Efficient elimination of Pb(II) ions from aqueous solutions using magnetic Fe3O4 nanoparticles/activated carbon derived from agricultural waste

Agricultural by-products are promising adsorbent materials for wastewater treatment, for example, removal of heavy metals. In this study activated carbons (AC) prepared from rice straw agricultural waste (treated with concentrated sulfuric acid) are used to remove lead ions (Pb2+) from aqueous solutions in batch mode. The calcination of AC at 500 degrees C for 1 h shows improved removal efficiency. Synthesized magnetite nanoparticles (Fe3O4-NPs) are loaded on AC with different ratios (Fe3O4/AC(1)), (Fe3O4/AC(2)) using co-precipitation method. The chemical structure, surface composition and morphology are characterized by scanning electron microscopy-energy-dispersive X-ray, X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller and Raman spectroscopic analyses. The adsorption process depends on the initial metal ion concentration, temperature, solution pH, the adsorbent dose and contact time. Fe3O4/AC(2) has the highest adsorption capacity (68 mg g(-1)) at 100 mg L-1 metal ion concentration, adsorbent dose of 1 g L-1, room temperature (30 degrees C +/- 2 degrees C), shaking speed = 200 rpm, contact time = 1 h and pH = 5. The thermodynamic studies show that the adsorption process fits Freundlich model (R-2 = 0.997) better than Langmuir and Temkin models. The adsorption/desorption kinetics of Pb2+ ions proceeds via pseudo-second-order kinetics. The temperature-dependent study (carried out in the range of 20 degrees C-60 degrees C) confirmed that the adsorption process was endothermic in nature.