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ABSTRACT:Magnetite nanoparticles were applied for the removal of lead(II) ions from aqueous solution as a function of pH, contact time, supporting electrolyte concentration and initial analytical Pb(II) ion concentration. The highly crystalline nature of the magnetite structure with pore diameters of ca. 10 nm was characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The surface area was determined as 115.3 m 2 /g. The surface chemical properties of magnetite in aqueous solution at 25 ºC were investigated.Batch experiments were carried out to determine the adsorption kinetics and adsorption mechanism of Pb(II) ions by the magnetite nanoparticles. The adsorption of Pb(II) ions was mainly governed by surface complexation, with the adsorption process being pH-dependent. In NaCl solutions, Pb(II) ion adsorption increased with increasing ionic strength; however, in NaClO 4 solutions, Pb(II) ion adsorption exhibited little dependence on the ionic strength of the solution.Kinetic studies were performed to understand the mechanistic steps involved in the adsorption process. The adsorption kinetic data for Pb(II) ions were best fitted by the fractional power equation. The Langmuir and Freundlich adsorption isotherms were applicable to the equilibrium adsorption process and the corresponding constants were evaluated. The maximum adsorption capacity (q m ) calculated from the Langmuir isotherm was found to be 0.1105 mmol/g for Pb(II) ions at a pH value of 5.0 and at 25 ºC.

Magnetite nanoparticles were applied to remove Ni(II) from aqueous solutions as a function of pH, contact time, supporting electrolyte concentration, and analytical initial Ni(II) concentration. The highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The surface area was determined to be 115.3 m 2 /g. Surface chemical properties of magnetite at 258C in aqueous suspensions were investigated. The point of zero charge (pHzpc) was found to be 7.33 and the intrinsic acidity constants (pK s a1 and pK s a2 ) were found to be 9.3 and 5.9, respectively. The surface functional groups were investigated with Fourier transform-infrared spectroscopy (FTIR) as well. Batch experiments were carried out to determine the adsorption kinetics and mechanism of Ni(II) by these magnetite nanoparticles. The adsorption process was found to be pH dependent. In NaCl solutions, Ni(II) adsorption increased with increasing ionic strength while in NaClO 4 solutions, Ni(II) adsorption exhibited little dependence on the ionic strength of the solution. The adsorption process better followed the pseudo-second order equation and Freundlich isotherm.

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