Immobilization of layered double hydroxide in poly(vinylidene fluoride)/poly(vinyl alcohol) polymer matrices to synthesize bead-type adsorbents for phosphate removal from natural water

Abstract

Layered double hydroxide (LDH) has been widely used as an adsorbent to remove contaminants from aqueous solutions. However, LDH in powder form might not be suitable in water and wastewater treatment systems due to low hydraulic conductivity and sludge production. Therefore, it is necessary to synthesize bead-type adsorbents for application in treatment systems. In this study, LDH beads were prepared through immobilization of powdered MgFe LDH in polymer matrices, composed of poly(vinylidene fluoride) and poly(vinyl alcohol). The LDH beads had an average size of 2.4 ± 0.6 mm with a Brunauer-Emmett-Teller (BET) specific surface area of 30.41 m2/g and total pore volume of 0.12 cm3/g. Batch experiments were conducted on the use of the LDH beads for phosphate sorption in stream water (pH = 6.9, ionic strength = 613 μS/cm) collected from the Seoho stream located in Suwon, Korea. Fourier-transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical characteristics of the LDH beads before and after phosphate sorption. Phosphate sorption to the LDH beads remained relatively constant at initial pH values of 5–9. The LDH beads could be used repeatedly for phosphate sorption through desorption with a NaOH solution. The equilibrium time for the phosphate sorption was 3 h, whereas the maximum sorption capacity was 2.050 mgP/g. In addition, the phosphate sorption increased with a rise in temperature from 15 to 45 °C. Under dynamic flow conditions (flow rate = 4.9 and 9.8 mL/min; bed depth = 10, 20, and 30 cm; inner diameter of column = 2.5 cm), fixed-bed column experiments were performed to test the applicability of the LDH beads in the phosphate removal from the stream water. The phosphate sorption capacity of the column was quantified to be 1.175 mgP/g at given experimental conditions (bed depth = 30 cm; flow rate = 4.9 mL/min). The performance of fixed-bed columns was quantified by analyzing phosphate breakthrough curves with fixed-bed kinetic sorption models (Bohart-Adams and modified dose-response models). This study demonstrated that the LDH beads could be successfully applied as adsorbents for phosphate removal from natural water.