Adsorption removal of Cr(VI) oxyanions by kaoline/polyaniline composite from aqueous solutions

Polyaniline (PAn) and kaolin/polyaniline (Kn/PAn) composite samples were investigated for the adsorptive removal of Cr(VI) from model aqueous solutions. PAn and Kn/PAn samples were synthesized in 1 M aqueous H 2 SO 4 solution by chemical oxidation of aniline. Comparative adsorption studies of Kn/PAn and PAn samples were carried out in relation to Cr(VI) solutions in distilled water in the oxyanion concentration range of 100–500 mg/L. It is shown that the process of removal and adsorption of Cr(VI) is a three-stage process and depends on the initial concentration of Cr(VI) in the solutions. The removal of Cr(VI) in the first stage of the process proceeds quickly, while in the second stage it is much slower, which also depends on the concentration of Cr(VI) in the initial solutions. The percentage of removal and adsorption in the first stage is greater than the same parameters in the second and three stage. The total percentage of removal of Cr(VI) depends on the concentration of ions in the initial solutions. The study of the kinetics of the adsorption process of Cr(VI) oxyanions showed that the adsorption kinetics is well described by a pseudo-second-order kinetic equation, and the adsorption better corresponds to the Langmuir isotherm model. To study the adsorption of Cr(VI) by PAn and Kn/PAn samples, the following methods were used: electron spectroscopy (ES); scanning electron microscopy (SEM); energy-dispersive X-ray spectroscopy (EDX); chemical element mapping (CE) and infrared spectroscopy with Fourier transform (FT-IR). The kaolin particles used in the study served simultaneously as matrix carriers for polyaniline as an adsorbent for Cr(VI) and a complexing agent for Cr(III). The combination of polyaniline with polydisperse kaolin provided a synergistic effect on the detoxification of Cr(VI) from model aqueous solutions. Keywords: kaoline, polyaniline, kaoline/polyaniline, chromium, adsorption.