Treatment of chromium effluent by adsorption on chitosan activated with ionic liquids

This study proposes, verifies, and refines the use of biopolymers treated with two new ionic liquids (ILs) (sec-butylammonium acetate and n-octylammonium acetate), as a platform for chromium adsorption. The ILs were synthesized, characterized, and applied to chitosan treatment. Analyzing the size distribution of microparticles of chitosan and chitosan activated with ILs (sec-butylammonium acetate and n-octylammonium acetate), we observed that a little decrease in the particle size occurred with the activation of chitosan (176 ± 0.02 μm to 167 ± 0.054 and 168.5 ± 0.05 μm, respectively), as well as changes in the X-ray diffraction FTIR_ATR spectra. Further studies were performed using the best adsorbent – chitosan treated with sec-butylammonium acetate. In this case, the chromium VI concentration in the sample was reduced by more than 99% when using chitosan treated with IL sec-butylammonium acetate. The best reaction time was determined as 1 h, which allowed a chromium adsorption of 99.1% and the adsorption kinetic data were best represented by the second-order model (k₂ = 11.7258 g mg^?1 min^?1). The maximum adsorption capacity was obtained using the Langmuir isotherm model (20.833 mg g^?1 at pH 4 during 1 h, using 1.0 g of chitosan), and the adsorption efficiency was enhanced at 25 °C by the Freundlich isotherm model, in which the constants KF and n were determined as 0.875 mg L^?1 and 1.610, respectively.