Separation of Cr(VI) by zeolite-clay composite membranes modified by reaction with NO_x

摘要

In this work,we report the use of modified zeolite-clay composite ultrafiltration membranes (preparation of the unmodified (Z_1),the nitrated (Z_2,modified using NO_x) and the aminated (Z_3) membrane have been described in our earher publication [1]) for the separation of chromic acid solution.Experiments show that the observed rejection coefficients of the membranes increase on modification from approx 20% for Z_1 to approx 40% for Z_2 and approx 50% for Z_3 membrane.Experimental data is analyzed using the irreversible thermodynamic approach (Spiegler-Kedem equations) [2].The study shows that the chemical modification of membranes leads to a rise in the intrinsic rejection (highest R approx 50% for Z_1 to approx 60% for Z_2 and approx 66% for Z_3 membrane) coefficients.It is also found that while the observed rejection show anomalous trend with variation in pressure while the intrinsic rejection increases with increase in pressure,a trend typical of the separation of electrolyte through charged membranes.