Phosphate-functionalized ramie stalk adsorbent for efficient removal of Zn2+ from water: adsorption performance, mechanism, and fixed-bed column treatment of real wastewater.

ABSTRACT

A highly efficient adsorbent functionalized with phosphate groups made from a local agricultural waste, ramie stalk, was designed for Zn2+ removal from water. SEM, EDS, FTIR, zeta potential, and XPS tests were used to study the morphology and properties of modified ramie stalk (RS-P). The results showed that the phosphate groups were successfully grafted to the surface of the ramie stalk, which has a multilayered and porous structure and can provide large adsorption sites. Adsorption performance and mechanism were investigated in the static and dynamic adsorption experiments. The adsorption kinetics of Zn2+ by RS-P were better fitted by the pseudo-second-order model, indicating chemical adsorption. Adsorption isotherm was better described by Redlich-Peterson isotherm, which suggested heterogeneous and multi-site adsorption, with a maximum adsorption capacity of 0.558 mmol g-1. The characterization of adsorbents before and after adsorption indicated that a combined action of electrostatic interaction and ion exchange was the primary mechanism of adsorption. Dynamic adsorption experiments with fixed-bed column displayed excellent water treatment capabilities. RS-P exhibited good reusability in 5 cycles without much deterioration in its adsorption performances. Complex co-existing ions impaired Zn2+ adsorption during real wastewater treatment. This research benefits agricultural waste recycling and provides safe water to ensure economic, social, and environmental sustainability.