New oxygenated carbonaceous adsorbents prepared by combined radiant/microwave heating for the removal of Pb2+ in aqueous solution

This paper presents a new procedure to obtain efficient carbonaceous adsorbents for the removal of Pb2+ in aqueous solution. Experimental procedure includes a pre-treatment of pecan nut shells using radiant heating at low temperatures (280-340 degrees C), followed by microwave radiation heating (Microwave Assist Technology: MAT) and using a L-16 orthogonal array of Taguchi method to find the optimal preparation conditions, setting as the response variable the removal of Pb2+ in aqueous solution. The obtained materials were characterized using elemental analysis, FT-IR spectroscopy, potentiometric titration, nitrogen adsorption isotherms at -196 degrees C and SEM/EDX analysis. Full Pb2+ adsorption isotherms in aqueous solution were studied using stirred batch systems at 30 degrees C, pH 5, and using a mass to volume ratio of 2 g/L. The best performing adsorbent rendered an outstanding Pb2+ sorption capacity (261 mg/g), in spite of its rather low porosity. Such a high capacity was explained in terms of the materials surface chemistry, because the obtained carbons have a high amount of acidic and oxygenated groups, as well as calcium deposits. Also, the optimum conditions of each factor level obtained from the orthogonal array allowed to obtain a highly efficient carbon for Pb+2 removal. (C) 2015 Elsevier B.V. All rights reserved.