Bentonite and organobentonite nanocomposite for removing chromium species from aqueous solutions

Abstract

Batch adsorption studies were used to assess the effectiveness of bentonite and a synthetized Bentonite HDTMA⁺/clay nanocomposite in removing chromium species from aqueous solution. Characterization of adsorbents using XRD, FTIR, SEM/EDX, TGA/DTA, and BET method reveals that larger amount of HDTMA⁺ is located in the interlayer and outer surface of Bt, resulting in the efficiency modified Bt for higher removal of chromium species. The parameters involved in the adsorption process, including contact time, adsorption temperature, adsorbent mass, initial chromium concentration, and solution pH, were optimized. It was found that the HDTMA⁺/Bt composite had a higher adsorption capacity (250 mg/g) than Bt (2.73 mg/g) under optimal testing conditions: equilibrium period of 120 min for both adsorbents, pH = 2, m = 0.2 g of adsorbents, and chromium ion concentration of 2 10⁻⁴ M. The adsorption kinetics were found to be nonlinear pseudo-second-order, with intraparticle diffusion not being the main controlled adsorption step, and the thermodynamic parameters indicated the endothermicity of the spontaneous adsorption process. The isotherm data could be fitted by the Langmuir and Freundlich adsorption models. This could be owing to the surface heterogeneity of the adsorbents, resulting in a hybrid adsorption process at multi adsorption sites. The FTIR spectra revealed CrO bond vibration bands caused by electrostatic interactions, Van der Waals forces, and hydrogen bonding between adsorbents and chromium species. Regeneration tests demonstrate that theses adsorbents could be reused even after five cycles, which makes them much more cost-efficient and environmentally friendly, especially in applications like water treatment.