Removal of cadmium and zinc from aqueous solutions using red mud.

Red mud, an aluminum industry waste, has been converted into an inexpensive and efficient adsorbent. The product obtained has been characterized and utilized in batch and column operations for the removal of cadmium and zinc from aqueous solutions over a wide range of initial metal ion concentrations (1.78 x 10(-5) to 1.78 x 10(-3) M for Cd2+ and 3.06 x 10(-5) to 3.06 x 10(-3) M for Zn2+; contact time, 24 h) adsorbent dose (5-20 g/L), and pH (1.0-6.0). The removal of Cd2+ and Zn2+ was almost complete at low concentrations, while it was 60-65% at higher concentrations at optimum pH's of 4.0 and 5.0, respectively, with 10 g/L of adsorbent in an 8-10 h equilibration time. The adsorption decreased with increase in temperature. Kinetic studies have been used to describe the mechanism of adsorption. Chemical regeneration of the columns has been achieved with 1% HNO3.