Phosphate-ion-adsorption capability of granulated boehmite fabricated using organic binder (polyethylene terephthalate).

We investigated a method for producing granulated boehmite (BE) by using an organic binder and measured its phosphate-ion-adsorption capacity. BE was granulated using polyethylene terephthalate (PET), and its structure was characterized by scanning electron microscopy and X-ray diffraction analyses. The properties of granulated BE such as specific surface area, mean pore diameter, pore volume, amount of hydroxyl groups, and solution pH were also investigated. Furthermore, adsorption isotherm; effects of contact time, temperature, and solution pH on phosphate-ion adsorption; and recovery of phosphate ions (using sodium hydroxide solution) were evaluated. BE granulated by PET (BE-PET30S) could be successfully used for phosphate-ion removal by adsorption. The specific surface area and amount of hydroxyl groups of BE-PET30S were found to be 119.8 m²/g and 1.4 mmol/g, respectively. Granulated BEs reached equilibrium adsorption capacities within 24 h. The phosphate-ion-adsorption rate data were fitted to the pseudo-second-order kinetic model (r=0.981-0.998). The adsorption isotherm data were fitted to both the Freundlich (0.987-0.989) and Langmuir (0.905-0.944) equations. Based on the thermodynamic study, it was found that the phosphate-ion adsorption by granulated BEs is a spontaneous and exothermic process. The phosphate ions adsorbed onto BE-PET30S could be easily recovered by using a sodium hydroxide solution (1-1000 mmol/L) and their recovery percentage was found to be between 63.3% and 94.0%. The results obtained from this study could be useful for recovering phosphate ions and preventing problems related to water pollution.