A Study of the Recovery of Phosphorus from Aqueous Solutions Using Zr-Doped MgMn-Layered Double Hydroxide (MgMnZr-LDH)

Abstract

A new type of adsorbent, Zr-doped three metal element adsorbent MgMnZr-LDH(3), was synthesized using Mg(NO3)2·6H2O, Mn(NO3)2·6H2O, and ZrCl2O·8H2O and employed to adsorb phosphate ions from an aqueous solution. The materials were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), an X-ray diffractometer (XRD), thermogravimetric–differential thermal analysis (TG−DTA), Fourier-transform infrared spectroscopy (FT-IR), and nitrogen adsorption/desorption experiments (N2 Brunauer–Emmett–Teller (BET)). The influences of the contact time (0~48 h), pH value (3, 5, 7, and 9), initial concentration (0~50 μg/dm3), and temperature (15, 25, 35, and 45 °C) on the adsorption of phosphate (P) ions were studied to investigate P adsorption from wastewater. The results showed that the Zr-modified three metal element adsorbent MgMnZr-LDH(3) had a superior adsorption effect on phosphate anions, which was about 2.18 times greater than that of the two metal element adsorbent MgMn-LDH(3). The MgMnZr-LDH(3) adsorption process conformed to the pseudo-second-order model. The adsorption isotherm can generally be described more satisfactorily for P using the Langmuir isotherm, and the maximum adsorption capacity of P was shown to be 30.8 mg/g. Under optimum experimental conditions (contact time: 24 h; pH 8; and temperature: 25 °C), the effect of competing anions (Cl−, SO42−, and NO3−) on the adsorption of phosphate ions was also investigated, and only the phosphate ions showed high selectivity. The good adsorption performance of MgMnZr-LDH(3) towards phosphate (P) ions was attributed to the anion exchange and complex reaction.