In-situ modification of activated carbon with ethylenediaminetetraacetic acid disodium salt during phosphoric acid activation for enhancement of nickel removal

Abstract

Ethylenediaminetetraacetic acid disodium salt (Na2EDTA) was employed to in-situ modify activated carbon from Typha orientalis during phosphoric acid activation to improve its Ni(II) adsorption capacity. The Ni(II) adsorption capacities of original activated carbon (AC) and Na2EDTA-modified activated carbon (AC-Na2EDTA) were evaluated by batch adsorption experiments. The adsorption isotherms of activated carbons conformed to the Langmuir model. The adsorption equilibrium data showed that the calculated maximum Ni(II) adsorption capacities of the samples enhanced from 15.4mg/g to 27.9mg/g after modification with Na2EDTA. The physicochemical properties of AC and AC-Na2EDTA were characterized by N2 adsorption/desorption isotherm, Boehm's titration and X-ray photoelectron spectroscopy (XPS) analysis. No obvious differences of AC and AC-Na2EDTA in nitrogen adsorption/desorption curves and pore size distributions could be observed. However, AC-Na2EDTA (80.9% and 2.10mmol/g) exhibited a higher (N+O)/C atomic ratio and total functional groups content than AC (26.2% and 1.35mmol/g). These results suggested that chemisorption is mainly responsible for Ni(II) adsorption on activated carbon. Based on the results of batch adsorption experiments and XPS analysis, Ni(II) cations were mainly bound with the O-containing and N-containing groups through the mechanisms of cation exchange, electrostatic attraction and surface complexation. Desorption experiments showed maximum Ni(II) recovery in HCl solution.