Enhancement of Pb and Cd Adsorption in Water Samples by Magnetite Using Humic Acid as Modifier

Abstract

BACKGROUND Magnetite is widely used as a green and cheap mineral material to adsorb heavy metals in water samples, but it has the disadvantages of low adsorption capacity, poor selectivity and easy reunion. Surface modification of magnetite could overcome these problems and improve its adsorption properties. OBJECTIVES To enhance the adsorption properties of magnetite by using a humic acid modifier. METHODS The morphology and structure of magnetite and humic acid-modified magnetite were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The effect of conditions such as optimal pH and adsorption time on Pb2+ and Cd2+ adsorption rate were investigated by static equilibrium experiment. RESULTS Carboxyl and hydroxyl groups in humic acid were successfully absorbed onto the surface of magnetite. At room temperature, the initial pH of the solution had little effect on the adsorption rate of Pb2+, but had a greater influence on Cd2+. When pH=7, the adsorption rates of Pb2+ and Cd2+ reached 95%. The optimal adsorption equilibrium time of Pb2+ and Cd2+ with initial mass concentration of 10mg/L was 360 minutes, and the adsorption process accords with the quasi-second-order kinetic equation. The order of competitive adsorption was Pb2+ followed by Cd2+. The Langmuir isothermal adsorption model yielded maximum adsorption capacity of Pb2+ and Cd2+ of 39.27mg/g and 28.95mg/g, respectively. CONCLUSIONS The adsorption capacity of humic acid-modified magnetite was higher than that of magnetite, indicating that the ability of humic acid-modified magnetite was enhanced to adsorb Pb2+ and Cd2+ in water samples.

Keywords

• water samples
• pb
• cd
• heavy metals
• adsorption
• modified magnetite
• humic acid
• fourier transform infrared spectroscopy
• scanning electron microscopy
• x-ray photoelectron spectroscopy