An amino-functionalized ramie stalk-based adsorbent for highly effective Cu2+ removal from water: Adsorption performance and mechanism

This study reports a potential application of a local agricultural waste, ramie stalk, as a raw material to design a highly effective adsorbent by chemical modification with tetraethylenepentamine for Cu2+ removal from water. Surface morphology and chemical structure, elements components and physicochemical properties of the adsorbent were characterized by using SEM, EDX, FTIR, Zeta potential Meter and XPS. After modification, the amine groups were successfully grafted onto the surface of ramie stalk, which have multilayered and porous structures. A batch and fixed-bed column method were used to investigate the adsorption performance and mechanism of Cu2+. The optimum pH for Cu2+ adsorption was found to be 5. In the batch adsorption experiment, the data of the kinetic experiment were better fitted by the pseudo-second-order model (R-2 = 0.9917), indicating that the adsorption of Cu2+ by modified Ramie stalk was mainly controlled by chemical adsorption. The adsorption equilibrium isotherm could be better described by Langmuir model (R-2 = 0.9929) which suggested a monolayer sorption and the maximum adsorption capacity was 0.587 mmol g(-1). In the dynamic adsorption experiment, the operation conditions, such as flow rate, initial concentration, and bed height were evaluated. The experiments results showed that with the higher initial concentration and the lower bed height, the adsorption capacity of the adsorbent increased and the fixed-bed column displayed good capacity for treating water under dynamic condition. The coordination bonding between Cu2+ and amine groups on the modified ramie stalk is the main adsorption mechanism. The new type adsorbent exhibited good reusability for 5 cycles without deterioration in its adsorption performances. Ramie stalk could be utilized effectively as an efficient adsorbent for treatment of the copper contaminated water environment. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.