LAUSR

Abstract Technology of phosphate adsorption is important in the field of wastewater treatment to prevent eutrophication. Granulation of powdered adsorbent maintaining the adsorption performance is essential for designing a column adsorption process. Herein, granular activated carbon (GAC) and pumice stone (PMC) containing lanthanum cerium or iron oxide were prepared and their phosphate adsorptive properties were then compared by a batch method in a diluted solution (1.9 mg-P/dm3). Phosphate adsorption was relatively slow compared with the adsorption on powdered adsorbent, and adsorption process continued for more than 380 h. Lanthanum oxide-loaded GAC and PMC showed large phosphate uptakes of 5–8 mg-P/g-ad, corresponding to the phosphate uptakes above 60 mg-P per gram of La(OH)3 in the granules. Cerium oxide-loaded GAC and PMC showed relatively large phosphate uptakes of 3–6 mg-P/g, whereas iron oxide-loaded ones showed considerably smaller phosphate uptakes of 0.5–2.5 mg-P/g. The intraparticle surface diffusivity of the phosphate ions was derived for the lanthanum oxide-loaded granules from the concentration decay curve, using the diffusion equation with the Langmuir-type adsorption isotherm. The diffusivities were approximately 1 × 10−11 m2/h independent of the types of support or particle size, indicating that the phosphate adsorption rates were strongly influenced by the external surface area of the granule. Structural characterization of the metal oxide-loaded GAC before and after the phosphate adsorption suggests that the phosphate adsorption on the lanthanum oxide-loaded GAC progresses by the chemical reaction from La(OH)3 to phosphate-displaced La2(CO3)38H2O, whereas that on the cerium oxide-loaded GAC progresses by the ion exchange with surface hydroxyl group of the CeO2 particle. The above results suggest that the lanthanum oxide- and cerium oxide-loaded GAC and PMC are promising materials for column phosphate removal in municipal wastewater.