One-Step Calcination of the Spent Bleaching Earth for the Efficient Removal of Heavy Metal Ions

Abstract

Attapulgite/carbon nanocomposites were fabricated via one-step calcination of the spent bleaching earth served as adsorbents for the efficient removal of heavy metal ions (Cu(II), Pb(II) and Cd(II)). The as-prepared nanocomposites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller techniques. The process parameters affecting the adsorption behaviors such as initial pH, calcination temperature, contact time and initial concentration of heavy metal ions were systematically investigated. The results indicated that the attapulgite/carbon nanocomposites derived from the low-cost available carbon precursors exhibited high adsorption capacity within a wide pH range, and the faster equilibrium was achieved at lower concentration. In addition, the adsorbed Cu(II), Pb(II) and Cd(II) can be partially desorbed using 0.1 mol/L HCl as the desorbing agent, rendering the as-prepared adsorbent good readsorption ability, especially for the removal of Cu(II). Using the adsorption of Cd(II) as an example, it has been confirmed that the electrostatic interaction, cation exchange and surface complexation between Cd(II) and functional groups on the attapulgite/carbon nanocomposites were the dominant mechanisms according to the results of the adsorption studies and XPS analysis. Furthermore, this research develops a feasible route for the application of the spent bleaching earth in the wastewater treatment.