Anthracite/talc-based porous activated composite loaded with DTAB surfactant for Cr(VI) adsorption: Characterization, performance, and mechanism

Abstract

A mixture of anthracite (An) and heated talc (HT) was activated with sodium silicate and then coated with dodecyltrimethylammonium bromide (DTAB) to prepare a new porous adsorbent (DTAB-HT/An) for removing Cr(VI) from solutions. FTIR, zeta potential, FESEM/EDX, and XRD methods demonstrated the effective modification of the adsorbent by the DTAB surfactant. The efficiency of DTAB-HT/An in removing Cr(VI) ions was enhanced to 91 % by DTAB support at the optimum pH of 3.0, as compared to 62 % of the untreated HT/An blend. Within the range of 25–55 °C, the adsorption data were fitted using conventional models, and the maximum capacities, as calculated by the Langmuir equation, varied between 162.60 and 124.03 mg/g. Furthermore, the density of DTAB-HT/An energetic sites, the elimination capacities at saturation, and the amount of Cr(VI) removed by each functional group were all analyzed though the statistical physics theory. The removal of Cr(VI) was found to be dominated by dissimilar mechanisms (i.e., surface complexation, pore filling, and electrostatic attraction), according to the experiments and theoretical studies. Over the adsorption process, Cr(VI) and Cr(III) displayed distinct geometric behaviors (mixed or vertical orientation) and interaction mechanisms (multi-docking or multi-ionic). Energetic and thermodynamic functions suggested that the adsorption system was exothermic and directed by a spontaneous mechanism. Based on the regeneration results up to six cycles, the DTAB-HT/An was really stable and appropriate in wastewater treatment.