The performance of activated carbon/NiFe2O4 magnetic composite to retain heavy metal ions from aqueous solution

A novel magnetic activated carbon composite (AC/NiF) was synthesized by a precipitation method and applied in retention of Cu(Ⅱ), and Zn(Ⅱ) ions from aqueous solutions. The impact of different sorption parameters such as: equilibration time, solution pH value, competing cations and ionic strength on the amount sorbed of Cu(Ⅱ), and Zn(Ⅱ) was clarified. Results illustrated that the magnetic composite had retention ability towards both metal ions significantly higher than that of activated carbon (AC). The magnetic composite exhibited an affinity to adsorb Cu(Ⅱ) higher than Zn(Ⅱ) ions. The maximum sorption capacities (Q_max) of the applied magnetic composite (AC/NiF) towards Cu(Ⅱ) and Zn(Ⅱ) were 105.8 and 75.1 mg·g^-1, respectively. Retention of Cu(Ⅱ) and Zn(Ⅱ) was proposed to be achieved though an ion exchange and surface adsorption in neutral conditions, while precipitation was believed to be the relevant mechanism in their removal from basic solutions. The kinetic studies showed that sorption process followed the kinetics of pseudo-second-order reactions with rate constant of 3 × 10^-3 and 2 × 10^-3 min^-1 for sorption of Cu(Ⅱ) and Zn(Ⅱ) onto AC/NiF composite. Removal of Cu(Ⅱ) slightly decreased with increasing the ionic strength of aqueous solution, using NaCl as a background electrolyte. In contrast, presence of Mn(Ⅱ), Mg(Ⅱ) and Co(Ⅱ) in reaction solutions highly depressed the sorption of Cu(Ⅱ) and Zn(Ⅱ) with a competing efficiency followed the order: Mg(Ⅱ) > Mn(Ⅱ) > Co(Ⅱ).The magnetic composite was rapidly recovered from aqueous solution by an external magnetic field, and effectively regenerated using 0.1 mol·L^-1 HCl and 0.1 mol·L^-1 FeCl₃ as eluents. Sorption of Cu(Ⅱ) and Zn(Ⅱ) onto the surface of AC/NiF composite occurred via a spontaneous reaction. And thermodynamically favorable process had ΔH^o values of 30.9 kJ·mol^-1 and 19.7 kJ·mol^-1, respectively. The results confirm that the magnetic composite can be viewed as a promising novel composite opens new opportunities for the attainment of required adsorption and operative magnetic separation.