Synthesis, characterization, electrokinetic and adsorption properties of an organo-modified adsorbent for selective removing of metal ions

Abstract

Firstly, sepiolite was modifed using N-1-[3-(trimethoxysiliylpropyl)]. In order to support the modification of sepiolite surface, FTIR, XRD, DTA/TG and SEM analyses were carried out. It was found that the chemical bonding took place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and methoxy groups of N-1-[3-(trimethoxysiliylpropyl)] diethyltriamine. Then, the removal of heavy metal ions was systematically investigated as a function of pH, ionic strength and temperature using AAS. It was found that the amount of adsorbed metal ions increased with increase in solution equilibrium pH and temperature, whereas it generally decreased with the ionic strength. The experimental data were analyzed using Langmuir and Freundlich isotherms to identify the adsorption mechanism of metal ions on organo-modified sepiolite, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. The Langmuir monolayer adsorption capacity of modified sepiolite was estimated as 118, 118, 110, 80, 37 and 30 mol for Cu(II), Zn(II), Fe(III), Mn(II), Cd(II) and Co(II), respectively. The affinity order of adsorption was Cu(II)=Zn(II)>Fe(III) >Mn(II)> Cd(II)> Co(II). The experiments demonstrated that Cu(II), Zn(II) and Fe(III) ions were more efficiently adsorbed than Cd(II) and Co(II) ions by modified sepiolite. The results show that modified sepiolite can be used as an alternative low-cost selective adsorbent in adsorption process, in chromatographic purification process and in nanocomposite synthesis. Finally, the zeta potential of the modified sepiolite suspensions was measured and it was found that the zeta potential of the modified sepiolite in studied concentrations and pH values was negative.