Adsorption of phosphate using calcined Mg3–Fe layered double hydroxides in a fixed-bed column study

A granular calcined Mg3–Fe LDH adsorbent was prepared by using co-precipitation method under low super saturation condition. The characteristic of the adsorbent was analyzed by powder X-ray diffraction (XRD) and scanning electron microscope (SEM). The continuous phosphate adsorption experiments were conducted in a glass fix-bed column. The results showed an increase in bed height and initial phosphate concentration improves the phosphate adsorption capacity probably due to the longer bed height allowing a longer empty bed contact time (EBCT) between the adsorbent and the adsorbate, meanwhile the higher initial phosphate concentration provides a higher driving force for the mass transfer; however, an increase in flow rate inhibits the phosphate adsorption due to the higher flow rate reduced the interaction time of the adsorbent in solution. The bed depth service time (BDST) model was found to predict the breakthrough curve well at a 0.024 L/h flow rate and 10 mg/L initial phosphate concentration using linear regression analysis. The Clark model was found to give a best fit to experiment data under various bed height, flow rate and initial phosphate concentration, followed by the Thomas and Yoon–Nelson models using non-linear regression analysis. The reusability experiment was conducted using actual anaerobic sludge filtrate as adsorbate. The results indicated that the adsorbent still had good selectivity in an anions coexisting solution, high phosphate adsorption capacity, and acceptable desorption efficiency.