The analysis of separation of Cr(VI) from its aqueous solution has been done by solving a two-dimensional (in cylindrical coordinates) space-charge model (SCM). A series solution of the nonlinear Poisson–Boltzmann equation has been generated, which leads to a considerable reduction in the computational time (from 15 h of batch time using the method reported earlier to 15 min for our method). The effective pore radius and wall potential of the unmodified and AEMs are evaluated by fitting the experimental data of the separation. The permeate flux calculated from this model matches well with the experimental values and a correlation is developed between the separation characteristic (rejection) and the wall charge developed by the chemical modification of the membrane. © 2005 American Institute of Chemical Engineers AIChE J, 2005