Adsorption of nitrate and phosphate from aqueous solution using amine cross-linked tea wastes

A low-cost and highly efficient tea waste biosorbent was prepared by amine cross-linking and tested for its ability to remove phosphate and nitrate ions from aqueous solutions. The tea waste (TW) and the amine cross-linked tea waste (ACTW) were compared using scanning electron microscopy (SEM), X-ray powder diffractometry (XRD), energy dispersive spectrometry (EDS), Fourier-transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The removal of nitrate and phosphate by both TW and ACTW were compared through a set of experiments that varied the adsorbent dosage, contact time, initial concentration of target ion and pH of the nitrate and phosphate solution. The results showed that TW had limited adsorption abilities for nitrate and phosphate, while ACTW showed considerable adsorption capacities for nitrate and phosphate over a wide pH range of 3-10. The adsorption could be explained by the Langmuir isotherm model. The maximum sorption capacity of ACTW for nitrate ions was 136.43 mg/g and for phosphate ions was 98.72 mg/g. These results revealed that the mechanism by which ACTW removes nitrate and phosphate ions might involve electrostatic attraction as well as ion-exchange. These results indicated that ACTW could serve as a novel biowaste material for the removal of nitrogen and phosphorus from eutrophic water.