Adsorption of heavy metal ions from water by Fe₃O₄ nano-particles

As one of the important contaminants of water pollution, the toxic heavy metals have harmful effects on the lives of human beings and the environments. For instance, chromium (Cr), copper (Cu), cadmium (Cd), and nickel (Ni) are listed in the 11 hazardous priority substances of pollutants. Hence, it is of utmost importance to purify water before use. The effective disposal of heavy metals has been arousing worldwide concern in the last few decades. Nano-particles are widely studied as heavy metal adsorbents because of their unique physical and chemical properties. The work purified the contaminated water using the magnetite Fe 3 O 4 nanoparticles with different particle sizes, adsorption time, and pH value. Adsorbents were conveniently separated from the resultant via an external magnetic field due to the magnetic properties of Fe 3 O 4 nanoparticles. Subsequently, a series of characterization methods, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic emission spectrophotometer, were used to characterize the structures of nano-particles obtained before and after the purification process and to test heavy metal content. The main results and conclusions in this work are summarized as follows: the removal of heavy metal ions increased with increasing adsorption time and decreasing particle size. The optimal pH of Cr 6+ , Cu 2+ , Ni 2+ , and Cd 2+ is 2, 4, and 11, respectively. All the removal rates were above 97%. The experimental results indicate that physical adsorption plays a dominant role in Fe 3 O 4 nanoparticles. It is a promising adsorbent for heavy metal ions.