La-modified ZSM-5 zeolite beads for enhancement in removal and recovery of phosphate

ZSM-5 zeolite beads (ZB) modified with lanthanum (La) were prepared by impregnating ZB in a lanthanum nitrate solution (denoted as La-ZB). La-ZB was characterized via SEM, BET, ICP-OES and XRD techniques, which confirmed the doping of La on the surface of the ZB. The surface area and pore volume of La-ZB decreased marginally after the La-modification due to a partial pore blockage by the La dopant. La-ZB showed an improved phosphate adsorption compared to ZB, and the maximum phosphate adsorption capacities by ZB and La-ZB (determined by Langmuir isotherm) were 59.8 and 106.2 mg/g, respectively. Moreover, the adsorption kinetics proceeded according to the mechanism of the pseudo-second-order model. The phosphate adsorption by La-ZB exhibited an optimum at pH 6. In regeneration process of phosphate-loaded La-ZB, five times adsorption-desorption cycles were applied and 81.8% phosphate was recovery. In a test using wastewater containing a high phosphate concentration (218.6 mg/L), La-ZB exhibited 96.8% phosphate removal, which is 1.8 times higher than that of ZB (53.5%). The results indicate that La-ZB can be a promising recyclable adsorbent for the removal and recovery of phosphate from wastewater.