Single and competitive adsorption of V-EDTA and Ni-EDTA complexes onto activated carbon: response surface optimization, kinetic, equilibrium, and thermodynamic studies

Extraction with an aqueous solution of ethylenediaminetetraacetic acid (EDTA) is a convenient method to recover vanadium and nickel from their secondary resources, such as spent catalysts and fly ash. In this paper, V-EDTA and Ni-EDTA complexes were adsorbed from aqueous phase using activated carbon (NAC) in single and competitive adsorption systems. The operational parameters were metal concentrations (C-i,C-M), EDTA concentration (L/M), solution pH (pH(i)), and adsorbent dosage (C-Ads). At single adsorption of these complexes, the maximum q was obtained 15.39 mg g(-1) for V-EDTA and 15.82 mg g(-1) for Ni-EDTA. Competitive studies were conducted at three concentrations of the initial metal. At the following conditions, C-i,C-V = 120 mg L-1, C-i,C-Ni = 40 mg L-1, pH(i) = 3.0, and C-Ads = 12 g L-1, the ratio of adsorbed vanadium to nickel (q(V)/q(Ni)) was obtained 11.84 after 7 h. Likewise, a modified pseudo-second-order kinetic model was given for the first time to describe the whole competitive adsorption process. Moreover, adsorptions of free EDTA and Na+ at competitive experiments were investigated. The results of equilibrium and kinetics experiments illustrated that the pseudo-second-order kinetic model and Freundlich and Dubinin-Radushkevich isotherms could describe experimental data well.

Automated summary

The extraction with an aqueous solution of EDTA is a convenient method to recover vanadium and nickel from secondary resources. This study investigated the adsorption of V-EDTA and Ni-EDTA complexes using activated carbon in single and competitive systems, revealing the competitive adsorption process with a modified pseudo-second-order kinetic model. The experimental results illustrated that the pseudo-second-order kinetic model and Freundlich and Dubinin-Radushkevich isotherms could describe the data well.