Fabrication of bentonite/thiourea-formaldehyde composite material for Pb(II), Mn(VII) and Cr(VI) sorption: A combined basic study and industrial application

A new composite material was obtained by in situ polymerization of thiourea and formaldehyde in the presence bentonite microgranules as a support. This material was characterized by Scanning electron microscope (SEM), Energy Dispersive X-Ray Analysis (EDX), X-ray diffraction (XRD). SEM and EDX analyses confirm the homogeneity of the sorbent in term of composition. The composite sorbent was used for the removal of Pb(II), Mn(VII) and Cr(VI) from their aqueous solution. Sorption uptake was highly dependent on pH, initial metal ion concentration and the mass of the adsorbent. The optimum pH is being close to 4 for Mn(VII) and Pb(II) sorption, while maximum Cr(VI) sorption was at pH 2. Kinetic experiments were carried out and different models were applied in order to elucidate the rate-controlling mechanism, the uptake kinetics was modeled using the pseudo-second order rate equation. The sorption isotherm can be best described by the Langmuir sorption isotherm and the maximum sorption capacities are 13.38, 14.81 and 4.20 mg g−1 for Pb(II), Mn(VII), and Cr(VI), respectively. The sorbent was successfully tested for Pb(II) and Cr(VI) removal from industrial effluents, while Mn(VII) was not detected the studied samples. Pb(II) desorption was performed using an aqueous solution of 0.1 M HCl, while Mn(VII) and Cr(VI) desorption was done using an aqueous solution of 0.1 M NaOH. The recycling of the sorbent was tested, maintaining a removal efficiency and a metal recovery over 90% for four successive sorption/desorption cycles. The effect of temperature was also evaluated, verifying the endothermic nature of the sorption process.