Diatomite-Based Adsorbent Decorated with Fe₃O₄ Nanoparticles for the Removal of Hazardous Metal Ions

Diatomite has been verified as an economical adsorbent to treat wastewater. Unfortunately, limited by poor regeneration and an inert surface with less active silanol groups, the retrievable and efficient diatomite-based adsorbent needs to be further explored. Here, on the basis of the thorough activation treatments of the raw diatomite, we developed a diatomite-based adsorbent with a uniform assembly of Fe 3 O 4 nanoparticles on the surface. The nanocomposite possesses a high specific surface area, the trait of magnetic separation, and more functional groups for adsorption. The maximum adsorption capacities of Pb 2+, Ni 2+, and Cd 2+ at 314 K reached 0.97, 1.18, and 0.88 mmol/g, respectively, which were more competitive than those of previously reported diatomite-based adsorbents. The experimental data fitted well with the pseudo-second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption was mainly derived from the electrostatic interaction and chelation between the hydroxyl/carboxyl groups on multilayer surfaces and the hazardous metal ions. According to the analytical results of the adsorption isotherms and response surface optimization, the removal efficiency can exceed 94%, obtained by increasing the pH and reaction temperature. The activation-enhanced surface engineering can arouse the adsorption potential of a diatomite-based adsorbent and provide universal perspectives into the concept design of a nanocomposite adsorbent with lower cost recovery and higher adsorption efficiency.