Adsorption of arsenic from aqueous solution on naturally available red soil

In the present study arsenate and arsenite removal from naturally available red soil in and around Western Ghats of Maharashtra near Mumbai has been investigated. The parameters like adsorbent dose, operating pH, contact time, initial arsenite concentration, adsorbent particle size, etc. on the removal of arsenite and arsenate are examined. Kinetic study in centrifuge vessel reveals that uptake of As (III) ions is rapid in the first two hours and slows down thereafter. Maximum removal efficiency of As (III) achieved is 98% at an adsorbent dose of 45 g l(-1) with initial As (III) concentration of 1000 microg l(-1) in batch studies and 95% at 25 g l(-1) absorbent dose under the same conditions. Equilibrium time is almost independent of initial arsenite concentration. Equilibrium studies show that As (III) ions have high affinity towards red soil even at very low concentration of arsenite. In speciation study about 25% conversion to As (V) from As (III) is observed, with initial As (III) concentration of 1000 microg l(-1) and at 25 g l(-1) adsorbent dose. The results suggest that red soil could be used as effective filter medium for removal of arsenic from water.