Adsorption of heavy metals in water by modifying Fe3O4 nanoparticles with oxidized humic acid

Magnetic nanoparticles require a protective coating to enable them to be used to adsorb heavy metals from wastewater, given their oxidation properties and instability in acidic media. Humic acid (HA) has an affinity for magnetic nanoparticles, but its adsorption capacity is low. To improve adsorption capacity, we synthesized a novel adsorbent (HA-O/Fe3O4) through chemical modification and examined its adsorption of Pb (II), Cu (II), Cd (II), and Ni (II) ions. The effects of pH competition, adsorption mechanism, isotherm, kinetics, regeneration, and stability were investigated. The HA-O/Fe3O4 exhibited faster kinetic performance (10 min), conforming to the pseudo-two kinetics equation, and the adsorption isotherm conforms to the Langmuir model with maximum adsorption capacities of 111.10, 76.92, 71.43, and 33.33 mg/g, respectively. The interaction between metal ions and functional groups of the adsorbent was further characterized by Fourier-transform infrared spectroscopy, and the results indicated that adsorption by cation exchange at low pH and complexation at high pH. Additionally, the adsorbent was recycled four times, and the removal rate was not significantly affected. A recycling efficiency of more than 90 % indicates good sustainability and reusability. The stability test shows that the amount of organic matter and heavy metals desorbed by the adsorbent were negligible. Most importantly, at low concentrations, all four metal ions meet the industrial emission standards, and Pb (II) and Cu (II) meet the drinking water standards.

Automated summary

The novel adsorbent HA-O/Fe3O4 exhibited fast kinetic performance and high adsorption capacities for heavy metal ions, showing effectiveness in various environmental conditions. It demonstrated good sustainability, reusability, and stability in adsorption of heavy metals, with negligible desorption and meeting industrial and drinking water standards.