Simultaneous extraction and preconcentration of some metal ions using eucalyptus-wood based activated carbon modified with silver hydroxide nanoparticles and a chelating agent: optimization by an experimental design

Abstract

In the present work, the solid phase extraction (SPE) of Cr(III), Cu(II), Pb(II), Ni(II), Cd(II), and Co(II) metal ions was carried out using a new adsorbent, activated carbon modified with silver hydroxide nanoparticles and a chelating agent. The activated carbon was produced by the acid treatment of the carbon obtained from eucalyptus wood. The effects of different parameters on the metal ion preconcentrations were studied and optimized by a central composite experimental design, which is one of the most applicable response surface methodologies used in the design of experiments. The four major variables affecting the adsorption process, consisting of the pH value, amount of adsorbent, amount of ligand, and flow rate of the sample solution, were optimized. In the desorption process, the volume, concentration, and flow rate of the eluting solvent were considered as the variables affecting the amount of metal ion preconcentration. At the end of each step, the metal ions were quantified by flame atomic absorption spectrometry (FAAS). Under the optimal conditions, the recovery percentage and enrichment factor for all the metal ions under study were higher than 98% and 100, respectively (except for the Ni(II) ion, with an enrichment factor of 83.6), which indicate the high performance of the presented preconcentration method. Also, the detection limits for the Cr(III), Cu(II), Pb(II), Ni(II), Cd(II), and Co(II) ions were found to be 4.7, 3, 4, 1.7, 1.6, and 2.3 μg L⁻¹, respectively. The relative standard deviation values for six replicate measurements of 0.2 mg L⁻¹ of each metal ion were lower than 2.62%. Thus this preconcentration method can have a high accuracy and precision in the determination of trace amounts of potentially toxic metal ions.