Improving the Adsorption of Heavy Metals from Water Using Commercial Carbons Modified with Egg Shell Wastes

We introduce the application of hen egg shell waste to improve the adsorption capacities of heavy-metal ions using commercial carbons via the modification of their surface chemistry. Specifically, a calcium solution extracted from egg shell waste has been used as a low-cost activation agent to improve the adsorption properties of three commercial carbons. An orthogonal array of the Taguchi method has been applied to identify the optimal conditions for the adsorbent modification process using the Zn(2+) batch adsorption, at 30 degrees C and pH 5, as the response variable. Our results show that maximum adsorption capacities of Cd(2+), Ni(2+), and Zn(2+) ions, at 30 degrees C and pH 5, may increase up to 15 times, with respect to the results obtained using the commercial adsorbent without modification. The improvement of adsorbent performance may be related to the formation of calcium phosphate on the carbon surface. Finally, adsorption studies in binary metal solutions were performed to identify the competitive effects in multicomponent adsorption, using calcium-modified carbons.